Summary:
The Toquepala deposit is considered to be an example of a copper–molybdenum porphyry deposit.
The Toquepala deposit is hosted mainly within latest Cretaceous rhyolitic and andesitic flows and ash fall deposits of the Toquepala Group and to a lesser extent within an Eocene dioritic batholith of the Yarabamba intrusive suite.
The deposit is ovoid, extending over a 3.3 x 3.5 km area. Mineralization has been drill tested to about 950 m from the original land surface. Drilling from within the pit base indicates primary mineralization extends for an additional 930 m below the pit bottom.
Mineralization is closely associated with a complex, 1,500 m diameter intrusive center dominated by four phases of porphyritic dacite plugs, referred to as "T", "Main", "L/M" and "Late", a dacite diatreme and agglomerates, extensive hydrothermal breccias and latite porphyry stocks and dikes.
In the mine area, the Toquepala Lineament appears to control some aspects of mineralization. The lineament is based on the distribution of three porphyry stocks, two breccia bodies, numerous pebble, and thin intrusive dikes within the mine as well as the Cerro Toquepala, Cerro Azul and Totoral breccia pipes along a 20° azimuth. The lineament is controlled by a north– northeast-trending pre-mineral fault system.
Mineralization consists of leached capping, oxide, enriched, transitional and primary mineralization. The first four types have largely been mined out.
Mineralization types include:
• Leached capping is predominantly limonite (jarosite 30%, hematite 60% and goethite 10%) mostly disseminated and in fractures. It is mostly mined out; however, remnants occur around the periphery of the pit.
• Oxide mineralization is very sparse and may be entirely mined out.
• Enriched mineralization consists of 90% chalcocite, and 10% digenite, covellite, and bornite in breccia matrix, disseminations, and veinlets. This material has the highest copper grades and is mostly mined out.
• Transition mineralization is about 60% chalcopyrite, 25% chalcocite and 15% molybdenite and bornite as breccia matrix, disseminations, and veins associated with quartz. It is mostly mined out, but remnants are localized on the west edge of the pit.
• Primary copper mineralization occurs as hypogene sulfides mainly restricted to the dacite porphyry and breccias. Chalcopyrite is the dominant economic mineral (90% of mineralization) with 10% bornite, molybdenite, and enargite as disseminations fracture fillings, and breccia matrix. It is associated with potassic alteration (biotite and/or K-feldspar) with about 1% of pyrite (pyrite to chalcopyrite ratio of about 3:1) associated with magnetite and anhydrite. Economic molybdenite mineralization is associated with quartz veinlets and locally, with disseminated chalcopyrite.
In the phyllic zone, pyrite is present as 10% of the rock. The pyrite to chalcopyrite ratio is about 12:1, associated with minor molybdenite, bornite, chalcocite, sphalerite, and galena.