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Anyak, Darband and Jawkhar |
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Afghanistan |
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Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The stratabound, sediment hosted, Anyak copper deposit is located approximately 30 km SSE of Kabul in eastern Afghanistan, near the villages of Gulhamid and Aynak in Logar Province. The deposit covers an area of 7 km2, and has been the site of copper working since ancient times.
(#Location: 34° 16' 20"N, 69° 17' 36"E).
The Anyak deposit and related Darband and Jawkhar prospects lie within the Kabul block, a terrane split from the margin of Gondwana during the Permian and subsequently accreted to the Asian continent ahead of the collision from the south of the Indo-Australian plate, and now lies within the collision zone between those two plates. The tear-shaped, NNE-elongated, 200 x 50 km Kabul Block is bounded to the west and east by the major, NNW trending Charnan-Pagman and arcuate Tagab-Gahzni fault systems respectively. It northern margin abuts the generally east-west to ENE-trending suture with the stable Turan plate of stable Asia to the north, but is otherwise surrounded by strongly deformed terranes.
The principal structure within the Anyak area is the asymmetric, 4 x 2.5 km, Anyak anticline, the southeastern limb of which dips gently to the SE, while the northeastern limb is steep to overturned with dips of as much as 45 to 70°SE. At the southwestern closure of the structure, the southern limk is also overturned and the axial plane dips to the NNE.
Regional basement comprises the Sherdarwaza Formation, which consists of gneisses, migmatites, granite gneisess and schists with subordinate marble, amphibolites and quartzites. These occur in rhythmic sequences, which when complete consist from the base upwards of quartzites, gneisses, mica schists, amphibolites and marbles. Individual cyclical units vary from several metres to several tens of metres in thickness, with the overall thickness of the Formation being more than 1900 m in the central parts of the Kabul block and more than 3000 m in the vicinity of Kabul. Radiometric dating suggests a late Palaeoproterozoic age, although it is believed to be older with dates reflecting a superimposed phase of recrystallisation related to a later tectono-thermal event.
The Sherdarwaza Formation conformably overlain by the 2500 m thick Kharog Formation, chiefly metamorphosed, granoblastic, cross-bedded quarzite that is interbedded with conglomerate, schist, gneiss, amphibolite and marble (Dronov, Abdullah and Chmyriov, 2008).
The oldest rocks in the Anyak district are the Late Neoproterozoic (Vendian) 1200 to 1500 m thick Welayati Formation, which regionally conformably overlie the Kharog Formation. They are composed of schists and gneisses and amphibolites, derived from volcanic protoliths. It comprises schist at the base, amphibolite in the middle, and alternating schist, gneises and amphibolite at the top. The schists and gneisses include assemblages of of biotite, staurolite-garnet-biotite, biotite-quartz, muscovite-quartz, and muscovite schist. Extensive, uniform thickness and composition amphibolites within the formation are interpreted to represent volcanic units or sills.
The Welayati Formation is overlain by the late Neoproterozoic to Cambrian Loy Khwar Formation, a cyclic sequence of dolomite-marble, carbonaceous quartz schist
and quartz-biotite-dolomite schist, which hosts the Anyak mineralisation. The lower Loy Khwar Formation is lithologically varied, consisting of basaltic-conglomerate, actinolite schist, calcareous-biotite schist, fine-grained breccia, banded biotite schist, quartzite and banded dolomitic marble. Pyrite, chalcopyrite, bornite, chalcocite, pyrrhotite and traces of molybdenite are present near the base of the formation. The middle sections of the formation are composed of marble, sandstone, quartzite and carbonate-rich schist. The upper sections the Loy Khwar Formation exposed at Anyak consist of carbon-quartz schist with dark-grey dolomite intercalations and grey, fine-grained, banded dolomite marble. The Loy Khwar Formation reaches a thickness of 420 m in the Western prospect and up to 880 m in the Central prospect.
The overlying Gulkhamid Formation is composed of a sequence of metamorphosed intermediate volcanic rocks with conglomerate, meta-sandstone and schistose tuff at the base and interstratified green-grey lava, tuff, breccia and tuffaceous sandstone of andesitic to dacitic composition in the upper part.
Numerous small intrusive bodies occur in the district, described as mainly plagiogranite porphyry and syenite porphyry, intruding the Welayati, Loy Khwar and Gulkhamid Formations, and are interpreted to be Late Neoproterozoic the Cambrian in age.
The copper mineralisation at Aynak is stratabound and characterised by bornite and chalcopyrite disseminated in dolomite-marble and quartz-biotite-dolomite schists of
the Loy Khwar Formation. In detail, the host sequence has been divided into the following members and mineral zones, from the base of the Loy Khwar Formation:
Member 1 - 16 to 52 m of calcareous biotite-schist and dolomite-marble, with pyrite and pyrrhotite;
Member 2 - 6 to 32 m of dolomite-marble and carbon-quartzite schist, with lesser pyrite and pyrrhotite;
Member 3a - 62 to 116 m of carbonaceous-biotite schist, carbon-quartzite and dolomite-marble, which chalcopyrite;
Member 3b - up to 60 m of dolomite-marble, with variable quartz, feldspar and biotite, characterised by bornite, with lesser chalcopyrite;
Member 4 - up to 100 m of calcareous-biotite-carbon-quartz schist, with chalcopyrite;
Member 5 - 25 to 170 m (averaging 80 m) of dolomite marble with variable quartz, feldspar and biotite, containing dominant bornite,
with a narrow chalcopyrite zone at the upper margin of the member;
Member 6 - 10 to 80 m of carbonaceous quartz schist, with a narrow chalcopyrite zone at the base, followed by pyrite-pyrrhotite;
Member 7 - up to 175 m of dolomite-marble with intercalations of carbon-quartz schist and quartzite and lesser pyrite-pyrrhotite.
The main zone of mineralisation in units 3b and 5 are dominated by bornite. The main ore body at Central Aynak is characterised predominantly by bornite. Chalcopyrite only occurs in minor amounts in the middle and lower parts of the body, but increases in the upper parts where in places it dominates over bornite. In contrast, about 80% of the mineralisation at Western Aynak is represented by chalcopyrite with bornite only accounting for about 20% of the mineralisation.
A primary mineral zoning is apparent within the deposit. The central part contains mainly bornite grading out to chalcopyrite and then pyrite and pyrrhotite. Cobalt concentrations also increase peripheral to the main ore zone and in places traces of cobaltite and, to a lesser extent, smaltite are found in association with pyrite and chalcopyrite. Traces of sphalerite are also developed in the peripheral parts of the deposit. The primary mineral zoning, both stratigraphically and laterally, from the core outwards at Western Aynak comprises bornite, to bornite + chalcopyrite, to chalcopyrite, to pyrite + pyrrhotite.
The depth of oxidation is variable with the deepest occurring 250 m below the surface in the northern part of Central Aynak, below thick Neogene cover. The oxidised zone is reported to contain chalcocite and native copper, passing downwards into a mixed zone of oxidised and primary sulphides.
Soviet era drilling outlined and orebody up to 210 m thick, with subsequent work leading to a 'drill-indicated resource' of 240 Mt @ 2.3% Cu, which includes a number of small lenses that may not be suitable for economic exploitation. The deposit is largely amenable to open pit extraction.
Geology from Bohannon, USGS, (2010), a "Minerals In Afghanastan" pamphlet published by the Afghanistan Geological Survey (~2006), and a 2006 Anyak Tender Information Package produced by the BGS and Afghanistan Geological Survey.
The most recent source geological information used to prepare this decription was dated: 2010.
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.
Anyak
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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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