Podiform Chromitites and PGE Mineralization in the Ulan-Sar’dag Ophiolite (East Sayan, Russia)

Abstract

In this paper, we present the first detailed study on the chromitites and platinum-group element mineralization (PGM) of the Ulan-Sar’dag ophiolite (USO), located in the Central Asian Fold Belt (East Sayan). Three groups of chrome spinels, differing in their chemical features and physical–chemical parameters, under equilibrium conditions of the mantle mineral association, have been distinguished. The temperature and log oxygen fugacity values are, for the chrome spinels I, from 820 to 920 °C and from (−0.7) to (−1.5); for chrome spinels II, 891 to 1003 °C and (−1.1) to (−4.4); and for chrome spinels III, 738 to 846 °C and (−1.1) to (−4.4), respectively. Chrome spinels I were formed through the interaction of peridotites with mid-ocean ridge basalt (MORB)-type melts, and chrome spinels II were formed through the interaction of peridotites with boninite melts. Chrome spinels III were probably formed through the interaction of andesitic melts with rocks of an overlying mantle wedge. Chromitites demonstrate the fractionated form of the distribution of the platinum-group elements (PGE), which indicates a high degree of partial melting at 20–24% of the mantle source. Two assemblages of PGM have been distinguished: The primary PGE assemblage of Os-Ir-Ru alloys-I, (Os,Ru)S2, and IrAsS, and the secondary PGM assemblage of Os-Ir-Ru alloys-II, Os0, Ru0, RuS2, OsS2, IrAsS, RhNiAs with Ni, Fe, and Cu sulfides. The formation of the secondary phases of PGE occurred upon exposure to a reduced fluid, with a temperature range of 300–700 °C, log sulfur fugacity of (−20), and pressure of 0.5 kbar. We have proposed a scheme for the sequence of the formation and transformation of the PGMs at various stages of the evolution of the Ulan-Sar’dag ophiolite.

Platinum Group Elements in Geosphere and Anthroposphere: Interplay among the Global Reserves, Urban Ores, Markets and Circular Economy

“…Nowadays, various industry sectors require Pt, Pd, and Rh primarily, and these elements are most often found at the unique Bushveld Complex in South Africa, followed by Norilsk deposits in Russia and Stillwater in the USA [1,6,13,14] as highlighted in Figure 1. Mineralogy and genetic aspects of similar related podiform chromitites in the East Sayan ophiolite massif are described recently [15,16]. The concentration of all PGEs is at least 10,000 times higher in sulfide melts of magmas than elsewhere [17,18], meaning that specific geological areas determine the geographical location of mining and extraction.…”

Nd-Sr Isotopic Study of Magmatic Rocks and 40Ar/39Ar Dating of the Mafic Dike of the Proterozoic Ulan-Sar’dag Ophiolite Mélange (Southern Siberia, East Sayan, Middle Belt, Russia)

“…It occurs as an ophiolitic mélange, composed of various structurally mixed different ages, origins, lithostratigraphic units. These units are represented by ophiolitic altered ultramafic-mafic rocks with podiform chromitites, foliated serpentinites, deep sea sedimentary cherts, shaled volcanic-sedimentary (Ilchir suite) rocks with MORB, island-arc and OIB-like geochemical affinities, mafic dikes, and limestones (Irkut suite) (Figures 3 and 4) [24][25][26]. The volcanic-sedimentary slice is composed of two units: lower-metavolcanic unit and upper-black, black-quartz-carbonate schists and marbles.…”

“…Generally, geochemical signatures for the magmatic rocks associated with Eastern Sayan ophiolites reveal a wide compositional series: mid-ocean ridge basalt (MORB)-type basalts (tholeiites), boninites, island-arc andesites and dacites, and ocean island basalt (OIB)-type basite rocks. There are numerous isotopic data of the island arc assemblage and ophiolites in a different segment of CAOB, but isotope geochemical data of Proterozoic Eastern Sayan ophiolites are limited [4,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. [35,36].…”

Metallic-Mineral Prospecting Using Integrated Geophysical and Geochemical Techniques: A Case Study from the Bela Ophiolitic Complex, Baluchistan, Pakistan

“…The Ophiolites play an important role in understanding plate tectonics, ocean floor composition, and earth evolution [1][2][3]. The ophiolite sequence constitutes exhumed oceanic lithosphere that contributes to economic mineralization [4][5][6]. The sequence offers promising prospects for metalliferous mineral enrichment, such as Fe, Cu, Au, Ag, Cu, Pb, Zn, Ni, and Cr [7][8][9][10].…”