ARTICLE

M. F. El-Sharkawy

Talc mineralization of ultrama®c af®nity in the Eastern Desert of Egypt

Received: 26 March 1999 /Accepted: 10 October 1999

Abstract Petrographical and petrochemical studies ofthe talc host rocks of Rod Umm El-Farag and WadiThamil in the Eastern Desert of Egypt reveal that theyconsist mainly of metavolcanic rocks, whilst the geology,petrography, mineralogy, chemistry and quality of theenclosed talc lenses reveal that the ore has ultrama®ca�nity. The setting of the talc ore is similar to thathosted by metavolcanic rocks in terms of the type ofhost rocks, but it di�ers in its ultrama®c a�nity, re-sembling the talc ore hosted by ultrama®c rocks. Theparent ultrama®c rocks occur in the form of small bodiesobducted later along a tectonized fault plane withinmetavolcanic host rocks (Precambrian) and their tu�-aceous equivalents. The metavolcanic host rocks consistmainly of metabasalts, meta-andesites and metatu�swith a smaller amount of dacite, rhyolite and tu�aceouslava. The metamorphic grade is low corresponding togreenschist facies. The calc-alkaline and tholeiiticcharacters of the volcanic rocks are determined by thebehaviour of trace elements on some chemical discrim-ination diagrams. After the emplacement of the ultra-ma®c bodies, they underwent regional metamorphismwhich was accompanied by further serpentinization.Metasomatic changes, related to regional metamor-phism (corresponding to the emplacement of graniticplutons at a distance) include talc, carbonate, tremoliteand chlorite formation. SiO2, H2O and CO2 have beensupplied from hydrothermal solutions but all otherconstituents are considered indigenous to the ultrama®c

bodies, and none of the metavolcanic components havebeen added during talc formation. Mineralogically, thetalc ore is relatively simple, including talc, tremolite,actinolite, chlorite and chromite. On the basis of mineralabundances, pure talc (>90% talc), chlorite-rich andtremolite-actinolite-rich (50±70% talc) ore types havebeen recognized. Chromite is largely zoned and occursas disseminated grains within the talc matrix. Cr, Al andMg were released during the formation of ferrite chro-mite and accommodated in the talc and chlorite struc-tures. The chemical data show that there is very littlevariation in the contents of MgO, Fe2O3, FeO, NiO,Cr2O3, and Co between the parent ultrama®c rocks andtalc ore. Al2O3, CaO, Fe2O3 and FeO are the main im-purity oxides in the talc ore. They decrease the whitenessof the ore and consequently limit the use of talc.

Introduction

The majority of talc occurrences in Egypt are derivedfrom and hosted by ultrama®c rocks, mainly by ser-pentinite. Serpentinite bodies characteristically occur inbelts of low-grade metamorphic sedimentary and volca-nic rocks. These talc deposits are widely variable inshape, and are mostly pod-shaped, lenticular, thin shellsand irregular masses. At Gebel El Maiyit, Hammuda,Wadi El-Sodmein, Rod El-Tom, Umm Dalalil, and AbuQuraiya, the association of rocks characteristically con-sist of a talc core, surrounded by a shell of talc-carbonateand a shell of serpentinite rock. The adjacent countryrocks are altered to chlorite and biotite rocks. Talc occursas a secondary mineral formed by alteration of magne-sium carbonates (magnesite and dolomite) and silicatessuch as serpentine, tremolite and chlorite (Chidester et al.1978; Pohl 1984; El Gaby et al. 1988; Hussein 1990).

Salem (1992) distinguished two distinct types ofultrama®c-derived talc ore; pure talc and chlorite-talc.He also proposed that the talc deposits hosted by ultra-basic rocks were formed through a processes of regionalmetamorphism and thrust faulting of serpentinized

Mineralium Deposita (2000) 35: 346±363 Ó Springer-Verlag 2000

Editorial handling: O. A. R. Thalhammer

M. F. El-Sharkawy (&)Geology Department, Faculty of Science,Tanta University, Tanta 31527-Egypte-mail: m9835210@hotmail.com

Present address:Mining University, Institute of Geosciences,Franz-Josef Str 18, 8700 Leoben, Austriae-mail: m9835210@hotmail.comFax: +43-03842-4029902

ultrama®cs and followed by percolation of hydrother-mal solutions.

The other type of talc deposits in Egypt (metavolca-nic-derived talc) occurs within a volcanic suite of tho-leiitic a�nity and Early Precambrian age (comprisingbasalt, rhyolite, dacite and their volcanoclastic equiva-lents). These rocks have been transformed by successivephases of metasomatism into amphibolititized, chloriti-zed, talc and talc-carbonate rocks. These talc depositshave been attributed to the ¯ow of hydrothermal solu-tions rich in Si, CO2, Fe and S along tectonized shearzones (Said 1962; Hassan 1969). Abdel Kader andShalaby (1982) studied the alteration at the Atshan talcmine and recognized three stages, i.e. serpentinizationand carbonatization, sericitization or argillization, andtalci®cation. Hussein (1990) proposed that the talc de-posits hosted by volcanic rocks in Egypt were formedthrough a process of intense Mg-metasomatism associ-ated with a volcanic exhalative episode. This exhalativeepisode was responsible for the formation of the massiveZn±Cu±Pb deposits, with which the talc has a closespatial association.

The purpose of the present study is to present pe-trography, mineral chemistry and geochemistry of theultrama®c derived talc ore as well as the host metavol-canics to show their non-genetic relation. The studyareas include Wadi Thamil and Rod Umm El-Farag.

These talc deposits are located along the Idfu-MersaAlam Road. In Wadi Thamil (W.Th) area (ca. 20 kmNW of El-Sheikh Salem), the talc-deposits are found intwo small occurrences along the Wadi Thamil El-Sodaand Wadi Thamil El-Hamra. In Rod Umm El-Farag(RUF) area, the talc deposits are recorded in two sites atca.55 (then ca.11 km to the north) and ca.57 km west ofMersa Alam (Fig. 1).

Analytical methods

To con®rm the mineralogical composition of talc ore and slightlytalci®ed rocks, both X-ray di�raction (XRD) and scanning electronmicroscope (SEM) techniques were used. Quantitative analyseswere performed on talc, chlorite, actinolite, tremolite, chromite,rutile and titanite using a JEOL 840 SEM with an Oxford instru-ments energy dispersive X-ray spectrometer (EDS Link AN 10000System) housed at the Laboratories of Camborne School of Mines(CSM), University of Exeter, UK. An accelerating voltage of 15 kVand a current of 20±50 nA with a live time of 100 s were thestandard operating conditions. Data were automatically reducedusing the ZAF4 FLs and Link analytical systems software. Thewhole rock analyses were done by X-ray ¯uorescence (XRF,Phillips PW-1400) at the Laboratories of CSM. Major and traceelements were determined in fused and pressed pellets respectively.Calibration is achieved by running international standards plus afew synthetics such as calcium carbonate, silica and aluminumoxide through the procedure. The analyses were carried out fortotal iron and Fe2+ (by titration against KMnO4) separately, thusFe3+ is obtained by calculations.

Geologic setting

In the Egyptian shield, which is a part of the Arabian-Nubianshield, the metavolcanic rocks of Precambrian age crop out over a

wide area. Younger ultrama®c intrusions crosscut the metavolcanicbelt in ophiolitic melanges and, in the study areas, are obductedwithin the metavolcanic and their tu�aceous equivalents. They areemplaced along a tectonized left lateral thrust fault plane andcompletely talci®ed with no relics of serpentinites. The contactbetween metavolcanics and talc lenses is marked by a zone in whichmetavolcanics and parent ultrama®c rocks are hydrothermallyaltered.

The obducted ultrama®c bodies are altered to talc, giving rise totalc deposits of ultrama®c a�nity in metavolcanic terrains. Thehost rocks are composed of metamorphosed basic volcanic rockswith minor intercalations of tu�aceous lavas of same compositions.The change from basic to acidic composition is graditional. Thesehost rocks are intruded by Homret Waggat granitic rocks (535 Ma,El-Manharawy 1977). Numerous basic to intermediate dykescrosscut the host rocks in NE and ENE directions.

Petrography and mineralogy of the host metavolcanics

The metavolcanic rocks are mainly metabasalts and meta-andesites.The mineral assemblage (albite, actinolite, chlorite, epidote, calciteand quartz) indicates that the areas were a�ected mainly by low-grade green schist facies metamorphism. The possible conditions ofmetamorphism are T � 350±450 °C and P � <9 kbar (Yardley1989). However, both metabasalt and meta-andesite have under-gone further intense hydrothermal alteration processes in the formof chloritization, tremolitization and silici®ation. Chloritization is

Fig. 1 Location map of Egypt showing the areas studied which havethe following coordinates; Wadi Thamil, 34°29¢30¢¢E and 25°08¢00¢¢Nand Rod Umm El-Farag, 34°25¢35¢¢)34°25¢20¢¢E and 25°03¢30¢¢)25°08¢15¢¢N

347

the most common and advanced alteration type, and resulted in thereplacement of plagioclase and ma®c minerals.

The metabasalt is a ®ne-grained rock and has a dark grey col-our. It consists essentially of plagioclase, actinolite and accessoriesof ilmenite, magnetite and titanite. Chlorite, muscovite, zoisite,calcite and talc are the common alteration products. The ground-mass consists of intergranular ®ne-grained plagioclase laths, ac-tinolite, dolomite, chlorite, muscovite, talc, ilmenite, magnetite andtitanite. It displays original microporphyritic and subophitic igne-ous textures. In the porphyritic variety, plagioclase crystals are themain phenocryst phase present within the ®ne-grained groundmass.The plagioclase crystals are usually saussuritized. Veinlets of zoisite(0.1 mm in width) are occasionally observed intersecting the rock.

