کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4702703 1638066 2012 20 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Gold and copper in volatile saturated mafic to intermediate magmas: Solubilities, partitioning, and implications for ore deposit formation
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
Gold and copper in volatile saturated mafic to intermediate magmas: Solubilities, partitioning, and implications for ore deposit formation
چکیده انگلیسی

The solubility of Au and Cu in hydrous andesite melts was determined at 1000 °C and 200 MPa. The data show that the solubility of Au is highly influenced by reduced S (S2−), and to a lesser degree, by the Cl concentration in the melt. Other melt compositional parameters such as K2O/Na2O ratio, or FeO concentration have no significant effect. The simultaneous presence of S2− and high concentrations of Cl (0.7–1.3 wt.%) yield Au solubilities higher than expected from separate contributions of Au-sulfide and Au-chloride species. The strong effect of S and Cl on Au solubilities suggests dissolution mechanisms similar to those observed in magmatic volatiles. The most likely dominant dissolved species are AuSH or AuS(K/Na) in sulfur-bearing, and AuCl in Cl-bearing, S-free systems. At the S2−/S6+ transition (∼NNO+0.2), the solubility of Au sharply drops by a factor of 5. Copper shows markedly different behavior from that of Au; its solubility is influenced only slightly by the presence of S and Cl in the melt. This shows that the dominant Cu species is CuO0.5, with the exception of melts with unrealistically high Cl concentrations for natural systems, where Cu-chloride complexes become significant. Calculated volatile/melt partition coefficients of Au based on solubility data in melts and volatiles reach values up to ∼200 in a pyrrhotite saturated high-K calc-alkaline andesite melt below NNO+0.5, but sharply drop by an order of magnitude at the H2S to SO2 transition in the volatile phase. The predicted volatile/melt partition coefficients of Cu are much lower and vary in a narrow range (0.5–2). Consequently, volatiles released from mafic to intermediate magmas below NNO+1 may be important for the formation of magmatic-hydrothermal Au deposits and will favor high Au/Cu ratios in the overlying hydrothermal systems.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Geochimica et Cosmochimica Acta - Volume 91, 15 August 2012, Pages 140–159
نویسندگان
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