economic geology and photogeology of by...
TRANSCRIPT
Economic geology and photogeologyof the Tsumeb area, South West Africa
Item Type text; Thesis-Reproduction (electronic); maps
Authors Readdy, Leigh Arthur, 1936-
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/557374
ECONOMIC GEOLOGY AND PHOTOGEOLOGY OF
THE TSUMEB AREA, SOUTH WEST AFRICA
by
Leigh Arthur Readdy
A T hesis Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In P ar tia l Fulfillm ent of the Requirements • For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 7 2
STATEMENT BY AUTHOR
This th e s i s h a s been subm itted in p a r t ia l fu lfillm ent of r e quirem ents for an ad v anced degree a t The U niversity of Arizona and is d e p o s ited in the U n iv ers ity Library to be made a v a i la b le . to borrowers under ru le s of the Library „
Brief quo ta tions from th is th e s i s are a llow able w ithout sp e c ia l p e rm iss io n , provided th a t accu ra te acknow ledgm ent of source is m a d e . Requests for perm iss ion for ex tended quotation from or reproduction of th is m anuscrip t in whole or in part may be granted by the head of the m ajor departm ent or the Dean of the G raduate College when in h is ju d g m ent th e proposed u se of the m ate ria l is in the in te re s ts of s c h o la r s h ip „ In a l l o ther i n s t a n c e s , how ever, pe rm iss ion m ust be ob ta ined from the a u th o r .
APPROVAL BY THESIS DIRECTOR
This th e s i s h as been approved on the da te shown below:
/ SPENCER R. TIT LEYP rofesso r of G e o sc ie n c e s
ACKN OWLEDG ME NT S
The m ateria l p re sen ted in th is th e s i s was o r ig ina lly prepared
by the author a s two Kennecott Copper C orpora tion , G eo log ic Research
D iv is ion r e p o r t s . The author is indeb ted to Kennecott Copper Corpora
tion for th e ir perm ission to u se th e se d a ta as th e s is m a te r ia l .
The au thor ben ef ited g rea tly from d isc u s s io n w ith .and c r i t ic a l
rev iew from h is former c o l le a g u e s w ithin the G eologic Research D iv is ion
of Kennecott Copper C orporation , p a r t ic u la r ly Dr. John W ilso n and Dr./
T. W . M itcham , p re se n t and former C hiefs of the D iv is io n , r e s p e c t iv e ly .
I ap p rec ia te the encouragem ent and support by the members of my th e s i s
co m m ittee , D rs . Spencer R. T i t le y , Evans B. M a y o , and John S. Sumner.
My s p e c ia l thanks go to M r. Eugene D em eter, who spen t many
hours help ing me t ra n s la te the e a r l ie r German lite ra tu re for the area of
s tu d y .
The high s tan d a rd s of p ro fess io n a lism of the d rafting p e rso n n e l
w as very much a p p re c ia te d . P ar ticu la r thanks are due M r s . M argret
Strom who typed the numerous rough drafts of the o r ig ina l reports and
M rs . Linda Shaw and M iss Linda De Long who typed the th e s i s d r a f t s .
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS . . . . . . . . . o . . . . . . . . v i
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . v i i i
INTRODUCTION . . . . . . . . . . ........................ . '. 1
REGIONAL GEOLOGY ........................ 6
Stra tig raph ic Problems . . . . . ,. . . . . . . . . . . . . 7P seu d o ap li te ........................ .... . . . . . . . . . . . . . 8Karst F ea tu res ........................ 9
ECONOMIC GEOLOGY . . . . . . . . . . . . . . . . . . . 11
Types of D ep o s i ts . . . . . . . . . . . . . . . . . . . 11Tsumeb Ore Body. . . . . . . . . . . . . . . . . . . . 12
Geology of the Tsumeb Mine . . . . . . . . . . . . . 12Alteration ........................ 18Igneous In trusive Rocks. .................... 19
Tsumeb W e s t . . . 7 . . . . . . . . . . . . . . . . . . 19Vanadium O ccu rren ces . . . . . . . . . . . . . . . . . 23D is c u s s io n of O ther M ines and P ro sp ec ts . . . . . . . . . 25
Tsumeb E a s t . . . . . . . . . . . . . . . . . . . . 25Abenab and Abenab W est . . . . . . . . . . . . . . 26Alt Bobos . . . 30Bobos . . . . . . . . . . . . . . . . . .................... 30Uris and Karavatu . . . . . . . . . . . . . . . . . 31
ORE CONTROLS AND ORE GUIDES ........................ 32
S tra tig raph ic C ontro ls . . . . . . . . . . . . . . . . . 32Structural Contro ls . . . . . . . . . . . . . . . . . . . 33Favorable S tructural Settings ........................ 34Vanadium as an Ind icator M eta l .................................. 37S inkholes . . . . . . . . . . . . . . . . . . . . . . .- 37Upper Tsumeb Substage . . . . . . . . . . . . . . . . . 38Aeromagnetic S u rv e y s . . . . . . . . . . . . . . . . . . 38
PHOTOGEOLOGIC STUDY . . . . . . . . . . . . . h . . . . 40
D isc u ss io n of Photo in te rp re ta tive M aps ............................. 42Photogeologic Structure Map . . . . . . . . . . . 42In te rp re ta tive S tra tigraphic Map . . . . . . . . . . . 42
iv
V
TABLE OF CONTENTS— Continued
Page
Road N et Map . . . . . . . . . c . . . . . . . . . 43 .Rose Diagram s of Linear E lem ents . . . . . . . . . . . 43
OTAVI VALLEY DEPOSITS . . . . . . . . .. . . . . . . . . . 47
Kombat M ine . . . . . . . . . . . . . . ... . . 47Asis M in e . . . . . . . . . . . . . . . . . . . . . . . 53
Ore in P seudoap li te . . . . . . . . . . . . . . . . 54Copper O ccurrences in T ec to n ica lly Trapped
P seudoap li te Blocks . . . . . . . . . . . . . . . 59C opper-bearing Breccia V e i n s ............................ 59
A sis East-End . . . . . . . . . . . . . . . . . . . . . 60Asis East . . . . . . . . . . . . . . . . . . . . . . . . 61Baltika . . . . . . . . . . . . . . . . . . . . . . . . 62Berg Aukas . . . . . . . . . . . . . . . . . . . . . . 62G au ss 4 6 ........................ . . . . . . . . . . . . . . . . . 64G ro s s -O ta v i . . . . . . . . . . . . , . .. . . . . . . . . 64
P seudoap li te Ore B o d y ................................... ... . . . . . . 64O re -b e a r in g , S an d -f i l led S in k h o le s . . . . . . . . . . 6 6Eastern Group of S inkholes . . . . . . . . . . . . . . 6 6
G uchab . . . . . . . . . . . . . . . . . . . . . . . . . 69O re-b ea rin g S inkholes . . . . . . . . . . . . . . . 71The " E isener Hut" O c c u r r e n c e ...................................... 72
G uchab E a s t . . . . . . . . . . > .. .. . . . . . . . . . . 74H aras ib 317 . . .. . . . . . . . . . . . . . . . . . . . 74O lifan ts fon te in 9 . . . . . . . . 75O tjirukaku 42 . . . . . . . . . . . . . . . . . . .- . . 75Reitfontein 344 . . . . . . . . . . .. . ... . . . . . . . 75Toggenburg 591 . . . . . . . . . . . . . . . . . . . . 76U itsa b 654 . , . . . . . . . . . . . . . . . . . . . . 76
SELECTED BIBLIOGRAPHY 77
LIST OF ILLUSTRATIONS
Figure Page
1 . Index Map for Tsumeb Photogeologic S tudy ,South W est Africa ........................ 2
2. P rospec t Location M a p , Tsumeb Area,South W e s t Africa ...................................... 3
3. O tav i M ountains S tratigraphy andPhotogeologic Expression in pocke t
4 . G eologic C ross Section through Tsumeb Ore Body. . . . 10
5. G eolog ic P lan , Level 26, Tsumeb Ore B o d y ............... 13
6 . Road Net Map Showing Location of Tsumeb M ining. Corporation Sampled A reas, Tsumeb and Vicinity . . 14
- ■ »7. Geology of Tsumeb Area, South W est Africa . . . . . . 15
8 . D iagram m atic Section through the Tsumeb W e s t 'P seudoap li te P i p e ................................. 20
» 9 . Photogeologic S tructure M ap, Tsumeb Area,South W es t A f r i c a in pock e t
10. Abenab Mine , South W e s t Africa, Showing the• N orth eas t Face of the O p en cas t and Section
. through the M ain Ore Body . . . . . . . . . . . 27
11. N orth -sou th Section through Abenab M i n e ............................. . 28
12. Volcanic Belts of Late Karroo Age, Angolaand South W e s t A f r i c a ................... .... . . . . . . . 35
13. G en era lized Sketch of the S tructura l Settingof the Berg Aukas M ine, South W es t Africa . . . . 36
14. S tra tig raph ic D is tr ib u tio n , Tsumeb Area,South W es t A f r i c a in pock e t
15. Rose Diagram s of Linear Elements andG eographic Base M ap, Tsumeb Area,South W es t Africa . . . . . . . . . . . . . . in pocke t
v .
v ii
LIST OF ILLUSTRATIONS— Continued
Figure Page
16. Index M ap, O tav i Valley Region,South W es t Africa ........................ 48
17 . P rospec t Location M ap, O tavi Valley Region,South W e s t Africa . . . . . . . . . . . . . . . 49
18. G eolog ic Sketch Map of the Ore D e p o s i t s ,O tav i V alley , South W es t Africa . . . . . . . . . . 50
19. Id ea l ized Section through Kombat Ore B odies. . . . . . 52
20. Plan of Asis (Kombat) Mine Area,O tav i Valley, South W e s t Africa . . . . . . . . . 55
21. Plan of the 30- and 60-m eter L e v e ls , Asis M ine . . . . 56
22. P rospec t Area a t G ro ss-A tav i, O tav i V alley,South W e s t Africa . . . . . . . „ . . . . . . . . . .67
23. Typica l Section through G ro ss -O ta v i C opper-bear ing Karst D e p o s it , O tav i Valley,South W e s t Africa . . . . . . . . . . . . . . . 67
24. G eolog ic Map of Guchab Copper O c c u r re n c e s ,O tav i V a lley ................. ....... ......................................................... 70
ABSTRACT
The b a s e -m e ta l d ep o s its of the O tavi M o u n ta in s , South W est ■' ■ '
Africa, occur as r e p la c e m e n ts , d issem in a ted m inera liza tion in p se u d o -
a p l i te , a rock of d ispu ted o rig in , and in b recc ia p ipes and zones of
b recc ia t io n w ithin the th ick Precambrian carbonate sequence of the O tavi
S e r ie s . The d e p o s its are ch a ra c te r iz e d by very lo ca l c a lc i te and quartz
a l te ra t io n of the do lom ite . M inera lized a reas have a g rea te r inc idence
of s ink h o les as a r e su l t of the c a lc i t ic a l te ra t io n , and the s tudy of s in k
hole d is tr ibu tion by a irphoto a n a ly s is is a p o ten tia l ly u se fu l exp loration
techn ique for the O tav i M ountain a r e a .
: The two major b a s e -m e ta l d e p o s i ts of the O tav i M oun ta in s ,
Tsumeb and Kombat (A sis), are c lo se ly re la te d to p seu d o ap li te bod ies
w ith in dolom ites and lim esto n es of two s tra tig rap h ic z o n e s .o f the Upper
Tsumeb s u b s ta g e . The sp a t ia l a s so c ia t io n of p seu d o ap li te with Tsumeb
Zones 7 and 8 m akes the a rea l d is tr ibu tion of th e se zo n es of exp lo ra tion .
s ig n if ic a n c e . The th ree zones of the Tsumeb s u b s ta g e , Zones 6 , 7, and
8 , are the m ost e a s i ly d is t in g u ish a b le ca rb o n a te u n its of the O tavi
Series during fie ld or photogeo log ic m apping.
Three major reg ional s tru c tu res appear to con tro l m inera liza tion
in the O tav i M o u n ta in s . These .are the two d e e p e s t s y n c l in e s , the Tsumeb
and the O tav i Valley s y n c l in e s , and a probable N. 50° E . basem ent s t ru c
tu re . Surface ex p re ss io n of the b asem en t s truc ture in c lu d es a s e r ie s of
roughly p a ra l le l do ler ite d ik e s . B edding-p lane f a u l ts , zones of b re c c ia
tion and b recc ia p ip es form important ore lo c i w ith in the O tav i M ountains .
v ii i
Structura l s e tt in g s m ost favorable for the formation of zo n es of in ten se
fracturing are drag folding a s s o c ia te d with the major e a s t - w e s t f o ld s ,
in te rse c t io n s of reg iona l folds and c ro ss fo ld s , and the p er ipheries of
p seu d o ap li te b o d ie s .
INTRODUCTION
In Septem ber 1967, a req u es t w as m ade.by th e New York office
of Kennecott Copper Corporation for a s tudy of the Tsumeb d e p o s i t ,
South W est A frica. Through 1959, th e Tsumeb mine h as produced
426, 720 to n s of copper , 1 ,1 0 3 , 510 to n s of l e a d , 507 ,970 tons of z in c ,
2 2 ,7 4 1 ,8 4 2 ounces of s i lv e r , and su b s ta n t ia l am ounts o f cadmium and
germ anium . The purpose of the req u es ted study w as to de term ine , i f
p o s s ib le , w hether or not the Tsum eb.pipe w as g e n e t ic a l ly re la ted to
prem ineral c a v e r n s . A second o b jec t iv e w as to be a s tudy of the pho to -
geo log ic fea tu res of the immediate Tsumeb mine area to d e te c t p o s s ib le
s truc tu ra l con tro ls pe rtinen t to ore search in the rem ainder of the Tsumeb
and G rootfontein m ag is tra te d i s t r i c t s . A third ob jec tiv e w as the p rep a ra
tion of a geo log ic map for part of the O tavi M ountains w ith in the Tsumeb
and G rootfontein d is t r i c t s (F igs . 1 and 2) .
This t h e s i s sum m arizes the g en era l geology of th e O tavi M oun
ta in s and the econom ic gfeology of the a rea mapped p h o to g e o lo g ic a l ly .
D isc u ss io n of ore con tro ls and p o s s ib le ore gu ides p re ced es the sec t io n
on the photogeologic s tu d y . v
During the tw o-m onth ass ig n m en t in South W est A frica , the
Tsum eb-G rootfontein photographs w ere quickly s tud ied on a regional
s c a le , se le c te d photographs were s tud ied in d e ta i l , and in i t ia l an n o
ta ted o ver lays were p re p a re d . Two days were spent a t Tsumeb and '
Tsumeb W e s t , and one day a t the Kombat m ine. Several r e c o n n a is sa n c e
tr ip s were made through the O tavi M ounta in la n d . In it ia l l i te ra tu re s tudy
18 °
G r o o t f o n t e i nOtavi
2 0 °
OutjQ-
Omaruru
Ok ah o nd j qU s a k o s 2 2 °
Ko r i b i b
G o b o b i s
.Wind n o ek
R e ho b ot h o
2 4 °
M o n e n f a I
M al ta ho he OGi b e o n
E x p l a n a t i o n
2 6 °I n f e r n a f l o n o l B o u n d o n ' e :
B o u n d a r i e s o f M a g i s f r o f e D i s t r i c t s
R a i l r o a d sL u d e r i t z K e e t m a n s h o o p
Ka r o s burg 2 8 °
100 100Wo rm bo
e j s u ) r a n j e m u n dScale in miles
16° 20 °
Figure 1. Index Map for Tsumeb Photogeologic Study, South W es t Africa
L I T H O L O G I C D E S C R I P T I O N
V) V) N
MAXIMUMT HI CKNESS
f>G
P H O T O G E O L O G I C E X P R E S S I O N
a n r a v w a c k e . e l a t v 1 h f a r k u' «H PHtk ->«• r#rl
f r o e h r x p i . n u r r w e a t h r r m v I
f«tght g r a y h r d H e d d o l o m i t e tw o o r t h r e e p r o m i n e n t e i t t c e o u e bed* d o o l i t e s s h o w in g <. r . - a s b e d d in g n e a r t h e t , , p . ;f t h e s e c t n - n . T h e l i g h t g r a y d o l o m i t e ; s l a m i n a t e d t o t h i c k b e d d e d , c o n t a i n i n g a b u n d a n t s t r i n g e r s «>t t h e a nd a t l e a s t tw s t r o m a t o l i t e m a r k e r s i n a d d i t i o n t o a c h e r t y s t r o m a t o l i t i t . b e d n e a r t h e b a s e
•1 !»• if a n d d a r k - g r a y b e d d e d d o l o m i t e w i th i n t e r t>eil« t d e n s e t h in b e d d e d h*h« r t i t e I h r un i t c o n t a i n * fe n flO* n* r s i s t e n t m l e r b e d s o f b l a c k c r y s t a l l i n e l i m e s t o n e ' s t i n k Walk' , u p t«. t w e l v e I I / ' u n i t s >i f i n e l y l ao i n a ' r d b l a ck - h a i e. ex t r w e i y n u n i e r o p a t h in c h e r t l a y e r s . *«»: r ' w h i c h a r e oo l i t i c O ne m a r k e r l l n e # t " n e un i t t h a t c o n t a i n s y< .it t er«»d •. a I c l u s t e r s o f c o a r s e c r y s t a l l i n e c a l . i t e an d a m a r k e r "". . i t .* b e d a t o r n e a r t h e b a s e >f t h e s e c t i o n .!'h«- O t a i V a l l e y p h y l l l t e b e l o n g s l t h i s m r a t i g r a p h o /• ne.
X i i «ht n r a v b e d d e d d o l o m i t e w i th m a n y s t r o m a t o l i t e b e d s ant i a b u n d a n t c h e r t . f h * u p p e r h a l t o f t h i s r .one i s , y o s . d ,f w e l l • V d d e d d o l o m i t e w i th n u m e r o u s l a y e r s o f u n i f o r m c h e r t an d a p p r o x i m a t e l y t w e l v e (1 .!t pm. - r r e d
a r g i l l a c e o u s s e a m s . Th e l o w e r ha l f if t h e / o n e i s . h a r a c t e n / e r i by a s e r i e s o f c h < r t y s t r o m e t o l i i l c d o h i n i t# b e d s . I t r e t . ia t v n a lo n g be d d in g p l a n e f a u l t s i s Con r r n th r. ugh u t t h e r o n e
l . i gh t g r a y m a s s i v e a nd b e d d e d d o l o m i t e c o n t a i n i n g e ig h t 8 n i a r r a r h« r i s»» ns of t h r e a d y a r g i l l a c e o u s s e a m :
2 3 0 0 '
8 0 0 '
Lig h t t o m e d i u m to n e w i t h m o d e r a l e - t o w e a k - b a n d e d c h a r a c t e r , f o r m s t h e u p p n p o r t i o n of s t r i k e r i d g e s . T h e o o l i t e m a r k e r be d* m th e T s u m e b ( an d K o m b a t ) a r ea ( s^ ) f o r m n a r r o w w a l l - l i k e r i d g e uo t o D f e . i h i g h . T h e s r s i l u i f r ed o o l i t e m a r k e r s a r e t h e on ly b e d s t h a t c an be t r a « e d w i t h go od c o n t i n u i t y on t he a e r i a l p h o t o g r a p h s . S l op e* a r e u s u a l l y l e s s t h a n 10 . D r a i n a g e i s c h a r a c t e r i s e d by a f l at b o t t o m e d d i v e r g e n t d r a i n a g e p a t t e r n T h e f l a t t e r t he s l o p e , t h e m o r e n u m e r o u s t h e b r a n c h i n g s t r e a m s S t r e a m s e n t e r i n g f l a t - l y i n g a r e a s e n d in g r a v e l p i l e d i n f i l t r a t i o n p o in t* . V e g e t a t i o n . s s p a r s e , m o r e a b u n d a n t v e g e t a t i o n i s l o c a l i s e d a lo n g t a l u s t r a p p e d a b o v e t h e o o l i t e r i d g e s . I h e c o n t a c t of t h i n z o n e w i t h t h e o v e r l y i n g M u l d e n f o r m a t i o n c a n be p l a c e d a t a p o in t 0 t o *•() f e e t s t r a i i g r a p h i c a 1!y a b o v e t h e u p p e r o o l i t e un i t w h e r e t h e r e a r e s l o p e , l o n e , a n d v e g e t a t i o n c h a n g e s
1 3 0 0 '
I O O O
7 0 0 '
M e d i u m - t o m e d i u m - d a rk - t o n e d , f l a t , s o i l - c o v e r e d a r e a s . G e n e r a l l a ck o f w e l l - d e f i n e d d r a i n a g e , m o s t d r a i n a g e i s i n t e r n a l . A b u n d a n t t h o r n b u s h a n d o t h e r v e g e t a t i o n .
V a r i a b l y t o n e d f r o m m e d i u m (o l a r k g r a y w i th t o n - l i g h t e n in g p r o g r e s s i v e t y - w e s t of T s u m e b . I n d iv id u a l b e d d in g t r a c e * a r e d i s c o n t i n u o u s . T h i s z o n e f o r m s t h e m i d d l e p o r t i o n of t h e u p p e r T s u m e bs t r i k e r i d g e s . S l o p e s a r e g e n e r a l l y l e s s t h a n 1 0° . D r a i n a g e i s i n t e r m e d i a t e t o t h a t of Z o n e S a n d Z o n e b (b e l o w ) . V e g e t a t i o n is s i m i l a r t o Z o n e fl w i t h s h o r t e r t r e e t y p e s t ha n t h o s e c ha r a c t e n s t iof Z o n e b V e g e t a t i o n d e n s i t y >* a l s o lew* t h a n t h a t o f Z o n e b. S m a l l s i n k h o l e s m a y f o r m a l i g n m e n t s a l o n g f a v o r a b l e b e d d i n g p l a n e s . I h e m a r l y u n i t s in t h e m i d d l e p o r t i o n of t h i s z o n e a r e t yp ic a l l y c o v e r e d by s h o r t , b r o w n i s h - r e d g r a s s w i t h f ew s h r u b s o r t r e e s .
A l t e r n a t i n g b a n d s o f v e r y l i ght a n d m e d i u m - t o n e d b e d d in g t on e g r a d u a l l y d a r k e n s t o w a r d t h e t op . A b u n d a n t b e d s o f l i g h t - t o n e d c h e r t f o r m s m a l l r i d g e s T h i s un i t f o r m s s t r i k e r i d g e s w i t h s l o p e s of 2 0 ° t o 40 * . D r a i n a g e .* a l o n g s l e e p , d e e p l y im i s e d , s h a r p , V s h a p e d c u t s . V e g e t a t i o n i s g e n e r a l l y d e n s e a n d s i m i l a r t o t h a t of Z o n e s 4 a n d 5 ( be l ow ) T h e c h e r t b e d s l o r n , t a l u s d a m s a n dl o c a l i z e z o n e s o f m o r e a b u n d a n t v e g e t a t i o n . T h e s e c h e r t b e d s ar«- g e n e r a l l y d i s c o n t i n u o u s a n d c a n on ly be f o l l o w e d t o r a f ew t h o u s a n d f ee t a l o n g s t r i k e T h e r e i s a d e c r e a s e in t h e n u m b e r ofr e s i s t a n t c h e r t b e d s t o w a r d t h e t o p of t h e z o n e . T h e m o s t c o n t i n u o u s c h e r t b e d s a r e t h e " T u t e n " m a r k e r u n i t s , T j a n d T g . of S c h n e i d e r ho lm ( I 420 ) w h ic h f o r m tw o p a r a l l e l 1- t o 6 - foo t r i d g e s MSt r e t , s t r a t . g r a p h i c a l l y , a p a r t . T h e c o n t a c t of Z o n e s h a n d 7 is o f t e n m a r k e d by t h e r i d g e l i n e o r a t t e a s i by a c h a n g e in s l o p e .
U n i f o r m l i g h t t o m e d i u m to n e w i th a v e r y f ew w e a k s u g g e s t i o n * of t h in d i s c o n t i n u o u s b e d d in g t r i n s i m i l a r t o Z o n e 4 t h a t l o r p r a c t i c a l p u r p o s e * it * s u g g e s t e d t ha t Z o n e S be g r o u p e d w i th Zoi
M o s t of t h e b e d d in g t r a c e * w i l l be n e a r t h e Z o n e b b o u n d a r y L a n d f o r m , v e g e t a t i o n , e t c e x c e p t f o r a r e a * w h e r e t h e v a r t b e d d e d n a t u r e is b e s t d e v e l o p e d .
•i.ght - g r a y m a s h i ; e d o lu m i f e w i th l o c a l a r e a s of r i h g r I s t r o m a t o l i t e s . 3 2 0 0 'T h i s z o n e f o r m * th e l a r g e s t p a r t of t h e O ta v i M o u n ta in l a n d a n d e x h i b i t s a m o n o t o n o u s , u n i f o r m , l i g h t - t o m e d i u m - l i g h t - g r a y t on e w i th e x t r e m e l y r a r e , w e a k s u g g e s t i o n s of b e d d in g . B e c a u s e o f i t s u n i f o r m m a s s i v e c h a r a c t e r , t h e u n i t f o r m s t h e h i g h e s t p a r t s of t he r e g i o n a n d f o r m s r o u n d e d a n d e l l i p t i c a I h i l l s a n d g r o u p * o f h i l l s f r o m w h i c h r o u n d e d e x t e n s i o n s r a d i a t e T h e r o u n d e d h i l l s o f t e ns u r r o u n d * d e p r e s s i o n . D e n s e t h o r n b v s h g r o w t h , w i th m e d i u m - h e i g h t t r e e s a n d u n d e r b r u s h , is c h a r a c t e r i s t i c . D r a i n a g e i s m o s t l y i n t e r n a l t h r o u g h v e r y s m a l l k a r a t f e a t u r e s
L i g h t - t r a y l a m i n a t e d an d t h in l y b e d d e d d u l u n i te . 6 0 0 ' M e d i u m - t o l i g h t - g r a y t o n e w i th a b u n d a n t c l o s e l y s p a c e d b e d d i n g t r a c e s . T h i s z o n e g e n e r a l l y f o r m s f l a t s o r l o w r o l l i n g h i l l s c o v e r e d w i th a l a b b y t a l u s . V e g e t a t i o n i s a l m o s t e x c l u s i v e l y l i m i t e d i s h o r t g r a s s g r o w t h . A b r e c c i a z o n e a t t h e b a s e of t h i* un i t m a y f o r m a n a r r o w t o p o g r a p h i c l ow a l o n g t h e Z o n e 2 - 1 b o u n d a r y .
f ~ r
Ligh t c» r a v l a m i n a t e d an d t h in l y b e d d e d l i m e a t o n e . L " b » r ■>( t h i s />.ne i I -c t i K »« pt eki .xh r yeMowf&sh 2 3 0 0 ' M e d i u m - l i g h t - t o m e d i u m g r a y t o n e ( t an t o b r o w n c o l o r ) w i th a b u n d a n t c l o s e l y s p a c e d b e d d in g t r a c e s . A l t h o u g h t h i s un i t d o e s f o r m s o m e h i gh g r o u n d , it t y p i c a l l y f o r m s r o l l i n g l ow h i l l s * i t h eht-i g r a s * a* t h e e x c l u s i v e v e g e t a t i o n . A w e l l - d e f i n e d , w h i t e c a l c r e t e r i d g e f o r m * a u s e f u l p h o t o m a r k e r un i t a t t h e ba we of t h i s z o n e m th e S a r g b e r g a r e a .
T i i l i t e .- #ingi<»n*erate. q u a r t ' i t e s h a l e m a r b l e , and s i r<ima t - i t t e m a r k e r u n i t s . T h e n l l v e t * g r a y w h e n f r e s h w e a t h e r i n g t o a d e e p b r o w n an d m a y c u n t a i r a b u n d a n t p v r i l e .
-----------------------------------------------------------------u n c o n f o r m i t y ---------------------------------------------- -----------------
7 0 0 '[ ) » rk t o n . ( t i l l i t , . , I t . m a t i n g With n t . d i u m t o n , ( s h a l e ) a n d l i g h t - t o m e d i u m l i g h t - t o n e d 1 d o l o m i t e ) u n i t s . T h e t n t e r b e d d e d u n i t s o< t h i s z o n e a r e w e a k ly r e s i s t a n t t o w e a t h e r i n g a n d g e n e r a l l y l o r t r . i l a l x o r low ro l l . ng h i l l s . T h e t i l l i l e m e m b e r s , w h e r e p r e s e n t , g e n e r a l l y p r o t e c t a few f e e l a b o v e t h e s u r r o u n d i n g m a t e r i a l f o r m i n g l ow , r o u n d e d r i d g e s . M ic r o d r a m a g e t e a t u r e s in t h e t i l l i t e a r e c u r v e d . T h e r o c k s o f t h i s z o n e l o r m a d a r k s o i l a n d y e l l o w i s h s a n d w h ic h s u p p o r t s p a r s e g r a s s c o v e r . T h e t i l l i t e m e m b e r s o f t h i s z o n e a r e r e g i o n a l l y d i s c o n t i n u o u s . L o c a l l y , t h e r e m a y be a t h i n d e v e l o p m e n t o f w h i t e d o l o m i t e ( l i g h t t o n e )
Wedded a n d m a s s i v e m e d i u m g r a y d o l o m i t e , w e a t h e r i n g tt, * d a r k br«» g r a y wed/ fed l i m e s t o n e m a y be d e v e l o p e d
a! lv l i gh t g r a v b e d d e d d«»J«>mite • I 100 D a r k t o m e d i u m t o n e d , w i th bo th b e d d e d a n d non b e d d e d p o r t i o n s , f o r m i n g r u g g e d c l i f f s a n d l a r g e , r e s i d u a l b o u l d e r s . T h e un i t i v e g e t a t i o n a n d d r a i n a g e c h a r a c t e r i s t i c s .
n ly m a s s i v e a n d p r o b a b l y r e s e m b l e s 1 s u r n e b Z o n e s b a n d 4 i
M a s s i v e l i g h t g r a y d o l o m i t e w i th l o c a l l y d e v e l o p e d o o l i t e / .one*. 2 4 0 0 M e d i u m - t o l i g h t - t o n e d m a s s i v e s e q u e n c e , s i m i l a r t o T s u m e b Z o n e 4 , b u t s l i g h t l y l e s s v e g e t a t e d t h a n Z o n e 4. M o r e a b u n d a n t v e g e t a t i o n n e a r t h e b a s e t h a n in t h e r e m a i n d e r of t h e m a s s i v e s e q u e n c e .
D a r k - an d l i g h t - g r a y l a m i n a t e d a n d m a s s i v e d o l o m i t e , l i m e s t o n e , s h a l e g r a y w a c k r a n d g r i t W i t h i n t h e l i m e s t o n e s i n t e r m i t t e n t l a y e r s •»( g r i t t y m a t e r i a l a r e d e v e l o p e d . T h e g r i t s a r e d o m i n a n t l y p a r t i c l e s o f d o l o m i t e w i th s u b o r d i n a t e a m o u n t s o f c h e r t a n d q u a r t z . T he a n g u l a r g r i t f r a g m e n t s a r e f r o m a t ew i r .m to 4 i n c h e s i n d i a m e t e r T h i s s e c t i o n a l * v c o n t a i n s a b l u i s h -b lack l i m e s t o n e w i th s p o r a d i c l a y e r s ,f g r a y p h v l i i t e o r y e l l o w i s h s h a l e . G r a y w a c k e . a r k o s e . an d q u a r t / i t e a r c a l s o r e p o r t e d .
2 7 0 0A l t e r n a t i n g l i g h t - , m e d i u m - , a n d d a r k - t o n e d m e m b e r s . D e v e l o p m e n t of b e d d in g t r a c e s i s v a r i a b l e . T h e l o w e r h a l f of t h i s s e q u e n c e h a s m o r e e v i d e n c e o f b e d d i n g t r a c e s T he L o w e r A b e n a b f o r m s g e n t l y u n d u l a t i n g t o p o g r a p h y .
L p i d o s i t e . s c h i s t , a g g l o m e r a t e a r k o s e . a n d q u a r t / i t e .
- u n c o n f o r m i t y -
C o n g l o m e r a t e q u a r t / i t e , a r k . i s r . g r i t p h y I I i t e m a y l o c a l l y c o n t a i n t h i n b e d d e d d o l o m i t e .
5 0 0 '
2000 '
M e d i u m - t o d a r k - t o n e d u n i t s w i th o r w i t h o u t e v i d e n c e s of b e d d in g . T o p o g r a p h y v a r i e s f r o m c l i f f s t o r o u n d e d h i l l s . T h e N o s i b is d e n s e l y w o o d e d . AU f e a t u r e s , w i t h t h e p o s s i b l e e x c e p t i o n o f v e g e t a t i o n , v a r y w i t h t he v a r i a t i o n * of t h e l i t h o lo g y .
- u n c o n f o r m i t y
READDY GEOSCIENCES THESIS 1972
FIGURE 3. OTAVI MOUNTAINS STRATIGRAPHY AND PHOTOGEOLOGIC EXPRESSION
\ B o b o s^ - T s u m e b
V - 1^ ^ T s u m e b W e s t
b o s . v ”
^ F r i e s e n b e r g r _ ' j / |
' • ' v . . '
I
v 5? A b e n a bI ' ‘
<4xJX / \ y .V >A -• V' G r o o t f o n t e i n
i \ ; —I ' ' " 'O t a v i _y
^ TK o m b a
\E X P L A N A T I O N
--------------- b o u n d a r y o f p h o t o g e o l o g i c m a p p i n g
^ m i n e
• p r o s p e c t
T s u m e b Z o n e 8 m i n e r a l i z a t i o n ( l e a k a g e ? )
10 20 30
sca /e in miles___
Figure 2. P rospect Location Map, Tsumeb Area, South W est Africa
accom panied the re c o n n a is s a n c e scan of th e large co l le c t io n of ae r ia l
photographs for the r e g io n . The prelim inary li te ra tu re s tudy in d ica ted
some photo k e y s , and f i r s t - p a s s overlay tem p la te s were prepared for 65
photographs s e le c te d from the sev era l hundred photographs s tu d ied .
No good b a se maps were, " a v a i lab le " for th is a r e a . The b ase
map used in th is report w as ob ta ined by trac ing portions of four farm
boundary maps showing the pos it io n of photo cen te rs for Government
M apping P ro jec t 502. The s h e e ts from w hich the b a s e map w as tra c e d
w ere produced by a w et p ro c e ss and unfortunate ly con ta ined d is to r t io n s
w hich could not be e lim inated .
Additional photographs were required for a study of the pho to -
geo log ic fea tu res of the Berg Aukas d e p o s i t , w hich i s not covered by
P rojec t 502 photography . The photographs were ordered but did not a r
rive un til s ev era l w eeks af te r my departure from W in d h o ek .
The ea r ly a rriva l of the ra iny s e a so n s e r io u s ly lim ited the field
check ing of o f f ice -d e f in e d photo marker u n i t s . C o n seq u en tly , the r e
m ainder of the p ro jec t w as com pleted more by pho to in te rp re ta tion th an by
f ie ld -c h e c k e d photogeolog ic m apping.
Our re q u e s t for pe rm iss ion to remove sev e ra l hundred se le c te d
pho tog raphs, including the 65 in i t ia l ly s tu d ied , w as su b seq u en tly d e n ie d .
This is u n fo r tu n a te , s in ce a la rg e r a rea could have been mapped w ith
more geo log ic and p lan im etric c o n t ro l . Subsequent read ing of h a rd - to -
o b ta in , ea r ly German l i te ra tu re h as brought out s tra t ig ra p h ic ty p e -
sec t io n lo c a l i t ie s and sp ec if ic p ro sp ec t a re a s which should have been •
incorporated into th e p re sen t s tu d y . Had th e data from th is l i te ra tu re
b een on hand a t the beg inn ing of the p ro je c t , more re l ia b le and much
f a s te r pho togeologic mapping would have been p o s s i b l e . In ad d it io n ,
th e p re sen t photo s tudy would have co n cen tra ted on the a rea ju s t north
of the O tavi Valley w ith only minor mapping in the Tsumeb (Fig. 2) .
As a re s u l t o f the n e c e s s a r i ly lim ited photo d a ta th a t can be
tran sfe rred to overlay s h e e t s , a co n s id e rab le amount of com pilation of
s tra t ig ra p h ic 'd a ta sc a t te re d in the l i te ra tu re w as requ ired b e fo re 'th e map
ping could be a d eq u a te ly c o m p le te d .
REGIONAL GEOLOGY
. The a rea o f the O tav i M ountain land is ch a ra c te r iz e d by a th ick
carbona te sequence of th e la te Precam brian Otavi g ro u p , g en tly folded
in the northern a r e a , and more in te n se ly fo ld e d , in f a c t , o v e rfo ld ed ,
toward th e n o r th , and th ru s t fau lted in th e southern a r e a . The M ulden
form ation, prim arily a fe ld sp a th ic q u a r tz i te , o v e r l ie s th e O tavi group
w ithin the troughs of reg ional e a s t - w e s t s y n c l in e s . M uch of the reg ion
i s covered by a th in v en ee r of Tertiary co n tin en ta l d e p o s i t s , c a l ic h e ,
and Kalahari s a n d s . The O tavi group r e s t s unconformably upon v ar iab le
th ic k n e s s e s of N osib formation (maximum th ic k n e s s , 2 ,500 fee t) , w hich
i s a mixture of q u a r tz i te s , a rk o s e s , co n g lo m era tes , and m eta lav as w h ich ,
in turn is s ep a ra ted from the basem en t by an unconform ity . W here the
N osib i s a b s e n t , th e low erm ost member of the O tavi g ro u p , the Abenab,
r e s t s d ire c t ly on the o lder Precam brian b asem en t of s c h is t and g ran ite .
The basem en t r o c k s , where ex p o sed , have a grain th a t i s roughly p a ra l
le l to the e a s t - w e s t ax is of folding w ith in the r e g io n .
The O tavi S er ie s i s subdivided into the Tsumeb and Abenab
s ta g e s , sep a ra ted by a d isc o rd a n c e . The A benab , w hich forms the low er
h a lf of the O tavi g ro u p , h a s been subdiv ided into th ree p a r ts and com
p r is e s a maximum to ta l th ic k n e s s of s lig h tly more than 6 ,000 fe e t , The
upper h a lf of the O tav i g ro u p , the Tsumeb s ta g e , has been subdiv ided ,
into th ree su b s ta g e s com prised of a to ta l of e igh t z o n e s . The maximum
to ta l th ic k n e s s of th e Tsumeb s tage i s reported ly 10 ,600 f e e t . These
6
s tra tig rap h ic su b d iv is io n s are g rap h ica lly shown and d e sc r ib e d in Figure
3 (in pocket) „ .
S tra tig raphic Problems
In the Kombat area (Fig. 2), i t .is apparen t th a t th e O tavi Valley
phy ll i te and the p se u d o a p l i te s are contem poraneous w ith Zones 7 and 8
of the Upper Tsumeb s u b s t a g e . The O tav i Valley phy llite h a s been c o n
sidered to be part o f Tsumeb Zone 7 (Sohnge, 1963) but may be e q u iv a
le n t to both Zones 7 and 8 and be p a r t ia l ly co rre la tive w ith the M ulden
a s w e l l . The p se u d o ap li te a t Kombat is a l s o , accord ing to the Kombat
geo lo g ica l s ta f f , a sed im entary unit in terbedded w ith in th e Tsumeb Zones
7 (?) and 8 . Zone 7 ap p ears to be m iss in g in the Kombat a r e a . The O tavi
Valley phy ll i te and the p seu d o ap li te (fe ldspath ic quartz ite ) le n s e s can
be con s id e red to 'form a r e g re s s iv e - t r a n s g re s s iv e sequence prior to and
culm inating in th e d e p o s it io n of th e main m ass of the O tav i Valley p h y l
l i t e , w hich may be the southern eq u iv a len t of the M ulden .
N ear T sum eb , th e M ulden sed im en ts are d e f in ite ly p o s td e p o s i -
t io n a l to Zone 8 . The M ulden is s ep a ra ted from th e Tsumeb Zone 8
do lom ites by a lo ca l unconform ity in a reg ion w e s t of Tsumeb (Martin,
1965) but ap p ears (?) to be conform able in the Tsumeb a re a .
O ther s tra t ig rap h ic un its w ith in the O tavi M oun ta ins show
marked la te ra l fa c ie s ch an g es which often make d iff icu lt th e i r reco g n i
t io n during reg ional m ap p in g . The re la t iv e abundance of chert and the
p re se n c e of o o li t ic b a n d s , bedding c h a r a c te r i s t i c s , sp ec if ic ty p es o f
s tro m a to li te s , and d isco n tin u o u s t i l l i te ban d s allow c e r ta in zo n es to be
mapped with fa ir r e l ia b i l i ty .
P seu d o ap li te
W ithin the Tsumeb and Kombat m in e s , a rock type occurs which
h a s c a u se d co n s id e rab le d e b a t e . The rock is referred to a s p s e u d o a p l i te .
