Light Stable Isotopes in Volcanic-Hosted Massive Sulfide Ore Systems

Abstract Volcanic-hosted massive sulfide (VHMS) deposits, the ancient analogues of “black smoker” deposits that currently form on seafloor, are products complex mineral systems involving interaction seawater with underlying volcanic pile and associated magmatic intrusions. Light stable isotopes, particularly those oxygen, hydrogen sulfur, have had a strong influence in determining sources ore fluids sulfur as well elucidating geological processes important VHMS systems. Oxygen isotope data indicate evolved was dominant ore-forming fluid through time, although small proportion including high sulfidation tin-rich may significant, or dominant, magmatic-hydrothermal component. Higher-temperature (> 200 °C) alters rock below producing δ 18 O depletion anomalies at deposit district scales can be used vector to ore. In contrast, lower-temperature hydrothermal alteration results O-enriched zones commonly cap mineralized positions. An apparent decrease degree temperature time relate increasing importance felsic-dominated host successions younger deposits. potential an exploration tool, contributed directly discovery. The other contribution isotopes understanding system is quantification sources. Conventional 34 S data, when combined Δ 33 acquired using recently developed technologies, source igneous either leached from introduced volatile (these not distinguishable). thermochemical reduction sulfate also important, but subordinate, source. Estimation age that, average, it has increased 5–10% Archean 20–25% Phanerozoic. This most likely reflects increase contents time. Although untested variations utility discriminating fertile barren accumulations providing vectors ores scale. As tools, light suffer relatively cost slow turn-around If these limitations overcome, new analytical methods developed, emerge another tool for exploration, discoveries made greater depth under cover.