natural mineral formations that contain arsenic in quantities sufficient to make feasible extraction of the element and its compounds. More than 120 arsenic-bearing minerals are known, the most common of which include arsenopyrite, FeAsS, containing 46 percent As; loellingite (leucopyrite), FeAs2 (72.8 percent); realgar, AsS (70.1 percent); and orpiment, As2S3 (61.0 percent).
Most arsenic ore deposits belong to the endogenic series and the plutonogenic and volcanogenic classes of the hydrothermal group. Arsenic compounds usually occur in association with nonferrous and noble metals (copper, zinc, lead, gold, silver, and so on). The arsenic in such ores exists in the form of independent minerals or as an isomorphous admixture in sulfides and other compounds. Arsenic ores are divided into several known types according to the commercial classification of ore deposits: arsenic (arsenopyrite and realgar-orpiment), gold-arsenic, complex-metal-arsenic, copper-arsenic, arsenic-cobalt, and arsenictin ores. Commercial ores contain a maximum of 2 percent As, but ores with a 5–10 percent As content are usually selected for processing; lower-grade ores are enriched by gravitational methods and by flotation.
Arsenic ore deposits are found in the USSR. Major deposits abroad are located in the USA (Butte, Mont., and Gold Hill), Sweden (Boliden), Mexico (Matehuala and Chihuahua), Japan (Kamioka and Sasagatani), and Bolivia (Potosí).
V. I. SMIRNOV