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Maricunga Belt - Lobo, Marte, Refugio, Cerro Casale, Aldebaran, Cathedral Peak, La Pepa, Caspiche

Chile

Main commodities: Au
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The ~200 km long and 30 km wide Maricunga metallogenic belt, is located bewteen 26 and 28°S in the volcanic high Andean Atacama Region of northern Chile, near the Argentine border, due east of Copiapo. It represents a linear metallogenic unit defined by at least 14 zones of gold and/or silver mineralisation between latitiudes 26 and 28°S, related to a belt of large, compound, Miocene, calc-alkaline stratovolcanoes. Since 1980, a total of more than 1250 tonnes (40 Moz) of gold have been defined in the belt, (Muntean and Einaudi, 2000). Deposits in the belt include Refugio/Maricunga, Amalia, Cerro Casale (Aldebaran), La Pepa, Marte, Lobo, Valy, Santa Cecelia, Cathedral Peak and Caspiche.

The projected alignment of mineralised centres continues southward, through the Caserones (formerly Regalito) porphyry copper deposit, to the El Indio belt, characterised by high-grade vein (e.g., El Indio) and bulk-tonnage (e.g., Pascua-Lama, Veladero), high sulphidation epithermal gold±silver deposits. Miocene porphyry gold prospects are found to east, in westernmost Argentina, in the backarc to the Maricunga belt.

The Maricunga belt is made up of a series of coalescing composite, latest Oligocene to Miocene andesitic to rhyolitic volcanic complexes and comagmatic subvolcanic stocks that extend for 200 km along the western crest of the Andes. The volcanic rocks, which host multiple associated porphyry gold±copper and high sulphidation epithermal gold±silver deposits, as well as numerous other smaller mineral occurrences, overlie older sedimentary and volcanic rocks of Mesozoic and Palaeozoic age.

The Maricunga belt is located along the southwestern edge the Altiplano-Puna plateau which spans the boundary between the currently active Central Volcanic Zone of the Andes and the nonvolcanic segment to the south, between 28 and 33°S, which corresponds to the transition from moderate-angle to flat-slab subduction (Thorpe et al., 1982; Cahill and Isacks, 1992; Kay and Mpodozis, 2002).

Basement to the Maricunga belt comprises late Palaeozoic metasedimentary and felsic volcanic rocks and granitoids, similar to those that form large parts of the Cordillera Frontal zone further east in Argentina (Mpodozis and Ramos, 1990). These rocks are overlain by Triassic bimodal volcanic and sedimentary rocks which were deposited in extensional rift basins, and by Jurassic to Early Cretaceous marine and continental sedimentary rocks that accumulated in a backarc basin that was developed throughout northern Chile (Mercado, 1982; Mpodozis et al., 1995; Cornejo et al., 1998; Iriarte et al., 1999; Arriagada et al., 2006). Following the tectonic inversion of this latter basin, and eastward migration of the Andean arc, Late Cretaceous to Eocene arc to back arc volcanic rocks and continental redbeds formed (Cornejo et al., 1998; Iriarte et al., 1999; Mpodozis and Clavero, 2002). In the southern Maricunga belt, as well as further east and south, the Paleocene volcanic units are covered by Oligocene continental sedimentary sequences, composed of red sandstone, siltstone and conglomerate, which include evaporitic horizons (Mpodozis and Kay, 2003). Further south, these rocks unconformably overlie Eocene redbeds and volcanic rocks (Mpodozis et al., 1991; C. Mpodozis, written comm., 2011). Oligocene siliciclastic redbeds are a major host rock to the porphyry deposits.

Arc magmatism in the Maricunga belt commenced in the late Oligocene to early Miocene, at ~26 Ma, and is predominantly medium- to high-K calc-alkaline andesite to dacite in composition (Kay et al., 1994; McKee et al., 1994; Mpodozis et al., 1995). These rocks are largely the products of extinct stratovolcanoes and volcanic dome complexes, which have been variably eroded and dissected (Vila and Sillitoe, 1991; Kay et al., 1994; Mpodozis et al., 1995). The often closely linked porphyry and high sulphidation epithermal deposits were generated beneath stratovolcanoes and volcanic dome complexes during two principal metallogenic epochs, namely the latest Oligocene to earliest Miocene (26 to 21 Ma) and mid-Miocene (14 to 10 Ma).

