Tintaya, Antapaccay, Coroccohuayco
Super Porphyry Cu and Au|
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The Tintaya skarn Cu-Au deposit is located in the Cuzco Department in the southeastern Andes of Peru, approximately 650 km south-east of Lima (#Location: 14° 54' 4"S, 71° 19' 20"W).
The stratigraphy in the Tintaya district includes, from the oldest exposed,
Lower to Mid Cretaceous
Yura Group - Soraya (or Hualhuani) Formation - 1000 m of sandstones to quartzites;
Mara (or Murco) Formation - 480 m of shale, siltstone, minor sandstone and minor gypsum and/or anhydrite;
Ferrobamba (or Arcurquina) Formation - 300 to 800 m of relatively pure carbonate rocks, altered to calc-silicates and skarn;
Pliocene to Pleistocene
Huaycha Formation - 310 m of rhyolite and dacite tuff and agglomerate;
Casanuma Formation - 100 m of andesite volcanic flows and breccias;
Yauri Formation - 250 m of Pliocene lacustrine sediments;
Quaternary - 30 m of glaciofluvial sediments overlain by up to 50 m of alluvium,
These rocks are intruded by Eocene-Oligocene intermediate (diorite) to felsic (monzonites) composition rocks of the Andahuaylas-Yauri batholith and by Tertiary mafic sills.
The Tintaya deposit comprises multiple garnet- and magnetite-dominant exoskarn developments hosted by carbonates of the Cretaceous Ferrobamba Formation, distributed around the margins of a late 2 x 1.5 km stock, which is, in turn, intruded into a multiphase, NW-SE elongated 11 x 6 km Oligocene to Eocene monzonitic porphyry intrusion, part of the regional Andahuaylas-Yauri batholith. This larger intrusion is exposed in the core of a regional NW-SE trending anticline. The mineralised skarns are hosted within enclaves of Ferrobamba Formation within the broader intrusion, mainly in a faulted, NE-SW corridor between two lobes of the larger intrusion, where the main mineralisation related stock was also intruded. The altered limestones of the Ferrobamba Formation are underlain by metamorphosed fine-grained clastic rocks (hornfels) of the Mara Formation immediately to the SE of the ore deposit (Maher and Larsen, 2007; Maher, 2005, Maher, 2010).
The exoskarn occurs as a <40 to >100 m wide, almpost continuous outer 'skin' to the mineralisation related stock. The bulk of the mineable resource is hosted by garnet- and magnetite-dominant skarn alteration. Locally, molybdenite is important in endoskarn in monzonitic porphyries. The temperature of sulphide precipitation was approximately 325°C and mineralisation is locally related to magnetite replacement of earlier calc-silicates (Maher, 1999), occurring as disseminations or generally thin (>5 mm) A-type veinlets which carry significant mineralisation in the form of chalcopyrite and/or lesser bornite. Mineralisation is accompanied by prograde alteration in the outer monzonite composed of biotite, accompanied by K feldspar. There is significant retrograde sericite-clay-chlorite alteration at Tintaya, which imparts a pale-green overprint to potassic alteration (Maher and Larsen, 2007; Maher, 2005, Maher, 2010).
Garnet, diopside, epidote and actinolite are the characteristic prograde calc-silicate assemblages in the endo- and exoskarns. The bulk of the Cu(-Au, -Mo) mineralisation at Tintaya was introduced during prograde events, typically as chalcopyrite and, less commonly, bornite. Retrograde alteration is manifested by locally intense and nearly complete replacement of garnet and pyroxene by massive magnetite. The magnetite mineralisation occurs with other phases such as quartz, carbonate, amphibole, or serpentine. Much of the magnetite is intergrown with copper sulphides (Maher and Larsen, 2007; Maher, 2005, Maher, 2010).
The distal environment is in part occupied by structurally and lithologically controlled, yellow-brown jasperoid developed in limestone beyond the skarn front at Tintaya.
