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Exotica, Mina Sur
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Exotica (or Mina Sur) is a large exotic channel fill secondary copper deposit adjacent to the Chuquicamata deposit in northern Chile and developed as part of the supergene processes operating in the district.

The main lenticular mineralised zone commences at the palaeo watershed at the topographic divide over the centre of the Chuquicamata deposit and extends southwards for some 6.5 km on a slope of 3 to 7°S. The northern margin outcrops in the Chuquicamata pit while the southern extremity is concealed by 200 m of barren gravels.

The bedrock in the deposit area comprises a Palaeozoic to Lower Triassic igneous-metamorphic complex composed of metamorphosed volcanic, sedimentary and granitic rocks, juxtaposed across the north-south West Fissure with with Mesozoic volcanic rocks and other Palaeozoic to Eocene granitoids. The basement metamorphic rocks are altered to a propylitic assemblage of plagioclase, calcite, chlorite, epidote and pyrite, parly related to the Chuquicamata orebody, but also in part due to regional metamorphism.

The first 3 km of the palaeochannel is tightly confined by erosional bedrock banks adjacent to the West Fissure. Between 3 and 5 km below the head of the channel, it curves eastward and has a gentler gradient, before becoming more narrowly confined over the last 2 km, where it may follow a fault parallel to the West Fissure.

The channel gravels are composed of two interlayered units of talus gravel and mud flows respectively. K-Ar age dating of volcanic ash deposited within the upper part of the sedimentary unit provides a minimum age of 8.4 Ma for the host gravels (Hunt, 1970, in Munchmeyer and Urqueta, 1974). However, radiometric K-Ar age dating of supergene alunite from the palaeo-channel indicates that the main supergene processes at Chuquicamata, and the development of the exotic mineralisation, presumably in older lower gravels, occurred between 19 and 15 Ma (Sillitoe and McKee, 1996).

Copper mineralisation was developed in the basal section of the gravels throughout the palaeochannel to form a sinusoidal, lenticular body with a maximum width of 1.2 km and a maximum thickness of 110 m. In section, the deposit has a horizontal upper surface and an irregular concave lower surface following the topography of the base of the palaeochannel.

The copper ore minerals are, in decreasing order of abundance, atacamite [Cu2Cl(OH)3], copper wad (a copper-rich Mn-Fe oxide) and chrysocolla [Cu2H2Si2O5(OH)4].

The distribution of mineralisation is intimately related to the distribution of argillic alteration of the host gravels, mainly as kaolinite and montmorillonite. Chrysocolla predominates over atacamite in less altered rocks, whilst in strongly kaolinised gravels, chrysocolla is absent and copper wad and lesser atacamite are dominant. Mineralisation is also found within strongly altered bedrock to the gravels where the transporting fluids have penetrated into that bedrock.

Mining of the deposit commenced in 1969 on a 'reserve' of 160 Mt @ 1.65% Cu. Reserves in 1991 were 640 Mt @ 0.69% Cu. Published resources in 2000 (Camus, 2003) were 171 Mt @ 1.18% Cu at a cut-off of 0.2% Cu, whilst reserves were 32 Mt @ 1.17% Cu.

For more information consult the references below.

The most recent source geological information used to prepare this decription was dated: 1998.    
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.

    Selected References
Munchmeyer C  1996 - Exotic deposits - products of lateral migration of supergene solutions from copper deposits: in Camus F, Sillitoe R H, Petersen R (Eds),  Andean Copper Deposits: New Discoveries, Mineralisation, Styles and Metallogeny Soc. Econ. Geologists   Spec. Publ. No. 5 pp 43-58

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