sulfosalts

Sulfosalts are a class of complex sulfide minerals in which sulfur combines with metals and semimetals, most commonly arsenic, antimony, or bismuth. The defining characteristic is the partial substitution of semi-metal elements for metal cations within the sulfide lattice, yielding a family with variable stoichiometry and intricate crystal structures. This results in a wide range of chemical compositions that still behave as a coherent mineral group.

Chemically, sulfosalts form networks in which sulfur is bonded in covalent-like frameworks, accommodating semi-metals in specific lattice positions. The variability in the arrangement and proportion of copper, silver, lead, or other metals alongside arsenic, antimony, or bismuth gives rise to numerous minerals that can be difficult to distinguish by simple sulfide patterns alone. The most important and widespread subgroup is the tetrahedrite–tennantite series, where copper-rich compositions range toward Cu12(Sb, As)4S13 and substitutions between Sb and As occur.

Sulfosalts commonly occur in hydrothermal ore deposits and polymetallic sulfide systems. They form in copper- and silver-rich environments and are frequently found with other sulfides such as sphalerite and galena. They may be primary crystallization products or form during later hydrothermal alteration and metasomatic processes.

Notable sulfosalts include tetrahedrite (often expressed as Cu12Sb4S13 with arsenic-for-antimony substitutions), proustite (Ag3AsS3), pyrargyrite (Ag3SbS3), bournonite (PbCuSbS3), freieslebenite (PbAgSbS3), and cylindrite, a bulk sulfosalt with a complex lead–tin–antimony–iron sulfide composition. These minerals are economically interesting as carriers of copper, silver, antimony, and related metals, though they are typically less abundant than simpler sulfide ores.

See also: sulfide minerals, arsenic minerals, antimony minerals.