Home – Home – Jornals – Russian Geology and Geophysics 2001 number 1-2

The regularities of distribution of S, Se, Te, U, Mo, B, P, Cu, Ag, Au, Sn, Zn, Pb, and organic carbon in Cenozoic sediments of various taphrogenic depressions in the Baikal Rift Zone have been studied. The fine-grained carbonaceous deposits of all depressions, particularly carbon partings and lutites of Lake Baikal, have concentrations of U several times higher than its clarke. The sediments of some river valleys are noticeably enriched in Au, which was supplied there from gold-ore deposits of sourcelands.
Organic matter and clayey sediments (or their lithified analogs) are the major concentrators and carriers of the above-listed elements. The most differentiated (according to the content of organic carbon) rocks exposed by BH-S-1 in the Tunka depression, where the concentration of C^org varies from 0.3 to 83% (in coal), show a certain distribution of elements between the organic and clayey matter, in accordance with their strength of bond with the latter: C^org-S-Se-U-Ag-Mo-B-Au-Te-Cu-Sn-Pb-Zn-clay.
The organic matter concentrates S, Se, U, Mo, and Ag, and the clayey matter concentrates Pb, Zn, Sn, and Cu. Gold and tellurium (which can bind with B, Mo, and Cu) behave in a specific way and indifferently with respect to the organic and clayey matter of the sediments, forming an independent terrigenous sedimentary material, probably, bearing native gold. Sometimes additional concentrators - phosphates, sulfates, and sulfides - are produced. In places, the behavior of these elements is different and even more intricate as a result of changes in the granulometric and mineral compositions of sediments. Diagenesis leads to a stronger separation of elements. Groups of elements tending to isolation as a result of differentiation at the sedimentation and diagenesis stage form associations typical of various ore deposits. It is suggested that the chemical processes of deposition and early diagenesis of the formed sediments in sedimentation basins are the initial stage of pre-ore differentiation of ore-forming elements in the originating source of matter for future deposits. This initial differentiation already exhibits the specific features of the forthcoming ore genesis.