Fluid Origin of the Stratabound Fluorite and Celestite Deposits in Coahuila, Mexico.

HR: 0800h
AN: V31A-1422 [Abstracts]
TI: Fluid Origin of the Stratabound Fluorite and Celestite Deposits in Coahuila, Mexico.
AU: * Tritlla, J
EM: jordit@geociencias.unam.mx
AF: Geofluidos, Centro de Geociencias, UNAM, Carr. Qro.-SLP km 15,5, Juriquilla, queretaro, 42 76230 Mexico
AU: Gonzalez-Partida, E
EM: egp@geociencias.unam.mx
AF: Geofluidos, Centro de Geociencias, UNAM, Carr. Qro.-SLP km 15,5, Juriquilla, queretaro, 42 76230 Mexico
AU: Banks, D
EM: D.Banks@earth.leeds.ac.uk
AF: Earth Sciences School, The University of Leeds, Leeds, Leeds, LS2 9JT United Kingdom
AU: Levresse, G
EM: samuelbaca@yahoo.com.mx
AF: Geofluidos, Centro de Geociencias, UNAM, Carr. Qro.-SLP km 15,5, Juriquilla, queretaro, 42 76230 Mexico
AU: Baca-Gasca, S
EM: samuelbaca@yahoo.com.mx
AF: Fluorita de Mexico S.A. de C.V., Avenida del Parque 245, Muzquiz, 26340 Mexico
AU: Rodriguez-Santos, A
EM: arodriguez@alfil.com.mx
AF: Fluorita de Mexico S.A. de C.V., Avenida del Parque 245, Muzquiz, 26340 Mexico
AB: The Mesozoic units that outcrop north of Coahuila State in northern Mexico host numerous celestite, celestite-fluorite and fluorite deposits, mainly enclosed in the Cretaceous limestone units. Celestite and celestite-fluorite deposits are lens-shaped bodies, up to 2 m thick and a total length exceeding 500 meters, intercalated within the carbonates of the Cupido Formation (Aptian) or equivalents. Celestite-free fluorite bodies, mainly enclosed in the Aurora Formation (Albian-Cenomanian), appear as sub-concordant lenses with abundant evidences of hydraulic fracturing, usually near low-angle fractures. The celestite brine halogen composition on a Cl/Br vs Na/Br molar ratio plot on the trend defined by the evaporation of seawater, while in a ppm Cl vs Cl/Br plot away from the seawater evaporation line but parallel to it, indicating that the solution was mainly modified by dilution. The fluids involved in the genesis of the La Encantada fluorite deposit probably are evolved seawater that undergone some degree of evaporation. Mixing of fluids is clearly delineated by both microthemometric and halogen data, where salinities calculated are too low for the halogen ratios found, indicating a mixing with a low-salinity end-member. Hydrocarbon-bearing fluid inclusions repeatedly show the presence of solid bitumen trapped along with heavy oils, indicative of thermal degradation. Both, mixing and thermal degradation of hydrocarbon-rich fluids along with hydraulic fracture of the host rock points to an "in situ" organic matter maturation, due to the mixing of a saline, oxidant, sulphate and CaCl2-rich "bittern", which probably transported fluorite, with an organic-matter rich fluid present in the cretaceous carbonates. It is noteworthy that these previous results suggest that both celestite and fluorite-dominated deposits formed from brines from similar origin, showing the same halogen systematics. Strontium enrichment can be explained by leaching of Sr from the carbonate series during diagＯesis, probably related with the inversion from aragonite to calcite. Transport of fluor is favored and maximized by (basinal) brines enriched in Ca2+, probably originated after seawater evaporation or evaporite dissolution prior to F leaching. Then, the distribution of celestite-dominant or fluorite-dominant deposits can be controlled by both the sort of rocks locally present in the basement as well as the depth of brine circulation.
DE: 3665 Mineral occurrences and deposits
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting