The deposits within the Cerro Negro Operations are considered to be examples of lowsulphidation, epithermal gold–silver deposits.
Mineralization characteristically comprises pyrite, electrum, gold, silver, and argentite. Other minerals can include chalcopyrite, sphalerite, galena, tetrahedrite, and silver sulphosalt and/or selenide minerals. In alkalic host rocks, tellurides, roscoelite, and fluorite may be abundant, with lesser molybdenite as an accessory mineral.
Deposits are typically zoned vertically over about a 250 m to 350 m interval, from a base metal poor, gold–silver-rich top to a relatively silver-rich base metal zone and an underlying base metal-rich zone grading at depth into a sparse base metal, pyritic zone. From surface to depth, metal zones grade from gold–silver–arsenic–antimony–mercuryrich zones to gold–silver–lead–zinc–copper-rich zones, to basal silver–lead–zinc-rich zones.
Silicification is the most common alteration type with multiple generations of quartz and chalcedony, which are typically accompanied by adularia and calcite. Pervasive silicification in vein envelopes is flanked by sericite–illite–kaolinite assemblages. Kaolinite illite–montmorillonite ± smectite (intermediate argillic alteration) can form adjacent to veins; kaolinite–alunite (advanced argillic alteration) may form along the tops of mineralized zones. Propylitic alteration dominates at depth and along the deposit margins.
Vein mineralogy d ........
