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Don Javier |
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Peru |
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Cu Mo
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Super Porphyry Cu and Au
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The Don Javier porphyry copper deposit is located 12 km southeast of the Cerro Verde deposit and 25 km SSE of Arequipa, in the Yarabamba district of southern Peru (#Location: 16° 37' 7"S, 71° 27' 2"W).
The first geological and geochemical investigations in the area had been undertaken by the Cerro de Pasco Corporation in 1955, including a drilling program, looking for porphyry copper mineralisation. Sporadic exploration work was subsequently undertaken by a private prospector. The Junefield Group Company discovered the deposit after a more comprehensive exploration program between 2009 and 2012, including induced polarisation and magnetic geophysical programs, rock geochemistry and 136 diamond drill holes on an ~70 x 70 m grid pattern for 138 011 m of core.
The Don Javier deposit is located on the southwestern slope of the Western Cordillera in southern Peru, at the northern extremity of the Central Andean Paleocene-early Eocene porphyry belt (Acosta et al., 2019, Sillitoe and Perelló, 2005). This porphyry Cu belt hosts a number of very large copper deposits in southwestern Peru, including Toquepala, Cuajone and Cerro Verde (Cooke et al., 2005, Sillitoe and Perelló, 2005).
For background on the regional tectonic, structural, geologic and metallogenic setting of the deposit, see the Andean Cu-Au-base metals province - Central Andes and Bolivian Orocline and the Cerro Verde records.
Geology
The pre-mineralisation country rocks include:
• Upper Jurassic Labra Member of the Yura Group, which is the oldest exposed unit in the deposit area. It is composed of thick-bedded, light-colored, fine-grained quartz sandstones outcropping in the eastern and southern parts of the deposit. Locally, the sandstone hosts joints and fractures filled with tourmaline and quartz, aligning parallel to the other breccias at Don Javier with a strike of 330°. The sequence is finely bedded into layers ranging in thickness from 15 to 20 cm, with a total thickness varying from 25 to 40 m.
• Coastal Batholith, Yarabamba Superunit, an intrusive complex emplaced as numerous plutons, generally with steep walls (Myers, 1975). At Don Javier, the Yarabamba Superunit is subdivided into granodiorite and diorite plutons. Granodiorite is the primary host to mineralisation, whereas the diorite occurs as local outcrops in the southern and eastern parts of the deposit area. The Yarabamba plutons are light to dark grey with subhedral, equigranular texture and are characterised by the mineralogical association plagioclase - hornblende - K feldspar - quartz - biotite. The grain size averages 0.1 to 1.2 mm across, with a maximum of ~2.5 mm.
The porphyry mineralisation associated intrusions and hydrothermal breccias that were emplaced into the Yarabamba plutons include:
• Don Javier dacite porphyry intrusions that outcrop along a 300 to 800 m wide and >2 km long corridor controlled by regional NW-trending faults. The dacite porphyries contain 20 to 50 modal.% plagioclase, 3 to 7 modal.%quartz, and 3 to 8 modal.% biotite phenocrysts set into a microgranular groundmass. The plagioclase phenocrysts are anhedral to subhedral and up to 5 mm long. Quartz phenocrysts up to 4 mm long and have been magmatically corroded to rounded or subrounded grains.
• Mineralisation-related hydrothermal breccias, the most common of which at Don Javier are spatially associated with the porphyries, forming pipe-like bodies with variably sized subrounded to subangular clasts of up to ∼10 cm across. In the mineralised zone, these clasts are predominantly composed of granodiorite and dacite wall rock lithologies. Both matrix-supported and clast-supported breccias are all common. The matrix comprises tourmaline, quartz and sulphides, such as pyrite, chalcopyrite, galena and sphalerite, although veinlets are not common within the clasts. Disseminated sulphides are found in the clasts, while sulphides alsp locally infill cavities. Hydrothermal alteration, including sericite and chlorite, typically affect the breccias, in both the clasts and matrix.
A number of post-mineral dykes intrude the deposit and cross-cut mineralisation, controlled by NW- and NE-trending faults. They can be divided into those with andesitic and aplitic compositions, and are generally unaltered.
Structure
Three sets of steeply dipping faults are have been recognised, occurring as NNW-striking pre-mineral and NE- and ENE-striking post-mineral structures. The NNW, 345° striking set appear to have controlled emplacement of the dacite porphyry complex and the veinlets, with mineralised veinlets also oriented at ~345°. The prominent NE-fault set strikes at ~60°, almost perpendicular to the NNW set. It facilitated vertical displacement of blocks after mineralisation. The ENE-trending fault set strikes at 80° and is a major structural influence in the southern part of the Don Javier deposit area. These faults have strike lengths of 0.5 to >2 km and accommodate vertical movement of mineralised blocks.
