geology of the kvikne mines with special reference … · geology of the kvikne mines with special...

GEOLOGY OF THE KVIKNE MINES

WITH SPECIAL REFERENCE TO THE

SULPHIDE ORE MINERALIZATION

ODD NILSEN & ANANDA DEB MUKHERJEE

Nilsen, O. & Mukherjee, A. D.: Geology of the Kvikne mines with special reference to the sulphide ore mineralization. Norsk Geologisk Tidsskrift, Vol. 52, pp. 151-192. Oslo 1972.

The Kvikne group of mines and prospects Iies within strongly folded metasediments and metavolcanics in the central Norwegian Caledonides. In general, the sulphide ore bodies are stratabound in nature, and have a ruler shape with parallel alignment and F2 linear structure. They occur adjacent to and at the border between a thin horizon of amphibolite (Gula greenstone) and calcsilicate bearing biotite schists (Gula schists). A short range metasomatism has. affected the ore-bearing border zone bringing about a deprivation of lime and thereby a relative enrichment of Al, Mg and Si, giving rise to cummingtonite/ anthophyllite-, garnet-, and quartz-bearing wall rocks. The ores have been broadly classified into pyrrhotitic ores and pyritic/chalcopyritic ores. A probable epigenetic origin is suggested, depending on the trace element distribution and micromineralogy.

O. Nilsen, Institutt for Geologi, Universitetet i Oslo, Blindern, Oslo 3, Nor

way. A. D. Mukherjee, Institutt for Geologi, Universitetet i Oslo, Blindern, Oslo 3, Norway.

Present address: Department of Geological Sciences, Jadavpur University, Calcutta- 32, India.

Introduction

The Kvikne mines are situated in latitude 62°33'N and longitude 10°25'W (Fig. 1). They comprise a great number of workings within an area of about 30 km2 (Figs. 2 and 3). Kaltberget gruve and Olkar gruve, which are within the mapped area but do not belong to the Kvikne group, will be treated separately.

The mines lie at an altitude of between 800 and 900 m a.s.l. Ore deposits were found in 1629 and copper rnining started in 1631, 13 years earlier than

at Røros. From then until 1812, when all the mines were closed down, production was carried out but with several interruptions. Prospecting and mining

operations continued on a minor scale until World War l. Helland (1902)

and Støren (1951) have given historical accounts of the different working periods of the Kvikne mines. A brief account of the development of the

individual mines is also given below since it has some bearing on the ore occurrences (discussed later) in the region. Numbers in parentheses indicate

the workings listed in Fig. 3.

• Publication No. 3 in the 'Røros project' of the Institute of Geology, University of Oslo.

152 O. NILSEN & A. D. MUKHERJEE

l

Fig. l. Key map showing the location of Kvikne and the Kvikne mine area. In black: the Gula greenstone. Grey: Trondhjemite intrusions. Small circles: mines and prospects. Scale 1:250000.

The first mine in operation was Prestens Gruve, which now constitutes the upper parts of Segen Gottes gruve (9, 10, 17). It was later developed. In 1631

a richer ore was found some hundred metres to the south, where Gabe

Gottes mine (12, 13, 14, 27) was developed. At Gabe Gottes ore was mined about 120 m in the strike direction and about 200 m along the dip.

In 1642 a vertical shaft (Shested's synk) (27) was sunk in order to make

transportation easier from lower levels. But in 1677, when the roof collapsed

because of ruthless exploitation, Gabe Gottes was abandoned. Work at

Prestens Gruve, however, continued. In 1666 a vertical shaft (Gammel

sjakten) (9) was sunk, and, in 1672 poor quality ore was mined 150 metres

along the dip. From 1670 to 1680, when there was a great financial crisis,

the Kvikne mines were flooded.

GEOLOGY OF THE KVIKNE MINES 153

After the turn of the century the mine was reopened and baled out through an inclined shaft below Prestens Gruve. Fortunately in 1730 they hit the Segen Gottes ore. Meanwhile an extensive prospecting took place and some new mines were exploited: Vangsgruvene (3,25) around 1670, and Banken gruve (26) and Gruve 1707 (7). Between 1732 and 1739 a vertical shaft (Nysjakten) (17) was sunk at Segen Gottes to make ore transportation easier and to bring about proper ventilation.

In summer 1789 a serious accident caused the closing down of most of the mines. Heavy rain and mild weather which brought about a sudden melting of snow in the mountains flooded the mines completely. Segen Gottes was totally abandoned and from then on exploitation was concentrated on the Banken gruve and Vangsgruvene.

In 1795 and 1796 exploitation of two new mines started - Olkar (A) and Kaltberget (B). The Kvikne mines were finally closed down in 1812.

In 180 years, the Kvikne mines produced 7,343 tons of copper. Since 181 2 mining has taken place on a limited scale. The workings at Odden I (1), Odden Il (2), and Dalsgruven (4, 5) date from between 1 909 and 1912 when prospecting was carried out by a German company. The age of the other prospects in the area is uncertain.

So far, very little has been published on the geology of the Kvikne mines partly because of the very limited geological activity which has taken place in the Kvikne region as a whole. Investigations made since the closing of the mine cover only the e:Msting ore.

The Kvikne mines were mentioned by Voss (1783) in an old review of Norwegian ore deposits. Vargas-Bedemar (1 819) gave the first geological description of the ore and wall rocks at Kvikne. He also mentioned the amphibolite and the characteristic gamet-bearing quartzites accompanying the ore. Later Helland (1873) gave a more extensive geological description of the mines together with some sketches. Kjerulf (1879) mentioned the Kvikne mines in connection with his description of the Gula schists and showed two geological W-E profiles through the area investigated.

A survey of the copper production from the mines over the years has been given by J. H. L. Vogt (1899).

General geology REGIONAL SETTING

The Kvikne mines lie within strongly folded metasediments and metavolcanics in the central Norwegian Caledonides. Stratigraphically they belong to the Gula schists which Kjerulf (1879) supposed to be of the youngest lithological units in the Cambro-Silurian sequence in the Trondheim region. However, later investigations in the northem part of the Trondheim region have revealed that the Gula schists are included in the oldest part of the stratigraphical column proposed by Wolff (1967) and are given the name Gula schist group. The group is supposed to be of Cambrian age. Geological


o

scate:

qs 1km

Contour interval: 20m

Biotite -quartz schist

lcalc-silicate bearing)

do. with intercalations

of blad< schist

Sericite-quartz schst

Banded quartzite

Hydrothermal quartzite

�bo lite

T rondhjerrite

• Mine, prospect

(A) Olkar rrine

(Bl Kaltberget rrine

� Soapestone quarry

r-=l Ultrabasics

L@J lill Bog

Fig. 2. Geological map of the Kvikne mine region.


Fig. 3. Map showing the mined ores of the Gabe Gottes (closely ruled) and Segen Gottes (in black) mines and the different workings of the area (small circles):

l Odden I 2 Odden Il 3 Øvre Vangsgruve 4 Dalsgruven 5 Dalsgruven 6 Storbekken prosp. 7 Gruve 1707 8 Estensvangen Il 9 Gammelsjakten

10 Segen Gottes (adit)

11 Estensvangen I 12 Gabe Gottes (adit) 13 Gabe Gottes (adit) 14 Gabe Gottes (adit) 15 Prospect 16 Prospect 17 Nysjakten 18 Kojan Ill 19 Kojan Il 20 Kojan I

21 Grubeåsen gruve 22 N. Berstjern prosp. 23 M. Berstjern prosp. 24 S. Berstjern prosp. 25 Nedre Vangsgruve 26 Banken 27 Shested's synk (collapsed) 28 GjØkåsen prosp. 29 Odden prosp.


investigations carried out throughout the last five years have shown that the Gula schist group in the southern part of the Trondheim region comprises a variety of rock types. Here the group is made up mainly of metasandstones (mostly in the eastern areas) and calc-silicate bearing mica-schists and phyllites of various metamorphic grades. The petrography of the calc-silicate bearing Gula schists has been described by Goldschmidt (1915).

Within the metasediments there occur same thin horizons of metavolcanics (later referred to as 'Gula greenstone'), limestones, conglomerates and black schists.

A great number of sulphide deposits confined to the narrow horizons of the Gula greenstone run in a SSW-NNE direction from Røstvangen through the Kvikne district to Gauldalen. The extension of the amphibolite horizons in the Kvikne district together with the location of mines and prospects are shown on the key map (Fig. 1).

From Kvikne westwards the supracrustals are intersected by small er bodies and swarms of trondhjemite. Smaller bodies of ultrabasics (serpentinites, metaperidotites) occur adjacent to one of the amphibolite horizons as lenses conformable with the enclosing schistose rocks.

STRUCTURAL SET-UP

The rocks of the Gula schist group in the Kvikne area are folded into tight, isoclinal folds with nearly horizontal fold axes having a NNE-SSW trend (F 1). The falding pattern gives a uniform schistosity of the Gula schists in the area investigated - a NNE-SSW strike and a gentle (20°-40°) dip to the east predominates. In the mine area the stri.ke direction varies between N35°E and 45°E and the dip 25°-30° to the east.

A younger F 2 lineation is defined by marked parallelism of elongated aggregates of individual minerals (biotite, amphibole and calcite ). This F 2

direction is very well-developed within the mine area and has a NW-SE trend and a SE plunge (Fig. 4A).

