Cu Au Ag Mo
Super Porphyry Cu and Au|
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The Haquira porphyry copper deposit is located at an altitude of 3500 to 4400 m asl., ~270 km NW of Arequipa, 65 km SE of Abancay and ~80 km SW of Cuzco in the Apurimac Department of southern Peru (#Location: 14° 09'S, 72° 20'W).
Haquira is part of the Las Bambas cluster of deposit, located ~7 km south of Chalcobamba. It lies within the Oligocene Andahuaylas-Yauri Belt in the southeast part of the Andean cordillera in Peru, where parallel belts of Palaeozoic and younger rocks are intruded by Tertiary (Oligocene) diorites and monzonites, including the Haquira porphyry. The northern part of this belt is characterised by east west striking, north-verging Cretaceous thrust faults, a trend transverse to the NNW-trending magmatic arcs in most of Peru. Oligocene intrusive bodies lie in an east-west trend, and intrude faulted and folded Jurassic to Cretaceous sedimentary sequence. These intrusive rocks have given rise to skarn and porphyry-style mineralisation of copper, molybdenum, and gold in several districts.
At Haquira, the Jurassic to Cretaceous sedimentary sequence comprises, from oldest to youngest:
Chuquibambilla Formation - intercalated, grey-black, thin-bedded shales, siltstones, and sandstones;
Soraya Formation - light grey, thin- to thick-bedded arenites to quartzites with three intercalated siltstone units near the top of the sequence and a localised limestone lens within the arenite. The quartzite unit is the most abundant sedimentary rock type at Haquira and hosts a significant portion of the known secondary copper mineralisation, especially at Haquira West. Individual quartzite beds can be massive several tens of metres thick, but it is very common to find the quartzites with minor intercalations of fine- to medium-grained clastic sedimentary rocks and some pebble conglomerate; and
Mara Formation - red shales, siltstones and sandstones. The Oligocene intrusions have silicified the arenites and converted the red-beds into epidote-bearing hornfels.
Apart from the Soraya Formation quartzites, much of the remainder of the sequence is composed of a mixed sequence of siltstones and mudstones which are commonly gently dipping to the west, very thinly bedded and fairly well-sorted. When fresh or very weakly altered, these rocks vary from dark grey to brown or dark green, although alteration imparts a bleached colouration. They occur intercalated with quartzites of the Soraya Formation in the central part of the property, but also represent much of the Chuquibambilla and Mara Formations. Diagenetic pyrite is common within the black, fine-grained sedimentary rocks, especially the Chuquibambilla Formation. Hypogene mineralisation appears to be preferentially hosted by certain of these rocks when located close to a mineralised intrusion, possibly those containing very fine grained carbonates.
The overlying Ferrobamba Limestone does not outcrop in the immediate area of known mineralisation, although it does occur nearby. The sedimentary rocks are folded into a series of major doubly plunging folds with wavelengths of 1 to 3 km, accompanied by some thrusting.
Oligocene intrusives occur as stocks and sinuous dykes, the latter spatially related to NNW-striking faults and/or fractures. Most are medium-grained to porphyritic diorites, quartz diorites, monzonites and monzodiorites. These intrusions silicified the arenites and converted some of the finer grained siltstones and shales into diopside-, biotite- and epidote-bearing hornfels. The most significant is the Haquira monzonite porphyry, interpreted to be the main mineralising intrusive body, containing abundant disseminated sulphides and the better hypogene copper grades.
The Haquira Porphyry is the oldest known intrusive unit in the deposit area. It is typically an equigranular to porphyritic, leucocratic, medium- to coarse-grained monzonite, with
locally developed, narrow, late-stage aplite dykes. Phenocrysts are 30 to 40% tabular-shaped, subhedral plagioclase, 5 to 8% biotite, occasional amphibole. The chilled margin is variably porphyritic, with plagioclase and biotite phenocrysts set in an aphanitic groundmass. The Haquira Porphyry contains abundant disseminated chalcopyrite, pyrite and molybdenite in the groundmass, and has associated classic “A-” and “B-” type quartz-sulphide veins and veinlets; both as stockworks and sheeted vein systems. Other Oligocene intrusives, ranging from dykes to stocks and porphyries to coarse are found in the area, including the Lahuani, Pararani and Ccahuanhuire porphyries.