The meta-andesite is a massive, ®ne-grained rock which isspotted with dark green actinolite and lighter coloured alteredplagioclase phenocrysts. The actinolite and plagioclase are enclosedin a pilotaxitic groundmass of ®ne plagioclase laths with intersertalcryptocrystalline materials and specks of actinolite, chlorite, phlo-gopite and accessories of titanite and iron oxides. Texturally, it ischaracterized by porphyritic texture. Plagioclase phenocrysts showlamellar twinning and zoning. Actinolite phenocrysts occur in theform of tapered prismatic crystals. Moreover, the metatu�s aredominated by massive, ®ne, and crystal lithic coarse metatu�s andtu�aceous lavas of dacitic, andesitic and basaltic composition.

Mineralogically (Table 1), plagioclase is mainly oligoclase(An13±21) in basaltic rocks and andesine-labradorite (An43±48) inandesite. Pennine [Mg7.896 Fe

2�1:803Alvi2:243 Mn0.023 (Si5.815 Aliv2:185) O20

OH)16] and ripidolite [Mg5.498Fe2�3:684Alvi2:744Mn0.045 (Si5.350Aliv2:650)

O20 (OH)16] are the main chlorite minerals. The amphibole min-erals are represented by actinolite; [Ca1.908 (Mg3.331Fe

2�1:439Fe

3�0:021

Mn0.034 Alvi0:239) (Si7.722 Aliv0:278)O22(OH,F)2] and actinolitic horn-blende; [Ca1.816 (Mg3.502Fe

2�0:864Fe

3�0:583 Ti0.039 Alvi0:082) (Si7.37Aliv0:63)

O22 (OH,F)2]. Titanite [Ca0.986 Ti0.942 Al0.061 Fe3�0:012 Si0.996 O5] isformed after primary ilmenite and/or rutile.

Petrochemistry of the host metavolcanics

The analyzed samples show a wide range of compositional varia-tion with respect to the major constituents (Table 2). The samplesare classi®ed as basalts, andesites, basaltic-andesites, rhyolite anddacite (Fig. 2) which are interpreted to be derived from subalkalinemagma (Fig. 3). Most of the basalts exhibit tholeiitic a�nity whileandesites, dacite and rhyolite show calc-alkaline characteristics(Fig. 4). Ti, Zr and Y are believed to remain constant after low-grade metamorphism (at/or above greenschist facies, Pearce andCann 1973). On a Ti-Zr-Y diagram (Fig. 5), the basalt samples fallwithin island arc tholeiite ®eld whilst the andesites lie within andclose to the calc-alkaline basalt ®eld.

Talc deposits

The talc bodies are surrounded outwards by: (1) slightlytalci®ed rocks, (2) hydrothermally altered metavolcanics(Fig. 6) and (3) freshmetavolcanics. The altered rocks arefound along shear zones and joint planes. Mineralogi-cally, they have mixed assemblage from metavolcanics

Table 1 Mineral chemistry of the metavolcanic rocks

Minerals Pennine Ripidolite Actinolite Actinolitichornblende

Plagioclase Titanite

No. M3 M6 AA5 AA6 MM12 M29 AA4 AA2 AA7 AA1 AA8 MM11 MM8 MM13 MM10 MM9

SiO2 28.76 29.12 25.43 52.99 52.71 51.62 62.19 62.79 63.53 54.52 58.73 54.41 55.84 60.83 61.49 30.30Al2O3 19.20 18.19 21.75 3.30 2.71 4.23 22.45 22.00 21.49 27.38 24.94 27.80 27.16 23.24 22.77 1.58TiO2 0.07 0.04 0.03 0.00 0.36 0.37 0.06 0.07 0.00 0.05 0.05 0.18 0.04 0.00 0.03 38.12FeOa 10.22 11.24 20.94 11.61 12.28 12.11 0.24 0.14 0.13 0.11 0.17 0.30 0.27 0.02 0.18 0.44CaO 0.16 0.09 0.07 12.23 12.14 11.87 3.76 3.45 2.77 9.83 4.33 9.81 8.95 4.57 4.11 27.98MgO 26.22 26.50 17.53 15.42 15.17 16.46 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.00 0.00 0.00MnO 0.17 0.10 0.25 0.19 0.35 n.d 0.00 0.02 0.00 0.00 0.11 0.00 0.00 0.06 0.07 0.00Na2O n.d n.d n.d n.d n.d n.d 9.49 9.79 10.11 5.84 7.99 6.06 6.56 9.02 8.62 0.04K2O n.d n.d n.d n.d n.d 0.14 0.05 0.16 0.06 0.07 1.44 0.11 0.03 0.10 0.34 0.00Cr2O3 n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.dNiO n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d

Total 84.80 85.28 86.00 95.74 95.72 96.79 98.23 98.42 98.09 97.80 97.77 98.70 98.85 97.84 97.61 98.46

Atomic proportionsSi 5.787 5.843 5.350 7.729 7.715 7.370 2.812 2.828 2.866 2.522 2.688 2.473 2.528 2.745 2.792 0.996Aliv 2.213 2.157 2.650 0.271 0.285 0.630 1.196 1.168 1.143 1.492 1.344 1.489 1.449 1.236 1.219 0.061Sum 8.000 8.000 8.000 8.000 8.000 8.000 ± ± ± ± ± ± ± ± ± ±Alvi 2.341 2.144 2.744 0.296 0.182 0.082 ± ± ± ± ± ± ± ± ± ±Ca 0.035 0.020 0.017 1.911 1.904 1.816 0.182 0.167 0.134 0.487 0.212 0.478 0.434 0.221 0.200 0.986Mg 7.865 7.927 5.498 3.353 3.309 3.502 0.000 0.000 0.000 0.000 0.000 0.002 0.000 0.000 0.000 0.000

Fe2+ 1.719 1.886 3.684 1.416 1.462 0.864 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Fe3+ 0.000 0.000 0.000 0.000 0.041 0.583 0.009 0.005 0.005 0.004 0.007 0.011 0.010 0.001 0.000 0.012Ti 0.011 0.006 0.005 0.000 0.040 0.039 0.002 0.002 0.000 0.002 0.002 0.006 0.001 0.000 0.001 0.942Mn 0.029 0.017 0.045 0.023 0.044 ± 0.000 0.001 0.000 0.000 0.004 0.000 0.000 0.002 0.030 0.000Na ± ± ± ± ± ± 0.832 0.855 0.884 0.524 0.709 0.534 0.576 0.789 0.759 0.003K ± ± ± ± ± 0.025 0.003 0.009 0.003 0.004 0.084 0.006 0.002 0.006 0.020 0.000Cr ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±Ni ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±Mg/Mg+Fe

0.821 0.808 0.599 0.703 0.694 0.802 ± ± ± ± ± ± ± ± ± ±

Tb (°C) 252 245 287 ± ± ± ± ± ± ± ± ± ± ± ± ±

a Total iron as FeObTemperature of chlorite formationn.d. not detected

348

Table

2Majorandtrace

elem

ents

analysesofthemetavolcanic

rockshostingtalc

ore

deposits

Area

RodUmm

El-Farag

WadiThamil

Rock

type

Andesite

Basalt

Rhyolite

Chloritized

MV

Andesite

Basalt

Dacite

Chloritized

MV

No.

