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Russian Geology and Geophysics

2005 year, number 6

THE ERDENETIYN-OVOO PORPHYRY Cu-Mo DEPOSIT, NORTHERN MONGOLIA: 40Ar/39Ar GEOCHRONOLOGYAND FACTORS OF LARGE-SCALE MINERALIZATION

V.I. Sotnikov, V.A. Ponomarchuk, D.O. Shevchenko, and A.P. Berzina
United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Porphyry Cu-Mo mineralization, intrusive complexes, 40Ar/39Ar geochronology, 87Sr/86Sr ratios, Erdenetiyn-Ovoo porphyry Cu-Mo deposit, Mongolia
Pages: 620-631

Abstract

40Ar/39Ar geochronology shows that the formation of the Erdenetiyn-Ovoo porphyry Cu-Mo deposit in Northern Mongolia related to the Erdenet ore-bearing porphyry complex was preceded by multiphase gabbro-granitoid magmatism in the region which produced the 258.6 ± 3.3 and 247 ± 3.7 Ma Selenge granitoids and the 244.6 ± 1.0-239.3 ± 1.4 Ma Shivota complex. The ore-bearing porphyry complex underwent a rhythmic evolution. The main mineralization stage was associated with porphyry magmatism of the first (234.6 ± 1.7 Ma) and second (225.3 ± 1.0-220.3 ± 5.8 Ma) pulses. The 40Ar/39Ar age of sericite from metasomatic rocks of the main mineralization stage is 235.8 ± 1.9 Ma. Intrusives of different ages (dated on accessory apatite) and early high-temperature ore formation products (on anhydrite) have low 87Sr/86Sr ratios of 0.70393-0.70437 corresponding to the mantle values. Mantle sources are likewise indicated by δ34S of sulfides which approach the chondrite norm. Repeated magmatism and mineralization in the Erdenet region provided favorable conditions for the formation of a large porphyry Cu-Mo deposit. Especially important was the rhythmic development of the ore-bearing porphyry complex in which each rhythm was accompanied by mineralization and metasomatism.