Small kink hands or puckerings with horizontal axes are sometimes developed on the schistosity planes, overprinting the F 2 lineation. This F 3

p hase coincides more or less with the F 1 direction (i.e. NNE-SSW) (Fig. 4B). These structures are not so well-developed within the mine area, but are frequently seen in the areas east of the mine.

To the west and north-west of the mine area a small flexure in the schistose rocks can be seen. To the WNW the strike gradually turns into an E-W direction and the dip decreases to below 10° to the south. This is a regional flexure which can be traced from the Kvikne area to Innset and may be due to the emplacement of the Oppdal-Innset intrusive complex.

A dominant joint system is very well-developed within the area and represents the youngest structural element. The joints are nearly vertical and run in a WNW-ESE direction. The valley of Storbekken, together with the lower parts of the river Y a, and the valley of Gryta represent major regional joints of the area. Negligible movements have taken place at the joint planes


N

A

N

B

Fig. 4A. F2 lineations (linear preferred orientation of minerals and mineral aggregates) in the Gula schists from the Kvikne area. Equal area projection, lower hemisphere. Contours: 25%-20% - 10%-5% pr. 1% of area. 106 observations. (X): Direction of the ore axis of the Segen Gottes ore. Fig. 4B. F3 lineations (axes of crenulations, puckerings and kinkbands) in the Gula schists from the Kvikne area. Equal area projection, lower hemisphere. 70 observations. Contours: 10% -5.5% -3% -pr. 1% of area.

and small scale faults parallel to the major joint system are recorded from

the ores at Gabe Gottes and Segen Gottes.

PETROGRAPHY OF THE DIFFERENT ROCK UNITS

The major rock units developed in the area can be classified thus:

Mi ca schists ( calcareous or calc-silicate bearing) Black schists Banded quartzites Amphibolite Trondhjemite and related rocks

Ultrabasics

Mica schist ( calcareous or calc-silicate bearing)

A brownish to grey muscovite-biotite-quartz schist occupies most of the

bedrock in the Kvikne area. The schists are fine-grained and well-foliated.

Thin lenticular veins (1-20 cm) of greenish calc-silicates are often inter

calated with the schists and show parallelism with the foliation of the

schists. The calc-silicate bearing schists are best developed east of Kalt

berget and at Gråhøa. Usually thin lenticular veins of coarse-grained quartz

occur within the mica schists. The calc-silicate veins are replaced by schlie

ren of granular quartz and calcite at the SW slope of Kaltberget. These can

be studied in the river valley of Orkla, south of the farm Grøtliplassen.


Brown biotite and quartz constitute between 80 and 90 vol.% of the schists. Muscovite occurs in lesser amounts and plagioclase, chlorite, garnet, clinozoisite, apatite, sphene, tourmaline, zircon and ore are accessory constituents. The carbonate content of the mica schists varies between 0--10 vol.%- Carbonate-bearing schists occur especially in the western areas, i.e. around the lower parts of the Y a near the junction of Gryta and Orkla, and around Kaltberget. Modal analyses of the different schists are listed in Table l.

The rocks are fine-grained (grain size: O.l-l mm) and have a lepidoblastic texture. Quartz and plagioclase occur as a saccharoidal groundmass with a grain size of 0.1-0.3 mm. Thin veins of quartz often run parallel to the foliation.

Reddish brown biotite occurs as flakes, 0.1-0.5 mm across, with a preferred orientation parallel to the foliation. A very weak banding may be observed. The

'biotite is replaced to a limited extent by quartz and often

shows a poikiloblastic texture. Inclusions of zircon are common. The mineral is very often replaced by chlorite.

White mica occurs in lesser amounts as poikiloblastic flakes, O.l-l mm

across. Usually their orientation is parallel to the foliation, but several individuals cut the foliation planes at a high angle.

Plagioclase occurs sparsely in the schists. Twinning is uncommon. The An content is in the range of An35.47• The garnet content seems to increase towards

. the amphibolite horizons in the area. The porphyroblasts attain a

size of 1-5 mm across and have a poikiloblastic texture. Very often an elongation parallel to the foliation can be observed. Pressure shadows containing coarse, granular quartz occur where the foliation wraps around the garnet. The mineral occurs most frequently within and adjacent to the calcsilicate veins near the amphibolite zone.

Calcite is evenly distributed in the quartz-plagioclase matrix in some of the schists as ragged individuals and to a great extent is replaced by quartz. Ore, apatite, sphene and tourmaline constitute about 0.5 vol.% of the rock. There is staurolite in one specimen from the mine area.

The calc-silkate layers are greenish grey in colour and show a granoblastic texture. They are massive in appearance and are composed mainly of a greenish amphibole, quartz and clinozoisite with minor quantities of plagioclase (An35.45), garnet, carbonate and chlorite, while apatite, sphene, rutile and ore are accessory constituents.

Amphibole occurs as slender poikiloblastic prisms, 0.5-3 mm in length, which have a slight preferred orientation parallel to the foliation of the enclosing schists and are elongated nearly parallel to the F2 direction (Fig. 4A). The pleochroism is weak: a - colourless, p - light olive green, y - light greyish green. The mineral is replaced by quartz which occurs as small ( ± 0.04 mm) inclusions.

Quartz occurs as a fine-grained (0.1-0.5 mm) granular groundmass together with clinozoisite and carbonate. Quartz often occurs as thin veins


with individual grains being coarse in size. Garnet occurs very often as corroded porphyroblasts 1-3 mm across and usually replaced by quartz, chlorite and carbonate.

Further north, near the large trondhjemite bodies (Fig. l), the calc-silicate bearing schists occur as banded and gneissic rocks. The calc-silicate here consists mainly of a greyish green pyroxene ( diopside ) . These contact rocks

were described by Goldschmidt (1915) as 'calc-silicate gneiss'.

Black schists

Black schists occur frequently among the Gula schists. The thickness of the horizons may vary from a few metres to between 10 and 20 metres, alternating with calc-silicate free biotite-quartz schists. The content of car

bonaceous matter varies to a large degree, the black schists showing vanations from coal black phyllites to grey, carbonaceous sericite schists.

A zone of black schists can be followed from Orkla, via Kaltberget and northwards. The extension of the black schist horizons in the western areas

is more uncertain. This may be due to lateral variations and the tectonics. The rnineralogical composition of the black schists is much the same as

that of the rnica schists, except for a higher content of carbonaceous matter

(mainly graphite), sericite and sulphide ore. The ore of Odden mine I (l) and Odden prospect (29) is a sulphide-bearing black schist. These are wellexposed in the Y a river valley.

Of the opaque constituents, pyrrhotite is the major mineral and occurs as

irregular 'clouds' with a ragged outline, somewhat elongated parallel to the

foliation of the rock. Chalcopyrite, which is very rarely included, occurs as

small blebs within the pyrrhotite. Ilmenite and rutile are common accessory constituents among the black schists and occur as small ( ± 0.02 mm) grains near the sulpbides. Graphite usually occurs as fine-grained scaly masses and aggregates.

Banded quartzites

Horizons of banded quartzites occur intercalated within the rnica schists in the areas south of Kaltberget and north of the mine area in the Ya valley.

The boundaries of the enclosing rnica schists are diffused and the horizons

are laterally transformed into more massive and quartz-rich varieties of the biotite schists.

The mineralogy does not differ from the mica schists in the area, except

for the lack of carbonate and calc-silicates and the relatively high percentage of quartz (80 -90 vol.'jl0). The dark constituents occur mostly as thin (1-3 mm) layers parallel to the foliation of the enclosing rocks.

Amphibolite

Several thin horizons of amphibolite occur in the mine area and represent the northern continuation of the western zone of the Gula greenstone indicated on Fig. l. The horizons lie conformable to the enclosing schists and


have a variable thickness, never exceeding 20 m in the mine area. The

amphibolites wedge out in the strike direction and occur as thin lenses arranged in an 'en echelon' pattem.

The several ore deposits in the area are confined to a major horizon running from Berstjem in a NNE direction. In the Gruvehagen area the horiwn seems to branch into at least four minor horiwns which wedge out north of the Odden farm. Due to a heavy covering the southem continuation of the amphibolite zone cannot be clearly delineated.

The outcrop of the major amphibolite horizon in the Kojan-Berstjem area is extensive due to its position paraBel to the slope of the hill.

Usually the amphibolites occur as banded and weakly foliated fine-grained rocks with a greyish green to greenish black colour. The border facies of the rock may attain a coarse-grained, massive look. However, the latter variety usually appear as wall rock of the many ore deposits and will be treated as wall rock of the ores in a later chapter.

Homblende and plagioclase are the major constituents and occur in a fine-grained mosaic (0.1-0.5 mm), the homblende with a preferred orientation parallel to the foliation. It has a poikiloblastic texture and shows a weak pleochroism: a - light yellowish grey, f3 - light olive green, r - light greyish green.

Plagioclase occurs in varying amounts (0--30 vol.%) in the different bands of the am.phibolite. It occurs as a granoblastic, fine-grained groundmass and as more coarse-grained segregation veins in the rock. The plagioclase replaces the amphibole along the lobate grain boundaries of the latter. The An content varies between An25 and An32•

Biotite, chlorite, clinozoisite and carbonate occur as rninor constituents and in varying amounts. Calcic amphibolites occur frequently within the western branches of the main amphibolite exposed south of Vangsgruvene. Usually carbonate and clinozoisite occur as distinct thin (1-10 mm) bands together with plagioclase or quartz. Cross-cutting veins of carbonate are

aften seen. At certain places biotite occurs as thin bands within the amphibolite. Rutile occurs sparsely as small (O.l mm) grains and forms an accessory constituent. Sphene and apatite are found among the more calcic varieties.