40±1

38±12

37±1

37±2

40±2

38±10

38±1

39±1

38±3

21±8

15

22±8

22±9

722±5

9

SiO

263.15

61.04

60.00

59.73

52.54

50.14

49.41

73.39

27.58

59.25

58.82

52.61

51.43

45.83

67.56

27.68

Al 2O

315.16

16.82

16.09

14.35

15.77

14.41

14.86

11.55

20.27

17.86

18.80

18.89

17.16

19.38

15.24

25.26

Fe 2O

30.75

0.46

0.86

0.91

1.34

1.14

0.99

0.45

3.11

0.10

0.11

0.10

1.52

0.87

0.05

1.74

FeO

3.62

2.67

4.89

5.48

6.54

7.41

7.66

1.63

8.36

4.42

5.69

7.38

7.51

7.06

3.55

9.48

TiO

20.45

0.46

0.71

0.67

1.01

0.99

1.08

0.34

0.87

0.77

0.86

1.06

0.82

1.17

0.61

1.19

CaO

5.51

4.75

2.62

3.13

7.86

7.68

9.32

1.52

0.29

4.69

1.74

8.26

8.69

7.66

2.65

1.04

K2O

0.60

0.64

2.55

1.56

0.16

0.59

0.53

3.15

0.06

1.31

1.97

0.89

0.46

0.91

1.84

0.50

MgO

4.27

3.05

4.01

6.33

6.30

9.18

8.51

1.14

25.34

2.57

3.80

5.49

5.62

9.01

3.00

21.07

Na2O

3.44

4.40

4.46

3.09

0.65

2.21

1.99

4.27

0.04

3.29

2.92

2.86

2.69

1.52

2.39

0.12

MnO

0.07

0.02

0.11

0.21

0.15

0.17

0.15

0.04

0.32

0.11

0.13

0.15

0.11

0.17

0.10

0.25

BaO

0.05

0.03

0.11

0.10

0.02

0.04

0.02

0.07

0.00

0.05

0.05

0.04

0.01

0.03

0.03

0.04

S0.00

0.01

0.00

0.00

0.00

0.01

0.00

0.00

<0.01

0.00

0.00

0.00

0.02

0.00

0.00

<0.01

P2O

50.09

0.08

0.19

0.11

0.11

0.13

0.09

0.04

0.18

0.33

0.18

0.22

0.07

0.08

0.15

0.41

Cr 2O

30.03

0.03

0.03

0.02

0.04

0.08

0.07

0.03

0.03

0.03

0.03

0.04

0.04

0.04

0.03

0.02

Cu

0.00

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

NiO

0.01

0.01

0.01

0.07

0.01

0.02

0.01

0.01

0.03

0.01

0.01

0.01

0.01

0.02

0.02

0.06

LOI

1.27

3.71

1.47

2.78

5.12

3.37

3.06

1.27

11.00

4.39

2.96

1.22

3.09

4.12

2.44

9.96

Total

98.47

98.19

98.11

98.54

97.62

97.57

97.75

98.90

97.48

99.18

98.07

99.22

99.25

97.87

99.66

98.82

As

<5

<5

5<5

<5

<5

<5

<5

12

5<5

<5

5<5

<5

27

Pb

<5

520

914

<5

<5

10

<5

813

<5

15

811

<5

Zn

66

75

82

91

94

97

87

44

145

93

99

86

109

91

62

98

Co

24

14

30

41

54

56

66

866

26

34

46

61

64

19

93

V71

39

87

107

164

168

185

17

162

87

133

166

267

206

63

168

La

<5

717

85

12

<5

8<5

511

<5

<5

<5

12

17

Nd

<5

<5

63

16

<5

<5

13

27

<5

18

23

<5

<5

20

29

27

Ce

<5

16

76

42

<5

24

12

26

<5

30

31

9<5

15

52

40

Ga

19

19

18

22

19

20

18

17

19

21

26

21

19

18

14

25

Sc

10

413

12

20

27

26

420

712

23

55

32

719

Nb

33

19

12

45

36

410

96

51

11

18

Zr

88

73

270

195

100

122

77

169

175

227

182

132

40

98

198

179

Y8

539

21

17

17

12

24

22

23

28

19

321

28

17

Sr

362

309

614

206

217

331

236

88

5373

142

277

281

315

117

27

U<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

Rb

16

587

26

512

984

137

50

26

134

65

9Th

<1

<1

13

11

22

<1

10

46

42

1<1

94

349

and ultrama®cs (chlorite, tremolite, albite, talc, calcite,muscovite, titanite, quartz, chromite and rutile).

Talc bodies appear to have replaced the entire parentultrama®c rocks. Talc deposits occur as lens-shapedpockets and sheet-like bodies of di�erent extensions anddirections (Fig. 7). Talc bodies extend up to 30±50 m inlength and are between 2 and 5 m wide. The talc sampleshave di�erent colours ranging from pale green to greythrough green and greyish green. They are usuallymassive, although they are locally ®brous, foliated andfriable. Weathered talc samples are soft and lighter inweight with a schistose appearance. The normal tech-niques to extract the talc deposits are small surfacemining operations by pick and shovel. Talc-carbonatealteration caps are dominated by ®ne grains, greasy feeland reddish brown colour.

Talc ore consists mainly of talc, tremolite, actinoliteand chlorite with minor amounts of chromite and rutile.On the basis of the mineral abundances, the studied

deposits display di�erent talc ore types and slightlytalci®ed rocks. The ore types are represented by puretalc, chlorite-rich talc and tremolite-actinolite-rich talc,while the slightly talci®ed rocks are represented bychloritized, actinolitized and tremolitized rocks(Table 3). The amount of talc decreases from ca. 90% inpure talc ore to ca. 50±70% in chlorite and tremolite-actinolite-rich ores to ca. 10% in slightly talci®ed rocks.The presence of bowlingite (a product of olivine altera-tion to talc) and complete absence of serpentine mineralsre¯ect to some extent the possibility of direct talci®cat-ion of parent ultrama®c rocks without serpentinization.

Fig. 2 Nomenclature of the metavolcanics using the Le Maitre et al.(1989) classi®cation

Fig. 3 SiO2-K2O + Na2O diagram (after Irvine and Baragar 1971)of the metavolcanic rocks. Symbols as in Fig. 2

Fig. 4 AFM diagram (after Irvine and Baragar 1971). Symbols as inFig. 2

Fig. 5 Tectonic settings of the metavolcanics using Ti/100-Zr-3Ydiagram (after Pearce and Cann 1973). Symbols as in Fig. 2. WPBWithin plate basalt, VAB volcanic arc basalt, MORB mid oceanicridge basalt and CAB calc-alkaline basalt

350

Microscopically, talc occurs in the form of ®neshreds, plates and rarely as coarse to medium-grained¯akes. The ®ne crystals are sometimes oriented in asubparallel arrangement and occasionally show abanded texture. In turn, the ¯aky nature and cleavageplanes of chlorite are still preserved in talc (Fig. 8) andsecondary iron oxide minerals and rutile are formedfrom the Fe and Ti released by the breakdown of chlo-rite to talc.

Amphibole minerals are represented mainly bytremolite and actinolite. They occur in tabular, pris-matic, acicular and ®brous forms. Tremolite and actin-olite are slightly to moderately altered to chlorite and/ortalc, where ®ne relics of actinolite laths are randomlydistributed within the talc matrix.

Chlorite occurs in the form of disseminated anhedralplates and massive lenses of very ®ne-grained shreds. It

usually accompanies and encloses chromite due to itsdevelopment as a consequence of the alteration ofchromite grains and releasing of Al, Mg and Cr (Fig. 9).In turn, and due to the retrograde alteration, thetransformations of tremolite to talc [Eq. (1)], actinoliteto chlorite and chlorite to talc [Fig. 8 and Eq. (2)] can beclearly observed.

Ca2Mg5Si8O22�OH�2 � 4CO2

�Mg3Si4O10�OH�2 � 2CaMg�CO3� � 4SiO2 �1�Mg5Al2Si3O10�OH�8 � SiO2 � 2CO2

�Mg3Si4O10�OH�2 � 2MgCO3 � 2Al�OH�3 �2�Pure talc and tremolite-actinolite-rich types contain alimited amount of disseminated chromite. In contrast,an assemblage of chromite, rutile and titanite are de-tected in the chlorite-rich talc ore type and slightlytalci®ed chloritized rocks.

Chromite is abundant in the talc deposits which isconsistent with an ultrama®c source. Microscopically, ithas greyish colour with a faint blood red stain in air anda darker greyish brown in oil. Deformational cataclasticfractures are common, where chromite appeared to havebeen formed of cemented lamellae. The average VickerHardness Number (VHN) of chromite is 1415. Chromiteshows a slight degree of alteration, in which zoned grainshave a narrow irregular zone of ferrite chromite aroundtheir cores and/or along cracks. Ferrite chromite haslighter colour (pale brownish grey), higher re¯ectivityand lower VHN (850). As the zoned chromite is heter-ogeneous with respect to colour, re¯ectivity and internalre¯ections, the composition is interpreted to be variable(Fig. 10) due to some changes in the degree of oxidationaccompanying its formation and/or regional metamor-phism.

Zoning in chromite can be attributed to magmaticreactions, serpentinization and regional metamorphism(Beeson and Jackson 1969; Bliss and MacLean 1975;Khudeir et al. 1992; Khudeir 1995). In the studied areas,the serpentinization process may be ruled out where thetalc deposit (containing zoned chromite) is possiblyformed directly from parent ultrama®c rocks withoutany suggestion of the occurrence of serpentinization, i.e.the zoning is presumably attributed to the magmaticreactions and/or regional metamorphism.

Rutile occurs as relics in the slightly talci®edchloritized rocks and chlorite-rich talc ore type in theform of rod-like and tabular crystals. In re¯ected light, itis characterized by a grey colour, usually with palebluish tints, lamellar twinning, strong anisotropism witha reddish brown colour and strong internal re¯ections.

Mineral chemistry of talc deposit

The talc grains show a wide compositional range(Tables 4 and 5) from 60.99±62.81% SiO2, 28.33±30.36% MgO, 2.86±5.01% FeOt and 3.71±5.72% LOI.Al2O3 is largely depleted (0.00±0.07%). The chemical

Fig. 6 Tremolitization of the metavolcanic rocks as one of thehydrothermal alteration processes. The width of the frame is 1 mm

Fig. 7 Close-up view showing the mined talc lens, talc-carbonate andthe surrounding metavolcanics

351

Table

3Types

oftalc

oresandtheirmineralassem

blages

asobtained

from

XRD

andpetrographic

studies,thecolourmeasurements

are

presentedasL

degreeofwhiteness;ared;

)agreen;byellow;and

)bblue

No.

