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Collahuasi District - Ujina, Rosario, Quebrada Blanca, La Profunda, Huinquintipa |
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Super Porphyry Cu and Au
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The Collahuasi operation is based on two large porphyry copper deposits, Ujina and Rosario, which are 7 km apart in northern Chile, located some 180 km south-east of Iquique and 5 to 10 km west of the border with Bolivia (#Location: Ujina - 20° 59' 35"S, 68° 38' 17"W; Rosario - 20° 58' 19"S, 68° 42' 22"W).
In addition to Ujina and Rosario, high grade massive sulphide veins at La Grande, which are related to the Rosario porphyry, have been surrounded by secondary enrichment halos, while a small exotic copper oxide deposit, Huinquintipa is hosted by palaeo-channel gravels draining the Rosario deposit. Historically, mining activity had focused on the Cerro La Grande, Poderosa and Monctezuma areas where high sulphidation Cu-Ag-Au and intermediate-sulphidation Ag outcropped in high-grade veins with up to 0.3 Mt @ 25% Cu, 180 g/t Ag, 2 g/t Au, having been mined from these veins up to 1930.
Further porphyry mineralisation is known at the La Profunda porphyry system which is developed within a down-faulted block directly to the east of Ujina, below 400 m of gravel cover, and the Quebrada Blanca deposit some 8 km WSW of Rosario (#Location: 21° 00' 00"S, 68° 48' 36"W [Quebrada Blanca]).
These deposits are within two main operations, the Collahuasi (Rosario, Ujina and La Profunda) and Quebrada Blanca mines.
For details of the regional setting, see the Central Andes and Bolivian Orocline record.
This cluster of four main porphyry systems occurs within an upthrown inlier of Permo-Triassic volcano-sedimentary basement rocks bounded by the Domeyko and Loa faults to the west and east respectively, that define the broader the Domeyko fault system. This fault system is continuous with the West Fissure Zone which passes through Chuquicamata 200 km to the south, and is a continuation of the same fault system that straddles Escondida even further south.
The four main porphyry systems are developed on three separate 35 to 33 Ma, Eocene to Oligocene, intrusive/mineralised complexes which together define a broadly east-west belt of deposits spread over an interval of near 25 km between the Domeyko and Loa faults and lie along the trace of a significant NW-trending photogeologic lineament in the uplifted Collahuasi Formation. Sinistral movement on these faults developed a conjugate set of NW and NE trending faults, which influenced Tertiary volcanic activity and the formation of the ore deposits (Masterman et al., 2004; 2005).
At Collahuasi, the north-trending Domeyko/West Fissure and Loa faults define three principal stratigraphic domains. To the west of the Domeyko Fault, Cretaceous continental volcanic and arenitic rocks, the Cerro Empexa Formation, overlie deep to shallow marine Jurassic sedimentary rocks of the Quehuita Formation. Both formations unconformably overlie continental to shallow marine volcanic and sedimentary rocks of the Permo-Triassic Collahuasi Formation which are the dominant basement in the horst between the two major faults (Masterman et al., 2005).
The Collahuasi Formation of the horst comprises a >4000 m volcano-sedimentary sequence of andesitic to rhyolitic composition, including two cycles of andesite flows, with intercalated sediments. The lowermost La Grande unit comprises an alternating succession of rhyolites, dacites and andesites with intercalations of volcaniclastics and limestone which are of probable Permian to Triassic age. They are in part intruded by Permian (262 to 231 Ma) diorite to quartz-monzonite granitoid intrusives of the Collahuasi Complex (Masterman et al., 2005).
Extensive Cainozoic ignimbrite covers the basement stratigraphic units between the faults in the northern part of the district, mainly the 17.1 Ma Miocene Huasco Ignimbrite, whilst the 9.3 Ma Ujina Ignimbrite is found in the vicinity of the Ujina deposit to the west and east of the Loa Fault. Chains of Miocene-Pliocene andesite stratovolcanoes, defining the Western Cordillera, are found straddling, but mainly to the east of the Loa fault, whilst the Pleistocene 0.75 Ma Pastillos Ingimbrites straddle the Loa Fault to the north of Ujina, and Miocene conglomerate and sandstone straddle the Domeyko Fault to the NW of Rosario (Masterman et al., 2005; Vergara and Thomas, 1984).
Intrusive bodies ranging from diorite to monzonite, granodiorite and granite are found throughout the Collahuasi district. Palaeozoic granite and granodiorite are restricted to the Collahuasi Formation, whilst Late Cretaceous to early Tertiary quartz diorite and granodiorite occur throughout the Cerro Empexa,
Quehuita and Collahuasi Formations. The mineralised Upper Eocene to Lower Oligocene quartz-monzonite intrusions hosting the Rosario and Ujina porphyry Cu deposits, were exclusively emplaced within the Collahuasi Formation (Munchmeyer et al., 1984; Vergara and Thomas, 1984).