Trondhjemite and related rocks

Lenticular trondhjemite bodies and dikes intersect the Gula schists. Usually they Iie conformably to the enclosing rocks, but cross-cutting veins are observed. The dikes are 1-20 m in thickness and are well-exposed in the Y a valley.

The trondhjemites are medium- to fine-grained rocks with a granular texture. Plagioclase and quartz are the major components and biotite and muscovite occur in lesser amounts. Gamet, chlorite, apatite and ore are accessory constituents. Plagioclase occurs in an allotriomorphic mosaic together with quartz with a grain size varying from 0.5 to 2 mm. Albite


twinning is common and the An content varies between An15 and An35•

The mineral is weakly clouded and is often zoned. A dark brown biotite

and muscovite occur sparsely as flakes 1-2 mm across without any preferred

orientation.

In the western part of the area a trondhjemite dyke of variable thickness

can be followed for about 8 km in a NE direction from the farm Hanshus

vangen. Impregnations of sulphide ore minerals are frequently observed at

the border of the trondhjemite and the enclosing schists. Moreover, pyrrho

tites occur as irregular amegates within the rock and include blebs of

chalcopyrite and molybdenite.

In the lower part of the Ya river, dikes and pegmatite veins of granitic

composition are found. Microcline, quartz and plagioclase are the major

constituents, while muscovite and biotite are the accessories.

Ultrabasics

Three small lenticular bodies of ultrabasic rock occur 100 m below the top

of Kaltberget on the western slope of the mountain. They are links in a

chain of small bodies of ultrabasics which can be followed from the Røstvangen area (Fig. 1) adjacent to the main amphibolite horizon to Kvikne.

Extensive quarrying took place in one of the bodies at Kaltberget in the

old days for the manufacturing of pots and vessels (Helland 1902, Skjøls

vold 1961) and a great number of moulds and cavities are visible on the

rock surface.

The ultrabasics are coarse- to medium-grained massive rocks which have

a bleached and rusty appearance on the surface. Fresh specimens collected

from the dumps of Kaltberget mine and from the quarries have a greenish grey look and show a mass of stout prisms of amphibole. Phlogopite-bearing varieties are common.

In thin section the amphibole shows a poikilitic habit. It has a very faint

pleochroism: a- colourless, {J = y - faint brownish grey. Well rounded in

clusions, 0.1-0.5 mm across, contain a felty mass of tale and chlorite in equal amounts. Some inclusions contain small relics of olivine - thus the

inclusions seem to represent pseudomorphs after olivine. Phlogopite occurs

frequently as intimate intergrowths with the amphibole. Chlorite replaces

the amphibole along cracks parallel to the c-direction.

The ultrabasics have a feldspathic border zone. The ores of Kaltberget

mine are confined to this zone. Saussuritized plagioclase occurs as larger,

somewhat cataclastic aggregates between bundles of the colourless amphi

bole. Here the rounded talcjchlorite inclusions are missing. Sphene occurs

frequently in the border zone as 0.5-2 mm anhedral grains included in the

amphibole.

The bodies of ultrabasics Iie conformable to the enclosing rocks and

cross-cutting features are never seen. The enclosing mica schist is strongly

deformed, but has the same mineral composition as the ordinary schists of

the area, except for a weak impregnation of pyrrhotite and chalcopyrite.

The ores


The Kvikne mines comprise a great number of mines and prospects (Fig. 3). Though the mine area is heavily covered, the many old workings have exposed the ore-bearing horizons at different places and have facilitated mapping of the area. However, thorough study of the ores and wall rocks

of most of the mines and prospects is difficult. The workings are completely flooded and as a result the findings are based mostly on sampling from the dumps and examinations of the outcrops.

GENERAL CHARACTERISTICS AND LOCATION OF ORES

The major ore deposits at Kvikne mine are confined to the amphibolite

horizons in the area and occur usually at the border between the amphibolite and altered varieties of the enclosing mica schists. Depos.its within the amphibolite are never seen, but sulphide mineralizations frequently occur

in the schists adjacent to the amphibolite. The following mines and prospects will be described:

Gabe Gottes (12, 13, 14, 27) Segen Gottes (9, 10, 17) Banken gruve (26) Gruve 1707 (7) Dalsgruven ( 4, 5) Øvre Vangsgruve (3) Nedre Vangsgruve (25) Kojan prospect I (20) Kojan prospect Il (19) Kojan prospect Ill (18)

Odden gruve I (1) Odden gruve Il (2) Odden prospect (29) Storbekken prospect (6) GjØkåsen prospect (28)

Estensvangen prospect I (11) Estensvangen prospect Il (8) Berstjem prospects N, M, S (22, 23,

24) Grubeåsen gruve (21)

Here the Gabe Gottes, Segen Gottes, Banken gruve, Gruve 1707, and the Gjøkåsen and Storbekken prospects seem to be confined to a relatively thin eastem ore-bearing amphibolite horizon. The rest of the deposits are confined to the major amphibolite horizon which shows a tendency to branch and split to the north (Fig. 2). Odden gruve Il and Dalsgruven are confined to an eastem branch, Nedre Vangsgruve to a central branch and the Øvre Vangsgruve to a western branch.

The rest of the workings are minor prospects confined to the roof of the major amphibolite zone between Berstjem and Gruvehagen. Sulphide mine

ralizations occur in connection with the two eastem amphibolite horizons crossing Y a, but exploitation has not taken place.

THE DEPOSITS

The deposits can be divided into two principal classes:

Pyriticjchalcopyritic ore deposits Pyrrhotitic ore deposits


The deposits of the first dass comprise from an economical point of view the most important sulphide mineralizations in the area on which the most extensive exploitation has taken place. The second dass of deposits often accompanies the ores of the first dass and occurs in general as a border

zone between the mica schists and the amphibolite. They are all deficient in copper ore and must be regarded as pyrrhotite-impregnated wall rocks of the amphibolite.

Pyriticfchalcopyritic ore deposits

Gabe Gottes. The outcrop of the ore at Gabe Gottes can be seen in the adit near V. Gruvebekk just below the Gruvehagen farm. Inclined shafts lead to the flooded and collapsed parts of the mine and the ore is unattainable

in places. However, an impression of the sulphide ore from the mine can be seen from the dumps near the adit. Samples from the upper parts of the mine can be found in dumps near the brook and the inner and deeper parts are

represented in samples from the big dump of Shested's synk to the north of the road across the V. Gruvebekk.

The upper parts of the ore were pyritic, while the lower parts were rich in chalcopyrite and pyrrhotite. The ore zone is reported to be between 0.5-6 m in thickness, with an average of 3 m. The pillars left in the mine are thought to have ore 0.5 m in thickness left. The ore zone is reported to wedge out towards the margins of the mine to a few cm.

Segen Gottes. The adits of the Segen Gottes mine are completely flooded,

but samples from the mine can be found outside Gammelsjakten (9) (the

upper levels of the ore, including Prestens Gruve) and Nysjakten (1 7) (the lower levels). The dumps are estimated to contain 8000 ms and 15000 ms,

respectively, of ore and waste rock. The upper parts of the ore (at Prestens Gruve) were pyritic, but the central

parts were rich in copper - twice as rich as the Gabe Gottes ore. The lower parts of the ore consist mostly of a fine-grained, pyritic ore. The Segen Gottes mine produced a total of 5000 tons of copper throughout the years 1 730-1 789. According to old reports the ore was 2-3 m thick. It is said that there are between 50, 000 and 100, 000 tons of ore in the remaining

pillars.

V angsgruvene ( ØvFe- and Nedre-) are situated south of Storbekken - the

lower at the bank and the upper 70 -80 m above. The ores occur as sulphide impregnated veins of quartzite at the border between amphibolite and biotite bearing sericite-gamet schists at two different levels. At the upper

mine a short tunnel leads to an inclined shaft which must be of considerable

depth according to the big dumps outside. The shaft is said to lead down to the Nedre Vangsgruve which belongs to an eastem amphibolite 'Zone,

thereby crossing the dip of the mica schists between. The ores consist mainly of impregnations of pyrrhotite and chalcopyrite


in a medium-grained quartzite - often cummingtonite-bearing. Sometimes

pyrite and sphalerite are seen in hand specimens. The impregnations of

sulphides are seen as thin veins and irregular aggregates within the host quartzite.

The lower mine is situated near the bank of the river and a shaft (flooded)

has been sunk near the border between amphibolite and mica schists. The ore from the Nedre Vangsgruve is of the same kind as the Øvre Vangsgruve.

Banken gruve. The adit and workings at Banken gruve are completely

flooded, but as in the case of Gabe Gottes, the ore has been mined by means of an inclined shaft. The dump outside the shaft is partly washed away by

the river and no information about the interior is available. Samples from the

dump reveal a pyritic, quartz rich ore.

Gruve 1707. The mine was opened in 1707, hence the name. The adit is

above the Ø. Gruvebekk and an inclined shaft is sunk parallel to a coarsegrained amphibolite. Sulphide impregnation occurs in thin bands of quartzite

within the amphibolite.

GjØkåsen prospect. A Iittle excavation reveals a massive, pyritic ore in connection with cummingtonite-bearing quartzite. The area around is heavily covered and the geological setting is not clear.

