The Quebrada Blanca mine is owned by a Chilean private company, Compañía Minera Teck Quebrada Blanca S.A. (QBSA). Teck holds an indirect 60% interest in QBSA (66.67% of the Series A shares); a 30% interest ((33.33% of the Series A shares) is owned indirectly by Sumitomo Metal Mining Co., Ltd. and Sumitomo Corporation (together referred to as SMM/SC), and 10% (100% of the Series B shares, which does not require Codelco to fund capital spending) is owned by Corporación Nacional del Cobre de Chile (Codelco), following their acquisition of the interest from the previous owner, Empresa Nacional de Minería (ENAMI), in 2024.
- subscription is required.
Summary:
The porphyry-style mineralization at Quebrada Blanca is considered to be typical of an Andean porphyry copper–molybdenum deposit.
To the northwest of the Quebrada Blanca deposit, sedimentary rocks of the Quehuita Formation unconformably overlie the Collahuasi Formation. The unit consists of deep to shallow marine limestone, calcareous sandstone, arenites, and conglomerates reflecting the extensional evolution of a Jurassic backarc basin in northern Chile. Within the same Mesozoic belt, the Cretaceous Cerro Empexa Formation crops out to the west and southeast of the Quebrada Blanca area, and consists of dacite lavas, volcaniclastic breccias, and inter-bedded arenite and conglomerates. Granite stocks have intruded the Cerro Empexa Formation and reflect the marginal shift of a Cretaceous arc into the Quebrada Blanca district.
The deposit is hosted in nine individual or groups of rock types. These include a Paleozoic quartz monzonite to granodiorite, and Late Eocene to Early Oligocene pre- to syn-mineral feldspar porphyries and syn-mineral hydrothermal breccias that intrude Collahuasi Formation lithologies.
Supergene leaching of the upper portions of the deposit and subsequent remobilization of copper produced supergene mineralization consisting of chalcocite and, to a lesser degree, copper oxides (chrysocolla, copper wad, copper clays, and minor atacamite, cuprite, and locally brochantite).
The hydrothermal breccias are interpreted to be formed by a single event, with textural and hydrothermal facies representing different energy conditions and hydrothermal zonation. The eastern area, dominated by tourmaline, and biotite–magnetite and biotite–potassic feldspar cements, is interpreted to be a better conserved column in the hydrothermal system. The western breccias do not contain tourmaline at the top. Lower-temperature quartz-rich and molybdenum-rich breccias have been recognized in the shallower parts of the breccia body.
The leach cap varies from about 7–200 m in thickness, whereas the thickness of the secondary copper zone ranges from 10–200 m. Continuous supergene copper mineralization has been traced over a 2.5 x 1.5 km area.
Hypogene mineralization occurs over a 2 x 5 km area, extending to at least 1.5 km vertical depth. Hypogene mineralization remains open to the west, northeast, east, southeast, and at depth.
Alteration zoning patterns at Quebrada Blanca are typical of porphyry copper deposits, and a detailed paragenetic sequence has been established. The three major alteration stages include:
- Early stage potassic alteration event: defined by secondary K-feldspar and biotite with associated biotite veinlets (EB), dark mica veins (EDM with biotite and green mica), and A veins (mainly quartz with K-feldspar halos). Brecciation occurred during the potassic event, permitting these hydrothermal minerals to develop locally as breccia cement. Chalcopyrite ± bornite occur as disseminations, in veins and/or in the cement of the breccia;
- Transitional stage alteration event: consists of grey-green sericite (SGV) and quartz as cement in breccias and/or as veins in coherent rocks. Quartz veins with sulfides (chalcopyrite and molybdenite and B veins) occur in this event as well as a biotite-, or biotite–magnetite- and chalcopyrite-cemented hydrothermal breccia;
- Late stage alteration event: consists of sericite–quartz–pyrite (phyllic; QS alteration) mainly as planar veins showing a prominent alteration halo (typical of D veins) and intermediate argillic alteration with kaolinite–smectite clays dominant.
Mineralization consists of supergene (chalcocite and, to a lesser degree, copper oxides such as atacamite, cuprite, and locally brochantite) and hypogene (chalcopyrite, bornite, molybdenite) mineralization. Mineralization displays two major trends.
Within the east–northeast trend, bornite mineralization forms two distinct zones that are interpreted to represent two different mineralizing centres as they do not spatially coincide with the higher copper grade areas hosted in chalcopyrite. Bornite is mainly concentrated in the southwestern part of the pit and in the northeastern portion of the east–northeast corridor that controls the porphyry and breccia intrusions. Chalcopyrite is controlled by the east–northeast trend in early potassic alteration as well as in transitional grey–green sericite and magnetite–chalcopyrite. Molybdenite mineralization is controlled by the same east–northeast-trending structures controlling higher copper grades (>0.5% Cu), but is also associated with northwest-trending structures in the eastern portion of the deposit.
Supergene Mineralization: secondary mineralization appears to be preferentially concentrated close to structures and more permeable rocks. The lower portions of the secondary enrichment zone transition into primary copper mineralization, resulting in a mixed low-grade ore type that was processed through run-of-mine (ROM) dump leaching.
Hypogene Mineralization: in the hypogene environment, mineralization occurs mainly as disseminated, veinlet-like and breccia cement mineralization forming an east–northeast-trending area within the Paleozoic quartz monzonite to granodiorite, feldspar porphyry intrusions, and breccias.
Within the northwest trend, pyrite distribution is generally related to quartz–sericite alteration and highly concentrated in late veins, typical of the northwest-trending principal faults where they also control supergene copper mineralization. The supergene mineralization is characterized by chalcocite and minor covellite. Gold and silver distributions correlate with copper mineralization grading >0.5% Cu. The locations of higher metal grades also appear to be structurally controlled, with grades increasing towards the hanging wall of the main fault. These minerals can locally occur outside of the main trends.
Alteration associated with the emplacement of the porphyritic and related intrusions includes chalcopyrite- and bornite-related veins, disseminations, and cement fill associated with potassic alteration. A large, vertically zoned hydrothermal breccia developed in association with the potassic event. This breccia has biotite, biotite-magnetite, chalcopyrite and locally bornite preserved at depth, whilst at shallower levels it transitions to a tourmaline-rich breccia with pyrite and chalcopyrite. A series of quartz-molybdenite veins are commonly associated with the biotite- magnetite breccia on the east side of the deposit. A subsequent chalcopyrite and molybdenite event cuts across the system and is characterized by grey-green sericite and quartz veins. This type of transitional alteration is best preserved in the western part of the deposit. A late quartz-sericite-pyrite assemblage cuts the copper-bearing stages and is strongly controlled by northwest-oriented structures. This phyllic event also occurs along northeast-oriented structures, which were a key control in the location of the supergene mineralization at surface. The mineralized porphyries and hydrothermal breccias are hosted by a quartz monzonite intrusive and the Collahuasi formation volcanics. Supergene enrichment processes have dissolved and redeposited primary (hypogene) chalcopyrite as a blanket of supergene copper sulphides, the most important being chalcocite and covellite, with lesser copper oxides/silicates such as chrysocolla in the oxide zone. Irregular transition zones, with locally faulted contacts, separate the higher- and lower-grade supergene/dump leach ores from the leached cap and hypogene zones.