The Costa Fuego Project is controlled by Hot Chili Limited (ASX: HCH) through its 100% subsidiary Sociedad Minera El Corazón SpA.
Productora (including Alice) deposit is 100% owned by Sociedad Minera El Aguila SpA, a joint venture, 80% held by Sociedad Minera El Corazón SpA (100% subsidiary of Hot Chili Ltd.) and 20% by Compañía Minera del Pacífico S.A.
Cortadera deposit controlled by Sociedad Minera Frontera SpA, which is 100% owned by Sociedad Minera El Corazón SpA (100% subsidiary of Hot Chili Ltd.); controls an area approximately 12.5 x 7 km through various option earn-in agreements and 100% ownership of certain leases.
San Antonio deposit controlled through Frontera (100% owned by Sociedad Minera El Corazón SpA, 100% subsidiary of Hot Chili Ltd.); subject to an option agreement with a private party to earn a 100% interest.
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Summary:
The four deposits which comprise the Costa Fuego Project (Productora, Cortadera, Alice, and San Antonio) lie proximal to one another, at low altitude (800 m to 1,000 m), approximately 600 km north of Santiago. The La Verde exploration area is located 35 km south of Productora.
Deposit Types
The Costa Fuego Project encompasses several different deposit types and mineralisation styles. Cortadera and La Verde mineralisation are associated with a classic copper-gold-molybdenum porphyry deposits, while San Antonio mineralisation is interpreted to be a lode-style copper skarn deposit often found proximal to porphyry deposits. Productora displays characteristics of both IOCG and Manto-type copper mineralisation, but subsequent structural deformation and alteration had made classification complicated. The Productora proximal Alice mineralisation is a copper-molybdenum porphyry.
Productora
The Productora deposit is located within the Chilean Iron Belt, which extends for more than 600 km along a 20 to 30 km wide, north-northeast trending zone at the east side of the Coastal Cordillera. The deposit is hosted in the (lower Cretaceous) Bandurrias Group, a thick volcano-sedimentary sequence comprising intermediate to felsic volcanic rocks and intercalated sedimentary rocks which dips gently (15 to 30°) west to west-northwest. Dioritic dykes intrude the host rocks at Productora, typically along west- to northwest-trending late faults, and probably represent sub-volcanic feeders to an overlying andesitic sequence not represented in the Project area.
At the Productora deposit, major fault zones are associated with extensive tectonic breccia (damage zones) that host copper-gold-molybdenum mineralisation. Late faults offset the host rocks showing a west to northwesterly strike and while generally narrow, are locally up to 20m wide.
The distribution of alteration mineral assemblages at Productora and spatial zonation suggest a gentle northerly plunge for the Productora mineral system, disrupted locally via vertical and strike-slip movements across late faults. These late faults appear to be trans-tensional and nominally normal to the distal Atacama fault system.
Mineralisation at the Productora deposit strikes north-northeast and is structurally controlled, hosted within a hydrothermal tourmaline breccia unit, and generally forms sub-vertical narrow (~2-5 m) zones. Wider highgrade mineralised zones near the upper surface of the tourmaline breccia vary in orientation but tend to dip sub-vertically or ~70° west. There are also some steeply east dipping high grade zones present at Productora (e.g. Habanero lode).
Secondary and relatively lower-grade mineralisation is evident as manto (or manto-like) horizons in the southern, far northern, and far eastern flanks of Productora. Lodes within the manto horizons are typically shallow dipping at 20° to 30° to the east or west and enclosed by lower grade mineralisation.
Alice
The Alice porphyry is located immediately beneath an extensive, pyrophyllite-rich advanced argillic lithocap, with a porphyry stock of quartz diorite to granodiorite, characterised by biotite and hornblende phenocrysts. The lithocap overprints Alice and the regional volcanic stratigraphy and can be seen in multiple silica ridges indicating telescoping in this porphyry system. It is comprised of numerous advanced argillic alteration types, including quartz-alunite, quartz-pyrophyllite, alunite-dominant and pyrophyllite-dominant zones.
The mineralisation at Alice is hosted in a northeast trending dyke-like porphyry with sheeted and stockwork A- and B-type quartz veinlets, within additional locally disseminated background mineralisation. Highest grade mineralisation is associated with alteration overprinting, with replacement of the biotite-altered porphyry by quartz, actinolite, chlorite and magnetite.
Cortadera
Cortadera is a copper-gold-molybdenum porphyry deposit, comprising a series of mineralised centres (Cuerpos 1, 2, and 3) within a northwest striking structural corridor. Mineralisation continues to at least 1.3 km below the surface.
The Cortadera deposit is characterised by early- and intra-mineralisation, porphyritic tonalitic to quartz dioritic intrusions and adjacent volcano-sedimentary wall-rocks that have been recrystallised to hornfels and skarn. Hydrothermal alteration consists of moderate to strong phyllic (+chloritic) alteration, characterised by quartz/silica, sericite, and lesser amounts of chlorite.
Chalcopyrite occurs as disseminations of variable intensity within the porphyritic host rocks, particularly in association with stockwork A- and B-type veins. There is a clear correlation between increased percentage of quartz-bearing stockwork veining and sulphide content with elevated copper-gold grades.
Vein systems at Cortadera are typical of those found within porphyry-style mineralised systems. Early quartzrich veins observed at Cuerpo 1 and Cuerpo 2 exhibit unidirectional solidification textures (UST) that are commonly associated with high-temperatures during vein emplacement. Veins formed subsequent to UST veins comprise quartz rich A-veins (chalcopyrite-pyrite± magnetite), banded MAB veins (quartz-magnetitechalcopyrite-pyrite) and B-veins (molybdenite), cut by sericitic/chlorite C-veins (pyrite-chalcopyrite), D-veins (quartz-pyrite-sericite) and late calcite-bearing fractures. Anhydrite is locally present within some of the B and C veins.
San Antonio
The San Antonio deposit has been interpreted as a skarn copper deposit with mineralisation presenting in lodes with strong structural and lithological control. The deposit is characterised by mineralisation along an NNE-SSW trending shear zone through the host rocks, which comprise a shallowly east-dipping sedimentary and volcanic sequence.
Mafic and felsic dyke intrusions are common through the San Antonio deposit, mostly striking NE-SW and dipping steeply to the east. The abundance of structure and dyke is highest in the central section of San Antonio (decreasing to the north and south). Structure at San Antonio is interpreted as being due to the emplacement of an intrusion at depth, rather than crustal scale faulting.
Mineralisation is focussed on the through-going San Antonio shear and associated fault zones (nominally less than 2 m width - striking between N30E and NS) and the cross-cutting mafic dykes. The intersection lineation between these structures is interpreted to plunge approximately 30° to the south and is thought to be a significant control on mineralisation.
While the mafic dykes can be mineralised (although only displaying weak to moderate alteration), the intensely skarn altered (epidote-chlorite) fault zones are the more significantly mineralised. Mineralisation is observed both as supergene and hypogene principally associated with high levels of epidote-chlorite alteration.
The dominant sulphide species at San Antonio are chalcopyrite and pyrite, which occur as disseminations around the fault zone. High copper grades (up to 2%) occurring along these fault zones is associated with intense epidote > chlorite ± magnetite ± albite ± calcite and minor specular hematite.