Sohnge e t a l . (1961) d e sc r ib e s th is a s " . . . a p e c u l ia r rock with the
petrograph ic c h a ra c te r is t ic s of a fe ld sp a th ic q u a r tz i te , but undoubtedly
in t ru s iv e , having been em placed af te r folding of the dolom ite and a fte r
the peak of sh ea rin g , b re c c ia t io n , and cy lin d rica l frac tu ring . The a b
sen ce of c o n ta c t m etamorphic e f fec ts in d ic a te s th a t the p seu d o ap li te w as
in jec ted a t low te m p e ra tu re ." From d is c u s s io n s with the g eo lo g ica l
s ta f f of Tsumeb and Kombat m in e s , it .is apparen t th a t th e ir f ie ld d e f in i
tion of "p seu d o a p li te " is m inera lized quartz i t e . It it is no t m in e ra l iz e d ,
it is quartz ite or a rk o se . ■ ■
The p se u d o ap li te of Tsum eb.W est co n ta in s many fea tu res in
common w ith the nearby M ulden fo rm ation , including p eb b le s and
rounded g ra ins of q u a r tz , The n o n -q u artz c o n s t i tu e n ts have been la rge ly
converted to s e r ic i te and minor amounts of c l a y .
The p se u d o ap li te in the upper portion o f the Tsumeb mine co n
ta in s 1 0 p e rcen t rounded grains of quartz up to 1 mm and is very s im ilar
to the nearby M ulden sed im en ts . Pebb les of u n sp e c if ie d com position
have a lso been reported from the p seu d o ap li te in the upper le v e ls of the
Tsumeb m ine . The p seu d o ap li te in the low er le v e ls h as not y ie lded
pebb les ; and heavy m ineral s tu d i e s , accord ing to Sohnge (1962), in d i
ca te a s tronger affin ity w ith in trus ive igneous r o c k s .
Sohnge (1962) repo rts the com position of p se u d o a p l i te to be
70% q u a r tz , 15% to 20% m icrocline and o r th o c la s e , 5% to 10% sodic
p l a g io c la s e , with b lot i t e , m u sco v ite , s e r ic i t e , r u t i l e , le u c o x e n e ,
9
i lm en ite , z i r c o n , and tourm aline a s a c c e s s o ry m in e ra ls . The 1-mm
g ra in s have been c rushed and further modified by re c ry s ta l l iz a t io n ,
s i l i c i f i c a t io n , quartz overgrow ths , and c a lc i t iz a t io n ; how ever, rounded
g ra ins of quartz and fe ld sp a r su g g es t iv e of sedim entary m ateria l are s t i l l
recogn izab le in m ost th in s e c t io n s of p seu d o ap lite tak en from above the
. 24 lev e l (Fig. 4) . The problem is further com plica ted by the marked
s im ila r ity of the p se u d o ap li te w ith both the M ulden fe ld sp a th ic q u a r tz -
i t e s and the q u a r tz i te s in the N osib s e c t io n .
Karst Fea tu res
Karst fea tu re s are very abundant in the O tavi M ountain lan d .
The type and degree of k a rs t developm ent are dependen t on the var ia tio n
of so lub il i ty w ithin the d ifferen t ca rbonate u n i ts , pe rfec tion of bedding
and bedding a t t i tu d e , jo in t in g , fau lting , and loca l hydrology.
The area s tud ied is w e ll known for two of i ts sp e c ta c u la r k a rs t
fe a tu re s , the O tjikoto See and the G u in e ss See, w hich are la rg e , deep
s in k h o les p a r t ia l ly f illed w ith w a te r . The O tjikoto s in k h o le , 700 by 650
f e e t , i s a w a te r -su p p ly source for the Tsumeb mine and h as been r e
ported ly plumbed to a depth of 600 fe e t . .Other s ink h o les are known to
ex tend to a dep th of a t l e a s t 300 fe e t , bottoming in c o l la p se b re c c ia .
Karst fea tu re s include poorly developed d ra in a g e , van ish ing
stream c o u r s e s , open s in k h o le s , in f i l tra t io n p o in ts , c a v e s , and sev era l
v a r ia t io n s of p it-m ount to p o g ra p h y . In a re a s underla in by the more s o l
uble and th in ly bedded u n its of the O tav i group, tha t i s , Tsumeb Zones 2
and 3, c l a s s i c ro lling k a rs t topography is d ev e lo p ed . Several such a re a s
a re ind ica ted on the photogeolog ic s truc tu ra l map sim ply a s " k a r s t . "
1 0
SOUTH NORTH
0 f e e t
IOOO
2000
3 0 0 0
D e W e t S h o r t N o 1 S h o f t
r,
I
N o . 5 S h a f t = -
E X P L A N A T I O N
| f e l d s p o t h i c q u o r t z i t e , g r e y w o c k e , S l a t e ) - Malden Ser i es
Dedded l ig h t gr ey do lo m ite , c h e r t , ool i te
bedd ed d o r k g re y d o l o m i t e , oo l i te s
be dde d l i g h t- g re y d o l o m i t e , a l g o l c h e r tMiddle Tsu meb
U p p e r T s u m e b — S u b s t o g e
m a s s i v e l i g h t- g re y d o lo m it e
| p s e u d o o p h f e
| S/j m a s s i v e o re
•«‘I b re c c i a
S u b s t o g e
8 level
— 12 level
— 16 level
20 level
24 level
28 level
- 30 level
10 0 0 8 0 0 6 0 0 4 0 0 2 0 0 0_________________________________________1000
Sct7/e in f e e t
Figure 4. G eologic C ross Section through Tsumeb Ore B ody .—After Sohnge e t a l . (1961)
ECONOMIC GEOLOGY
Types of D ep o s its
The hypogene m in era liza tio n s of th e O tavi M ounta ins are t e l e -
thermal b a s e -m e ta l d e p o s i ts of copper , l e a d , and z inc w ith variab le
am ounts of cadm ium , germ anium , and s i lv e r . The four p r in c ip a l types
of m inera liza tion are (1) rep lacem ent bod ies in b recc ia zo n es in dolomite
o f the O tavi S e r ie s , (2) rep lacem en t periphera l to b recc ia p ip es or
p se u d o a p li te m a s s e s , (3) branching v e in s in do lom ite , and (4) d is s e m i
n a ted m inera liza tion in do lom ite , b re c c ia z o n e s , or p s e u d o a p l i t e .
No igneous in tru s iv e s are known a t th e s e d e p o s i ts o ther than
postm inera l d ik es of do le r ite and k e r s a n i te . A lteration of the dolom itic
h o s t rocks c o n s is t s of re c ry s ta l l iz a t io n of the dolomite and the add ition
of c a lc i te and q u a r tz . C a lc i te and quartz are the m ost common a l te ra t io n
m inera ls in the r e g io n . G raphitic a l te ra t io n and minor a lb i te a l te ra t io n
are reported by Sohnge (1962). Q u a r tz -s e r ic i te a l te ra t io n with or w ithout
the addition of c a lc i te is common in the m inera lized p s e u d o a p l i t e s .
R esidual d e p o s i ts of c h a lc o c i te have been mined from sa n d -
fil led s ink h o les th a t formed by so lu tion of the c a lc i t ic a l te ra t io n e n
v e lo p es surrounding v e in s o f primary c h a lc o c i te or c h a lc o c i te -b e a r in g
p se u d o a p l i te .
Supergene vanadium d e p o s i ts have formed by th e add ition of
vanad ium , from c ircu la t in g ground w a te r s , to ox id iz ing hypogene d e
p o s i ts con ta in ing le a d . ,
11
. 1 2
The O tavi M ountains can be subdiv ided into two co p p e r-r ich
a r e a s , one near Tsumeb and one along the north s ide o f th e O tavi Valley
50 m iles south of Tsumeb (Fig. 2). O ther than review ing the d e p o s i ts in
the O tavi Valley reg ion , th is th e s i s is re s t r ic te d to the Tsumeb or n o r th
ern portion of the O tav i M o u n ta in s .
' Tsumeb Ore Body
G eology of the Tsumeb M ine
The la rg e s t and b e s t known mine of the O tavi M ountains is the
Tsumeb mine (see F i g s . 2, 4 , 5, 6 , and 7) w hich , from 1907 through
1959, produced 4 2 6 ,720 tons of copper , 1 ,1 0 3 ,5 1 0 to n s of le a d ,
507 ,970 tons o f z inc (1949-1959), and more th an 2 3 ,0 0 0 ,0 0 0 ounces of
s i lv e r . The sp h a le r i te a t Tsumeb co n ta in s approxim ate ly 1.7% cadmium,
w hich w as not recovered a t the Tsumeb mine un til 1927 when a C ottre l
p lan t w as in s ta l le d a t the Tsumeb sm elte r . W illem se e t a l . (1944) report
th a t 2 ,3 0 0 ,0 0 0 pounds of cadmium w as produced from th e Tsumeb mine
be tw een 1927 and 1941. Zinc w as dumped with the sm elte r s lag s prior
to 1949 when th e Tsumeb C orporation in s ta l le d a s e le c t iv e flo tation
p l a n t . Total production figures for germanium produced by Tsumeb are
not av a ila b le . P e l le t ie r (1964) repo rts a da ily production of 120 pounds
of germanium in 1961. P ub lished re se rv e s for the Tsumeb mine in 1959
were 8 ,1 3 2 , 000 tons of ore averag ing 5.3% copper, 14.4% le a d , 4 .4%
z i n c , 0.013% germanium, and an es tim a ted 2 to 4 ou n ces of s ilv e r per
ton; su b seq u en t d ril l ing h as added su b s ta n t ia l r e s e r v e s .
The Tsumeb ore body i s lo ca ted on the north limb of an e a s t -
plunging reg ional sy n c lin e . The o r ig ina l outcrop w as a sm all,
55
40
6045 A <
AO, 5055
50
Figure 5. Geologic Plan, Level 26, Tsumeb Ore Body
i
E X P L A N A T I O N
o r e b o d y
m o s s i v e o r e
p s e u d o o p l i t e
b r e c c i o
N
100sco/e in feet
From Sohnge (1962).
T s u m e b M i n e
V V T s u m e b
T s u m e b W e s t
Scale m miles
s ze of CriQi.not T su^ec Oa»CfOD
E X R L - A N A T I O N
$ 3 ^ 5 efl c reos Show ng spoc ■ 0#Cut Dy ’’sumeD M -rt-g Co'pO'O ’ on
oh c to c en t e r s
Figure 6 . Road Net Map Showing Location of Tsumeb Mining Corporation Sampled Areas # Tsumeb and Vicinity
5a4d o l e r i t e d i k e
T S U M E B E A S T ,
45
4 5T S U M E B
55 > -
35
T S U M E B . W E S T
45
20
50
20
-< 3 0
5 a4
E X P L A N A T I O N
I I
M u l d e n q u o r t z i t e
l i g h t d o l o m i t e w i t h o o l i t i c c h e r t
d o r k d o l o m i t e w i t h l i m e s t o n e a n d s h a l e
K- r
III 5 a4
MVJ44ft»44
l i g h t d o l o m i t e w i t h o b u n d o n t c h e r t
l i g h t - g r a y m a s s i v e d o l o m i t e
b r e c c i a z o n e s
p s e u d o a p l i t e
c o p p e r a n d v a n a d i u m p r o s p e c t s
o o l i t e m a r k e r b e d s i n T s u m e b z o n e 8
0 1/2
scale in miles
Figure 7. Geology of Tsumeb Area, South W est A frica. --M od ified from maps by Schneiderhbhn (1929) and Sbhnge (1958).
16
tw o -p eak ed h i l l , approxim ate ly 500 by 100 fee t and 36 fee t h igh , lo ca ted
en tire ly w ith in the Upper Tsumeb s u b s ta g e , Zone 7, about 200 feet north
o f the Tsumeb Zone 7 -Zone 8 c o n ta c t . The h i l l w as com posed e s s e n t ia l ly
o f m a la c h i te , c h a lc o c i te , and g a le n a , w ith l e s s e r am ounts of o ther c o p
p e r , l e a d , and z in c m inera ls ; p seu d o ap li te formed th e sad d le be tw een
the sm all peak s of m ass iv e o re .
The ore body is an e l l ip so id a l p ipe com posed o f m ass iv e r e
p lacem ent o res w ith d is se m in a te d ore in b recc ia and p s e u d o a p l i te . From
th e su rface to about 770 fe e t , a ce n tra l low -grade core of p seu d o ap lite
s e p a ra te s th e ore pipe in to the w e s t and e a s t ore b o d ie s . P a r tia l ly
d eveloped cy lin d r ica l f rac tu res around th e p seu d o ap li te in the w este rn
ore body formed the lo cu s for sev e ra l r ich copper v e in s above a depth o f
515 f e e t .
The pipe c h an g es plunge re p e a te d ly a s the ore s truc tu re t r a v
e r s e s u n its of d iffering com petency within the Tsumeb do lom ites (Fig. 4).
The c h an g es in plunge are accom panied by var ia tion in p lan area of the
ore p ip e , being sm alle r in th e portions tha t conform to th e dip of the
sed im en ts and notably larger where it cu ts sharp ly a c ro s s the b edd ing .
Maximum plan d im ensions of th e ore p ipe are 600 by 200 fee t a t a depth
of 2 ,390 f e e t .
The ore pipe p lunges s tee p ly to th e south a s i t t r a v e rs e s the
upper part of Zone 7 but f la t ten s out to cu t gen tly a c ro s s the bedding of
the low er portion of th is z o n e . As the more b r it t le ch e r ty dolom ites of
Zone 6 are en co u n te red , the ore body aga in changes to a very s tee p ly
plunging pipe cu tting nearly a t right an g le s to the more com petent d o lo
m ite s . This e f fec ts a r e v e rsa l in plunge of the ore body from
17
approx im ate ly 55° S. to approxim ate ly 75° N. A b recc ia p ipe forms the
core of the d e p o s i t w ith in Zone 6 (F ig s . 4 and 5) . The b recc ia core- b e
g ins a t 2,015: fee t and con tin u es to a t l e a s t a depth of 3 ,2 6 5 fe e t .
W ithin Zone 6 (Fig. 4) , the ore body in te rs e c ts many so u th -
d ipping b ed d in g -p la n e f a u l t s , including the North Break Fracture Zone
(NBFZ), a b re c c ia zone up;to TOO fee t th ic k . This b recc ia zone in te r
s e c ts the main ore pipe a t a depth of 2 ,890 f e e t ., O ther bedding fau lts
are numerous in Zones 6 and 7, but the NBFZ is the m ost im portant e c o
nom ica lly , a s i t is the locus for th ree manto wings of h ig h -g rad e m ass iv e
o r e . The NBFZ co n ta in s d issem in a ted m inera liza tion and sm all pods of
p seu d o ap li te for s e v e ra l hundred fee t on e ither s ide of the ore body.
B edding-p lane b re c c ia s in c re a se below a depth of 2 ,640 f e e t , reach
th e ir maximum developm ent in the NBFZ, and occur on down to a depth
of a t l e a s t 3 ,140 fe e t , a t l e a s t ten h ig h -g rad e m antos ex tend ing up to
300 fee t aw ay from the pipe have been e n c o u n te re d . One of th e se m an tos ,
ju s t below th e NBFZ, a t a depth of 3 ,015 fe e t , con ta ined 75 ,000 tons o f
ore averag ing 23% copper .
Between the dep ths of 1 ,890 and 2 ,765 fe e t , the ore pipe is
c lo se ly re la te d to a sm all lo c a l iz e d s y n c lin e , the "orebody s y n c l in e ,"
superim posed on the reg iona l sync line with the long ax is of the pipe in
p lan view roughly co in c id en t with the a x is of the "orebody syncline"
(Fig. 5). Radial fracturing a t each end and con cen tr ic fracturing su r
rounding the ends of the " orebody sync line" are lo ca lly w e ll deve lo p ed .
The ore body con tin u es its 75° N. plunge to a depth of 3 ,150
fee t below the s u r f a c e , w ell into Zone 5 . Sohnge e t a l . 's (1961) s e c t io n
(F ig . 4) shows the ore body d e c reas in g in d iam eter and in d ic a te s the
18
beginning of a re v e rsa l in the p lu n g e . D rilling below a dep th of 3 , 515
fee t by th e Tsumeb Corporation h as shown tha t a r e v e rs a l h as indeed
occurred and th a t the ore body has becom e tab u la r and sp li t into sev e ra l
z o n e s . T hese ta b u la r ore zo n es are r icher in copper than in lead and may
correspond to rep lacem en t a long the th in a rg i l lac eo u s u n its o f Zone 5 or
to rep lacem ent a long frac tu res in Zone 4 .
A lteration
A lteration a s s o c ia te d w ith th e Tsumeb ore body in c lu d es c a l c i t -
iz a t io n , s i l i c i f i c a t io n , s e r ic i t iz a t io n , a lb i t iz a t io n , and the convers ion .
o f carbon to g raph ite . D e ta iled information on the d is tr ib u t io n of a l t e r a
t ion is p re se n t ly la c k in g .
C a lc i t i z a t io n . Developm ent of c a lc i te and r e c ry s ta l l iz a t io n of
the dolomite ad ja c e n t to the ore body is the c h a ra c te r is t ic a l te ra t io n f e a
ture of the Tsumeb m in e . C a lc i te h a s a lso been added to the p se u d o -
a p l i t e . C a lc i t iz a t io n , w hich is the m ost ty p ic a l a l te ra t io n type found a t
th e mines of the O tav i M o u n ta in s , ta k e s the form of v e in le ts of c o a r s e
gra ined c a lc i te w ith quartz g rains and a s d issem in a ted c a lc i te of v a r iab le
gra in s iz e in the do lom ite . C a lc i t iz a t io n a t Tsumeb h a s formed a l a r g e ,
c o a rse -g ra in e d c a lc i te plug be tw een 3 ,390 and 3 ,765 f e e t .
S i l i c i f i c a t io n . S i l ic if ica tio n of th e dolomite near the surface
of the Tsumeb pipe is reported by Schneiderhohn (1929) . S i l ic if ica tio n o f
the dolomite is w eakly p re se n t in the in term ed ia te le v e ls of the mine
from dep ths of 515 to 2 ,640 f e e t . The re la t iv e abundance of quartz in
c r e a s e s below 2 ,640 fee t un ti l the gangue becom es h igh ly s i l ic e o u s and
forms a d en se q u a r tz - r ic h core a t 3 ,8 9 0 fe e t . S i l ic if ica tio n of dolom ite
' " . . 1 9
and quartz vein ing a s s o c ia te d with c a lc i t iz a t io n is a l s o reported in o ther
p a r ts of the O tav i M o u n ta in s . The p seu d o ap li te a lso h a s been s l ig h tly
s i l ic i f ie d .
S e r ic i t iz a t io n . M ost of the o r th o c la se fe ld sp a rs in the pdeudo-
ap li te have been a l te re d to s e r i c i t e . Seric ite grains are a lso found in the
dolomite im m ediately a d ja c e n t to the ore b o d y .
A lb i t iz a t io n . Sohnge (1962) reports sporad ic occu rren ces of /
a lb i te rep lac ing dolomite near the p seu d o ap lite be tw een a depth of 1 , 1 0 0
and 2, 390 fe e t .
G ra p h i t iz a t io n . G raphitic a l te ra t io n of the dolomite below
2 ,140 fee t is m an ifes ted as a gradual darkening of the dolom ite per iphera lt
to the ore body.
Igneous In trusive Rocks
Several pos tm inera l d ikes and s i l l s of k e r s a n t i te , a dark p la g io -
c la s e b io tite rock belonging to the lamprophyre s e r i e s , cu t the ore body, '
but as y e t no o ther truly, igneous in trus ive rocks have been encoun tered
in the workings or in the deep drill ing conducted by the Tsumeb M ining
C o rp o ra t io n .
Tsumeb W es t
During O ctober 1967, I sp en t o n e -h a l f day a t the Tsumeb W e s t
p ro sp e c t , 1 .9 m iles so u th w est of the Tsumeb mine (F ig s . 2, 6 , 7, and
8 ) with M r. C il l ie rs of the Tsumeb geo log ic s ta f f . According to C i l l i e r s ,
the poorly exposed Tsumeb W es t p seu d o ap li te body h a s an a rea l ex ten t
ten tim es th a t of the o r ig ina l Tsumeb o u tc ro p . Previous d rilling by the
Tsumeb Mining Corporation a s w ell as g eo p h y s ic a l su rveys (L ow enste in ,
* £ s r
s s/b/
7
Pi'Pe.~_
f /<sr
N)O
FIGURE 9E X P L A N A T I O N
5T RHOTOOEOLOGIC: STRUCTURE, MARTSUMER AREA
SOUTH WEST AFRICAm miles
rtnqmol Tsum^b OutC?0£)
x»- X - Xm x«»
vi'zz
Z z
pnoio df t . t ed d ps
X »
/ /
XX
//x«
X
r* r Z
x »
x»>X*
READDY GEOSCIENCESTHESIS 1972
* 21 ,
1950) have been d isco u rag in g . Future p lan s for th is a rea include ad d i
t io n a l d r il l in g .