Talc

ore

androck

type

Megascopic

description

Mineralogicalcomposition

Colourmeasurements

Major(>

40%)

Minor(40±10%)

Rare

(<10%)

La

b

R.U

mm

El-Faragarea

40±7

Pure

talc

Talc

±Chlorite-chromite

93.80

)1.23

2.97

38±11

''Talc

±Chlorite-chromite

90.75

)1.38

2.31

38±5

''-G

reen,pale

greenishgrey,

brownishwhite

Talc

±Chlorite-actinolite-chromite

90.63

)1.18

4.11

37±6

''Talc

±Chlorite-chromite

87.07

)1.88

1.77

41±1

''-Soft

Talc

±Chlorite-chromite

90.59

)1.14

2.61

40±5

''-Finegrained

Talc

±Chlorite-chromite

92.15

)1.16

1.72

40±3

''Talc

±Chlorite-chromite

91.57

)1.15

2.48

39±3

''Talc

±Chlorite-chromite

89.60

)1.60

1.89

40±8

''Talc

±Chlorite-chromite

90.65

)1.43

1.91

37±7

Chlorite-rich

Talc

Chlorite

Titanite

82.14

)1.09

2.97

37±3

''-Finegrained,massive

Talc

Chlorite

Chromite

77.90

)1.06

1.72

37±4

''-D

ark

green

andspotted

bydark

green

chlorite

lenses

Talc

Chlorite

Actinolite-rutile-titanite

81.58

)1.80

3.11

37±8

''Talc

Chlorite

Chromite-titanite

76.78

)1.50

3.74

37±5

''Talc-chlorite

Actinolite-tremolite

Chromite

82.84

)1.71

4.31

41±3

Talci®ed

rock

-Fibrous,®negrained

yellowish

)greyishgreen

Actinolite

Talc-chlorite

Chromite-rutile

87.37

)2.20

3.56

38±2

''Chlorite

±Talc-R

utile

72.06

)5.46

4.73

38±3

Chloritizedmetavolcanics

-Massiveanddark

green

Chlorite

±Muscovite-Ilmenite-rutile

74.40

)2.84

5.36

WadiThamilarea

1±1

Pure

talc

Talc

±Chlorite-chromite

92.11

)1.33

0.29

1±2

''Talc

±Chlorite-chromite

91.81

)0.07

2.95

5''

Talc

±Chlorite-chromite

93.61

)1.80

1.63

11

''Talc

±Chlorite-chromite

92.41

)1.52

2.07

12

''Talc

±Chlorite-actinolite-chromite

92.14

)1.08

3.98

13

''-Finegrained

Talc

±Chlorite-chromite

90.29

)1.14

3.19

14

''-M

assive

Talc

±Chlorite-chromite

91.31

)0.18

6.26

21±1

''-G

reenishgrey,

greyishgreen

Talc

±Chlorite-chromite

91.77

)1.11

2.00

21±2

''Talc

±Chlorite-chromite

92.35

)1.53

1.68

21±4

''Talc

±Chlorite-chromite

91.81

)1.38

2.07

21±5

''Talc

±Chlorite-chromite

93.15

)1.70

2.88

21±7

''Talc

±Chlorite-chromite

93.11

)1.63

5.04

22±1

''Talc

±Chlorite-chromite

94.09

)1.65

2.15

22±2

''Talc

±Chlorite-chromite

91.30

)1.49

2.62

22±4

''Talc

±Chlorite-chromite

92.95

)1.30

4.27

20

Actinolite-rich

-Specked

bychlorite

and

trem

olite

lenses

Talc

Actinolite-tremolite

Chlorite-chromite

89.62

)1.44

5.69

16

''Talc

Actinolite

Chlorite-chromite

89.12

)1.88

3.47

21±6

''-Finegrained

andmassive

Talc

Actinolite

Chlorite-chromite

89.60

)1.59

2.26

2Talci®ed

rock

-Finegrained,massive,

®brous,greyishgreen,

andgreenishgrey

Actinolite

Talc

Chlorite-chromite

91.53

)2.45

4.42

3''

Actinolite-Tremolite

Chlorite-talc

Chromite

85.21

)3.03

4.79

19

''Chlorite

Talc

Chromite

75.73

)5.61

3.62

18

''Chlorite

±Actinolite-talc-chromite

70.20

)9.21

4.26

9Chloritizedmetavolcanics

Massiveandgreyishgreen

Chlorite

±Muscovite-titanite-albite

76.64

)2.19

5.91

352

formula of talc from WTh is Mg2.810Fe2�0:141Fe

3�0:061

Ni0.009Cr0.003Si3.972O10(OH)2 and that of RUF is Mg2.831Fe2�0:134Fe

3�0:059Ni0.002 Cr0.003Si3.967Aliv0:001O10(OH)2. In

addition to the marked presence of Cr and Ni, the Fe/(Fe + Mg) ratio ranges from 1.81±8.13% (X � 4.65%)which fall within the ranges characteristic of talc derivedfrom ultrama®c rocks (1±10%, Smolin et al. 1974).

The amphibole minerals (Tables 4 and 5) are alwaysenriched in Si, Cr and Ni and depleted in Alvi relative tothe amphibole minerals associated with the host rocks(Table 1). The chemical formulae calculations revealedthat the content of Si ranges from 6.642 to 7.983 andMg/(Mg + Fe) from 0.849 to 1. Using the nomencla-

ture of Leake (1978), the amphibole minerals fall mainlywithin the tremolite and actinolite ®elds and rarely intremolitic-hornblende, actinolitic-hornblende and Mg-hornblende ®elds (Fig. 11). The pure talc ore type ischaracterized by actinolite and tremolite, whilst theslightly talci®ed chloritized rocks are characterized byactinolitic-hornblende and tremolitic-hornblende. Onthe other hand, the slightly talci®ed tremolitized rocksare characterized by Mg-hornblende.

Chlorite analyses lie mainly in clinochlore and pen-nine ®elds (Fig. 12). Both chlorite minerals have high Crcontents in their structures compared to pennine andripidolite in the host metavolcanic rocks.

Fig. 8 Chlorite is completely altered and talc exhibits its ¯aky nature.Iron oxides are formed from the released iron. The width of the frameis 1 mm

Fig. 9 Formation of chlorite from the released Cr, Al and Mg duringchromite alteration. The width of the frame is 1 mm

Fig. 10 SEM elemental distri-bution map showing the distri-bution of Mg, Al, Si, Cr and Feamongst the zoned chromite.Chromite grain is 0.03 mmacross

353

Chromite has a variable composition which variesbetween core (dark) and rim (light ferrite chromite) insome grains (Table 6). The Cr2O3, Al2O3 and MgOcontents show a notable decrease from the core to-wards the rim while FeO, Fe2O3, MnO, V2O5 and TiO2

show a marked increase (Fig. 13). Talc and chloritecoexisting with chromite are relatively enriched in Cr,Al and Mg, suggesting that a subsolidus di�usion ofthese elements has occurred between chromite and theassociated silicate minerals. Using Stevens' (1944)classi®cation, the chromite core analyses fall mainlywithin aluminum chromite ®eld (except for three sam-ples that occupy the chromian spinel ®eld) while allferrite chromite samples fall within the ferroan chro-mite ®eld (Fig. 14).

Using the data reported in the literature (Thayer1960, 1970; Irvine 1967; Dickey 1975), it is apparent thatthe studied chromite has a compositional range similarto the alpine (podiform) type. These include (for chro-mite core); <0.10% TiO2, average Fe2O3 content is

0.31%, average Cr/Fe ratio is 1.60%, average Cr/(Cr + Al) ratio is 0.639%, average Cr2O3 content is47.28%, and the average Cr/Al ratio is 2.03%.

The average chemical formula of rutile (Table 6) isTi0.977Cr0.012Fe

3�0:003O2. Titanite is formed where Ca is

available and has the following formula; Ca1.00Ti0.950Al0.028Fe

3�0:012Cr0.001Si1.001O4. Al andFe3+ are recorded in

the analyses of titanite occupying the octahedral sites. Itaccommodates Cr in its structure (Tables 4 and 5) com-pared to that associated with metavolcanics (Table 1).

Chlorite geothermometry

Cathelineau and Nieva (1985), Walshe (1986), Kranidi-otis and MacLean (1987) and Zang and Fyfe (1995)reported that the temperature of chlorite formation canbe determined on the basis of Alivcorrected, where T °C =106.2Alivcorrected + 17.5. The correction is made to com-pensate the increase in temperature with high Fe/

Table 4 Chemical composition and the atomic proportions of the minerals identi®ed in the talc ore samples

Minerals Talc

Area W.Thamil R.U.El-Farag

No. U21 U2 U6 MA6 MA7 MA11 MA13 Ann8 Ann9 AR3 AR10 MA19 MA22

Type Act-rich ore Pure ore Pure ore

SiO2 62.81 61.87 61.51 62.01 62.55 62.16 61.49 61.33 61.55 62.01 62.19 61.10 62.11Al2O3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

TiO2 0.02 0.02 0.00 0.09 0.00 0.01 0.00 0.07 0.07 n.d n.d 0.05 0.00FeOa 3.18 4.22 3.96 5.01 3.01 2.86 3.36 4.13 4.08 3.40 2.90 2.92 3.56CaO n.d n.d 0.03 0.00 0.02 0.00 0.00 0.00 0.05 n.d n.d 0.00 0.00MgO 30.21 28.33 29.22 28.58 29.95 29.93 29.24 29.78 29.27 30.33 30.36 29.94 29.31MnO 0.05 0.00 0.10 0.00 0.03 0.00 0.02 0.00 0.09 n.d n.d 0.00 0.00Cr2O3 0.00 0.03 0.03 0.02 0.00 0.11 0.02 0.08 0.00 0.25 0.00 0.03 0.03ZnO 0.02 0.00 0.04 0.00 0.12 0.05 0.00 n.d n.d n.d n.d 0.00 0.00NiO n.d n.d n.d 0.16 0.19 0.33 0.27 0.28 0.33 n.d n.d 0.24 0.07V2O5 n.d n.d n.d 0.00 0.00 0.00 0.01 0.00 0.02 n.d n.d 0.00 0.00K2O n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d

Sum 96.29 94.47 94.89 95.87 95.87 95.45 94.41 95.67 95.46 95.99 95.45 94.28 95.08

