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Canariaco |
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Peru |
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The Cañariaco porphyry copper deposit is located within the Western Cordillera of the Peruvian Andes in the Cañaris District in Northwestern Peru, approximately 700 km north-west of the capital, Lima, and around 110 km to the north-east of the city of Chiclayo (#Location: 6° 5' 32"S, 79° 16' 42"W).
Regional Setting
The Cañariaco porphyry copper system is located towards the centre of the Cajamarca mineral belt in the Western Cordillera of the northern Peruvian Andes, a generally north-south trending belt of Oligocene to Miocene porphyry copper deposits that extends for 350 km from Cajamarca in the south to the Ecuadorian border and includes two geochemically distinct groups of deposits along this trend namely: i). porphyry Cu-Mo deposits which include La Granja, Michiquillay, El Galeno, Cañariaco and Rio Blanco; and ii). porphyry Cu-Au deposits which include Cerro Corona, Minas Conga and La Carpa.
These systems are mostly associated with dacite to monzonite to diorite intrusions, which intrude basement rocks of Upper Jurassic to Lower Cretaceous quartzites, limestones and mudstones of the Goyllarisquizga Formation and Early Tertiary sequences of andesitic to dacitic lavas and tuffs of the Llama and Porculla Formations which together comprise the Lower Calipuy Group.
For detail of the broad regional setting and geology of the Peruvian Andes, see the separate Peruvian Andes record.
Basement in the region comprises Precambrian to Early Palaeozoic pelitic schists of the Olmos Complex which includes Precambrian metamorphic rocks, overlain by Ordovician shales and sandstones. These are unconformably overlain by Permian conglomerates, sandstones and volcanic flows and tuffs, which are in turn overlain by Late Triassic-Early Jurassic marine sediments intercalated with minor volcanic units of the La Leche Formation. These are succeeded by the Early to Late Jurassic volcano-sedimentary sequence of the Oyotún Formation. The Mesozoic rocks were deposited in ensialic, extensional, marginal basins related to eastward subduction, which extend the length of the Andes. During the Latest Jurassic to Early Cretaceous the region was uplifted and eroded by the mid-Cretaceous Mochica tectonic phase.
By the late Early Cretaceous, subsidence resulted in an eastern sub-basin bounded to the east by the basement Marañon High, and the deposition of 2 to 3 km of Cretaceous strata. The oldest of these sediments are thick regionally extensive deltaic sandstones with shales and coal, and a thin marine limestone which collectively form the Early Cretaceous Goyllarisquisga Group which unconformably overlies the older rocks. From the close of the Early Cretaceous to the middle of the Late Cretaceous, a marine transgressive sequence of up to 1500 m of marls, shales and limestone were deposited across the region. Sedimentation ceased abruptly at the beginning of the Early Tertiary when the basin was deformed by the Late Paleocene Incaic I (59 to 55 Ma) and Middle Eocene Incaic II phases (43 to 42 Ma), which resulted in the formation of a foreland thrust and fold belt with SW-dipping, NE-verging thrust sheets, and the development of open, upright folds. Some thrusts were reactivated and folded during the Quechua 1 orogenic pulse (17 Ma). These periods of activity were accompanied by the eruption and deposition of volcanic units of the Eocene and Miocene Llama and Porculla Formations, which together comprise the 55 to 15 Ma Calipuy Group.
This episode was followed by uplift and erosion and then by renewed magmatism and volcanic activity with the eruption of the 12 to 10 Ma Yanacocha volcanic complex and the Middle to Late Miocene Huambos Formation which capped the stratigraphic sequence in the region.
Geology
The geology of the Cañariaco deposit area comprises andesite to dacite volcanics and tuffs of the Early Tertiary Calipuy Group, which were intruded by a series of porphyry stocks and dykes, dated at 17.9 to 15.8 Ma (K/Ar and Re-Os). Three mineralised 1 to 2 km diameter porphyry centres have been identified, Cañariaco Norte, Cañariaco Sur and Quebrada Verde distributed over a NNE trending interval of ~6 km. The bulk of the economic resource is associated with the Cañariaco Norte centre.