During the Oligocene to Miocene the region was subjected to intense uplift and erosion. Although movement on the Domeyko Fault had ceased by the end of the Tertiary, activity was by then centred on the Rio Loa Fault where large volumes of Miocene to Holocene volcanic and ignimbritic sequences were accumulated contemporaneously with development of basins in the east of the district, including major 19 to 14 Ma and 9.4 Ma aged ignimbrite units. The most recent activity has involved the development of a series of andesitic to dacitic strato-volcanos on the Bolivian-Chilean border dated at around 0.75 Ma.
Exhumation and erosion of the overlying pile at Quebrada Blanca and Ujina to an epithermal environment depth are interpreted to have been a district-wide event that was contemporaneous with epithermal mineralisation at Rosario. Certainly, the Ujina deposit had been eroded to at least the top of the hypogene sulphides by the middle Miocene, as oxidation of pyrite is inferred to have formed alunite, thus providing a minimum age of 15 Ma for the supergene enrichment in the Collahuasi district (Masterman et al., 2005).
For a map of the regional setting within Central Chile, see the Central Andes and Bolivian Orocline record.
Quebrada Blanca
The Quebrada Blanca intrusive complex occurs within a Permian granite batholith that intruded a north-trending anticline of folded Collahuasi Formation volcanic units (Munchmeyer et al., 1984; Rowland and Wilkinson, 1998). The volcanic sequence comprises several andesite flows that are interfingered with andesitic epivolcaniclastic sandstone. The andesite and sandstone units are overlain by rhyolitic and dacitic pyroclastic rocks (Hunt et al., 1983). The mineralised intrusions have an ENE-trend, cutting across the axis of the anticline. Copper mineralisation is associated with several generations of igneous activity.
The principal intrusive rocks in the mine area are:
• Diorite - a dark green to black, equigranular diorite to quartz-diorite, with 1 to 5% quartz, 65 to 80% plagioclase, 10 to 35% secondary plagioclase, amphibole and biotite, and <5% K feldspar and magnetite. It is part of the Palaeozoic basement package, and has been affected by a regional or early metasomatic event of biotite (hornfels) and local hydrothermal alteration and mineralization associated with the younger mineralised porphyries. It is predominantly found in the northern portion of the pit.
• Granodiorite - historically referred to as quartz monzonite, was intruded into basement andesite and diorite, and is perceived to be of Permian, and possibly Cretaceous age. It has been strongly altered and consistently dated as of Eocene age, regarded to be due to resetting.
• Feldspar porphyry - a series of syn-mineral granodioritic feldspar porphyry dykes, and small irregular crowded feldspar porphyry stocks, dated at about 37 Ma, that have invaded the central portion of the granodiorite stock. The majority of these dykes are steeply SE to NE dipping and trend NE to NNE, roughly parallel to the elongation of the granodiorite stock. These dykes have been cut by the later igneous brecciation event, described below, and have been, in many cases, incorporated as blocks or fragments within the breccia. According to Allan et al. (2012), the accepted interpretation is that a large feldspar porphyry dyke/stock was emplaced toward the southern portion of the deposit, in an area which is now mostly occupied by an igneous breccia unit. The feldspar porphyry dykes are grey, and characterised by phenocrysts of predominantly plagioclase with lesser quartz and biotite. The matrix is a micro-aplite, and was formed by a late magmatic/early hydrothermal potassic fluid. The quantity of phenocrysts varies from <30 to >50%, and as such may infer multiple injections. A possible later event of similar composition, but with lesser phenocrysts in a grey matrix, has been recognised and is known as feldspar porphyry 2 (Allan et al., 2012).
