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Qingchengzi Ore Field - Qingchengzi, Zhenzigou, Diannan, Erdao, Benshan, Xiatongjiapuzi, Xiquegou, Gaojiapuzi |
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Liaoning, China |
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Pb Zn Au Ag
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Super Porphyry Cu and Au
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The Qingchengzi Pb-Zn Ore Field is situated ~90 km SSW of Shenyang and 70 km NW of Dandong on the northern root of the Liaodong Peninsula in eastern Liaoning Province, northeastern China. The more significant Pb-Zn deposits within the 11 x 9 km ore field include Qingchengzi, Zhenzigou, Diannan, Erdao, Benshan, Xiatongjiapuzi, Xiquegou and Gaojiapuzi (#Location: 40° 44' 2"N, 123° 36' 33"E).
Zhenzigou, an example described below, is one of the larger Zn-Pb deposits of the Qingchengzi ore field. Qingchengzi is one of the major Pb-Zn polymetallic ore fields of China and has a mining history spanning >400 years. More recently, over fifty years of exploration have resulted in the discovery of more than ten Pb-Zn, one silver deposit and four gold deposits containing ~1.5 Mt of contained Pb + Zn metals, 2000 t of Ag metal, and 100 t of Au metal (Zhou et al., 2020). The Au and Ag deposits belong to the coincident Liaodong gold district, also referred to as the Qingchengzi Au-Ag Orefield (e.g., Li et al., 2020) is described in the separate Changbaishan Mountains Gold Province record.
Regional Setting
The Qingchengzi Ore Field is situated within the Palaeoproterozoic Liaodong Rift Zone, that is located on the northeastern segment of the North China Craton and extends for ~700 km over a ENE trend. This rift is currently obliquely truncated by the Late Triassic to Paleocene continental scale NNE-SSW Tan-Lu Fault Zone to the west and structures that follow the shoreline of the Sea of Japan in the east, and overlaps the Jiao-Liao-Ji Belt. Its history has included Palaeoproterozoic crustal extension, post-rift thermal subsidence and inversion by compressional folding (Fang et al., 1994). It is bounded to the north and south by Archaean basement and has been internally divided into three east-west trending domains, the i). northern marginal slope,ii). central depression where the Qingchengzi Ore Field is located, and iii). southern marginal slope (Yu et al., 2009).
The stratigraphy of the ore field is dominated by the Palaeoproterozoic Liaohe Group, with minor migmatite and migmatitic granite outcrops of the Archaean Anshan Group which is considered to represent the basement of the rift zone. Detrital zircons from members of the Liaohe Group return unimodal 207Pb/206Pb age peaks at ~2.2 to 2.1 Ga (Wang et al., 2020).
The Liaohe Group comprises a lower succession of volcano-clastic rocks, subdivided into the Yujiabaozi and overlying Langzishan formations; and an upper sequence dominated by carbonate and clastic rocks with volcanic interbeds. This upper sequence is further subdivided into the Dashiqiao and overlying Gaixian formations. At ~1.80 Ga, the volcanic and sedimentary rocks in the Liaohe Group were subject to intense metamorphism from greenschist to granulite facies during the 'Lvliang Movement', forming amphibolite, granulite, schist and marble (Jiang, 1987; Fang et al., 1994; Chen et al., 2005). Dating of metamorphic minerals yielded an age of 1822±92 Ma (UDSGS MRData database, viewed December 2020, after references cited therein).
Two major structures, the NNW trending Jianshanzi and the NE trending Erdao faults, bound the Qingchengzi area to the NW and NE respectively, whilst a series of intersecting NW and NE trending secondary faults were developed, as well as ore-bearing veins and abundant dykes. Other regional structures include several extensive east-west folds. Some folds were later deformed by a secondary tectonic pulse (Fang et al., 1994; Liu, 1998).
The area has also undergone extensive magmatism over discrete intervals from the late Palaeoproterozoic to Cretaceous. Palaeo- to Mesoproterozoic magmatism is characterised by gabbro-dolerite dykes and granitic stocks (Liu, 1998) such as the >6 km across Dadingzi biotite plagiogranite that intrudes the Palaeoproterozoic Dashiqiao and Gaixian formations in the southeast of the ore field. Mesozoic magmatism was influenced by three major tectonic events, namely the Central Asian Orogeny to the north, the Dabie-Sulu Orogeny to the south, and he Palaeo-Pacific Orogen to the east. The interplay of these tectonic events induced extensive magmatism during the Triassic, that is spatially associated with Zn-Pb mineralisation in the Qingchengzi Ore Field.
