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Dengjiashan |
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Gansu, China |
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Zn Pb Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Dengjiashan stratabound Pb-Zn deposit is located in south-eastern Gansu Province, approximately 350 km south-east of Lanzhou, the provincial capital, in northern China, and 300 km WSW of Xi'an.
The deposit lies within the generally WNW-ESE trending two part Qinling orogenic belt which lies along the suture between the North China and Yangtze Cratons. This fold belt is divided into the North and South Qinling Fold Belt by the transcrustal Shangnan Suture. The North Qinling Fold Belt represents the southern active margin of the North China Craton, and comprises a Proterozoic metamorphic complex of meta-greywackes, marbles and meta-tholeiites and an ophiolite suite. The South Qinling Fold Belt is the northern margin of the Yangtze Craton and is composed of a Proterozoic metamorphic complex of paragneiss, marble, tholeiites and alkaline basalt, Cambrian carbonaceous rocks, and Silurian and Devonian sequences.
The Dengjiashan deposit and the similar Changba deposit to the west (see the separate Changba record) are hosted by the South Qinling Fold Belt, within Devonian sedimentary rocks deposited in subordinate, fault bounded troughs characterised by beach, tidal flat, inner shelves, carbonate platforms, outer shelves and continental slope facies. The outer shelf facies comprise segments of shallow clastic carbonates and deep water, fine clastic-argillaceous-carbonates. Both Dengjiashan and Changba occur on both sides of restricted carbonate banks on the outer shelf, deposited within an extensional tectonic setting.
The Dengjiashan orebodies crop out in the cores of the Dengjiashan and Mogou isoclinal anticlines. The intensely folded and faulted host Middle Devonian sedimentary sequence of the Xihanshui Formation comprises:
i). a lower carbonate and upper argillaceous member - of >190 m of grey to dark grey bioclastic micrite with thin layers of calcarenite;
ii). an upper argillaceous member - of interbedded phyllites and micritic limestone with abundant brachiopod bioclasts.
The ore is hosted in chert in gradational stratigraphically conformable contact with the underlying footwall bioclastic micrite and the overlying hangingwall phyllite of the argillaceous suite. The limestone and phyllites of the Xihanshui Formation hosts 16 orebodies, of which the #1 and #9 are the largest within the Dengjiashan and Mogou anticlines respectively. These two deposits account for 95% of ore reserves.
The #1 orebody is up to 20 m thick, with a 4 km east-west length and 300 m down-dip extent. The #9 orebody is up to 21 m thick, averaging 6.3 m, with a 2 km strike length and 350 m down dip extent.
The massive sulfide lenses are mainly composed of intergrowths of sphalerite, galena and pyrite, with minor chalcopyrite, tetrahedrite, cinnabar, pyrargyrite, freibergite, boulangerite, polybasite, and trace amounts of owyheeite and native gold. The gangue is dominated by quartz, calcite, barite, and ankerite, with minor amounts of sericite, chlorite, celsian, cymrite, and albite.
Primary sedimentary and diagenetic textures, as well as bedding and laminae are preserved, although the lenticular sulphide orebodies are characterised by recrystallised veins and breccias related to the tectonic and metamorphic processes following the deposition of the orebodies.
The deposit has a quoted mineral resource of: 25 Mt @ 4.77% Zn, 1.27% Pb, 14 g/t Ag, 0.1 g/t Au, 160 ppm Cd and 650 ppm Hg.
The most recent source geological information used to prepare this decription was dated: 2007.
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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Guoliang Ma, Georges Beaudoin, Shaojun Zhong, Ying Li and Zhangren Zeng 2007 - Geology and geochemistry of the Dengjiashan Zn-Pb SEDEX deposit, Qinling Belt, China: in Can. J. Earth Sci. v44 pp 479-492
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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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