Geochemical analysis of organic matter associated with gold in ore deposits: A study of Kazakhstan and Hungary

Abstract

This study comprises the relationship between organic matter (OM) and gold occurrence using two distinctive ore deposits of the Bakyrchik gold-sulfide deposit (Kazakhstan) and Western Mecsek uranium ore deposit (Hungary). The two ore deposits are identified as organic-rich sedimentary formations linked to the Variscan gold cycle globally. Characterizing OM is essential because it can act as a carrier for gold, influencing its distribution and behavior within the deposit. Understanding the nature and distribution of OM can provide insights into the processes of gold deposition and help optimize exploration and extraction strategies in mining operations. The primary objective is to characterize OM by identifying its elemental composition, thermal maturity, functional groups, and soluble fractions; and extract gold from OM using a two-step sequential extraction method (hydrogen peroxide and aqua regia) combined with geochemical techniques. Analytical and experimental results from samples of both ore deposits indicate the presence of finely disseminated solid bitumen and reworked vitrinite, originating from thermally matured (RmcRo%—3.76 in Bakyrchik; Ro%—2.25 in W-Mecsek) terrigenous high plants. Both deposits exhibit extremely low extractable bitumen yield and TOC (0.34% in Bakyrchik; 0.25 wt% in W-Mecsek), characterized by an aromatic carboxylic acid organic structure and a composition rich in sulfur-containing (1.17% in Bakyrchik; 5.81% in W-Mecsek) aromatic hydrocarbons. Gold occurrence and enrichment within OM were confirmed through the sequential extraction method employing ICP-OES and LA-ICP-MS techniques. The sequentially extracted gold content from OM reached up to 3 ppm in Bakyrchik and up to 3.28 ppm in Western Mecsek, accompanied by Ag (ranging from 0.01 to 0.32 ppm). Higher concentrations of Au (4 ppm) and Ag (27 ppm) were extracted from residue materials, which are likely associated with sulfide minerals. The presence of gold in OM was further validated using LA-ICP-MS. Gold bonding within OM structure, gold is preserved in the form of lattice gold or structurally bonded metal most likely within the aromatic hydrocarbon fractions of the OM in both the W-Mecsek and Bakyrchik deposits. These findings underscore the profound potential of ongoing exploration endeavors, offering pivotal revelations regarding the extraction and practical application of Au and Ag derived from OM within the geochemical framework of both ore deposits.