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Kolar Gold Field |
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India |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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The Kolar Gold Field lies within a schist belt of the Archaean Dharwar Craton in Karnataka State, southern India (#Location; 12° 57' 31"N, 78° 15' 57"E).
The Kolar Schist Belt occuppies a north-south elongated area some 80 km long and 2 to 4 km in width in the eastern block of the Dharwar Craton. It encloses an Archaean succession of volcanic dominated rocks composed mainly of 2.7 Ma mafic (komatiitic and lesser tholeiitic) metavolcanics, now represented by amphibolites. A well foliated felsic unit is found along the eastern part of the belt with local xenoliths of granitoids, amphibolites and banded iron formation. Banded iron formations are the only recognisable sedimentary components of the belt, and form prominent ridges within the schist belt, interbanded with amphibolites, and graphitic and sulphidic schists.
The belt is enclosed on both sides by foliated and sheared granitoids with tectonic contacts. On the western side monzodioritic to granitic intrusives are 2630 to 2550 Ma in age, although some 3100 Ma granitic crust is also indicated. The eastern granitoids are 2530 Ma granodioritic gneisses.
Two types of gold deposit are recognised in the Kolar gold field, i). Gold-quartz-sulphide lodes, and ii). gold quartz-calcite vein systems. These deposit types are associated with all of the rock types in the schist belt. The latter accounted for 90% of the gold production of the field.
Lodes are generally disposed parallel to the north-south trending foliation of the amphibolites and are localised within the fine grained schistose varieties of the amphibolites.
The quartz lodes, the best example of which is the 10 km long Champion reef, which comprises parallel and en echelon veins of quartz within sheared, schistose amphibolites. The lode zones and individual veins pinch and swell both along strike and down dip and have gradational margins with the enclosing country rocks. These reefs are typically around 2 m thick except where thickened by folding.
The sulphide lodes, the best example of which is the 2 km long and 1.6 m wide Oriental lode, which consist of alternating bands and layers of quartz, sulphides and silicates which have sharp contacts with the enclosing amphibolites and are associated with magnetite bearing ironstone and argillaceous sulphidic rocks.
The Kolar gold field has been systematically worked for over 200 years and has produced around 700 t of gold.
Operations in the Kolar Gold Field were closed in 2001, having produced >800 t of gold during its 120 year history of mining (Geological Survey of India). Over it's first two decades of operation from 1884 to 1904, ore produced from shallow underground working averaged 45 g/t Au, whilst over its total life, the average ore grade was 15 g/t Au. Gold has primarily been extracted from three main mines within the East Kolar region: Champion, Mysore and Nundydoorg. By the late 1990s, however, mining had become uneconomic due to declining grades and increasing costs, and operations were finally abandoned in 2001. By this time production had reportedly reached a depth of 3200 m, whilst workings stretched over a 7.3 km strike and included 100 shafts and 1400 km of underground development.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1988.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Kolar Gold Field
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Mishra B, Panigrahi M K 1999 - Fluid evolution in the Kolar Gold Field: evidence from fluid inclusion studies : in Mineralium Deposita v34 pp 173-181
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Siddaiah N S, Hanson G N, Rajamani V 1994 - Rare earth element evidence for syngenetic origin of an Archean stratiform Gold Sulfide deposit, Kolar Schist belt, South India: in Econ. Geol. v89 pp 1152-1566
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Siddaiah N S, Rajamani V 1989 - The geologic setting, mineralogy, geochemistry, and genesis of Gold deposits of the Archean Kolar Schist Belt, India: in Econ. Geol. v84 pp 2155-2172
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