On January 15, 2025, Lundin Mining completed a joint acquisition of the Filo del Sol project with BHP and a 50% sale of the Josemaria project to form Vicuña Corp., resulting in Lundin Mining Corp. indirectly holding a 50% interest in Vicuña, which owns the Filo del Sol project and the Josemaria project. BHP indirectly owns the remaining 50% interest in Vicuña.
Vicuña will be the operator, acting independently from Lundin Mining and BHP, and will be responsible for the development, operation, and management of the projects.
Work is ongoing to outline an integrated project incorporating the two deposits.
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Summary:
The Josemaria project area is underlain most extensively by Permo-Triassic rocks assigned to the Choiyoi Group, which forms the Andean basement in the region. They include volcaniclastic and ignimbritic rhyolites as well as broadly equivalent granites. Triassic intrusive complexes of tonalite, diorite and granodioritic composition intrude the rhyolites and granite. Swarms of andesite dykes, which are typical of the Permo-Triassic in this region, cut the older Permo- Triassic units.
Porphyry intrusive rocks and associated porphyry and epithermal mineralized systems are largely hosted within basement rocks. Late Oligocene systems form a north-south trend extending from Josemaria to the Sillimanita and Cerro Blanco Cu-Au porphyry prospects formed around similar dacitic intrusions. Middle Miocene systems such as the Filo del Sol porphyry-epithermal Cu-Au-Ag deposit and the Los Helados porphyry Cu-Au deposit occur several kilometres westward.
The Josemaria porphyry copper-gold deposit is centred on a Late Oligocene dacitic porphyry intrusive complex emplaced into Permo-Triassic rhyolite and tonalite. Porphyry ascent and localization appears to have been guided by a pre-existing north-south structural zone.
The Cu–Au mineralization at Josemaria is hosted within a porphyry system that includes two main types of hypogene mineralization. These two types occur in proximity to one another due to a high degree of telescoping of high-sulphidation alteration and mineralization over deeper mineralization related to potassic alteration. Late supergene enrichment within the northern part of the deposit has upgraded copper values over part of the system. Deposit dimensions, defined by the current resource, are ~1000 m east-west, ~1500 m north-south, and 600 to 700 m vertically.
The first and most widespread type of hypogene Cu and Au mineralization is associated with the upper parts of the potassic alteration zone (Min zone PyCpy). Disseminated and vein-style chalcopyrite mineralization is associated with an A-type quartz-magnetite veinlet stockwork in the area above and around the porphyry intrusions. Minor bornite is present, but in an approximate ratio of 30:1 (chalcopyrite:bornite) within the potassic zone.
Sericite-chlorite-clay alteration overprints potassic but was not grade-destructive and some of the best Cu grades are found in the SCC domain. Where overprinted, which is through much of the deposit, the sulphide assemblage has been variably reconstituted to pyrite-chalcopyrite with pyrite:chalcopyrite ratios of approximately 3-10:1. Copper and gold values are in the range of ~0.35% Cu and 0.2 g/t Au.
This Cu-Au mineralization is overlapped by a molybdenite-bearing annulus best developed on the northern and eastern sides, with grades averaging > 50 ppm Mo. It is related to molybdenitebearing B-veins surrounding the central part of the system.
The second type of hypogene sulphide mineralization is located along the western and central parts of the system, associated with the advanced argillic domain and the underlying sericitic alteration (Min zone PyCc(H)). This high-sulphidation assemblage includes disseminated grains of pyrite rimmed by hypogene chalcocite, bornite and/or covellite with trace amounts of tennantite and enargite. Arsenic values are relatively low, in the range of ~10–100 ppm. Pyrite:copper-bearing sulphide ratios are roughly 10:1.
In the central part of the system, where the highest degrees of alteration telescoping are mapped, the high-sulphidation alteration extends downward over the potassic- and SCC-related chalcopyrite mineralization. In this area, the early potassic-related sulphide mineralization is reconstituted and upgraded by the high-sulphidation sulphide assemblage, reflected in higher gold and hypogene copper grades in the central part of the system. In places values of ~0.6% Cu and ~0.7 g/t Au are attained in the south-central, highest grade part of the system.
Supergene copper enrichment (PyCc(S)) is focused along the NNE structural zone through the northern part of the deposit. The Late Oligocene erosional event removed the upper parts of the mineralized system, but erosion took pace at a rapid rate that did not allow for development of an extensive leached cap or supergene enrichment at that time. Only more recently, likely during most recent glacially-aided erosion into the system, has a leached cap been developed over the system (Ox and Mix) with an underlying supergene enrichment zone. The leached zone ranges from 10–20 m in thickness over the relatively impermeable felsic volcanic rocks in the west to a maximum of 230 m within the Josemaria NNE structural corridor and the tonalite farther east where it was facilitated by damage zones along faults and increased permeability through groundwater removal of sulphate veins. The underlying supergene enrichment domain attains grades in the range of 0.8-1.5% Cu.
Appreciable oxide Cu (malachite and neotocite) mineralization is restricted to a small zone of fractures within the leached cap (Ox) in the northern part of the deposit. This is interpreted to be the result of leaching of the pyrite-poor potassic domain. Also, a significant Au-rich portion of the leached cap occurs along the centre of the deposit, between section lines 4100N and 4600N, with values averaging 0.35 g/t Au within the oxide zone. This area corresponds to the central, and perhaps deepest, parts of the advanced argillic alteration zone within the system.
Based on geological features and location, the Josemaria deposit is classified as a Cu–Au porphyry system.