Atomic proportionsSi 3.977 4.023 3.966 3.982 3.980 3.971 3.980 3.920 3.951 3.937 3.962 3.945 3.994AlIV 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Sum 3.977 4.023 3.966 3.982 3.980 3.971 3.980 3.920 3.951 3.937 3.962 3.945 3.994AlVI ± ± ± ± ± ± ± ± ± ± ± ± ±Ca ± ± 0.002 0.000 0.001 0.000 0.000 0.000 0.003 ± ± 0.000 0.000Mg 2.850 2.745 2.808 2.735 2.841 2.850 2.822 2.837 2.801 2.870 2.883 2.881 2.810Fe2+ 0.120 0.229 0.141 0.242 0.098 0.092 0.144 0.072 0.130 0.066 0.079 0.053 0.181Fe3+ 0.048 0.000 0.072 0.027 0.062 0.061 0.038 0.149 0.089 0.114 0.076 0.104 0.011Ni ± ± ± 0.008 0.010 0.017 0.014 0.014 0.017 ± ± 0.013 0.004Ti 0.001 0.001 0.000 0.004 0.000 0.000 0.000 0.003 0.003 ± ± 0.003 0.000Mn 0.003 0.000 0.006 0.000 0.002 0.000 0.001 0.000 0.005 ± ± 0.000 0.000Cr 0.000 0.002 0.002 0.010 0.000 0.006 0.001 0.004 0.000 0.013 0.000 0.002 0.001Zn 0.001 0.000 0.002 0.000 0.007 0.003 0.000 ± ± ± ± 0.000 0.000V ± ± ± 0.000 0.000 0.000 0.000 0.000 0.001 ± ± 0.000 0.000K ± ± ± ± ± ± ± ± ± ± ± ± ±Fe + Mg 2.970 2.974 2.949 2.977 2.939 2.942 2.966 2.909 2.931 2.936 2.962 2.934 2.991Fe/Fe + Mg 0.040 0.077 0.048 0.081 0.033 0.031 0.049 0.025 0.044 0.022 0.027 0.018 0.061Tb (°C) ± ± ± ± ± ± ± ± ± ± ± ± ±

a Total iron as FeObTemperature of chlorite formation

354

Fe + Mg ratio. In the present study, the equationwould be Alivcorrected � Alivmeasured ± 0.48 [Fe/(Fe + Mg) ±0.163] as constrained from the Aliv ± Fe/(Fe + Mg)linear relationship. Application of this equation in thisstudy suggests that the chlorite of RUF is formed atlower temperature (212 °C) than that of WTh (251 °C).In contrast, the pennine and ripidolite in metavolcanicsare formed at about 249 and 287 °C respectively.

Chemistry of talc ore

The primary focus of the geochemical investigation ofthe studied areas is the whole rock analysis of di�erenttalc types and slightly talci®ed rocks. The major andtrace element data are used to elucidate the behaviour ofelements during the talc formation process as well as thechemical characteristics of the talc ore.

Silica, magnesia and H2O are the essential compo-nents of talc (Tables 7±8). The total content of thesecomponents decreases from pure talc type (93.31%) to

tremolite and actinolite-rich (90.00%), chlorite-rich(84.74%), and slightly talci®ed tremolitized (78.30%)and chloritized rocks (70.31%), depending on theamount of impurity minerals as shown in Fig. 15a, bwhere pure talc ore type exhibits very narrow ®eld to-wards the minimum values of these elements. Compar-ison with the SiO2 and MgO contents of commonultrama®c rocks (Tables 7±8) suggests that talc ore wasformed by addition of silica to the system (Fig. 15c).LOI is approximately 4.8% for pure talc. It increaseswherever chlorite is found (about 6.21% in chlorite-richore) and decreases where tremolite is present (about4.41% in tremolite-rich ore). Other major elements(Al2O3, Fe2O3, FeO, Cr2O3, CaO and TiO2) are en-countered as the main impurities reducing the quality ofthe ore and re¯ect the presence of chlorite, chromite,tremolite, actinolite, rutile and titanite.

Figure 15d±f shows that the talc ore is Cr, Ni and Co-enriched and V, Zr and Sr-depleted compared to thehost metavolcanics. Because they lie in the contact zone,the slightly talci®ed rocks are enriched in Cr, Ni, Fe,

Tremolite

W.Thamil

RA3 RA4 U15 MM2 MM3 MM4 MM6 MM7 MM5 MM1 U22 U20 U3 U5 U10

Chl-rich S. Talci®ed rock Act-rich

61.75 61.83 60.99 56.70 57.01 54.59 56.59 56.39 56.79 58.38 57.35 57.86 57.10 56.45 56.710.00 0.00 0.07 1.39 1.14 7.89 0.82 0.51 1.18 0.40 0.31 0.02 0.61 0.86 1.03

0.00 0.00 0.04 0.03 0.09 0.00 0.00 0.14 0.05 0.02 0.00 0.00 0.03 0.05 0.013.75 4.04 4.49 4.90 4.86 6.10 5.53 4.56 5.09 4.70 4.58 4.95 5.96 6.79 5.160.04 0.04 0.00 13.30 10.60 8.20 12.73 12.69 12.96 13.39 13.14 12.59 12.71 12.33 12.4129.10 29.21 28.60 20.96 23.13 22.82 21.20 21.76 20.93 21.81 21.97 22.10 20.76 20.70 21.67n.d n.d 0.03 0.23 0.27 0.11 0.40 0.14 0.29 0.20 0.22 0.28 0.21 0.34 0.230.01 0.06 0.04 0.17 0.05 0.08 0.00 0.13 0.00 0.03 0.35 0.38 0.54 0.51 0.770.00 0.00 0.02 n.d n.d n.d n.d n.d n.d n.d 0.00 0.02 0.17 0.01 0.11n.d n.d n.d 0.02 n.d n.d 0.04 n.d n.d 0.05 n.d n.d 0.04 n.d n.d0.00 0.09 n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.dn.d n.d n.d 0.05 0.07 0.00 0.13 0.00 0.00 0.02 n.d n.d n.d n.d n.d

94.65 95.27 94.28 97.75 97.22 99.79 97.44 96.32 97.29 99.00 97.92 98.20 98.13 98.04 98.10

3.991 3.974 3.969 7.816 7.868 6.642 7.866 7.893 7.902 7.970 7.904 7.962 7.921 7.845 7.8240.000 0.000 0.006 0.184 0.132 1.355 0.134 0.083 0.098 0.030 0.050 0.003 0.079 0.141 0.1673.991 3.974 3.975 8.000 8.000 7.997 8.000 7.976 8.000 8.000 7.954 7.965 8.000 7.986 7.991± ± ± 0.041 0.053 0.000 0.000 0.000 0.095 0.035 0.000 0.000 0.022 0.000 0.0000.003 0.003 0.000 1.964 1.568 1.281 1.896 1.903 1.933 1.958 1.940 1.856 1.889 1.836 1.8352.803 2.799 2.774 4.307 4.759 4.955 4.391 4.540 4.341 4.438 4.514 4.533 4.292 4.287 4.4550.185 0.181 0.190 0.373 0.495 0.000 0.484 0.447 0.539 0.536 0.424 0.538 0.691 0.687 0.4980.018 0.036 0.055 0.192 0.066 0.744 0.158 0.087 0.000 0.000 0.104 0.032 0.000 0.103 0.098± ± ± 0.002 ± ± 0.003 ± ± 0.040 ± ± 0.030 ± ±0.000 0.000 0.002 0.003 0.010 0.000 0.000 0.015 0.005 0.002 0.000 0.000 0.004 0.005 0.001± ± 0.002 0.027 0.031 0.014 0.047 0.017 0.034 0.024 0.026 0.033 0.025 0.040 0.0270.001 0.003 0.002 0.019 0.005 0.010 0.000 0.014 0.000 0.003 0.038 0.042 0.059 0.065 0.0840.000 0.000 0.001 ± ± ± ± ± ± ± 0.000 0.002 0.017 0.000 0.0110.000 0.004 ± ± ± ± ± ± ± ± ± ± ± ± ±± ± ± 0.010 0.010 0.000 0.017 0.000 0.000 0.002 ± ± ± ± ±2.988 2.980 2.964 4.680 5.254 4.955 4.875 4.987 4.880 4.974 4.938 5.071 4.983 4.974 4.9530.062 0.061 0.064 0.080 0.094 0.000 0.099 0.090 0.110 0.108 0.086 0.106 0.139 0.138 0.101± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

355

Mg, Co (characteristic of ultrama®c rocks), Ti, P, Zn, V,Ga, Sc, Zr and Sr (characteristic of metavolcanic rocks).Finally, the chloritized metavolcanics contain elementswhich characterize the metavolcanics. Cr occurs withinchromite, chlorite, talc and tremolite while Ni and Coare accommodated in the silicate minerals by substitu-tion for Mg and Fe. The content of Cr2O3 and NiO inultrama®c rocks is 0.40 and 0.30% respectively (afterEdelstein 1963; Turekian 1963; Wedepohl 1963; Hessand Otalora 1964; Stueber and Goles 1967). The talcdeposits have inherited trace elements from the parentultrama®c rocks and contain no trace elements from themetavolcanics nor hydrothermal solutions where thelatter seem to have lower concentrations of theseelements.

Summary and conclusions

The talc deposits from Rod Umm El-Farag and WadiThamil have characters and quality that are inconsistent

with a metavolcanic precursor, i.e. there is no geneticrelationship between talc ore and the host metavolca-nics. A genetic link of these talc deposits to an ultrama®csource is proposed on the basis of the following geo-logical, mineralogical and chemical criteria:

1. The talc hand samples are dark green with degree ofwhiteness (mostly between 75 and 90%) lower thanwas expected for talc hosted by metavolcanics.