The deposit area is cut by two parallel NW-SE trending district-scale faults. One bisects the Cañariaco deposit, while the second is located 7 km to the northeast. These faults can be traced for several kilometres and are interpretted to be reactivated, reflecting basement structures. A series of NE-SW trending faults cross-cut the deposit area as conjugate sets related to the common theme along the Cordillera of approximately ENE-WSW directed principal stress. In addition a series of north-south to NNW-SSE structures are evident and appear to control the emplacement of the early phases of the Cañariaco intrusive complex as well as the main periods of copper mineralisation and the minor late stage high sulphidation alteration and associated mineralisation. These faults produce a dextral kink where they change orientation from NNE-SSW to north-south when they cross the main NW-SE structure.
A number of circular features/intrusions have been identified in the district, including a single 8 x 10 km circular feature that encompasses all three mineralised centres at Cañariaco, which appear to be controlled by the intersection of NW-SE and NE-SW faults.
The Cañariaco Norte multiphase intrusive-breccia complex is a NNW-SSE elongated 1.7 x 1.1 km a body that extends to a depth of more than 770 m. The majority of the Cu-Au mineralisation is hosted within the intrusive and breccia units, but locally extends for variable distances into the enclosing volcanic units. Intrusive host comprise ~55 to 60% of the deposit, breccias ~30 to 35%, and pre-mineral volcanic rocks approximately 5 to 10%. The intrusive units are nested and together form a roughly oval in shape, with older intrusive rocks being cut by successively younger intrusive bodies. The intrusive units, in general, trend north-south and are steeply dipping. The breccia units cut the intrusive units, are oval to circular in shape and are steeply plunging. Dykes
generally strikeNW-SE with a steep SW dips. The shape and location of the intrusives, breccias and dykes was largely controlled by NW-SE and NE-SW trending faults.
At least three igneous intrusive phases, four magmatic-hydrothermal breccia stages and three volcanic episodes have been identified at Cañariaco Norte that vary in both intensity and type of veining, mineralisation and alteration styles they contain. These include:
Pre-mineral country rocks - andesitic, dacitic and rhyolitic volcanics of the Calipuy Group, occurring as a series of dacite tuffs with lesser, bedded, rhyolite tuffs overlain by andesite porphyry flows and pyroclastic rocks. Andesite pyroclastic rocks and flows dominate to the west, north and south of the intrusive complex where elevations are higher. The eastern side of the intrusive complex is lower in elevation, and thus the dacite and rhyolite volcanic rocks that underlie the andesite volcanic rocks are exposed adjacent to the intrusive complex. These rocks have been variably altered and mineralised with quartz and fracture veins and stockworks containing pyrite, chalcocite and chalcopyrite (Thomas et al., 2011; McCrea 2006);
- andesitic porphyry volcanics which occur as roof pendants and rafts within the main porphyry intrusive and have been variably metasomatised, mineralised and altered with chalcocite, chalcopyrite and pyrite both disseminated and with micro fracture and quartz stockwork, variably affected by potassic (biotite), phyllic, argillic and silicic alteration (McCrea, 2006).
Early-mineral phase - Dioritic crowded feldspar quartz porphyry which is moderately to stongly altered and is the main intrusive phase hosting copper mineralisation at Cañariaco Norte, which has the largest areal extent and contains the bulk of the copper mineralisation. It has 35% crowded feldspar phenocrysts, 3 to 5 mm in size, 1 to 3% isolated quartz eyes, <3 millimetres in size and 3 to 5% hornblende-biotite within a fine ground mass and has been overprinted by potassic, phyllic and argillic (intermediate and advanced) alteration and chalcocite and chalcopyrite mineralisation (Thomas et al., 2011; McCrea 2006).
Inter-mineral phases - Biotite feldspar porphyry that is interpreted to be granodioritic in composition, with 3 to 5% quartz eyes, 15 to 20% feldspar phenocrysts, 2 to 5% euhederal biotite, and traces of hornblende. Grain sizes typically range from 3 to 5 mm. This intrusion occurs along the eastern margin of the crowded feldspar quartz porphyry mass, and has been variably altered and mineralised with potassic, phyllic and argillic alteration, carrying chalcocite, pyrite and locally chalcopyrite (Thomas et al., 2011; McCrea 2006).
