Gold Mineralisation in Chigargunta Area of the Kolar Schist Belt, South India- A Part of the Archean Greenstone Belt

Abstract

Gold mineralisation is reported for the first time in ‘Champion gneiss’ (quartzo-feldspathic schist) a felsic unit,in the eastern sector of the Chigargunta area (Lat: 120 430300N, Long:780 150 000E) of the Kolar schist belt, South India, during 1979-80. Quartzo-feldspathic gneiss and hornblende schist are the predominant rock types of the area. These rocks are characterised by a strong pervasive foliation trending N50E –S50W to N200E - S200W with easterly dips of 70-85. In the northern part of the area the rocks are folded with the foliation which is axial planar. Lower to middle amphibolite facies metamorphism is widespread in the area. Gold mineralisation is localised along shear zones which are ductile to brittle in nature. These zones are parallel to subparallel to the trend of foliation in the host rock and are characterized by strong mylonitic fabric, profuse quartz venation and hydrothermal alteration. Pyrite and pyrrhotite are the dominant sulphides. Gold occurs in native form. This felsic hosted gold mineralisation termed as E-2 lode (for exploration purpose) is estimated to contain a reserve of 3.13 million tonnes averaging 4.7 g/t gold. Besides, this lode there are several loads ( E-1,E-3, etc) occur within mafic units as well as in felsic unit adjacent to E-2 lode with different reserves, within the schist belt. Epigenetic gold mineralisation shows a close temporal and spatial relationship to late Archean (2700-2500 m.y) crustal accretion, stabilisation and granulite formation in the South Indian Shield. The present work delineate, the nature of mineralization in felsic unitwithin the schist belt which was not considered as source rock of gold mineralization during the period and left untouched until the present work