The outcrops of the Tsumeb W e s t pipe is lo c a te d in fla t- ly ing ,
dolomite and lim estone of the Upper Tsumeb s u b s ta g e , Zone 7, near the
ax is of a lo ca l no r th - trend ing a n tic l in e which t r a n s g re s s e s the reg ional
e a s t - w e s t fold a x is of the Tsumeb s y n c l in e . Surface m inera liza tion of
th is p ipe is m a la c h i te , p la n c h e i te , c u p r i te / copper v a n a d in a te s and
a r s e n a t e s , and fine ly d issem in a ted c h a lc o c i t e . A grab sam ple of
p se u d o ap li te c o l le c te d from the e a s te rn co n ta c t of the pipe a s sa y e d
6.1% copper and s lig h tly over 0 .5 ounce of s i lv e r per ton (F ig s . 7 arid
8 ) . Because of the immediate proximity of the chem ica lly reac t iv e do lo
m ite , it is e x p ec ted th a t th is va lue is probably fairly re p re se n ta t iv e of
the o r ig ina l copper v a lu e . It is in te re s t in g to note th a t th is grab sam ple
y ie lded a copper va lue id e n tic a l to .th e average for p se u d o a p li te mined
from the f irs t s ix le v e ls of the Tsumeb mine . This grab sample of
p seu d o ap lite c o n s is t s of rourided but sh ea red quartz g ra ins up to 1 mm
in s i z e , abundant s e r ic i te rep lac in g fe ld sp a r , a sm all pebble of do lom ite ,
and abundant green copper ox ides with g o e th i te . The copper oxide a s
semblage, is m ostly m alach ite with p la n c h e i te , SCuSiOg • H 2 O . A sm all
amount of d u f t i t e , (Pb, Cu)3 (ASO4 ) 2 (Pb, Cu) (OH2) , is p re s e n t , and X -ray
tech n iq u es ind ica te t ra ce amounts of sp a n g o li te , Cu6 A1C1 (SC>4 ) (OH) 1 2 ,
and la n g i te , Cu^SO^^OH) g - H gO .
The Tsumeb W es t p seu d o ap li te body d esc r ib ed by Schneider-
hohn (1921) is an e l l ip t ic a l pipe 650 fe e t long e a 's t -w e s t by 260 fee t
wide n o r th -so u th . This v e r t ic a l ly plunging pipe w as te s te d about 1921
by two sh a fts with minor underground workings and s e v e ra l sm all
22
p ro sp e c t p i ts a long th e w es te rn c o n ta c t . The d eeper of the two s h a f t s ,
165 fe e t , w as sunk v e r t ic a l ly in the middle of the p seu d o ap li te body.. A
c ro s s c u t which w as driven north from the bottom of th is sh a ft in ter
se c te d a v e r t ic a l in tru s iv e c o n ta c t be tw een p se u d o ap li te on the south
and Zone 7 dolomite on the north . The p se u d o ap li te co n ta in s angular
do lom ite , l im e s to n e , and chert fragm ents n ea r the c o n ta c t „ Branching
p se u d o a p l i te d ik e le ts and sm all c h a lc o c i te v e in s with a q u a r tz -c a lc i te
gangue ex tend short d is ta n c e s into the do lom ite . C on tac t e f fec ts are
s l ig h t with only minor r e c ry s ta l l iz a t io n of the dolomite a t the p seu d o
ap li te c o n ta c t . The second shaft w as sunk a t the northern co n tac t of
the p seu d o ap li te p ip e . This shaft is 50 fee t deep with only two short
a d v a n c e s , one a t 43 fee t and the o ther a t the bottom of the sh a f t .
Schneiderhohn (1921) s ta te s th a t the p seu d o ap li te n ea r the co n
ta c t is more h ighly m inera lized than the c en te r of the body; th is may be
a function of the primary m inera liza tion p r o c e s s . H igher grade ore is
found s im ilarly s i tu a te d a t the p seu d o ap li te -d o lo m ite c o n ta c ts a t Tsumeb
and Kombat. At Tsumeb W e s t , th is may be partly the re s u l t of leach ing
of the copper ore m inera ls w ithin the c e n tra l , non reac tive part of the
p seu d o ap li te body . If there h as been le a c h in g , there is the p o s s ib i l i ty
of an enrichm ent b lan k e t a t depth w ith in the cen tra l p a r t of the p se u d o
a p li te p ip e . A h y p o th e t ica l sec tio n through the Tsumeb W e s t p seu d o ap lite
showing a p o s s ib le enrichm ent b lan k e t is shown in Figure 8.
Severa l s a n d - f i l le d s in k h o le s 'n e a r the p se u d o a p li te pipe co n
ta in sm all m a sse s of ch a lc o c i te d is tr ib u ted through the re s id u a l f i l l .
One of th e se s in k h o le s , ju s t 10 fee t e a s t of the 6.1% copper grab
sam p le , w as exam ined during my v i s i t to the a re a . The s inkhole is more
23
th an 40 fee t in. d iam eter and h as been mined to a depth of 30 fe e t . A
sm all remnant of the o rig ina l brown sandy fill w ith abundant re s id u a l
p ie c e s of c h a lc o c i te is found above th e no n - ore -b earing red c la y which
forms the p re se n t floor of the s in k h o le . Approximately 4 pounds of 1 to
2 inch p ie c e s of c h a lc o c i te w ere removed from one cub ic foot of th is
m ate ria l by th e au tho r .
In add ition to the o re -b ea r in g s in k h o le s , there are numerous
o ther o ccu rren ces of copper in the Tsumeb W e s t a r e a . C ro ss folding
(Fig. 9, in pocket) h as developed bod ies of b recc ia and long itud ina l
and ex ten s io n frac tu res w hich have b een m inera lized by c h a lc o c i te ,
qu ar tz , and c a l c i t e . Small rep lacem ent pods of c h a lc o c i te , quartz , and
c a lc i te are a lso found in the nohbrecc ia ted dolom ite , a s are ve ins of
c h a lc o c i te w ith a gangue of c a lc i t e , q u ar tz , and dolom ite or rare ly w ith
c a lc i te a s the only gangue m in era l. D issem in a ted c h a lc o c i te is a lso
found in a re a s of in te n se c a lc i t ic a l te ra t io n . C h a lc o c i te is the only
primary su lfide mineral reported from th is a rea ; how ever, sm all am ounts
of en a rg i te , t e t r a h e d r i te , g a le n a , and pyrite may have been p re se n t in
the o r ig ina l su lf ide a s se m b la g e .
Vanadium O ccurrence s
Schneiderhohn (1920-1921) d e sc r ib e s sev e ra l vanadium d e p o s i ts
south of the Tsumeb W est p seu d o ap li te p i p e . One o re -b ea r in g s a n d -f i l le d
s inkhole w as found 985 fee t south of th e p i p e . Surface in d ica tio n s of th is
o re -b e a r in g k a rs t fea ture were se v e ra l b locks of g re e n ish -b la c k vanadium
ore in the th in sand cover and a few ribs of limonite - s ta in ed s i l ic if ie d
do lom ite . The vanadium ore w as probably m o ttram ite ,
(Pb, Cu) 3 V2 O 8 (Pb, Cu) (OH) 2 . U nusually d e n se thornbush may a lso have
been an in d ica t io n of the s in k h o le . Filled s inkho les often support more
abundant p lan t life a s a function of so il dep th and m oisture retention-:;
D en se thornbush growth would probably form a sm all v eg e ta t io n anomaly
on a e r ia l photography . H ow ever, s in ce no pre-m ine a e r ia l photography
e x i s t s , it i s not known if a definab le anomaly e x is te d over th is s in k h o le .
When d ev e lo p ed , th is s inkhole proved to be 65 feet long , 30 to 50 fe e t
w id e , and 16 fee t d e e p . The f il l m ateria l c o n s is t s of red san d , b locks
of le a c h e d , and s i l ic i f ie d dolom ite w hich are coa ted w ith lim onite and
vanadium o re s , and h e a d - s iz e m a ss e s o f vanadium o re s .
The h o s t rock w hich c o n s is t s of s il ic i f ie d dolom ite w ith chert
ban d s i s probably the Upper Tsumeb s u b s ta g e , Zone 7. The dolomite a t
th is point s tr ik es e a s t - w e s t and d ips 3 0 ° -4 0 o S . , in d ica tin g a sou therly
plunge of the sm all n o r th -so u th a n t ic l in e and the p re se n c e of a very
lo c a l iz e d e a s t - w e s t s y n c lin e . In add ition to the ore in the cave f i l l ,
th e vanadium m in era liza tio n follow s the bedding p lan es for a short d i s
ta n c e . A vanad ium -bearing f is s u re , cu tting a c ro s s the bedd ing , w as
followed for 72 fee t north from the bottom of the s in k h o le . A sim ilar
vanadium occu rrence w as mined 360 fee t south of th is d e p o s i t . Both
o ccu rren c es are apparen tly re la ted to minor c o p p e r - le a d -z in c m in e ra liza
tion and a s s o c ia te d c a lc i te -q u a r tz a l te ra t io n . The s in k h o le s .d e v e lo p e d
on the c a lc i t i c a l te ra t io n e n v e lo p e . Sm all, c le a r , d ipyram idal c ry s ta ls
of quartz line c e l lu la r par t i t ions w ith in the c a v i t ie s and portions of the
s inkhole w a l l s . Vanadium has been added to the ox ida tion products of
the primary m ineral a s se m b la g e by c ircu la t in g ground w ate r a t a much
25
la te r t im e . The vanadium ore m inera ls reported from the a rea are m ot-
t ra m ite , (Pb, Cu) 3 V2 O g(Pb, Cu) (OH2 ) , and d e s c lo iz i t e , (Pb,Zn)3 V2 0 g-
(Pb, Zn) (OH) 2 •
Klinger (1938) pub lished p roduction figures for the early v a n a
dium mining a t Tsumeb W est a s 200 m etric to n s in 1912 and 450 m etric
to n s for the period 1913-1914 .
D isc u ss io n of O ther M in es and P ro sp e c ts
Tsumeb East
M inor am ounts of m inera liza tion occur on both the north and
south lim bs and around the nose of the Tsumeb sync line (Fig. 7) . These
show ings occur in Tsumeb Zones 7 and 8 . Only one of t h e s e , Tsumeb
E a s t , i s d esc r ib ed in the l i te ra tu re of the a r e a . •
The Tsumeb E ast p ro sp ec t w as d isco v e red during road c o n s tru c
tio n 1 .6 (1 mile) e a s t of Tsumeb on the north side of th e r e s i s ta n t r idge
formed by th e Upper Tsumeb do lom ites (Fig. 7) . Schneiderhohn (1921)
d e s c r ib e s the v e in zone a s being com posed of numerous v e in s of ga len a
w ith w id ths up to 20 cm . A c o a rse -g ra in e d gangue of quartz and c a lc i te
w ith t ra c e s of m alach ite and copper a r s e n a te s is a s s o c ia te d w ith the
g a le n a . Although the lead m in era liza tio n reached the s u r f a c e , the o u t
crop didjiot_shjow_yisi^ a t the point of d isc o v e ry . Fur- .
th e r p rospec ting in the area re su l te d in trac ing th e zone for severa l
k ilom eters a long the s tr ike b y following t ra c e s of m a lach ite in the su r
face f lo a t .
26
Abenab and Abenab W es t
The Abenab d e p o s i t , 17 m iles north of G rootfontein and 30 m iles
e a s t - s o u th e a s t of Tsumeb on farm Abenab 707 (Fig. 2), produced 50 ,000
tons o f lead and vanadium c o n c e n tra te s up to 1940. The d e p o s i t is a
p ip e -sh a p e d m inera lized b recc ia of mixed te c to n ic and so lu tion origin
a t the fau lted co n tac t be tw een th e underlying p la ty lim estone (Tsumeb
Zones 2 and 3) and the overly ing dolom ite (Tsumeb Zone 4) . This fau lt
co n tac t and the ore zone dip s tee p ly to the no rthw est , more or l e s s p a ra l
le l to the dip of the sed im en ts on the south limb of an e a s t - w e s t sync line
(Fig. 10) . The in te r s t i t ia l space of the b re c c ia co n ta in s secondary v a n a
d a te m in e ra ls , c a lc i t e , and red c la y .
A large so lu tion c a v i ty , p a r t ia l ly f illed w ith c a lc i t e , mud, and
some v a n a d a te s , i s exposed near the b re c c ia body by the o p e n - c a s t
mining opera tion (Schw ellnus, 1945) . V anadium -bearing s in k h o les occur
in th e v ic in i ty of the m ine . The b recc ia p ip e , which is 250 fee t in d iam
e te r a t a depth of 500 fe e t . Deep dril l ing by the South W es t Africa
Company in d ic a te s th a t the pipe c o n s tr ic ts to a narrow th roa t a t 1 ,500
fee t (Fig. 11) (Sohnge, 1963).
The main ore m inera l is d e s c lo iz i t e , (Pb,Zn)gV2 O 0 ° (Pb,Zn) (OH)2 *
Sulfides of lead and copper have never been found w ith in the Abenab pipe
but are reported to occur in sm all p a tc h e s north a n d .w e s t of the m ine.
The co n c e n tra te s con ta in ed 18% V2 O 5 , 45% P b , .14% Zn, and 1% C u .
The Abenab W est d e p o s i t l ie s 900 feet so u th w es t of the Abenab
mine and is a m ine ra l-b ea r in g so lu tion f is su re which formed along a
b e d d in g -p la n e fau lt in the p la ty l im estone of Tsumeb Zones 2 and 3 . The
f is su re is f illed w ith a b r ic k - re d , sandy c lay con ta in ing 2% V2 O 5 . Ore
27
N O R T H W E S T S O U T H E A S T
P S E !
E X P L A N A T IO N
T s u m e b Z o n e 4 b l u e - g r e y m a s s i v e d o l o m i t e T s u m e b Z o n e s 2 8 3 w e l l - b e d d e d p l a t y l i m e s t o n e
n o n b e d d e d g r a n u l a r c a v e d e p o s i t s
w e l l - b e d d e d , f i n e g r o i n e d c a v e d e p o s i t s
n o n m i n e r o l i z e d c o l l a p s e b r e c c i a
m i n e r a l i z e d c o l l a p s e b r e c c i a
f a u l t s
a d i t s
u n d e r g r o u n d w o r k i n g s b e l o w
iIB isJflJU d' I h v « «el
/
P w i 'p f m
r aMoim
LclJLiU
Zir-im ------------
Q c o Z7 CP ^
30 0 50 100 150
sca/e in f e e t
Figure 10. Abenab M in e , South W est A frica, Showing the N ortheast Face of the O p en cas t and Section through the M ain Ore Body. - -M o d if ied from Schwellnus (1945) .
28
N O R T H SOUTH
5 I
H.c
5 0 05 0 0
scale in fee I* * 7 T s u m e b Z o n e 4
/ m a s s i v e d o l o m i t e ( m c l . b r e c c i a )
tt- 1- I T - T s u m e b Z o n e 2 Q <S’ " C K o H H q H I i m o c t n n o
v a n a d a t e o n e in b r e c c i a
A A b e n o b b r e c c i a p i p e
A b e n o b W e s t o r e z o n eT s u m e b Z o n e Ib e d d e d d o l o m i t e a n d s h a l e
Figure 11. N orth-sou th Section through Abenab Mine . - M odified from Sbhnge (1963).
EVEL
E V E L
L E V E L
m inera ls inc lude d e s c lo iz i t e , v a n a d in i te , c e r u s s i t e , g a le n a , and su b
o rd ina te am ounts o f o ther oxide m in e ra ls , including abundant w illem ite
a t th e e a s te rn e n d . The o re -b ea r in g f is su re filling v a r ie s from 2 to 20
feet w ide and h a s been followed along s tr ike for 1 ,500 fe e t . The m in e ra l-
bearing c la y seam is conform able to the enc lo s in g sed im en ts , s tr ik ing
n o r th e a s t and dipping 45o -7 0 ° NW./ - '
The orig inal c h a ra c te r of the m inera lized b e d d in g -p la n e fau lt
has been la rge ly obscured by th e so lu tion a c t iv i ty re sp o n s ib le for the
re s id u a l c la y fill and the supergene vanadium m in e ra l iz a t io n . Local
p a tc h e s of b recc ia ted lim estone a re p reserved a d ja c e n t to the a ren aceo u s
c lay seam .
Small s tr ingers and b lo tch es of ga lena are reported to occur in
th e n o n -b re c c ia te d w a ll rocks (Schw ellnus, 1945, and W illem se e t a l . ,
1944) . L en ses and pods of spha le r i te and g a le n a , each surrounded by a
sh e l l of v a n a d a te s , occur below 500 fee t and have been followed to a
dep th o f 1 ,250 f e e t .
Prior to 1940, s e v e ra l underground t e s t workings w ere d r iv e n .
M ill t e s t s were run on 52 bulk sam ples to ta ling 3 ,9 6 4 t o n s . These .
sam ples were reduced to 714 tons of co n c e n tra te s averag ing 60% lead ;
of th e s e , 290 tons of co n c e n tra te s averag ing 12% V2O 5 were sh ipped .
Remaining re se rv e s on th is p roperty , according to W illem se e t al.. (1944),
are e s tim a ted to be equ iva len t to 2 , 0 0 0 tons of c o n c e n tra te s con ta in ing
15% V2 O 5 and 60% le a d .
Alt Bobos
Alt Bobos ap p ea rs from the l i te ra tu re to be a s e p a ra te and d i s
t in c t d e p o s i t from B o b o s . Sohnge (1958) d e sc r ib e s th e Alt Bobos d ep o s it
(Pig. 2 ) a s c o n cen tra t io n s of nodular copper o res a long calcitized.
b ed d in g -p la n e fau lts in the south limb of th e Tsumeb sy n c lin e . Bedding-
p lane sh ea r zones are repo rted ly a s s o c ia te d w ith drag folds and show
"flow b r e c c ia " and a s s o c ia te d c a lc i t i z a t io n , with c h a lc o c i te occurring
a s " n e s ts " in the c a lc i t i c do lom ite . .
Bobos
The Bobos d e p o s it is 16 m iles w e s t of Tsumeb along the pro
je c te d a x is of the Tsumeb s y n c l in e , s e v e ra l hundred m eters e a s t of a
sm all c lo se d portion of the syn c lin e ( F ig s . 2 and 9). C opper o res occur
in ro u n d - tb -e l l ip s o id a l s a n d -f i l le d s in k h o les 6 6 to 1 0 0 feet d eep , w hich
range from 3 to 33 fee t in d iam e te r . The o re -b ea r in g s in k h o les are a l l
lo c a te d w ith in a sm all a rea in f la t- ly in g d o lo m ite . A cen tra l core or
p i l la r of dolom ite is sometim es p re se n t in the la rger s in k h o le s .
Copper ore in the s a n d -f i l le d s inks o ccu rs m ostly a s m a la c h ite ,
commonly with co res of c h a lc o c i te . The ore fragments range from sand
s iz e up to cub ic m eter b locks of a lm ost pure c h a lc o c i te . The average
ore p iece is about f is t s ize and com posed of rad ia l ly s truc tu red m a la
ch ite around a ce n tra l p a r t ic le of c h a l c o c i t e . The ore co n ten t v a r ie s b e
tw een s in k h o le s . Although the w a lls of some of th e s in k h o le s are
covered in p la c e s by ce n t im e te r - th ic k c ru s ts of m a la c h i te , nearly a l l
th e developed ore reported by Schneiderhohn (1921) cam e from the sand
f i l l in g .
31
The filling of th e o re -b ea r in g s in k h o les c o n s is t s of leached and
l im o n ite -co a ted remnant b locks of the dolom ite hos t rock , m a s s e s of
m alach ite and c h a lc o c i te , a few m a ss e s of g o e th i te , and ra re ly rad ia l
s tructured m a ss e s of p s ilo m e la n e ; the rem ainder of the f il l is, red or
b ro w n ish -b lack s a n d . Schneiderhohn (1921) m ain ta ins th a t the sand in
th e s e s inkho les is id e n t ic a l in a l l r e sp e c ts to the surface sands in the
a r e a . In some a r e a s , the sand fill i s cem ented by c a lc i te and l im o n i te .