2. The mineral assemblage of talc ore contains chromite.3. The Cr2O3, NiO and Co contents are high in talc ore

samples. Also, the contents of these elements in thestructure of silicate minerals are higher compared tothose in the host rocks.

4. The contents of the impurity oxides in the talc ore(FeO, Fe2O3, CaO and Al2O3) are high (up to 21%).

5. The average Fe/Fe + Mg ratio in the talc structure ishigh (4.65%).

In general, there are no di�erences in mineralogy, geo-chemistry and quality of talc ore from either Rod UmmEl-Farag or Wadi Thamil.

Table 5 Further details of the chemical composition and atomic proportions of the talc ore minerals

Minerals Tremolite Chlorite

Area R.U.El-Farag W.Thamil

No. TM14 U12 TM9 TM12 U17 TM16 U18 TM7 U1

Type Chlorite-rich Act-rich

SiO2 58.00 58.06 57.92 58.01 57.48 58.23 53.69 53.62 30.26Al2O3 0.00 0.06 0.28 0.29 0.61 0.33 5.06 3.25 19.82TiO2 0.00 0.11 0.00 0.00 0.00 0.06 0.89 0.08 0.00FeOa 5.34 5.66 6.27 4.93 6.23 5.36 7.21 6.47 9.95CaO 13.02 12.18 12.11 12.56 12.55 12.81 11.89 9.98 0.04MgO 22.25 22.14 21.60 22.10 21.03 21.72 19.36 22.58 28.16MnO 0.42 0.26 0.15 0.45 0.26 0.24 0.41 0.24 0.14Cr2O3 0.00 0.00 0.06 0.00 0.10 0.08 0.11 0.34 1.49ZnO n.d 0.00 n.d n.d 0.07 n.d 0.03 n.d 0.10NiO n.d 0.07 n.d n.d n.d n.d n.d 0.03 n.dV2O5 n.d n.d n.d n.d n.d n.d n.d n.d n.dK2O n.d n.d n.d n.d n.d n.d n.d n.d n.d

Sum 99.03 98.54 98.39 98.34 98.33 98.83 98.65 96.59 89.96

Atomic proportionsSi 7.912 7.974 7.983 7.965 7.943 7.976 7.427 7.465 5.746AlIV 0.000 0.009 0.017 0.035 0.010 0.024 0.573 0.534 2.254Sum 7.912 7.983 8.000 8.000 7.953 8.000 8.000 7.999 8.000AlVI 0.000 0.000 0.028 0.012 0.000 0.029 0.252 0.000 2.181Ca 1.907 1.792 1.789 1.848 1.858 1.880 1.762 1.489 0.007Mg 4.524 4.533 4.437 4.522 4.331 4.434 3.994 4.685 7.970Fe2+ 0.433 0.629 0.723 0.543 0.717 0.614 0.712 0.272 1.580

Fe3+ 0.176 0.021 0.000 0.023 0.003 0.000 0.123 0.481 0.000Ni ± 0.006 ± ± ± ± ± 0.002 ±Ti 0.000 0.011 0.000 0.000 0.000 0.006 0.093 0.008 0.000Mn 0.048 0.031 0.017 0.052 0.030 0.028 0.049 0.028 0.023Cr 0.000 0.000 0.006 0.000 0.011 0.009 0.012 0.037 0.224Zn ± 0.000 ± ± 0.007 ± 0.007 ± 0.014V ± ± ± ± ± ± ± ± ±K ± ± ± ± ± ± ± ± ±Fe + Mg 4.957 5.162 5.160 5.065 5.048 5.048 4.706 4.957 9.550Fe/Fe + Mg 0.087 0.122 0.140 0.107 0.142 0.122 0.151 0.055 0.165Tb (°C) ± ± ± ± ± ± ± ± 257

a Total iron as FeObTemperature of chlorite formation

356

The rocks which host the talc deposits are meta-morphosed basic and acidic volcanic rocks. These rocksappear to have undergone regional metamorphism fol-

lowed by hydrothermal alterations (chloritization,tremolitization and silici®cation). The volcanics haveboth tholeiitic and calc-alkaline magmatic a�nities and

Titanite

R.U.El-Farag

U4 U9 TM13 U13 U19 U14 U131 AR1 AR4 RA5 RA7 AR6 RA2 TM8

Pure ore Chlorite-rich Pure ore

30.05 29.86 31.32 29.82 30.25 30.31 31.69 32.03 31.60 31.44 30.92 33.23 34.56 31.0819.48 18.36 19.31 20.50 19.30 17.84 17.74 14.56 14.97 16.69 15.49 14.82 13.78 0.730.01 0.00 0.11 0.02 0.01 0.00 0.00 n.d n.d 0.00 0.05 n.d 0.00 39.229.51 9.53 10.64 12.20 11.40 11.09 10.98 9.71 9.49 9.69 9.61 9.18 9.32 0.440.03 0.00 0.08 0.02 0.05 0.08 0.06 n.d n.d 0.00 0.10 n.d 0.04 28.9727.45 27.85 28.85 26.19 26.91 25.77 27.07 30.47 29.41 28.69 28.60 29.75 28.69 0.160.10 0.10 0.09 0.28 0.10 0.15 0.11 n.d n.d n.d n.d n.d n.d 0.001.30 1.95 1.03 0.33 0.82 0.35 0.26 3.56 2.90 0.98 2.71 2.86 2.40 0.040.03 0.05 n.d 0.00 0.03 0.00 0.07 n.d n.d 0.00 0.00 n.d 0.00 n.d

n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.dn.d n.d n.d n.d n.d n.d n.d n.d n.d 0.10 0.02 n.d 0.00 n.dn.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d n.d87.96 87.70 91.43 89.36 88.87 85.59 87.98 90.33 88.37 87.59 87.50 89.84 88.79 n.d

5.832 5.818 5.853 5.748 5.844 6.091 6.180 6.070 6.117 6.115 6.054 6.314 6.690 1.0012.168 2.182 2.147 2.252 2.156 1.909 1.820 1.930 1.883 1.885 1.946 1.686 1.310 0.0288.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 ±2.288 2.035 2.106 2.406 2.239 2.317 2.258 1.321 1.532 1.940 1.629 1.633 1.833 ±0.007 0.000 0.015 0.003 0.011 0.017 0.013 ± ± 0.000 0.021 ± 0.009 1.0007.941 8.088 8.035 7.524 7.749 7.721 7.868 8.607 8.486 8.319 8.347 8.480 8.280 0.0081.543 1.553 1.662 1.968 1.842 1.864 1.791 1.539 1.537 1.577 1.573 1.458 1.510 0.0000.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.012± ± ± ± ± ± ± ± ± ± ± ± ± ±0.001 0.000 0.016 0.003 0.015 0.000 0.000 ± ± 0.000 0.007 ± 0.000 0.9500.016 0.017 0.014 0.045 0.016 0.026 0.018 ± ± ± ± ± ± 0.0000.200 0.301 0.153 0.050 0.126 0.055 0.040 0.533 0.444 0.151 0.420 0.429 0.367 0.0010.004 0.007 ± 0.000 0.004 0.000 0.011 ± ± 0.000 0.000 ± 0.000 ±± ± ± ± ± ± ± ± ± 0.005 0.001 ± 0.000 ±± ± ± ± ± ± ± ± ± ± ± ± ± ±9.484 9.641 9.697 9.492 9.591 9.585 9.659 10.15 10.02 9.896 9.920 9.938 9.790 ±0.163 0.161 0.171 0.207 0.192 0.194 0.185 0.152 0.153 0.159 0.159 0.147 0.154 ±

248 249 245 254 245 219 210 223 218 218 224 197 157 ±

Fig. 11 Nomenclature of the detected amphibole minerals using theLeake (1978) diagram

Fig. 12 Chlorite analyses plotted on the Hey (1954) classi®cationdiagram

357

are interpreted to have erupted in an island arc wellbehind the deep oceanic trench and on the continentalside. The mantle-derived ultrama®c bodies were tecton-ically emplaced in the volcanic arc rocks on the crust ofocean and continent representing a case of crustal-mantle contamination. The slickensided surfaces of therocks suggested that they were emplaced along faultplanes. After the emplacement of the ultrama®c bodies,they underwent regional metamorphism which was ac-companied by serpentinite formation and shearing.

Metasomatic changes associated with hydrothermalalteration are related to the emplacement of nearbyyounger granitic intrusions of Homret Waggat. Theseinclude the formation of talc and minor quantities oftalc-carbonates. SiO2, H2O and CO2 have beenintroduced to the system but all other constituents areinherited from the parent ultrama®cs. It is proposed thatSiO2 in the hydrothermal solution altered the entireserpentinized body to talc. The mineral reactions includealteration of olivine to serpentine [Eq. (3)], serpentine totalc [Eq. (4)] and talc-carbonate [Eq. (5)], alteration of

tremolite to chlorite and talc [Eq. (6)] and alteration ofchlorite to talc.

