A thermochemical study of alunite, enargite, luzonite, and tennantite deposits

摘要: Temperature dependent phase relationships and irreversible reactions between fluids minerals in the systems K 2 O-Al O 3 -SiO -SO -H FeO-Cu O-H S-SO -As have been computed using thermodynamic data taken from literature. Pyrophyllite, rather than kaolinite, forms at temperatures below 200 degrees C if fluid is supersaturated with respect to quartz. Pyrophyllite formed under these conditions expected occur a metastable silica phase. Decreasing temperature constant ion activity favors precipitation of alunite over silicate minerals. Formation requires acid high sulfate activity. In volcanic rocks which are more reduced hematite-magnetite oxygen buffer, presence indicates H S contained greater 0.001 molal total sulfur when was 300 C. This fact greatly enhances likelihood that alunite-producing also produced mineralization depth. enargite (luzonite) tennantite copper sulfide iron If above porphyry pluton oxidized pluton, will oxidize as it flows upward. oxidation formation alunite, quartz, (luzonite), other studied. These facts suggest vertical vein mineral zonation plutons overlain by pyrite-chalcopyrite-potassium feldspar upward (luzonite)-tennantite-alunite rocks.Irreversible hydrothermal equilibrium potassium feldspar, biotite, pyrite, chalcopyrite decreases stability all solution, except some instances, kaolinite or pyrophyllite. Irreversible reaction an andesite solution quartz produces following zonations, alunite: kaolinite: montmorillonite: muscovite: maintains pyrophyllite: supersaturates