Association of Siderite with Iron Sulfides and Silicates in Rocks of the Mikheevskoe Cu(Mo,Au) Porphyry Deposit (Southern Urals).

The mineral association of siderite with Cu–Fe sulfides, cronstedtite, and goethite were first recognized when studying the Mikheevskoe Cu(Mo,Au)–porphyry deposit. This association is confined to fault zones, where it fills a network of mineralized fractures developed on porphyry- and argillizite-type ores. Minerals of this association were also identified in some argillizite samples of this deposit. The formation conditions of this mineral association and its relation to the evolution of the Late Paleozoic porphyry system or other endogenic–exogenic processes manifested during the subsequent geological history of the study area were studied. The integrated research included microprobe analysis and the measurement of O and C stable isotopes in minerals of the studied association in the "Geoanalitik" (Yekaterinburg) and "Geonauka" (Syktyvkar) Centers for Collective Use. The study of mineral compositions and their relationships indicates that the studied mineral association deposited at temperature of about 70°C from neutral or low-acid solutions with varying , HS^–, and aSiO₂ (aq) contents. The measurements of δ¹³C (from –5.5 to –18.2‰) and δ¹⁸O (from 20.4 to 33.4‰) values in siderite made it possible to calculate the composition of a mineral-forming fluid. It was established that such a fluid has the following parameters: δ¹⁸O H₂O from –3 to +10‰ and δ¹³C CO₂ from 15 to –28‰. It could correspond to magmatogenic water fluids mixed with C_org-bearing surface water. Based on the obtained results, it is suggested that this mineral association is related to argillizites, the development of which occurred at the last stage of endogenic mineral formation at the Mikheevskoe deposit. Nevertheless, it is not excluded that it may be related with other low-T hydrothermal processes at the stage of Meso-Cenozoic tectonomagmatic activation of the Urals. There is no evidence of the relation of the studied mineral association with weathering crusts. [ABSTRACT FROM AUTHOR]