Metallogenic model of the Eocene Santa Mara and Antares Zn-Pb(-Ag) skarn deposits, Velardena Mining District, Durango, Mexico

The Santa Mar & iacute;a and Antares Zn-Pb(-Ag) skarn deposits in the Velardena Mining District are located in central-NW Mexico. They lie 470 m apart along the contact between Oligocene felsic intrusions and Cretaceous limestones, and were developed during prograde, retrograde, post-ore (Santa Maria), and late stages. Firstly, the prograde stage was formed by fluids at similar to 600 degrees C and 15 wt% NaCl equiv., and consists of garnet + wollastonite +/- clinopyroxene and biotite +/- K-feldspar assemblages. Secondly, the retrograde/ore stage was formed by fluids at 300-500 degrees C with salinities of 20-30 wt% CaCl2 (Santa Mar & iacute;a) and > 40 wt% NaCl equiv. (Antares). It comprises assemblages of chlorite, amphibole, epidote, calcite, scapolite, quartz, sericite, adularia, fluorite, and muscovite associated with sphalerite, pyrite, galena, pyrrhotite, arsenopyrite, chalcopyrite, and Pb-Bi-Sb sulfosalts. Thirdly, the post-ore stage was formed by fluids at similar to 400 degrees C and 20-30 wt.% CaCl2 and comprises poorly mineralized calcite veins. Fourthly, the late stage was formed by fluids at < 300 degrees C and 20-30 wt.% CaCl2 (Santa Mar & iacute;a) and similar to 15 wt% NaCl equiv. (Antares), and crystallized tetrahedrite-group minerals and pyrite + marcasite. delta O-18(fluid) between similar to 14 parts per thousand and 23 parts per thousand at Santa Maria and between similar to 12 parts per thousand and 17 parts per thousand at Antares show a less-modified magmatic affinity for mineralizing fluids at Antares; delta C-13(fluid) between 0 parts per thousand and -6 parts per thousand register recycling of sedimentary C. Moreover, sulfides with delta S-34(VCDT) between -3 parts per thousand and 2 parts per thousand reveal a magmatic source for S. Altogether, these data suggest that, at Santa Mar & iacute;a, magmatic-derived fluids actively interacted with the wall rocks, whereas at Antares the fluid-rock interaction was milder. In both deposits, metal deposition was triggered by the cooling and neutralization of ore-bearing fluids with carbonate rocks. Our Ar-40/Ar-39 dates for adularia of ca. 37.5 Ma place the deposits within the Eocene-early Miocene metallogenetic epoch of central-NW Mexico, during which other world-class skarn-epithermal systems were emplaced (e.g., Concepcion del Oro and Mazapil-Penasquito).