Ore Mineralization in the Kharbei Metamorphic Complex in the Zone of the Khadata–Khanmei Thrust (Polar Urals)

Ore mineralization (Au, Ag ± Pt, Pd) and host metasomatic rocks were studied in amphibolites of the Kharbei metamorphic complex (Polar Urals). The predicted gold-ore cluster is well exposed in the zone of the Khadata–Khanmei thrust zone (the Skalistiy Creek basin), where it is controlled by a NW-striking fault. The host rocks are represented by amphibolites that have been altered to a degree (up to the higher-pressure epidote–amphibolite facies of metamorphism). During diaphthoresis, amphibolites underwent alteration transformations, such as chloritization, albitization, muscovitization, and silicification. The most sulfides were deposited during the late silicification. Ore minerals are represented by sulfides and rare inclusions of tellurides, selenides, and native elements. Three stages of the sequential hypogenic hydrothermal ore formation were identified. At an early stage of hydrothermal–metasomatic alterations of rocks, high- and medium-temperature ore minerals, associated with chlorite (ripidolite) were formed including pyrite, pentlandite, Ni-pyrrhotite, chalcopyrite, and molybdenite. The next stage of ore formation was associated with high- and medium-temperature hydrothermal processes and the development of quartz veins and veinlets. At this stage, the following minerals crystallized: pyrite, matildite–galena, galena, sphalerite, molybdenite, chalcopyrite, bornite, pyrrhotite, chromferride, Hg electrum, tsumoite, and low- and medium-grade gold. Medium- and low-temperature hypogenic minerals of the third stage, associated with pycnochlorite–brunsvigite and ripidolite–daphnite are represented by Ni- and Co-bearing pyrite, chalcopyrite, galena, clausthalite–galena, hessite, melonite, merenskyite, and merenskyite–melonite. Recent hypergenic alterations in ores are represented by secondary acanthite, hessite, naumannite–acanthite, hessite–acanthite–naumannite, native silver, and covellite.