A new type of gold-platinum-copper mineralization in northern Transbaikalia

Abstract

The northern Transbaikal region situated at thesouthwestern margin of the Aldan Shield incorporates aunique ore district (Fig. 1). Giant ore deposits, such asUdokan (copper, silver), Chinei (iron, titanium, vana-dium, copper, and noble metals), and Katun (rare metaland rare earth elements), are located 30–100 km southof the Novaya Chara station along the Baikal AmurMainline [2].Despite unfavorable natural mining–geological andtechnological features of the Udokan copper deposit, itsexploitation in the nearest future is inevitable [7].Therefore, solution to problems related to enhancementof the efficiency of raw mineral mining in the depositand ore district has become a crucial issue. This districtis characterized by juxtaposition of two large deposits(Udokan and Chinei). Moreover, these deposits aresuperlarge (giant) objects with respect to resources ofmajor metals (Cu and V). This fact is of paramount sig-nificance in the strategy of economic development ofnorthern Transbaikalia. Extraction of associated orecomponents and elucidation of new types of complexores are essential for enhancement of the efficiency offuture mining–metallurgical plants in the region. In thisrespect, assessment of the genesis, abundance, andscale of gold–platinum–copper mineralization, whichwas first found in the Udokan–Chinei ore district, isvery important.Quartz veins with noble metals and copper weredetected in the nearest framing of the Chinei Massif andthe Pravoingamakit deposit. The Pravoingamakitdeposit was exploited for cupriferous sandstones by theUdokan Expedition in the 1960s. However, we scruti-nized ores of this deposit in 2004–2006 and revealedthat its structure is more complicated and differs signif-icantly from that of the standard cupriferous sandstonedeposit (Udokan). Orebodies of the Pravoingamakitdeposit are hosted in terrigenous–carbonate rocks ofthe middle section of the Chitkanda subformation of theLower Proterozoic Udokan Formation. The discontinu-ous cupriferous horizon is traced as a NW-striking (dipazimuth 350, dip angle 65°–70°) zone extending overnearly 10 km on the surface and 400–500 m along thedip. Economic grade mineralization is developed over4.5 km. The deposit includes orebodies of two types:(1) veins and lenses of milky white massive quartz withstringers and patches of sulfides (Fig. 2); (2) echelon ofmassive sulfide bodies surrounded by dissemination ofpyrite and chalcopyrite. Quartz veins (0.3–1 m thick)extend along the strike over a few tens of meters. Sul-fide bodies are 3–5 m thick and 300–440 m long. Theorebodies are characterized by significant content of Cu(0.47–2.5 wt %) and very high variation of the Cu/Niratio (from 10 to 700 in various sectors).Ores are represented by the pyrite–chalcopyritevarieties with typical stringer and breccia structures(Fig. 2). The maximal concentration of Ni in quartzveins is related to high contents of nickel minerals (mil-lerite and pentlandite). The quartz vein ore is alsoenriched in noble metals (g/t): Pt 0.1–2.2, Pd 0.9–6.2,and Au 0.1–0.4. The ore includes fine (up to 10 µm)inclusions of clausthalite Pb