Geochemical criteria of gold-bearing content of weathering crusts of the Sukharinskoe ore field (Gornaya Shoria)

Relevance. In recent decades, high concentrations of gold have been identified in the skarn-magnetite deposits of Gornaya Shoria. However, these deposits have not received due attention in developing iron ore deposits. Of particular interest are the weathering crusts that are extensively developed in this region, in which the gold content occasionally exceeds its concentration in primary ores and dispersion halos by an order of magnitude. The industrial development of these objects is constrained by a number of theoretical issues, including the relationship between the gold content of weathering crusts and the formation of anomalous geochemical fields. Aim. To identify the geochemical features of the weathering crusts of the Sukharinskoe ore field in order to resolve issues of predicting their gold content. Object. Weathering crusts in the rocks, metasomatites and ores of the Sukharinskoe ore field. Methods. Chemical composition of the weathering products was determined using semi-quantitative spectral analysis for 24 elements (Ag, Pb, Cu, Zn, Cd, As, Sn, Bi, Te, Mn, Co, Ni, Ti, V, Cr, P, Mo, W, B, Zr, Li, Sr, Ba and Fe), as well as spectrochemical analysis for gold (Au). In samples containing greater than 0.1 g/t of Au, the presence of Au and Ag was confirmed using atomic absorption and fire assay methods. The samples were then compared using non-parametric criteria, discriminant and factor analyses. These were carried out using the STATISTICA program. Results and conclusions. Linear gold-bearing weathering crusts in the Sukharinskoe ore field were formed as a result of oxidation of gold-bearing beresite-sulfide-quartz and magnetite-sulfide ores against the background of the formation of Mesozoic weathering crusts of the areal type. During the formation of gold-bearing weathering crusts, there was an additional accumulation, in comparison with the original ores, of Au, Ag, As, Pb, Cu, Zn, Ni, Co, Fe, Mn, P, Bi, W, Mo, to a lesser extent – V, Zr, Ba, and a significant decrease in Sr concentrations. The mean gold content in brown iron ores, which are formed subsequent to gold-bearing magnetite-sulfide ores, undergoes an increase by an order of magnitude during oxidation. In ochre-clay weathering crusts on beresite-sulfide-quartz ores, the average Au content remains relatively constant. However, dispersion exhibits a marked increase, resulting in the formation of localised areas of metal accumulation.