Qinling-Dabie Mo Belt - Shapinggou, Gaijing, Qianechong, Dayinjian, Baoanzhai, Tiangjiaping, Yaochong, Xiaofan, Tianmugou, Huangjiagou, Mushan, Doupo
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The Qinling Molybdenum Belt is located in Shaanxi and Henan Provinces, central China, within the Qinling-Dabie Orogenic Belt separating the southern margin of the North China Craton/Paraplatform (also known as the Sino-Korean Craton) from the Yangtze Craton of the South China Block. It is one of the largest molybdenum provinces in the world, and contains a number clusters of deposits in two parts, the Qinling East and Dabie segments to the west and east respectively. Porphyry copper mineralisation is also encountered within the belt, as a numerous gold deposits.
A selection of representative deposits within the Tongbai-Hong'an-Dabie (Dabie) segment are described below, namely:
Yaochong; Qian'echong; Baoanzhai; Dayinjian; Shapinggou; Tiangjiaping; Huangjiagou, Tianmugou; Mushan and Doupo. These include 2 'giant' deposits (i.e., >0.5 Mt of contained Mo), namely Qian'echong and Shapinggou
Similarly, representative deposits and clusters within the East Qinling segment are described in the East Qinling Mo Belt record, and include:
Jinduicheng and Shijiawan; Huanglongpu; Nannihu, Sandaozhuang and Shangfanggou; Huoshenmiao; Shiyaogou; Yinjiagou; Yuchiling; Donggou; Leimengou; Huangshui'an District; Qiushuwan Cu-Mo; Yechangping; Dahu Au-Mo; Zhifang Mo; Yindonggou Ag-Au-Mo; Tumen Mo-F and Zhaiwa Mo-Cu.
See the Regional Setting section of the separate East Qinling Mo Belt record for a detailed description.
Yaochong, Xinxian County, Henan Province.
The Yaochong porphyry Mo deposit is located in the northwestern Dabie Mountains, ~330 km ESE to SE of the of the Nannihu, Sandaozhuang and Shangfang cluster of deposits. It is towards the eastern extremity of an ~200 km long string of deposits in the Dabie Mountains that include, from WNW to ESE, Tianmugou, Xiaofao, Mushan, Dayinjian, Qiane'chong, Yaochong, Tiangjiaping and Shapingou. This string of deposits cuts obliquely across the orogen, with Tianmugou located within the Kuanping Group on the northern side of the belt, whilst Shapingou lies to the south of the Qinling Group within the Dabie/Tongbai complex of the northern Yangtze Craton.
The granitic gneisses of the Dabie/Tongbai complex, which are extensively developed in the district, are the country rock to the Yaochong deposit. They are intruded by Late Palaeozoic plutonic rocks and Cretaceous intrusions and porphyry dykes which were emplaced in the north of the deposit. These plutons include:
• Late Palaeozoic gneissic, fine grained eclogites containing <5% granite, with magnetite as an accessory mineral (Li et al., 2001);
• Early Cretaceous quartz diorite, fine- or medium-grained monzogranite, porphyry stocks and dykes, typically occurring as multistage intrusions (Guo et al., 2004), with diorite or plagioclase amphibolite enclaves within the quartz diorite and monzogranite.;
• Porphyry stocks/dykes which are several hundred metres long and a few to several tens of metres wide, and NWW or east-west trending, are emplaced along faults. These stocks/dykes contain K feldspar, plagioclase, quartz with minor epidote and biotite, associated with the Mo mineralisation (Li et al., 2012).