- Coarse quartz monzonite porphyry the youngest intrusive unit, comprising a coarse quartz porphyry, which is composed of 5 to 10% quartz
eyes (grain size range from 3 to 5 mm), 15 to 20% euhedral feldspar crystals (<3 mm) and traces of biotite (1 to 2 mm). It intrudes the crowded feldspar quartz porphyry along the western side of the Cañariaco Norte complex and has been variably mineralised and altered with fracture and quartz stockworks, strong phyllic alteration and disseminated chalcocite and pyrite with local chalcopyrite and bornite (Thomas et al., 2011; McCrea 2006).
- Igneous intrusive breccia (after McCrea, 2006) which occurs within the central portion of the defined porphyry system at Cañariaco Norte, as vertical and elongate but irregular bodies trending NW-SE, parallel the main trend of the intrusives. The breccia clasts are composed of the mineralised crowded quartz feldspar porphyry. The clasts contain quartz stockwork mineralisation with predominatly chalcocite and pyrite and are set within a microgranular dioritic matrix. Alteration of the breccias is intermediate argillic to phyllic as in the main mineralised crowded quartz feldspar porphyry. The intrusive breccias are inter-mineral as the matrix is mineralised with mainly chalcocite and pyrite.
- Feldspar porphyry dykes that are from 2 to 30 m thick, with a NW-SE strike, and a steep, southwesterly dip. They have a fine-grained ground mass with 10 to 20% feldspar phenocrysts (3 to 10 mm) and 5 to 10% hornblende phenocrysts (2 to 8 mm), and commonly have cooling contacts. Where dykes intersect the breccias, dyke fragments occur as large (>10 m), rotated, and weakly-fractured blocks within the breccias. The dykes have only been weakly altered, and contain minor copper mineralisation where they have been brecciated by the hydrothermal breccia unit. They have been modified by variable propylitic and very weak argillic alteration and weak copper mineralisation (Thomas et al., 2011; McCrea 2006).
Late-mineral phases - Igneous hydrothermal breccia, composed of matrix-supported angular to sub-angular biotite-feldspar and crowded feldspar-quartz porphyry and quartz-vein fragments that are variably mineralised and show little or no evidence of transport. Fragment sizes in the centre of the breccia are generally 1 to 5 cm in a fine grained crowded feldspar-quartz porphyry. Near the southern margin of the breccia, there is a high proportion of feldspar porphyry dyke fragments up to tens of metres in size. It is not well mineralised, with copper grades related to the inclusion of mineralised porphyry fragments. The margins of the hydrothermal breccia can show crackle brecciation (Thomas et al., 2011; McCrea 2006).
- Tourmaline breccia is polylithic and has a fine-grained matrix consisting of quartz and tourmaline. It is extensive, and was emplaced along the northeastern margin of the intrusive bodies. Clasts are angular to sub-angular, 1 to10 cm in size, and include biotite-feldspar porphyry, crowded quartz-feldspar porphyry and the hydrothermal breccia. The breccia is not mineralised, apart from copper grades related to the inclusion of mineralised porphyry fragments.
- Polylithic breccia is a late-stage breccia with an erratic shape, cross-cutting all earlier units. It is composed of sub-rounded to rounded clasts, which include vein quartz, all three intrusive units, and the two earlier breccia phases. Fragments range from 0.5 to 10 cm, with the breccia margins often grading into a crackle breccia. It exhibits multiple breccia pulses, the last of which is a fluidised microbreccia with rounded fragments that are typically <3 mm in size, crosscutting all other pulses. Copper mineralisation occurs in both the matrix and clasts with pre- and post-breccia mineralisation in a matrix that has been variably altered and mineralised.
- fault breccia, a highly milled breccia with strong phyllic alteration and intense Cu mineralisation and a local gouge matrix (McCrea 2006).
Post-mineral phases - Feldspar porphyry dykes which occur within the central portion of the main crowded feldspar quartz porphyry mineralised intrusive and are unaltered, comprising 3 to 10 mm feldspar, 2 to 8 mm hornblende and local 2 to 4 mm quartz phenocrysts in a fine grained matrix with variable clots of biotite and no Cu mineralisation (McCrea 2006).
