Platinum-group elements and gold in sulfide melts from modern arc basalt (Tolbachik volcano, Kamchatka)

• Published in: Lithos
• Main Authors: Zelenski, M, Kamenetsky, VS, Mavrogenes, JA, Danyushevsky, LV, Matveev, D, Gurenko, AA
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science Bv 2017
• Subjects: Earth Sciences; Geology; Igneous and Metamorphic Petrology; Norilsk; Tolbachik; Kamchatka; norilsk
• Online Access: https://doi.org/10.1016/j.lithos.2017.08.012; http://ecite.utas.edu.au/121102

Sulfide melt inclusions entrapped in primitive olivine phenocrysts can be used to understand the compositions of early sulfide melts that may ultimately contribute to magmatic sulfide ore deposits. Sulfide globules hosted in olivine (8692 mol% Fo) from the Tolbachik basalt (the 1941 eruption) are characterized in terms of their major and trace element abundances using electron microscopy and LAICPMS analysis. Distribution of major elements within individual sulfide globules varies from homogeneous to heterogeneous. Phases include monosulfide solid solution (MSS) and intermediate solid solution (ISS) intergrowths and exsolved low-temperature minerals such as pyrrhotite, pentlandite, chalcopyrite and cubanite. Trace elements (platinum-group elements PGE, Ag, Te, Au, Pb and Bi) are also present in solid solution in sulfide phases and as micron-sized particles (nuggets). Such nuggets of dominantly Au, Pt, AuPd and PdTe are contained randomly within sulfide matrices or, more commonly, at phase boundaries. Nuggets are also attached to outer surfaces of sulfide globules. Concentrations of PGE in sulfides follow a log normal distribution over four orders of magnitude. The highest measured noble metal concentrations in the analyzed globules (436 ppm Au + PGE) are 13.3 ppm Au, 115 ppm Pt and 299 ppm Pd, whereas 40% of globules have b15 ppm of noble metals. Gold and PGE concentrations correlate, suggesting these elements were concentrated by the same process(es). We propose that a number of anomalous concentrations of one or several noble metals in the analyzed globules can be best explained by entrapment of AuPGE-rich particles (solid or liquid) fromthe silicate melt. Although the individual Tolbachik sulfide globules have variable PGE abundances, their mean composition resembles those of major PGE-sulfide ore deposits (e.g., Norilsk, Sudbury, Platreef and Merensky Reef).