Triassic magmatic rocks comprise the Xinling and Shuangdinggou granites to the north and SW of the main Qingchengzi Ore Field deposits respectively (Wu et al., 2005). The Xinling type granite is exposed as a 2 km diameter stock within the immediate ore field and as a marginal phase of the much larger (>15 km diameter) Shuangdinggou granite that outcrops within a few km the SW of the main centre of mineralisation. Numerous dykes with a range of compositions including lamprophyre, gabbro-dolerite, diorite, granite-porphyry and quartz-porphyry, were emplaced between the Triassic and Early Cretaceous, occurring mostly within NE and NW striking primary and secondary faults (Fang et al., 1994; Liu, 1998; Liu and Ai, 2002).
Jurassic magmatism is less intense, forming the ∼166 Ma (U-Pb zircon) Yaojiagou Granite that was accompanied by an episode of Mo mineralisation dated at ∼165 Ma (molybdenite Re-Os; Duan, 2015).
NOTE: The Liaohe Group on the northern margin of the Liaodong Rift Zone and Jiao-Liao-Ji Belt also carries sediment hosted Cu mineralisation of the Shanghua-Yunpan Sulphide Belt. See that record for the stratigraphic subdivision of the Liaohe Group.
The Qingchengzi Ore field
There is a metal zonation across the ore field, from Pb-Zn deposits with Pb/Zn of ∼4, e.g. Xiquegou and Benshan which are concentrated on the western side of the field, progressing to predominately Zn-Pb mineralisation to the east where the Pb/ Zn ratio is 0.5 to 1, as at Zhenzigou. Most of the Au and Ag is concentrated in the eastern part of the ore field, including the Gaojiabaozi Ag-Pb-Zn deposit and the Baiyun, Linjiasandaogou and Xiaotongjiabaozi Au deposits (Liu and Ai, 2002; Xue et al., 2003). The main gold deposits are aligned in a NNW-SSE trend ~2 to 4 km to the NE of the Pb-Zn mineralisation and parallel to the Jianshanzi Fault, immediately to the east, although, these and other lesser gold occurrence in the district appear to form a halo peripheral to the Pb-Zn deposits. The majority of Pb-Zn-(Ag) mineralisation is hosted within marble of the Dashiqiao Formation (Zhou et al., 2020), whilst the bulk of the gold mineralistion is within the Gaixian Formation.
Three styles of Pb-Zn-(Ag) mineralisation have been differentiated (Zhou et al., 2020):
• Concordant, stratabound layers and lenses that occur in the lower part (D1 Unit) and occasionally in the upper section (D33 Unit) of the Dashiqiao Formation (Li et al., 2005), that are adjacent to granulite and schist interbeds, and are concentrated in the east of the ore field;
• Veins and irregular bodies that cut through the marble and occur in the western part of the ore field;
• Composite ore bodies in the west of the ore field, that are partially developed along a fault and partially hosted within interbedded fractures (Yu et al., 2009).
The second and third ore styles contain grades of ~50 to 100 g/t Ag. The country rock that host the mineralisation is only weakly altered, with restricted 1 to 3 m zone around the orebodies being altered to an assemblage that includes silica, sericite, dolomite and carbonate, with the mineralogy at any location influenced by the composition of the country rock (Fang et al., 1994).
Zeng et al. (2020) demonstrate three distinct fluids were involved in deposition of the mineralisation:
i). an early influx of relatively low in temperature (<150°C) syn-sedimentary/diagenetic fluids at ∼2052 Ma, enriched in Cu, Pb, Zn, Ag, and depleted in Co, Ni, and As. Pyrite (Py0) was the principal sulphide mineral precipitated, with weak Cu-Pb-Zn, forming a pyrite core and scavenging most of the available trace elements. Re-Os dating of early sulphides returned an age of 2119±57 Ma (UDSGS MRData database, viewed December 2020, after references cited therein).
ii). an intermediate episode of high in temperature (>300 °C) metamorphic fluids at ∼1800 Ma which precipitated overgrowths of pyrite (Py 1) and crystallisation of sphalerite (Sph1) and arsenopyrite (Aspy1), together with minor galena (Ga).
iii). a final episode of hydrothermal fluids, also at >300°C, related to the Triassic magmatism, forming another overgrowth of pyrite (Py2), sphalerite (Sph2) and arsenopyrite (Aspy2), accompanied by minor of galena (Ga).
