| Popis: |
The Gorevskoe Pb-Zn-Ag Mine is currently the largest producer of Pb and Zn in Russia, exploiting one of the largest sediment-hosted Pb-Zn deposits worldwide. Despite its size and economic importance, the Gorevskoe deposit remains poorly understood. It is located on the western margin of the Siberian Craton within the Yenisei Ridge, a Neoproterozoic orogenic belt. Mineralization consists of three tabular orebodies that are in turn composed of multiple stacked stratiform to stratabound lenses of galena-pyrrhotite-sphalerite-rich massive sulfide ores, hosted in organic-rich marine metalimestones and calcareous slates of Stenian to Tonian age (1,020 ± 70 Ma). Extensive Fe-Mg-Mn-carbonate alteration haloes surround the ore lenses in the hanging wall and the footwall. The Pb isotope signature of the deposit is consistent with derivation of the Pb, and probably all associated metals, from an evolved crustal source at the time of formation of the host rocks. The sulfur-isotopic composition of pyrrhotite, along with sphalerite, galena, arsenopyrite and pyrite (δ34S = 16.0 – 20.4 ‰) is within the range reported for contemporaneous seawater, indicating complete reduction of marine sulfate as the main source of sulfide. The available geological and geochemical data indicate that the Gorevskoe deposit belongs to the sediment-hosted massive sulfide class of Zn-Pb deposits, with an affinity to Selwyn-type deposits. Hydrothermal mineralization appears to be related to rifting and distal mafic volcanism in a passive margin setting. Geological relationships suggest that sulfide orebodies formed in a diagenetic environment. Furthermore, the predominance of primary pyrrhotite over pyrite as the major iron sulfide, the presence of abundant siderite, and the virtual absence of barite from the deposit, all indicate highly reducing conditions during ore-formation. They also constrain the character of the metal-bearing fluid to be similarly reducing, and of moderate temperature (200 – 300°C). Gorevskoe may thus be regarded as one of the world’s largest Selwyn-type SHMS deposits. |
