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Toki |
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Chile |
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Cu Mo
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Super Porphyry Cu and Au
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The Toki porphyry copper deposit is located approximately 15 km south-west of the Chuquicamata mine and 165 km northeast of Antofagasta in northern Chile (#Location: 22° 25' 10"S, 68° 56' 40"W).
The country rock in the vicinity of Toki consists of folded and faulted Palaeozoic schist with a dominant north-northeast structural grain, overlain by Permian to Triassic volcanic rocks which are covered by Jurassic to Early Cretaceous marine and terrestrial sedimentary rocks and intruded by Eocene stocks. The deposit area is completely concealed by 120 to 200 m of Miocene gravel and lacustrine sediments.
In the vicinity of the Toki deposit, the Permian to Triassic and Cretaceous sedimentary rocks are intruded by the 40 to 37.5 Ma Fortuna granodiorite complex, which is composed of an early dioritic phase, followed by monzodiorite, granodiorite and tonalitic and dacitic porphyries. The Toki deposit is related to a multiphase tonalite porphyry and associated breccia complex intruding Permian to Triassic aphanitic to porphyritic andesitic rocks and dacitic tuffs and pyroclastic breccias and late Eocene medium grained equigranular tonalitic rocks of the early Fortuna complex. The tonalitic porphyry complex is equated with the late tonalites and dacites of the Fortuna complex. The dacitic tuffs and breccias are the main host to mineralisation. The main, mineralisation related intrusive occurs as numerous, irregular, NE trending, subvertical dyke like bodies composed of K feldspar, quartz, biotite and amphibole phenocrysts in a matrix of K feldspar and plagioclase.
At least two phases have been recognised in the tonalite porphyry, The earlier phase which hosts much of the mineralisation has abundant A-type quartz veins, which is followed by a late pyritic phase is devoid of quartz veining and has only weak Cu mineralisation. Conspicuous NW-trending D-type veins with associated sericite alteration crosscuts the earlier hypogene mineralisation and represents a late hydrothermal event.
The dominant structure in the Toki area is the West Fault which passes 2 km east of the centre of the deposit. The same fault passes through the MM deposit to the north, the western sections of the Chuquicamata deposit, and can be traced northward to the Colluhuasi mine. The same structure is part of the Domeyko fault system that passes through the Escondida deposit to the south. A conspicuous set of northeast trending faults predates the West fault. Porphyry dykes and veining mainly follows the NNE to NE direction of faulting, while WNW and NW faults offset both hypogene and supergene mineralisation.
The Toki ore deposit covers a plan area of approximately 2.5 x 1 km and has been tested to a vertical depth of >800 m. Half of the orebody is oxide, mixed oxide-sulphide and supergene enriched sulphide mineralisation, while the lower half is composed of hypogene copper-bearing sulphide ore.
Hypogene mineralisation is zoned outward from a core of bornite (digenite) and chalcopyrite to a zone of chalcopyrite and pyrite. Alteration displays a centrally located, pervasive potassic assemblage related to moderate to intense quartz-K feldspar veins, grading outward to a peripheral propylitic zone. Biotite from the potassic zone has been dated at 37.3 ±1.3 Ma. The late D vein sericite alteration which crosscuts the earlier alteration pattern has been dated at 34.52 ±0.20 Ma.
The supergene profile comprises of an upper 100 to 160 m thick oxide zone (characterised by malachite, chrysocolla, atacamite and wad), locally interrupted by leached D veins and parallel faults. This is grades downward into an irregular, structurally controlled, mixed oxide-sulphide, (atacamite-chalcocite) zone, and then to a weakly to moderately enriched chalcocite-covellite interval, between 50 and 200 m thick.
Postmineral, NW-trending faults dislocate the orebody, which is tilted to the south. The mineralising events that generated the Toki deposit is interpreted to have taken place at ~37 Ma, preceded emplacement of the Chuquicamata porphyry copper complex, dated at between 35 and 31 Ma.
Inferred resources at Toki are >2.4 Gt @ 0.5% Cu, one-third of it oxide and mixed oxide-sulphide mineralisation (Rivera and Pardo, 2004).
The most recent source geological information used to prepare this decription was dated: 2004.
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.
Toki
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Selected References:
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Palacios, C., Ramirez, L.E., Townley, B., Solari, M. and Guerra, N., 2007 - The role of the Antofagasta-Calama Lineament in ore deposit deformation in the Andes of northern Chile : in Mineralium Deposita v.42, pp. 301-308.
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Rivera S L and Pardo R, 2004 - Discovery and geology of the Toki porphyry copper deposit, Chuquicamata district, northern Chile: in Sillitoe R H, Perello J and Vidal C E, 2004 Andean Metallogeny: New Discoveries, Concepts and Updates, Society of Economic Geologists, Denver, SEG Special Publication 11 pp 199-211
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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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