Evolution of the Monte Negro acid-sulfate Au-Ag deposit, Pueblo Viejo, Dominican Republic; important factors in grade development

摘要: This study was undertaken to determine the geologic factors that were important in making Pueblo Viejo, which contains over 600,000 kg of gold relatively high-grade ore, one few acid sulfate deposits be mined economically on a large scale. Orebodies at including Monte Negro, focus this study, are found around maar-diatreme complex formed upper part Lower Cretaceous Los Ranchos Formation. Ore is hosted by spilite, spilite-derived conglomerate, and intramaar carbonaceous sandstone mudstone. Regional seawater alteration these rocks overprinted two stages advanced argillic alteration, both associated with precious metals. Stage I produced deep alunite + quartz pyrite overlying kaolinite assemblages deposited association disseminated wall rock. II, stage I, pyrophyllite or - diaspore an (recrystallized) silica cap. Pyrite sphalerite enargite veins probably response hydrofracturing cap contain grades as much 100 ppm. Vein density assay data show approximately 60 percent Negro remainder II veins.Phase equilibria sulfur isotope thermometry took place below 260 degrees C pH values between 2 3. formation occurred above 285 C, from fluid initial 1 1.5, while caps 220 C. Geologic constraints indicate wall-rock sulfidation Fe-rich rock, whereas vein-hosted could have cooling, boiling, mixing ground water. Use programs SOLVEQ CHILLER evaluate relative efficiencies ore-forming processes confirms capable depositing gold, vein boiling related pressure release during subsequent water.These observations development grade tonnage Viejo greatly facilitated (1) porous-permeable complex, large, shallow hydrothermal cells served conduit for rising magmatic gases, (2) presence iron-rich caused early deposition "background" sulfidation, (3) later activity impermeable hydrofractured create overprint. Remobilization background into might also been factor upgrading deposits. Exploration similar should areas explosive volcanism andesitic island arc terranes.