Alunite
Alunite is a potassium aluminum sulfate mineral, KAl₃(SO₄)₂(OH)₆, commonly formed when acidic, sulfate-rich fluids alter volcanic rocks.
Sulfate minerals: Minerals containing the sulfate anion, SO₄²⁻, as a major structural component. Alunite belongs to this mineral group because sulfate is part of its defining composition.
Acid-sulfate alteration: Hydrothermal alteration by acidic, sulfur-bearing fluids that leach rock and produce sulfate minerals. This alteration process commonly creates the chemical conditions in which alunite forms.
High-sulfidation epithermal deposit: A shallow hydrothermal ore deposit formed by acidic, sulfur-rich fluids above a magmatic system. Alunite commonly marks the advanced argillic alteration associated with these deposits.
Marysvale volcanic field: A volcanic region in Utah with extensive hydrothermal alteration and alunite deposits. Its alunite deposits have been mined and studied as products of volcanic hydrothermal systems.
Alunite supergroup: A mineral supergroup whose members share related structures built from octahedral and tetrahedral units. Alunite is the namesake mineral of this structurally related group.
Steam-heated alteration: Near-surface alteration caused when rising volcanic gases condense and oxidize in groundwater. Condensing sulfur gases can acidify groundwater and precipitate alunite above geothermal systems.
Porphyry copper deposit: A large, disseminated copper deposit associated with intrusive igneous rocks and hydrothermal fluids. Alunite-bearing acidic zones can overlie or border porphyry copper systems.
Cerro Quema: A high-sulfidation epithermal gold-copper prospect in Panama. Alunite alteration at Cerro Quema helps characterize its acidic hydrothermal system.
Crystal structure: The ordered, repeating arrangement of atoms in a crystalline solid. Alunite’s structure accommodates sulfate groups, aluminum octahedra, and potassium.
Hydrothermal alteration: Chemical and mineralogical change in rock caused by circulating hot, reactive fluids. Alunite is one product of hydrothermal alteration under acidic, sulfate-rich conditions.