科研之友
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摘要
The opening of the Gulf of Mexico during the Mesozoic led to the formation of the Sabinas Basin. Large carbonate platforms were developed throughout the Lower and Middle Cretaceous. The basin provided ideal conditions for the formation of a suite of carbonate-hosted, stratabound deposits such as barite, celestine, fluorite, and lead-zinc of Barremian-Aptian age. These deposits resemble Mississippi Valley-type (MVT) and associated deposits. The mining district of Sierra de Santa Rosa is located approximately similar to 7 km SE from Melchor Muzquiz in the state of Coahuila, Mexico. Barite is the economic mineral and the shape of the ore bodies is considered "mantos", the gangue minerals are calcite, local gypsum, traces of celestine, silica, and iron (oxy) hydroxides. The barite deposits show relict textures such as rhythmic, alternating black and white bands due to the presence of organic matter, and globular clusters similar to the "chicken-wire" anhydrite, typical of evaporites. A fluid inclusion and stable isotope analysis (S from barite, C and O from carbonates) were conducted. The lower manto yielded a melting ice temperature between -26 degrees C and -5 degrees C (salinities of 7.9 to 27 wt.% NaCl equiv.) and a homogenization temperature ranged between 59 degrees C to 155 degrees C. The eutectic temperature was -51 degrees C +/- 2 degrees C denoting a primary calcic brine. The upper manto yielded a melting ice temperature between -22 degrees C and -15 degrees C (salinities of 18.6 and 24 wt% NaCl equiv.) and a homogenization temperature was ranging from 60 degrees C to 126 degrees C. Isotopic analysis of barite showed delta(34)SvcDT ranges from +14.9%. to +19.5 parts per thousand (average of 16.9 parts per thousand). Sulfur isotope data for barite from the Sierra de Santa Rosa is consistent with a sulfur source formed during the Lower Cretaceous, which coincides with the age of the Cupido Formation. The carbon isotope analysis of the host limestone yielded a delta C-13(VPDB) range from -0.01% to +0.11 parts per thousand The delta C-13 values for clear and gray calcites ranged from -0.15 parts per thousand to -1.5 parts per thousand, and -1.41 parts per thousand to -2.3 parts per thousand, respectively. The oxygen isotope analysis showed a range between delta O-18(VSMOW) -4.55 parts per thousand and -10.04 parts per thousand. Fluid inclusion microthermometry and isotopic measurements lead us to conclude that brines from the Sabinas Basin led to the replacement of the evaporite strata (gypsum) by barite in the Cupido Formation and thus classify these deposits within the category of MVT and associated deposits.
- 出版日期2017-3
