Porphyry and Hydrothermal Cu-Au Deposits

The Muruntau gold deposit, Uzbekistan, is localized in a shear zone related to upper Carboniferous to lower Permian accretion of the Kazakhstan-North Tien Shan and Karakum-Tarim tectonic plates. The gold ore was deposited syndeformationally in an extensional stepover along a northwest-striking left-lateral fault zone under ductile to brittle conditions. The host rocks are carbonaceous shales, siltstones, sandstones, and chert. Early stage alteration was quartz-albite-biotite-chlorite-oligoclase with some pyrite and gold. The predominant period of gold-sulfide deposition accompanied K-feldspar, phlogopite, muscovite, Mg-Chlorite, and Fe-Mn carbonate alteration. Later stage veinlets contain tourmaline, and the latest stage of alteration was calcite veinlets with pyrite, TiO2 and rare-earth element minerals.

Muruntau is probably the greatest gold deposit in the world, with a global resource of more than 1 bt @ 3.5 to 4 g/t Au for 4500 to 5000t of contained gold (140 to 150 Moz) amenable to open pit extraction. The current pit is approximately 2.5x3.5 km and 300 m deep. It produces around 64 t (2 Moz)of gold per year. Mineralisation occurs as a stockwork vein system within asequence of lower Palaeozoic carbonaceous sediments, and is associated with syn-deformational granitoid intrusion in a structurally complex zone. The orebody is located within the great South Tien Shan gold belt.

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