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Panulcillo, Teresa de Colmo

Chile

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The Panulcillo and Teresa de Colmo deposits are contrasting iron oxide copper-gold occurrences in north-central Chile. Panulcillo is located in the Chilean Coastal Cordillera near the town of Ovalle, ~400 km south of Copiapo, ~70 km south of the city of La Serena, and 500 km north of Santiago. Teresa de Colmo is ~600 km north of Panulcillo, 220 km north of Copiapo and ~75 km SE of the port of Taltal.

Panulcillo

The geology of the coastal belt in and around the Panulcillo copper deposit (Bohnhorst, 1967) comprises of a thick sequence of Lower Cretaceous, Neocomian rocks which dip and young to the east. This sequence commences with marine andesitic volcanic rocks with minor intercalations of rhyolite, overlain by the Estratos del Reloj Formation, a transitional marine-continental sequence consisting mainly of porphyritic andesitic volcanics towards the base passing up into minor lenses of limestone and volcaniclastic sediments towards the top. These are overlain by mainly continental volcano-sedimentary rocks. This succession constitute the Ovalle Group, the stratigraphic equivalents of the Bandurrias Formation which hosts the Candelaria deposit 400 km to the North, and is overlain by a continental sedimentary sequence. This entire Cretaceous sequence has been intruded by coeval calc-alkaline plutons dominated by granodiorite to monzonite with smaller bodies ranging in composition from syenite through to gabbro.

The Panulcillo deposit is hosted entirely within the upper members of the Estratos del Reloj Formation, which in the district is dominated by andesitic rocks, with the lensoid "Morenita" Limestone in the middle. The sequence strikes north-south and dips to the east at between 40 and 70°.

Two km to the north of The deposit lies 2 km to the south of the contact with a large circular monzonite to quartz-monzodiorite mass (Carrascal, 1989), surrounded by a 2 to 4 km wide, district-scale metamorphic aureole. The Panulcillo deposit lies entirely within this contact metamorphic aureole. The andesitic rocks have been recrystallised to fine-grained meta-andesites, dominated by highly variable proportions of biotite, amphibole, pyroxene and magnetite, together with lesser calcic and sodic feldspars. The limestones have been recrystallised to grossular and andraditic garnets.

The Panulcillo deposit consists of several elongate lensoid "Manto" bodies of copper mineralisation that strike north-south, dip to the east, subparallel to the stratigraphy of the Estratos del Reloj Formation, and are stacked pancake-style one upon the other. The mantos are developed within the Morenita Limestone and in the footwall rocks of the underlying andesitic sequence, with characteristics dependant on the host rocks. Of the several mantos, two of them are of significant grade and tonnage. The Upper Manto is hosted within the Morenita Limestone and the Lower Manto, hosted within the lower andesitic sequence.

Mineralisation in the Upper Manto comprises chalcopyrite, pyrite, pyrrhotite and minor sphalerite and galena infilling veins, incipient breccias and intergranular spaces in garnet-dominant skarn, with grades generally highest near the marble-hornfels contact or in subvertical veins. Minor gold, averaging about 100 ppb, occurs in association with skarn alteration. Skarn-style sulphide mineralisation in the Upper Manto has undergone supergene processes.

The central portion of the Upper Manto had a strike length of 160 m and a thickness of 45 to 50 m at surface increasing to 70 m at a depth of 150 m (Ardilla, 1993). Although the lens pinches and swells along its length, the total strike length of the carbonate-hosted skarn-style mineralisation is on the order of 1500 m.

The Lower Manto within the lower andesites, occurs at a depth of 250 to 300 m, and with a main axis that extends for ~800 m along a north-south strike, and is up to 250 m wide east-west. The thickness of mineralisation varies from about 20 to 150 m, averaging ~30 m. Andesitic rocks in the axial section of the lens are flooded by variable amounts of abundant, often texturally destructive, K feldspar, silica and albite, with K feldspar in the shear-related core, passing outwards to magnetite- and biotite-rich andesitic rocks accompanied by albite and scapolite.

Within the axial zone, chalcopyrite and bornite with lesser pyrite and pyrrhotite mainly occur as as blebby disseminations, hairline crackle-veinlets or breccia infill which cut the silica-feldspar altered andesitic rocks. In the outer magnetite halo sulphides occur as veins, veinlets and intergranular disseminations.

Teresa de Colmo

The regional geological setting of the Teresa de Colmo area comprises a gently dipping sequence of porphyritic andesite flows and volcanic breccias with intercalated sandstone and conglomerate layers, of the Lower Cretaceous Aeropuerto Formation (Ulricksen, 1979). These stratified units are intruded by 112 Ma medium-grained granodioritic rocks (Naranjo et al., 1984), that form part of the Coastal Batholith, and are discordantly overlain by Tertiary intermediate to acid volcanic rocks of the Chile-Alemania Formation (Chong, 1973).

