Automated Mineralogy for Gold Deportment: A Case Study of a Skarn Fe–Au–Polymetallic Deposit in the Eastern Kunlun Orogenic Belt, NW China

Gold deportment data are essential for understanding mineralization mechanisms and guiding beneficiation and metal recovery. Scanning electron microscope (SEM)-based automated mineralogy (SEM-AM) allows for the numeric assessment of ores’ compositional and textural properties. In this study, a new SEM-AM technique, BGRIMM Process Mineralogy Analyzing System, abbreviated as BPMA, was employed to characterize the gold deportment of a skarn Fe–Au–polymetallic deposit in the Eastern Kunlun Orogenic Belt (EKOB), NW China. The results show that the gold minerals in the ore are primarily native gold (Au), which contributes 78.27% of the Au, followed by maldonite (Au2Bi), which contributes 21.73% of the Au; the iron minerals consist mainly of magnetite, with a mass fraction of 23.00 wt%, contributing approximately 63.37% of the iron. The native gold is mainly intimately associated with grossular and magnetite, while the maldonite mainly coexists with arsenopyrite–(Co), löllingite–(Co), bismuth, and tetradymite, forming a complex and unique Au–Bi–(Te)–As–S±Co mineral/element group and texture. This indicates that the liquid bismuth collector mechanism could be a plausible hypothesis for enrichment, migration, and precipitation during mineralization, consistent with the observed textures. The nuggets primarily exist in the form of intergranular gold (37.04 wt%) and fissure gold (35.13 wt%), followed by inclusion gold (26.30 wt%). The grain size of nuggets is very fine; 94.32 wt% of gold grains are less than 10 μm. The grain sizes of the main gold-carrying minerals [i.e., magnetite and arsenopyrite–(Co)] are mainly distributed in coarse-grained size fractions (>295 μm) and medium-grained size fractions (+74 μm, −295 μm), making them easy to liberate during grinding. A preliminary recommendation of a principle flowsheet of “flotation for gold recovery–magnetic separation of flotation tailings for iron recovery–flotation desulfurization of magnetic concentrate” at a grind size of 65% passing 74 μm was proposed for gold and iron recovery.