Home – Home – Jornals – Russian Geology and Geophysics 2005 number 5

Not only hydrodynamic but also eolian processes have an effect on placer formation. Our experimental, mineralogical, and field studies as well as analysis of recent literature data permitted us to recognize a new morphologic type, eolian gold, and a new genetic type of gold deposits, eolian placers. Eolian gold is represented by gold flakes with ridgelike edges, toroidal grains and hollow spheroids 0.1 to 0.25 mm in size, as well as by compact disc-shaped, flat gold particles with ridgelike edges, and lump-shaped ones covered with a specific fibrous membrane measuring 0.25 mm and more. In addition to gold particles characterized by eolian features, gold-crustated quartz occurs. Analysis of distribution of eolian gold shows that the above-mentioned shapes of gold are widespread in Proterozoic-Cenozoic deposits almost in all platforms of the world. The eolian gold occurrences are well correlated with fragmentally developed surfaces of deflation paleodeserts, the halo of which can be reconstructed from findings of ventifacts. Both arid and nival climates are favorable for eolian placer formation because the epoch of glaciation is characterized by intense eolian processes that gave rise to placer formation. Eolian gold placers may be formed as the result of long-lasting activity of unidirectional winds owing to the deflation of a primary source itself, gold-bearing crusts of weathering or previously generated alluvial, beach, and other placers of varying genesis. We suggest to divide them into eolian gold placers and heterogeneous ones, i.e., eolian-proluvial, eolian-alluvial, eolian-marine, etc. Eolian gold placers have a specific structure: The producing horizon overlies the deflation surface like a blanket, with its thickness extremely small (tens of centimeters), and is complicated by jet series. This horizon is usually composed of sandstones and gravel with a low content of argillaceous matter containing ventifacts and wind-worn gold particles. The eolian gold placers are divided into autochthonous and allochthonous. Autochthonous deflation placers are generated by denudation of a primary source matrix either with deflation of the crust of weathering formed in the primary source or with deflation of the placer previously formed. Allochthonous eolian placers are basal (transit) and dune ones. Basal eolian placers are confined to the eolian denudation surface and are mainly developed in deflation basins and grooves. Allochthonous dune placers of gold occur between denudation and accumulation zones. Lying far from the primary source, they have no economical value because the metal particles that migrated together with blown sands are very small, dispersed, with low contents of gold. Not only remarkable shapes of gold particles and character of their surface, but also ventifacts, specific structure of producing bed, deflation relief structures, i.e., grooves and basins, and typical lithology of sedimentary deposits are exploration tools for revealing eolian gold placers. As far as wind-worn gold particles are not only of mineralogical interest but also form high concentrations of the metal, e.g., in the Witwatersrand gold placer, we believe that the discovery of eolian gold placers of varying age in platforms all over the world is quite promising, in particular, in the eastern European, Siberian, North American, South American, African, and Australian Platforms as well as in Tuva and Mongolia.