Early chalcopyrite-bornite mineralisation is coincident with the granodiorite stock and the suite of porphyry dykes, whilst late chalcopyrite-molybdenite-pyrite mineralisation is associated with cross-cutting igneous and hydrothermal breccia bodies (Rowland, 1998; Rowland and Wilkinson, 1998; Hunt et al., 1983). Veining and alteration stages may be summarised as follows (after Masterman et al., 2004 and Lee, 1994):
• Pre-ore - biotite-magnetite veining with or without a potassic halo;
• Early Stage - quartz-K feldspar-anhydrite-magnetite-sulphide veining that is associated with potassic or sericitic halos, followed by quartz veining with similar halos;
• Hydrothermal breccias - containing quartz-molybdenite-chalcopyrite±anhydrite veining ±sericitic halos. These breccias range from igneous to hydrothermal and occupying the central part of the granodiorite stock and feldspar porphyry intrusive dyke/stock zone. They are highly variable, from clast-rich to clast-poor and from fine-grained to an inequigranular aggregate of quartz, K feldspar and micro-fragments of pre-existing rocks and crystals with a variable amount of biotite (Allan et al., 2012);
• Tourmaline breccias - containing tourmaline-chalcopyrite-bornite-molybdenite-pyrite veining with associated tourmaline veining. This is a hydrothermal breccia containing fragments of granodiorite, and feldspar within a tourmaline-quartz matrix, ranging from matrix supported to crackle breccia;
• Late stage - characterised by pyrite and lesser quartz veining with strong sericitic to argillic halos (Allan et al., 2012).
The Quebrada Blanca intrusions are intensely biotite altered along the northern contact, which Hunt et al. (1983) corresponding to the discrete mafic diorite intrusion. The main potassic alteration is centrally located within the deposit and has an ENE elongation, occurring as K feldspar and secondary biotite associated with the granodiorite stock, intrusive breccias and feldspar porphyry dykes. This potassic alteration is very variable, but occurs in two general associations: i). K feldspar dominant, where primary feldspars are being replaced and/or overgrown by K feldspar, replacing the matrix of porphyritic units or in the margins of quartz veining, andii). biotite dominant, where secondary biotite replaces primary mafic minerals and fine-grained biotite in silica magnetite flooding has also been part of the early biotite veining event(Allan et al., 2012). Disseminated bornite-chalcopyrite mineralisation is spatially associated with potassic alteration in the core of the granodiorite intrusion (Masterman et al., 2005).
A variation of this potassic alteration occurs in the central and western part of the deposit, characterised by K feldspar, phlogopite, sericite (muscovite) and albite ±andalusite ±corundum, and is often associated with higher grade zones. This alteration also surrounds the strong potassic bornite-rich alteration in the southern and south-western parts of the deposit. The sericite is part of an earlier event, prior to the phyllic stage and has a high correlation to elevated copper grades (Allan et al., 2012).
This potassic alteration grades out into a propylitic halo in the southern sector of the deposit (Hunt et al., 1983), enlarging the hydrothermal footprint to a conservative estimate of 6 by 5 km. The propylitic alteration is characterised by a pervasive assemblage of essentially chlorite and epidote, with locally developed veins of actinolite, epidote, calcite, magnetite and specularite (Allan et al., 2012).
Phyllic alteration, characterised by sericite, quartz, pyrite, chalcopyrite ±chlorite, occurs throughout the deposit, and controlled by ground preparation, particularly in zones with strong faulting or jointing. NW-striking reverse faults around the deposit form the focus of linear phyllic alteration, although a strong zone of phyllic alteration in the south-western part of the deposit is lithologically controlled. The strong destructive sericitisation, followed by dissolution, formed distinctive, irregular cavities throughout the breccia zones (Allan et al., 2012).
The highest molybdenite grades are found along the NE-trending Quebrada Blanca Fault which cuts the porphyry-style mineralisation. A funnel-shaped zone of pervasive sericite alteration surrounds the vuggy hydrothermal breccia unit (Rowland, 1998). Secondary copper-arsenic oxide minerals are found at the top of the hydrothermal breccia body in the supergene zone (Masterman et al., 2005) suggesting they were derived by oxidation of primary copper-sulphosalt minerals. Masterman et al. (2005) suggest the vuggy breccia zone and associated copper-sulphosalts may have originated from hydrothermal fluids of high-sulphidation character.
At least two tourmaline breccia bodies containing chalcopyrite are also defined on the northern and eastern margins of the intrusive complex (Rowland and Wilkinson, 1999). Their relationship to breccia bodies in the central mineralised zone at Quebrada Blanca is unclear, although Hunt et al., (1983) speculated that tourmaline breccias postdate igneous breccias in the core of the Quebrada Blanca complex (Masterman et al., 2005).
