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Changba, Lijiagou |
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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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The Changba and Lijiagou stratabound Pb-Zn deposits are located ~350 km south-east of Lanzhou, the capital of Gansu Province in northern China and 300 km WSW of Xi'an. The underground Lijiagou deposit is <2 km east of the Changba open pit (#Location: 34° 00' 00'N 105° 30' 00"E).
The two deposits lie within the Li Chang Ore Field, an east-west elongated 100 x 30 km mineralised zone which contains numerous other similar deposits, at least five of which are in production.
This mineralisation is hosted by the Middle Devonian Anjiaca Formation of the Western Qinling Hercynian Orogen. The Changba orebody which is hosted by biotite quartz schist and is the largest of 143 stratabound lenses that are hosted either in biotite quartz schist or marble within a 2000 x 500 m zone. These lenses occur as a series of moderately to steeply dipping, stratabound, well banded massive and semi-massive to disseminated sulphides contained within a Middle Devonian sequence of metamorphosed carbonate and clastic rocks.
The individual lenses, which are up to 1000 m in length and 1 to 70 m thick, have been traced by drilling to 650 m down dip.
The Changba-II deposit is composed of two types of mineralisation, namely:
i). Bedded facies - which is made up of three sulphide sub-facies, from base to top of:
a). banded sphalerite intercalated with quartz albitite;
b). interbedded massive pyrite and sphalerite; and
c). banded sphalerite intercalated with banded barite.
A Rb-Sr isochron age of 389.4±6.4 Ma for sulphide layers and the interbedded hydrothermally altered sediments is similar to the age of host Mid-Devonian strata.
ii). An underlying breccia lens of albitised biotite-quartz schists cemented by sulphides and tourmaline.
The host sequence has been folded around east-west axes and metamorphosed to an upper greenschist facies assemblage. The carbonate rocks have been converted to marbles while the clastic rocks are represented by quartz-biotite schist and quartzite.
The mineralised lenses are located on the northern limb of the large Wujiasham antiform where they have been overturned with southerly dips of 40 to 85°. The shallower dips are in the area of the Changba open pit.
The primary sulphides are fine to coarse pyrite, sphalerite and galena with lesser pyrrhotite, arsenopyrite and boulangerite in a gangue of quartz, mica and calcite. Other metallic elements are silver, cadmium, gallium, germanium, indium and tellurium.
A series of north-east trending faults cut the stratigraphy in the area of the Changba mine, one of which separates the Changba and Lijiagou deposits which apear to be faulted sections of the same original deposit.
At least ten mineralised zones have been defined at Changba, with the bulk of the reserves contained in Zones I and II. Mineable reserves in the Changba mine in 1995 were estimated at 19.55 Mt @ 9.3% Zn, 1.5 % Pb.
Lijiagou, to the east of Changba, is composed of three steep sulphide lenses, all of which dip at 75 to 80°S. The Mineable reserves at Lijiagou in 1995 were estimated at 13.56 Mt @ 12.5% Zn, 2.1% Pb.
The National Resources of Canada website quotes a geological resource for the combined Changba & Lijiagou deposits of 68.1 Mt @ 11% Zn, 1.9% Pb.
The most recent source geological information used to prepare this decription was dated: 2006.
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, Beaudoin G, Sijing Qi and Ying Li 2004 - Geology and geochemistry of the Changba SEDEX Pb-Zn deposit, Qinling orogenic belt, China : in Mineralium Deposita v39 pp 380-395
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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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