The latest Oligocene to earliest Miocene volcanic activity, and associated precious and base metal mineralisation, is interpreted to have taken place in a neutral to weakly extensional tectonic setting, which gave way to contraction at the beginning of slab flattening between 20 and 18 Ma (Mpodozis et al., 1991, 1995; Kay et al., 1994, 2008; Kay and Mpodozis, 2001). This contraction resulted in the diminution of volcanism, compressive deformation, and crustal thickening (Kay et al., 1994; Mpodozis et al., 1995). The gold-deficient Caserones porphyry copper-molybdenum deposit and nearby prospects, immediately south of the Maricunga belt, were generated during this compressive event (Mpodozis and Kay, 2003; Perelló et al., 2003; Sillitoe and Perelló, 2005).

Widespread and voluminous extensional conditions and volcanic activity was again prevalent between 17 and 12 Ma, an interval that concluded with the second, mid-Miocene (14 to 10 Ma), precious and base metal mineralisation event. This was followed by renewed contraction and marked geographic localisation of volcanism between 11 and 5 Ma, when all volcanic activity ceased in the Maricunga belt prior to reestablishment at the site of the present- day magmatic arc, some 60 km further to the east (Kay et al., 1994, 2008; Mpodozis et al., 1995).

Reverse faults striking parallel to the Andean axis have uplifted hypabyssal intrusive rocks beneath the extrusive volcanics exposing porphyry-hosted gold-copper deposits. Major fault systems cut Palaeozoic, Mesozoic and Tertiary units, the oldest of which strike north-westerly over an interval of 50 to 60 km, and are most likely extensional structures, perpendicular to the direction of plate subduction.

Major, through-going lineaments trend NE and appear to mark boundaries between major basement lithological domains. Younger lineaments and faults cut Tertiary and Quaternary volcanic rocks, striking north, 40°, 310° and east. Mineralisation in individual deposits is generally aligned along one or more of these structural trends.

Major alteration zones and gold and gold-copper mineralisation in the Maricunga Volcanic Belt are coincident with subvolcanic intrusive rocks of diorite and granodiorite composition below andesitic-(dacitic) stratovolcanoes, with intrusives generally occurring at the intersection of major structural lineaments. These volcano-intrusive complexes were more deeply dissected in the eastern of the two sub-belts. In the eastern sub-belt the volcanic systems were intruded by dioritic plugs, but also by quartz-diorite to the west.

Gold-copper mineralisation was accompanied by K-silicates and overprinted by sericite-clay-chlorite assemblages of intermediate argillic alteration.   Much of the gold occurs in quartz-stockworks.   Magnetite and hematite make up around 5 to 10% of the mineralised zones.   Pyrite is the dominant sulphide with minor chalcopyrite and trace bornite and molybdenite.

See also the separate records for individual deposits within the belt.

This summary is drawn from the papers listed below.

The most recent source geological information used to prepare this summary was dated: 2013.     Record last updated: 12/5/2013
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:
Muntean, J.L., Einaudi, M.,   2000 - Porphyry gold deposits of the Refugio District, Maricunga Belt, Northern, Chile: in    Econ. Geol.   v.95, pp. 1445-1472.
Sillitoe R H, McKee E H, Vila T  1991 - Reconnaissance K-Ar geochronology of the Maricunga Gold-Silver belt, northern Chile: in    Econ. Geol.   v86 pp 1261-1270
Sillitoe R H, Tolman J and Van Kerkvoort G,  2013 - Geology of the Caspiche Porphyry Gold-Copper Deposit, Maricunga Belt, Northern Chile: in    Econ. Geol.   v.108 pp. 585-604
Vila T, Sillitoe R H  1991 - Gold-rich porphyry systems in the Maricunga Belt, northern Chile: in    Econ. Geol.   v86 pp 1238-1260


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