New Mexico Geological Society Annual Spring Meeting — Abstracts

Arizona Sonoran Copper Company is sponsoring research to better understand the nature of the supergene profile developed at the Cactus Mine (formerly Sacaton) porphyry copper deposit, with emphasis primarily on the Cactus and the Parks/Salyer bodies. The enrichment style at Cactus appears consistent, with only local variations in the weathering profile. This study has defined variations in the occurrence of covellite within a predominantly chalcocite supergene profile; furthermore, petrographic study shows that apparent hypogene covellite is associated with chalcocite. Due to chalcocite and covellite having substantially different responses to a heap leaching environment, the ASCU metallurgy team must understand the mineralogic association of chalcocite-covellite to efficiently engage in mine and copper recovery planning.

This research describes and defines the enrichment profile of the Cactus Mine, showing that there is important structural control, as well as alteration-related control, of sulfide formation and distribution. Our research shows that the petrographic and trace element characteristics of the Parks/Salyer mineralized zones consist of chalcocite-dominant enrichment, as chalcocite replaces chalcopyrite and pyrite grains, underlying a mature hematite-goethite leached capping. Recent exploration drilling performed in the southern section of the Parks/Salyer-Main Springs property has shown that covellite is the locally dominant sulfide, rather than chalcocite. Both thin-section and polished sections representing mineralization from covellite-dominant zones to determine the composition of covellite and covellite-adjacent minerals (blaubleibender, geerite, yarrowite) in the Parks/Salyer region. In addition to the enrichment characteristics, primary ore minerals and associated alteration show that local structural controls and protore alteration characteristics have had a crucial role in covellite vs. chalcocite formation.

Future work soon includes further petrographic review of the leached capping above the chalcocite and covellite zones, and an evaluation of the alteration mineral species found within the leached capping and in surrounding country rock. Our study-to-date, and observations by the ASCU geology team, indicate that the covellite bodies are related to specific alteration types, especially phyllic and transitional phyllic-potassic assemblages. Other work involves logging core holes in Parks/Salyer to better understand the numerous breccias and faults that transect the mineralization, as well as the variations in mineral zonation within the supergene profile. Use of Vulcan models being utilized to aid in interpretation of structure and alteration boundaries within the Parks/Salyer porphyry system.