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Natarajan, W. K.
- Tectonically-Controlled Gold Mineralisation in Chigargunta Area, South Kolar Schist Belt, Chittoor District, Andhra Pradesh
Authors
1 Geological Survey of India, Southern Region, Bangalore 560011, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 27, No 6 (1986), Pagination: 517-526Abstract
Several parallel to sub-parallel auriferous mineralised zones of economic significance occur over a strike length of 3 km and spread over a width of about 1 km in 'Chigargunta area of South Kolar schist belt. The host rocks for mineralisation are metamorphosed basalt and acid tuff ('Champion gneiss'). The mineralised zones represent ductile shear zones transecting the regional north-south trending schistosity (S2) at low angle. The pre-existing planar and linear fabrics of the rocks have been rotated into parallelism with the shear zone. The shear zones display mylonitic foliation with prominent downdip lineation, folds of variable orientation, boudinaging and crenulations. Such deformation features are confined only to these strongly tectonised zones believed to have evolved by simple shear deformation. A progressive grain size reduction accompanied by hydrothermal retrogressive metamorphism of the amphibolite facies host rocks culminates laterally into the centre of the mineralised zones with lower grade greenschist assemblage. Nondilatant pegmatite veins and some high temperature alteration minerals indicate possible strain heating. The auriferous lodes occurring in Kolar Gold Field might have a simiiar tectonic evolution.
- A Note on the Auriferous Banded Iron-Formation of Kolar Schist Belt
Authors
1 71, Dacosta Square, 3rd Cross, Bangalore 560084, IN
2 45, Bannergatta Road Layout Extension, Bangalore 560041, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 28, No 2&3 (1986), Pagination: 218-222Abstract
Banded Iron-Formation (BIF) comprising quartz, pyrrhotite/grunerite-actinolite and quartz, magnetitejgrunerite-actinolite occurs widely in Kolar schist belt as narrow (0.5 rom to few tens of metres wide) interbeds within the metamorphosed basic volcanic and acid volcanogenic rocks (' Champion gneiss '). All gradations between these two end members render the BIF bands heterogeneous in composition. The sulphidic BIF horizons occurring near the western margin of the schist belt in association with pillowed metabasaJts are persistent along strike for several kiJometres and are auriferous at places. The BIF horizons occurring towards the eastern margin of the schist belt are narrower) impersistent in strike and are not known to contain gold mineralization.
Two types of mineralization have been recognised in BIF. In sulphide facies BIF, native gold occurs in arsenopyrite which along with pyrrhotite and amphiboles form massive layers alternating with quartz. Here the auriferous sulphide layers are primary, subsequently modified by metamorphism and deformation. In the second type, gold mineralization is confined to syntectonic quartz veins in the sulphidic BIF. A volcanogenic model for the precipitation of auriferous BIF is favoured.
- Economic Potentiality of New Gold Mineralisation in South Kolar Schist Belt
Authors
1 Geological Survey of India, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 29, No 2 (1987), Pagination: 230-239Abstract
Auriferous zones are confined to ductile shear zones in the mafic unit (metabasalt/metagabbro) as well as in the felsic unit ('Champion gneiss'). The occurrence of significant gold mineralisation in the' Champion gneiss' comprising quartzo-feldspathic schist is being reported for the first time.
Low grade (about 4 grammes per tonne) gold reserve of the order of 4.7 million tonnes under all categories (probable+possible) in the new prospect has been established.