Hydrothermal alteration and mineralisation
Four types of hypogene alteration have been recognised at Don Javier, namely:
• Potassic altered rocks are only preserved in a small amount, ∼2 vol.%, of drill core, mainly at depth in the granodiorite, below 2000 m a.s.l., and occurs as an assemblage of hydrothermal K feldspar, biotite and minor quartz. This alteration style generally formed fine-grained, pinkish mineral aggregates reflecting the presence of K feldspar, and is associated with magnetite, chalcopyrite and minor bornite. This alteration is mainly overprinted by the later chlorite-sericite assemblage and is strongly associated with Cu-Mo mineralisation.
• Chloritic-sericitic alteration, which is generally found in the deeper parts of the deposit, overprinting the potassic zone. A large part of the chlorite-sericite zone is spatially associated with higher Cu and Mo grades, and likely is the result of the replacement of the original potassic assemblage.This alteration style is evident in ~10 vol.% of the drill core below ~2400 m a.s.l. It is characterised by it's light green colour. Plagioclase is wholly or partially replaced by sericite, whilst biotite and hornblende are replaced by chlorite.
• Sericitic alteration dominates, and is found in more than 50 vol.% of the drill core, surrounding the centre of the deposit. It strongly affects the upper parts of the fine-grained hypabyssal dacite. Both plagioclase, mafic phenocrysts and the matrix are replaced by illite to illite/smectite aggregates, resulting in a pale whitish colouration with residual anhedral quartz grains. The associated sulphides are mainly pyrite with minor chalcopyrite.
• Propylitic alteration is widespread, occurring in the distal sections of the dacite porphyries and surrounding granodiorite, and is recognised by it's greenish colour. It occurs in ~25 vol.% of the drill core, although the alteration zone, based on field mapping, is more than 1.5 km wider than the drilled area. Propylitic alteration at Don Javier is characterised by a chlorite-epidote-calcite mineral assemblage, and contains only traces of pyrite, and is generally barren.
Five alteration and mineralisation related vein types have been identified at Don Javier, and have been identified in nearly 40 vol.% of the drill core. Their emplacement has been divided into three stages, as follows:
• Stage 1, the earliest, which occurs as EB- and M-type veinlets. The distribution of these veinlets is limited to only 1 and 4 vol.% of veined drill core respectively.
EB veinlets are characterised by hydrothermal biotite, K feldspar and quartz, and are mainly preserved in the potassic alteration zone, but can also be observed to varying degrees in all other types of hypogene alteration. They formed at higher temperatures, earlier, and deeper levels than the Stage 2 EQ veinlets. The M-type veinlets are composed of hydrothermal magnetite, with locally associated minor quartz, pyrite and/or chalcopyrite. These veinlets are normally irregular and variable in width, mainly seen in the potassic, propylitic and sericitic alteration zones, and, in some cases, in the chloritic-sericitic zone.
• Stage 2, which is the Cu-Mo mineralisation stage, and is particularly rich in Mo. It is characterised by early quartz EQ-type and sulphide-quartz SQ-type veining, and is observed in all hypogene alteration zones, particularly in the sericitic zone.
EQ veinlets occur in 13 vol.% of the veined drill core. They are filled with fine granular quartz and locally pink to white K feldspar and/or albite, and generally do not have a central line along the veinlet axis. Sinuous veinlet margins and disseminated chalcopyrite are their main characteristic, and they are mostly randomly oriented and discontinuous, with widths generally ranging from 1 to 10 mm. Disseminated pyrite and hydrothermal biotite are common, and they locally contain chalcopyrite ±bornite ±pyrite ±anhydrite along their margins. In the deep sections of the deposit, the EQ-type quartz veinlet likely transitions to EB-type. EQ-type veinlets are usually cut by other late veinlets.
SQ veinlets are abundant and occur in 41 vol.% of the veined drill core. They are composed of coarse-grained quartz, with characteristic, relatively straight, wall edges and pyrite ±chalcopyrite ±molybdenite concentrated in their axes or in irregular bands parallel to the walls. They generally do not have alteration halos. The SQ veinlets at Don Javier are subdivided into molybdenite-quartz (MQ-type) and chalcopyrite-pyrite-quartz (CPQ) veinlets. The molybdenite in the MQ type is disseminated and/or occurs in multiple bands within and parallel to bands of quartz, commonly near the margins. Chalcopyrite and pyrite are absent in MQ veinlets. The MQ veinlets are usually cut by the CPQ veinlets, which contain abundant chalcopyrite and pyrite but much less molybdenite, with sulphide center-lines that vary from continuous or discontinuous.
