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Radomiro Tomic
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The Radomiro Tomic porphyry copper deposit is located ~5 km NNE of the giant Chuquicamata deposit in northern Chile, some and 40 km north of the town of Calama, 240 km NE of Antofagasta and 1690 km north of Santiago in the Antofagasta Region of northern Chile (#Location: 22° 13' 51"S, 68° 53' 6"W).

Four main belts of porphyry copper deposits are developed in association with continental magmatic arcs in the Central Andes if Chile and Peru. Of these, the Late Eocene to Early Oligocene belt (43 to 31 Ma), located along the 800 km long Domeyko Fault Zone (DFZ) in the Domeyko Cordillera, is one of the two most important, containing >15 porphyry copper deposits distributed in 5 deposit clusters. The Radomiro Tomic deposit is located in one of these clusters together with three others, all of them occurring along the well known West Fissure, one of the main strands of the DFZ.

Bedrock geology at Radomiro Tomic is divided by the West Fissure into two domains. The western domain is unaltered and dominated by the presence of the post-mineral Fortuna Granodiorite complex, a NNE-elongated intrusion 22 km long by 5 km wide, the eastern margin of which is defined by the West Fissure. The Fortuna complex comprises five intrusive bodies of fine- to medium-grained hornblende-biotite granodiorite. This 39 to 37 Ma complex (Dilles et aI., 1997) is intruded into late Cretaceous to early Tertiary andesitic volcanics.

The eastern domain is occupied by the northern extension of the Chuqui Porphyry, which hosts much of the Radomiro Tomic orebody. The Chuqui Porphyry is a medium- to coarse-grained granodiorite to monzogranite that is elongated north-south, 1 km wide and cuts the early Cretaceous Elena Granodiorite. Contact relations between the Chuqui Porphyry and its host rocks are poorly defined. Dating of the K-silicate and phyllic alteration in the Chuqui Porphyry at Radomiro Tomic gives an average age of 32.7±0.3 and 31.8±0.3 Ma (40Ar/39Ar; Cuadra et aI., 1997).

During late Eocene to early Oligocene time, the country rocks in the vicinity of the Radomiro Tomic and Chuquicamata orebodies were affected by dextral transcurrent north-south faulting. The resulting structures, part of the DFZ, were developed between the Mesabi fault on the east and La Tetera fault on the west and controlled intrusion of the Chuqui Porphyry and the associated alteration and copper-molybdenum mineralisation. The dextral structural elements recognised in the district include the main north-south faults, associated ENE- and NNE-striking structures, and the vertical NE-striking extensional fractures along which quartz-pyrite-chalcopyrite veins were emplaced. These structures also controlled circulation of ground waters resulting in the vertical and lateral migration of copper that resulted in the leached and oxidised zones and the underlying supergene sulphides.

The deposit is concealed beneath 40 to 150 m of Neogene gravels. The orebody is hosted by the Chuqui Porphyry which is elongated north-south, and 1 km wide, that intruded the Early Cretaceous Elena Granodiorite.

Supergene leaching and oxidation affected the K-silicate zone to depths of about 400 m beneath the gravel-bedrock contact, generally varying between 180 and 200 m. This formed a horizontal blanket of oxide copper minerals that extend for 4.3 km north-south and up to 800 m east-west. Oxide mineralisation begins immediately below the gravel contact with a typical vertical distribution of leached-oxide zone, mixed zone and secondary sulphide zone. Underlying this oxidation zone, there is continuous but irregular immature supergene enrichment zone over a thickness varies from 20 to 150 m, characterised by weakly developed chalcocite and covellite. Enrichment has locally reached depths of up to 800 m along quartz-sericite faulted veins.The underlying hypogene zone extends for >200 m below the top of the sulphides.

The upper part of the enrichment zone, immediately below the top of sulphides, is characterised by the highest grades and is defined by the presence of >80% hypogene sulphides coated by chalcocite. In contrast, in the lower part of the zone, the main supergene sulphide is covellite, with only minor chalcocite.

Hypogene mineralisation is marked by concentric bornite-chalcopyrite, chalcopyrite-pyrite and pyrite-chalcopyrite zones which average 0.5% total Cu. Some weak molybdenite mineralisation is present, either alone or associated with chalcopyrite and pyrite in quartz veins and veinlets striking north and dipping subvertically.

Pervasive K-silicate alteration is developed throughout the entire Radomiro Tomic deposit, typically represented by A veins composed of quartz and K feldspar, biotite alteration of hornblende phenocrysts and K feldspar introduction to the porphyry groundmass. The bulk of the hypogene copper mineralisation accompanied with the K-silicate alteration. Phyllic (quartz-sericite) alteration is less abundant and is controlled by NE- and north-south- striking subvertical structures, marked by quartz-pyrite-chalcopyrite D veins with sericitic haloes. In the upper oxidation zone, supergene argillic alteration occurs as montmorillonite-kaolinite coatings on fracture planes and replacement of plagioclase phenocrysts. Oxidation and leaching of quartz-pyrite veins produced a low copper jarositic leached capping.

Oxide mineralisation consists mainly of atacamite and chrysocolla that define two distinct horizons. The upper horizon, the Upper Oxide unit, is characterised by chrysocolla, copper clays and lesser atacamite. The underlying Lower Oxide unit is more homogenous and atacamite dominates over chrysocolla and copper clays.

The supergene sulphides represent an overall geological resource of 363 Mt @ 0.83% total Cu in the upper part of the zone, and 0.54% total Cu in the lower part. There is an intermediate mixed zone between oxides and supergene sulphides ("mixtos") of 40 Mt @ 0.83% total Cu.

A total geological resource of more than 1000 million tonnes averaging 0.56% total Cu is estimated for the Radomiro Tomic deposit.

This description is summarised from Cuadra and Camus (1998)

The most recent source geological information used to prepare this decription was dated: 1998.     Record last updated: 23/11/2012
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.

Radomiro Tomic

  References & Additional Information
   Selected References:
Arcuri T, Brimhall G,  2003 - The Chloride Source for Atacamite Mineralization at the Radomiro Tomic Phorphyry Copper Deposit, Northern Chile: in    Econ. Geol.   v98 pp 1667-1681
Brimhall G H, Levi B, Nystrom J O, Tidy F. E  2001 - Atacamite inclusions in rock-forming Feldspars and Copper-bearing smectites from the Radomiro Tomic Mine, Chile: Copper-insoluble mineral occurrences: in    Econ. Geol.   v96 pp 401-420
Cameron E M, Leybourne M I and Palacios C,   2007 - Atacamite in the oxide zone of copper deposits in northern Chile: involvement of deep formation waters? : in    Mineralium Deposita   v42 pp 205-218
Cuadra, C.P. and Rojas, S.G.,  2001 - Oxide mineralization of the Radomiro Tomic porphyry copper deposit, Northern Chile: in    Econ. Geol.   v.96, pp. 387-400.
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

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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