Mineralogy, geochemistry, and age constraints on the Zn-Pb skarn deposit of Maria Cristina, Quebrada Galena, northern Chile

The Maria Cristina Zn-Pb skarn deposit, hosted by carbonate rocks of the Lo wer Cretaceous Chanarcillo Group in northern Chile, is described to provide a basis of comparison to adjacent (similar to 2 km) barite deposits and re gional Pb-Zn and Ba deposits with Mississippi Valley-type affinities. Stron gly retrograded garnet (andradite to Ad(30)Gr(70)), diopsidic pyroxene, and epidote skarn, and barite-bearing massive sulfides (sphalerite-pyrite gale na-marcasite-magnetite) occur at the contact of potassically altered diorit e porphyry of mid-Cretaceous age. The skarn mineral compositions, similar t o those of Cu skarns, may reflect emplacement in a high f(O2) context. Sulf ur isotope values of sulfides (-8.8 to +7.1 parts per thousand) and barite (14.0-26.1 parts per thousand) indicate disequilibrium conditions and diffe rent sulfur sources, including magmatic sulfur. Lead isotope ratios of gale na and strontium isotope ratios of barite indicate a similar metal reservoi r for the different ore deposit types, constituted by the intercalated Lowe r Cretaceous volcanic rocks or mid-Cretaceous intrusive rocks. Ar-40/Ar-39 dating of hydrothermal K feldspar suggests an age between 94 and 90 Ma for the mineralization.