The w h i te - to -p in k chert bands in the dolom ite im m ediately a d
ja c e n t to the s in k h o les reported ly con ta in f lakes and g ra ins of c h a lc o
c i t e . Schneiderhohn (1921) m entions th a t m in e ra liza tio n is a lso found
in a nearby p seu d o ap li te (? ) . C lark (1931) a lso m entions a p seu d o ap lite
n ea r Bobos, but n e i th e r author g ives d e ta i l s on loca tio n or geology of
th is p se u d o a p li te b o d y . This p seu d o ap li te w as not d e te c te d during the
in i t ia l pho to in te rp re ta tion of th is a r e a .
Uris and Kara va tu
The Uris d e p o s i t i s shown on the geologic map of South W est
Africa a s occurring a t or near th e sou thern boundary o f Uris 481 (F igs .
2 and 9). C lark (1931) d e sc r ib e s the Uris d ep o s it a s a p ipe (sinkhole) ,
50 to 60 feet w ide , w hich p inched out a t a depth of 250 fe e t , adjoining
the Kara va tu m ine. The a rea w as f irs t worked for an accum ula tion o f
vanadium m inera ls in sm all surface d e p r e s s io n s . L a te r, the pipe
d e p o s it w as encountered and m ined . C o n ce n tra te s produced in 1926
con ta ined 19% V2 O 5 , 46% Pb, 10% C u, and 4% Zn.
ORE CONTROLS AND ORE GUIDES _ ;
S tra tig raph ic C ontro ls
M in e ra l iza t io n is not confined to any p a r t icu la r s tra t ig raph ic
horizon w ith in the ch em ica lly favorable carbonate seq u en ce of th e O tavi
S e r ie s . H ow ever, the Tsum eb, Tsumeb W e s t , B obos, and Uris m in es ,
a s w e ll a s the m ines along th e north s ide of the O tavi Valley (Fig. 2).,
a re a l l w ith in the Upper Tsum eb. This i s p a r t ia l ly exp la ined by the
b r i t t le nature of th e Upper Tsumeb, Zones 6 , 7, and 8 , w hich developed
abundant b ed d in g -p la n e fau lts and b recc ia bod ies during fo ld ing . These
fracture zo n es were favorab le for o re -f lu id m igration and ore d e p o s i t io n .
Another fac to r tending to lo c a l iz e ore depos it ion in the Upper Tsumeb is
the p re fe ren tia l occu rrence of p seu d o ap li te bod ies w ithin Zones 7 and 8 .
The a s s o c ia t io n of p seu d o ap li te w ith the Tsumeb and Kombat
ore bod ies m akes any occurrence of p se u d o ap li te worth in v e s t ig a t in g .
Although p se u d o ap li te occu rs w ith in Tsumeb Zone 6 in th e Tsumeb mine
w ork ings , m ost p seu d o ap li te o ccu rren ces in th e O tavi M ounta ins are r e
la ted tp Zones 7 and 8 and ap p ear to be of sed im entary orig in a lb e i t
rem obilized in m ost if not a l l c a s e s . P se u d o ap li te b o d ie s have co n tr ib
uted to the m inera liza tion p ro c e ss by forming ch an n e ls for the migration
of ore-form ing f lu id s . During fo ld ing , a le n s of fe ld sp a th ic quartz ite
(pseudoaplite) would form a zone of s truc tu ra l w e a k n e s s lo ca l iz in g
b ed d in g -p la n e fau lts with b re cc ia t io n a t the quartz ite (p seudoap li te )-
dolom ite c o n ta c t . A te c to n ic a l ly trapped feld spa th ic q u ar tz i te c o n ta in
ing form ational w a te rs would have in je c te d i t s e l f into any open fracture
32
33
formed during fo ld ing , which m a y ex p la in th e sm all v e in le ts of p se u d o -
a p l i te found near Kombat, a t Tsumeb W e s t , and o ther p la c e s in the O tavi
M o u n ta in s . Zones of co n cen tr ic fracturing could p o s s ib ly develop in the
a d ja c e n t dolom ite during the folding p r o c e s s . In add it ion to the s tru c
tu ra l c h a n n e ls d ev e lo p ed , the perm eab ility of the sheared p seu d o ap lite
(fe ldspath ic quartzite) offers a conven ien t channel for o re -f lu id m igration .
S tructural C ontro ls
The b e d d in g -p la n e fau lts and b recc ia zones referred to above
are major ore con tro ls in the d i s t r i c t . Sohnge (1962) r e la te s th ree o re -
bearing fracture zones in th e d is t r ic t to rev e rse b ed d in g -p la n e fau lts
formed in the s te e p e r limbs of m ajor sy n c l in e s , th a t i s , a t Tsumeb,
Abenab-Abenab W e s t , and a t the Kombat (Asis) mine along th e Otavi
V alley . -
Breccia p ip e s and zo n es of b re cc ia t io n are commonly re la ted
to m in era liza tio n in th e O tav i M o u n ta in s . M in e ra l iza t io n in th e b re c c ia s
may be a s m a ss iv e ore or a s d is s e m in a t io n s . B reccias re la te d to true
b recc ia pipe formation (example: Tsumeb) are known ore lo c i in the
Tsum eb-G rootfontein d i s t r i c t s . C o l la p se b re c c ia s a lso e x is t in the
r e g io n , forming from the c o l la p se of pos tm inera l c a v e s , a s for e x am p le ,
a t Abenab (S chw ellnus , 1945; S ohnge , 1963). The c o l la p se b recc ia of
th e Abenab mine forms th e locus for supergene vanadium m inera liza tion
which h as been added to the ox idation products of a p rev io u s ly ex is t in g
hypogene le a d -c o p p e r -z in c d e p o s i t . B reccias along b ed d in g -p la n e fau lts
a l s o form favorable loc i for m inera liza tion ; the m antos a t Tsum eb, e s p e
c ia l ly in and n ea r the North Break Fracture Zone, are e x c e l le n t e x a m p le s .
34
Known normal fau lts of reg ional ex ten t are lim ited in number' • f
an d , a t p re se n t , do not ap p ear to be of much im portance a s ore d e p o s i
tion con tro ls in the ind iv idual m ines of the d i s t r i c t . A N . 50° E. f rac
tu re zo n e , 2 m iles northw est of Tsumeb, con ta ins postm inera l do lerite
d ik es of probable la te Karroo age (Sohnge, 1962) . The Tsumeb s taff
p la c e s im portance on th is trend a s a deep reg ional basem en t s tructure
linking th is a rea w ith the Stromberg v o lcan o -p lu to n s of M essu m , Brand-i
berg , and Erongo, and to the a s s o c ia te d ca rb o n a te s to the sou thw est :
w hich have the same average trend a s does a s im ilar l ine of p lu tons and
ca rb o n a t i te s in Angola (M achado, 1958) (Fig. 12). The p ro jec tion of th is
trend to the n o r th e as t of Tsumeb p a s s e s near or through the Prince
Leopold mine and the Tsumeb mine is s tr ik in g . Both con ta in econom ically
im portant co n cen tra tio n s of copper , l e a d , and z in c , with germ anium ,
cadm ium , and s i l v e r .
Favorable S tructural Settings
In te rs e c t io n of small c ro s s folds with reg ional fo ld s , such a s a t
Tsumeb W es t (F ig s . 7 and 9), give r i s e to s tee p ly plunging zones of in
te n s e frac tu ring . S im ilar c ro s s - fo ld in te rs e c t io n s occurring betw een
minor fo lds a lso form favorable ore lo c i a s , for exam ple , a t . th e Berg
Aukas mine (Figs. 2 and 13). Fracturing at and near the nose of plunging
reg ional fo lds a lso ap p ears to form p o te n t ia l ore lo c i , for exam ple , Bobos
an d , in p a r t , Tsumeb W e s t .
P se u d o a p li te , a s d esc r ib ed under s tra t ig rap h ic c o n t r o ls , a p
pea rs to be the m ost im portant s ing le locus for the Tsumeb and Kombat
35
C h i » r c
2 Itngo3 l Of.qoj.io4 h i a n g c
5 Po.iU;r c$ € Cc;j o7 C h i u e c o
5 Uiomfo 10. Su imo l i C h c n j o I? Cooj 1 3 O u i ? u o
. 4 C h i m b O O
IS Bongo
L E O P O l O v h l E
' r i m S e r ' e p ' p e
'I UASDA
r AV-lQ
LLOI Ol D
A N G O l A
Mt-QAMI v.r i
Z A fvl i 1 I A
UV'.GSTON/
T S U M i Bv ABENAB
« WI7<rhOEK> AAuVIS BAY UOTSWANA
S O U T H
AFRiCA
S A AFRICA
i Copt Cross V e s s u m Bi-ordfceg
IV Dor osSp'l/nop*
VI E r o n g o VU OkonjejeVIII f isente rgIX PorosisX 0»orujis
n o l f c o r b o n o l i f e s o r ? u n d e r l i n e d
Figure 12. Volcanic Belts of Late Karroo Age, Angola and South W est A fr ic a .— M odified from M achado (1958).
36
N
-
Figure 13. G enera lized Sketch of the S tructural Setting of the Berg Aukas M in e , South W est Africa
FIGURE 14.E X P L A N A T I O N
STR ATIGRAPHIC DISTRIBUTIONTSUMEB AREA
SOUTH WEST AFRICApholo moike< ho rizon I zone boundory I
n te rp re le d zone boundo iy , do sh ed m h e 'e o p p ro n m o te
zone boundory from p u b lished m opping
zone boundory in te rred from pub lished m opping
M u 'den to r mo lion
centers
form b o u ndones
0115 o t
O H S o f synclm e
lo u l ts com piled Irom pub lished m opping
d o ie n te d lies trom pu b lish ed m opping
ne d i k e s ! 7 ) from pho tos
tpper Tsumefc |/o n e s 6 8 ) ]
M iddle Tsumeb ( /o n es 4 o nd 5 ) i
■Lower Tsumeb
in te-preio t'on based on photoqroph.c and ovbi'shed doio
I tone onom G l'es, possib ly p seu d o o p h te 0 ' th ick M uiden form ation \ zones i - 3 }
Abenob
Sohnqe, 1962 S chne iderhohn , 1929
S c tw eiinus, e 1 o t. >940
4 - ?
I-
5
XH -
- - f - -
mm
----------
* * sI
I~ ~ T : I 4 - gSHSSi
?
—
RE ADD Y GEOSCIENCESTHESIS 1972
H eid ttb e rg 29- / E londsv lok 8 58D nefontom 8 4 6ToevluQ 8 4 5Ph-'.odelphio 8 44
FIGURE 15
ROSE DIAGRAMS of LINEAR ELEMENTSand
GEOGRAPHIC BASE MAPTSLJMEB AREA
SOUTH WEST AFRICA
Posodeno 4 77D ynnenberg 4 7 8
u d w g sh o fen 4 8 0
X <30
6 5 9
Scale m milesw onnhe,m jqq
V Bobos (V) - 0 1 prOSIH 'S I u m m n c r i d 'C O te-155 SO-f^pied by fsum eb M-n«ng i.om pony
SDoc-ng jt sampled i.re s nd-ccied
o o g w f r o i 1 • e -j ' e i e n e n t s
accro 660ooerown 6 9 5
Ad » ia ,d e 66
Aden 662
V Bobos ( C u )Tsumeb
Tsumeb WestV Al t . Bobos ( Cu )
K o r a v o t u ( V ) V46 6m oy 664, Boston 67
y Ur i s ( V )
H vc* lend 665
very d o s e
V F r l e s e n b e r g (V)
Abenab ( Pb,V)
READDYTHESIS
GEOSCIENCES1972
37
m in e s , both b e c a u s e of th e i r perm eab il ity and a s a r e s u l t of th e ir e f fe c ts
on the deform ation of the surrounding dolom ite during fo ld ing .
The hydrotherm al na ture o f the Tsumeb d e p o s i t i s w ell d o cu
m en ted . No true igneous in tru s ive rocks o ther than th e la te or post-:
Karroo d o le r ite and k e rsa n t i te d ik es have been recognized in the a r e a ,
C o n ce iv a b ly , a buried p luton or ca rb o n a ti te e x is t s a t dep th which ac te d
a s a therm a l, and p o ss ib ly a m e ta l-su p p ly in g , s o u rc e . If such a buried
p luton e x i s t s , i t may have a s ligh t surface ex p re ss io n , such a s loca l
doming of s e d im e n ts , an anom alous fracture pa tte rn with p o s s ib ly w eak
a l te ra t io n ,o r m in e ra liza tio n leak ag e to the su rfa c e .
Vanadium a s an In d ica to r M eta l
M ost of the vanadium occu rren ces in the reg ion are l inked to
p a r t ia l ly ox id ized b a s e -m e ta l d e p o s i ts con ta in ing le a d . The recorded
occu rren c es of vanadium m in era liza tio n should be a u se fu l guide to lead
m in era liza tio n even in t ra c e am oun ts .
S inkholes
M any co p p er- lead -v an ad iu m d e p o s i ts of the reg ion are re la ted
to pos tm inera l so lu tion c a v i t i e s . These p a r t icu la r c a v i t i e s , in the form
of s in k h o les or so lu tion f is s u re s , are app aren tly g e n e t ic a l ly re la ted to
the ore d e p o s i t io n . The most l ik e ly ex p lan a tio n for the c lo se a s s o c i a
t io n of s in k h o les w ith ch a lc o c i te vein system s and p se u d o a p li te o ccu r
re n c e s is the c a lc i t i c a l te ra t io n of the dolom ite n ea r primary
m in e ra l iz a t io n . C a lc i t ic a l te ra t io n w as noted during my v is i t s to both
the Tsumeb and Kombat m ines and h a s been docum ented for many other
d e p o s i ts in the region by Schneiderhohn (1920-1921, 1921, and 1929).
38
H olland e t a l . (1964) , a f te r in v e s t ig a t in g th e chem istry of cav e w a te r s ,.
arrive a t a so lu b il i ty product of 10-17 for d o lo m ite , co n tra s te d with a
so lu b il i ty product o f 10."® for c a l c i t e . C a lc i t ic a l te ra t io n in the Tsumeb
region i s a lso accom panied by re c ry s ta l l iz a t ip n of the a d ja c e n t dolomite
w hich a lso s lig h tly in c re a se s so lu b il i ty . Fau lts and zo n es of b recc ia t io n
a re a l s o a re a s favorable for developm ent of both ore b o d ie s and s in k
h o le s . A com bination of in te n se fracturing or b recc ia t io n accom panied
by c a lc i t i c a l te ra t io n w ill undoubtedly prepare an area for abundant s ink-,
hole formation during w e a th e r in g . The p ic tu re i s com plica ted by the
e x is te n c e of normal k a rs t developm ent throughout the reg ion com ple te ly
un re la ted to a l te ra t io n or m in e ra l iz a t io n .
Upper Tsumeb Sub s tag e
P o ss ib le leak ag e of m inera liza tion a long bedding fau lts and
b re c c ia s w ith in the b r it t le Upper Tsumeb bed s (Zones 6 , 7, and 8) may
make th e s e zo n es u sefu l in the la te ra l geochem ica l d e tec t io n of non
outcropping ore d e p o s i t s . C opper, le a d , z in c , s i lv e r , and a rsen ic
would be u se fu l in d ic a to rs . C o n s id e ra b le surface contam ination by l e a d ,
z in c , a r s e n i c , and cadmium from ea r ly (p ro -1927) sm elte r d u s t should be
expec ted n e a r T su m eb . Search for ad d it io n a l p seu d o p a li te bod ies should
be co n cen tra ted in a re a s con ta in ing Zones 7 and 8 o f the Upper Tsum eb .
s u b s ta g e .
Aeromagnetic Surveys
An aerom agnetic survey could be used to map b asem en t s tru c
tu r e s , d ik e s , and p o s s ib le buried in t ru s io n s . A erom agnetics and
photogeology w ould , o f n e c e s s i ty , be in i t ia l to o ls in exp lo ra tion of ad
ja c e n t a re a s covered by Kalahari s a n d s .
PHOTOGEOLOGIC STUDY
The area o f th is study is covered by g o o d -q u a l i ty , conven tiona l
b la c k -a n d -w h i te , 1 :36 ,000 ae r ia l p ho tog raphy . The a e r ia l photographs
of the O tavi M ountains w ere rap id ly scanned to ob ta in an overa ll a p p re
c ia t io n of th e ir geologic information c o n te n t . Following th is rapid s c a n ,
th e photographs for the Tsumeb area w ere s tud ied in d e ta i l to determ ine
th e photographic e x p ress io n for each member of the Upper Tsumeb su b -
s ta g e , Zones 6 , 7, and 8 , and for the M ulden form ation. Once a se t of
te n ta t iv e photo c r i te r ia w a s e s ta b l i s h e d , re c o n n a is s a n c e tr ip s through
the Tsumeb a rea w ere made to verify the photographic e x p ress io n of
t h e s e u n i t s .
In it ia l o ver lay tem p la te s w ere prepared for 65 a e r ia l pho to
graphs rep resen tin g a to ta l a rea of 750 square m iles (F ig s . 1, 2, and
F ig s . 9 , 14 and 15, in pocket) . An ad eq u a te b a se map for the photo
d a ta w as ob ta ined by trac in g portions of four South W est Africa G overn
ment farm boundary m a p s .
The area of th is study is am enable to pho togeolog ic m ap p in g . ■
Some geo log ic d a ta can be ex trac ted from th e photographs in a re a s of
sand and c a l ic h e co v er . The p re sen t s tudy would have g re a t ly benefited
from an in i t ia l l i te ra tu re r e v ie w . The l i te ra tu re study , a f te r my return to
Salt Lake C ity , w as n e c e s s a ry to refine the cr i te r ia for d isc r im ina tion of
various dolom ite u n i t s . The l i te ra tu re sea rch re su lte d in sev e ra l long
d e la y s s ince much of the important l i te ra tu re on th is a rea w as pub lished
in h a rd - to -o b ta in jo u rn a ls . M any of the early d e ta i led repo rts were
40
w ritten in German and required t ra n s la t io n . I owe sp e c ia l th an k s to M r.
E . Demeter for h is many hours of help w ith the t ra n s la t io n of th is l i t e r a
tu re . Had th is l i te ra tu re study been com pleted before working with the
photographs in South W e s t A frica , the en tire nature and scope of the
p ro jec t would have been c h a n g e d . Photo recognition fea tu re s would have
required a fraction o f the time spen t in th is s tudy . Key a re a s would have
been v is i te d and worked up in d e ta i l a t th e s ta r t of the p r o je c t . Photo
geo log ic mapping would have s ta r ted a t the O tavi Valley and p rogressed
n o r th , in p reference to the area m apped, w ith d e ta i le d fie ld and pho to -
geo log ic mapping o f s e le c te d m ines and p r o s p e c t s . The photogeologic
mapping would have covered a much la rger a rea w ith far more d e ta i l in
a fraction of the time required for the p re sen t s tudy .
The u se of photogeologic te c h n iq u e s in the O tav i M ounta ins
a llow s rapid r e c o n n a is s a n c e m ap p in g . Rapid photogeo log ic mapping of
s tra t ig rap h ic u n i t s , e s p e c ia l ly the Upper Tsumeb s u b s ta g e , w ill a id in
the sea rch for favorab le s tra t ig ra p h ic -s t ru c tu ra l t a r g e t s , such a s b re c
c ia zones and p seu d o ap li te b o d ies . D e tec tio n of p seu d o ap li te and
b recc ia zones on co n ven tiona l a e r ia l photography is p o s s ib le but a s y e t
req u ires ad d it io n a l study to improve r e l ia b i l i ty . S tructural d a ta are
g en era lly w ell e x p ressed on the p h o to g ra p h s , a id ing rapid recognition
of p o te n t ia l ly favorable s truc tu ra l s e tt in g s sim ilar to th o se of Tsumeb
W est and Berg A ukas.
D is c u ss io n of Pho to in terp re ta tive M aps
Photogeologic S tructure Map
This map (Fig. 9 , in pocket) is a reduction of an orig inal
1 :36 ,000 map prepared from the photo overlay sh e e ts and an en largem ent
o f the traced farm boundary m a p . Many d is to r t io n s e x is t on th is map a n d ,
although s te p s w ere taken to keep the d is to r t io n s to a re a so n a b le m ini
mum, lo ca tio n of sp e c if ic geo log ic f e a tu re s , such a s bedding t r a c e s ,
f ra c tu re s , and s in k h o le s , m ust be regarded a s a p p ro x im a te .
