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La Huifa |
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Chile |
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Cu Mo
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Super Porphyry Cu and Au
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The La Huifa breccia-related Cu-Mo porphyry deposit located in the Andes of central Chile, 3 km northeast of the El Teniente porphyry Cu-Mo deposit, some 80 km to the southeast of Santiago in central Chile.
The El Teniente and La Huifa deposits lie within the southern segment of the late Miocene to Early Pliocene metallogenic belt of central Chile, and like the other deposits of the belt, are hosted by older Miocene plutons and by Early to Late Miocene arc-related volcanic rocks (23 to 6 Ma; Godoy, 1993; Charrier et
al., 2002; Piquer et al., 2017).
For details of the regional setting and district geology, see the Andean Cu-Au-base metals province - Central Andes and Bolivian Orocline and El Teniente records.
Although mineralisation in the La Huifa area has been known since 1959, the first drilling campaign was not completed until 1982. Later, during the late 1980’s and early 1990’s, an exploration adit was opened from which 10 diamond holes were drilled, resulting in an estimated geologic potential of 11 Mt @ 1.0% Cu, 300
ppm Mo. Exploration activities were reactivated in 2012 when La Huifa was selected as a target as part of an El Teniente brownfields program. One of the latter holes in the 8 drilled in 2012-13 had a total depth of 984 m, and in its lower segment, it intersected 510 m @ 1.0% Cu, 500 ppm Mo. Earlier holes in the program had cut 69 m @ 0.33% Cu and 51 m @ 0.31% Cu. In 2017, a new zone of the deposit, Cuerpo Central, with an intersection of with 1064 m @ 0.8% Cu, 337 ppm Mo (Piquer et al., 2023).
Geology
The oldest lithological units recognised at La Huifa are correlated with the volcanic and subvolcanic deposits of the Teniente Volcanic Complex. They comprise a sequence dominated by lavas of andesitic composition that have both porphyritic and aphanitic textures and dark grey groundmass. These andesites are intercalated with andesitic to dacitic lithic- and crystal-rich tuffs and polymictic, volcaniclastic breccias. The volcanic sequence is intruded by several mafic subvolcanic rocks of varying textures, that are mostly porphyritic basaltic-andesites with plagioclase phenocrysts, and by micro-phaneritic gabbros. These subvolcanic rocks are regarded as being similar to, and are correlated with the El Teniente Mafic Complex in the main El Teniente orebody. The Teniente Volcanic Complex (including the Teniente Mafic Complex at El Teniente) has been dated as middle to late Miocene , as detailed above. The volcanic and subvolcanic rocks of this complex are intruded by a series of equigranular to porphyritic intrusions, dominantly of diorite to quartz-diorite composition. These intrusive bodies, along with the Sewell quartzdiorite at El Teniente, are part of a single, ENE-trending, semi-continuous plutonic complex. At La Huifa, four different intrusive facies have been mapped, many of which have igneous breccia developed at their contacts with the enclosing volcanic host rock. The earliest intrusive phase comprises an equigranular to slightly porphyritic, amphibole-rich diorite to quartz-diorite, and is followed by dioritic and andesitic porphyry intrusives, which are largely differentiated on the basis of the groundmass grain size. A younger, amphibole-rich granodiorite porphyry is known but is only seen in a few drill holes. The most recent intrusive unit is a late diorite porphyry, a porphyritic rock characterised by a mostly aphanitic groundmass and sparse phenocrysts, composed of plagioclase and acicular amphiboles.
Alteration and Mineralisation
The hydrothermal system at La Huifa has been divided into four major stages, as follows:
Pre-mineralisation stage - defined by a large sodic-calcic alteration event that is characterised by albite, tourmaline and actinolite, occurring in vein systems, hydrothermal breccias, and as tourmaline rosettes in albitised rock. The veins are infilled by tourmaline, accompanied by varying amounts of actinolite, anhydrite, magnetite, pyrite and lesser chalcopyrite, surrounded by characteristic haloes of albite. The hydrothermal breccias are cemented by tourmaline, and are locally enriched in anhydrite, actinolite (commonly later altered to chlorite), quartz, magnetite and mushketovite. The clasts have been altered to actinolite-tourmaline-albite, with disseminated magnetite, rutile, and sphene in albitized rocks. This stage has a low copper content.
Early mineralisation stage - characterised by vein hosted mineralisation as a potassic alteration event. These veinlets are sparsely developed a and at <1% of the rock are volumetrically minor. Consequently, while containing chalcopyrite and bornite, they only contribute a very minor amount of copper to the deposit. In addition, it has been demonstrated that in some cases, these copper sulphides have been precipitated during later hydrothermal stages that reopened the veins of this stage. In these cases, younger sulphides and associated minerals are commonly precipitated in the central vein sutures, where present, or by reopening along the vein margin with the and host rock. Early stage mineralisation includes biotite-rich veins (EB and EBT veins of Gustafson and Quiroga, 1995), granular quartz veins with narrow K feldspar and albite halos (A veins of Gustafson and Hunt, 1975), and straight quartz veins, commonly without selvages, but where present, are composed of albite and K feldspar). The latter also contain variable anhydrite, molybdenite, chalcopyrite and bornite (B veins of Gustafson and Hunt, 1975).
