Journal
GEOLOGY
Volume 36, Issue 9, Pages 719-722Publisher
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G24920A.1
Keywords
magmatic anhydrite; dacite; mineral deposits; sulfur
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Funding
- U.S. National Science Foundation [EAR-0337798]
- Swiss Fonds National [PBGE2-115088]
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Magmatic anhydrite from andesites and dacites occurs as inclusions in high- and low-aluminum amphibole and pyroxene and indicates that sulfate-saturated magmas spanned a period of six million years at Yanacocha, Peru. Magmatic anhydrite from Yanacocha and other sites is characterized by light rare earth element-enriched patterns and elevated strontium contents distinct from magmatic-hydrothermal anhydrite. Petrologic arguments suggest that the hydrous and oxidized Yanacocha magmas contained more than similar to 1000 ppm sulfur both dissolved in the melt and as a separate sulfate phase, which is sufficient to provide all the sulfur for the genetically related giant sulfur-rich Yanacocha epithermal gold deposits. High-aluminum amphiboles contain unusual anhydrite with wormy and amoeboidal textures, which are tentatively interpreted to represent trapping of an immiscible CaSO4-water melt together with sulfur-rich apatite at a temperature of similar to 950 degrees C and a water pressure >3 kbar. Such unusually sulfate-rich magmas may be required to produce sulfur-rich magmatic-hydrothermal mineral deposits.
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