M uch ad d it io n a l work could be done on the d e n s i ty of fracture
t r a c e s , the d e l in e a t io n of reco g n izab le photo marker b e d s , and d is t r ib u
tio n of s in k h o le s . Some of the a re a s w hich have been g eochem ica lly
sam pled by the Tsumeb M ining C orporation are a lso in d ica ted on th is
m a p . The raw da ta p re sen ted on th is map w ere u sed for the p reparation
of the ro se diagram of l inear e lem ents and the in te rp re ta t iv e s tra t ig rap h ic
m ap.
In te rp re ta tiv e S tra tig raph ic Map
In te rp re ta tio n of a re a l d is tr ib u tio n for various u n its of the O tavi
Series and the M ulden quartz it e (Fig. 14, in pocket) i s b a se d on d e ta i l s
shown on th e photogeolog ic s truc tu ra l map and from pub lish ed d a t a .
C r ite ria u sed to s e le c t s tra t ig rap h ic b reak s for field mapping are not
n e c e s s a r i ly c o n s is te n t w ith fea tu res recogn izab le on photographs for
photogeologic mapping . In the sp ec if ic c a s e of the Upper Tsumeb Zone
8 -M ulden c o n ta c t , the prominent oo lite band near th e to p of Zone 8 is
often shown a s the boundary , s in ce the a c tu a l Zone 8 -M ulden boundary
could not be tra ced r e l i a b ly .
43
Line w eigh ts on the map in d ic a te re la t iv e re l ia b i l i ty . The h e a v
ie s t l in e s are photo marker un its shown on the s truc tu ra l map (Fig. 9)
w hich c lo se ly approxim ate zone b o u n d a r ie s . The next h e a v ie s t l in e s
correspond to in te rp re ted boundaries b ased on pho to - and l i te ra tu re -
derived da ta where no reco g n izab le photo marker u n its w ere shown on
the overlay s h e e t s . The w e a k e s t l in e s in d ica te boundaries from p u b lished
d a t a .
S ince se v e ra l s tra t ig rap h ic un its have p h y s ica l fea tu res th a t
commonly a c t a s ore c o n t r o ls , such a s the lo c a l iz a t io n of p seu d o ap lite
in Zones 6 , 7, and 8 and the abundant b ed d in g -p la n e fau lts of Zone 6 ,
know ledge of the d is tr ib u tio n of the carbona te un its and th e ir s truc tu ra l
se tting should be u sefu l in future exp lo ra tion in the a r e a .
Road Net Map
The road ne t map for the Tsumeb a rea (Fig. 6) w as prepared to
a s s i s t any future s tu d ies in the im m ediate Tsumeb mine a r e a . This map
w a s prepared by the te m p la te -a n d -ra y m ethod. Scale of th e th ree in
d iv idual flight s tr ip s involved are ad ju s te d to form a uniform map sc a le
w hich is approx im ate ly 1:36, 000 on the orig inal and approxim ate ly
1 :107 ,325 on the reduc tion accom panying th is t h e s i s .
Rose Diagram s of L inear Elements
P ho to -der ived fracture t r a c e s are p resen ted a s ro se diagram s
a s a percen tag e function of number of f rac tu res (north quadrants) and
len g th (south quadrants) (Fig. 15, in pocket) . Both p re se n ta t io n un its
were u sed to in d ica te re l ia b il i ty of fracture da ta for any g iven d irec tion .
F racture d ire c t io n s re la ted c lo se ly to the reg ional fracture pa tte rn should
; ' 44
have opposing ray s o f s im ilar m a g n itu d e . The sm all s ta t i s t i c a l pop u la
tions o f fracture, t ra c e s for some a re a s limit th e u se fu ln e s s of th e se
d iag ram s; Summation of the number of frac tu res and unit leng th is shown
for each diagram . A sm all number of large frac tu res would show a s a .
long ray on the lower portion and a s a much sm aller ray on th e upper
portion of th e d iagram . Bach ro se diagram re p re se n ts an a rea roughly
2 .8 by 3 .7 in c h e s on the reduced maps accom panying th is report, c o r
responding to 30 square m i le s .
The reg ional fracture pa tte rn conforms to the n o r th -so u th com
p re ss iv e fo rces re sp o n s ib le for the e a s t - w e s t folds of th e O tavi M oun
t a i n s . The predom inant fracture d ire c t io n s form a cu te a n g le s of from
20° to 30° with the n o r th -so u th com press ive c o u p le . 8 mit (1962) reports
the major fracture tre n d s form 30° to 40° an g le s w ith the n o r th -so u th
com press ive forces in the area so u th e a s t of O tavi (Figs. 1 and 2).
W ithin re a so n ab le l im its , th e fracture data b a se d on number of
frac tu res can be u sed for the p red ic tion of the normal fracture pa tte rn for
various portions of th e mapped a re a . I f the photographs of the mapped
a rea had been a v a i la b le for further a n a l y s i s , a more com plete mapping
o f fracture t ra ce d e n s i ty and d is tr ib u tio n could have been prepared ,
e s p e c ia l ly in the w e s te rn portion of the accom panying s truc tu re map
(Fig. 9).
Anomalous fracture d ire c t io n s no t c o n s is te n t w ith no rth -so u th
com press ive forces are ex p re sse d in se v e ra l ro se d iagram s (40/1252),
(53/1292), (33/675), (123/2575), (53/1218), (232/4593) . H ow ever, in
m ost o f th e s e c a s e s , the to ta l number of fracture t r a c e s i s too small to
make fracture a n a ly s is very r e l i a b l e . Several of the fracture ro se
45
d ia g ra m s , including the anom alous v a r ia t io n , are d e sc r ib e d ind iv idua lly
in th e following p a ra g ra p h s .
Rose d iagram s (40/1252) , 5 .5 m iles s o u th - s o u th e a s t of Tsum eb,
and (53/1292), 7 .5 m iles so u th e a s t of Tsumeb, co n ta in large rays p a ra l
l e l to the reg ional n o r th e as t do ler ite dike t re n d . This in d ic a te s a s tro n g
e r developm ent of th is fracture system in th is area th an w as p rev iously
in d ica ted on pub lished m a p s .
Rose diagram (33/675), 4 m iles sou thw est of Tsum eb, shows an. i
ad d it io n a l frac ture trend n o r th -n o r th e a s t and a sm alle r n o r th -so u th f ra c
ture trend rep resen tin g e x ten s io n frac tu res a long a small e a s t - w e s t a n t i
c l in e . The ax is of th is sm all a n t ic l in e could not be determ ined and is
not shown on the accom panying m a p s .
Rose diagram (123/2575) , 3 .5 m iles northw est of Tsumeb, th is
fracture p a t te rn shows strong e x te n s io n frac tu res pe rpend icu la r to the
a x is of the e a s t -w e s t - t r e n d in g a n tic l in e ; th is supports the minor b e d
ding t ra c e ev idence for lo c a l doming of th e sed im ents in th is a re a .
Minor doming is a l s o expec ted from the p ro jec tion of the sm all c ro ss
warp a n t ic l in e through th is a r e a . P o ss ib ly an in tru s io n e x i s t s a t depth
h e r e .
Rose diagram (53/1218), 7 .25 m iles w e s t - s o u th w e s t of Tsumeb,
in d ic a te s some te n s io n a l ex ten s io n frac tu ring . The no r th -no r thw est
fracture system is a lso more s trongly d ev e lo p ed .
Rose diagram (3 7 /887), 8 m iles n o r th e as t of Tsum eb, re p re se n ts
a normal fracture system n ear the no se of a fold and i s not anom alo u s .
Rose diagram (232/4593), 11 m iles n o r th e as t o f Tsumeb, shows
th a t th e frac ture p a tte rn in th is area i s s trongly in fluenced by ex ten s io n
46
f rac tu res perpend icu la r to the sy n c lin a l a x i s . There i s apparen tly no
lo ng itud ina l .f rac tu ring .
P ro g ress iv e ly e a s t from the p reced ing rose d iag ram , the frac
tu re p a t te rn s in d ica te a change in the com press ive fo rces from north -
sou th to more n o r th w e s t - so u th e a s t „ The e as te rn m o s t ro se diagram
, (44/765) , 22 .5 m iles e a s t -n o r th e a s t of Tsum eb , in d ic a te s a probable
sh if t o f the sy n c lin a l a x is from e a s t - w e s t to a more e a s t -n o r th e a s t trend
a s the sync line becom es p ro g ress iv e ly covered by Kalahari sand and
c a l ic h e to the e a s t .
The rem ainder of th is map is d es ig n ed to be a geograph ica l
supplem ent to the o ther m a p s . Farm nam es and numbers are show n , a s
a re the approxim ate lo c a t io n s of m ines and p ro sp ec ts and the cen te rs o f
a e r ia l photographs u sed in th is s tu d y . Areas sampled by th e Tsumeb
M ining Corporation are a lso shown w ith no ta tions a s to th e re la tive
spac ing of the b ru sh ed -o u t l in e s .
OTAVI VALLEY DEPOSITS
The d e p o s i ts in the southern O tav i M ountains are predom inantly
lo c a te d along the north s ide of the O tav i V alley, which runs e a s t - w e s t
be tw een O tav i and G rootfrontein (F ig s . 16 and 17) . M o st of the d e p o s i ts
were p ro sp ec ted and developed during the period 1910-1925 . For the
m ost p a r t , th e se d e p o s i ts were abandoned during the 1930 's and lay
id le until about 1957. The Tsumeb M ining C orporation began in ten s iv e
p rospec ting in th e A sis mine area during the m id -1950's and developed
w hat is now known as the Kombat m ine .
. Kombat M ine
The Kombat mine is lo ca ted along the north edge of the O tavi
V alley , 31 a i r m iles s o u th - s o u th e a s t of Tsumeb and 8 m iles w e s t of the
old G uchab m ine . The mine area co n ta in s th ree se p a ra te ore b o d ie s , the
E a s t , C e n t r a l , and W e s t . The e a r l ie r underground w orkings of the A sis .
mine are in th e v ic in i ty of the Kombat W est d isc o v e ry . Following favor
ab le geochem ica l sample re tu rns in th e a r e a , Tsumeb M ining 'C orpora tion
began a d rilling pro jec t b e tw een the old A sis mine w orkings and an i s o
la te d outcrop of p seu d o ap li te w ith in the dolomite of th e Upper Tsumeb
sub s ta g e , Zone 8 . The th ir t ie th drill ho le in te rcep ted w hat is now known
a s the Kombat W e s t ore body . Although surface e x p o su res are often poor,
S chneiderhohn 's (1921) geo log ic sk e tc h map of the A sis mine area a p p a r
en tly show s the p seu d o ap li te bod ies being mined' by th e Tsumeb M ining
C orporation and a ls o the small p seu d o ap li te body in a ra ilroad cut near
Kombat (Fig. 18).
47
10°
Ot ov i j
2 0 °
Outjg.
O m o r u r u
U s o k o sK o r i b i b
G o b a b i sW i t v l e i
R e h o b o t h o
2 4 °
M o r i e n t o l
M a l t a h o h e oGi b e o n
E x p l a n a t i o n
2 6 °I n t e r n a t i o n a l B o u n d a r i e s
B o u n d a r i e s o f M a g i s t r a t e D i s t r i c t s
R a i l r o a d sL u d e n t z K e e f m o n s h o o p
K ar o s burg 2 8 °
100100W a r m b a
O r a n j e m u n dScale in m iles
20 °
Figure 16. Index M a p , O tavi Valley Region , South W es t Africa00
4 9
O h f o n t s f o n t e i n
P b * Z n V \
H o r o s i bb.Zn
B e r g A u k o ^
^ : i '•x # H a r a s i b ( 6 4 8 ) / * T o g g e n b u r g
■ % % %Pb — Y
/G a u s s ' 4 6 4 v v G r o o t f o n t e i n X
X_ A P I ? , Z n
G r o s s O t a v i C u ' / / x
O t a v i
\/LrrF==bti!>< A s i s , - v o / / ^ X a > / K o m b o t «>|| x x ^ e O t j i r u k a k ' uPb.Znr \ \
" ' G u c h a bA s i s E a s t End
L^ R i e t f o n t e jn 3 4 4
E X P L A N A T I O N
M i n e a n d c o m m o d i t y
P r o s p e c t
O c c u r e n c e a n d c o m m o d i t y
0 10 20
P b , Z n
s c a l e in m i l e s
Figure 17. P rospect Location M a p , Otavi Valley Region, South W est Africa
Aurcs • Guess
'j
\ /
G r o s s - O t o v i
A y s ( K e m b o f )Guchob _
y / Rietfonfein • /
E X P L A N A T I O N
m e t a m o r p h o s e d s e d i m e n t s
O t o v i f o r m a t i o n u n d i f f e r e n t i a t e d ( i n c l u d i n g t h e O t o v i V a l l e y p h y l l i t e a n d s o m e N o s i b )
T ix / . b a s e m e n t
cSZ3> p s e u d o a p l i t e .
o r e o c c u r r e n c e s
l O O O O O O ________________ 3 0 0 0 0 0
Scal e in f e e l
Figure 18. Geologic Sketch Map of the Ore D e p o s i ts , O tavi Valley, South W es t A frica . — Modified from Schneiderhohn (1921).
51
Following the Kombat W es t d isc o v e ry , the East and C entra l ore
bo d ies were found by p rospecting known p seu d o ap lite o c c u r re n c e s .
Kombat C en tra l w as found by trench ing a p seu d o ap lite l e n s . Kombat
East w as d isco v e red by drilling an .a rea conta in ing se v e n .o r e igh t sm all
s tr ingers of p s e u d o a p l i te .
The m inera liza tion a t Kombat i s la rg e ly confined to p seu d o
ap l i te bod ies con ta in ed w ith in the Upper Tsumeb s u b s ta g e , Zone 8 , a t
and near, th e co n tac t be tw een the dolom ite and th e O tav i Valley p h y l l i t e .
At Kombat, the p seu d o ap li te is c o n s id e re d .to be a sed im entary rock e n
c lo se d w ith in the c a rb o n a te s of Zone 8 . C ro s s -c u t t in g v e in s and s to c k -
work s w ere noted during th e p re sen t in v e s t ig a t io n a t th e su rface in and
nea r th e Kombat ore b o d ie s .
The footw all co n tac t of the p seu d o ap lite w ith the dolom ite is
sheared and i s the lo cu s of m ass iv e o re . The Kombat W est ore body is
sheared and d is to r ted by a 3 0 -fo o t-w id e fracture zone of the Kombat W est
fau l t , w hich h a s both prem ineral and pos tm inera l m ovem ent. Shears
p a ra l le l to the Kombat W est fault are a lso m in e ra lize d . The nonsheared
c o n ta c ts of p seu d o ap li te and dolom ite are sharp and show no co n tac t
e f fe c ts o ther than the typ ica l q u a r tz -c a lc i te a l te ra t io n a s s o c ia te d with
th e hydrothermal d e p o s i ts of the O tavi M ountain la n d . Each ore body h a s
two known ore z o n e s , one above and one below a lo ca l ro ll in the
do lom ite -phy llite , c o n ta c t w hich d ips 45° S . a t the s u r f a c e . P resen t c u t
off grade is 0 .9% co p p er . An id e a l iz e d c ro ss sec tio n through a Kombat
ore body is shown in Figure 19.
M in e ra l iza t io n a t Kombat is such th a t the mine is a copper mine
down to th e 4 le v e l , a mixed c o p p e r - le a d mine from th e 4 to 6 l e v e l s ,
NORT H SOUTH
E X P L A N A T I O N
d o l o m i t e
p s e u d o o c l i t e w i t h m i o e r o .■ z o t i o n
O t o v i V a l l e y P h y H i t e
Figure 19. Idea lized Section through Kombat Ore Bodies
53
and a lead mine below the 6 l e v e l . E stim ated ore re se rv e s a t Kombat are
approxim ate ly 2 m illion to n s of 3.6% copper, 4.4% le a d , and 0.5% z in c .
In a d d i t io n , a s yet u n te s te d p o ten tia l e x i s t s for open p it o res w ith grade
and to n n ag es com parable to th e porphyry copper d e p o s i ts of the sou th
w es te rn United S ta te s .
C urren tly , the d e p o s i ts are being mined by very la rge open
s to p e s , b lock c a v in g , and c u t - a n d - f i l l m ethods. Production is 750 tons
per day from the b lock cav ing opera tions and 250 to n s pe r day by cut and
f i l l , for an overa ll d a i ly production o f 1 ,000 to n s . The Kombat mine pro
duced 2 m illion ounces of s ilv e r in 1966.
Since the A sis d e p o s it i s e s s e n t i a l ly synonymous with the p r e s
en t Kombat m in e , th e following sec t io n derived from the o lder l i te ra tu re
on A s is , e s p e c ia l ly Schneiderhohn (1921), im m ediately fo llow s th is s e c
tion a s ad d it io n a l supporting da ta on the ore o ccu rren c es in the Kombat
a r e a .
A sis M ine
Four ty p e s o f ore d e p o s i ts occur in a narrow e a s t -w e s t - t r e n d in g
zone w ith in the do lom ite , from 330 to 660 feet north o f the O tavi Valley
p h y ll i te -d o lo m ite c o n ta c t (Schneiderhohn, 1921):
1 . Branched ve in sy s tem s and groups of ve ins or l e n s e s of p se u d o -
aplite. in trude th e d o lo m ite . The p seu d o ap li te and ad jacen t
dolom ite co n ta in d issem in a ted b o rn ite , c h a lc o p y r i te , c h a lc o -
c i t e , and minor pyrite .
2 . L e n se s of p seu d o ap li te are fau lted or folded in to th e do lom ite .
At the pseudoap lite -do lom ite c o n ta c t , there are la y e rs of "red
54
iron" o res (hematite) and m a g n e t i te . Some of the m agnetite
occu rs d is se m in a te d in the p s e u d o p a l i te . Copper is a lso found
in some of th e se p seu d o ap li te l e n s e s .
3 . C a lc i te -q u a r tz -b e a r in g b recc ia v e in s con ta in ing c h a lco c ite .
4 „ Chaleo c i t e - and m a la c h i te -b e a r in g , s a n d - f i l le d s in k h o le s ,
a s s o c ia te d w ith b recc ia v e in s and s tr ingers of p se u d o a p l i te .
The d e p o s i ts a t Asis (Kombat) are lo ac ted in the 15- to 3 0 - fo o t-
high te rrace of dolomite th a t forms the northern boundary of the O tavi
V alley . The dolom ite is commonly b recc ia ted a t i ts c o n ta c t with the
O tavi Valley p h y l l i te . The dolom ite be longs to Zone 8 of the Upper
Tsumeb s u b s ta g e . The p se u d o ap li te may re p re se n t a l i tho log ic e q u iv a
len t of the M ulden fe Id sp a th ic quartz ite in terbedded w ith the do lom ite .
Schneiderh&hn (1921) re fers to in terbeds of phylli te and p seu d o ap lite
folded into the dolomite with in jec tio n of large and sm all v e in s and •
le n se s of p se u d o ap li te into the dolomite in other p a r ts of the d e p o s its
(Fig. 20). Ore occurs in both ty p es of pseudoaplite .. M inera liza tio n is
confined to p se u d o a p li te b o d ie s , th e ir immediate c o n ta c t a r e a s , and to
the e a s t - w e s t b recc ia v e in s .
Ore in P seudoap li te
In 1921, the Asis mine (F ig s . 20 and 21) w as co n s id e red to be
the m ost important ore d e p o s i t of the O tav i Valley. The mine is 985 fee t
north -north we s t of the old Asis ra ilroad s ta t io n d irec tly a c ro ss from the\40-knri mark of the O tav i-G roo tfon te in ra ilw ay (Fig. 18) . The mine w as
developed by a 115 -fo o t- lo n g by 6 6 - fo o t wide open p i t , part of which w as
jdDlW
A N A T
d o l o m i t e
p h y l l i t e
c h e r t
p s e u d o o p l i t eJlllllJ
4 b r e c c i a
o r e ( p r o j e c t e d t o s u r f a c e )
5 0 0
Sco'e in feet
Figure 20. Plan of Asis (Kombat) Mine A rea# O tavi Valley, South W est A fr ic a .— M odified from Sohnge (1958) .
56
e x p l a n a t i o n
m m e r o h z . d o p h t e "| q u o r l z - C0| C| I | 0 „ e r o , i on
w i t h b o r n i t e t r t id c h o l c o p y r i t e v . Zm i r. mr-n I i ♦,'#»*
J
3 0 m e t e r l eve l
m m e r o i i z e d d o l o m i t e ! m i n e r o l i z o t i o n
u n m i n e r o l i z e d d o l o m i t e
m o i n s h o f t
i m r
6 0 m e t e r level
Scale in feet
Figure 21. Plan of the 30- and 60-m eter L evels , Asis M in e .— Modified from Schneiderhohn (1920-1921).
