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Katebasu |
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Xinjiang, China |
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Au
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Super Porphyry Cu and Au
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The Katebasu gold deposit is located ~30 km south of the main town of Xinyuan County, ~350 km west to WSW of Urumqi in Xinjiang, NW China.
The deposit lies within the Tien Shan belt that passes west into Kyrgyzhstan and Uzbekistan where the major Kumtor and Muruntau deposits are located respectively. It is situated in a deformation zone associated with the north Nalati fracture on the northern margin of the Middle Tianshan Mountains.
Gold mineralisation at Katebasu is principally hosted within a brittle and ductile fracture zone cutting a Silurian volcano-sedimentary succession that is intruded by Mid Carboniferous monzogranite along the northern margin of the Central Tien Shan continental arc, adjacent to the Nikolaev Line - northern Nalati Fault (Xue et al., 2017).
Gold mineralisation occurs as shallowly dipping, ENE striking, lenses and tabular bodies in brittle and ductile fracture zones. Alteration comprises a central core of siliceous quartz-K feldspar-sericite with and peripheral shell of sericite-epidote-chlorite, mainly within a monzogranite host. Both zones carry gold-bearing pyrite and chalcopyrite. Gold occurs as electrum and native gold along grain margins, in fractures and as inclusions within chalcopyrite and pyrite, and as 'invisible gold' within pyrite grains (Liu et al.,2017; Xue et al., 2017).
The host monzogranite yielded an Early Carboniferous concordia age of 346.3±3.3 Ma (Zircon U−Pb), whilst the gold mineralised pyrite has been dated as Late Carboniferous at 310.9±4.2 Ma (Re-Os isochron age; n=5), ~35 Ma younger than monzonite granite (Xue et al., 2017).
In addition, skarn-style Cu-Au mineralisation and alteration is also recorded, both in the fault fracture zone and along the contact zone between the intrusion and wall rock marble. Metallogenesis is interpreted by Liu et al. (2017) to be related to monzonite granite and diorite dykes, respectively, with some spatial superposition.
Deformation in the surrounding district comprises (Zhao et al., 2019):
• D1, which was north vergent thrusting caused by a roughly north-south compression, reflected by ENE–WSW striking thrust faults. This compression was likely the result of closure of the South Tianshan Ocean and the resulting collision between the Tarim Craton and Middle Tianshan-Yili block (on the southern margin of the Central Asian Orogenic Belt).
• D2, which resulted in dextral strike-slip dislocation along the ENE-WSW striking faults, caused by a WNW-ESE stress field, and corresponds to Permian dextral wrenching in the Tianshan Orogen.
• D3, was the product of NE-SW compression that predominantly formed NW-SE striking reverse, and NNE-SSW trending dextral faults.
According to Xue et al. (2017), the deposit is genetically associated with a moderate temperature ~207 to 390°C, low-salinity ~7 to 16 wt % NaCl equiv. and CO2-rich fluid. These authors calculated the composition for δ18OH2O in gold-bearing quartz veins at 1.6 to 6.4‰ at a temperature of 300°C, and δDH2O ranges of from -64 to -107‰, suggesting a potential magmatic-metamorphic fluid mixing. They also suggest, that the relatively high initial 187Os/188Os ratio of 1.449±0.052 of the auriferous pyrite and the highly consistent Pb-isotopic compositions between the pyrite samples and their hosting monzogranite intrusion and Silurian volcanic rocks, indicate the ore metals might have originated from the upper crust of the Central Tien Shan continental arc at the Katebasu field. Sulphur isotope compositions of pyrite and chalcopyrite of between 6.92 to 12.15‰ (mean=9.48‰, n=13) are taken to suggest a dominant marine sediment source for the sulphur. They conclude that all of the deposit characteristics suggest the Katebasu gold deposit was formed in association with thrust and fold deformation during the Late Carboniferous collision between the Tarim Craton and the Middle Tien Shan continental arc.
The Katebasu deposit was discovered in 2010, and by the end of 2014 a proved reserve of 87 t of contained gold had been estimated at a cutoff grade of 3.84 g/t Au (Xue et al., 2017).
For more information consult the references listed below.
The most recent source geological information used to prepare this decription was dated: 2019.
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.
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Selected References:
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Liu, A., Han, Y., Li, Z. and Li, Y., 2017 - Geological characteristics, deposit type, and metallogenic epoch of the Katebasu gold-copper deposit in western Tianshan: in Special Issue:Geology of Silk Road - Tianshan Orogen (Vol. 3), Geological Journal, v.53, pp. 263-277.
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Xue, C., Zhao, X. and Mo, X., 2017 - Geology, geochemistry and geochronological constraints on the genesis of newly discovered Katebasu gold deposit, western Tien Shan, Xinjiang, NW China: in Society of Economic Geologists, Inc., 2017 Conference, Session 4: Orogenic Gold Deposits of Asia, September 17-20, 2017, Proceedings 1p.
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Zhao, W., Zhao, X., Xu, C., Symons, D.T.A., Cui, X. and Xing, L., 2019 - Structural characterization of the Katebasu gold deposit, Xinjiang, China: Tectonic correlation with the amalgamation of the western Tianshan: in Ore Geology Reviews v.107, pp. 888-902.
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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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