Dalsgruven is situated at the junction between the brooks of Gruvebekken and Storbekken and consists of two inclined shafts about 10 metres apart and sunk along the dip of a sulphide-bearing horizon. The shafts are flooded,

but the northern one is reported to be 8 m in depth. Due to heavy covering, the geological setting is not clear. Near the surface the ore is said to be 30 cm

thick, increasing with d:epth to about one m:etre. The ore consists of a rich impregnated plagioclase-quartz rock where

chalcopyrite and pyrrhotite are the major ore constituents. The ore occurs as a thin network and sometimes as bigger aggregates within the host rock.

Minor chalcopyrite impregnations occur too within a more coarse-grained cummingtonite rock.

Pyrrhotitic ore deposits

Odden gruve I is situated south of Odden farm. A tunnel has been worked

out in a NNW direction across the strike of a dark sericite schist through a

pyrrhotite impregnated black schist. The intention in developing the tunnel was to cut the ore-bearing horizons of the Vangsgruvene, but the work was

laid down after about 50 metres.

Odden prospect is situated about 150 m north of the western farm. Excavation reveals a pyrrhotite-impregnated black schist of the same type as

in Odden I.


Odden gruve Il is situated about 100 m east of Odden I. A tunnel has been

worked out to the east across the strike of a fine-grained biotite-bearing amphibolite. The amphibolite is overlain by the common wallrock - a biotite-bearing sericite schist. At the border between the amphibolite and

the schist, a thin ( ± 70 cm) zone of pyrrhotite-impregnated cummingtonitegamet-homblende quartzite is exposed at the adit. The tunnel is further worked out into barren sericite schist.

The Berstjern prospects (N, M, S) are situated west of Berstjem. The distance between the prospects is about 20 m. The ore-bearing horizon is best exposed at N. Berstjem prospect. Here a tunnel is worked out in a NNW direction through the 'roof' of the fine-grained amphibolite. The ore zone is exposed at the adit and consists of pyrrhotite-impregnated cummingtonitehomblende-gamet quartzite. This horiwn is about 50 cm thick and the tunnel is worked out into barren, fine-grained amphibolite.

The ores from the Middle (M) and Southem (S) prospects are of the same kind, except for the abundance of biotite instead of homblende in the gangue. Pyrrhotite is the major ore constituent. Ilmenite, magnetite, chalcopyrite and molybdenite are accessory constituents in decreasing order.

The Kojan prospects are situated near the Kojan farm. The ore at Kojan I is mainly confined to a cummingtonite-gamet quartzite as pyrrhotite impreg

nations. At Kojan Il and Kojan Ill pyrrhotite is impregnated into a coarsegrained gamet amphibolite adjacent to the cummingtonite quartzite. Ilmenite, magnetite and chalcopyrite are accessory constituents.

Grubeåsen gruve is a bigger excavation near Kojan farm. Ore is confined to a coarse-grained gamet amphibolite as pyrrhotite impregnations.

Estensvangen prospect I lies near the road to Kvikne. A pit is excavated through a heavy impregnated schistose gamet-quartzite containing minor amounts of biotite, sericite and plagioclase. The ore is overlain by a 30 cm thick layer of dark cummingtonite and gamet-bearing quartzite. The ore horizon grades downwards into the barren biotite-bearing sericite schist, resting on a thin wedge of the fine-grained amphibolite. Pyrrhotite is the

dominant ore mineral, ilmenite and chalcopyrite are accessory constituents.

Estensvangen prospect Il lies between Estensvangen and Gruvehagen. The geological setting is not clear due to heavy covering. Excavation reveals a

pyrrhotite-impregnated fine-grained anthophyllite-gamet quartzite, similar

to the ores of Kojan I and the Berstjem prospects.

SHAPE AND STRUCTURE OF THE ORE BODIES

Few data are available conceming the shape and structure of the ore deposits at Kvikne mine. Field evidence points to a stratabound nature of

the ores. Cross-cutting features are never met with in the field. However,


the different horizons often wedge out along the strike direction of the enclosing rocks.

A three-dimensional view of the major deposits - Gabe Gottes and Segen Gottes - can be seen from an old map issued by Henning Floer in 17 62 (Fig. 3) and from old reports.

The Gabe Gottes and Segen Gottes ores form two distinct ore bodies -the Segen Gottes ore on a somewhat higher level than the Gabe Gottes ore.

The bodies are lens- or ruler shaped, laterally wedging out towards the margins. The direction of the principal ore axis of the Segen Gottes ore corresponds to the principal F2 direction of the area (Fig. 4A (x)). This

correspondence between the direction of the ore axis and the linear 'flow direction' of the host rocks was pointed out by Th. Vogt (1952). He stated

that these directions are usually normal to the direction of the Caledonian mountain chain.

The Segen Gottes ore is faulted along three vertical zones, more or less parallel to the ore axis (Fig. 3, stippled lines). These fault zones may

correspond to the general WNW-ESE joint system of the area. It is uncertain whether the ores of Banken, Gruve 1707 and the Gjøk

åsen prospect lie on the same level as the Segen Gottes ore, but all deposits mentioned above seem to lie on the same horizon.

As previously stated, the pyrrhotitic ores are all confined to the border zone between amphibolite and mica schist and represent a more or less continuous plate, covering the roof and probably the bottom of the folded amphibolite horizon.

THE WALL ROCKS

The wall rocks of the ores at Kvikne mine are well exposed due to the ex

tensive prospecting in the area and some excavations reveal excellent sections through the ore-bearing stratas.

Chemical and mineralogical changes have taken place between the two chemically contrasting lithological units - the pelitic metasediments and the metavolcanics. Near the border zone the rocks are transformed into different rock types arranged in a characteristic pattem across the border. This pattem of alteration can be found all along the several horizons of the Gula greenstone - ore-bearing or not. Fig. 5 shows a general section through the ore-bearing border between mica schist and amphibolite at Kvikne mine. It shows the general distribution of wall rocks, their mineralogical composition and the deposits associated with them. The following wall rocks are to be considered:

Biotite-sericite schist

Gamet amphibolite Homblende-cummingtonite-garnet quartzite Biotite-cummingtonitejanthophyllite-gamet quartzite



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Biotite-sericite schist As an envelope of varying thickness, biotite-bearing sericite schists enclose the amphibolite horizon in the Kvikne area. The transition between the


brown Gula schists and the sericite schists are diffuse and in hand specimens

the transition can be followed by an increasing amount of white mica and

gamet. Moreover, the sericite schists are devoid of calc-silicates. In thin section one notes the absence of calcic minerals as plagioclase, clinozoisite and calcite. Three modal analyses of the sericite schists are compared with the ordinary biotite schists in Table 1.

The schists are silvery white in colour. The grain size and texture of the

rock are the same as for the biotite schists except for an oblique orientation of small biotite porphyroblasts with respect to the foliation. Gamet occurs in great amounts, especially near the amphibolite. The white mica is swerved

around the rounded porphyroblasts of gamet which attains a grain size of several mm.

Garnet amphibolite

Towards the border of the fine-grained and banded oligoclasejandesine

amphibolite, the rock becomes more massive and coarse-grained. Homblende

occurs as stumpy prisms, 1-5 mm in length, in aggregates together with gamet and do not show any preferred orientation in the rock. The gamet

attains a grain size of 1-3 mm and has a shattered, helicitic texture. Usually

it contains helicitic inclusions of ore and quartz. Quartz and sulphide ore

occur as an interstitial matrix between the aggregates, and biotite, chlorite,

sphene and rutile are accessory constituents. The sulphide ore (mainly pyrrhotite and pyrite) replaces the gangue, especially the gamet along cracks

and embayed grain boundaries.

Tab le l. Modal composition (vol.%) of biotite- and sericite schists in the Kvikne area. 1- Olkar gruve; 2- Y a; 3- Storbekken; 4- Kaltberget; 5 - Flatfjellet; 6 - Kaltberget; near Estensvangen; 7 - Kojan; 8 - Segen Gottes. Adit. x - accessory constituents.

Mineral Biotite schists li Sericite schists

l 2 3 4 5 6 7 8

Quartz 71.5 39 32 Plagioclase 79.5 66 74 70 65

X

Biotite 19 19 13 20 27.5 16 16 23

Muscovite 12 9.5 7 5 11 35 41

Garnet 2 9 4

Chlorite X X X X X X

Clinozoisite X X

Apa tite X X X X X X

Sphene X X X X X

Tourmaline X X X

Zircon X X X X X

Ore X X X X X X X

170 O. NILSEN & A.D. MUKHERJEE

The ores at Grubeåsen gruve, Kojan Il and Kojan Ill and partly Gabe Gottes are confined to this kind of rock as heavy impregnated pyritic and pyrrhotitic ores. In some places (i.e. Gabe Gottes and Gruve 1707) the rock occurs as wall rock for massive pyritic ore veins.