Eocene-Oligocene hypogene mineralisation and alteration at Quebrada Blanca was subjected to uplift and leaching, allowing supergene weathering and copper-sulphide enrichment processes that were active from at least 18 to 14 Ma, based on supergene alunite studies at other deposits in the district. Supergene mineralisation at Quebrada Blanca comprises mostly chalcocite and, to a lesser extent, copper oxides such as atacamite, cuprite and locally brochantite. This resultant secondary enrichment blanket was protected by the deposition of Tertiary gravels. During the supergene enrichment process, secondary mineralisation appears to be preferentially concentrated close to structures and more permeable rocks. The remnant leached cap varies from about 7 to 200 m in thickness, overlying 10 to 200 m of mainly secondary sulphides. Continuous supergene copper mineralisation has been traced over a 2.5 x 1.5 km area. In addition to the supergene blanket, supergene chalcocite is commonly concentrated in NW fault zones that formed permeable conduits, which often go deep into the hypogene ore, locally producing high-grade copper mineralisation. An argillic assemblage forms the last stage of alteration and is characterised by supergene silicate minerals such as kaolinite and montmorillonite. It is also closely related to zones of strong phyllic alteration. The lower margin of the supergene enrichment zone is transitional into hypogene copper mineralisation, producing in a mixed low-grade ore type that is processed by run-of-mine dump leaching (Allan et al., 2012).
Copper ore at Quebrada Blanca is predominantly mined from the supergene zone.
Rosario
The Rosario deposit comprises a dome shaped mass of copper mineralisation occupying an area of some 2 x 1.5 km, emplaced within a variety of hosts which include andesites and rhyolites of the La Grande unit, volcanic sandstones, calcareous sediments and rhyolites of the overlying units of the succeeding Permo-Triassic sequence. These rocks have been intruded by three main igneous phases, namely: i). the Collahuasi porphyry, a medium grained potassic granodiorite, ii). the Inés porphyry, a grey, strongly mineralised dacitic sill found only in the area of the deposit, and iii). the youngest, Rosario porphyry, a medium grained porphyritic granodiorite which occurs near surface as restricted dykes which coalesce into a stock at a depth of 400 m - this is believed to be the causative intrusive.
The Rosario mineralised system is strongly influenced by a set of NW trending, SW dipping faults, the most significant of which is the Rosario Fault which has controlled the emplacement of the Rosario porphyry, the distribution of primary mineralisation and the Rosario vein system.
Multiple overprinting generations of mineralisation and alteration are evident at Rosario. These may be summarised as follows (after Masterman et al., 2004 and Lee, 1994):
Porphyry style
• Pre-ore - dominated by disseminated and veinlet-style magnetite, in varying proportions, and is apparently barren;
• Early Stage I - quartz-biotite-albite-chalcopyrite-pyrite veining that cuts magnetite veining and is associated with biotite-albite alteration;
• Early Stage II - quartz-K feldspar-chalcopyrite-bornite±biotite±albite veining associated with K feldspar-biotite-albite alteration. Both early stages are associated with, and occur within and around the Rosario Porphyry, although only a small amount is found within the intrusion itself. Relict lenses of early-stage magnetite, biotite-albite and K feldspar altered rock have been preserved in the hanging wall near the Rosario Fault, but these facies mostly occur in the footwall where the rocks are less affected by faulting;
• Transitional - quartz-molybdenite veining, comprising flaky aggregates intimately intergrown with anhedral quartz and variable amounts of K feldspar. These transitional veins crosscut all early-stage veins and, in turn, have been cut by intermediate-stage veins;
• Intermediate Stage - quartz-pyrite±chalcopyrite veining, surrounded by illite-chlorite alteration envelopes;
• High-sulphidation epithermal Cu-Ag style, occurring as massive sulphide veining, which is localised by the SW-dipping Rosario fault system and defines a zone of high copper grades, locally containing >10 wt.% Cu.
• Late stage I - pyrite-quartz-alunite veining associated with quartz-alunite alteration;
• Late stage II - bornite-chalcopyrite-chalcocite veining;
• Late stage III - tennantite-enargite veining with associated pyrophyllite-dickite alteration proximal to veins, surrounded by a broader halo of muscovite-quartz.
The porphyry style disseminations and veins of chalcopyrite and secondary bornite is distributed in a series of concentric shells. Bornite is most abundant in the high grade core of the deposit at depth, in the vicinity of the Rosario porphyry and the Rosario vein system. It grades outwards and upwards into zones of bornite-chalcopyrite to chalcopyrite-pyrite to pyrite with decreasing quantities of chalcopyrite on the periphery. The potassic alteration predominates in the core of the Rosario deposit as K feldspar and secondary biotite, accompanying disseminated albite, and is associated with the porphyry phase on mineralisation (Bisso et al., 1998).
