Geological setting and genesis of stratabound barite deposits at Múzquiz, Coahuila in northeastern Mexico

Abstract

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 ~7km SE from Melchor Múzquiz 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°C and −5°C (salinities of 7.9 to 27wt.% NaCl equiv.) and a homogenization temperature ranged between 59°C to 155°C. The eutectic temperature was −51°C±2°C denoting a primary calcic brine. The upper manto yielded a melting ice temperature between −22°C and −15°C (salinities of 18.6 and 24wt.% NaCl equiv.) and a homogenization temperature was ranging from 60°C to 126°C. Isotopic analysis of barite showed δ34SVCDT ranges from +14.9‰ to +19.5‰ (average of 16.9‰). 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 δ13CVPDB range from −0.01‰ to +0.11‰. The δ13C values for clear and gray calcites ranged from −0.15‰ to −1.5‰, and −1.41‰ to −2.3‰, respectively. The oxygen isotope analysis showed a range between δ18OVSMOW −4.55‰ and −10.04‰. 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.