Hornblende-cummingtonite-garnet quartzite

With relatively sharp boundaries the garnet amphibolites usually grade into cummingtonite-bearing hornblende-garnet-quartz rocks. Together with the hornblende-free varieties (described in the following section) they occur as a thin ( ± 0.5 m) cap around the amphibolite. They are fine-grained rocks, massive and usually impregnated with pyrrhotite. Prospecting on the pyrrho

titic ore has taken place on several localities (Fig. 5). Quartz, garnet and cummingtonite are major components. In minor con

centrations a bluish green hornblende occurs together with mcide ore. Quartz occurs as a granoblastic groundmass with a grain size of 0.1-1.5 mm and have sutured boundaries. Garnet occurs as shattered poikiloblasts, replaced by quartz and sulphide ore. Cummingtonite occurs as bands of small bundles or wisps together with garnet. The single prisms are 0.1-0.6 mm in length and are replaced by quartz and sulphide ore along embayed grain boundaries and cracks. The amphibole is colourless and shows no pleochroism. It shows a characteristic narrow multiple twinning on (100). The extinction angle Z 1\ c is in the range 15°-18° and the birefringence is higher than hornblende. Monomineralic cummingtonite rocks are observed in the dumps of Dalsgruven and at Vangsgruvene. Hornblende occurs in varying minor amounts, usually in homoaxial intergrowths with cummingtonite. The

pleochroism is stronger than in the banded amphibolite: a - colourless, fl -light olive green, y - bluish green.

Biotite-cummingtonitefanthophyllite-garnet quartzite

As shown on Fig. 5 the cummingtonite-bearing rocks usually grade into hornblende-free biotite-bearing varieties towards the mica schists. The texture, grain size and mineral content are the same except for the introduction of biotite instead of hornblende. The content of biotite may vary from nil to several per cent of volume, but usually the biotite content is low. In some biotite-rich varieties near the pyritic ore horizons (i.e. at Ø. Gruvebekk and

near Segen Gottes adit) staurolite is found as aceessory constituents among the rocks. As for the hornblende varieties, the rock is usually impregnated with pyrrhotite.

Anthophyllite occurs instead of cummingtonite at Estensvangen Il as slender prisms, 0.1-1 mm in length, and has a straight extinction. Pleochroism is very weak: a- colourless, p= y -light brownish grey.


A fine- to medium-grained hydrothermal quartzite usually accompanies the pyriticjchalcopyritic ores at the Kvikne mines and occurs as discontinuous


layers, especially along the Gabe Gottes-Segen Gottes-GjØkåsen-Storbekken

line. The layers range from a few cm to 0.5 m in thickness and have a greyish,

brownish or white colour, depending upon the content of accessory constituents as mcide ore or iron hydroxides. The coarse-grained varieties have a glass y, bluish appearance.

The borders to the enclosing rocks (i.e. coarse-grained amphibolite (Gabe Gottes adit, Gruve 1707), sericite schist (Gabe Gottes adit, Estensvangen I, Storbekken prosp.) or cummingtonite quartzite (Vangsgruven, Kojan area)) are always sharp. Sulphide-impregnated varieties have been exploited (Vangsgruven, Se gen Gottes ).

Quartz constitutes about 95 vol.% of the rock and occurs as a granular

mosaic with a grain size of 0.5-4 mm. Sutured grain boundaries are common. Small, corroded grains of gamet and muscovite occur sparsely as accessory constituents.

The ores of the V angsgruvene and some of the ore types of Segen Gottes and Banken are confined to the quartzites as sulphide impregnations. A heavy magnetite impregnation occurs at certain places, for instance near Kojan farm. The oxide ore occurs as dusty banded aggregates - the indivi

dual magnetite grains have a grain size of 0.01-0.1 mm across. Flames of hematite are often exsolved within the magnetite.

General characters of the wall rocks At the ore-bearing contact between amphibolite and the mica schists certain mineralogical changes have taken place (Fig. 5). The formation of the wall rocks listed above is possibly due to a short range metasomatism in connection with the metamorphism of the two contrasting rock units. Mapping in the Røstvangen-Kvikne region has revealed that the 'wall rocks' occur

all along the several horizons of highly metamorphosed varieties of the Gula

greenstone whether it is ore-bearing or not. Thus in the Kvikne region their formation does not seem to have any relation with the emplacement of the pyriticf chalcopyritic o res.

In general the following rnineralogical changes have taken place towards the contact:

Calcic minerals as carbonate, clinozoisite and plagioclase disappear in both rock units.

The amount of gamet increases in the schists and appears for the first

time in the amphibolite dose to the border. The amount of quartz increases in both rock units. MgfFe-rich amphiboles as cumrningtonite and anthophyllite are introduced

at the expense of homblende and biotite, respectively, in both rock units.

Introduction of sulphides in both rock units.

It is evident from the above-mentioned statements that a general depri

vation of lime has taken place to an increasing degree towards the border,


thereby causing an enrichment in stable components such as Mg, Al and Si.

The deprivation of lime seems to have affected the hornblende of the amphi

bolite, transforming the green hornblende into colourless cum.mingtonite.

The formation of cummingtonite at the expense of hornblende has been

described by Tilley (1935) from contact metasomatic altered greenstones

and from regional metamorphosed basic flows (Tilley 1937). He states:

'Removal of lime from green hornblende leaves Mg, Fe, Si and Al in excess

of that required for cummingtonite, alternatively an excess of Si and Al'

(Tilley 1935). The formation of garnet and the silicification of the border

zone may be ascribed to this enrichment.

At the present moment no chemical analyses of the wall rocks are avail

able. Textural features indicate an influx of Si02 towards the border,

causing the formation of small veins on the wall rocks and the formation of

the quartzite adjacent to the pyriticjchalcopyritic ores. As opposed to the

above-mentioned wall rocks the formation of the quartzites seems to be

contemporaneous with the emplacement of the pyritic ores at the Kvikne

mines.

DEPOSITS ADJACENT TO THE KVIKNE MINES

Kaltberget gruve Kaltberget gruve is situated dose to the small bodies of ultrabasics at the

western slope of Kaltberget. An indined shaft is sunk at the lower border

between the massive, coarse-grained body of talc-chlorite-amphibole rock and deformed biotite schists. As already mentioned the sulphide-bearing

border zone of the ultrabasic is feldspathic and the ore occurs as an im

pregnated, medium-grained massive amphibole-plagiodase rock. The ore is mainly composed of pentlandite, pyrrhotite and chalcopyrite which occur as a thin network and as small aggregates within the host rock.

Thin sections of the ore reveal that a catadastic deformation has taken

place within the host rocks. The bigger grains of plagioclase have a very

doudy core and small plagiodase grains display a mortar texture around

the bigger grains and occur as an interstitial groundmass within cracks in the shattered amphiboles. Phlogopite, magnesite and chlorite are accessory

constituents. The ore zone has a thickness of about 3 m.

Olkar gruve Olkar gruve is situated on the banks of Orkla near Grøtliplassen. The deposit

lies within strongly deformed mica schists and is confined to a sulphide

bearing calc-silicate horizon, 2-3 m in thickness, running across the river

parallel to the foliation of the endosing schists. The ore zone is exposed on

the eastern bank.

The mine is reported to have been ane of the richest in the area with

respect to the copper content of the ore, but the location of the ore so dose

to the river caused much trouble with the underground workings. An attempt

to lead the river away from the ore-bearing horizon by working a channel


from the bridge northwards failed, and the mine was abandoned. Two

vertical shafts are sunk on each side of the river to the ore-bearing strata. From the dumps outside the western shaft {flooded) the rich ore from the

depth can be seen.

The ore consists of a heavily impregnated, strongly deformed and massive

calc-silicate rock. The rock has a greenish grey look, and irregular veins and bigger aggregates of chalcopyrite and nickeliferous pyrrhotite are seen in the hand specimens. The host calc-silicate rock is composed of a fine-grained,

felted mass of clinozoisite, greyish green amphibole and plagioclase. The

proportions between the major constituents varies - irregular veins and lenses of quartz and a greyish green amphibole-free calc-silicate occur frequently in the ore.

In thin section these calc-silicate rocks of the deeper parts of the mine show strong deformational and metamorphic textures. In the amphibole-rich

varieties, the amphibole and clinozoisite occur as shattered, strongly poikiloblastic grains 0.1-3 mm in length. The amphibole replaces clinozoisite and

plagioclase replaces both minerals as interstitial small grains which display

an undulose extinction. The ore is intersected by numerous thin veins filled with quartz and ore. Sericitization along the veins is common.

The lenses of light coloured calc-silicate are mainly composed of the same cloudy plagioclase (An30 _ 35) and small ( ± 0.2 mm) anhedral grains of

diopside, but display the same felted and veined texture. The enclosing rocks seen at the surface are the usual calc-silicate banded

biotite mica schists which to the north contain numerous intercalations of

black schist.

In general, the rocks around Olkar gruve are strongly deformed and metamorphosed. Textural evidence points to a relatively rapid recrystalli

zation during a high temperature metamorphism of the host rock, trans

forming parts of the amphibole into newly formed diopside. It is uncertain whether this local high grade metamorphism is due to a local contact meta

morphism or not. A few thin sills of trondhjemite cut through the Gula schists near by, but the thermal effect of these must have been negligible. The presence of an intrusive body (trondhjemite, ultrabasite) in the depth may possibly count for the local deformation, the metamorphism of the calcsilicates and the ore deposition at Olkar gruve.

DESCRIPTION OF THE ORE TYPES

We have principally divided the Kvikne group of mines into two classes, viz. pyriticjchalcopyritic and pyrrhotitic ore deposits on the basis of most

predominant ore minerals in them. Physically the ores of the first class can be grouped into massive and impregnated ores. The massive ore which is the

main type of ore in the Kvikne group of mines is composed almost entirely of sulphides and very little oxides and silicate minerals. Taking into account

the average grain size of pyrite, the most dominant mineral, the massive

ores can be further subdivided into the following types:


Type

Fine-grained ore Medium-grained ore Coarse-grained ore

A verage grain size of pyrite

O.l-l mm l-2 mm )2mm

The distribution pattem of ore minerals and chemical compositions (wt.% of Cu, Pb, Zn, and Fe) of different types of ores are shown in Table 2. It is evident from the mineralogical and chemical composition of the ores that pyrite is the most dominant sulphide mineral in all varieties of massive ore with varying amounts of pyrrhotite, chalcopyrite and sphalerite. Chalcopyrite and sphalerite attain their max.imum concentration in medium-grained massive ores, which is also indicated by the increase in concentration of Cu and Zn in them (Table 2).

