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Productora - Santa Innes, Monseratt, Remolina, Fortuna, Alice |
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Chile |
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Cu Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The extensive Productora iron oxide copper-gold mineralised system is located 15 km SSW of the town of Vallenar, and 170 km NNE of La Serena, and 625 km
north of Santiago, in the Third Region of north-central Chile.
The district lies within the "Chilean Iron Belt" which is associated with the long-lived, north-trending Atacama Fault Zone. This brittle-ductile structure has been active since the Early Cretaceous and has involved recurrent sinistral strike-slip displacements. The deposit is geographically centred around the Productora Valley which comprises several talus-filled basins. These basins are surrounded by, and lie along strike from, a north-trending zone of hydrothermal alteration (Fe oxide-albite- K feldspar-biotite-tourmaline-sericite-silica) that can be discontinuously traced over an 8 km length, reaching 3 km in outcrop width. It contains five small, shallow former mines (Productora, Santa Innes, Monseratt, Remolina and Fortuna) worked for Cu oxides and Au, as well as eight magnetite mines and more than eighty pits and occurrences with iron oxides±Cu±Au±U±REE±apatite mineralisation. These five mines lie within an almost continuous, NNE-SSW trending, >0.1% Cu contour that is ~8 km long and 200 to 800 m wide.
The geology of the region comprises a poorly exposed basement of Paleozoic rocks overlain by Mesozoic and Cenozoic volcanic and sedimentary sequences. Jurassic and younger deposition was mainly composed of calc-alkaline andesitic lavas and flow breccias with some continental clastic sediments (Aguirre et al., 1974; Clarke et al., 1976), laid down in a continental margin, back-arc environment (Coira et al., 1982). The Andean Orogeny commenced during the early Jurassic (Clark et al., 1976), and the subsequent volcanism and plutonism moved progressively eastwards with time. Jurassic plutons occur along the coast, while Cretaceous and younger plutons outcrop further east.
The immediate mineralised system developed within early to mid-Cretaceous andesites, rhyolitic tuffs, ignimbrites, arenites and quartzites that were intruded by upper Cretaceous to lower Tertiary calc-alkaline granodiorites, dacites, monzonites, and aplites, with the bulk of the volcanic rocks exposed along the main mineralised trend being siliceous and of rhyolitic composition. Dacites and andesites are also interlayered with the rhyolitic volcanics.
The Productora project area is associated with a NNE-trending fault zone, interpreted to be a splay from the NNW-SSE Atacama fault zone (AFZ) which is located 5 kms to the west. The associated widespread and intense metasomatic and hydrothermal alteration appears to be related to late Cretaceous to early Tertiary movement on the AFZ.
The sequence hosting the Productora mineralisation is composed of a rhyolitic breccia, while metasomatised middle-Cretaceous to early-Tertiary granitoid intrusions (Fortin, 1990) outcrop to the south and east of the mineralised zone. The host sequence is cross-cut by andesitic to latitic dykes which tend to be far less altered than the host sequence suggesting they were emplaced relatively late in the geological history.
Two zones of intense copper, gold, molybdenum, cobalt and uranium associated metasomatic surface alteration have been recognised along the main NNE-trending mineralised trend: one at Productora (central area) and the other at Carmen (northern area). Geochemical work has recognised a distinct metal association comprising copper, gold, molybdenum, cobalt, uranium, silver, vanadium, bismuth and phosphorus.
Alteration comprises silicification with pyrite and chalcopyrite, accompanied by potassic alteration (K feldspar), argillisation, tourmalinisation, iron-oxide alteration and sericitisation. There is an obvious zonation of alteration mineralogy from K feldspar-tourmaline in the south to chlorite-K feldspar-carbonate in the north, probably reflecting a temperature gradient, suggesting a cooling of the system northwards and a gentle northerly plunge to the hydrothermal system.
Discrete clockwise jogs along the Productora fault zone mark locally changes in its strike from N-S to NNE orientations. These jogs represent areas as they are likely to be associated with wider zones of fracturing promoting increased secondary permeability suitable for focusing hydrothermal fluids. The Productora fault trends NNE in the area between the Productora and Santa Innes mines, indicating these two mineralised zones are located broadly proximal to either end of a NNE-trending fault jog.
Another, sub-parallel but slightly convergent, fault has been mapped to the west of Productora, also associated with magnetite and copper mineralisation. This fault trends more uniformly NNE and joins the Productora fault approximately 2 km north of the old Productora mine. It is interpreted to be a splay off the Productora fault (referred to as the Western Splay fault) and has numerous abandoned copper workings distributed along its trace, many of which are weakly to moderately radioactive. Numerous cross-cutting NW-trending faults have been mapped, many of which are associated with copper mineralisation and variably elevated levels of radioactivity. In addition, numerous examples of E-W and NE-trending faults are evident, commonly associated with copper mineralisation. These observations suggest a close association between faulting and mineralisation.
Primary mineralisation appears to rely upon the interplay of favourable lithological units (with primary permeability), regional faults and cross faults (both providing secondary permeability). Locations where favourable lithological units coincide with cross-faults and with regional fault jogs (and fracture zones) represent favourable sites for mineralisation. In addition, areas where regional fault splays bifurcate from the master fault (e.g., 2 km north of the old Productora mine), appear to be associated with relatively large fracture zones containing many mineralised veins. The abundance of old copper shafts in the fracture zone between the Western Splay fault and the Productora fault is also relatively well mineralised.
Productura is the subject of a paper in the monograph: "Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective" volume 2, published by PGC Publishing, Adelaide, Australia.
