Potentially commercial Alapayevsk-Sukhoy Log porphyry copper zone (the Middle Urals)

NS-trending Alapayevsk-Sukhoy Log zone of porphyry-copper mineralisation in the Middle Urals is located 75 km to the east of Yekaterinburg and extends for 100 km from Alapayevsk to Sukhoy Log towns. Sulphide inclusions in rocks are pervasive, and there are numerous ore manifestations and small deposits. Like the commercial Mikheyevskoye porphyry copper deposit (over 1.7 million tonnes of Cu) in the Southern Urals, the zone is associated with the eastern part of East Urals volcanic megazone. It consists of several ore-producing NS-trending volcano-plutonic belts which represent the tectonic blocks. Rejuvenation from north to south of granitoid magmatism has been identified (U-Pb SHRIMP-II and LA ICP-MS zircon dating) in First magmatic stage (million years): from 412 (diorite-plagiogranodiorite-plagiogranite of Yaluninogorsk massif) to 404-406 (diorite-granodiorite-granite of Altynai-Artyomovsk intrusion), and then to 397 (plagiorhyodacite-porphyre of Shata area). Volumetrically sericitized and sulphidized quartz diorite of East-Artyomovsk massif was probably established during Second magmatic stage (369 ± 39 million years, Rb-Sr dating). All granitoids are of arc-island geochemical type, and have feature near-mantle isotopic signatures: (87Sr/86Sr)t = 0.7038-0.7049, (εNd)t = 6.6-8.7. Systemic and comprehensive study of Alapayevsk-Sukhoy Log zone should result in discovery of commercial large scale porphyry copper deposits (assuming current cut-off grade of Cu 0.15-0.20 wt %). The most attractive in terms of potential for high capacity stockworks is the East Artyomovsk massif which is similar in many respects to ore-magmatic system of Mikheyevsk deposit

PECULIARITIES OF FREE GOLD OF THE GUMESHEVSKOYE DEPOSIT: MORPHOLOGY, COMPOSITION, ZONAL DISTRIBUTION

The relevance of research is determined by the need for a detailed study of the composition and changes of free gold in conditions of hypogene-supergene processes within the Gumeshevskoye deposit. The methods of investigation are X-ray spectral microanalysis, scanning electron microscopy. Purpose of the study was to obtain data on the granulometric, morphological and chemical composition of free gold to identify vertical zoning in its distribution within the upper part of the deposit. Results of the research. The study of free gold from regolite of ore-bearing karst (Cu, Au) and argillizated rocks of the Gumeshevskoye copper-skarn deposit (Middle Urals) was carried out. Variations in the granulometric, morphological and chemical composition of gold at different depth levels of the tested section of the productive ore zone are considered. The signs of vertical zonation in the distribution of gold by granulometric and chemical compositions, as well as in the ratio of its main morphotypes, are revealed. It is shown that with the general predominance of fine gold (< 0.15 mm) at all levels, the average grain size of gold increases with depth. There is a significant variation in gold fineness from 591 ‰ to ≥ 980 ‰; most of gold is high-grade. Low-grade gold and electrums are found only in the upper part of the section (up to 35 m). By the ratio of these impurities there are three geochemical types of free gold: gold-silver, gold-silver-copper, and gold-copper. The most frequent in the deposit is Au-Ag-Cu type, which is 47% in the upper part of the ore zone to 70% at depths of more than 50 m. Pure Au-Cu natural alloys are much less common, amounting to no more than 5%. From 25 to 51% is accounted for Au-Ag alloys. Conclusions. The morphological and geochemical types of gold were identified, and data were obtained on their distribution in the deposit section

Rhythmical patterns of quartz-molybdenite and interpretation of its origin

Subject of the study was molybdenite aggregate (0.9 × 0.5 cm) in granite from Cu ± Mo-porphyry mineralisation (Altynai Massif, eastern part of Middle Urals). Microprobe analysis and electron microscopy identified fine alternating microlayers of molybdenite and quartz in all 0.4-5.0 mm flakes of molybdenite. Thickness of normally discontinuous layers of quartz is 0.5-3 μ, distance between layers - 8-100 μ or more. Quartz layers are aligned only with the basal cleavage of molybdenite. In some molybdenite flakes or parts of flakes quartz layers are absent or very few in number. Large flakes of molybdenite are surrounded by fine-grained aggregate of quartz, chamosite and molybdenite. Occasional grains of fluorite and galena have also been found within this aggregate. Molybdenite flakes in such areas contain no quartz layers, have random orientation, and can be seen as fragments cemented by chamosite and quartz. Molybdenite has consistently low rhenium content of 29 ppm (according to ICP-MS). It is suggested that molybdenite-quartz rhythms are likely to correspond to primary oscillatory distribution which was subsequently subjected to deformations and redistribution of silica in crushed areas