The impregnated ore on the other hand shows predominance of chalcopyrite and pyrrhotite over pyrite.

The ore deposits of the second class, i.e. the pyrrhotitic one is composed entirely of pyrrhotite with or without the other hypogene sulphide ore minerals.

Among the deposits adjacent to the Kvikne mine, ores of Kaltberget and Olkar appear to be chemically different from the Kvikne ores in that they are entirely devoid of zinc and are enriched in nickel. While pyrrhotite and chalcopyrite form the major ore mineral components of Olkar gruve, pyrrhotite and pentlandite form the major ore mineral components of the Kaltberget ores.

MINERALOGY OF THE ORES

Ore microscopic study reveals the presence of the following minerals in the different types of ores in the study area:

Hypogene

Magnetite Hematite Ilmenite Rutile Pyrite Chalcopyrite Sphalerite Cubanite Mackinawite Pyrrhotite Molybdenite

Galena Pentlandite

Fe304 Fe203 FeTi03 Ti02 FeS2 CuFeS2 ZnS

CuFe2S3 (Fe,Ni,Co,Cu)1 + xS Fe1-xS MoS2 PbS (Fe,Ni)S

Supergene

Goethite Lepidocroci te Pyrite Marcasite Bravoite

a-FeO(OH) y-FeO(OH) FeS2 FeS2 (Ni,Fe)S

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DESCRIPTION OF INDIVIDUAL ORE MINERALS

Oxides

Magnetite is the most common måde mineral and occurs as small subhedral to subrounded grains having an average size ranging frqm 0.05 to 0.6 mm across. Sometimes grains of magnetite are found to be elongated in nature. Magnetite is generally found to be associated with the gangue silicates but when it occurs within the sulphides it preserves its crystal boundaries against the sulphides which appear to have moulded round the magnetite and therefore to be later in age of crystallization. Moreover, magnetite when occurring within the gangue minerals is observed to be intimately intergrown with them, indicating its simultaneous formation.

Ilmenite occurs mainly as fine exsolved lamellae within magnetite and rarely as prismatic grains within the gangue.

Rutile is found to be commonly concentrated in the gangue and invariably associated with other oxides like magnetite and ilmenite.

The above-mentioned oxides which are mainly associated with the silicates and occasionally disseminated within the sulphides do not seem to be any stage of mineralization which has formed the sulphides and are the original constituents of the metasediments.

Sulphides

Pyrite is the most ubiquitous of all the sulphides present in the massive ores. The variation in grain size of pyrite has given rise to the subdivision of the ores. Subhedral to euhedral (mainly cubic and rarely octahedral) and subrounded to rounded grains of pyrite occur within the groundmass sulphides, e.g. chalcopyrite, pyrrhotite and sphalerite. When the groundmass is more homogeneous pyrite tends to be more idiomorphic. Embayment and corrosion of pyrite crystals mainly by chalcopyrite and sphalerite and rarely by pyrrhotite have been observed occasionally. Sometimes grains of pyrite are elongated in appearance which is probably due to stretching by deformation. In many cases pyrite crystals are highly fractured along cleavage planes (Fig. 6A) and still others intensely crushed, exhibiting cataclasis. These fractures are found to be filled up by chalcopyrite, sphalerite and pyrrhotite (Fig. 6B). There is a continuous variation of textures from crystals which are euhedral and unfractured to those which are broken up into pieces and floating into the groundmass sulphides.

Chalcopyrite is an important constituent of the medium-grained massive ores and impregnated ores. It is found as a matrix sulphide together with sphalerite and pyrrhotite. Though, in most cases it forms mutual boundaries with the other sulphides, yet it sometimes embays pyrite and fills up fractures in pyrite and pyrrhotite (Fig. 6).

Occurrence of exsolved grains of sphalerite, cubanite and mackinawite is commonly found within the chalcopyrite. Chalcopyrite very rarely occurs as exsolved blebs within sphalerite. The intemal texture of chalcopyrite is characterized by the presence of lance-like double concave inversion twin


Fig. 6A. Fracturing of pyrite along cleavage planes which are filled up with chalcopyrite. Cleavage planes are also sometimes bent. Plane polarized light. Fig. 6B. Crushed and fractured pyrite. The fractures are filled up with chalcopyrite (grey) and sphalerite (black). Plane polarized light.

Fig. 7. lnversion twin lamellae in chalcopyrite with exsolved cubanite lamellae cutting across both set� of twin lamellae. Crossed nicols.


,

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Fig. 8. Cubanite exsolved in two crystallographic directions of chalcopyrite. Plane polarized light.

lamellae (Ramdohr 1969) which are also cut across by exsolved cubanite lamellae in chalcopyrite, indicating its later age of formation than the twinning (Fig. 7). Sometimes the lance-like twin lamellae are bent due to deformation.

Cubanite is an important constituent of medium-grained massive and impregnated ores. It occurs as fine lamellae of varying thickness (0.01-0.05 mm) and length (O.l-l mm), exsolved in one, two or three crystallographic directions of chalcopyrite (Fig. 8).

The cubanite found in these ores is a normal orthorhombic variety with Co = 6.21. lts composition as determined by electron microprobe analysis agrees well with the composition of orthorhombic cubanite reported so far from different localities (Table 3).

Pyrrhotite forms a major constituent of all classes of ores. It occurs as anhedral to subhedral grains or group of grains and as allotriomorphic patches. The grain size varies from a fraction of a millimetre to one or more millimetres. Individual grains of pyrrhotite are sometimes elongated parallel to the schistosity which indicates the nature of metamorphism and deformation suffered by the ores (Fig. 9). Pyrrhotites also show excellent corrugation lamellae which have developed due to stress (Fig. 10). In case of pyrrhotitic ores in black schists of Odden prospect, schistosity has been found to be swerved around pyrrhotite porphyroblasts, indicating its syn

tectonic growth. Pyrrhotites of the nickel-rich ore of Kaltberget and Olkar


Table 3. The composition of cubanite reported from different parts of the world.

Wt.% Locality Modification

Cu Fe s Co Ni Reference

Sudbury Orthorhombic 22.06 42.13 36.30 0.01 Hawley (1962)

Birtavarre Orthorhombic 23.42 41.91 36.00 Mukherjee (pers. com.)

Outokumpo Orthorhombic 23.67 41.35 34.65 0.08 Mukherjee (pers. com.)

Kolihan, Orthorhombic 23.3 41.4 34.8 Mukherjee India (pers. com.)

Gabe Gottes, Orthorhombic 23.08 42.14 34.37 Nilsen &

Kvikne Mukherjee (1972)

O Mine, Japan Orthorhombic 23.91 40.95 35.06 0.08 Takeuchi et al. (1958)

Kamaishi, Orthorhombic 23.30 41.23 34.81 0.11 Takeuchi et al. Japan (1958)

Outokumpo Cubic 24.9 39.1 35.8 Mukherjee (pers. com.)

Kolihan, India Cubic 25.4 38.5 35.5 Mukherjee (pers. com.)

Pondoland and Griqualand, Abnormal 20.8 38.3 40.7 Scholtz (1934) S. Africa Cubanite

•

Fig. 9. Grains of pyrrhotite oriented parallel to the schistosity. Crossed nicols.


Fig. 10. Corrugation or translation twin lamellae in pyrrhotite. Individual lamellae are somewhat bent. Crossed nicols.

Fig. llA. Alteration of pyrrhotite along grain boundaries and basal partings and subsequent production of 'birds' eyes'. Plane polarized light. Fig. llB. 'Birds' eyes' showing concentric growth produced due to surficial alteration of pyrrhotite. Plane polarized light.


show no sign of deformation and contain exsolved blebs and flames of pentlandite in them.

Irrespective of classes or types of deposits pyrrhotite shows development of basal parting (0001) in the initial stage of supergene oxidation. In fact due to supergene oxidation pyrrhotite alters to marcasite and pyrite (secondary). The process of alteration starts from grain boundaries and basal partings and then proceeds inwards inside the grains (Fig. 11A). Development of 'bird's eye' -texture due to supergene alteration of pyrrhotite is very commonly observed and the bird's eyes often show concentric rhythmic growth (Fig. 11B).

Optical and X-ray studies reveal that in the present ores pyrrhotite is mainly hexagonal and only in a few cases are mixtures of both the monoclinic and hexagonal phases present (Table 4). Only the pyrrhotites of Kaltberget and Olkar ores are monoclinic or are mixtures of both phases. Pyrrhotite containing both phases can be identified by etching with HI when a lamellar texture is seen through mixing the two phases. The distribution of monoclinic and hexagonal pyrrhotites is found by measuring the ratio of [d (102) + d (202)]/d (202) as suggested by Arnold (1967). The bulk composition is determined by using the d (102) versus metal content curve of Arnold & Reichen (1962). Though initially the bulk composition of pyrrhotite was determined by using Arnold's curve, it has finally been recalculated by using the determinative equation of Yund & Hall (1969). The atomic %

Table 4. X-ray diffraction data of pyrrhotite from different ore occurrences of the area.

