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Qianan - Shuichang, Miaogou, Shirengou, Mengjiagou, Bangmoshan |
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Hebei, China |
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Super Porphyry Cu and Au
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The Qianan iron mining district encompasses a number of deposits, including Shuichang, Miaogou, Shirengou, Mengjiagou and Bangmoshan, and is located in the Yanshan Mountains, some 20 to 30 km from Tangshan City, Hebei Province, 150 km ENE of Beijing in north-eastern China.
The Qianan deposits are hosted by banded iron formation (BIF) of the 2.5 Ga Neoarchaean Qianxi Group within the north-eastern North China Craton. These deposits are part of the larger 300x50 km Jidong Metallogenic Belt of North China that hosts other BIF and gold deposits.
The Qianxi Group occurs as a NE trending belt of granulite facies supracrustal rocks of diverse compositions ranging from ultrabasic through basic-intermediate to acid, representing volcanic, sedimentary and intrusive protoliths.
The North China Craton is composed of the two older, north-south elongated, Eastern and Western Archaean Blocks, separated by a Central Orogenic Belt. It has been interpreted that the Eastern and Western Blocks collided at 2.5 Ga during an arc/continent collision, forming a foreland basin over the Eastern Block (the Quinglong foreland basin), a granulite facies belt on the western block, and a wide orogen between the two blocks. This was followed by post-orogenic extension and rifting, simultaneous with the development of a major ocean lapping onto the northern margin of the craton (Kusky and Jianghai, 2003).
An arc terrane, which is indicated to have developed in this ocean, elongated east-west parallel to the northern margin of the craton, collided with that northern craton margin by 2.3 Ga, to form a 1400 km long orogen known as the Inner Mongolia-Northern Hebei Orogen. A 1600 km long granulite-facies terrane formed on the southern margin of this orogen, representing a 200 km wide uplifted plateau as a result of crustal thickening. This granulite facies terrane comprises a southern belt of reworked Archaean basement and a northern metamorphosed accretionary belt. The orogen was converted to an Andean-style convergent margin from 2.20 to 1.85 Ga, reflected by belts of plutonic rocks, accreted metasedimentary rocks, and a possible back-arc basin. A pulse of convergent deformation is recorded at 1.9 to1.85 Ga across the northern margin of the craton (Kusky and Jianghai, 2003).
The Qianxi Group and host BIFs occur on the western margin of the Eastern Archean Block, deposited on the 2.55 to 2.50 Ma Quinglong foreland basin. The sequence is interpretted to have been metamorphosed to granulite facies in the southern belt of reworked Archaean basement of the Inner Mongolia-Northern Hebei Orogen (Kusky and Jianghai, 2003).
At Qianan, there are two belts of BIF deposits which occur in different parts of a complex fold: i). a western belt, which is 15 km long, 2 km wide, trends north-northeast, and contains the Shuichang, Mengjiagou and other deposits; and ii). the relatively small eastern belt.
The Shuichang deposit (#Location: 40° 15' 00"N, 118° 33' 40"E) comprises multiple concordant and lensoid layers, each with an average thickness of 10 m, which may locally range up to 170 to 300 m. The BIF ores are mainly banded with lesser laminated intervals, and are principally composed of coarse grained magnetite and silica, with minor pyroxene and garnet. The host lithologies that encompass the BIF are granulite facies biotite microgneiss, sillimanite gneiss derived from mafic volcanic rock, intermediate volcanic greywacke, felsic volcanic greywacke and muddy siltstone that formed in a moderately deep Archaean volcanic and sedimentary basin.
The Mengjiagou deposit (#Location: 40° 10' 00"N, 118° 31' 47"E) is also composed of concordant and lensoid accumulations of banded and lesser laminated BIF ores that are 9 to 63 m thick and are developed over a strike length of 4600 m, localised within a 'box syncline'. The ore comprises coarse-grained magnetite, silica, hypersthene and diopside with lesser amphibole, biotite and garnet.
The Shirengou deposit (#Location: 40° 14' 10"N, 117° 52' 50"E) occurs in the core of an overturned syncline of metamorphic hosts with two layers of concordant, banded, lensoid BIF with a strike length of from 2400 to 3000 m and width of 15 to 16 m. The host rocks comprise intercalated light and dark granulite and biotite micro-gneiss after mafic to intermediate and felsic volcanic rocks and volcanic greywacke protoliths. The BIF texture is mainly gneissic and banded, composed of medium-grained (0.05-0.5 mm) magnetite, silica and diopside, with minor amphibole, garnet, pyrite and ilmenite.
The Miaogou deposit (#Location: 40° 18' 00"N, 119° 39' 00"E) occurs as a small preserved outlier of several sq. km, on the margin of the Anzhiling migmatite rise. The lower to middle section of the host sequence includes amphibolite (after mafic lavas) intercalated with amphibole and biotite leptynite. The leptynites exhibit evidence of a protolith of intermediate-siliceous lava and tuff. The overlying upper part of the sequence comprises biotite leptynite, granulite and amphibole leptynite, with multiple intercalated layers of amphibole magnetite quartzite. In the mine area, there are four parallel concordant, lensoid bodies. The largest is 1400 m long and 22 to 125 m thick. The BIF comprises laminated and banded cummingtonite, magnetite and silica. with lesser grunerite and actinolite and trace sulphides. The sulphides include disseminated and veinlet pyrite, pyrrhotite and chalcopyrite which are a widely distributed late-stage hydrothermal product.
Resource figures include:
Shuichang resource - 100 Mt @ 20 to 35% Fe (Rodionov, et al., 2004, USGS Open File Rept. 2002);
Bangmoshan reserve - 6.6 Mt @ 20 to 35.04% Fe, concentrated to 68% Fe (Tangshan Iron and Steel website, 2007);
Shirengou reserve - 83.85 Mt @ 20 to 31.3% Fe, concentrated to 68% Fe (Tangshan Iron and Steel website, 2007);
Shirengou resource - 265 Mt @ 25 to 45 % Fe (USGS Open File 03-220);
Miaogou deposit - 23.6 Mt @ 20 to 30.73% Fe, concentrated to 65% Fe (Tangshan Iron and Steel website, 2007);
Mengjiagou deposit - 100 Mt @ 28 to 31% Fe (USGS Open File 03-220).
These mines provide feed for the steel operations of the Tangshan Iron and Steel Group Co., Ltd.
The most recent source geological information used to prepare this decription was dated: 2003.
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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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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