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Amantaytau, Amantaitau |
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Uzbekistan |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Amantaytau (Amantaitau) gold deposit is located 30 km south east of the city of Zarafshan and 20 km SW of Muruntau, in the central Kyzylkum region of western Uzbekistan (#Location: 41° 19' 2"N, 64° 18' 2"E).
The deposit occurs within a pile of imbricated thrusts that was deformed into east-west trending synforms and antiforms exposed towards the western limit of the southern Tien Shan tectonic province. It is hosted by a sequence of carbonaceous flyschoid rocks of the Cambrian to Silurian Besapan Formation, which have been complexly deformed and metamorphosed in the compressional thrust-fold belt. The deposit, along with Daughyztau and Vysokovoltnoe, each of which is a significant economic deposit, are all aligned along the Daughyztau-Amantaytau-Muruntau lineament, a major NE-trending structure that is clearly evident on satellite images as well as in gravity, magnetic and electric field data. This lineament is tens of kilometres long and is internally zoned. No indication of magmatism has been observed along this lineament at the current surface, apart from a few lamprophyre dykes which are locally evident along east-west faults. Geophysical data suggest the deposits of the lineament are located above a concealed, possibly granitic, pluton, the roof of which is inferred to lie at a depth of 5 and 3 to 4 km beneath the Daughyztau and Amantaytau deposits respectively (Zverev et al. 1999; Pasava et al. 2013).
The Amantaytau orebodies lie at one end of this zone, while silver-sulphosalt mineralisation in quartz-chlorite-albite metasomatites is found at the other (Zakharevich, 1993). The Amantaytau and nearby Daugystau deposits represent parts of a single system which have been dextrally offset by 10 km.
The deposit consists of a system of sub-parallel ore bodies, smoothly curved in plan, which strike in a northwesterly direction and dip steeply, generally at >60° to the northeast. These ore bodies each constitute a system of 'stockworks' within north-west trending faults/tectonic zones, which are generally conformable with the host sedimentary rocks. In detail, the individual stockworks vary from a combination of lenticular bodies and veins to stratabound lodes arranged in an en echelon pattern (Zverev et al., 1999). The ore bodies are truncated or off-set by 'through-going' north-east trending faults. 3D mapping shows the ore bodies are related to linear, 10 to 15 m wide and 250 to 270 m long tectonic zones, made up by cataclastic, foliated, silicified, albitised, and carbonate altered rocks that are enriched in sulphides (mainly pyrite and minor arsenopyrite) and accompanied by sericite alteration.
Ore has been outlined to a depth of 600 m. The host rocks were originally slightly carbonatic and slightly ferruginous, arkosic, polymict, greywacke and tuffaceous sandstone; polymict greywacke siltstones; and, silty and pelitic mudstone. The ore lies in the area of greatest alteration where the rocks have lost their bedded structure, are hydrothermally altered, and have cataclastic textures. The gold and silver mineralisation is predominantly localised within the meta-pelites, which have been very slightly de-silicified in parallel with an enrichment in Al. K was introduced, while Na was removed for a net decrease in the alkalis. Alteration appears to largely take the form of sericitisation (Zakharevich, 1993). Mineralisation is believed to have been emplaced between 260 and 270 Ma (Yakubchuk et al., 2002).
Gold occurs predominantly with pyrite, arsenopyrite, in stibnite and Ag-sulphosalts, as well as ankerite. Wall rock alteration consists of early albitisation, a subsequent stage of quartz, chlorite, muscovite and ankerite, and a final stage of calcite and manganiferous ankerite (Kurbanov et al., 1991). In the upper levels of the deposit, the quartz-sericite altered rocks host gold-arsenopyrite-pyrite pockets and disseminations, and veins are rare. At deeper levels, the altered rocks are enriched in carbonate, and gold-arsenopyrite-pyrite veins are developed more prominently. The altered rocks are cut by veins and veinlets of kaolinite and carbonaceous matter. Only the gold-arsenopyrite-pyrite assemblage is of economic importance at the Amantaytau deposit (Zverev et al., 1999). Since the amount of pyrite in the ore is twice as much as that of arsenopyrite, most of the gold is spatially related to pyrite in which it occurs as submicroscopic inclusions. This results a low gold recovery of gold from the ore (Pasava et al. 2013).