Mineralisation
The mineralisation varies in style and intensity in the different intrusive phases, in general, occuring primarily as disseminations, and in fractures, sulphide and quartz veins, faults and breccias. The density of fracturing strongly influences copper grades and alteration intensity, although breccias and faults are locally important.
Copper mineralisation developed as a series of pulses closely following the emplacement of each of the intrusive units and polymictic breccia units, occurring in three main phases of overprinting copper mineralisation have been recognised, namely i). chalcopyrite-(bornite)-pyrite, ii). chalcocite-covelite-digenite-pyrite, and iii). minor enargite-pyrite, as described below.
Copper mineralisation initially occurred as chalcopyrite, pyrite and minor bornite, introduced following emplacement of each of the crowded quartz-feldspar porphyry and biotite-feldspar porphyry units, with the bulk introduced after emplacement of the biotite-feldspar porphyry unit. This was followed by the development of chalcocite, covellite, minor tennantite-digenite, subsequent to intrusion of the coarse quartz porphyry unit. The mineralising process ended with enargite, chalcocite and covellite, minor tennantite-digenite, introduced concurrently with emplacement of the polymictic breccia unit.
The deposit has been intensely weathered near surface, resulting in the formation of a leached cap that contains <0.05% Cu, trace pyrite and tenorite and variable amounts of limonite, goethite, jarosite and hematite. This leached cap varies significantly in thickness, from<1 to as much as 120 m, averaging approximately 40 to 50 m. The water table is currently at, or near, surface.
Copper mineralisation occurs in four zones as follows:
i). A 6 to 72 m thick, sub-horizontal, 'leached zone' carrying 0.03 to 0.05% Cu with copper sulphates;
ii). A structurally controlled, up to 116 m thick high sulphidation 'hypogene enrichment' zone with 0.3 to 3.0% Cu comprising an assemblage of pyrite-chalcocite-covellite-digenite (resulting from the alteration of chalcopyrite) that underwent a series of extensive pyrite-rich overprints including 'intermediate argillic' (sericite-illite), 'advanced argillic' with a final 'phyllic' (quartz-sericite-pyrite-tourmaline) alteration event;
iii). A 'mixed zone' of both primary chalcopyrite-bornite with overprinted pyrite-chalcocite-
covellite-digenite mineralisation which can range from 30 to 90 m thick with grades of 0.3 to 1.0% Cu;
iv). A 'primary zone' with disseminated and/or fracture-controlled chalcopyrite-bornite-pyrite with
copper grades of from 0.3 to 1.5%; of undetermined thickness.
Alteration
The alteration occurs as distinct concentric zones, decreasing in intensity from the centre to the margins of the deposit, with i). a core of biotite, (potassic) alteration at depth, not exposed at surface; ii). a central zone at the surface of quartz-sericite/phyllic, argillic and advanced argillic alteration, overlapping, and partly overprinting the potassic core downward, and overprinting outward iii). a fringing zone of chlorite, epidote, carbonate (propylitic) and minor silicic alteration.
The intensity of alteration is directly related to the degree of fracturing in the hosting lithologies and brecciation in the polymictic breccia unit. The alteration distribution and intensity is locally controlled by NE and NW trending faults.
In the upper 50 to 300 m of the southern half of the deposit, and the upper 100 to locally 150 m of the northern half, phyllic and argillic alteration is dominant (i.e., below overburden and the leached cap). Most of the area of the northern and southern halves of the deposit at depth under the layer of phyllic and argillic alteration is dominated by potassic alteration, grading outwards into a propylitic periphery.
Each of these alteration types has the following characteristics at Cañariaco Norte:
• Potassic alteration comprises variable secondary K&bvsp;feldspar and biotite with chlorite and magnetite, associated with deposition of chalcopyrite(-bornite) and lesser pyrite.
• Propylitic alteration composed of illite, chlorite, epidote and smectite, and is associated with deposition of pyrite, chalcopyrite and minor bornite. Found mainly at deposit margin, but can locally occur within the deposit. Can extend for significant distances outside of the intrusive-breccia complex into the bordering volcanic rocks.