The summary above is based on Ray and Dick (2002), and the Hot Chili Limited website (2012)
However, Escolme et al. (2020) proposed the deposit represents a magmatic-hydrothermal breccia complex with closer affinities to porphyry systems than to IOCG style mineralisation. It is hosted within a thick sequence of broadly coeval rhyolite to rhyodacite lapilli tuffs dated at 128.7 ±1.3 Ma (U-Pb, zircon) and two major intrusions, the Cachiyuyito tonalite and Ruta Cinco granodiorite batholith, both dated at 92.0 1.0 Ma (U-Pb zircon). The describe hydrothermal and tectonic breccias, veins, and alteration assemblages at Productora to define five paragenetic stages:
• Stage 1, quartz-pyrite cemented breccias associated with muscovite alteration
• Stage 2, chaotic, matrix-supported tectonic-hydrothermal breccia with kaolinite-muscovite-pyrite alteration,
• Stage 3, tourmaline-pyritechalcopyrite ±magnetite ±biotite-cemented breccias and associated K-feldspar ±albite alteration,
• Stage 4, chalcopyrite ±pyrite ±muscovite, illite, epidote, and chlorite veins, and
• Stage 5, calcite veins.
The Productora hydrothermal system is seen to cross-cut earlier-formed sodic-calcic alteration and magnetite-apatite mineralisation that is associated with the Cachiyuyito stock, with main-stage mineralisation associated with the Stage 3 hydrothermal breccia. The dominant hypogene Cu mineral chalcopyrite which predominantly occurs as breccia cement with syn-breccia veins containing pyrite.
The Alice Cu-Mo porphyry style deposit, which occurs 1 km west of Productora, is characterised by disseminations of chalcopyrite and stockwork veins of quartz-pyrite-chalcopyrite ±molybdenite, hosted by a granodiorite porphyry stock. It is spatially associated with the Silica Ridge lithocap, which is characterised by massive, fine-grained, quartz-altered rock overlying alunite, pyrophyllite and dickite domains. Rhenium-Os Age dating of molybdenite (Re-Os) indicates main-stage mineralisation within the Alice porphyry at Productora took place at 130.1 ±0.6 Ma, and at 124.1 ±0.6 Ma.
Chalcopyrite and pyrite from Productora have δ34S sulphide values of from -8.5 to +2.2‰, consistent with a magmatic sulphur source and fluids evolving under oxidising conditions. No significant input from evaporite- or seawater-sourced fluids were detected. Stage 3 tourmalines were found to have average initial Sr of 0.70397, consistent with an igneous-derived Sr source.
Escolme et al. (2020) concluded the Productora magmatic-hydrothermal breccia complex formed as a result of explosive volatile fluid release from a hydrous intrusive complex. Metal-bearing fluids were of magmatic affinity and evolved under oxidising conditions. They also concluded that despite sharing many similarities with the Andean IOCG deposits and occurrences, namely strong structural control, regional sodic-calcic alteration and locally anomalous U, fluid evolution at the Productora Cu-Au-Mo deposit is more consistent with that of a porphyry-related magmatic hydrothermal breccia, namely it is sulphur-rich, has acid alteration assemblages and relatively low magnetite contents of <5 vol %. They therefore suggest the Productora deposits are an example of the close spatial association between Mesozoic magnetite-apatite, porphyry, and magmatic-hydrothermal breccia mineralization styles, also seen elsewhere within the Coastal Cordillera of northern Chile.
JORC compliant Mineral Resource estimates (Hot Chili Ltd website, 2013) at a 0.3% Cu cut-off are:
indicated resource - 70.6 Mt @ 0.6% Cu, 0.1 g/t Au, 0.014% Mo, 0.8% Cueq.;
inferred resource - 94.6 Mt @ 0.6% Cu, 0.1 g/t Au, 0.0126% Mo, 0.7% Cueq.;
TOTAL resource - 165.2 Mt @ 0.6% Cu, 0.1 g/t Au, 0.0132% Mo, 0.7% Cueq..
JORC compliant Mineral Resource and Ore Reserve estimates (Hot Chili Ltd website, viewed March 2018) are:
High grade Mineral Resource - 236.6 Mt @ 0.48% Cu, 0.10 g/t Au, 0.0135% Mo at a 0.25% Cu equiv. cutoff;
Low grade Mineral Resource - 218.0 Mt @ 0.16% Cu, 0.04 g/t Au, 0.0058% Mo at a >0.10 and <0.25% Cu equiv. cutoff;
Total Ore Reserves - 166.9 Mt @ 0.43% Cu, 0.09 g/t Au, 0.0138% Mo.
The Productora Resource, which includes the neighboring Alice Cu-Mo porphyry deposit, is estimated to contain (Escolme et al., 2020):
236.6 Mt @ 0.48% Cu, 0.10 g/t Au, 135 ppm Mo.
The most recent source geological information used to prepare this decription was dated: 2020.
Record last updated: 25/11/2021
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.
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Escolme, A., Cooke, D.R., Hunt, J., Berry, R.F., Maas, R. and Creaser, R.A., 2020 - The Productora Cu-Au-Mo Deposit, Chile: A Mesozoic Magmatic-Hydrothermal Breccia Complex with Both Porphyry and Iron Oxide Cu-Au Affinities: in Econ. Geol. v.115, pp. 543-580.
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Ray G E and Dick L A, 2002 - The Productora Prospect in North-Central Chile: An Example of an Intrusion-Related, Candelaria Type Fe-Cu-Au Hydrothermal System: in Porter T M (Ed.), 2002 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide v.2 pp. 131-151
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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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