Sulfur isotope geochemistry of the supergiant Xikuangshan Sb deposit, central Hunan, China: Constraints on sources of ore constituents

Abstract

The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ34S values (+5 ∼ +8 ‰) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ34S value (+7.5 ‰) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 ‰). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ34S values for early main-stage stibnite (+3.5 to +16.3 ‰, av. +7.5 ‰) compared to that for late main-stage stibnite (+5.3 to +8.1 ‰, av. +6.2 ‰) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ34Spyrite values at ca. +11 ∼ +24 ‰ and -7.0 ∼ -11 ‰. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids.