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Yanshan-Liaoning Molybdenum Belt - Lanjiagou, Yangjiazhangzi, Songbei, Xiaojiayingzi, Dazhuangke, Dawan, Xiaosigou, |
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Liaoning, China |
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Mo Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Lanjiagou Mo deposits are located in the Eastern or Yanliao Block of the North China Craton, ~450 km NE of Beijing.
Lanjiagou is one of 7 Mo deposits/resources that constitute the ENE-WNW trending, ~700 km long Yanshan-Liaoning Molybdenum Belt on the northern margin of the North China platform over the centre of the Eastern (or Yanliao) Block of the North China Craton. This belt extends from ~500 km ENE to 200 km WSW of Beijing and also includes Yangjiazhangzi, Songbei, Xiaojiayingzi, Dazhuangke, Dawan, Xiaosigou and Shouwangfen.
The Eastern, or Yanliao Block contains Archaean basement, represented by 3.5 to 3.85 Ga detrital zircons and fuchsite-bearing quartzites and ~3.5 Ga amphibolites in Eastern Hebei, and the 3.3 to 3.8 Ga granitoids and metasedimentary rocks in the Anshan area (Liu et al., 1992; Song et al., 1996). Mesoarchean basement rocks also outcrop in the Eastern Block, ranging in age from 3.5 to 3.0 Ga (Huang et al., 1986; Jahn et al., 1987; Kröner et al., 1988; Wu et al., 1991; Shen and Qian, 1995), occurring as enclaves, boudins and sheets within the 2.6 to 2.5 Ga trondhjemite-tonalite-granodiorite (TTG) and 2.5 Ga syntectonic granites that constitute much of the North China Craton (Wu et al., 1991; Kröner et al.,1988; Zhao et al., 2001). Neoarchaean 2.8 to 2.5 Ga TTG gneisses, ultramafic to mafic igneous intrusions and dykes are also widespread in the Eastern Block, with lesser (~30%) supracrustal sequences, mainly sedimentary and bimodal volcanic rocks (Zhao et al., 1998). All of these rocks have been deformed and metamorphosed to between greenschist and granulite facies at 2.48 to 2.50 Ga (Jahn et al., 1987; Wu et al., 1991; Zhao et al., 1998; Ge et al., 2003).
The North China Craton was cratonised at ~1.85 Ga (Zhao et al., 2001; Kusky et al., 2007), and subsequently covered by thick sequences of
Meso- to Neoproterozoic and Palaeozoic sedimentary rocks, including Neoproterozoic to Cambrian platformal limestone and dolostone successions (Lu et al., 2008). These rocks were intruded by diamondiferous kimberlites in Shandong and Liaoning Provinces during the Middle Ordovician. This implies the presence of a thick (~200 km), cold lithospheric root to the craton until at least as late as the Middle Ordovician (Zhou et al., 1991, 1994; Menzies et al., 1993; Griffin et al., 1998). The eastern part of the craton became tectonically active again during the Late Mesozoic, with large-scale magmatism, basin development, ductile deformation and displacement on large-scale faults from the Late Jurassic to Early Cretaceous (Yang et al., 2003). This was followed by eruptions at several localities of Cenozoic alkali basalts and minor tholeiitic basalts (Basu et al., 1991; Tatsumoto et al., 1992). Constraints from xenoliths in these Cenozoic basalts suggest the craton is now underlain by a hot lithosphere beginning at depths varying from 120 and 50 km (Ma et al., 1984), which is consistent with the available seismic and surface heat flow data. This indicates there was strong lithospheric thinning during Phanerozoic time, the result of delamination and detachment, predominantly in the Mesozoic and Cenozoic (Menzies et al., 1993; Menzies and Xu, 1998; Griffin et al., 1998), which was confirmed by the Os isotope studies of Gao et al. (2002) and Wu et al. (2003).
Lanjiagou
The intrusive complex at Lanjiagou is divided into coarse-grained and fine-grained granite, the largest block of which covers an area of ~20 km2. In plan, the surface outcrop of the intrusion has an irregular in shape, but in section, it occurs as large dyke-like bodies. The coarse grained granite is generally composed of 40 to 45% orthoclase, 15 to 20% plagioclase, 30 to 33% quartz, with 3 to 5% biotite and minor calcite, muscovite and sericite. The fine-grained granite generally contains 40 to 45% orthoclase, 15 to 20% plagioclase, 28 to 35% quartz and 1 to 3% biotite, with minor calcite, muscovite and epidote. Orthoclase crystals range from 0.36 to 3.5 mm in width. The coarse grained granite ranges from 178 to 186 Ma (K-Ar) while the fine-grained granite yields an age of 154±14 Ma (Rb–Sr whole-rock isochron; Han et al., 2009).
The Lanjiagou district deposit have been subdivided into the Upper, Middle and Lower Lanjiagou, Xiaomagou, Yuanbaoshan and Xishan groups, totalling over 100 mineralised bodies, distributed over a 3 x 2 km area in the central part of the fine-grained granite and on the contact zone between the coarse- and fine-grained granites. Individual orebodies vary from 76 to 1288 m in length and 3.1 m to 31.8 m in thickness, and persist for >400 m down dip. The main orebodies trend NW-SE and north-south and dip at ~45°.
Ores are characterised by 0.01 to 0.15 mm flakes of molybdenite with euhedral and subhedra textures, occurring as veinlet disseminated and brecciated masses. The principal metallic minerals are molybdenite and pyrite as well as minor sphalerite, chalcopyrite, galena, magnetite and electrum. Gangue minerals are mainly orthoclase, plagioclase and quartz, with lesser calcite, muscovite and chlorite. Wall rocks alteration comprises silica, sericite, carbonate, chlorite, with potassic alteration and greisenisation (Luo et al., 1991).
Eleven molybdenite samples from the deposit yielded an isochron age of 181.6±6.5 Ma (Re-Os; Han et al., 2009) during the Lower Jurassic. Mineralisation is interpreted to have been closely related to the subduction of the Pacific plate below the North China Craton (Han et al., 2009).
Mineral assemblages and cross cutting relations of ore veins, suggest five stages of mineralisation: i). an early stage characterised by gas-liquid metasomatism, accompanied by potassium feldspar, quartz and muscovite; ii). a second stage of mainly phyllic alteration, occurring as an assemblage of quartz-sericite-magnetite-pyrite that occurs as veins; iii). the main mineralisation stage, represented by the formation of veins containing quartz-molybdenite-pyrite-sphalerite; iv). the fourth stage, marked by the formation of a quartz-molybdenite-pyrite-sphalerite assemblage that occurs as veins and disseminations and is cut by barren calcite-quartz veins; and v). the final stage, characterised by the presence of carbonate (calcite)-chlorite-minor sulphides (Luo et al., 1991).
Ore reserves as quoted by Han et al. (2009) were 0.2168 Mt of contained Mo at a grade of 0.13% Mo which equates to ~167 Mt of ore.
Yangjiazhangzi
Yangjiazhangzi comprises skarn Mo mineralisation hosted by Middle to Upper Cambrian to Ordovician limestone, shale and skarn, intruded by porphyritic granite, granite-porphyry and has been subjected to silica, pyrite, chlorite and carbonate alteration. It occurs on the southern margin of the large Yangjiazhangzi pluton (Wu et al., 1990) which contains coarse-grained syenogranite with minor fine-grained syenogranite and granite porphyry (Huang et al., 1994; Wu et al., 2006). The coarse-grained syenogranite ranges from equigranular to porphyritic and was intruded by the fine-grained syenogranite and granite porphyry (Huang et al., 1994). A general absence of quartz veins, as well as only weak sericite alteration of the coarse-grained syenogranite up 100 m from the skarn mineralisation centre suggests the coarse-grained syenogranite was pre-mineral. The fine-grained syenogranite and granite porphyry intruded Precambrian carbonate rocks and were responsible for skarn mineralisation and er therefore are interpreted as syn-mineral intrusions (Oyang et al., 2020). The fine-grained syenogranite has been dated at from 189.0 ±4.0 to 188.0 ±2.0 Ma (Zircon U-Pb; Wu et al., 2006), coeval with molybdenite ages of 191.0 ±6.0 to 187.0 ±2.0 Ma (Re-Os molybdenite; Huang et al., 1994). The Songshuluo diorite that intrudes the country rocks 1 km west of the deposit has been dated at 221.0 ± 2.0 Ma (zircon U-Pb; Wu et al., 2006), indicating that it is a pre-mineral intrusion.
Reserves comprise 0.26 Mt of contained Mo at an average grade of 0.14% Mo in ~185 Mt of ore (Huang et al., 1989)
Songbei
Songbei is located ~3 km west of Yangjiazhangzi. Fine-grained syenogranite, granite porphyry and dolerite occur throughout the deposit area. A fine-grained syenogranite stock is exposed to the south of the deposit and was intruded by pink granite porphyry, the main body of which is intruded along the contact between Permian sandstone and Proterozoic to Paleozoic limestone, and into the limestone itself, where most of the Mo mineralization occurs. Biotite and quartz veins with K feldspar alteration selvages overprint the pink granite porphyry, indicating it was a synmineral intrusion. Dating of the granite porphyry yielded an Early Jurassic age of 184.0 ±2.0 Ma (Zircon U-Pb), contemporaneous with an Mo mineralisation age of 183.2 ±3.0 Ma (molybdenite Re-Os; Chu et al., 2017). The granite porphyries are silica rich (74 to 76 wt.%) and K2O rich (4.7 to 5.6 wt.%) and metaluminous to mildly peraluminous with A/CNK between 1.0 and 1.1 (Chu et al., 2017). They are also characterised by moderate fractionation between light rare earth elements (LREEs) and heavy rare earth elements (HREEs) (LaN/YbN = 2.6–15.2), strongly negative Eu anomalies (δEu = 0.1–0.5), and enriched Hf isotope compositions (εHf(t) values from -10.0 to -6.9), interpreted to indicate their parental magmas were the product of partial melting of ancient lower crust of the North China craton (Chu et al., 2017). Unaltered dolerite dykes cut the Mo orebodies.
Songbei has an indicated resource of 0.17 Mt of contained Mo at an average grade of 0.10% (Zeng et al., 2013) within ~170 Mt of ore.
Xiaojiayingzi
A porphyry-skarn Mo-Fe deposit, hosted by Neoproterozoic (Sinian) dolomitic limestone, chert-dolomitic limestone, intruded by porphyritic diorite, that has been subjected to skarn and K feldspar alteration, with overprinted pyrite, carbonate, sericite and chlorite. Reserves comprise 0.105 Mt of contained Mo in ~37.5 Mt of ore averaging 0.28% Mo, with an associated ~890 Mt of 33.4% Fe as magnetite (Han et al., 2009).
According to Ouyang et al. (2023), the Xiaojiayingzi deposit is related to an intrusive complex composed of gabbroic diorite, monzodiorite and granite porphyry. Molybdenite mineralisation occurs in two ore blocks, Xiaojiayingzi (0.11 Mt Mo) and Kangzhangzi (0.02 Mt Mo). In the Kangzhangzi ore block, Mo mineralisation is concentrated in skarn adjacent to a deep-seated granite porphyry, with minor disseminated and quartz veinlet mineralisation within the granite porphyry. In contrast, economic Mo mineralization in the Xiaojiayingzi ore block is concentrated in skarns located between the contact of steeply dipping monzodiorite and the Mesoproterozoic Wumishan Formation, with minor Mo mineralization found in quartz and endoskarn veins hosted in the monzodiorite. The Wumishan Formation comprises up to 4000 m of Mesoproterozoic carbonate rocks with lenses of calcareous shale, calcareous siltstone and sandstone. Skarn mineralisation in both ore blocks converges downward into the mineralised granite porphyry. In the Kangzhangzi ore block, skarn is zoned from deep proximal dark red-brown garnet to shallow distal dark-green pyroxene. In the Xiaojiayingzi ore block, proximal skarn is garnet rich, whereas pyroxene increases away from the monzodiorite-Wumishan Formation contact. In addition, pyroxene becomes more Fe and Mn rich with distance from the intrusions. Pb, Zn, and Ag increase toward the top of the system; and Mo and Fe increase with depth. High-precision U-Pb zircon geochronology (CA-ID-TIMS), coupled with crosscutting relationships, indicates the gabbroic diorite crystallised at 165.359 ±0.18 Ma, with subsequent crystallisation of the monzodiorite and granite porphyry at 165.361 ±0.19 and 165.099 ±0.18 Ma, respectively. High-precision Re-Os ages for molybdenite from the Xiaojiayingzi deposit distinguish at least three episodes of molybdenum mineralisation at 165.48 ±0.09 to 165.03 ±0.13; 163.73 ±0.09, and 163.11 ±0.11 Ma). Some of the Re-Os mineralisation ages overlap within uncertainty the high-precision U-Pb zircon ages of the monzodiorite and granite porphyry intrusions, consistent with a genetic link between Mo mineralisation and the two intrusions. However, several Mo Re-Os ages are significantly younger taken to suggest a later fluid event taken to suggest another deeper mineralising source. This paragraph is drawn from Ouyang et al. (2023). NOTE the difference in recorded ages of the host carbonate between the two sources.
