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Almalyk - Kalmakyr, Dalnee, Sarycheku

Uzbekistan

Main commodities: Cu Au
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Deposit Description

The Almalyk porphyry Cu-Au system, located 65 km to the southeast of Tashkent in eastern Uzbekistan.

The complex encompasses the ore deposits at Kal'makyr (2.5 Gt @ 0.38% Cu, 0.5 g/t Au) and Dalnee (2.8 Gt @ 0.36% Cu, 0.35 g/t Au). The Sarycheku orebody (200 Mt @ 0.5% Cu, 0.1 g/t Au) is part of the Saukbulak porphyry Cu-Au system, some 18 km to the south (Seltmann & Porter, 2005). Seltmann, 2012) quotes a total resource for the complex of 8 Gt @ 0.58% Cu, 3 g/t Ag, 0.5 g/t Au, 0.005% Mo.

Both systems are associated with the second, Middle- to Late-Carboniferous, pulse of magmatic activity within the Devono-Carboniferous Valerianov-Bel'tau-Kurama volcano-plutonic belt that is the main element of the Middle Tien Shan terrane in Central Asia. Previous K-Ar dating of the ore-related porphyry intrusive and the mineralisation has returned ages in the range of 310 to 290 Ma, whereas recent U-Pb zircon dating reported for the intrusive sequence in the Almalyk district partially overlaps in the range of 320 to 305 Ma, with Re-Os ages of ore-related porphyries of 315 to 319 Ma (U-Pb and Re-Os age dating from Seltmann & Porter, 2005).

Mineralisation at both Kal'makyr and Dalnee is predominantly in the form of stockworks with lesser disseminations, and is associated with Late Carboniferous quartz monzonite porphyry plugs intruding earlier dioritic and monzonitic intrusive rocks of the same magmatic complex. The orebodies take the form of a cap like shell developed above and draped over the flanks of the related quartz monzonite porphyry stock.

The dominant hosts to ore are the monzonite and diorite wall rocks, with the quartz monzonite porphyry only containing ore in its outer margins, surrounding and/or overlying a barren core. The focus of stockwork development is fracturing related to both the intrusive contact of the porphyry stock and to crosscutting faulting.

Alteration comprises an early K-silicate phase followed by albite-actinolite and peripheral epidote-chlorite-carbonate-pyrite propylites, overprinted by an abundant phyllic episode which is closely related to the final distribution of the ore.

Associated mineralisation commenced with barren quartz-hematite veining, followed by quartz-magnetite, quartz-pyrite-molybdenite-chalcopyrite with the bulk of the contained gold, quartz-carbonate-polysulphide with lesser gold, then by zeolite-anhydrite, and finally carbonate and barite veining. Subsequent oxidation and uplift developed a layer of oxide ore, a limited leached cap and supergene sulphide enrichment, largely in zones of fault related fracturing.

The Kal'makyr deposit is distributed around and within the outer margins of a central plug of Late Carboniferous quartz monzonite porphyry (QMP) intruding earlier Carboniferous monzonite and diorite. The deposit straddles a major fault and extends southwards toward a second fault zone. The main volume of the block defined by these two faults is occupied by monzonite and diorite, although remnants of Devonian volcanic and carbonate rocks are locally preserved.

Approximately 65 to 75% of the ore at Kal'makyr occurs in the form of stockwork veins and veinlets, while 30 to 35% occurs as disseminations. The distribution of the ore stockwork and the intensity of veining is controlled by the density of fracturing and brecciation related to both the intrusion of the QMP stocks and dykes, and to linear fracture zones associated with the Kal'makyr and Karabulak faults. As a result, the stockwork is represented by a downward expanding cone surrounding and capping the quartz monzonite porphyry plug, with a barren core corresponding with the centre of the plug.

The stockwork is represented by a network of fractures which have been healed by quartz veinlets, and less frequently by calcite or anhydrite, which contain large segregations of the ore sulphides, including pyrite, chalcopyrite, chalcocite, pyrrhotite, molybdenite and tetrahedrite. The veinlets vary in thickness from fractions of a millimetre to 3 or 4 cm, and are from a few to a few tens of cm in length. The interval between the veinlets if occupied by lesser disseminated pyrite, chalcopyrite, magnetite and occasionally other sulphides.

The stockwork zone is elongated in a northwest direction, with maximum surface dimensions of approximately 3520x1430 m and a maximum vertical extent of 1240 m. The inner annulus of high-grade ore is substantially smaller, with outer dimensions of approximately 1740x500 m and a maximum vertical thickness of 450 m. The most intense fracturing and the highest grade ore are related to the intersections of porphyry contacts with the east-west and northeast trending faults and tend to form a broken annulus within the monzonite and diorite wall rocks immediately surrounding the QMP. The grade rapidly decreases inwards to the barren core in the QMP plug. In contrast the high grade annulus is surrounded by a broad halo of medium grade ore before passing into a lower grade periphery. At depth the ore stockwork becomes less continuous and lenses-out downwards via a series of tongues. The primary Kal'makyr ore contains Cu, Mo, Au, Ag and admixtures of Se, Te, Re, Bi, and In.