Sulphide and sulphosalt minerals in the late-stage high sulphidation veining includes tennantite and accessory enargite, chalcocite, covellite, mawsonite (Cu6Fe2SnS8) and colusite (Cu3[As,Sn,V,Fe]S4), as well as pyrite, bornite and chalcopyrite. The quartz-alunite-pyrite alteration proximal to the late-stage veining is overprinted by an advanced argillic pyrophyllite-dickite assemblage, which passes outward through muscovite-quartz-pyrite to illite-smectite altered rocks distal to the veins. The muscovite-quartz-pyrite assemblage is interpreted to have formed contemporaneously with the pyrophyllite-dickite, obliterating the potassic assemblage (Masterman et al., 2004). The most intense quartz-sericite is developed in the Rosario fault and the Rosario vein system which comprises numerous 1 to 2 m wide, NW oriented veins. This vein system commenced with the introduction of pyrite, minor chalcopyrite, bornite and tennantite, then by a second pulse that produced abundant bornite with minor chalcopyrite, enargite, 'grey copper' and sulphosalts. In the upper part of the system the primary minerals have been almost entirely replaced by secondary chalcocite (Bisso et al., 1998).
Propylitic alteration at Rosario is best developed in the peripheral Jack Rock fault, while diopside, garnet, epidote and amphibole bearing skarns developed in the calcareous hosts with abundant magnetite and lesser chalcopyrite and pyrite as high grade, but low tonnage accumulations. Supergene enrichment and zones of oxide copper developed as irregular structurally controlled zones, although this style of ore is small compared to that at Ujina.
A 40Ar/39Ar age of 34.4 ±0.3 Ma was obtained for igneous biotite in the Rosario Porphyry that hosts copper mineralisation at the Rosario deposit. Illite and hypogene alunite from separate overprinting alteration events yielded 40Ar/39Ar ages of 34.5±0.5 Ma and 32.6±0.3 Ma, respectively. An Re-Os age of 33.3±0.2 Ma for molybdenite at Rosario is slightly younger than the 40Ar/39Ar age of illite, but older than the alunite (Masterman et al., 2004). A 40Ar/39Ar age of 32.7±1.6 Ma for hypogene alunite from the La Grande copper-silver-(gold) vein south of Rosario is indistinguishable from the age of Rosario alunite. This indicates that a second discrete episode of hydrothermal activity was superimposed, 1.8±0.4 m.y. later, telescoped onto and overprints the earlier-formed porphyry Cu system (Masterman et al., 2004).
At Cerro La Grande, 2 km SW of Rosario, the mineralisation comprises similar late-stage, massive sulphide veins and zoned alteration assemblages. The massive sulphide veins include pyrite-bornite-chalcocite-enargite with accessory mawsonite and colusite. As at Rosario, advanced argillic associations of pyrophyllite-alunite-dickite-quartz altered rocks are proximal to the veins, passing outward through sericite-quartz to epidote-chlorite alteration (Masterman, 2003).
The Capela vein group is located ~3 km SE of Rosario and is characterised by a series of massive pyrite veins, locally enriched in copper. The copper-silver veins at Poderosa lie along a NNW-trending structure that is rotated parallel to the Rosario Fault at the Rosario deposit. Vein sulphide associations consist of bornite-tennantite-chalcopyriteenargite-pyrite (Munchmeyer et al., 1984).
The Monctezuma intermediate-sulphidation Ag vein, which is to the SW of the Rosario system, dips sub-vertically to the west, and has been traced along surface and intersected in drill holes over a total strike length of ~7 km. It varies from 1 to 5 m in width, and outcrops as banded, cockade quartz that has been impregnated by manganese oxides and limonite. Sphalerite, pyrite, galena and chalcopyrite are found below the base of oxidation, with accessory polybasite, argentopyrite, argentite, stephanite, tetrahedrite, and native silver and gold in a quartz-rhodochrosite gangue. In a 1 km segment of the vein, several drill holes have intersected a narrow (20 to 30 m) vertical enrichment zone that occurs at the base of oxidation. This interval carries between 500 and 1000 g/t Ag, and passes down dip into hypogene mineralisation grading 200 to 500 g/t Ag. (Munchmeyer et al., 1984; Masterman et al., 2005).
Ujina
The Ujina deposit, which is 7 km east of Rosario, is largely covered by the 9.4 Ma Ujina ignimbrite that varies for 0 to 110 m, thickening to the east. Strongly fractured and leached Permo-Triassic rhyolites and andesites of the La Grande unit of the Collahuasi Formation outcrop to the west of the deposit, where they consist of a thick basal andesite (possibly several flows) overlain by rhyolite and sedimentary breccia (Bisso et al., 1998). These rocks are intruded by the mineralised granodioritic Ujina porphyry which includes abundant xenoliths and roof pendants of the volcanics, while a sedimentary breccia of the La Grande unit is intruded along its eastern margin. The Ujina porphyry comprises a cylindrical, 1200 m diameter granodiorite stock, which is, in turn, intruded by a series of fine grained, only weakly mineralised late stage dykes, the Inca porphyry, that are compositionally similar to the Ujina porphyry. The highest hypogene Cu grades are associated with the Ujina Porphyry, which is altered to K feldspar, biotite and muscovite-illite-quartz-chlorite-pyrite. The weakly mineralised Inca Porphyry is interpreted to have intruded the Ujina Porphyry before the cessation of hydrothermal activity. High grade chalcopyrite-bornite mineralisation is sometimes found in breccias along the margin of the Inca porphyry dykes (Masterman et al., 2004; 2005).
