A Two-step Sequential Extraction for Analyzing Hardly Accessible Precious Metals in Sulfide Ore-bearing Sedimentary Rocks

The work concentrates on extraction of precious metals (Au, Ag, Pd, Pt) and As, Sb, Cu, Pb, Zn, and Fe which are bound to sulfide-ore minerals in sedimentary rocks, using a two-step sequential extraction experiment with two chemical reagents (hydrogen peroxide and aqua regia) on three rock specimens from the black shale formation in Bakyrchik gold-sulfide deposit in North-East Kazakhstan. The experiment allows to determine the speciation of hardly accessible precious metals and to identify the most productive ore-forming stage from the three identified ones. Analytical methods are used for determining polysulfide mineral textures (optical microscopy), mineralogical (XRPD) and chemical compositions (XRF), and for measuring extracted metals concentrations (ICP-OES) in experimental procedures. The analytical results show that the first stage is more productive in gold (total extraction 2.8 ppm) than others and the second stage is more productive in Ag (total 1.6 ppm) and Pd (total 0.01 ppm), while the last stage is more productive in Pt (0.019 ppm) in the deposit.