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Title

District-scale fluid evolution in the Main Stage veins at Butte, Montana

Authors
Dilles, John H.
Rusk, Brian G.
Published in Porphyry systems and epithermal deposits. 2013, p. 849-852
Abstract To constrain the fluid evolution in the polymetallic Main Stage (MS) veins at Butte, USA, we present microthermometric measurements of fluid inclusions assemblages (FIAs) in co-genetic ore and gangue minerals through the different mineralization stages. Early quartz-hosted FIAs indicate the highest homogenization temperatures (Th, between 290° and 320 °C) with salinity similar to the intermediate density FI of the pre-Main Stage (4 to 6 wt. % NaCl equiv). During the Cu-rich mineralization stage, a drop in salinity to 2 wt.% NaCl equiv. at temperature ~280°C, precedes locally developed phase separation, witnessed by coexisting vapor-rich and liquid-rich FI with similar Th but with higher salinity (2.5 to 7 wt.% NaCl equiv.). Primary FIAs in sphalerite and rhodochrosite from the late mineralization stage indicate fluid temperature (Th~210°C) and salinity (1.7 to 4 wt.% NaCl equiv.) decrease through time, towards the periphery of the district. This study suggests that mixing of a high-temperature fluid with salinity similar to fluids from the pre-Main Stage quartz-pyrite veins with cooler and lower salinity fluids (potentially of meteoric origin) combined with local boiling processes are responsible of the ore precipitation in the MS veins.
Keywords Fluid inclusionsEnargiteSphaleriteEpithermal polymetallic veinsButte
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Structures
Research group Mineral Resources and Geofluids
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ORTELLI, Mélissa et al. District-scale fluid evolution in the Main Stage veins at Butte, Montana. In: Porphyry systems and epithermal deposits. [s.l.] : [s.n.], 2013. p. 849-852. https://archive-ouverte.unige.ch/unige:76242

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Deposited on : 2015-10-19

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