Locality Ore Type Structure d102(Å) Fe(At.%)

Segen Gottes Coarse H 2.0780 48.30

Medium M))H 2.0590 46.74

Gjøkåsen Coarse H 2.0698 47.66

Medium H 2.0698 47.66

Banken Medium H 2.0687 47.56

Fine H 2.0696 47.63

Gabe Gottes lmpregnated H))M 2.0673 47.43

Gruve 1707 Impregnated H 2.0696 47.63

O als gruben Impregnated H 2.0730 47.95

Ø. Vangsgruve lmpregnated H))M 2.0671 47.41

N. Vangsgruve lmpregnated H 2.0715 47.85

Storbekken pr. Pyrrhotitic H 2.0731 48.01

Kojan Pyrrhotitic H 2.0696 47.63

N. Berstjern Pyrrhotitic H 2.0701 47.68

M. Berstjern Pyrrhotitic H))M 2.0672 47.42

S. Berstjem Pyrrhotitic H 2.0730 47.95

Odden I Pyrrhotitic H 2.0705 47.72

Odden Il Pyrrhotitic H 2.0730 47.95

Estensvangen I Pyrrhotitic H 2.0715 47.81

Estensvangen Il Pyrrhotitic H 2.0704 47.71

Grubeåsen gruve Pyrrhotitic H)M 2.0667 47.38

Kaltberget gruve Nickeliferous M 2.0506 46.01

Olkar gruve Nickeliferous M))H 2.0600 46.80


of Fe as indicated in Table 4 shows that different types of massive ores and

pyrrhotitic ores do not show any significant variation in composition of

pyrrhotite, except in the case of the ores of Segen Gottes. On the other hand

the pyrrhotites of Kaltberget and Olkar gruve are deficient in iron with

respect to others.

Sphalerite like chalcopyrite forms an important ore constituent of the

massive and impregnated ores. It is invariably associated with chalcopyrite

and pyrrhotite and occurs as one of the groundmass sulphides. It occasionally

engulfs pyrite and fills in fracture in pyrite. It is frequently found as exsolved

streaks and blebs in chalcopyrite. Sometimes chalcopyrite occurs as orientated

exsolution blebs in sphalerite (Fig. 12). Polished sections of sphalerite when

etched with HI show excellent secondary lamellar twinning (Edwards 1954, Stanton 1960).

Mackinawite from the Norwegian sulphide deposits was first reported by

Ramdohr (1969). Perhaps this mineral is aften confused with valleriite

because of their similar optical properties. In the present ores mackinawite

occurs as fine streaks (not exceeding 0.04 mm in length) and blebs in one

or two crystallographic directions in chalcopyrite (Fig. 13). Electron microprobe analyses reveal the variation in composition of macki

nawites in the different types of ores in the area (Table 5). Chemically

mackinawite consists mainly of Fe and S with varying amounts of Ni, Co

and Cu (Takeno & Clark 1967, Springer 1968, Deb & Mukherjee 1969) and

shows a metal: sulphur ratio equal to one or slightly greater than one

(Table 5). These characteristics hold good for the mackinawites analysed in

the present area.

Fig. 12. Chalcopyrite blebs and streaks exsolved in two directions of sphalerite. Plane polarized light.


Fig. 13. Mackinawite exsolved in two crystallographical directions of chalcopyrite. Twinning in chalcopyrite is also visible. Crossed nicols.

Pentlandite is found only in the nickeliferous ores of Kaltberget and

Olkar. Pentlandite shows two modes of occurrence mainly: as flames and

blebs, and as granular types. Flames and blebs of pentlandite are generally

found in one or two crystallographic directions of pyrrhotites (Fig. 14A).

Occasionally the flames and blebs are arranged in rows flaring out from the

cracks in the pyrrhotite grains (Fig. 14B). The cracks usually serve as the

best local flanking into which the flames and blebs grow and project the

surrounding pyrrhotite grains. The granular pentlandite on the other hand is found to occur essentially in the intergranular spaces of two pyrrhotite grains or in between chalcopyrite and pyrrhotite grains (Fig. 15A).

Table 5. The chemical composition of mackinawites determined by electron probe microanalyser.

Composition (Wt.% Metall Locality Sulphur Formula, taking sulphur as l

Fe Ni Co Cu s Ratio

Gabe Gottes (Lower) 55.17 0.63 8.33 35.72 1.017:1 (Feo.888Nio.oo9Cu0.12)S

Gabe Gottes (Upper) 62.81 2.12 34.44 1.080:1 (Fe1.047Nio.33)S

N. Vangsgruve 56.26 0.71 7.60 0.53 34.94 1.055:1 (Feo.920Nio.o1 Coo.117Cuo.oo7)S

Olkar gruve 53.49 10.61 0.14 0.52 35.01 1.054:1 (Feo.B7sNio.tooCOO.oo2Cuo.oos)S

Analysed by ARL electron microprobe analyser


Fig. 14A. Flames of pentlandite exsolved in pyrrhotite. Plane polarized light. Fig. 14B. Flames and blebs of pentlandite arranged in paraBel rows flaring out from the cracks in pyrrhotite grains. Plane polarized light.

Fig. 15A. Granular pentlandite in the intergranular spaces of two pyrrhotite grains. Plane polarized light. Fig. 15B. Alteration of pentlandite to bravoite along fractures and cleavage planes of pentlandite. Plane polarized light.


Molybdenite is a common accessory constituent of most of the ores and

occurs as small flakes included within the sulphides or the gangue silicates. Galena has only been found as small grains in pyrite in the medium-grained

ores of Segen Gottes.

Marcasite and pyrite (secondary) are found only as the alteration products

of pyrrhotite. The occurrence of goethite and lepidocrocite is limited as

alteration products of pyrite (primary and secondary), pyrrhotite and magnetite. Bravoite is always found as a supergene alteration product of

pentlandite along its fractures and octahedral planes (Fig. 15B).

Texture and structure of the ore minerals

Exsolution, replacement and fracture fillings are the most important textural features observed in the ores. Exsolution textures are most beautifully displayed by several minerals like magnetite, ilmenite, pyrrhotite, pentlandite, sphalerite, chalcopyrite, cubanite and mackinawite. The frequencies of occurrence of exsolution textures are shown in Table 6. In all cases of

exsolution it is due to crystallographic intergrowth as is evident from orien

tation of the exsolved guest into one, two or three crystallographic directions of the host mineral. As regards replacement textures, corrosion and en

gulfing of pyrite by chalcopyrite, etc., can be mentioned as examples of probable extraneous replacement textures. While replacement due to alter

ation is well demonstrated by all stages of alteration of pyrrhotite to marcasite and secondary pyrite and from pentlandite to bravoite.

The fracture filling texture is well exhibited by the infilling of fractures in pyrite by chalcopyrite and sphalerite.

Deformational features are the only microstructures observed in the ore minerals, and are well evident from the cataclasis of pyrite crystals. The most

prevailing cataclastic texture found in the ores is the presence of subregular to irregular networks of fractures in pyrite. Frequently the fractures are guided by the cleavage directions in pyrite which are sometimes found to be

Table 6. Exsolution features.

Amounts Frequency

Host guest pair Form of exsolved mineral exsolved

of observations

Magnetite Ilmenite Thin lamellae Small Uncommon

Cha l co-Sphalerite

Starlets, tiny crystals Small Common

pyrite and linear streaks

Sphalerite Chalco-

Minute blebs and streaks Traces to

Common pyrite large

Chalco-Cubanite Thin lamellae Small Common pyrite

Chalco- Mackina-Thin streaks, blebs Small Common p y rite wite


curved in appearance. These fractures are now occupied by matrix sulphides

and most cornrnonly by chalcopyrite. The matrix sulphides like chalcopyrite,

pyrrhotite and sphalerite show no effects of cataclasis like pyrite due to the ductile nature. But effect of deforrnation is obvious from the elongated

nature of pyrrhotite grains and presence of translation lamellae showing

rnicrofolding and rnicrofaulting in them.

Distribution of trace elements in the ore minerals

Monomineralic fractions of sulphide ore rninerals were analysed by atomic

absorption spectrophotometer to deterrnine their trace element contents.

Among the pyriticjchalcopyritic ores, pyrite and pyrrhotite can easily be

separated so that the Ni and Co contents are specially looked for (Table 7)

because of the genetic importance. The medium-grained massive ore on the

other hand can easily be separated into monomineralic fractions of pyrite,

chalcopyrite and pyrrhotite. These individual mineral fractions are analysed

for Ni, Co, Mn, Cu, Cr, Pb, Zn, Cd, Ga, Ti, V, Mo, Ag, and Bi.

The analyses of Ni and Co from same samples of different types of massive

ores indicate the concentration of Ni in pyrrhotite and Co in pyrite. More

over, coarse- and medium-grained pyrite always contain higher Co than

Table 7. Distribution of Co and Ni in pyrite (Py) and pyrrhotite (Po) separated from the same sample from the pyritic/chalcopyritic ores.