The upper sections of the ore deposit were subjected to oxidation and supergene enrichment, best developed in areas of more intense fracturing on the QMP contacts and along zones of fault related fracturing. The degree of oxidation, leaching and supergene enrichment varied across the deposit, from oxide to secondary sulphide to mixed oxide-sulphide zones, although the supergene sulphide enrichment was only weakly developed. Oxidation was developed to a maximum depth of 65 m, averaging around 20 m, while leaching, where it replaced in situ oxidation, persisted over a similar thickness. The principal mineral within the oxide zone was malachite, with chrysocolla and turquoise being locally important. Where present, supergene sulphide enrichment, principally as chalcocite and covellite, had a maximum thickness of 70 m, averaging 19 m, while a mixed ‘complex’ oxide-supergene sulphide zone, where developed, also averaged 19 m in thickness.

The Dalnee group of deposits are a west to northwest, down-plunge continuation of Kal'makyr at deeper levels. The >0.1% Cu outline unites these deposits into a common ellipsoidal sub-economic mineralised mass in plan view. However, post-mineral normal and sinistral strike-slip displacement on both the Karabulak and Kal'makyr faults dissected the ellipse into three blocks. The northern Karabulak block is displaced by 2 km to the west and the Central block (the main Dalnee deposit) for 0.5 km to the west of the southern block and Kal'makyr. The northern block encompassing Karabulak is the least eroded, while the deepest exhumation has affected the southern block and Kal'makyr.

The main Dalnee deposit in the Central area is located within a downward widening tectonic wedge between the Karabulak and Kal'makyr faults which have truncated the mineralised system and displaced ore on the flanks of the underlying QMP. Approximately 58% of the ore in the deposit is hosted by the monzonite, 35% by the diorite and 7% by the QMP. The stockwork is elongated parallel to the east-west direction of faulting and widens downward due to the outward dip of the bounding faults, while the base of mineralisation closely follows the apical surface of the underlying QMP stock. The average vertical extent of mineralisation is about 700 m with a maximum of 1200 m on some sections. The higher grade Cu mineralisation occurs below a depth of 150 to 200 m, while the highest grade core is at a depth of 500 to 600 m. The Karabulak deposit to the north is the least economically important of the Dalnee deposits. Drill holes intersected 'high-grade' Cu mineralisation extending along the Karabulak Fault at depth, associated with a small stock of quartz monzonite porphyry (QMP).

The Sarycheku deposit is related to the hanging wall of the Miskan Fault, with the ore grade mineralisation being confined to the tectonic wedge between the Miskan and Sargalam faults. The host rocks are represented by Devonian rhyolite porphyry, which is cut by Late Paleozoic porphyry intrusion. The oxidised and chalcocite ores have virtually been exhausted, while the underlying hypogene sulphide ore is concentrated within a zone which is 1160 m long and has been traced to a depth of 340 m.

This summary is drawn from Seltmann & Porter (2005).

The most recent source geological information used to prepare this summary 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.


  References & Additional Information
 References to this deposit in the PGC Literature Service Collection: Want any of these papers ? Click Here
Golovanov I M, Seltmann R and Kremenetsky A A,  2005 - The Porphyry Cu-Au/Mo Deposits of Central Eurasia; 2. The Almalyk (Kalmakyr-Dalnee) and Saukbulak Cu-Au Porphyry Systems, Uzbekistan: in Porter T M, (Ed.), 2005 Super Porphyry Copper & Gold Deposits: A Global Perspective PGC Publishing, Adelaide,   v.2 pp 513-523
Meshchaninov Ye.Z and Azin V N  1973 - Distribution of gold in a copper porphyry deposit, Almalyk region: in    International Geology Review   v15 pp 660-663
Pasava J, Vymazalova A, Kosler J, Koneev R I, Jukov A V and Khalmatov R A,  2010 - Platinum-group elements in ores from the Kalmakyr porphyry CuĖAuĖMo deposit, Uzbekistan: bulk geochemical and laser ablation ICP-MS data: in    Mineralium Deposita   v.45 pp. 411-418
Seltmann R and Porter T M,  2005 - The Porphyry Cu-Au/Mo Deposits of Central Eurasia: 1. Tectonic, Geologic & Metallogenic Setting and Significant Deposits: in Porter, T.M. (Ed), 2005 Super Porphyry Copper & Gold Deposits - A Global Perspective, PGC Publishing, Adelaide,   v.2 pp. 467-512
Zvezdov V S, Migachev I F and Girfanov M M  1993 - Porphyry copper deposits of the CIS and the models of their formation: in    Ore Geology Reviews   v7 pp 511-549

 References to this deposit in PGC Publications: Want any of our books ? Pricelist
Seltmann R and Porter T M, 2005 - The Porphyry Cu-Au/Mo Deposits of Central Eurasia: 1. Tectonic, Geologic & Metallogenic Setting and Significant Deposits,   in  Porter T M, (Ed),  Super Porphyry Copper and Gold Deposits: A Global Perspective,  v2  pp 467-512
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Golovanov I M, Seltmann R and Kremenetsky A A, 2005 - The Porphyry Cu-Au/Mo Deposits of Central Eurasia: 2. The Almalyk (Kalímakyr-Dalnee) and Saukbulak Cu-Au Porphyry Systems, Uzbekistan,   in  Porter T M, (Ed),  Super Porphyry Copper and Gold Deposits: A Global Perspective,  v2  pp 513-523
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