The known resource at Amantaytau is of the order of 700 t of Au at a grade of 7.5 g/t Au in the oxide ore and 14.2 g/t Au in the primary sulphides. These resources/reserves are based on Soviet era testing patterns and reserve classifications, and include 250 t of Au in class C1 and 450 t in class C2. The deposit was discovered in 1975, with detailed exploration beginning in 1980. The results of subsequent JORC compliant testing and reclassification of the reserves and resources by Oxus Gold plc were:
Sulphide Ore - Amenable to underground mining via decline access, using trackless mining equipment.
Reserve - 60 tonnes of contained Au @ 12 g/t Au (which equates to 5 Mt of ore);
Total resource - 84 t of contained Au @ 12 g/t Au (which equates to 7 Mt of ore).
Oxide Ore - Amenable to open pit mining.
Proven + probable reserve of 5.47 Mt of ore @ 11.54 g/t Au (63 t Au);
Total resource of 7.15 Mt of ore @ 11.68 g/t Au (83 t Au).
with significant potential to expand the reserves and resources based on more widely spaced drill intersections.
At the end of 2012, the remaining resources and reserves in the suspended open pit operation amounted to (Pasava et al. 2013 after Oxus Gold):
Mineral Resources - 37.07 t of contained gold in ore @ 1.36 g/t Au (which equates to 27.25 Mt of ore), including
Proved + Probable Ore Reserves - 8.27 t of contained gold in ore @ 1.27 g/t Au (which equates to 6.5 Mt of ore).
A feasibility study had been completed for an underground operation with an estimated:
Mineral Resource - 6.7 t of contained gold in ore @ 8.70 g/t Au (which equates to 0.77 Mt of ore), including
Probable Ore Reserves of 3.7 Mt of gold in ore @ 7.71 g/t Au (which equates to 0.48 Mt of ore).
Background: In late 2003, the Amantaytau Goldfields joint venture launched mining operations and a concentration plant at Amantaytau which could process 1 Mt of oxide ore per year to produce 6.3 t of gold from Amantaytau, Daughyztau and Vysokovoltnoe. The government of Uzbekistan decided to terminate the joint venture in January 2011 due to the 'ineffective implementation of the program to increase the amount of gold mined'. Operations at the mine were suspended at that time. In 2013 Amantaytau Goldfields was declared bankrupt, at which time its shareholders were Oxus Gold (50%), the State Committee of Uzbekistan for Geology and Mineral Resources (40%) and the Navoi Mining and Metals Plant (10%). Legal proceedings between Oxus and the government of Uzbekistan have continued since then (various sources). The mine appears to have remained inactive and is not expected to restart before 2028 (Wood Mackenzie, 2021).
The most recent source geological information used to prepare this decription was dated: 2013.
Record last updated: 21/11/2023
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.
Amantaytau
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Pasava, J., Frimmel, H., Vymazalova, A., Dobes, P., Jukov, A.V. and Koneev, R.I., 2013 - A two-stage evolution model for the Amantaytau orogenic-type gold deposit in Uzbekistan: in Mineralium Deposita v.48, pp. 825-840. DOI 10.1007/s00126-013-0461-8.
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Zakharevich A A 1993 - Petrology and geochemistry of the mineralized clastic sequence at the Amantaytau gold deposit: in International Geology Review v35 pp 658-665
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Zverev, Yu., Kremenetsky, A., Minzer, E. and Shatov, V. 1999 - The Amantaitau-Daughyztau ore field: in Shayakubov, T., Islamov, F., Krementsky, A. and Seltmann, R., (Eds.), Au, Ag, and Cu deposits of Uzbekistan International Field Conference of IGCP-373, Excursion B6 of the Joint SGA-IAGOD symposium, London/Tashkent, 27/28 August - 4 September 1999 Excursion guidebook pp 17-36
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