The Antapaccay project is owned and operated by Compañía Minera Antapaccay S.A. (CM Antapaccay), a Peruvian company that is an indirect wholly-owned subsidiary of Glencore.
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Summary:
The Antapaccay project contains a porphyry-skarn type (copper-silver-gold) deposit located in the Eocene-Oligocene Andahuaylas-Yauri strip, 9.4 kilometres southwest in a straight line from the Tintaya mine, in the area of the old Atalaya mine. The Eocene-Oligocene Andahuaylas-Yauri strip is located 250 to 300 kilometres west of the current Peru-Chile Trench, above a thick cap of sialic crust (50 to 60 kilometres), in a transitory zone between the flat subduction slab of central Peru and the normal subduction of southern Peru and northern Chile and immediately to the southeast of the Abancay deflection. It consists geologically of a thick cretaceous sedimentary sequence folded during the Andean deformations and widely intruded by stocks, sills and dykes of Andahuaylas-Yauri batholith, covered by Cenozoic lacustrine and volcanic deposits and quaternary deposits.
The copper mineralization at Antapaccay is mainly contained in intermediate intrusive rocks with dissemination, veinlets, hydrothermal breccias which are in contact with pre-mineral rocks such as diorites and sedimentary rocks (limestones, calcareous shales, siltstones and sandstones), forming contact mineralized breccias, exoskarn and stockwork in sedimentary bodies with a clear predominance of chalcopyrite over bornite up to 350 metres; the roles reverse at a greater depth and are associated with a level of anhydrite-gypsum.
The dominant mineralization within the porphyry is chalcopyrite, followed by bornite and chalcocite. Mineralization consists of both disseminations and veinlets, with the highest grades of gold corresponding to intense bornite rich stockwork zones. The dominant alteration type within the porphyry is a potassic alteration of the host diorite. The porphyry is also in contact with cretaceous sedimentary rocks, which have formed irregular skarn (limestones) and stockwork (hornfels and quartzites) containing high copper values, but represent a minor component of all the resources.
The conditions for the occurrence of a metasomatic process exist in contact with limestones, generating irregular garnetmagnetite +/-pyroxene exoskarn, mainly with chalcopyrite patches. Extensive areas of intense grey quartz veinlet stockwork with a high bornite and chalcopyrite content were identified always near the hornfels-intrusive rock contact, expanding into the hornfels for several metres.
Coroccohuayco
The Antapaccay property also includes the Coroccohuayco project, a satellite deposit that is located within 10 kilometres of the Antapaccay plant. At this stage, exploration, drilling and engineering studies at Coroccohuayco have focused on defining Mineral Resources and Mineral Reserves and no mining activities are being undertaken.
The main copper bearing minerals at Coroccohuayco are bornite, chalcopyrite and chalcocite, with the host rock consisting of Cretaceous sedimentary rocks of the Ferrobamba and Mara formation intruded by monzonitic plutons of the Eocene— Oligocene Andahuaylas—Yauri batholiths. The Coroccohuayco deposit is dominantly a skarn-hosted deposit, whereas the Antapaccay deposit is dominantly porphyry-hosted.