There are two main stages of hypogene porphyry-style mineralisation and alteration at Ujina. Veining and alteration stages may be summarised as follows (after Masterman et al., 2004):
• Early stage - centered on the Ujina Porphyry, characterised by quartz-chalcopyrite-bornite disseminated and veinlet mineralisation with a K feldspar core that grades outward into biotite alteration. Accessory calcite has been recognised in association with hydrothermal biotite and K feldspar.
• Intermediate stage - quartz-molybdenite veins, which lack recognisable alteration haloes, but cut the early-stage veins, and are, in turn, cut by the main-stage veins.
• Late or Main stage - comprising pyrite-chalcopyrite-quartz veining surrounded by white mica/illite-chlorite-quartz alteration envelopes.
• Kaolinite and smectite occur in patches across the top of the Ujina alteration system and are possibly supergene.
Hypogene mineralisation at Ujina is concentrically zoned about the Ujina Porphyry (Bisso et al., 1998), and according to DeBeer and Dick (1994) contains a low-sulphide, low grade core of chalcopyrite-bornite grading outwards through the main chalcopyrite-pyrite ore zone to low grade pyritic mineralisation with lesser chalcopyrite. Hypogene copper distribution is also concentrically zoned, with the highest Cu grades forming an annulus about the low-sulphide potassic core (Bisso et al., 1998). This high-grade zone coincides with the cylindrical contact of the Ujina Porphyry with the Collahuasi Formation host rocks.
Mineralisation typically occurs as veins, fracture planes and as disseminations in the matrix of the host. The ore averages 0.66% Cu at a 0.4% Cu cut-off, with the best grades of 0.8 to 1.0% Cu in a 100 to 200 m wide, steeply dipping annulus near the contact between the Ujina porphyry and the andesites. Primary alteration comprises a core of potassic feldspar alteration, grading out into a potassic biotite ring, then to a quartz-sericite phase containing the higher grade primary ore, then to propylitic alteration with reduced grades. A zone of mixed sericite-chlorite is common with chlorite increasing outwards as the sericite content declines.
Moderate to intense argillic alteration (sericite, kaolinite and montmorillonite) accompanies supergene enrichment. Leaching has affected the upper levels, passing down into a zone of low grade oxides. Leaching, oxidation and enrichment is promoted by fracturing and faulting and the breccias on the margin of the Inca porphyry. The degree of secondary enrichment is variable, vertically and laterally depending on the amount of chalcocite-covellite developed from the primary chalcopyrite-bornite. Low grade enriched pyrite with chalcocite rims occurs in the outer pyritic shell.
At Ujina, the 40Ar/39Ar age of igneous biotite for the Ujina Porphyry that hosts copper mineralisation is 35.2±0.3 Ma.
By contrast, the late- to post-mineralisation Inca Porphyry, carrying grades of <0.4% Cu, yielded a biotite 40Ar/39Ar age of 34.7±0.3 Ma (Masterman et al., 2004).
Huinquintipa Exotic Cu Deposit
The Huinquintipa exotic copper mineralisation occurs within the east-west striking Huinquintipa palaeodrainage system, and was derived from the Rosario mineralised centre to its east. Gravels were transported from the east and impregnated with exotic copper oxide minerals following their deposition in the palaeo-channel (Munchmeyer, 1996). The present drainage system has dissected the original deposit, dividing the remaining preserved mineralisation into several isolated bodies (Munchmeyer et al., 1984). Economic copper mineralisation occurs over an area of 1 x 0.15 km, and averages 10 m in thickness. Zonation of exotic copper species and hydrothermal alteration minerals is evident along the 6 km length of the palaeochannel (Munchmeyer, 1996). Near Rosario, the gravels are unaltered and cemented by abundant limonite, while ~2 km from Rosario, pervasively kaolinised gravel fragments are cemented by copper wad and kaolinite. Further west, weakly altered to unaltered gravel fragments are cemented by chrysocolla and accessory copper wad. The mineralised area is abruptly terminated at the transition from the palaeochannel into a small 1.5 km wide palaeobasin that is ~100 m deep. Munchmeyer (1996) suggested the increasing pH (due to rock-fragment reaction and possibly fluid mixing) triggered deposition of exotic copper at Huinquintipa. The fluids were strongly diluted when they entered the palaeobasin preventing further significant copper precipitation.
