Resumen

BORDESE, Sofía et al. Geología y aspectos metalogenéticos de la mineralización de fluorita-baritina del distrito Chus-Chus - Pircas Coloradas, provincias de La Rioja y Catamarca. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.1, pp.37-49. ISSN 0004-4822.

A fluorite mineralized district (±barite± base metal sulfides) extends over the bordering region between La Rioja and Catamarca provinces, in the Western Sierras Pampeanas. The Chus-Chus deposit consists of fluorite-barite-base metal sulfide veins that crosscut rhyolite porphyry dykes of the Permian-Triassic Río Tendal Formation, and metamorphic country-rocks of the Neoproterozoic Espinal Formation. In the Pircas Coloradas prospects, fluorite is also associated with barite, quartz and base metal sulfides, though rarely forming veins but preferentially cementing rhyodacitic volcanics of Carboniferous age. The total rare earth element (REE) content in fluorite of both areas is variable (~ 30 to 107 ppm). Both show enrichment in mid REE, with Tb/La and Tb/Ca ratios that suggest crystallization from moderately fractionated fluids. The negative Eu/Eu* and Ce/ Ce* values for both areas would suggest low oxygen fugacity during precipitation, though an inherited pattern is not discarded. Temperature-salinity plots suggest that the Chus-Chus fluorite precipitated from hydrothermal fluids mixed with cooler, less saline fluids within a thermal regime of 104 to 149 °C. In Pircas Coloradas, the evolution of mineralizing solutions also indicates a nearly isothermal mixing of fluids of contrasting salinity within the temperature range of 111 to 146 ºC, representative of subsurface precipitation. Both occurrences would be representative of Permian-Triassic epithermal systems related to extensional tectonics. Chus-Chus might be genetically related to the rhyolitic magmatism of the Río Tendal Formation, tentatively assigned to the expiration of the Choiyoi magmatic cycle.

Palabras clave : Fluorite; Epithermal; Sierras Pampeanas Occidentales; Microthermometry; Rare earth element-geochemistry.

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