Reprint of Silicate-sulfide liquid immiscibility in modern arc basalt (Tolbachik volcano, Kamchatka): Part II. Composition, liquidus assemblage and fractionation of the silicate melt

Abstract In this contribution, we analyze 30 years of mine development data and quantitatively identify the processes that control the grade and tenor of the mineralized rock. An assay database of more than 60,000 samples was used to examine variations in ore grade and tenor of the sulfide mineralization in the J-M reef horizon of the Stillwater Complex along the strike and down the dip of the deposit in the area of the Stillwater mine. We compare these results with data from the East Boulder mine and whole-rock lithogeochemistry of samples collected along the entire strike length of the complex. We find significant variation in the composition of the reef sulfides in different spatial domains of the Stillwater mine area and between the Stillwater and East Boulder mines. Most of the variation in the grade and tenor can be explained by a variation in the mass of silicate magma with which the sulfide liquid equilibrated (i.e., R factor); however, geochemical and textural evidence suggests that parts of the reef may have experienced significant S loss following initial sulfide melt segregation. Some variability in the reef tenor and grade can be attributed to variable amounts of sulfur loss due to low-temperature hydrothermal fluids and the overestimation or underestimation of metal concentrations in reef assays due to the nugget effect. Furthermore, we address the Pd/Pt ratio of the reef samples and suggest that the lower solubility of Pt in the parental silicate melt may have caused the crystallization and removal of Pt alloys at some point before the melt reached sulfide saturation and Pt could partition into the sulfide liquid. This disparity between the prior evolution of Pt and Pd in the silicate melt resulted in the observed Pd/Pt ratio of ~3.65 across all areas of the reef—a value significantly larger than anticipated for primitive mantle-derived magmas.

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Silicate melt removal and sulfide liquid retention in ultramafic rocks of the Duke Island Complex, Southeastern Alaska

Mineralogy and Petrology ◽

10.1007/s00710-014-0321-y ◽

2014 ◽

Vol 108 (5) ◽

pp. 727-740 ◽

Cited By ~ 2

Author(s):

Eric C. Stifter ◽

Edward M. Ripley ◽

Chusi Li

Keyword(s):

Silicate Melt ◽

Ultramafic Rocks ◽

Sulfide Liquid ◽

Liquid Retention ◽

Duke Island

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Liquid immiscibility and problems of ore genesis (according to experimental data)

Петрология ◽

10.31857/s0869-5903275577-597 ◽

2019 ◽

Vol 27 (5) ◽

pp. 577-597

Author(s):

Yu. B. Shapovalov ◽

A. R. Kotelnikov ◽

I. N. Suk ◽

V. S. Korzhinskaya ◽

Z. A. Kotelnikova

Keyword(s):

Partition Coefficients ◽

Liquid Immiscibility ◽

Ore Deposits ◽

Silicate Melt ◽

Distribution Of Elements ◽

Ore Minerals ◽

Silicate Liquids ◽

L1 And L2 ◽

Salt Systems ◽

Alkaline Fluid

The results of an experimental study of phase relations and distribution of elements in silicate melt–salt systems (carbonate, phosphate, fluoride, chloride) melt, silicate melt I–silicate melt II, and also in fluid – magmatic systems in the presence of alkali metal fluorides are presented. Salt extraction of a number of ore elements (Y, REE, Sr, Ba, Ti, Nb, Zr, Ta, W, Mo, Pb) was studied in liquid immiscibility processes in a wide temperature range of 800–1250°С and pressure of 1–5.5 kbar. It is shown that the partition coefficients are sufficient for the concentration of ore elements in the quantity necessary for the genesis of ore deposits. In the fluid-saturated melt of trachyrhyolite, the separation into two silicate liquids has been determined. The partition coefficients of a number of elements (Sr, La, Nb, Fe, Cr, Mo, K, Rb, Cs) between phases L1 and L2 has been obtained. The interaction processes of a heterophase fluid in the granite (quartz)–ore mineral–heterophase fluid (Li, Na, K-fluoride) system were studied at 650–850°C and P = 1 kbar. The formation of the phase of a highly alkaline fluid–saturated silicate melt – Ta and Nb concentrator is shown as a result of the reaction of the fluid with the rock and ore minerals.

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Fe-carbide and Fe-sulfide liquid immiscibility in IAB meteorite, Campo del Cielo: Implications for iron meteorite chemistry and planetesimal core compositions

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2013.04.024 ◽

2013 ◽

Vol 117 ◽

pp. 80-98 ◽

Cited By ~ 8

Author(s):

Andrew G. Tomkins ◽

Eleanor R. Mare ◽

Massimo Raveggi

Keyword(s):

Liquid Immiscibility ◽

Iron Meteorite ◽

Sulfide Liquid

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Liquid Immiscibility in a Silicate Melt

Nature ◽

10.1038/176305a0 ◽

1955 ◽

Vol 176 (4476) ◽

pp. 305-305 ◽

Cited By ~ 5

Author(s):

W. A. CASSIDY ◽

E. R. SEGNIT

Keyword(s):

Liquid Immiscibility ◽

Silicate Melt

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Origin of noble-metal nuggets in sulfide-saturated arc magmas: A case study of olivine-hosted sulfide melt inclusions from the Tolbachik volcano (Kamchatka, Russia)

Geology ◽

10.1130/g47086.1 ◽

2020 ◽

Vol 48 (6) ◽

pp. 620-624

Author(s):

Vadim S. Kamenetsky ◽

Michael Zelenski

Keyword(s):

Noble Metals ◽

Melt Inclusions ◽

Basaltic Magma ◽

Sulfide Liquid ◽

Direct Crystallization ◽

Arc Magmas ◽

Tolbachik Volcano ◽

Sulfide Melt ◽

Significant Uptake

Abstract Minerals that contain platinum-group elements (PGEs) and occur in some magmatic Cu-Ni sulfide deposits have been ascribed to crystallization from an originally PGE-rich sulfide liquid. The occurrence of PGE-bearing minerals (PGMs) in some sulfide-undersaturated primitive melts has been envisaged and recently reported, whereas direct crystallization of PGMs in sulfide-saturated silicate magmas is seemingly hindered by strong partitioning of PGE into immiscible sulfide melts. In this study, we discovered abundant nanoparticles containing noble metals in association with sulfide melt inclusions entrapped inside primitive olivine phenocrysts (Fo85–92) from the recent basaltic magma of the Tolbachik volcano (Kamchatka arc, Russia). These nuggets occur in swarms on the surface of the sulfide globules and are represented by native metals, sulfides, and alloys of Pd, Pt, Au, Pb, and Bi. The nuggets on different globules can be either Pd- or Pt-rich nuggets, and the compositions are highly variable, even among adjacent nuggets. We argue that the diffusive supply of Pd from the external nuggets can be responsible for significant uptake of Pd (up to 2 wt%) in the sulfide melt. We consider direct crystallization of PGMs in a primitive basaltic melt undergoing sulfide unmixing, and possibly sulfide breakdown due to oxidation, as another mechanism additional to their “classic” origin from the PGE-rich sulfide melt in response to solidification.

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