57
deve loped to a -dep th of 1 0 0 fee t where it w as connec ted to a 98-foo t
(30-meter) underground le v e l . This p it h a s s ince been b a c k f i l le d . Ad
ja c e n t to th i s former p it i s a 197-foot (60-meter) deep sh a ft with two
developm ent l e v e l s , one a t 30 m e te r s , the o ther a t 60 m eters (Fig.. 21) .
The d ep o s it i s reported to have a second s h a f t , the lo ca t io n of w hich is
not shown on th e accom panying se t of m a p s .
The surface ex p o su res in the mine a rea w ere poor, but
Schneiderhohn (1921) fe lt th a t there w ere a t l e a s t th ree sep ara te p se u d o -
ap li te le n s e s w ith w id ths of 26, 13, and 1 .6 fe e t . Narrow and irregu lar
la y e rs of ph y ll i te are known to occur a t sev e ra l of the p seu d o ap li te
b o u n d a r ie s . These p seu d o ap lite l e n s e s w ere w e ll m inera lized with m a la
ch ite and azu r ite a t th e su rface an d , in a d d i t io n , b lo ck s of co p p er- and
iron -bear ing s i l ic i f ie d dolom ite occurred w ith in th e p s e u d o a p l i t e . The
dolom ite a t the main A sis shaft is c ro s se d by a vein zone of p seu d o ap li te
which i s a ligned so u th w est and a lso p lunges so u th w e s t . The ind iv idual
v e in s are often b ranched and sinuous w ith w id ths of from 8 in ch es to 5
f e e t . The co n tac t b e tw een the p se u d o ap li te and the dolom ite is g rad a
tio n a l and w as d iff icu lt to d is t in g u ish underg round . At the c o n ta c t , the
dolom ite is c o a rse r g ra in ed , but th is change only p e r s i s t s for a few
m il l im e te rs . The p seu d o ap li te is w e ll m inera lized w ith d issem in a ted
copper o r e , w hile the ad ja c e n t dolomite co n ta in s ore in v e in s and pods
for sev era l m eters aw ay from.the co n tac t and a s sm alle r s tr ingers and
zo n es of d issem in a ted m inera liza tion s t i l l farther away from the c o n ta c t .
The length of th e ore zone i s 260 to 295 fee t on both working le v e ls ; ore
w id ths are from 16 to 82 f e e t .
58
The ore on th e 3 0 -m e te r lev e l (F ig . 21) i s m ostly azu r ite and
m a la c h i te , but some la rger m a ss e s o f su lf ide o res w ere.found near and
a t the p seu d o ap li te -d o lo m ite c o n ta c t . The m inera liza tion in the 60-m ete r
lev e l is a l l su lf id e . The predominant ore m inera ls on th e 60-m eter le v e l
are reported to be ch a lcopyrite and b o m i te , w ith r a r e , very sm all gra ins
of c h a lq o c i t e . The ch a lcopyrite and bornite occur a s f ine ly d ivided d i s
sem inations , a s m ass iv e p o d s , or as v e in s . Pods of m a ss iv e ore up to
head s iz e were common. The ore m inera ls rep lace both the p seu d o ap lite
and the do lom ite . In the d o lo m ite , the ore m inera ls are c lo s e ly re la ted
to c o a rse -g ra in e d a re a s of c a lc i te and dolom ite irregu la r ly d is tr ib u ted
through the d en se r do lom ite . The dolom ite n ea r the d e p o s i t has been
s lig h t ly s i l ic i f ie d .
The m inera lized dolomite a d ja c e n t to the p se u d o a p li te is cu t by
many sm all v e in le ts of p seu d o ap li te to the south and w e s t of the main
w o rk in g s . These v e in le ts are a l l m inera lized a t the su rface with m ala
ch ite and azu r ite ; t r a c e s of ore occur in the dolomite, near th e p se u d o
ap l i te s tr in g e rs . The lo ca t io n of th e s e sm all p seu d o ap li te v e in s w as
u s u a l ly marked by an a ligned s e r ie s o f v e r t ic a l s in k h o les f illed with a
mixture of sand and r ich co n cen tra tio n s of c h a lc o c i te ore lo c a l iz e d in
the c a lc i t i c a l te ra t io n en v e lo p e . The mine workings are confined to the
c a lc i t iz e d and s i l ic i f ie d dolomite and to the p seu d o ap li te b o d ie s .
Schneiderhohn (1921) repo rts a very minor occurrence of c o a rse -g ra in e d
g a le n a , a l te red to c e ru s s i te a t the s u r f a c e , in dolom ite an u n s p e c i f ie d .
d is ta n c e north of the A sis m ine. O ccu rren ces such a s th is may e a s i ly
have been m is se d , a s the w eathered su rface of ga lena a lte r in g to c e r u s
s ite is very s im ila r in appearance to the w eathered su rface of s l ig h tly
59
a lte red d o lo m ite . A p o s s ib le field guide to a lte ra t io n would be the
"craggy su rface" w eathering re la ted to re c ry s ta l l iz a t io n of the dolomite
and enrichm ent in the more so luble CaCOg molecule..
C opper O ccu rren ces in T ec to n ica lly Trapped P se u d o ap li te Blocks
Several p seu d o ap li te b e d s , m inera lized a t the su rface with
azu r ite and m a la c h ite , crop out in the san d -co v e red f la ts 1 ,476 feet
(450 m eters) e a s t of the p it of the A sis mine (Fig. 18); th i s may rep re
sen t the Kombat E ast o reb o d y . This a rea w as p ro sp ec ted prior to 1921 by
a 148-foo t (45-meter) inc lined shaft and by a large number of small p ro s
p e c t p i t s . The main occurrence is a le n s of p s e u d o a p l i te , s trik ing e a s t -
w e s t , 3 9 5 fee t long and up to 6 6 fee t w id e , which jo in s a t i t s e a s t end
w ith a phy ll i te len s 985 feet long and 100 feet w ide surrounded by the
do lom ite . Phyllite and p seu d o ap li te w ere a lso encountered a t a 148-
foot dep th in a c ro s s c u t to the south from the sh a f t . In the c ro s s c u t ,
th e p s e u d o a p l i te , w hich w as 46 .3 feet wide in the upper l e v e l s , i s only
6 .5 fe e t w id e . "It a p p ea rs th a t to g e th e r w ith the s la te / p h y l l i t e / , the
p seu d o ap li te forms a ro o t le s s fo ld ed -in wedge w ith in th e do lom ite .
M in era l iza t io n apparen t does not extend to depth" (Schneiderhohn, 1921).
I f th is is indeed th e Kombat E ast o rebody, the p se u d o a p li te h a s en larged
ag a in w ith d e p th .
C opper-bearing Breccia Veins
A large number of b recc ia v e in s very s im ilar in form and m iner
a l iz a t io n to the b recc ia v e in s of G uchab cu t the dolom ite 260 to 330 fee t
north of the p seu d o ap li te le n s e s d e sc r ib e d in the p reced ing s e c t io n s .
60
These v e in s were developed by a 260-fo o t- lo n g t r e n c h , 33 fee t d e e p ,
and by a n o r th -so u th , d e e p trench 130 fee t long . Schneiderhohn (1921)
rep o rts th a t s ev e ra l deeper, p ro sp ec t p its have e s ta b l i s h e d th a t . th e b re c
c ia v e in s d ie out a t d e p th . P o ss ib ly the b recc ia "v e in s" behave in a
m anner s im ila r to the p seu d o ap li te l e n s e s and may en large again with
d e p th .
A s is East-End
The A sis East-End d ep o s it (Fig . 18) i s a 6 5 0 -fo o t- lo n g m iner-/
a l iz e d zone con ta in ing p seu d o ap li te ve in swarms which o ccu r on a low
dolom ite h i l l 1 .1 m iles e a s t of th e Asis mine sh a f t . The A s is East-End
h i l l is bounded on the south by the A s is-G u ch ab road and on the w e s t by
a sm all c ro s s v a l le y through which p a s s e s the A s is -G u a ss -G a u b -N o s ib
ro ad . The e a s t - w e s t zone of ore and p seu d o ap lite is 650 fee t long and
from 65 to 130 feet w id e . The m in era liza tio n ex ten d s a c ro s s two small
h i l l s . The summit of the e a s te rn h ill is occupied by a sm all open pit
w hich is partly in p seu d o ap lite (north) and partly in the dolom ite (so u th ) .
The p seu d o ap li te occu rs a s a l e n s , 148 fee t long and 26 feet wide a t th e
m idd le . The c o n ta c t b e tw een the p seu d o ap li te and th e dolom ite is
marked by a very narrow se lvage of p h y l l i t e . South of th e open p i t , the
dolom ite i s com ple te ly r idd led by v e in s 1 cm th ick and v e in swarms of
p s e u d o a p l i te . Southw est of the main p i t , there are se v e ra l sm aller p i ts
cu t in dolom ite tra v e rse d by p seu d o ap li te v e in s ; th e s e p i ts do not exceed
26 fee t to ta l depth and are confined to the oxide z o n e . M in era l iza t io n in
th e p seu d o ap li te c o n s is t s of iron oxide s ta in ing w ith a z u r i te , m a la c h ite ,
and a y e l lo w -g reen a rse n ic -b e a r in g m inera l, p o ss ib ly c h e n e v ix i te (?)
61 •
The p seu d o ap li te a p p ea rs to be s trongly leach ed or w e a th e re d . D eep
s a n d - and o re -f i l le d s inkho les in the dolomite are a ligned along the
p seu d o ap li te v e i n s .
North of the main open p i t , the re is a r e s i s ta n t quartz " r e e f , "
197 fee t long and 6 .5 fee t w id e , w hich forms a rib 26 to 33 feet h igh .
The dolom ite ad ja c e n t to the north s ide of th is quartz "reef" is " strongly"
m inera lized w ith c h a lc o p y r i te . This ore zone h as been p rospec ted by a
4 0 - fo o t-d e e p shaft put down from the bottom of a long , deep p rospec t
t r e n c h .
On the w e s te rn h i l l , the dolom ite i s a lso m inera lized and cut
by numerous w e l l-m in e ra l ized p seu d o ap li te v e in s . M any o re -b ea r in g
s in k h o les are a lso c lo s e ly a s s o c ia te d w ith the p seu d o ap li te v e in s in
th is part of the d e p o s i t .
A sis East
The A sis East d e p o s it is 2 .2 m iles e a s t of th e production shaft
of the A sis mine (Fig, 18) . Between the A sis East-End d e p o s i t p rev ious ly
d esc r ib ed and th is d e p o s i t , there is a more or l e s s con tinuous line of low
h i l l s con ta in ing a narrow m inera lized z o n e . W ithin th is m inera lized z o n e ,
th e dolomite forms small r e s i s ta n t k n o b s , p o ss ib ly a s a re s u l t of s ligh t
s i l i c i f i c a t io n , and there are s tr ingers of w eakly m inera lized p se u d o
a p l i t e . Several occu rren ces of ga lena are a lso reported in th is c o n n e c t
ing zone by Schneiderhohh (1921).
The A sis E as t mine w as abandoned before World W ar I . W ork
ings c o n s is te d of a 6 0 -m e te r-d eep shaft w ith severa l d r if ts and c r o s s
c u t s . The workings are in a large p seu d o ap li te body w hich is w ell
62
m inera lized a t the s u r f a c e . Schneiderhohn (1921), from an exam ination
of the dumps and surface w o rk in g s , concluded th a t a t l e a s t part of the
underground workings were in p seu d o ap li te but th a t the p seu d o ap li te a t
depth w as w eakly m in era lized .
Baltika
Schw ellnus (1945) d e sc r ib e s the Baltika d e p o s i ts (Fig. 17), 11
m iles e a s t of O tavi on farm 515, a s o re -b e a r in g , f il led s inkho les ( san d -
sacks) and as ore in a v e r t ic a l c a lc i te "vein" (filled so lu tion f is su re ? ) ,
in the Upper Tsumeb dolom ites north of the O tavi V alley.
The s a n d -f i l le d s inkhole d e p o s its continue downward into la rger
so lu tion c a v i t ie s which are a lso f il led with sand a n d /o r red c la y . Vana
dium m inera ls occur d issem in a ted in the sand and c la y , as co a tin g s on
the dolomite w a lls , or as a. cem enting m ateria l betw een dolomite c o l la p se
b re c c ia b lo c k s . C aliche p a r t ia l ly cem ents the f il l m ate ria l a t the su rfa c e .
The "vein" occurrence p in ch es and sw e lls a long s tr ike from le s s than 1
foot to more than 6 fe e t , w ith an open cav ity in the c e n te r a t the th ick e r
portions of the d e p o s i t . The "vein" c o n s is t s of a l te rn a t in g layers of c a l
c i t e , very th in bands of ore m in e ra ls , and thin bands of c lay ; in p la c e s ,
the "vein" is en t ire ly barren c a l c i t e . The "vein" has been mined over a
s tr ike length of 1 0 0 f e e t .
Berg Auk as
The Berg Aukas m ine, 15 m iles n o r th e as t of G rootfon te in , is
d esc r ib ed by Schw ellnus (1945) as a v e r t ic a l , irregu lar "p ipe" c o n ta in
ing the seco n d ary z in c m in e ra ls , s m i th s o n i te , and ca la m in e , with
boulders of dolom ite in a matrix of "brow nish c a lc a re o u s ' c l a y ' ." In the
, 63
" p ip e ," vanadium m inera ls occu r a s en c ru s ta t io n s on the dolomite bou l
ders and as d isco n tin u o u s coa tings on the pipe w a l l s . N ear the "p ipe"
d e p o s i t , a f is su re con ta in ing over 3 fe e t of m ass iv e vanadium ore w as
mined to a depth of 1 0 fee t where the p h rea tic zone w as encoun tered and
the f is su re and vanadium m inera liza tion abruptly en d ed .
P e lle t ie r (1964) g ives a more u p - to -d a te p ic tu re of the geo log ic
se tt in g and p re se n t mining of the d e p o s i t by the South W e s t Africa
Com pany, L td . The ore body is lo c a l iz e d a t a po in t where a c ro ss warp
in te rs e c ts the s te e p ly dipping north limb of a lo c a l , m oderately w es tw ard -
plunging syn c lin e formed in the southern limb of a reg iona l e a s t - w e s t
syn c lin e (F ig„ 13). The c ro ss warp is of a lo ca l nature and only d is tu rbs
the so u th -d ipp ing beds for 700 fee t a long th e ir s t r ik e . The h o s t rock is a
700 - fo o t- th ick bed of dolom ite in the lower part of the O tav i form ation.
This 700- fo o t- th ic k bed of dolom ite h as been h ighly r e c ry s ta l l iz e d , d i s
tin g u ish in g it from the a d ja c e n t dolomite and l im es to n e . The re s u l t of
th e se lo c i is a s te e p ly p lunging ore body 700 by 700 fee t in plan sec t io n
with a proven depth of over 2 , 0 0 0 f e e t .
Vanadium h as been added by supergene w ate rs to the ox ida tion
products of the primary m in era liza tio n , g a le n a , and s p h a le r i te . The
p r in c ip a l vanadium m inera l is d e s c lo iz i t e . The ore body is primarily a
vanadium producer to the 400-fo o t le v e l . Although d e s c lo iz i te has been
found to the g re a te s t dep ths exp lo red , th e re is a g radual d e c re a se in
vanadium co n ten t u n ti l vanadium becom es a byproduct a t about a 500-
foot d e p th . The vanadium ore occurs rep lac in g the primary m inera ls in
the m ass iv e ore body, in dolomite b re c c ia z o n e s , as en c ru s ta t io n s on
the roofs and w a lls of so lu tion c a v i t i e s , and in the c o l la p se filling of
: . 64
large so lu tion c a v e r n s , The ore body is a z inc and lead d e p o s it below
500 fe e t . O xidation-of the primary ore is developed to g rea t d e p th . The
ox id ized ore co n ta in s very abundant w illem ite and some c e r u s s i t e . The
su lf ide o r e , where i t e x i s t s , forms large rep lacem en t bod ies of m ass iv e
ore as w e ll as d issem in a ted ore in dolomite b r e c c i a s .
Large re se rv e s of z inc and lead are inferred from P e l le t ie r 's
(1964) d esc rip t io n of the d e p o s i t . This is su b s ta n t ia te d by the January
1968 i s s u e of M ineral Trade N otes (Baker, S p ro u se , and W ilc o x ) , w hich
reports a 1 5 -y ea r c o n ta c t be tw een the Berg Auk as mine and the South
African Iron and S teel Corporation (ISCOR) w hereby the mine w ill produce
36 ,500 to n s of e le c tro ly t ic z in c annually for ISCOR, rep resen tin g 100
tons of e le c tro ly t ic z in c per day or ju s t over o n e -h a l f m illion tons of
m e ta ll ic z in c over the co n trac t pe riod .
G au ss 46 •
Very minor g a le n a , p o ss ib ly sy n g e n e t ic , is reported from th is/ ’
farm (Fig . 17), 43 m iles e a s t of O tav i, by W illem se e t al„ (1944) . The
g a lena w as n o ticed in m ass iv e dolomite on top of a high h i l l 1 mile
n o rth -n o r th w es t of the fa rm h o u se .
G ro ss -O ta v i
P seudoap lite Ore Body
The p seu d o ap li te ore body a t G ro ss -O ta v i is 1 km north of the
2 9 .5 -km mark of the O tav i-G rootfon te in ra ilw ay (Figs . 17 and 18). The
d e p o s i t is lo ca ted on the low. te r race of dolomite h i l ls th a t forms the
northern boundary of the O tav i V alley . The d e p o s it began developm ent
in 1913 and in 1919, when Schneiderhfthn (1921) v is i te d th is m ine, w as
65
developed by a sh a ft from th e te rrace and by a connecting ad it driven
from the m id -e lev a tio n of the te r ra c e . A w inze was sunk from the bottom
of the shaft a c ro ss the ore body and into th e foo tw all. At a depth of 80
fee t below the ad it le v e l , the w inze in te rse c te d se v e ra l so lu tion f is su re s
w hich con ta ined c ru s ts and c ry s ta l agg reg a tes of copper and lead v a n a
d a te s . Schw ellnus (1945) may have been referring to th is d e p o s it in h is
d esc r ip t io n of the vanadium occurrence a t G ro s s -O ta v i . Schw ellnus d e s
c r ib es the vanadium occurrence as a conformable so lu tion f is su re f il led
by redd ish san d , c la y , and e r ra t ic a l ly d is tr ib u ted p a tc h e s of vanadium
. o r e .
The su rface ex p re ss io n of th is d e p o s i t w as a sha llow e l l ip t ic a l
d e p re s s io n , 330 fee t by 100 fe e t , w ith numerous s c a t te re d b locks of
goe th ite con ta in ing c e r u s s i t e , m a la c h i te , a z u r i te , and many o ther yellow
and green ox idation m inera ls of lead and copper . The h o s t rock is a
den se dolomite with a pronounced layering of s e v e ra l p a ra l le l beds of
s i l ic i f ie d o o l i t e s . The s i l ic i f ie d oo lite beds p ro jec t as sharp ribs with
the se p ta of dolomite eroded to form tro u g h s . The s i l ic i f ie d oo lite beds
s tr ike e a s t - w e s t and dip 50° to 60° S. (Schneiderhohn, 19 21). This
dolomite m ust re p re se n t Zone 8 of the Upper Tsumeb s u b s ta g e .
In the a d i t , three d is t in c t zones of the ore body were recogn ized
by Schneiderhohn (1921): (1) a c en tra l zone of lead and iron m in e ra liza
tion e n c lo se d by (2) two copper- iron z o n e s , and (3) a footw all co n tac t :
zone which is a snow -w hite layer of so f t , g reasy se r ic i te (phyllite)
s c h is t ( ? ) . The p seu d o ap li te pipe d e sc e n d s concordantly w ith the do lo
mite bedding (60° tq 70° S . ) . The s i l ic i f ie d oo lite beds n ea r the ore body
often con ta in m ic ro sco p ica lly fine p a r t ic le s of d issem in a ted c h a lc o p y r i te .