2Mg2SiO4 � 2H2O �Mg3Si2O5�OH�4 �MgO �3�Mg3Si2O5�OH�4 � SiO2 �Mg3Si4O10�OH�2 �H2O

�4�2Mg3Si2O5�OH�4 � 3CO2

�Mg3Si4O10�OH�2 �MgCO3 � 3H2O �5�Ca2Mg5Si8O22�OH�2 � 4CO2

�Mg3Si4O10�OH�2 � 2CaMg�CO3� � 4SiO2 �6�

The degree of whiteness re¯ects to some extent the purityof the ore, as it decreases with increasing amount ofimpurity oxides such as Al2O3, FeO and Cr2O3 andconsequently the content of chlorite and chromite. Theharmful elements (As, S, P, Mn and Cu) are low (exceptfor a few samples), so that the talc should have a wide

Table 6 The chemical composition of zoned chromite and rutile which are identi®ed in the talc ore

Chromite Dark zone

No. 1 2 3 4 5 6 7 8 9 10 11 12 13

SiO2 0.12 0.22 0.27 0.19 0.31 0.23 0.30 0.04 0.24 0.47 0.15 0.41 0.22TiO2 0.00 0.05 0.09 0.00 0.00 0.01 0.00 0.03 0.05 0.04 0.01 0.00 0.04Al2O3 11.01 11.95 8.31 16.01 15.72 14.92 12.30 13.87 15.38 16.33 19.11 19.34 20.80CaO 0.11 0.04 0.10 0.01 0.03 0.02 0.00 0.02 0.00 0.04 0.04 0.00 0.00Fe2O3 0.42 0.00 2.01 0.00 0.00 0.00 1.47 1.04 0.00 0.00 0.24 0.00 0.00FeO 20.13 20.60 26.53 26.52 23.88 29.02 31.39 30.18 29.53 27.62 29.35 30.79 29.24Cr2O3 58.79 57.72 56.26 51.67 50.77 50.46 50.39 49.87 49.85 48.88 45.61 45.54 43.91MgO 9.00 8.82 3.97 4.42 5.75 1.95 1.10 1.18 1.43 4.08 1.73 1.71 1.75ZnO 0.27 0.42 0.55 0.62 0.43 0.74 n.d 1.02 0.79 n.d 1.50 n.d 1.31NiO 0.00 0.00 0.02 0.00 0.06 0.03 0.07 0.05 0.05 0.01 n.d 0.00 0.00V2O5 0.31 0.19 0.33 0.29 0.35 0.38 0.36 0.38 0.23 0.26 n.d 0.23 0.30MnO 0.32 0.19 0.84 0.59 0.57 1.31 1.42 1.73 1.41 0.85 1.68 0.94 1.76

Sum 100.48 100.20 99.28 100.32 97.87 99.07 98.80 99.41 98.96 98.58 99.42 98.96 99.33

Atomic proportionsSi 0.033 0.060 0.075 0.050 0.083 0.063 0.085 0.011 0.066 0.128 0.040 0.112 0.060Fe3+ 0.083 0.000 0.424 0.000 0.000 0.000 0.311 0.219 0.000 0.000 0.049 0.000 0.000Ti 0.000 0.010 0.019 0.000 0.000 0.003 0.000 0.007 0.010 0.007 0.002 0.000 0.007Cr 12.266 12.102 12.460 10.914 10.869 11.023 11.232 10.983 10.921 10.476 9.767 9.768 9.342Al 3.424 3.735 2.743 5.042 5.016 4.859 4.087 4.552 5.023 5.219 6.099 6.185 6.595

Sum 15.806 15.907 15.721 16.006 15.968 15.948 15.715 15.772 16.020 15.830 15.957 16.065 16.004

Mg 3.540 3.488 1.656 1.759 2.320 0.804 0.462 0.492 0.589 1.650 0.698 0.693 0.702

Fe2+ 4.444 4.436 6.214 5.926 5.409 6.706 7.401 7.032 6.843 6.262 6.649 6.986 6.580

Zn 0.052 0.083 0.114 0.123 0.086 0.150 ± 0.210 0.163 ± 0.300 ± 0.026Ni 0.000 0.000 0.040 0.000 0.013 0.007 0.015 0.011 0.010 0.003 ± 0.000 0.000Ca 0.031 0.011 0.031 0.002 0.009 0.007 0.000 0.005 0.000 0.013 0.011 0.000 0.000V 0.054 0.033 0.062 0.052 0.063 0.069 0.066 0.070 0.042 0.046 ± 0.041 0.053Mn 0.072 0.042 0.198 0.134 0.131 0.306 0.340 0.408 0.332 0.196 0.385 0.216 0.400

Sum 8.193 8.093 8.315 7.996 8.031 8.049 8.284 8.228 7.979 8.170 8.043 7.936 7.761

a Total iron as FeO

358

range of uses in industry without treatment. The talcproducts have whiteness of less than 90%, which is ap-propriate for use in the paint industry, but the talcwould require considerable processing before being ac-

ceptable to the paper, paint and cosmetics industries.The pure talc ore is of economic importance while theproperties and qualities of the other ore types do notmeet the industrial speci®cations.

Light zone Rutile

14 15 16 17 18 19 20 21 22 23 24 25 26 1 2

0.53 0.26 0.19 0.20 0.16 0.32 0.87 0.51 0.46 0.76 0.54 0.18 0.49 0.14 0.270.05 0.05 0.00 n.d n.d 0.10 0.73 0.70 1.46 1.09 1.64 0.30 1.61 99.01 97.5519.97 20.75 22.79 29.95 29.26 27.44 3.48 8.49 2.91 3.86 2.57 9.65 6.66 0.34 0.000.07 0.00 0.04 n.d n.d 0.03 0.10 0.08 0.06 0.07 n.d 0.04 0.00 0.06 0.070.00 0.65 0.00 0.00 0.00 0.00 11.10 6.37 17.28 13.44 17.85 9.62 19.50 ± ±30.83 29.48 28.91 29.42 29.51 28.41 31.62 29.73 31.43 29.16 32.17 27.74 31.62 0.17a 0.39a

43.29 43.21 41.55 37.38 36.80 36.40 44.96 42.24 40.99 40.80 39.15 38.20 34.26 1.01 1.171.77 1.62 2.08 2.96 2.72 2.88 0.49 0.47 0.59 0.43 0.33 1.65 0.59 0.07 0.02n.d 2.36 1.13 n.d n.d 1.56 0.92 1.27 n.d 0.60 n.d 1.82 0.51 n.d n.d0.06 n.d 0.12 n.d n.d 0.00 n.d 0.04 0.02 0.09 0.02 0.00 0.04 n.d n.d0.28 n.d 0.35 n.d n.d 0.16 0.89 0.28 0.41 0.56 0.63 0.28 0.67 n.d n.d1.02 1.59 1.88 n.d n.d 1.57 1.10 2.72 1.46 2.71 1.52 2.06 2.39 0.14 0.00

97.87 99.97 99.04 99.91 98.45 98.87 96.27 92.90 97.07 93.58 96.42 91.54 98.34 100.77 99.08

0.144 0.070 0.050 0.051 0.041 0.083 0.265 0.149 0.139 0.238 0.165 0.053 0.143 0.002 0.0040.000 0.131 0.000 0.000 0.000 0.000 2.541 2.484 3.943 3.162 4.117 3.580 4.323 0.002 0.0040.011 0.010 0.000 ± ± 0.019 0.167 0.155 0.332 0.256 0.378 0.065 0.356 0.978 0.9769.343 9.156 8.763 7.540 7.551 7.493 10.812 9.807 9.826 10.082 9.489 8.734 7.974 0.011 0.0126.424 6.552 7.165 9.006 8.949 8.421 1.247 2.938 1.040 1.422 0.928 3.289 2.312 0.005 0.000

15.922 15.919 15.978 16.597 16.541 16.016 15.032 15.533 15.280 15.160 15.077 15.721 15.108 0.998 0.996

0.721 0.647 0.827 1.124 1.053 1.116 0.222 0.205 0.269 0.200 0.149 0.713 0.261 0.001 0.0007.037 6.605 6.448 6.278 6.405 6.186 8.043 7.221 7.969 7.623 8.248 6.606 7.789 0.000 0.000± 0.467 0.222 ± ± 0.300 0.207 0.275 ± 0.272 ± 0.389 0.112 ± ±0.013 ± 0.027 ± ± 0.000 ± 0.010 0.005 0.023 0.005 0.000 0.009 ± ±0.021 0.000 0.011 ± ± 0.007 0.034 0.024 0.019 0.023 0.000 0.013 0.000 0.001 0.0010.051 ± 0.061 ± ± 0.028 0.179 0.054 0.083 0.116 0.127 0.054 0.131 ± ±0.236 0.362 0.426 ± ± 0.346 0.283 0.677 0.374 0.717 0.395 0.505 0.596 0.002 0.000

8.079 8.081 8.022 7.402 7.458 7.983 8.968 8.466 8.719 8.974 8.924 8.280 8.898 0.004 0.001

Fig. 13 The elemental variations along zoned chromite grainsshowing the behaviour of major components during the alteration

Fig. 14 Type of the disseminated chromite grains using the Stevens(1944) diagram

359

Fig. 15 Comparative distribution of some major and trace elements amongst the di�erent talc ore types on one side and between talc depositsand the host metavolcanics on the other side

Table

7Whole

rock

chem

icalanalyses(m

ajorelem

ents

inwt%

andtrace

elem

ents

inppm)forthedi�erenttalc

ore

types

andslightlytalci®ed

rocks

Area

RodUmm

El-Farag

WadiThamil

Type

Pure

talc

Chlorite-rich

Talci®ed

trem

olitized

rock

Talci®ed

chloritzed

rock

Pure

talc

No.

