Abstract

Tosham igneous complex occurs along northern part of the middle Proterozoic North Delhi fold Belt and metasediments of Delhi Supergroup. It comprises of Tosham porphyritic granite, rhyolite and quartz-porphyry. The Tosham granite and rhyolite hosts the tin-tungsten and copper mineralisation. Cassiterite and Wolframite occurs within the quartz veins and associated with other ore minerals such as chalcopyrite, pyrrhotite and pyrite. The foliation trend of the metasediments is N20° to 40°E parallel to the long axis of the hill. The mineralisation occurs near the granite-metasediments or granite-rhyolite contact in the western and eastern mineralised zones within Tosham hill. EPMA studies confirm the presence of cassiterite, pyrite, chalcopyrite, pyrrhotite, sphalerite etc. The fluid inclusions study reveals the existence of aqueous-gaseous (H2O-CO2+NaCl) fluid that underwent phase separation and gave rise to gaseous (CO2) inclusion. The carbonic inclusions show depression in Tmco2 (-65.2°C) due to the presence CH4 with CO2 and also large no. of CH4 inclusions are present and were confirmed by Raman spectroscopy and it was first time reporting in this area. The abundant of CH4 inclusions over the CO2 inclusions considered to be one of the diagnostic features of reduced porphyry copper type deposits. The salinity of tin/ tungsten mineralisation shows high to low (1.9 to 42.68 wt % NaCl equivalents) and trapped at the estimate PT range from 2.1 to 3.5 kbar and 310 to 460ºC. The eutectic temperature (Te) ranges from -50°C to -30°C reveals that the presence of chloride complexes such as FeCl2/MgCl2 and CaCl2 indicating the involvement of brines or complicated chloride mixtures in transporting Sn-W to the fluid system and evaluation of Sn-W ore fluids by high-salinity and high-temperature with the magmatic-hydrothermal activity either by immiscibility or mixing of fluids and evolution of granite/rhyolite induced the fluidisation and the presence of CH4/CO2 influx might have triggered precipitation Sn-W and Cu mineralisation in the area.