Complex Ore

an ore in which the principal valuable components are lead and zinc and the secondary components are copper, gold, silver, cadmium, bismuth, tin, indium, and gallium. In some complex ores, barite, fluorite, and sulfur associated with sulfide ores are of industrial value.

The major minerals of complex ores are galena (PbS) and sphalerite (ZnS). Frequently, pyrite (FeS₂) and chalcopyrite (CuFeS₂) are present. Sometimes, fahlores, arsenopyrite (FeAsS), and cassiterite (SnO₂) are also present. Copper is usually found in complex ores as chalcopyrite, and silver and bismuth are often associated with galena. Gold is found in complex ores in a free state or as a minute admixture in pyrite and chalcopyrite. Cadmium is contained primarily in sphalerite. The content of the major valuable components in industrial deposits of complex ores may constitute a very small percentage or may exceed 10 percent. Depending on economic and mining conditions, as well as on the content of valuable components, a deposit of complex ores is said to have low total reserves (100,000-200,000 tons of the metal), average total reserves (200,000-500,000 tons), or large total reserves (greater than 1 million tons). Among the largest deposits of complex ores, the best known are at the Pine Point (13 million tons) and Sullivan (8 million tons) in Canada and Broken Hill (about 6 million tons) in Australia. At Broken Hill, the lead content is 11–13 percent, the zinc content 10–13 percent, and the silver content 80-230 g/ton (data from the early 1970’s).

Primary complex ores were formed in various geological epochs—from the Precambrian to the Cenozoic—by the crystallization of hydrothermal solutions. They are mostly confined to geosynclinal downwarps deposited on median masses and, as a rule, occur among acidic volcanic rocks. In the absence of noticeable amounts of copper, complex ores are usually localized in geanticlinal uplifts among carbonate rocks.

The rocks surrounding complex ores are usually strongly altered by hydrothermal processes, namely, chloritization, sericitization, and silicification. In addition to hydrothermal deposits, oxidized (secondary) complex ores, which form as a result of weathering of the surface segments of ore bodies (to a depth of 100–200 m), have some significance. These deposits usually contain iron hydroxides bearing cerussite, PbCO₃; anglesite, PbSO₄; smithsonite, ZnCO₃; calamine, Zn₄[Si₂O₇][OH]₂ · H₂O; malachite, Cu₂[CO₃](OH)₂; and azurite, Cu₃[CO₃]₂(OH)₂. Complex ores are classified according to the concentration of the ore minerals as massive or disseminated. The ore bodies of complex ores are distinguished by their variation in size (ranging from several meters to several kilometers), types of deposits (sheet deposits, lenses, stocks, veins, pockets, complex pipes), and the conditions of the bedding (gently sloping, steeply inclined, and conformable bedding; crossbedding).

Deposits of complex ores are mined by underground or open-cut systems. Open-pit mining is expanding every year and accounts for about 30 percent of production.

In the mining of complex ores, two major types of concentrates are obtained, one with a lead content of 40–70 percent and the other with a zinc and copper content of 40–60 percent. In the course of mechanical concentration, silver enters the lead concentrate. In metallurgical treatment, in addition to the primary component, the remaining secondary components are extracted.

In the USSR, deposits of complex ores are known in the Rudnyi Altai, central Kazakhstan, Eastern Siberia, Middle Asia, the Northern Caucasus, Western Siberia, and the Primor’e.

In 1973 the total reserves of lead and zinc in capitalist and developing countries were estimated at 103 million and 172 million tons, respectively. In 1972 these countries produced about 2.5 million tons of lead and 4.2 million tons of zinc. About 80 percent of these reserves are located in the United States, Canada, Australia, Peru, Japan, the Federal Republic of Germany, and Spain. These same countries accounted for 70 percent of production. In 1973 about 45 percent of the silver produced in the capitalist countries was obtained as a secondary product of complex ores (Canada, United States, Peru, Mexico, Australia, and Japan).