40±7

37±6

41±1

40±5

40±3

39±3

40±8

37±7

37±3

37±4

37±8

37±5

41±3

38±2

1±1

1±2

5

SiO

261.62

60.86

60.38

60.25

59.94

59.66

59.45

59.13

55.67

52.32

47.05

43.37

52.51

30.29

58,66

60,03

60,09

Al 2O

30.83

0.42

0.86

0.69

0.66

0.92

0.94

1.61

2.67

4.44

7.15

9.54

3.72

16.89

1,20

0,56

0,61

Fe 2O

30.46

0.06

0.25

0.70

0.31

1.02

0.30

1.08

1.06

0.31

0.21

0.10

1.47

1.60

0,10

0,54

0,29

FeO

3.29

4.56

4.47

3.65

4.10

3.68

4.54

4.29

5.03

6.39

7.64

9.24

6.66

10.40

4,18

3,43

3,12

TiO

20.05

0.03

0.02

0.04

0.05

0.05

0.05

0.31

0.07

0.42

0.53

0.10

0.19

0.57

0,10

0,07

0,07

CaO

0.00

0.00

0.06

0.00

0.00

0.02

0.00

0.05

0.06

1.94

0.13

1.86

10.54

0.04

0,02

0,03

0,06

K2O

0.01

0.03

0.05

0.03

0.02

0.06

0.05

0.07

0.04

0.02

0.06

0.09

0.04

0.07

0,02

0,02

0,01

MgO

28.46

28.29

27.25

28.15

28.15

28.18

27.95

27.91

27.98

25.85

27.55

25.81

19.95

26.63

28,22

28,15

28,28

Na2O

0.07

0.18

0.08

0.06

0.03

0.06

0.04

0.05

0.06

0.05

0.06

0.06

0.08

0.05

0,05

0,03

0,05

MnO

0.02

0.04

0.05

0.04

0.04

0.02

0.04

0.07

0.07

0.12

0.15

0.17

0.24

0.14

0,03

0,04

0,05

BaO

0.00

0.00

0.00

0.00

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0,00

0,00

0,00

S<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

0.01

0.01

<0.01

0.01

<0.01

<0.01

<0.01

<0.01

0,02

P2O

50.00

0.00

0.03

0.00

0.00

0.00

0.00

0.02

0.00

0.04

0.08

0.01

0.02

0.02

0,00

0,00

0,00

Cr 2O

30.09

0.71

0.28

0.22

0.30

0.17

0.17

0.07

0.67

0.11

0.19

0.75

0.13

0.07

0,44

0,17

0,17

Cu

0.00

0.01

0.00

0.00

0.00

0.00

0.00

0.00

0.04

0.00

0.00

0.00

0.00

0.00

0,00

0,00

0,00

NiO

0.13

0.07

0.22

0.21

0.23

0.21

0.19

0.17

0.37

0.33

0.20

0.16

0.11

0.12

0,27

0,28

0,31

LOI

4.62

4.57

4.82

4.83

4.84

4.98

4.96

4.79

5.52

5.64

7.41

7.70

3.40

10.90

4,72

4,53

4,59

Sum.

99.65

99.83

98.82

98.87

98.68

99.03

98.68

99.62

99.32

97.99

98.41

98.97

99.06

97.79

98,01

97,88

97,72

As

<5

<5

<5

<5

<5

<5

<5

<5

476

<5

20

<5

<5

9<5

<5

<5

Pb

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

Zn

32

33

81

39

44

51

42

50

57

53

63

81

139

80

27

30

34

Co

43

37

51

52

56

54

54

49

83

67

83

85

66

109

52

51

51

V2

515

67

98

19

49

74

138

96

88

164

71

2La

<5

<5

<5

<5

5<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

Nd

<5

<5

<5

<5

<5

<5

<5

17

<5

76

<5

<5

<5

<5

<5

10

Ce

<5

<5

<5

11

<5

8<5

24

<5

15

8<5

<5

<5

<5

<5

11

Ga

1<

11

11

1<1

<1

48

11

18

833

2<1

<1

Sc

<1

<1

<1

<1

11

31

46

18

413

12

<1

<1

<1

Nb

<1

<1

12

1<1

<1

2<1

33

23

11

<1

1Zr

<1

<1

<1

<1

<1

<1

<1

29

943

63

13

41

41

<1

<1

<1

Y<1

<1

<1

1<

1<1

<1

14

28

64

81

<1

<1

<1

Sr

<1

21

2<1

11

12

31

38

21

12

U<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

Rb

<1

<1

1<

1<

11

<1

<1

<1

<1

11

<1

1<1

<1

1Th

<1

<1

<1

11

12

13

33

23

4<1

<1

2

361

Table

8Further

whole

rock

analysescontinuingfrom

Table

7

Area

WadiThamil

Type

Pure

talc

Tremolite-rich

Talci®ed

trem

olitized

rock

Talci®ed

chloritized

rock

Serp.

rock

a

No.

11

12

13

14

21±1

21±2

21±4

21±5

21±7

22±1

22±2

22±4

20

16

21±6

23

19

18

Av

SiO

260.62

60.59

60.35

60.93

61.22

61.43

61.22

60.46

60.64

61.22

60.62

60.69

60.40

60.40

57.02

56.97

52.31

36.04

29.73

41.01

Al 2O

30.59

0.42

0.75

0.29

0.27

0.39

0.40

0.76

0.66

0.48

0.76

0.60

0.37

0.52

2.06

0.99

4.62

15.81

20.26

1.17

Fe 2O

30.63

0.85

0.51

0.65

0.86

0.19

1.01

0.47

0.47

0.72

0.74

0.10

0.63

0.69

0.51

0.10

0.30

0.51

1.45

6.19

FeO

4.04

3.48

3.48

3.17

3.54

4.09

3.07

3.42

3.37

3.79

4.00

4.72

4.55

3.62

3.87

4.64

5.90

7.10

6.79

±TiO

20.07

0.08

0.06

0.06

0.06

0.07

0.07

0.07

0.06

0.05

0.06

0.07

0.03

0.06

0.06

0.07

0.06

0.06

0.07

0.28

CaO

0.01

0.78

0.02

0.03

0.03

0.02

0.02

0.05

0.02

0.02

0.03

0.07

3.10

1.87

2.66

10.71

10.80

0.04

0.50

1.02

K2O

0.04

0.08

0.09

0.05

0.05

0.00

0.04

0.00

0.00

0.00

0.00

0.00

0.00

0.06

0.00

0.02

0.00

0.02

0.00

0.02

MgO

27.99

27.20

28.33

27.97

27.33

28.34

28.18

28.48

29.03

28.12

28.05

28.35

24.90

26.68

27.38

22.59

21.08

27.85

27.99

37.67

Na2O

0.09

0.07

0.05

0.05

0.07

0.03

0.05

0.10

0.02

0.07

0.05

0.05

0.06

0.07

0.06

0.08

0.10

0.04

0.04

0.23

MnO

0.04

0.05

0.04

0.03

0.03

0.05

0.02

0.05

0.04

0.07

0.05

0.06

0.07

0.07

0.11

0.14

0.29

0.12

0.18

0.35

BaO

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

±S

0.01<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

0.01

<0.01

<0.01

<0.01

±P2O

50.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.12

Cr 2O

30.25

0.21

0.22

0.17

0.26

0.24

0.16

0.20

0.11

0.32

0.28

0.26

0.25

0.26

0.28

0.17

0.17

0.21

0.27

0.38

Cu

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.01

NiO

0.22

0.21

0.23

0.14

0.28

0.25

0.20

0.30

0.25

0.36

0.29

0.28

0.23

0.22

0.21

0.17

0.19

0.21

0.23

0.36

LOI

4.68

4.52

4.92

5.01

4.65

4.67

4.68

4.62

4.66

4.35

4.40

4.42

3.87

4.52

4.83

2.78

3.30

10.00

11.50

11.15

Sum.99.28

98.54

99.05

98.55

98.65

99.77

99.12

98.98

99.33

99.57

99.33

99.67

98.46

99.04

99.05

99.44

99.12

98.01

99.01

99.96

As

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

9<5

<5

<5

<5

<5

<5

±Pb

<5

65

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

51

Zn

54

61

46

37

38

49

37

36

29

47

42

35

68

56

56

36

102

78

115

85

Co

52

49

43

37

55

50

48

55

51

64

61

57

60

50

50

39

52

71

72

2000

V8

55

83

46

53

24

314

711

327

39

36

±La

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

7<5

<5

<5

±Nd

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

±Ce

<5

5<

5<

5<

5<

5<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

±Ga

21

41

<1

1<1

11

<1

<1

<1

22

4<1

11

28

31

±Sc

<1

1<

1<

1<

11

<1

<1

<1

<1

<1

<1

<1

<1

63

52

<1

±Nb

11

<1

11

<1

<1

<1

<1

<1

22

11

1<1

11

1±

Zr

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

<1

±Y

<1

<1

<1

<1

<1

<1

1<1

<1

<1

<1

<1

1<1

1<1

<1

<1

<1

±Sr

<1

1<

11

1<

1<

1<1

11

11

32

28

51

21300

U<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

<5

±Rb

<1

1<

11

1<

1<

1<1

<1

1<1

11

<1

1<1

11

<1

41

Th

<1

1<

1<

11

<1

<1

<1

1<1

<1

11

1<1

<1

<1

4<1

±

aSalem

(1992)

362

Acknowledgements The author would like to thank Prof. PeterScott and all the technical sta� at Camborne School of Mines,Exeter University, England for their kind assistance. Also, it is apleasure to acknowledge the help of Prof. Walter Prochaska andDr. Ian Scrimgeour at the Institute of Geosciences, Leoben, Aus-tria, for discussions, critical comments and language improvement.The e�orts of the editors and reviewers are also very much appre-ciated.

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363