Barite-rich massive sulfides from the Semenov-1 hydrothermal field (Mid-Atlantic Ridge, 13°30.87′ N): Evidence for phase separation and magmatic input

摘要: Abstract The ultramafic-hosted Semenov-1 hydrothermal field is a part of the Semenov group sulfide deposits located at 13°30′ N Mid-Atlantic Ridge. comprise fine-crystalline, colloform, nodular, and banded barite–marcasite–pyrite assemblages, which are result moderately- to low-temperature venting (Fe, Ba)-rich fluids. precipitates contain low concentrations Cu (0.02–0.55 wt.%) Zn (0.01–0.08 wt.%), variable Au content (0.35–4.76 ppm). Fe-disulfides relatively enriched in typical trace elements (As, Ag, Pb, Mn, Tl). most higher earliest, fine-grained decrease late coarse-crystalline pyrite. Based on fluid inclusion data, barite precipitated from (244–83°С), low-salinity (0.6–3.8 wt.% NaCl eq.), carbonate–sulfate–aqueous fluids, incorporated low-density component produced by phase separation. presence CO 2 SO inclusions barite, as revealed Raman spectroscopy, may indicate magmatic volatile contribution fluid. main amount marcasite pyrite was formed temperatures below 240°С, after precipitation barite. occurrence isocubanite, chalcopyrite pyrrhotite station 292 indicates later high-temperature (~ 300°С) overprint. sulfur isotopic composition (+ 21.0 + 21.3‰) closely matches that seawater. sulfides 186 (− 3.26 − 0.08‰) suggests possible light reduced derived disproportionation or leaching basalt has degassed . δ 34 S values (− 0.08 + 1.53‰) reflect heavy seawater sulfate. Although considered be associated with serpentinized ultramafic rocks (Beltenev et al., 2007), mineralogical precipitates, particularly, their high contents, more EMORB-hosted seafloor (e.g., Lucky Strike Menez Gwen fields). Thermodynamic modeling fluid–rock systems using flow reactor model demonstrates basalt–seawater interaction generates fluids can produce only minor amounts irrespective Ba basalt. Addition gas system produces highly acidic capable extract larger Fe, form mineral assemblages similar studied ones. In contrast, between rock (peridotite) seawater, without gas, results barite-free assemblages. above do not support an signature for suggest mafic control composition.