• Stage 3, the final mineralising stage, predominantly containing D-type veinlets, which occur in all alteration zones and are abundantly distributed in 41 vol.% of the mineralised drill core. The veinlets are composed of coarse pyrite ±chalcopyrite ±quartz with extensive greenish-grey sericite alteration halos, and are continuous and multi-directional. Minor sphalerite ±galena ±calcite locally occurs within these veins. Overall, the D-type veinlets at Don Javier have a low Cu grade, although they contain appreciable amounts of Cu where spatially associated with EQ- and SQ-type veinlets of the high Cu grade (>0.3% Cu) mineralisation zone.
Mineralisation was developed as quartz-chalcopyrite ±pyrite in EQ and SQ veinlets, and as disseminations throughout stockworks and breccias around the contacts between the dacite porphyry intrusions and pre-mineral granodiorite plutons. Plotting the distribution of above a 0.2% Cu cutoff, projected to surface, the Co-Mo mineralised zone at Don Javier has a maximum width of ∼500 m in in a NE-SW direction, by ∼800 m NW-SE. Within this envelope, the highest Cu and Mo grades are found in the NW, above ∼2000 m a.s.l. and the central core below ~1900 m a.s.l.
As detailed above, the higher-grade ore zones are mainly associated with EQ and SQ quartz veinlets that developed in the potassic alteration zones, which were strongly overprinted by later chloritic-sericitic alteration. Consequently, the chloritic-sericitic alteration zone that is spatially associated with the high-grade mineralisation may correspond to the earlier potassic alteration. The spatial distribution of Cu and Mos correlate reasonably well, although the higher values of these two metals are inconsistently found below ~1500 m a.s.l. The higher Cu levels are in the centre of the mineralised zone, while the higher Mo values are to the northwest. This pattern suggests decoupled introduction and precipitation of metals in the deeper portion of the deposit. The Cu-Mo correlation coefficient for the entire deposit is 0.38. Minor late Pb-Zn mineralisation is observed in the matrix of breccias in the shallow part of the deposit.
Supergene mineralisation
There is no well developed supergene zone at Don Javier. The preserved leached cap is only 1 to 5 m thick and is composed of supergene argillic alteration with limonite and boxwork after sulphide mineralisation without the formation of a notable underlying chalcocite enrichment blanket. This is different to what is found in other nearby deposits with similar ages, e.g., Cuajone, Quellaveco and Toquepala (Clark et al., 1990), and Cerro Verde (Quang et al., 2003, Stegen et al., 2018), which have much thicker leached caps with supergene Cu blankets. In contrast, the leached cap at the nearby Cerro Verde deposit, 12 km to the NW, averages 70 m in thickness and locally persists to depths of 250 m (Quang et al., 2003).
Mineral Resources
At a 0.3% Cu cutoff, the total estimated resource comprised (after Webster et al., 2013) an:
Indicated Mineral Resource - 182 Mt @ 0.45% Cu, 0.02% Mo, 2.96 g/t Ag, containing 0.819 Mt of Cu, 36 4000 tonnes of Mo, and 538.7 tonnes of Ag; plus
Inferred Mineral Resources - 121 Mt with 0.39% Cu, 0.01% Mo, 2.11 g/t Ag, containing 0.4719 Mt of Cu, 12 100 t of Mo, 255.3 t of Ag.
The most recent source geological information used to prepare this decription was dated: 2022.
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.
Don Javier
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Selected References:
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Chen, N., Mao, J., Ye, Z., Duan, Z. and Li, H., 2022 - Rapid transition to fertile magma and promotion of porphyry mineralization: A case study from the Don Javier deposit: in Ore Geology Reviews v.147, 16p. doi.org/10.1016/j.oregeorev.2022.104964.
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Ye, Z., Mao, J., Lu, M., Zhu, X., Chen, N., Wei, H., Jin, W. and Meng, X., 2022 - Geology and geochronology of the Don Javier Cu-Mo porphyry deposit, southern Peru: in Ore Geology Reviews v.143, 18p. doi.org/10.1016/j.oregeorev.2022.104777.
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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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