The stored waste from processing Ni–Co arsenide ores of the Khovu-Aksy deposit (Republic of Tyva, Russia) is a unique geochemical system, in which the joint behavior of As and metals (Fe, Co, Ni, Cu, Zn, and Pb) under exogenous conditions can be directly traced. We have studied the mineralogical and geochemical specifics of the distribution of arsenic (from primary arsenides to newly formed phases) and associated metals in waste with a high As content (up to 4%) throughout the section of trench burial No. 3. These strata are characterized by a slightly alkaline environment with pH = 7.7 and Eh = 486 mV. Four horizons are distinguished in the section. According to elemental analysis (XRF-SR), As, Mo, Pb, Sb, Co, and Cu accumulate in horizon 2 (80 cm), whereas Cd, Zn, and Ni, in horizon 3 (110 cm). In the processed ores, nonmetallic (rock-forming) minerals are represented by quartz, calcite, dolomite, garnet, amphibole–chlorite aggregates, single grains of K-feldspar (Kfs), apatite, barite, and muscovite. Arsenic minerals are distributed extremely unevenly throughout the section and are absent from the soil horizon (horizon 4). Arsenic is found in the section as: (1) arsenic minerals, namely, safflorite with hovuaksite, conichalcite, scorodite, arseniosiderite, sarmientite, hörnesite, annabergite, and picropharmacolite; (2) isomorphic impurity in secondary products (iron hydroxides developed after pyrite, amorphous silica, and chlorite). The presence of carbonate minerals in primary ores and the applied technological scheme of ore dressing with purification of solutions from arsenic affect directly the secondary assemblage of arsenic minerals.

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