Model for the formation of the Cu stratabound deposits in red beds of Las Vigas (Chihuahua, Mexico)
Por:
Gonzalez-Partida, Eduardo, Camprubi, Antoni, Pironon, Jacques, Alfonso, Pura, Cienfuegos-Alvarado, Edith, Morales-Puente, Pedro A., Canet, Carles, Gonzalez-Ruiz, Luis E., Diaz-Carreno, Erik H.
Publicada:
1 ene 2017
Categoría:
Earth and planetary sciences (miscellaneous)
Resumen:
In the tract of the Chihuahua and Sabina intracratonic basins,
stratabound copper deposits are systematically hosted by siliciclastic
rocks of the Las Vigas, San Marcos and Huizachal formations. The
deposits in the Las Vigas area, Chihuahua, occur in the upper part of
the Valanginian-Hauterivian Las Vigas Formation, which is conformably
overlain by gypsum and limestones of the Barremian La Virgen Formation.
Other local evaporites are those found in the Jurassic La Casita
Formation. The Las Vigas stratabound copper deposit was mined with
grades between 2 and 4 % Cu and occasional grades of 1 g/t Au and 80 to
100 g/t Ag in four 1 to 4 m-thick mantos. The hypogene metallic minerals
in this deposit are chalcopyrite, bornite, pyrite, sphalerite and
galena, along with quartz and calcite, mostly as disseminations.
Notably, part of these ores occurs as replacements of fossil tree logs
(m-sized) that contain the same minerals as mantos. The close
examination of fossil tree logs emphasizes the epigenetic and
stratabound character of copper ores. Representative fluid inclusion
associations were studied in calcite and quartz from mantos, lenses and
fossil logs. Fluid inclusions contain halite, calcite and chalcopyrite
daughter crystals, as determined by means of Raman microspectroscopy.
The calculated salinity of mineralizing fluids ranges between 16.6 and
32.0 wt. % NaCl equiv., temperatures of homogenization range between
104 degrees and 205 degrees C, and relevant N-2, CO, CO2 and CH4
contents were determined. delta S-34(VCDT) values in chalcopyrite range
between -12.0 and 13.7 parts per thousand. These values are compatible
with sedimentary or metasedimentary sources for sulfur, significant
amounts of sulfates that were leached from evaporites, besides the
occurrence of bacteriogenic sulfate reduction processes orthe
interaction of mineralizing fluids with organic matter. delta C-13(VPDB)
and delta O-18(VSMOW) values in hydrothermal calcite range between -7.96
and -0.71 parts per thousand and between 22.38 and 26.39 parts per
thousand, respectively; these are compatible with a trend in diagenesis
due to burial of marine sediments, much alike MVT deposits in Coahuila
and Texas.
The above data indicate that mineralizing fluids in Las Vigas are
basinal brines with minor meteoric inputs, which underwent convection
within the siliciclastic series by means of differences in density as
they dissolved evaporites of the overlying La Virgen Formation. Abundant
organic matter in the Las Vigas Formation would have enabled mineral
precipitation by means of sulfate reduction - such interpretation is
supported by the occurrence of Cu ores along with silicification in
fossil tree logs. As a consequence, the Las Vigas deposit is generically
ascribed to the group of epigenetic copper deposits hosted by red-bed
series that rim marine basins, or deposits of the Kupferschiefer type.
Filiaciones:
Gonzalez-Partida, Eduardo:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Blvd Juriquilla 3001, Santiago De Queretaro 76230, Qro, Mexico
Camprubi, Antoni:
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, Mexico City 04510, DF, Mexico
Pironon, Jacques:
Univ Lorraine, CNRS, CREGU, GeoRessourceslab, Blvd Aiguillettes, F-54506 Vandoeuvre Les Nancy, France
Alfonso, Pura:
Univ Politecn Cataluna, Escola Tecn Super Engn Mines Manresa, Dept Engn Minera & Recursos Nat, Av Bases Manresa 61-73, Manresa 08242, Catalunya, Spain
Cienfuegos-Alvarado, Edith:
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, Mexico City 04510, DF, Mexico
Morales-Puente, Pedro A.:
Univ Nacl Autonoma Mexico, Inst Geol, Ciudad Univ, Mexico City 04510, DF, Mexico
Canet, Carles:
Univ Nacl Autonoma Mexico, Inst Geofis, Ciudad Univ, Mexico City 04510, DF, Mexico
Gonzalez-Ruiz, Luis E.:
Univ Lorraine, CNRS, CREGU, GeoRessourceslab, Blvd Aiguillettes, F-54506 Vandoeuvre Les Nancy, France
Geol Mineria & Consultoria SA, CV, Cipres 104, Santiago De Queretaro 76100, Qro, Mexico
Diaz-Carreno, Erik H.:
Univ Nacl Autonoma Mexico, Posgrad Ciencias Tierra, Blvd Juriquilla 3001, Santiago De Queretaro 76230, Qro, Mexico
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