Petrology, Geochemistry, and the Origin of Sulfide-Bearing and PGe-mineralized Troctolites from the Konnikov Zone in the Yoko-Dovyren Layered Intrusion
| Autor: | Vasiliy O. Yapaskurt, S. N. Sobolev, Leonid V. Danyushevsky, G. S. Nikolaev, I. V. Pshenitsyn, Marco L. Fiorentini, E. V. Kislov, Alexey A. Ariskin |
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| Rok vydání: | 2020 |
| Předmět: |
chemistry.chemical_classification
010504 meteorology & atmospheric sciences Sulfide Geochemistry chemistry.chemical_element Geology 010502 geochemistry & geophysics 01 natural sciences Copper Mineralization (biology) Sulfur law.invention Chalcogen Geophysics Layered intrusion chemistry law Crystallization 0105 earth and related environmental sciences Solid solution |
| Zdroj: | Russian Geology and Geophysics. 61:611-633 |
| ISSN: | 1068-7971 |
| DOI: | 10.15372/rgg2019185 |
| Popis: | —The exposures, structure, mineralogy, and composition of unusual sulfide-bearing troctolites from the Yoko-Dovyren layered intrusion in the northern Baikal area (Russia) are described in detail for the first time. The troctolite succession (referred to as the Konnikov Zone) is characterized by the presence of pegmatoid poikilite sulfides and sulfide dissemination with diverse PGE mineralization. The former are dominated by pyrrhotite–troilite products of exsolution of monosulfide solid solution (mss), and the latter is composed mostly of cubanite–chalcopyrite assemblages produced from an intermediate Ni–Cu–Fe solid solution (iss). The positive covariations between the contents of sulfur and chalcogens (Se, Te) along with the sublinear dependence of the Pd, Pt, Au, and Cu contents on the Te contents indicate a sulfide control of the distribution of these elements in troctolite cumulates. According to the sulfide-normalized contents of these elements in rocks, the average “100% sulfides” in the samples are subdivided into two groups: (1) strongly depleted in PGE, Au, Cu, and Te and (2) with 10–50-fold enrichment in them. This division is consistent with the morphological and mineralogical differences between the groups. Of genetic significance is the fact that the mss assemblages are somewhat poorer in PGE and Te than the primitive sulfides from the Dovyren basal zone, whereas the assemblages with predominant copper sulfides are significantly richer in these elements. This fact is confirmed by LA-ICP-MS data on the trace-element composition of the sulfide phases. The established specific features indicate a limited scale of fractionation of immiscible sulfides during the solidification of the troctolite cumulates. The formation of PGE- and Te-rich assemblages can be related to the course of crystallization of a sulfide precursor similar to the most primitive sulfide liquid. This is consistent with the known laws of crystallization of sulfide systems and explains the abnormally high S/Te ratios in pegmatoid troctolites enriched in mss products. Thus, sulfide melts act as an agent that transports precious metals and chalcogens in the troctolite cumulate area. This conclusion requires specification of the physical mechanisms and parameters (rheology, permeability, wettability by sulfides of different phases, etc.) of the cumulus medium favoring the spatial separation of a monosulfide solution and Cu-containing PGE-rich fractions with their subsequent infiltration and deposition at the boundaries of critical low permeability. |
| Databáze: | OpenAIRE |
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