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Ore mineralization and genesis of the Yuzhka gold–limonite occurrence, Elmus area, Karelia

2018; Karelian Research Centre of RAS; Issue: 11 Linguagem: Inglês

10.17076/geo761

2312-4504

Людмила Владимировна Кулешевич, Иван Леонидович Олейник, L. V. Kuleshevich, Ivan Oleynik,

Mineralogy and Gemology Studies

Yuzhka gold-limonite occurrence is the first one to have been found in the linear-type brecciation and oxidation zone in the Archean greenstone rock oxidation zone, Elmus area, Central Karelia. The oxidation zone formed along the broken quartz-sericite-chlorite schist, which contains a pyrite ore horizon and broken quartz veins. The mineral limonite mixture was studied using Raman, thermal, X-ray, chemical, ICP-MS and microprobe analyses. The upper portion of the oxidation zone consists primarily of unconsolidated yellow-brown ochre, sintered packages and gossan (consolidated rocks). Iron oxides and hydroxides in the upper unconsolidated portion of the limonite zone were found to consist of goethite (hydrogoethite) and hematite. Pyrite ores of chalcopyrite-pyrite composition occur in lower horizons; they are broken and replaced by either hematite or both hematite and goethite. Broken quartz veins in the oxidized and ferruginized schist sequence form breccia with angular fragments of varied size, which contain scarce sulphide (pyrite, chalcopyrite, galena), sulphosalt and sulphoarsenide inclusions and are cemented by goethite and hematite. Persisting non-oxidized sulphosalts and sulphoarsenides in the ores and broken veins are composed of semseyite, tetrahedrite, jamsonite, plagionite, cobaltite and gersdorffite; melonite is occasionally encountered. The gold is fine-textured and high-grade (Ag 1–10 %). It is intergrown with goethite near the oxidized pyrite ore horizon; its concentration is 1–2.6 g/t. The geochemistry of the limonite zone (As, Sb, Pb, Ni, Cu, Co) reflects the composition of primary pyrite ores and quartz vein associations in the Elmus area, suggesting that these oxidized rocks were the source of the gold.