The late metamorphic and magmatic fluids remobilised As, Co and Ni but only at mineral grain scale. The same fluids were enriched in In, Cd, Au, As, Ag, Cu, Pb, Sb, Sn, Co and Ni, and depleted in Bi, W, Mo, Te and Se. Pyrite is the main host of Co, Ni, Pb, and As, while arsenopyrite hosts a major amount of Sb and Pb, and a minor amount of Au. Sphalerite is the primary host to Cd, In, Cu, and the secondary host of Ag and Sn; galena is the primary host of Ag, Sb, Sn, and subordinately hosts Cd, In and As. The great majority of the In and Cd was carried by the hydrothermal fluids associated with the Triassic magmatism, which the authors suggest indicates that the contribution of magmatic hydrothermal fluids to the mineralisation is significant.
Zhenzigou Deposit Geology
The Zhenzigou Zn-Pb deposit is situated in the east of the Qingchengzi Ore Field and occurs as conformable layers and lenses deposited within intercalated fractures that strictly follow the folded bedding. The majority of the ore occurs in two stratigraphic intervals. These are the graphite-bearing marble of the lower Dashiqiao Formation and the lower section of the Langzishan Formation which is composed of graphite-bearing marble interbedded with amphibolite and biotite schist bands. Subordinate vein-type mineralisation also occurs, crosscutting the strata.
Six orebodies have been defined within the Zhenzigou deposit (Zhou et al., 2020) each named after the concordant hosting fracture system. The mineralogy of these deposits dominantly comprises sphalerite, galena, pyrite and pyrrhotite with minor arsenopyrite, marcasite and argentite with grades of ~2 to 6% Pb and 2 to 10% Zn, with a Pb/Zn ratio varying between 0.5 and 1, with ~50 g/t Ag. The gangue minerals include dolomite and calcite, very similar to those of the enclosing wall rock. Within the layered orebodies, the sulphide and gangue minerals are rhythmically interlayered and range from disseminated to semi-massive and massive banded sulphides and carbonates. In the lens-shaped bodies, pyrite frequently forms the core of the lens, enclosed by bands of sphalerite and galena and again can occur as massive sulphides. Sulphide minerals within wall-rock schist and granulite occur as disseminations, with sphalerite and galena being both coarse and fine grains, although wall-rock alteration is poorly developed. Most sulphide minerals are euhedral and subhedral, although framboidal pyrite and micro-framboidal sphalerite are frequent. Pyrite and sphalerite occasionally occur along the margin of detrital dolomite grains (Fang et al., 1994; Liu et al., 2001).
The #2 orebody is intercalated with the granulite and graphitic marble units of the Langzishan Formation, parallel to the #289 orebody, occurring as concordant bands and veins, primarily composed of sphalerite with subordinate galena and pyrite. It comprises four mineralised lenses, distributed over a total strike length of 2500 m, each ~100 m long, extending over widths of 30 to 90 m, with an average thickness of 8 m. It contains ~0.025 Mt of Pb and 0.042 Mt Zn at an average grade of 6.04% Pb and 10.10% Zn, which equates to ~0.42 Mt of ore (Zhou et al., 2020 and references cited therein).
The #289 orebody is hosted by graphitic marble in the basal section of the Langzishan Formation within concordant to semiconcordant fractures, occurring as galena, sphalerite and pyrite distributed sub-parallel to bedding, and to a lesser degree disseminated in cross-cutting veins. It is composed of two mineralised sections that together define a belt striking at 290 to 300° and dipping at 40 to 70°NE. Individual zones within these mineralised sections range from 50 to 150 m in length, 30 to 60 m in width, and from 0.8 to 1.5 m in thickness. The orebody contains ~0.038 Mt Pb and 0.033 Mt Zn at an average grade of 2.33% Pb and 2.01% Zn, which equates to ~1.64 Mt of ore. The mineralisation occurs sub-parallel to bedding, and subordinately as disseminated ores in cross-cutting veins. The ore minerals are galena, sphalerite and pyrite (Zhou et al., 2020 and references cited therein).