RESERVES AND RESOURCES
Collahuasi
Reserve and resource figures are estimated as follows (2002):
Proven reserve - 320.25 Mt @ 1.02% Cu,
Probable reserve - 1.53 Gt @ 0.90 % Cu,
Measured resource - 48.2 Mt @ 0.57% Cu,
Indicated resource - 427.77 Mt @ 0.63% Cu,
Inferred resource - 1.84 Gt @ 0.72% Cu.
The total resource at Collahuasi at December 2007 (Xstrata, 2008) was stated as:
5.19 Gt @ 0.83% Cu, including 746 Mt @ 1.06% Cu at Rosario Oeste.
JORC compliant ore reserves and mineral resources at 31 December 2011 (Anglo American plc, 2012) were:
Flotation
Proved + probable reserves - 1.9253 Gt @ 0.95% Cu, 0.0022% Mo,
Measured + indicated resources - 0.6301 Gt @ 0.91% Cu, 0.021% Mo,
Inferred resources - 2.6053 Gt @ 0.93% Cu,
Low grade flotation
Proved + probable reserves - 0.9352 Gt @ 0.49% Cu,
Measured + indicated resources - 0.1537 Gt @ 0.46% Cu, 0.050% Mo,
Inferred resources - 1.3158 Gt @ 0.45% Cu, 0.021% Mo,
Oxide/mixed heap leach
Proved + probable reserves - 35.4 Mt @ 0.63% Cu,
Measured + indicated resources - 15.1 Mt @ 0.60% Cu,
Inferred resources - 4.2 Mt @ 0.62% Cu.
JORC compliant ore reserves and mineral resources at 31 December 2015 (Anglo American plc, 2016) were:
Flotation - direct feed
Proved + probable reserves - 1.9652 Gt @ 1.05% Cu, 0.024% Mo,
Measured + indicated resources - 1.4640 Gt @ 0.89% Cu, 0.050% Mo,
Inferred resources - 3.3972 Gt @ 0.96% Cu, 0.021% Mo.
TOTAL direct feed reserves + resources - 6.8264 Gt @ 0.97% Cu, 0.028% Mo.
Flotation - low grade stockpile
Proved + probable reserves, low grade flotation - 1.1276 Gt @ 0.49% Cu, 0.010% Mo,
Measured + indicated resources - 0.4620 Gt @ 0.40% Cu, 0.017% Mo,
Inferred resources - 1.4535 Gt @ 0.45% Cu, 0.005% Mo.
TOTAL low grade reserves + resources - 3.0431 Gt @ 0.46% Cu, 0.009% Mo.
Heap leach
Proved + probable reserves - 30.0 Mt @ 0.68% Cu,
Measured + indicated resources - 53.3 Mt @ 0.67% Cu,
Inferred resources - 25.2 Mt @ 0.54% Cu.
TOTAL heap leach reserves + resources - 108.5 Mt @ 0.58% Cu.
NOTE: Reserves are additional to resources in these estimates.
The Collahuasi project is managed by the Compania Minera Dona Ines de Collahuasi owned by Glencore (44%), Anglo American (44%) and a Japanese consortium.
Quebrada Blanca
The adjacent Quebrada Blanca deposit is a leach operation that was owned 76.56% by Aur Resources from 2000 until 2007, when Aur Resources was acquired by Teck Resources. It had reserves and resources in 2002 of:
Leach reserve (proven + probable) - 132 Mt @ 0.87% Cu
Leach resource (measured + indicated) - 153 Mt @ 0.91% Cu
Leach resource (inferred) - 54 Mt @ 0.60% Cu
Published ore reserves and mineral resources at Quebrada Blanca (Teck Resources website, viewed November 2016) were:
Heap leach proved + probable ore reserve - 10.1 Mt @ 0.46% Cu
inferred resource - 0.1 Mt @ 0.32% Cu
Dump leach proved + probable ore reserve - 3.4 Mt @ 0.20% Cu
inferred resource - 0.2 Mt @ 0.19% Cu
TOTAL leach proved + probable ore reserve - 13.5 Mt @ 0.39% Cu
TOTAL inferred resource - 0.3 Mt @ 0.23% Cu
Mill ore proved + probable ore reserve - 1584.5 Mt @ 0.49% Cu, 0.019% Mo,
measured resource - 5.3 Mt @ 0.44% Cu, 0.004% Mo,
indicated resource - 838.5 Mt @ 0.40% Cu, 0.015% Mo,
inferred resource - 2216.9 Mt @ 0.36% Cu, 0.017% Mo.