A significant body of breccia occurs near the south-central portion of the deposit, mainly comprising clast-supported quartz arenite blocks, although locally more polymictic, with scattered quartz and muscovite-altered porphyry clasts, finer grained sedimentary rocks, and wispy green fine-grained rock. Clasts vary in sorting and diameter, although rounding is generally good. Sill-like bodies of breccia penetrate the country rock in many places, giving the impression of laccolith-like bodies. Overall, the geometry of the main body of breccia seems to be intermediate between a sill and a dyke. The matrix, commonly <10 vol.%, comprises sugary granular quartz, apparently derived from milling of the quartz arenites.
The Jurassic-Cretaceous sedimentary sequence is blanketed by 1 to 5 Ma Pliocene, (post-mineral) columnar jointed dacitic ash flow tuffs and ignimbrites, correlated with the Sencca Tuff and overlying alluvium.
The Haquira suite of Oligocene porphyries was intruded under broadly east-west extension, with the dominant controlling faults being sub-vertical and north-south striking. There appear to be several N- to NNW-striking, sub-vertical belts, which focus porphyry dyke swarms. Several of these structural corridors have a monoclinal appearance, with downthrows to the west. The Haquira deposit occurs in the overturned limb of an east-west-trending syncline, which lies in the hanging wall of an east-west striking, north-vergent thrust fault. Swarms of en echelon quartz tension gashes occur in the sandstones of the Chuquibambilla Formation and less commonly in the Soraya Formation.
The mineralisation at Haquira is part of a porphyry-copper systems related to the Oligocene intrusives, including the Haquira Porphyry. It occurs as a copper oxide zone, sub-parallel and overlying a supergene enriched chalcocite blanket at the interface with the hypogene copper sulphide-bearing stockworks and sheeted-vein systems of the underlying hypogene porphyry-copper style. In addition, there is evidence of some skarns developed in carbonate rocks adjacent to the porphyry intrusives.
The hypogene mineralisation is spatially associated with two stock-like bodies of Haquira Porphyry and related dyke swarms. The Haquira East porphyry transits from a dyke-swarm-like geometry near the surface through to a stock-like body ~450 m wide at depth, although the western and eastern ends are more tabular to dyke-like (~200 m wide), steeply dipping to the south at ~75 to 85°. The sedimentary wall rocks strike ~east-west to slightly WNW-ESE and dip at 20 to 50°S. The porphyry is emplaced into both quartzites and intercalated fine-grained sedimentary rocks of the Soraya Formation and finegrained red-bed sedimentary rocks of the Mara Formation, which are overturned to form part of a large recumbent synclinal structure with rocks of the Mara formation coring that synclinal structure. The Haquira West area is very similar to that described above for the Haquira East area, the main difference being the more dyke-like geometry and the presence of additional intrusive rocks.
Quartz- and sulphide-bearing stockworks and sheeted-vein systems are recognised in these stocks and the surrounding sedimentary wall rocks, particularly in proximal silicified and hornfelsed fine-grained sedimentary rock units. The hypogene mineralisation has a strong structural control, with pyrite, chalcopyrite, molybdenite and trace amounts of bornite and gold occurring in well-fractured structural zones. Outward from the central cores, the sulphides are pyrite-chalcopyrite, and beyond a halo of pyrite-specularite. Disseminated and fracture controlled mineralisation occurs in arenites and quartzites.
Alteration within the Haquira deposit is strongly influenced by host rock-type and composition. Porphyry intrusive rocks are variably altered, while the chemically inert arenites and quartzites are silicified. Fine-grained siltstones and mudstones are variably hornfelsed to biotite, amphibole, pyroxene, and locally garnet-bearing rocks, while the Mara red-beds are variably hornfelsed to epidote and locally biotite-bearing rocks.
The following alteration types are recognised: i). Potassic feldspar; ii). Secondary biotite; iii). Early dark mica; iv). Calc-silicate (diopside, actinolite, garnet, tremolite); v). Chlorite (±epidote); and vi). Locally developed phyllic (quartz-sericite-pyrite). Cu-Mo-Au mineralisation is spatially associated with potassic feldspar and secondary biotite alteration within the Haquira East porphyry intrusive rocks.
