Geology of Galeana Barite District, Nuevo Leon, Mexico

Delfino Ruvalcaba-Ruiz

The Galeana district consists of monomineralic barite veins in Late Triassic red beds spatially associated with igneous sills and dikes close to the contact with Upper Jurassic evaporites (chiefly gypsum). The district lies at the western margin of the Sierra Madre Oriental in southern Nuevo Leon, Mexico, and it has been one of the leading BaSO₄ producers of the country. Ore barite filled reactivated steeply dipping (50-88° northwest) fractures striking N40-50°E and, to a lesser extent, steeply dipping (60-85° southwest) fractures striking N60-80°W, all formed at the crest of the San Marcos anticline. The latter represents a local apical portion of a northwest-trending segment of pre-Mesozoic basement 2,000-3,000 m anomalously high in the re ion. The massive barite contains up to 10 wt. % SrSO₄.

The proposed genetic model for the mineralization involves a convective cell activated by magmatic pulsations or emanations of hydrothermal solutions, whose migration through the permeable clastic host rocks was propitiated by Laramide fracturing, folding, and rock uplift. These Ba²⁺ and (Sr²⁺)-rich fluids reacted with the SO_4^2--contributing evaporites and perhaps with descending H₂O, yielding sudden precipitation of Sr-bearing BaSO₄ at the preexisting fractures and brecciated zones. S and Sr-isotope analyses on ore barite reveal that the S source was the overlying evaporites, whereas the Sr was derived from the underlying and adjacent host and country rocks within the realm of the postulated system. The massive barite robably formed under high P_O2 and P_SO4 near neutral pH, temperatures below 210°C, P_T nearly or equivalent to hydrostatic at relatively shallow depths, within an H₂O-rich system with great chemical activity of Ba²⁺, Ca²⁺, (Sr²⁺), SO_4^2-, CO_3^2-, HCO_3^-, and perhaps HPO_4^2-, Mn_XO_X, and H₂S.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.