TOTAL resource - 3060.7 Mt @ 0.37% Cu, 0.016% Mo.
Note: in the leach ores, proved + probable reserves account for the entirety of measured + indicated resources (which are not quoted). In the Mill ore, reserves are included within resources.
For more detail consult the reference(s) listed below which were the principal source of the information on which this summary was based.
The most recent source geological information used to prepare this decription was dated: 2012.
Record last updated: 4/4/2017
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.
Ujina Rosario Quebrada Blanca
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Selected References:
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Baker, M.J., Wilkinson, J.J., Wilkinson, C.C., Cooke, D.R. and Ireland, T., 2020 - Epidote Trace Element Chemistry as an Exploration Tool in the Collahuasi District, Northern Chile: in Econ. Geol. v.115, pp. 749-770.
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Bisso B., C, Duran M, Gonzales A., A 1998 - Geology of the Ujina and Rosario copper porphyry deposits, Collahuasi District, Chile: in Porter T M, 1998 Porphyry and Hydrothermal Copper and Gold deposits: A Global Perspective PGC Publishing, Adelaide, Australia pp. 133-148
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Dick L A, Chavez W X, Gonzales A, Bisso C 1994 - Geological setting and mineralogy of the Cu-Ag-(As) Rosario vein system, Collahuasi District, Chile: in SEG Newsletter Oct., 1994, No. 19, pp1, 6-11
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Djouka-Fonkwe, M.L., Kyser, K., Clark, A.H., Urqueta, E., Oates, C.J. and Ihlenfeld, C., 2012 - Recognizing Propylitic Alteration Associated with Porphyry Cu-Mo Deposits in Lower Greenschist Facies Metamorphic Terrain of the Collahuasi District, Northern Chile - Implications of Petrographic and Carbon Isotope Relationships : in Econ. Geol. v.107, pp. 1457-1478.
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Masterman G J, Cooke D R and Moore R L, 2005 - Geology and Discovery of Porphyry Cu-Mo-Ag Deposits in the Collahuasi District, Northern Chile: in Porter, T.M. (Ed), 2005 Super Porphyry Copper & Gold Deposits - A Global Perspective, PGC Publishing, Adelaide, v.1 pp. 175-188
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Masterman G J, Cooke D R, Berry R F, Walshe J L, Lee A W and Clark A H 2005 - Fluid Chemistry, Structural Setting, and Emplacement History of the Rosario Cu-Mo Porphyry and Cu-Ag-Au Epithermal Veins, Collahuasi District, Northern Chile: in Econ. Geol. v100 pp 835-862
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Masterman, G.J., Cooke, D.R., Berry, R.F., Clark, A.H., Archibald, D.A., Mathur, R., Walshe, J.L. and Duran, M., 2004 - 40Ar-39Ar and Re-Os Geochronology of Porphyry Copper-Molybdenum Deposits and Related Copper-Silver Veins in the Collahuasi District, Northern Chile: in Econ. Geol. v.99, pp. 673-690.
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Nelson, M., Kyser, K., Clark, A. and Oates, C., 2007 - Carbon Isotope Evidence for Microbial Involvement in Exotic Copper Silicate Mineralization, Huiquintipa and Mina Sur, Northern Chile: in Econ. Geol. v102, pp. 1311-1320.
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Sillitoe R H, McKee E H 1996 - Age of supergene oxidation and enrichment in the Chilean Porphyry Copper Province: in Econ. Geol. v91 pp 164-179
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Urqueta, E. Kyser, T.K., Clark, A.H., Stanley, C.R. and Oates, C.J., 2009 - Lithogeochemistry of the Collahuasi porphyry Cu-Mo and epithermal Cu-Ag (-Au) cluster, northern Chile: Pearce element ratio vectors to ore: in Geochemistry: Exploration, Environment Analysis v.9, pp. 9-17.
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| References in PGC Publishing Books: | |
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Bisso B. C, Duran M, Gonzales A. A, 1998 - The Collahuasi Copper Mine, Northern Chile , in Porter T M, (Ed.), Porphyry and Hydrothermal Copper and Gold Deposits: A Global Perspective, pp 133-148
 Abstract
Masterman G J, Cooke D R and Moore R L, 2005 - Geology and Discovery of Porphyry Cu-Mo-Ag Deposits in the Collahuasi District, Northern Chile, in Porter T M, (Ed), Super Porphyry Copper and Gold Deposits: A Global Perspective, v1 pp 175-188
Abstract
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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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