The #320 orebody strikes 60°at 40 to 70°NE. It is 15 to 30 m long, has a width of 30 to 60 m and is 0.5 to 1.2 m thick. The ore minerals are galena, sphalerite and pyrite with grades that can locally reach >20% Pb and 28% Zn, but averages 3.5 and 7.6% respectively. Mineralisation occurs as both concordant sphalerite-galena bands or as cross-cutting disseminated veins, and as galena veins also cross-cutting the strata (Zhou et al., 2020 and references cited therein).
The #321 ore parallels #320 and is composed of three mineralised veins distributed over a zone that is 800 m long x 90 m deep. The main orebody is relatively small, covering an area of 20 to 60 m in long, 15 to 45 m wide, and 0.8 to 1.5 m thick. The grade of Pb reaches up to 11.2% locally with an average value of 5%, while the highest grade of Zn is 5.1% at an average of 3.5%. The ore minerals are galena, sphalerite and pyrite (Zhou et al., 2020 and references cited therein).
In the Zhenzigou deposit, the concordant stratabound mineralisation typically comprises fine-grained, layered and/or disseminated sulphides. Light brown sphalerite is abundant, in association with minor galena and pyrite. Much of the ore at Zhenzigou has been modified near and within the layered mineralisation. The ore minerals are primarily sphalerite and locally developed medium to coarse grained galena and/or pyrite in a gangue of calcite, dolomite and minor quartz, and occurs as massive or vein stockworks. This modified ore style is distinguished by the characteristic dark brown colour of sphalerite, the medium to coarse grain size of sulphides, and the relatively low abundance of galena. Fault-fracture style vein or breccia mineralisation exploit faults as fluid migration pathways and provide open-space for the precipitation of ore and gangue minerals, forming vein and vein-stockwork mineralisation that crosscut stratification, e.g. the #320 orebody described above. Marble breccia which forms locally in fault zones hosts minor disseminated sphalerite, pyrite and/or galena mineralisation in veins. Lamprophyre dykes are developed across the mine area, some of which host Pb-Zn mineralisation veins, while others crosscut the galena-pyrite veins, suggesting a spread of formation ages (Zhou et al., 2020 and references cited therein).
Resources
Quoted resource/reserve figures include the following:
• Rodionov et al., (USGS, Northeast Asia Metallogenc Belt Descriptions; 2004) quote reserves of 0.7289 Mt of Pb metal and 0.3493 Mt of Zn metal at average grades of 2.64% Pb and 1.90% Zn. This would equate to 27.6 Mt of Pb ore and 18.4 Mt of Zn ore. Presumably this is an amalgamation of resources in a number separate Pb-Zn and lesser Zn-Pb orebodies.
• Wikipedia (viewed December 2020) quotes Wood Mackenzie (unspecified date) as allocating a reserve of 29.9 Mt @ 2.64% Pb, 1.9% Zn containing 0.73 Mt of lead and 0.35 Mt of zinc. Note that these figure have a shortfall in the amount of contained Zn for the ore tonage and grade.
• The USGS MRData database (viewed December 2020) quotes a resource of 27.6 Mt @ 2.6% Pb, 1.9% Zn, 75 g/t Ag based on references cited therein (most recent 2005). These figures are inconsistent with the contained Zn metal quoted elsewhere.
It is uncertain if these figures represent remaining resources or historic production + remaining resources, and at what date.
The most recent source geological information used to prepare this decription was dated: 2020.
This description is a summary from published sources, the chief of which are listed below.
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Qingchengzi Ore Field (centre)
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Selected References:
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Duan, X., Zeng, Q., Yang, J., Liu, J., Wang, Y. and Zhou, L., 2014 - Geochronology, geochemistry and Hf isotope of Late Triassic magmatic rocks of Qingchengzi district in Liaodong peninsula, Northeast China: in J. of Asian Earth Sciences v.91, pp. 104-124.
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Zhou, L., Zeng, Q., Liu, J., Duan, X., Sun, G., Wang, Y. and Chen, P., 2020 - Tracing mineralization history from the compositional textures of sulfide association: A case study of the Zhenzigou stratiform Zn-Pb deposit, NE China: in Ore Geology Reviews v.126, 18p. doi.org/10.1016/j.oregeorev.2020.103792
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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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