66
O re-b ea r in g , S and-f i l led S inkholes
There are two a re a s of o re -b ea r in g s in k h o le s . The w es te rn a rea
w as the in i t ia l d isco v e ry for th is type of d e p o s it w ith in the O tavi M oun
ta in land (F ig s . 22 and 23). This d e p o s i t is 1 km north of the 29-km
mark of the O tav i-G roo tfon te in ra i lw ay . The s in k h o les were found on the
e a s te rn s lope of a sm all v a l ley cu tting the O tavi Valley dolomite te rrace
and a l s o on the main t e r r a c e . The zone con ta in ing th e se s a n d - f i l le d ,
o re -b ea r in g s in k h o les and sm all ch a lc o c i te v e in le ts is 500 fee t e a s t - w e s t
by 100 to 230 fee t n o r th -so u th . The h o s t rock is aga in the dense dolo
mite of Zone 8 w ith p a ra l le l s i l ic i f ie d o o li te beds s tr ik ing e a s t - w e s t and
dipping 40° S. The s in k h o les con ta ined large m a sse s of ore with b locks
of m ass iv e ch a lc o c i te up to 24 cub ic m eters (847 cub ic feet) encoun tered
during the mining o p e ra t io n s . In November 1909, a block of nearly pure
c h a lc o c i te 2 by 3 by 4 m eters (6 . 5 x 9 . 8 x 13.1 feet) w as found at a
depth of 4 m eters com plete ly surrounded by sand within the en c lo s in g
s in k h o le . The m ost common s iz e of the ore fragments w as from nut to
f i s t s i z e . H ow ever, p e a - s i z e p ie c e s were so common th a t the f il l m a te
r ia l w as sc reen ed to recover th e se finer ore p a r t ic le s . In add ition to the
m alach ite and c h a lc o c i te m a s s e s , a l e s s e r number of intergrown c h a l
co c i te and g a lena ore p ie c e s were found and , ra re ly , some com posed
only of g a le n a . Ore m a sse s were found only in the s in k h o les th a t in te r
se c te d sm all ch a lc o c i te v e in le ts in the d o lo m ite .
Eastern Group of S inkholes
The second occurrence of th e s e o re -b ea r in g s in k h o le s is north
of the 35-km mark of the O tav i-G rootfon te in ra ilw ay and is a lso located.
67
I
Scale in feel
Figure 22. P rospect Area at G ro ss -O ta v i , O tavi V alley , South W est A frica . - -M o d if ie d from Kuntz (1904).
Figure 23. Typical Section through G ro ss -O tav i Copper- bearing Karst D ep o s it , O tavi Valley, South W est A frica . - -M o d if ied from Kuntz (1904).
\I
a t the mouth of a sm all c ro ss v a l le y which cu ts the O tav i Valley dolomite
t e r r a c e . The so lu tion p ipes are confined to a re la t iv e ly sm all a rea and
are from 80 to 100 fee t d eep . The p ipes u su a lly die out by an 80-foot
depth; where they p e r s i s t fa rther , they are barren below about 80 fe e t .
This o re -b ea r in g k a rs t w as worked by the O tav i Exploring Syndicate and
w as in production during the early 1 9 2 0 's . The c h a lc o c i te ore m asse s
were up to one cub ic m eter in s ize ; the ore was m ost commonly about
nut s iz e . The sm alle r p ie c e s of c h a lc o c i te had been a lm ost com pletely
converted to m alach ite with a rad ia l fibrous s truc ture surrounding a p a r t
ly converted c h a lc o c i te n u c le u s . Rarely, d io p tase may occur w ithin the
ore m a sse s a s sm all v e i n l e t s . P la n c h e ite , another copper s i l i c a te , h as
a lso been reported from the m alach ite rind of th e se ore m a s s e s .
W ithin the s in k h o le s , la rger fragments of the dolomite h o s t rock
are very rare; and when they do o ccu r , they are g rea tly w ea thered and
co a ted by a rind of goeth ite (Schneiderhbhn , 1921). The w a lls of the
ind iv idual s in k h o le s are often covered with a n e t l ik e , in te rg row n ,
c e n tim e te r - th ic k c ru s t of m alach ite and c h a lco c ite which never p en e tra te
very far into the w a ll rock; th is ore c ru s t is to ta l ly a b se n t from the b o t
tom of the p ip e s . The h o s t rock is again the d e n s e , gray dolomite of the
Upper Tsumeb s u b s ta g e , Zone 8 , con ta in ing p a ra l le l o o li t ic chert beds
s tr ik ing e a s t - w e s t and dipping 400 S. In one p ip e , an e tc h e d , large
rem nant p iece of a c o a rse -g ra in e d c a lc i te vein w as found supported in
the sand f il l . in approxim ately the same p o s it io n as i ts corresponding
v e in , which con tinued on into the dolomite h o s t r o c k .
Some of the f il l in th e se p ip es con ta ins the bones and tee th of
l a r g e , recen t m am m als . The v e r teb ra te m ate ria l is s c a t te re d throughout
69
the p ip es a t a l l l e v e l s . Some of the bones are rep laced by a b lu e -g re e n
copper p h o s p h a te .
Klinger (1938) reports th a t the ore of G ro ss -O ta v i con ta ined
grades up to 40% copper. It is uncer ta in a s to which of the three d e -. i
p o s i ts th is figure r e fe r s .
Guchab
Guchab. is 33 m iles s o u th - s o u th e a s t of Tsumeb and 21 m iles
so u th w est of G rootfonte in . The p ro sp e c ts occur in a m inera lized zone
500 to 985 fee t wide w hich trends e a s t - w e s t along the north s id e of the
O tav i Valley (Schneiderhohn , 1921). The zone co n ta in s over 50 w e l l -
defined v e in s . Longitudinal v e in s s tr ik e approxim ately N. 80° W. and
dip s te e p ly south; the c ro ss v e in s s tr ike N . 65° to 70° E. and dip s te e p
ly w e s t (F ig . 24). The dip of th e s e v e in s is a lw ays s te e p with a mini
mum angle of 75° , but more often the ve in s dip v e r t ic a l ly . The ind iv idual
v e in s do not have sharp boundaries and are more tru ly ve in zones com
posed of narrow lodes a l te rn a tin g with b r e c c i a . Often s e v e ra l of th e se
z o n e s , 16 to 26 fee t w id e , p a ra l le l one ano ther and are s e p a ra ted by
no n b recc ia ted zones of s im ilar w id th . M ost of the ind iv idua l vein zones
have a "proven ore width" of 6 .5 to 13 fe e t . The m inera liza tion d ies out
along s tr ik e . E longate le n s e s of ore w ithin th e se ve in zones may be 985
fee t lo n g . Larger bod ies of ore occur a t and near the in te rse c t io n of c ro ss
v e in s and long itud ina l v e in s , for exam ple , the "E isen er Hut" (Iron Hat)
ore body d e sc r ib ed in a following s e c t io n . The G uchab v e in s , as d e s
cribed by Schneiderhohn (1921), con ta in ch a lco c ite and c o v e ll i te a s the.
only iden tif ied su lf id es and a wide v a r ie ty of copper ox ides . C hem ical
f isener iHut
Guchob - Berg
-r _v^ ^ - r-r^-v-TT^-T- -r >T r\ T rr -rcr 7\vTr\T T
X R L _ A N A T I O N
" \ < \ V
^ \x\x\x 'Ot a v i t a l s c h i e f e r ( Otav i V o l l e y P h y l l i t e ) -K l o t z i g e r Do l omi t e ( b l ocky or m a ss i ve d o l o m i t e ) ^ = d rP f-Q u o r t z i t e s t o c k e ( Wa h r s c he in l i c h )( J os pe r o i d or s i l i c i f i ed p s eu do op l i t e
+ ++ + i i £a nd / o r dolomi t e )
... V e rq u a r z t e Zonen ( Ve r k i ese l te R i f f g e s t e m e )I K ( s i l i c i f i e d zones , p s eu d oo p l i t e ? )
T e k t o ms c he Brekz ienzonen ( t ec t on i c b recc i o zone )
Vererz f e B r ek z i e n g bn g e ( m i n e r o l i z e d brecc i a ve ins
Toube( b a r r e n v e i n s )
Junge A r o g o n i t g d n g e ( l a t e a r a g o n i t e v e i ns )
IOOO 1000 2000 3 0 0 0 4 0 0 0 5 0 0 0
Scale in feet
Figure 24. G eologic Map of Guchab Copper O c c u rre n c e s , O tavi V a l le y .— From Schneiderhbhn (1929) .
a n a ly s is of the ore has shown the p re sen ce of z inc and l e s s e r amounts
of lead and a r s e n ic , but ore m inerals of th e se e lem ents have no t, a c
cording to Schneiderhohn (1921), been iden tif ied from th e se v e in s . The
e h o s t rock is a s i l ic i f ie d dolomite with abundant ch e r t . W ithin the vein,
b r e c c ia s , the p r in c ip a l gangue m inera ls are c a lc i t e , lim onite and c a lc i te
cem enting the vein b r e c c ia s , and lo c a l iz e d o ccu rrences of qu a r tz . The
b re c c ia s th a t jo in the ind iv idual v e in s are not ore bearing but are c a l
careous and iron s ta in e d . The long itud ina l ve ins con ta in the copper
s i l i c a te s p lan ch e ite and d io p tase . These long itud ina l v e in s a lso have
undergone p o s t-o re movem ent, forming open sp a c e s which are fil led by
la te r a rag o n ite .
The ore grade d e c re a se s no tab ly a t about 33 fee t below the su r
fa c e , and both the ore and the b recc ia zones die out a t about 165 fee t
with only s l ig h t b recc ia t io n below th is d ep th .
O re-bea ring S inkholes
The m ajority of ore produced from the Guchab d e p o s i ts prior to
1921 w as produced from s a n d -f i l le d so lu tion p ip e s . The f i l l m ateria l
w ith in the p ipes is com posed of re s id u a l m ate ria l developed during the
so lu tion p ro c e s s , such a s r e s id u a l b locks of do lom ite , s i l ic i f ie d do lo
m ite , quartz , ore m in e ra ls , and eo lian s a n d . The o r ig ina l surface w ork
ings in the a rea were begun in 1907 and were dep le ted by 1908. The
tenor of th e se su rface d ep o s its is g iven by Schneiderhohn (1929) as 29%
to 3 3 % copper and 0 .032% to 0.04% (7 .7 to 9 .6 ounces per ton) s i lv e r .
Schneiderhohn (1921, p . 235) s ta te s th a t "w herever there is m in e ra liza
tion there is a g rea te r abundance of th e s e s in k h o le s ." He a ttr ibu ted the
72
c lo se a s s o c ia t io n of s in k h o les with the m inera lized v e in s to so lu tion
a c t iv i ty accom panying ac id developed, during the breakdown of c h a lc o -
citeV A more a c c e p ta b le exp lanation is th a t the c a lc i t i c a l te ra tio n
aureo le surrounding the primary ore d e p o s i ts c re a te s a reas of p re fe ren
t ia l ly h igher so lu b il i ty and therefore h as a na tu ra lly h igher den s ity of
s inkho le developm ent.
Only th o se s in k h o les th a t cu t ch a lc o c i te ve ins con ta in ore a c
c u m u la t io n s . In some of th e se o re -b ea r in g s in k s , the o r ig ina l vein
p o s it io n is vague ly p rese rv ed by an alignm ent of the re s id u a l vein m a te
r ia l . In g e n e ra l , the p ie c e s of ore are randomly d is tr ib u ted throughout
the p ip e , w ith l i t t le or no s iz e d iffe ren tia t ion within the d e p o s i t .
The "E isen er Hut" O ccurrence
The E isener Hut is d esc r ib ed by Schneiderhohn (1921). This is
the h ig h e s t and la rg e s t outcrop in the group and o c c u p ie s the en tire sum
mit of a 6 , 248-foot mountain (Fig. 24). The outcrop is 262 fee t long by
165 fee t wide and 100 fee t h ig h . The entire upper 100 fe e t of th is moun
ta in is a com plex b recc ia com posed of angu la r to rounded fragments o f
do lom ite , dense w hite q u a r tz i te , and f in e -g ra in ed pink c h e r t . The b re c
c ia fragments vary from pea s iz e up to se v e ra l cub ic m e te rs . There is no
apparen t s tra t i f ic a t io n or s iz e d iffe ren tia tion within the b re c c ia . The
b recc ia fragm ents are s e t in a ca lc a re o u s -d o lo m it ic and s la ty pu lverized
m atrix , cu t by a network of quartz v e in le ts from paper th in up to a c e n t i
m eter t h i c k , accom panied by quartz b leb s and a network of ch a lco c i te
v e in s up to 10 cm t h i c k . In the su rface ou tcrop , the m atrix h as been
com ple te ly w ea thered aw ay , and the b re c c ia b locks form a lo o se - ru b b le .
73
The quartz v e in s and la rger b recc ia b locks remain in p la c e . The outcrop,
forms a p i t te d , deep ly w ea th e red , jum bled m ass of quartz v e in s , with
b locks of quartz ite (p seu d o ap li te? ) and dolomite . The quartz v e i n s ,
which have w eathered f r e e , as w ell as the w alls of numerous so lu tion
c a v i t i e s , are co a ted with sm all quartz c r y s t a l s , a dark red-brow n lim o-
n ite (hematite + g o e th i t e ? ) , and numerous copper oxide m in e ra ls .
C h a lco c ite v e in le t s , 5 to 10 cm in w id th , accom pan ied by co p
per ox ides have r e s i s te d the w eathering p ro c e ss and rem ain in the upper
part of the outcrop as f re e -s ta n d in g ribs w ithin so lu tion c a v i t ie s and as
ve in s cu tting through b locks of dolomite and quartz i t e . D ruses in the
quartz ite b locks are often fil led with _secondary copper o r e s . The o c cu r
rence is the type lo c a l i ty of b a r th i t e , 3ZnO, CuO, 3AS2 O 5 , 2H 2 O, w hich
partly pseudom orphoses quartz in th is d e p o s i t , ind ica ting the e x is te n c e
of a t l e a s t some z inc and a rse n ic -b e a r in g s u lf id e s , probably sp h a le r i te
and e n a r g i te , before ox id a tio n .
A m inera lized b recc ia vein s tr ik ing N. 80° W. with a 70° S.
dip forms the northw este rn boundary of th is d e p o s i t . Another m inera lized
v e in , roughly p a ra l le l to th i s , ex ten d s from the so u th w es t s ide of the
main b re c c ia body. A b re c c ia te d c ro ss v e in , N. 50° E . , ex tends from
the northern c o rn e r . All of th e se rad ia t in g ve ins are m in era lized , with
the m inera liza tion ex tend ing for a t l e a s t 1 0 0 meters, aw ay from the main
b recc ia body and d e c re a s in g g rada tiona lly un ti l the b re c c ia ve ins becom e
b a r re n . The N. 80° W. v e in s c o n n e c t to o ther m inera lized b recc ia v e in s
to the w e s t .
W ithin the quartz b r e c c ia , n ea r the southern boundary of the
main b re c c ia body, a vein of w e l l -b a n d e d a ra g o n i te , up to 2 m eters w id e ,
74
s tr ik e s N . 80° W. e a s t of the d e p o s i t and to the w e s t v a r ie s in s tr ike
u n ti l i t n ear ly p a ra l le ls the N„ 50° E. v e in s . The aragon ite and a so ft
m ass of b recc ia co n ta in the s h e l ls of re c e n t land m o l lu s k s , docum enting
the very re c e n t origin for the f illing of th e s e pos tm inera l f i s s u r e s .
Guchab East
The Guchab E ast d e p o s i t , which is d esc r ib ed by Schneiderhohn
(1921), is on the north s ide of Rodger M ountain , approxim ate ly 30 m eters
below the summit (F ig . 24). The h o s t rock is a d e n s e , g ray , loca lly
s i l ic i f ie d dolomite b re c c ia . The dolomite is cu t by irregular v e in le ts and
m a sse s of w h i te , c o a rse -g ra in e d c a l c i t e . The ore zone is 10 to 13 fee t
th ic k . Ore l e n s e s , 16 to 26 fee t long and 6 .5 to 1 0 f ee t w id e , a l te rn a te
w ith cub ic m eter pods of c a lc i te which con ta in only narrow s tr ingers of
o r e . The su lfide ore in the main ore le n se s is a f in e -g ra in ed m ass of
intergrown c h a lc o c i te g r a in s . Q uartz and c a lc i te occur as intergrowths
a t the boundaries of the ore le n se s and ra re ly w ithin the ore le n se s
th e m se lv e s . Small ore sh o o ts branch d iagona lly away from the main ore
zo n e . P a ra l le l to th e se d iagonal ore shoo ts is a s l i c k e n s id e d , dense
quartz b recc ia with v e in le ts of c h a lc o c i te and a z u r i te . The ch a lco c ite
occurs as m ass iv e co a t in g s and very fine branching v e in le ts in p la ty to
f in e -g ra in ed quartz in the q u a r tz -c h a lc o c i te b r e c c ia s . Bordering the
quartz b recc ia is a lam inated and in te r lay e red zone of c a lc i te and s i l i
ceous m a la c h i te .
Harasib. 317 ..
T races of g a lena and sp h a le r i te are reported by W illem se e t a l .
(1944) from th is farm and the ad jo in ing farm, No s ib 655 (Fig. 17), 30
75
m iles n o rthw est of G ro o tfo n te in . Surface tren ch es on th is occurrence are
lo c a te d 1 mile n o r th -n o r th e a s t of the farm b u i ld in g s . W eak m in era liza
tion has. been tra ced 1 ,500 to 1, 800 fee t along s tr ik e . Two other o ccu r
ren ces with the name H aras ib (F ig . 17) are shown on the geo log ic map of
South W es t Africa; both occur on block 648.
; O lifan ts fon te in 9
D e sc lo iz i te (basic vanada te of le a d , z in c , and copper) occurs
in a strongly b recc ia ted and s i l ic i f ie d m ass iv e dolomite (W illemse e t a l . ,
1944) on th is farm, 18 m iles northw est of Grootfontein a t a point 2 m iles
north of the farmhouse n ea r the boundary of farm Khuisib (Fig. 17).
Small sp eck s of g a lena w ere reported in the nonbrecc ia ted dolomite in
the v ic in i ty of the d e s c lo iz i te o c c u r re n c e .
1 Otj irukaku 42
A m inera lized zone with sm all p a tc h e s of g a len a is reported by
W illem se e t a l . (1944) as occurring n ea r the no r thw est-co rner of th is
farm, 22 m iles so u th w est of Grootfontein (Fig. 17). The m inera lized zone
s tr ik e s n o r th -n o rth w est and is reported ly 1 , 2 0 0 fee t long, ex tending onto
farm Okombongor 43; no width da ta are g iv en . Vanadium m inera liza tion
is found nearby in b recc ia and in f il led so lu tion c a v i t i e s .
Rietfonte in 344
Vanadium m inera liza tion (desc lo iz ite ) occurs as irregular m a ss e s
. in red and gray ca lc a re o u s c lay and as co a tin g s on dolom ite boulders in
a f illed s inkhole on th is farm, approxim ate ly 45 m iles e a s t - s o u th e a s t of
O tav i (F ig . 17). Animal bones of re c e n t sp e c ie s have been found in th is
76
d e p o s i t , including some tha t were coa ted with vanadium m inera ls . G a
lena and copper su lf id es are reported ly p re se n t (S ch w elln u s , 1945) in
sm all am ounts in the m ass iv e dolomite a d ja c e n t to the d e p ress io n and in
some of the boulders in the c lay f i l l . No su lf ide m inera ls have been r e -
ported from the c la y .
I Toggenburg 591
Numerous occu rren ces of vanadium m inera ls occur on th is farm,
approxim ately 19 m iles northw est of Grootfontein (Fig., 17). Schwellnus
(1945) fe lt th a t only one of three m erited d e sc r ip t io n . This occurrence
w as a number of so lu tion c a v i t ie s (sinkholes) con ta in ing vanadium m in
e r a l s , 2 m iles south of the h o m estead , from which s e v e ra l tons of v a n a
dium ore were rem o v ed . These s in k h o les were mined to a depth of 10 to
12 f e e t . Small rep lacem en t p a tc h e s of g a len a with quartz are found in
the surrounding do lom ite . A s e r ie s of a ligned vanadium o ccu rrences is
shown on the geo log ic map of South W es t Africa as p a s s in g through th is
fa rm .
U itsab 654
This now -dorm ant o p e n - c a s t mine is lo ca ted on farm U itsab
654, 27 m iles w e s t of G rootfontein (F ig . 17). V anadin ite , d e s c lo iz i te ,
and pyromorphite occu r a s lo c a l iz e d in te r s t i t ia l f il l ings in a tec to n ic
b re c c ia . The d e p o s it w as exp lo ited by o p e n - c a s t m e th o d s . Total pro
duction is reported ly in e x c e s s of 800 tons of c o n c e n tra te s . W illem se
e t a l . (1944) found d issem in a ted g a le n a , pyrom orphite , and c e ru s s i te in
the m ass ive dolomite ad jo in ing the b re c c ia zone and reported th a t pyro
morphite w as " fairly abundant" on the dump.
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