Home – Home – Jornals – Russian Geology and Geophysics 2005 number 6

In the Amur region, a series of gold-ore occurrences belonging to gold-polysulfide-quartz and gold-quartz formations (Tomskoe, Chitkan, Vyruchka, Urusha) have been recognized within the northern periphery of the Argun' terrane. These occurrences are associated with the formation of Late Paleozoic magmatic arc on the active continental margin. The latter is a chain of gabbro-diorite-granodiorite-granite intrusions of the Urusha complex with the isotopic age of 274-278 Ma (U-Pb zircon method), which extend along the structural boundary between the terrane and the Mongolo-Okhotsk fold belt. In geochemical and isotope-geochemical characteristics ((⁸⁷Sr/⁸⁶Sr)₀ = 0.70527-0.70724 at ε _Nd (t) = -1...+2.2) the granitoids of this association correspond to type I and are similar to granitoids of active continental margins. The ore occurrences under study are localized within endo- and exocontact zones of Late Paleozoic granitoids or slightly off them and are quartz-sulfide veinlets inheriting tectonic zones of weakness. Gold contents in the veinlets reach 30 ppm (atomic-absorption analysis). The orebodies are composed mainly of quartz, chlorite, sericite, zoisite, arsenopyrite, pyrite, galena, sphalerite, and chalcopyrite. Gold is present both in free (Chitkan) and in sulfide-associated (Tomskoe) forms. In the latter case, its content in sulfides reaches 300 ppm (chemical-spectral analysis). These ore occurrences evidence that the setting of active continental margin that existed along the northern periphery of the Argun' terrane in the Late Paleozoic favored the formation of various ore objects, including gold-bearing ones. The subsided tectonic blocks of this structure seem to be promising for commercial gold deposits.