Contrary to traditional conception about passivity of gold in supergene conditions more and more data appears about it’s active remobilization, especially in weathering crusts.
The examples of studied gold deposits in lateritic weathering crusts of West Africa (Guinea) and kaolinit weathering crusts of Salair, Kuznetski Alatau, Altai, Northern Kazakhstan and Ural show that along with surviving (residual) gold the supergene gold present. The last one is presented by secondary native agregats and the finest neoformations on the cover of previous gold particles. Using our materials coserned to auriferous of kaolinit and lateritic weathering profiles was carried out comparative analysis of mineralogical-geochemical features, characterizing new "supergene" gold.
It was shown that the result of chemical redistribution of gold from cuirass and top part of saprolit layer of laterites of Guinea appears in specific morphology of its particles. Probably, a part of them is a result of dissolution of gold particles margins - so-called "smooth" gold - and a part is a result of colloidal and (or) bacterial formation. New supergene gold in forms of spongy and "brain-shaped" formations grows on previous massive gold grains. Smooth gold, isometric grains and ideal gold spheres from lateritic horisont are characterized by greater dimensions (0.2-0.3 mm) than gold particles in underlying horisonts of argillic weathering crust.
In kaolinit weathering crust of Suzdal gold deposit (Kazakhstan) dominates the gold of fineness -0.1 mm. It is characterized by high standard (960 - 1000 ‰) idiomorphic and crystal shapes and complex splices of crystals. At the same time octahedral crystals with flat and planed faces prevail over other shapes. In the zone of intensive crushing was noted singular small crystals and their bipyramidal joins and also thin triangle plates with shiny surfaces. It was detected that wire and hair-like grains quite often have faceted ends. Also it’s registered flat laminated crystals with hexagonal corroded cross profiles. Traces of the spiral growth are typical for them. Neogenic gold, identified as authigenic, very often presented by the finest grains (first mkm) in the form of globules and laminar crystals.
Received results make an additionally contribution in argumentation and subsequent development of author’s views about mobility of gold in exogenous zone in contrast to fixed notion about it inertness. This fact seems very important because it enable along with other characters to fine evidence of possibility of formation in kaolinit weathering crust of significant gold concentrations not only at the expense of oxidized ores of endogenous deposits but also at the expense of weakly gold-bearing zones of ingrain-string sulphide and sulphide-quartz mineralization, and also of endogenic halations of different hierarchy levels.
The investigation was supported by RFBR (project 06-05-64697).