Reserve and resource figures quoted by X-strata (2006) at Tintaya include:
Proved reserve - 51 Mt @ 1.45% Cu, 0.16 g/t Au
Probable reserve - 60 Mt @ 1.25% Cu, 0.11 g/t Au
Measured resource - 60 Mt @ 1.44% Cu, 0.15 g/t Au
Indicated resource - 77 Mt @ 1.25% Cu, 0.11 g/t Au
Inferred resource - 13 Mt @ 1.25% Cu, 0.13 g/t Au
Total reserve + resource - 261 Mt
Antapaccay, which is 9 km SW of Tintaya, (#Location: 14° 57' 36"S, 71° 23' 0"W). It is a moderate grade Cu-Au porphyry deposit with zones of high grade Cu-Ag skarn and high grade epithermal Cu-Au-Ag-Pb-Zn-Mo mineralisation. Hydrothermal activity persisted over a period of 4.4 m.y in association with multiple intrusive and mineralising events. The copper mineralization was introduced during the formation of retrograde exoskarn; during the sodic-calcic, potassic, transitional and phyllic stages of hydrothermal porphyry-style alteration and with argillic epithermal alteration. Magmatic-hydrothermal evolution accompanied by uplift and erosion resulted in the telescoping of the system and the superimposition of shallow epithermal mineralisation on deep hydrothermal porphyry and skarn phases.
The mineralisation at Antapaccay is associated with the extensive Abancay Batholith and in detail with the Antapaccay suite which have an atypical, medium to high-K, calcalkaline chemistry and range from hornblende gabbro cumulates, through quartz tonalites to trondhjemites.
Resource figures quoted by X-strata (2006) at Antapacay include:
Measured resource - 58 Mt @ 0.70% Cu, 0.12 g/t Au, 2.0 g/t Au, 0.004% Mo
Indicated resource - 61 Mt @ 0.62% Cu, 0.10 g/t Au, 1.6 g/t Au, 0.006% Mo
Inferred resource - 23 Mt @ 0.65% Cu, 0.07 g/t Au, 1.7 g/t Au, 0.007% Mo
Measured resource - 81 Mt @ 0.82% Cu, 0.17 g/t Au, 1.6 g/t Au, 0.008% Mo
Indicated resource - 156 Mt @ 0.78% Cu, 0.17 g/t Au, 1.6 g/t Au, 0.006% Mo
Inferred resource - 93 Mt @ 0.73% Cu, 0.15 g/t Au, 1.8 g/t Au, 0.006% Mo
Total resource - 470 Mt @ 0.7% Cu.
The Coroccohuayco deposit lies 7 km SE of the Tintaya open pit. It is a porphyry-related copper skarn deposit associated with the Andahuaylas-Yauri batholith, hosted by the Cretaceous Ferrobamba Formation, occurring within the hinge zone of a synform.
In the Coroccohuayco district, magmatic activity associated with the composite Andahuaylas-Yauri batholith commenced at ~40.4 Ma, when a district-scale hornblende-bearing basic complex was intruded, mostly as a gabbrodiorite (Chelle-Michou et al., 2014). At Coroccohuayco, this complex occurs as a sill-like intrusion, capping the limestone of the Cretaceous Ferrobamba Formation. Unexposed Deep-seated magmatism resumed at ~37.5 Ma and continued until a hornblende porphyry was emplaced, followed by a hornblende-biotite porphyry at ~35.6 Ma (Chelle-Michou et al., 2014), both emplaced as stocks and NW-SE, E-W and NE-SW trending dykes. Both of these porphyry phases are crosscut by NNW-SSE trending subvolcanic rhyodacite porphyry dykes, probably emplaced soon after the porphyries (Chelle-Michou et al., 2014). Late stage alkali basaltic dykes oriented north-south crosscut the whole sequence.
Magmatic rocks are mostly emplaced into the Jurassic Yura Group clastic and Cretaceous clastic (Mara-Soraya formation) and carbonate (Ferrobamba formation) sedimentary rocks. The limestones of the Ferrobamba Formation are the main host of skarn-type mineralisation.
Both hornblende and hornblende-biotite porphyries, as well as the gabbro-diorite along mutual contacts, are affected by porphyry-style alteration and veining. Potassic alteration is represented by biotite replacing hornblende and secondary K feldspar replacing plagioclase in vein envelopes. This alteration is frequently overprinted by weak to moderate pervasive sericite-chlorite alteration, in which hornblende is partially replaced by chlorite and plagioclase is variably altered to sericite. Locally tabular, 1 to 5 mm thick quartz veining with minor sulphides and potassic alteration halos are well developed with up to 30 vol.% veining. The younger rhyodacite is uniformly altered to a pervasive mafic-destructive sericite-chlorite(± hematite) alteration, but is not veined (Chelle-Michou et al., 2015).
Skarn alteration and mineralisation, largely controlled by the permeability of the carbonate protolith, are mostly developed at ~200 to 300 m below the present erosional surface in the Ferrobamba Formation, extending from its basal contact with the immediately underlying siliciclastic sediments of the Cretaceous Mara-Soraya formation, to its upper contact with the overlying pre-skarn sill-like gabbrodiorite complex (Chelle-Michou et al., 2015).