Main mineralisation stage - resulting from emplacement of the main breccia complex that is characterised by strongly chlorite and sericite altered angular clasts in a hydrothermal cement of tourmaline and anhydrite that is sometimes very coarse grained, with crystals also infilling open spaces within the clasts. The cement may also contain adularia and local epidote. The breccia accompanies the main Cu input, with abundant bornite and chalcopyrite contained in the hydrothermal cement and disseminated in the clasts. Molybdenite is also locally important, occuring as part of the hydrothermal cement. A 6.64 to 6.51 Ma age range (based on three Re-Os molybdenite ages; Pardo 2015) has been established for the main mineralisation and breccia-forming event. This hydrothermal breccia crosscuts quartz veins of the early mineralisation stage. Distal to the breccia complex, veins with the same mineralogy as the breccia cement, i.e., anhydrite, tourmaline, chalcopyrite and bornite, have been observed crosscutting volcanic and intrusive rocks and earlier tourmaline breccias of the pre-mineralisation stage. These veins also carry high Cu grades. The stage is accompanied by a phyllic alteration event, characterised by two sets of sulphide-rich veins with grey and white sericite selvages respectively. The former also commonly contain chlorite haloes external to the typical grey sericite selvages. These two varieties are considered to be equivalent to the C and D veins defined at El Salvador (Gustafson and Hunt, 1975; Gustafson and Quiroga, 1995). C veins predominate at deeper levels of the system, while D veins are shallower. In the C veins at La Huifa, the sulphide infill is, in most cases, due to chalcopyrite, although it can also include bornite close to the core of the deposit, and pyrite in more distal sections. These veins make an important contribution to the copper content of the deposit. They also include quartz, anhydrite and tourmaline infill. Crosscutting relationships between C veins and the main hydrothermal breccia complex are rarely seen, and on some occasions, C veins appear to crosscut the anhydrite-tourmaline infill, while the converse has also been recorded. D veins, which have white sericite haloes, are pyrite rich and crosscut the main hydrothermal breccia complex, as well as the C veins. Younger hydrothermal breccias were also emplaced coeval with the main phyllic event. These also have a hydrothermal cement, mostly composed of tourmaline, quartz and anhydrite, although the clasts are altered to white sericite and clays and have a much lower Cu content than the main breccia complex. They have a sulphide mineralogy characterised by pyrite over chalcopyrite and minor amounts of tennantite-tetrahedrite, molybdenite and specular hematite. Tourmaline and anhydrite related to this late breccia-forming event may also be present in the sutures of D veins.
Late mineralisation stage veinlets crosscut all the earlier veins and hydrothermal breccias, and are characterised by a low-temperature assemblage of carbonates, gypsum and tourmaline, with selvages, where present, that is argillic, composed of illite and kaolinite. Pyrite is the dominant sulphide, with minor chalcopyrite, sphalerite and galena. This stage also has associated, volumetrically minor, rock-flour breccias, that contain clasts with truncated quartz veins from the early and main mineralisation stages. They also contain clasts of earlier tourmaline-anhydrite breccias, whilst the rock-flour matrix is sometimes weakly cemented by late tourmaline. These breccias are crosscut by the late diorite porphyry (Fig. 8F).
Reserves and Resources
The deposit is reported to contain (Codelco's Mining Resources: History and Strategy, Codelco, 2014):
Resource - 161 Mt @ 0.805% Cu.
It was reported to be a deep deposit with potential resources of between 200 and 600 Mt @ 0.8 to 1% Cu, 550 ppm Mo (Codelco 2014).
In 2016, reconnaissance work indicated a geological resource, at a 0.2% CuTotal cut-off grade (Codelco Annual Report, 2016) of:
606 Mt @ 0.4% Cu.
The La Huifa resource is believed to have since been expanded, refined and amalgamated into that of El Teniente as a satellite.
The information in this summary is drawn from Piquer et al. (2023).
The most recent source geological information used to prepare this decription was dated: 2023.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Piquer, J., Hermosilla, J., Oyarzun, N., Cuadra, P., Floody, R., Troncoso, L. and Pardo, R., 2023 - Geology and Structural Evolution of the La Huifa Ore Deposit, Central Chile: A Newly Discovered Porphyry Cu-Mo System in the El Teniente District: in Econ. Geol. v.118, pp. pp. 371-390. doi: 10.5382/econgeo.4980.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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