Dazhuangke
A porphyry Mo deposit, hosted by Neoproterozoic (Sinian) carbonate rocks that are intruded by monzonite (Kjelsasite) that has undergone K feldspar alteration and silicification, overprinted by pyrite, sericite and chlorite. Mineralisation includes molybdenite, pyrite, sphalerite, ilmenite and chalcopyrite. Reserves comprise 0.01 Mt of contained Mo in ~12.5 Mt of ore averaging 0.08% Mo (Han et al, 2009).
Dawan
A porphyry-skarn Mo-Cu-Zn-Ag deposit hosted by Neoproterozoic (Sinian) dolomitic limestone intruded by rhyolite porphyry that has undergone K feldspar alteration, overprinted by silicification, skarn alteration, serpentinisation and late carbonate veining. The mineral assemblage includes molybdenite, pyrite, pyrrhotite, sphalerite, galena and chalcopyrite. Reserves comprise 0.259 Mt of contained Mo in ~215 Mt of ore averaging 0.12% Mo (Han et al, 2009).
Xiaosigou
A porphyry-skarn Mo-Cu deposit hosted by Neoproterozoic (Sinian) dolomitic limestone to chert intruded by granodiorite porphyry that has undergone K feldspar alteration, overprinted by pyrite, skarn alteration and serpentinisation. The mineral assemblage includes chalcopyrite, chalcocite, pyrite, molybdenite, bornite and tetrahedrite. Reserves comprise 0.598 Mt of contained Mo in ~664 Mt of ore averaging 0.09% Mo, with an associated 0.018 Mt of Cu at a grade of 0.75% Cu (Han et al, 2009).
Shouwangfen
A skarn Cu-Mo-Fe deposit hosted by Neoproterozoic (Sinian) dolostone to chert intruded by porphyritic granodiorite that has undergone skarn, chlorite, sericite and silica alteration, and has been serpentinised. The ore mineral assemblage comprises chalcopyrite, bornite, molybdenite, magnetite, sphalerite and galena. Reserves comprise 0.022 Mt of contained Mo in ~0.7 Mt of ore averaging 0.31% Mo, with an associated 0.02 Mt of Cu at a grade of 0.72% Cu (Han et al, 2009).
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.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Han, C., Xiao, W., Zhao, G., Sun, M., Qu, W. and Du, A., 2009 - A Re-Os study of molybdenites from the Lanjiagou Mo deposit of North China Craton and its geological significance: in Gondwana Research v.16, pp. 264-271.
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Ouyang, H., Gaynor, S.P., Selby, D., Mao, J., Shu, Q. and Li, C., 2023 - High-Precision Geochronology of the Xiaojiayingzi Mo Skarn Deposit: Implications for Prolonged and Episodic Hydrothermal Pulses : in Econ. Geol. v.118, pp. 485-507. doi: 10.5382/econgeo.4984.
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Ouyang, H., Mao, J. and Hu, R., 2020 - Geochemistry and Crystallization Conditions of Magmas Related to Porphyry Mo Mineralization in Northeastern China : in Econ. Geol. v.115, pp. 79-100.
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