SULPHIDE MINERALISATION IN CRYSTALLINE LIMESTONES AND GRANITIC ROCKS OF SANKARIDURGAM, TAMIL NADU

摘要

Specks of pyrile, pyrrhotite, chalcopyrite, chacocite, bornile, covellite, galena, sphalerite, molybdenite and, native copper, stains and films of malachite and azurite are found in crystalline limestones and granitic gneisses occurring in and around the village of Sankaridurgam, Erode District, Tamil Nadu. Sulphide mineralisation is restricted to only along foliation, cleavage and joint planes present at the contacts of mafic and felsic layers in almost all the rocks occurring in this area (11 deg 27 min-11 deg 21 min N & 77 deg 44 min-77 deg 56 min E). Molybdenite, graphite, apatite, beryl, topaz, tourmaline, biotite and muscovite-bearing pegmatites are also very common in this area. Formation of scapolite, vesuvianite, wollasionite and the effects of silicification and migmatisation reveal that volatiles played a critical role in the evolution of the granitic terrain. Liquid CO_2- and brine solutions-bearing fluid inclusions were reported from this area (Holland. 1900; Ramasamy, 1982a). The host rocks and their water extracts are respectively enriched with chalcophile elements and F contents (Tables 1 & 2). The paper explores the causes of enrichment of fluorides with sulphide mineralisation.