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Dongshengmiao, Dongsheng |
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Inner Mongolia, China |
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Zn Pb Cu
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Super Porphyry Cu and Au
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The Dongshengmiao stratabound sediment hosted zinc-lead deposit is located within the Mesoproterozoic Langshan-Zha'ertai-Bayun Obo ore belt of Inner Mongolia, ~250 km WSW of Byan Obo and 400 km west of Hohhot (#Location: 41° 10' 00"N, 107° 04' 00"E).
The deposit is hosted by greenschist facies mica schist, carbonaceous shale, dolomitic marble and quartzite, with interlayered felsic and mafic metavolcanic
rocks of the Neoproterozoic Langshan Group. The protoliths of this sequence are mainly sandstone, siltstone, mudstone and carbonates, which defines
a coastal or shallow marine environment in a rift setting. The Langshan Group is divided into the First, Second and Third formations, from the bottom to the top, respectively. All the orebodies are hosted in the Second Formation, which is mainly composed of carbonaceous mica schist and dolomitic marble, with intercalated metavolcanic rocks at the base.
The Langshan Group is unconformably underlain by Archaean basement, consisting of high-grade metamorphosed basaltic and sedimentary rocks, now represented by gneiss and migmatite. It is overlain by undeformed Early Cretaceous terrestrial sedimentary rocks, including red sandstone, conglomerate and mudstone.
Northwest-dipping thrust faults and related mylonites are well developed in the Dongshengmiao deposit area. These structures are generally parallel to sedimentary bedding within the Proterozoic rocks, and dip consistently 30 to 45°NW. Minimum displacement on the major thrusts is ~300 m. The age of thrusting is constrained at 135.5±0.9 Ma, by 39Ar/40Ar dating of muscovite separated from shear deformed Proterozoic schist (Zhong et al., 2015).
Permian to Triassic granitoids are widely exposed to the NW of the deposit, separated from the early Cretaceous sedimentary rocks by a thrust fault. These plutons are composed of several phases of intrusive rocks emplaced between 287 and 228 Ma, including Permian quartz diorite and porphyritic granite (287 to 275 Ma; Hu et al., 2015), Triassic monzogranite (245±5 Ma; Liu, 2012) and granodiorite (228±4 Ma; Liu, 2012).
The orebodies are mostly hosted in carbonaceous mica schist and dolomitic marbles of the Langshan Group, and are overlain by the early Cretaceous molasse. They are mostly NE trending, with dips of 25 to 65°NW. The morphology of orebodies varies across the mining field. In the SW, where thrust faults are well developed and closely spaced, the orebodies are steeply dipping, with dip angles similar to that of the thrust faults. The orebodies are asymmetrically folded as a result of thrusting, with mineralisation upgraded in fold hinges (Chen and Peng, 2008). In these orebodies, mineralisation is generally parallel to sedimentary bedding, but locally crosscuts lithological units. In addition to Zn-Pb, most of the known Cu mineralisation occurs in this southwestern part of the deposit.
In contrast, orebodies in the NE section of the deposit were relatively weakly deformed, and are generally stratabound, because thrust faulting was not as well developed as in the SW. The deposit in this section is predominantly composed of Zn-Pb mineralisation, whereas Cu is generally subeconomic, averaging 0.08% Cu, although silver is elevated, averaging 11.9 g/t Ag.
The ore occurs as massive and banded sulphides in 18 orebodies, distributed over an east-west trending strike length of 2.5 km and width of 1 to 2 km. The largest of these orebodies has lateral dimensions of 1900 x 555 m and is 9.2 m thick.
Massive pyrite commonly accompanies Zn-Pb-Cu mineralisation, and it is mined as sulphur ore for sulphuric acid production. Most massive pyrite is relatively coarse-grained (>100 µm) as a result of metamorphic recrystallisation, although fine-grained pyrite with typical grain sizes of ~10 µm is locally preserved. Some massive pyrite was tectonically brecciated and cemented by pyrite, pyrrhotite, Cu-Pb-Zn sulphides and carbonates.
In deformed schist-hosted ores, sphalerite, galena and chalcopyrite occur in microstructures that formed during shear deformation of the host rocks. The ore-hosting carbonaceous schist has been tectonically brecciated under shear stress, forming discrete, oriented and asymmetric rhombic fragments. Sulphide-bearing veinlets are developed parallel to the shear banding i.e., the C foliations of the mylonites. Syn-ore hydrothermal gangue minerals in the veinlets include muscovite and quartz, which are are oriented parallel to the S foliations of the mylonitic host rock. This indicates that the ore-bearing fluid was introduced during shear deformation of the host rock. High grade Zn-Pb ores are predominantly hosted by chemically active Fe-rich marble, which is mainly composed of siderite-magnesite. Sulphides are distributed along grain boundaries of the carbonate host rocks, which are locally corroded and replaced. Biotite is commonly developed at the contact between sulphides and Fe-Mg carbonates. The Zn-Pb-Cu sulphides of the deposit are generally accompanied by pyrrhotite or pyrrhotite-pyrite or pyrite ±magnetite, biotite, muscovite, chlorite, carbonates and quartz, which are common hydrothermal gangue minerals observed in most ores. Barite also accompanies these sulphides, whilst witherite is developed at the contact between barite and carbonate host rocks. Magnetite was mostly formed during the earliest stage of sulphide precipitation, commonly occurring at contacts between hydrothermal veinlets and host rocks, accompanying pyrite and pyrrhotite.
The deposit is quoted (Inner Mongolian Bureau of Geology & Mineral Resources geologists, pers. comm., 1999) as having a resource of:
147 Mt @ 3.3%Zn, 1%Pb in 1999.
Published resource estimates are (Zhing and Li, 2016): 4.83 Mt of contained Zn in ore grading 2.85% Zn; 0.96 Mt of contained Pb in ore grading 0.67% Pb; and 0.11 Mt of contained Cu in ore grading 0.86% Cu; which would equate to;
140 to 170 Mt of ore averaging 2.85% Zn, 0.67% Pb, with smaller zones of Cu mineralisation.
The most recent source geological information used to prepare this decription was dated: 2016.
Record last updated: 13/3/2019
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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Peng, R. and Zhai, Y., 2010 - Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China: A Case Study of the Langshan‐Zha ertaishan Belt, Inner Mongolia, China: in Acta Geologica Sinica v.78, pp. 534-545.
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Zhong, R. and Li, W., 2016 - The multistage genesis of the giant Dongshengmiao Zn-Pb-Cu deposit in western Inner Mongolia, China: Syngenetic stratabound mineralization and metamorphic remobilization: in GeoScience Frontiers v.7, pp. 529-542.
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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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