The main structures are strike-slip faults parallel to the Atacama Fault System, which has a long-lived deformation history, initiated during the Middle Jurassic (Scheuber et al., 1990).

The deposit is hosted by andesitic volcanic and sedimentary rocks, cut by medium-grained Lower Cretaceous granodioritic stocks. The volcanic rocks are dominantly brown-green, porphyritic to aphanitic andesites, with intercalated fine to medium grained sandstone and conglomerate with a medium-grained matrix. The volcano-sedimentary package is apparently concordantly underlain by an evaporite sequence which persists to depths of >200 m and consists of well-laminated layers of gypsum, anhydrite and calcite, with some thin intercalations of chlorite, hematite, tourmaline, pyrite, and plagioclase (Correa, 1999).

Fine to medium-grained granodiorite and a porphyritic diorite outcrop to the west of the deposit, intruding the volcanics, sediments and, presumably, the evaporites. The intrusives are not significantly altered, but contain an anomalous amount of specular hematite, as disseminations and in veinlets. In addition to these intrusive bodies, a leucodiorite stock was identified 500 m below, with moderate albite alteration and weak disseminated chalcopyrite, pyrite and bornite mineralisation.

The deposit consists of a specularite-rich sub-vertical breccia body, developed in a dilational jog related to sinistral strike-slip faulting. The breccia body appears to be located at the intersection of groups of NNW- and WNW-trending faults. Brecciation is more intense at the intersection of the two group of faults. and coincides with high-grade Cu mineralisation. These structures have been subjected to several phases and directions of syn- and post-mineral faulting. Superposition of these deformation phases onto a breccia style of mineralisation has produced a complex and irregular pattern of mineralisation.

The mineralised body at Teresa de Colmo is a subvertical hydrothermal-tectonic breccia system, that extends for 600 m in a NNW direction. Its width varies from 180 to 300 m and to a depth of ~450 m. The breccia is usually matrix-supported and poorly sorted. It normally contains sub-angular to sub-rounded fragments 1 to 60 cm in diameter, composed of different types of andesites and sandstones, set in a dark, dense, coarse-grained specularite matrix. The breccia, which dominates the core of the deposit, contains sub-rounded polymictic clasts, and in many cases shows evidence for more than three stages of brecciation.

The copper mineralisation in the deposit primarily occurs in the breccia matrix, with lesser veinlet-hosted and disseminated mineralisation, in a ratio of 4:1:1. Textural and paragenetic relationships indicates that the pyrite-chalcopyrite-specularite hypogene mineralisation was deposited during at least two separate stages.

The first stage is characterised by idiomorphic pyrite and subidiomorphic chalcopyrite, the latter frequently nucleating on the former, suggesting that the chalcopyrite is later than the pyrite. Chalcopyrite occurs in three forms: i). coarse-grained brecciated clumps within veins and the matrix of the more strongly brecciated zones; ii). veins of pure chalcopyrite up to several centimetres in thickness; and iii). disseminated in microveinlets within andesites, and in the matrix of coarse grained sandstones and conglomerates. Alteration accompanying this stage is mainly albite (sodic alteration) and chlorite with minor silicification and calcite. Albite partially replaces plagioclase phenocrysts and pervasively affects the groundmass of the volcanic rocks. Chlorite replaces hornblende phenocrysts and to a lesser extent plagioclase feldspars.

The second stage is characterised by specularite mineralisation, which generally uses the same fractures as the earlier sulphides, and is interpreted to be lower temperature and brittle, representing an explosive pressure release, resulting in the formation of collapse breccias, with well-developed space-infilling textures. The specularite commonly comprises coarse-grained idiomorphic blades lining vein margins, or clasts within the breccia bodies. Coarse grained idiomorphic calcite frequently envelopes the specularite and, along with minor gypsum, forms the final phase to crystallise within the open spaces.

Panulcillo contains a remaining resource of 10.4 Mt @ 1.45% Cu after historic production of 3 Mt @ 3.5 to 10% Cu. Teresa de Colmo has a resource of around 70 Mt @ 0.8% Cu.

These deposits are the subject of a paper in the monograph: Porter T M (Ed.) "Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective" volume 1, published by PGC Publishing, Adelaide, Australia. This summary is based on, and in part quotes from, that paper.

The most recent source geological information used to prepare this summary was dated: 2000.     Record last updated: 16/7/2013
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.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Hopper D and Correa A,  2000 - The Panulcillo and Teresa de Colmo Copper Deposits: Two Contrasting Examples of Fe-Ox Cu-Au Mineralisation from the Coastal Cordillera of Chile: in Porter T M (Ed), 2000 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.1 pp. 177-189

 References to this deposit in PGC Publications: Want any of our books ? Pricelist
Hopper D, Correa A, 2000 - The Panulcillo and Teresa de Colmo Copper Deposits; Two Contrasting Examples of Fe-Ox Cu-Au Mineralisation from the Coastal Cordillera of Chile,   in  Porter T M, (Ed.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v1  pp 177-189
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