• Phyllic alteration, which predominantly constitutes sericite and quartz with quartz veinlets and stockworks of 0.5 to 1.5 cm thick veins. It is primarily associated with the formation of chalcocite, covellite and minor tennantite and digenite, and is commonly intermixed with argillic alteration. It altered sections of the crowded quartz-feldspar porphyry and biotite-feldspar porphyry intrusions, and all of the coarse quartz porphyry and polymictic breccia units. Late-stage phyllic alteration extended outwards from the polymictic breccia unit, along NE and NW trending faults, and affected rocks distal from the polymictic breccia.
• Argillic alteration comprises kaolinite and illite, and is associated with the deposition of chalcocite, covellite and minor tennantite and digenite. It altered parts of the crowded quartz-feldspar and biotite-feldspar porphyry units, and all of the coarse quartz porphyry and polymictic breccias.
• Advanced argillic alteration is composed of alunite, kaolinite, pyrophyllite and dickite, and is associated with development of enargite, chalcocite and covellite (tennantite and digenite). It is principally associated with the polymictic breccia unit, but also variably affected the bordering coarse quartz porphyry and biotite-feldspar porphyry units, and extended outward from the polymictic breccia along NE and NW trending faults to alter distal rocks.
• Silicic alteration is mainly confined to the deposit margin, but can occur locally elsewhere within the deposit. Locally it extends for significant distances beyond the intrusive-breccia complex into the bordering volcanic rocks.
Other Deposits
At Cañariaco Sur, which is approximately 750 m SSW of Cañariaco Norte, Calipuy Group volcanic rocks are intruded by a diorite to quartz monzonite porphyry stocks. A 750 x 500 m quartz monzonite appears to be the oldest and largest in the complex, intruded by diorite stocks that are around 100 x 50 m.
The porphyry copper centre is dominated by potassic (biotite) alteration with co-extensive chalcopyrite-bornite-molybdenite mineralisation. The mineralisation is hosted by similar porphyry rocks as at Cañariaco Norte. Gold grades appear to be higher at Cañariaco Sur than Norte. Extensive hypogene high sulphdation mineralisation and alteration had not been observed in 2006.
At Quebrada Verde, which is 1.5 kilometres to the southwest of Cañariaco Sur, an approximately 1000 x 750 m diorite porphyry stock intrudes the Calipuy Group volcanic rocks. A 400 x 400 m satellite stock of the same diorite porphyry is located 200 metres to the northeast, while a 1 km x 100 m east-west striking post mineralisation granodiorite dyke intrudes both the volcanic rocks and the larger diorite porphyry stock. Mineralised corresponds to a generally propylitic altered zone with locally structurally controlled sericite and quartz stockwork alteration with minor Cu mineralisation.
Resources
The preliminary resource at Cañariaco, predominantly at Cañariaco Norte have been quoted at from 365 Mt @ 0.5% Cu to a potentially open pit mineable inferred resource of 820 Mt @ 0.45% Cu at a 0.3% Cu cut-off, of which 43.3% is chalcocite with minor copper oxide, and 51.6% chalcopyrite. This comprises measured + indicated resources of 643 Mt @ 0.45% copper + an inferred resource of 177 Mt @ 0.45% Cu (Cadente Resources, 2007).
There is a near surface, highly leachable, Starter Zone of 107 Mt @ 0.6% Cu, comprising 61% chalcocite and 39% chalcopyrite (Cadente Resources, 2007).
This summary is largely derived, and paraphrased, from "McCrea, J.A., 2006 - Technical Report on the Cañariaco Copper Porphyry Prospect, Department of Lambayeque, Northwest Peru: Technical report prepared for Candente Resource Corp." and "Thomas, D.G., Melnyk, J., Lipiec, T. and Kozak, A., 2011 - Cañariaco Project, Lambayeque Department, Peru, NI 43-101 Technical Report on Pre-feasibility Study Progress Report; An NI 43-101 Technical Report prepared by AMEC Americas Limited for Candente Copper Corporation, 186p."
The most recent source geological information used to prepare this decription was dated: 2011.
Record last updated: 24/6/2016
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.
Canariaco
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Selected References:
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Mathur R, Ruiz J, Casselman M J, Megaw P and van Egmond R, 2012 - Use of Cu isotopes to distinguish primary and secondary Cu mineralization in the Canariaco Norte porphyry copper deposit, Northern Peru: in Mineralium Deposita v.47 pp. 755-762
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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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