Vitim-Olekma Belt of Epicratonic Copper-Bearing Troughs

A series of terrigenous troughs forming the extended arched Vitim-Olekma belt are recognized among the Precambrian structures of the Chara-Olekma craton. The troughs appeared within the age interval from 2,200 to 1,800 Ma just after the adjacent Archean greenstone troughs formed. They mark the epicratonic stage of Precambrian block evolution in the western Aldan-Stanovoi Shield. The troughs are filled with clay-sandy complexes with layers of carbonatic, more rarely siliceous, rocks, sometimes with lenses of conglomerates, breccia-conglomerates and gravelstones. There are two formation rhythms recognized in the complex structure to mirror the two-stage development of the troughs. Carbonate-terrigenous flyschoid formations, in particular carbonaceous ones, with stratiform uranium, silver-copper, sometimes chrome mineralization were accumulated at the early rifting stage. The late stage was characterized by accumulation of subaeral copper-bearing molasse formations in inherited overrift depressions. A regular change in composition and thickness of epicratonic complexes is noted from west to east, and northeastward.