The veining chronolgy, from oldest to youngest, comprises: i). Un-mineralised quartz-K feldspar veins; ii). Un-mineralised calc-silicate (pyroxene-amphibole) veins and patches; iii). Mineralised Early Dark Micaceous veins, associated with the higher grade Cu-Au zones; iv). A-type (hotter) and B-type (cooler) veins, both of which are mineralised; v). Mineralised sulphide only veins without selvedges; vi). Mineralised banded quartz-molybdenite veins; vii). Mineralised enargite overprint of bornite and chalcopyrite; and viii). Late mineral D-type veins of quartz-pyrite±chalcopyrite.
The hypogene mineralisation consists of chalcopyrite, bornite and molybdenite, with peripheral pyrite forming a "pyritic-halo" to the deposit. Bornite-rich zones typically carry elevated gold levels. There is a strong asymmetrical distribution of the primary copper sulphide mineral species, Au:Cu metal ratios, and EDM vein distribution at Haquira East. The north to NE margin of the porphyry body is dominantly pyrite±chalcopyrite which passes rapidly into chalcopyrite±pyrite, chalcopyrite, bornite, and bornite±chalcopyrite towards the south to SW and is still open (in 2010). Molybdenite mineralisation appears to form a shell-like cupola that is coincident with the top and margins of the main porphyry body.
Quartz- and sulphide-bearing stockworks and sheeted-vein systems are recognised in the intrusive rocks and the surrounding sedimentary stratigraphy, particularly in proximal silicified and hornfelsed fine-grained sedimentary rock units. The hypogene mineralisation has a strong structural control, with the primary sulphides occurring in well-fractured structural zones and as disseminations, both within the host porphyry intrusion and within the fine-grained sedimentary wall rocks.
Supergene mineralisation is found at both Haquira East and Haquira West as copper oxide minerals and local development of a secondary chalcocite blanket. Most of the supergene mineralisation is characterised by black copper oxides (predominantly tenorite), Cu-bearing goethite and pitch limonite, suggesting a low-pyrite system. Brochantite and chrysocolla usually result from the oxidation of chalcocite. Chalcocite "blankets" are best formed in and proximal to structures, affording high permeability, and allowing repeated leaching/enrichment, as manifested by the rare occurrence of cuprite, chalcotrichite and native copper. Minor malachite has also been identified. The supergene domain over the mineralised system is characterised by a number of vertical zones, namely: i). Leached cap; ii). Oxide zone, with secondary Cu-oxides (chrysocolla, malachite, brochantite, cuprite, black Cu oxides, Cu-Mn wads, etc); iii). Mixed oxide and supergene sulphide enrichment; iv). Supergene sulphide enrichment, with secondary chalcocite; v). Mixed supergene enrichment and primary Cu-Mo-Fe sulphides; vi). Hypogene Cu-Mo-Fe sulphides, with chalcopyrite, bornite, molybdenite, hypogene chalcocite, pyrite and minor secondary chalcocite.
Published mineral resource estimates at September 2010 (Rozelle and Lips for Antares Minerals Inc., 2010), were:
Measured + indicated resources - open pit, 560.94 Mt @ 0.485% Cu, 0.03 g/t Au, 1.15 g/t Ag, 0.010% Mo;
Inferred resources - open pit, 307.78 Mt @ 0.372% Cu, 0.022 g/t Au, 1.15 g/t Ag, 0.007% Mo;
TOTAL resources - open pit, 867.72 Mt @ 0.445% Cu, 0.029 g/t Au, 1.39 g/t Ag, 0.009% Mo;
Measured + indicated resources - underground, 21.02 Mt @ 1.03% Cu, 0.086 g/t Au, 3.36 g/t Ag, 0.013% Mo;
Inferred resources - underground, 20.83 Mt @ 1.10% Cu, 0.104 g/t Au, 4.026 g/t Ag, 0.011% Mo;
TOTAL resources - underground, 41.85 Mt @ 1.07% Cu, 0.096 g/t Au, 3.74 g/t Ag, 0.012% Mo
This summary closely follows: Rozelle, J.W. and Lips, E.C., 2010 - Haquira Copper Project, Apurimac, Peru, Preliminary Economic Evaluation Update; an NI 43-101 Report, prepared by Tetra Tech MM, Inc. for Antares Minerals Inc., 266p.
The most recent source geological information used to prepare this summary was dated: 2010.
This description is a summary from published sources, the chief of which are listed below.
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