Effects of fluid boiling on Au and volatile element enrichment in submarine arc-related hydrothermal systems

Shallow (<1500 mbsl) submarine arc-related hydrothermal systems can host base (Cu), precious (Au) and volatile elements (As, Se, Sb, Te, Tl) in significant quantities. Their wide application the high-tech industry, but a potential eco-toxicological footprint gives them strategic importance. However, processes that concentrate these systems, compared to their mid-ocean ridge counterparts are still debated, it is unclear whether boiling-related and/or contribution of magmatic volatiles key for enrichment. We present bulk sulfide-sulfate, isotope (S Pb), high-resolution microanalytical data sulfides from Niua South fore-arc volcano north Tonga, where numerous black-smoker type sulfide-sulfate chimneys emit boiling fluids with temperatures (up 325 °C) near seawater curve at ~1170 m water depth. Hence, this system represents an ideal natural laboratory investigate effect fluid on base, precious, element enrichment associated seafloor mineralization. At South, textural chemical variations multiple pyrite (framboidal, euhedral massive), chalcopyrite (linings), sphalerite (dendrites linings) generations indicative sulfide precipitation early low-temperature (~240 underwent abundant mixing ambient (low Se/Tl Co/Ni ratios pyrite) later high-temperature (high pyrite). In addition, crustiform inclusion-rich precipitated shows low Bi/Pb, Tl/Pb Sb/Pb due loss (e.g., Tl Sb) vapor phase formed during temperature stage. By contrast, late (~280 enriched affinity Cl-complexes like Mn, Co, Ni, Ga, Cd, In, Sn, therefore corresponding Cl-rich liquid phase. Gold occurs solid-solution as boiling-induced particles native Au, electrum, Au-rich Bi-tellurides 144 ppm Au), 60 37 Au). These (<5–10 µm) probably causing extreme Au (>30 ppm) mature stage chimney formation. Lead indicate scavenged metals not only deeper basement reaction zone (20–40%), also young dacitic volcanic rocks upflow (60–80%). Sulfur (?34S = ?0.3 4.4‰) Se/S*106 values (<1500) provide no evidence influx S, most semi-metals were likely leached rocks. Tl), enrichments be decoupled instead result trace fractionation – process, which has been underestimated date.