Chlorite thermometry and fluid inclusion studies on vein-type Tintini copper deposit, Eastern Dharwar Craton, India: Ore genetic implications

Abstract

The Archaean Dharwar Craton was intruded by mafic dyke swarms during early Paleoproterozoic and some of the E-W trending dykes show evidence of copper mineralisation. In the present study, we have conducted detailed mineralogical, fluid inclusion and C-O isotopic study of the Tintini copper deposit (TCD), which is hosted by a mafic dyke (ca. 2.21 Ga) in the Yelagatti granitoid near the Hutti-Maski greenstone belt. The main copper mineralisation is hosted in steeply dipping quartz-calcite veins that cut across N85°E trending diabase dyke. The TCD shows a typically zoned alteration pattern akin to magmatic-hydrothermal deposits, with a narrow potassic alteration zone at the centre and a peripheral wide propylitic alteration halo. Formation of hydrothermal K-feldspar and amphiboles indicate high temperature (>450 °C) of alteration during potassic alteration stage. The proximal central alteration zone was affected by later pulses of cooler fluids that caused extensive propylitisation of the early potassic alteration assemblage. Geothermometry based on mineral chemistry of hydrothermal chlorites (type-I trioctahedral) of propylitic stage show 260–300 °C temperature of formation. The main sulfide ores were precipitated during a later stage after propylitisation, at a temperature (180–200 °C), much lower than the formation temperature of the early chlorite (260–300 °C). The pressure of emplacement of ores is calculated as 1.2–2 kbar. It is inferred that copper was carried as aqueous chloride complex and that ore precipitation took place because of change in fluid pH due to fluid-rock interaction. The δ13Cfluid(VPDB) (–6.38 to –6.03‰) and δ34SH2S(VCDT) (1.0 to 3.7‰) compositions of hydrothermal fluid are consistent with a magmatic source for the hydrothermal fluid. The alteration assemblage and sulfide mineralisation of TCD show evolution and cooling of hydrothermal system from high temperature (>450 °C) potassic alteration stage, to intermediate temperature (260–300 °C) chlorite stage, to low temperature (180–200 °C) main sulfide stage. The oxygen fugacity of ambient fluid shows wide variation. TCD can be classified as intrusion related, fracture-controlled, vein-type epithermal deposit.