Distri- Distri-Type Co bution Ni bution

Locality of (ppm) of Co (ppm) of Ni Co:Ni

ore Py:Po Py:Po

Segen Gottes Coarse Py: 650 58 12

P o: 250 2.52:1 260 0.22:1 0.96

Medium Py: 520 36 15

P o: 220 2.3:1 280 0.12:1 0.79

Nysjakten Fine Py: 350 40 8.7

GjØkåsen Coarse Py: 660 48 13.7

P o: 310 2.06:1 290 0.16:1 1.06

Medium Py: 500 55 9.1

P o: 400 1.2:1 250 0.22:1 1.6

Banken Fine Py: 310 40 7.7

P o: 80 3.8:1 300 0.13:1 0.26

Medium Py: 490 110 4.5

P o: 100 4.9:1 330 0.33:1 0.33

Gruve 1707 Impr. Py: 600 130 4.6

P o: 110 5.4:1 330 0.39:1 0.33

Gabe Gottes lmpr. Py: 640 50 12.8

P o: 270 2.3:1 200 0.10:1 1.3


Table 8. Distribution pattern of Ni, Co and Ag in coexisting pyrite (Py), pyrrhotite (Po) and chalcopyrite (Cp) from medium grained massive and impregnated ores.

Ni Distribution

Co Distribution

Ag Distribution

Locality of Ni of Co of Ag (p pm)

Py:Po:Cp (p pm) Py:Po:Cp (p pm)

Py:Po:Cp

Segen Gottes Py: 36 520 14

P o: 280 0.13:1:0.09 220 2.3:1:0.17 8 1.75:1:11

Cp: 26 40 88

GjØkåsen Py: 55 500 30

P o: 250 0.22:1:0.14 400 1.2:1:0.25 6 1.87:1:16.6

Cp: 37 100 100

Banken Py: 110 490 27

P o: 330 0.33:1:0.03 100 4.9:1:0.08 9 1.79:1:17.41

Cp: 11 8 148

Gruve 1707 Py: 130 600 14

P o: 336 0.39:1:0.04 110 5.45:1:0.25 6 2.6:1:16.0

Cp: 16 28 96

Gabe Gottes Py: 50 640 16

P o: 200 0.25:1:0.06 270 2.3:1:0.11 6 3:1:15

Cp: 12 30 75

fine-grained pyrite. The ratio of Co:Ni in pyrite from different mines and

prospects ranges from 4.6 to 15 (Table 7), and in pyrrhotite from 0.26 to 1.3.

Of the several elements analysed, Ni, Co and Ag show characteristic pattems

of distribution in individual mineral fractions of coexisting pyrite, pyrrhotite

and chalcopyrite (Table 8). The nature of distribution pattems can be

stated as follows:

Decrease in content of Co from pyrite-pyrrhotite-chalcopyrite. Decrease in content of Ni from pyrrhotite-pyrite-chalcopyrite. Decrease in content of Ag from chalcopyrite-pyrite-pyrrhotite.

The pyrrhotites of the pyrrhotitic ores were also analysed for the trace

elements mentioned above. In these pyrrhotites nickel is always found to be

predominating over cobalt (Table 9) and the ratio of Ni:Co ranges from 1.5 to 6.9. On the other hand the pyrrhotites in the Kaltberget and Olkar ores

show maximum concentrations of nickel. The distribution of all the trace

elements from different mineral fractions from the different mines and

prospects are summarized in Table 10.

DISCUSSION ON THE TEMPERATURE OF FORMA TION AND PRO BABLE GENESIS

The sulphide ore deposits of Kvikne and adjacent mines and prospects form

a part of the massive sulphide deposits of the Caledonides whose origin is

unknown. Moreover, the ores show a variation in chemistry and mineralogy.


Table 9. Distribution of Ni and Co in pyrrhotite of pyrrhotitic ores.

Locality

Storbekken pr. Kojan Ill N. Berstjern M. Berstjern S. Berstjern Odden I Odden pr. Estensvangen I Estensvangen Il Grubeåsen gruve

Ni (ppm)

180 590 280 250 280 400 160 330 290 690

Co (ppm)

120 244 140 130 160 148

90 170

44 230

Ni:Co

1.5 2.4 2.0 1.9 1.7 2.7 1.8 1.9 6.9 3.0

The pyriticjchalcopyritic ores consist mainly of the elements Fe, Cu, Zn, and S. The pyrrhotitic ores on the other hand essentially comprise Fe and S and

are generally devoid of Cu and Zn except for insignificant traces of Cu in certain mines. The ores of Kaltberget and Olkar mines exhibit a different

chemistry in containing Cu, Fe, Ni, and S as their main constituent elements.

It is pertinent to mention here that though the pyriticfchalcopyritic ores are

more akin to the massive pyritic sulphide deposits of the other parts of the Caledonides, the pyrrhotitic ores have no kinship with the typical pyrrhotitic

ores of the Caledonides (Vokes 1962). In fact the nickeliferous ores of

Kaltberget and Olkar form a separate paragenetic group from the s<realled Caledonian massive sulphide deposits.

From the foregoing discussion it is clear that the present area of our work has suffered three major phases of regional deformation. An earlier F 1

fold movement is followed by a late F 2 phase of deformation. The metamorphosed nature of the Caledonian sulphides is a more or less accepted view.

Similarly, evidence of regional metamorphism and deformation are well imprinted (discussed earlier) on the pyriticjchalcopyritic and pyrrhotitic ores

of the present ores. Of these two types the pyriticjchalcopyritic ores at least afford some dues to help interpret the temperature of formation of the ores depending on the mineral assemblage and textures. Presence of exsolved

starlets and skeletal crystals and streaks of sphalerite in chalcopyrite indicate the high temperature of ore formation (Ramdohr 1969) and the common

exsolutio!l of chalcopyrite from sphalerite futher emphasizes that the tem

perature of formation might have been very high initially (550 °C- Borchert

1934, 525 °C - Lyon 1959). In addition to this the existence of inversion

twin lamellae in chalcopyrite which is found to be due to inversion of high

temperature cubic chalcopyrite to low temperature tetragonal phase below

547 ± 5 °C (Kullerud 1966) also supports this high temperature of for

mation of the ores.

The presence of exsolved cubanite lamellae in chalcopyrite points to the

fact that separation took place below 252 °C (Kullerud 1966). Exsolution streaks and blebs of mackinawite within the chalcopyrite are

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also of geothermometric significance. In fact the stability of this mineral is broadly dependent on its Ni and Co content because the stability increases with the increasing substitution of Fe by Ni and Co which is experimentally verified by Clark (1967). He established that the upper stability limit of mackinawite rises from 135 °C ± 5 °C for Fe1 +XS to 200-250 °C for macki

nawite with 8-9 wt.% or more Ni + Co. Considering the Ni and Co con tent of mackinawites of the pyriticfchalcopyritic ores it appears that they have

formed within the temperature range of 135 ± 5° and 250 ± 5 °C.

Summing up these observations it is clear that the main bulk of the hypogene sulphides have formed within the temperature range 550 to 135 °C. It is worth mentioning here that the highest grade of metamorphism attained by the country rocks surrounding these ores corresponds to the staurolitealmandine subfacies of amphibolite facies (Winkler 1967). Moreover, the

maximum temperature of formation of the ores (550 °C) agrees well with the highest temperature generally accepted for staurolite-almandine subfacies.

Due to the metamorphosed nature of the pyriticjchalcopyritic ores its original genesis is very difficult to establish. The variation in grain size of pyrite can be explained by difference in local recrystallization rates. As a consequence of recrystallization there is a marked increase in the content of Co from fine-grained to coarse-grained pyrites (Table 7). On the other hand

the constant prevalence of Co over Ni (Co:Ni ratio ranging from 4.6 to 15) probably points to an epigenetic nature of ore formation (Rankama &

Sahama 1950, Hegemann 1943, Waltham 1969).

The general monomineralic nature of the pyrrhotitic ores and absence of any indicative geothermometer does not help in deciphering its temperature of formation. Like the pyrrhotitic ores of other parts of the Caledonides it does not show any indication of its later age of formation than the adjoining pyriticjchalcopyritic ores. Moreover, the present pyrrhotitic ores show all signs of metamorphism and recrystallization. Its pre- or syntectonic nature is well illustrated by the co-folded and deformed bands of pyrrhotite in the black schists of Odden I and Odden prospects. The metamorphosed character of these ores is also supported by the prevalence of Ni over Co in pyrrhotite (Cambel & Jarkovsky 1966).

The ore minerals of Kaltberget and Olkar mines, which form a different type from the general massive sulphide ores of the Caledonides, do not

show any effect of metamorphism or deformation in spite of the opposite appearance of the gangue. The presence of exsolution textures between pentlandite and pyrrhotite indicates that the pentlandite is formed below 610 °C and round about 550 °C (Kullerud 1963). This implies that the initial temperature of formation of these ores was as high as 550 °C. With gradual cooling of the deposit mackinawite exsolved within chalcopyrite

below 250 °C as is evident from the composition of the mackinawite (Table 5). The close association of these ores with the ultrabasics and exceptionally

high content of Ni in pyrrhotite in contrast to Co probably indicates its magmatic affiliation.


Acknowledgements. - The authors are grateful to Prof. dr. J. A. W. Bugge for his guidance and encouragement during the study. The authors are indebted to Dr. F. J. Langmyhr, Kjemisk Institutt, Universitetet i Oslo for guidance and constant help during the trace element analysis of the ore minerals by atomic absorption. Thankful acknowledgement is due to cand. real. I. J. Rui, E. Rohr-Torp and S. Frodesen for constant help in the field. The financial assistance by the Royal Norwegian Council for Scientific and Industrial Research (NTNF), the Norwegian Agency for International Development (NORAD) and the Mining Industries is also acknowledged.

April 1971

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