DIGITAL STRUCTURAL-LITHOLOGICAL SIMULATION OF GOLD-BEARING CRUSTS OF WEATHERING WITHIN DEPOSITS AND OCCURRENCES OF MIDDLE-BUH REGION

Abstract

Placers of residual gold in the crusts of weathering over the gold-bearing objects (deposits Serhiivske, Balka Zolota, Balka Shyroka, Yuriivske, Maiske, Klyntsivske, Bobrykivske, Chemerpilske, Polyanetske, Bakshynske, Savranske, etc.) are much com-mon in Ukraine. The gold content in them sometimes reaches several tens of grams per ton. Kapitanivska, Savranska and Chemerpilska areas that spatial and paragenetic asso-ciate with the same-name gold occurrences are the promising objects. Gold-containing areal and linear crusts of weathering have been developed there on the gold-bearing rocks of the crystalline basement. Kapitanivska area is connected with the same-name deposit of silicate nickel ore and chromite, Savranska and Chemerpilska – with the Savranska group of gold deposits and occurrences. The crust of weathering at the Maiske deposit has a little capacity, so no practical interest. On the basis of digital structural-lithological modelling, we built appropriate models of the gold-bearing crust of weathering, which cover the set of graphic materials: (1) to-pographic maps of the crust of weathering bottom and surface, (2) maps of the total ca-pacity of gold-bearing eluvium, (3) maps of the gold content lateral distribution in the crust of weathering, (4) graphs of the gold content distribution in the profile of the crust of weathering on the various gold-bearing rocks. Following zones are allocated in the crust of weathering section in Kapitnanivska area (bottom-up): (1) disintegration and leaching, (2) hydrolysis (nontronite-montmoril-lonite) and (3) final hydrolysis and oxidation (clay-hydrogoethite, heavily impregnated with secondary silica in the form of opal and chalcedony), and in Savranska and Chemerpilska areas – (1) the zone of disintegration and leaching, (2) hydrolysis (side-rite-nontronite-psilomelane-hydrogoethite) and (3) final hydrolysis and oxidation (kao-linite) with intense ferruginization and silicification. The character of gold mineralization in the crusts of weathering is complicated due to the presence of several petrotypes of gold-bearing crystalline rocks within each gold occurrence and variegated distribution of gold in them, mainly in the zone of disintegra-tion and leaching. The mobility and intensity of the gold concentration in various zones of eluvial se-ries were different. There was an active hypergene redistribution of gold in the hydroly-sis zone and the zone of final hydrolysis and oxidation; its intensity and character de-pend on the material composition and values of pH and Eh in the zone. Digital struc-tural-lithological modelling of gold-bearing crusts of weathering gave the possibility to visualize the character of capacity, the bottom and the surface of these crusts, lateral and vertical distribution of gold in them, as well as to allocate the areas with a high content of metal.