The exoskarn is mostly massive, and is mineralogically zoned around the hornblende and hornblende-biotite porphyries, extending laterally along bedding, passing outward to calc-silicate marble and marble (Maher, 2010). The anhydrous high-temperature prograde skarn assemblage is dominated by garnet and pyroxene with less abundant quartz, magnetite, K feldspar, plagioclase and titanite, with accompanying chalcopyrite-bornite±chalcocite disseminated as grains within the calc-silicates. Garnet and pyroxene hosted fluid inclusions suggest that anhydrous skarn formed between >600 to 400° C (Maher, 2010). The precious metal mineralisation takes the form of gold and silver minerals dominantly associated with bornite-chalcocite which is disseminated within more distal granular garnet alteration. Quartz-hosted fluid inclusions suggest copper mineralisation was introduced at between 400 and 250°C, accompanied by magnetite over the upper part of this temperature range.
Retrograde alteration is generally magnetite (+carbonate-silica) replacement of calc-silicates and is locally associated with copper mineralisation, and in some locations, results in the nearly complete replacement of garnet and pyroxene by massive magnetite. The lowest-temperature retrograde alteration is characterised by carbonate, hematite, silica, and clay (±amphibole ±chlorite ±serpentine) as alteration products of garnet and pyroxene. Hydrous retrograde alteration is of lesser importance at Coroccohuayco, possibly due to the overlying diorite sill either impeding the influx of meteoric water or buffering the late stage fluids.
Endoskarn is locally developed in the gabbrodiorite, and in the hornblende and the hornblende-biotite porphyries. Endoskarn in the gabbrodiorite consists of plagioclase, epidote, pyroxene ±titanite ±later zeolite, and is mostly observed at the lower contact of the gabbrodiorite with the carbonate rocks of the Ferrobamba Formation or along faults and fractures. In the porphyries, garnet, pyroxene, epidote, and plagioclase are the main endoskarn alteration minerals. No endoskarn-type alteration is recognised in the rhyodacite (Chelle-Michou et al., 2015).
The Cu sulphides, which include chalcopyrite, bornite and digenite/chalcocite, are primarily hosted in the garnet-dominant massive exoskarn and in the endoskarn in the porphyritic intrusions or in the gabbrodiorite. Porphyry-style veined and disseminated mineralisation in the magmatic rocks is usually <0.4 wt % Cu, but may be higher grade in the vicinity of the Cu-rich skarn mineralisation. Pyrite is found in the distal skarn or disseminated in sericitised magmatic rocks such as the rhyodacite. A few galena ±sphalerite bearing veinlets crosscut the massive skarn. Minor supergene enrichment at Coroccohuayco is only developed along faults, faulted veins, and at few places where the skarn body outcrops, mostly in the north (Chelle-Michou et al., 2015).
In the southern part of the deposit area, the skarn and Cu mineralisation is zoned around a stock of hornblende porphyry and forms a bell-like ore shell, whilst to the north, the highest Cu grades mostly occur close to the hornblende-biotite porphyry intrusions, although minor dikes of hornblende porphyry are also present.
The total resource outlined at Coroccohuayco amounts to 155 Mt @ 1.57% Cu, 0.16 g/t Au, 6.3 g/t Ag (0.55% Cu cut-off; Maher, 2010), or
92 Mt at 3.10 wt % Cu (1.5 wt % cutoff; Chelle-Michou, 2015).
The most recent source geological information used to prepare this summary was dated: 2015.
Record last updated: 4/3/2015
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.
Maher K C and Larson P B, 2007 - Variation in Copper Isotope Ratios and Controls on Fractionation in Hypogene Skarn Mineralization at Coroccohuayco and Tintaya, Perú : in Econ. Geol. v102 pp 225-237|
Maher KC, 2010 - Skarn Alteration and Mineralization at Coroccohuayco, Tintaya District, Peru: in Econ. Geol. v105 pp 263-283|
Perello, J., Carlotto, V., Zarate, A., Ramos, P., Posso, H., Neyra, C., Caballero, A., Fuster, N. and Muhr, R., 2003 - Porphyry-Style Alteration and Mineralization of the Middle Eocene to Early Oligocene Andahuaylas-Yauri Belt, Cuzco Region, Peru: in Econ. Geol. v.98., pp. 1575-1605.|
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