The El Mochito mine, located in west-central Honduras, exploits a distal Zn-Pb-Ag skarn-hosted deposit. The bulk of economic mineralization, occurring either as steeply dipping pipes or flat-lying manto bodies, is hosted by Cretaceous Atima Formation limestone. Skarn mineralogy consists of early grossularitic garnet followed by andraditic garnet and hedenbergitic pyroxene, with pyroxene skarn the principal host to sphalerite mineralization. Ore minerals, which post-dated silicate precipitation, comprise sphalerite of variable Fe content, galena, magnetite, pyrrhotite, chalcopyrite, pyrite and trace amounts of arsenopyrite. The distribution of ore metals in the orebodies is zoned from Zn-Fe-rich cores to adjacent Pb- and Ag-rich zones reflecting the sequential saturation of sphalerite and galena in the fluid with decreasing temperature. / Skarn formation was accompanied by significant additions of Si, Fe, Mg, Al, and Mn and variable changes in Ca during early alteration. Apparent decreases in the concentrations of Ti and Zr suggest that the fluid:rock ratio was high. Variations in component activities of the hydrothermal fluid indicate that andraditic garnet skarn was stable at lower log(aCa2+/aH+ 2), log(aAl3+/aH+3), and log aSiO2aq , and higher log(aFe3+/aH+3) than its grossularitic garnet skarn precursor, whereas hedenbergitic pyroxene skarn was stable at lower log(aCa2+/aH+2) and log(aFe3+/aH+3) and higher log aSiO2aq than its andraditic skarn precursor. / delta34S values of sphalerite, galena and pyrrhotite cluster between -1 and +2‰, and their corresponding fluid delta 34 SH2S values ranged from -3.7 to +5.4‰, indicating that the sulphur was primarily igneous in origin, and lead isotope ratios of galena are similar to those of the Miocene-Pliocene Padre Miguel ignimbrite. Variation in the delta 34S values of sphalerite and the whole-rock Pb isotope ratios of the host limestone are interpreted to reflect decreasing alteration toward the southwest. / Microthermometric measurements for garnet-, pyroxene- and sphalerite-hosted fluid inclusions indicate that two end-member fluids, a saline formational brine and a Fe-rich orthomagmatic fluid, formed skarn and ore at the deposit. The first, hosted by grossularitic garnet and low-Fe sphalerite, is characterized by homogenization temperatures ranging from 260 to 390°C, and salinities from 7 to 45 wt.% NaCl equivalent. The second, hosted by pyroxene, andraditic garnet, and medium-Fe sphalerite, is characterized by a higher homogenization temperature (320 to 400°C), lower salinity (1 to 15 wt.% NaCl equivalent) and an elevated Fe concentration. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85122 |
| Date | January 2004 |
| Creators | Ault, Katherine M. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Earth and Planetary Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002209370, proquestno: AAINR12802, Theses scanned by UMI/ProQuest. |
Page generated in 0.0017 seconds