The Yaochong deposit comprises four individual orebodies predominantly hosted by Neoproterozoic granitic gneisses and is related to concealed porphyry dykes formed between 140 and 135 Ma (Zircon U-Pb LA-ICP-MS dating). Dating of the host returned an age of 133.3±1.3 Ma (LA-ICPMS zircon U-Pb weighted average; Chen et al., 2013). The main deposit is ~960 m long and 480 to 800 m wide, composed of lenticular or sheet like bodies dipping north to NW, which branch and pinch out along strike (Wang et al., 2013). The principal ore minerals are molybdenite and pyrite, with minor chalcopyrite, magnetite and sphalerite. The main gangue minerals include quartz and K feldspar, with lesser sericite, biotite, epidote, chlorite and fluorite. Ore occurs as disseminations, veinlets, stockworks and breccias. Dating of 5 molybdenite samples has yielded ages of 134±2 to 136±2 Ma (Re-Os; Chen et al., 2013), while another 6 samples gave an age if 136.9 ± 1.2 Ma (Re-Os isochron; Luo et al., 2013)
Alteration assemblages include:
• Potassic - predominantly characterised by K feldspar and biotite, occurring within the Yanshanian host porphyry and wall rocks;
• A quartz-dominated suite, which is widespread in the porphyry and wall rocks, occurring as siliceous blocks and quartz-sulphide stockworks;
• A sericite-dominated assemblage, mainly the product of alteration of feldspar and biotite, with disseminated pyrite in veins and wall rocks;
• Propylitic - predominantly comprising chlorite, epidote and calcite;
• Carbonate-dominated assemblages, mainly as carbonate veins; and
• Fluorite-bearing zones, largely represented by disseminated purple fluorite grains (Wang et al., 2014).
Yaochong has a proved reserve of 88 Mt of ore @ an average grade of 0.058% Mo, containing 51 kt of Mo metal.
This summary is paraphrased from Mi et al. (2017).
Qian'echong, Xinxian County, Henan Province (#Location: 33° 08'39 "N, 112° 14' 20"E).
The Qian'echong porphyry Mo deposit is located in the northwestern Dabie Mountains, ~20 km NW of the Yaochong deposit, but to the south of the Guishan-Meishan fault.
The country rocks at Qian'echong belong to the Nanwan Formation of the Xinyang Group and of the Xiaojiamiao Formation (the local name for the Sujiahe Group), separated by the Tongbai-Shangcheng fault. The Neoproterozoic to Ordovician Xiaojiamiao Formation consists of muscovite-albite schist, muscovite-quartz
schist, two-mica oligoclase schist with lenticular marble intercalations, whilst the Devonian to Triassic Nanwan Formation is composed of two-mica quartz schist, epidote-biotite quartz schist, and biotite plagioclase schist (see the sequence described in the Yaochong summary above).
Structure in the deposit area is dominated by subsidiary faults to the regional Tongbai-Shangcheng fault, namely: i).WNW- to NW-trending structures that range from 600 to 2500 m in length and are 0.5 to 5 m wide, with 70 to 90°SW dips; ii).NNE to NNW faults which are hundreds to thousands of metres in length, 0.5 to 10 m wide and 70 to 90° dips to either the west or the east, locally crosscutting the WNW to NW faults.
Three types of igneous dykes are exposed in the Qian'echong area.
• Diorite dyke swarms which trend WNW and composed of plagioclase, hornblende, K feldspar and quartz with accessory apatite and magnetite. These are crosscut by NNE to NNW trending faults.
• Quartz porphyry dykes, which cut the diorites and comprise quartz, K feldspar, plagioclase and minor mica.
• Rhyolitic to granite porphyry dykes follow the WNW trending faults and are composed of quartz, plagioclase, K feldspar and minor biotite phenocrysts. The rhyolitic porphyry dykes have a similar mineralogy to the granite porphyry dykes, although their phenocrysts are more idiomorphic and the grains of the matrix are too fine to be visible. No crosscutting relationship has been observed between the rhyolitic to granitic porphyry dykes and the diorite or the quartz porphyry dykes.
The syn-mineral Qian'echong granite porphyry stock intrudes schists of the Nanwan Formation and is totally concealed, having been intersected at depths of 80 to 900 m below surface. The stock has areal dimensions ~500 x 400 m, elongated WNW. It may connect upward to the thin granite porphyry dykes encountered in drilling and granitic to rhyolitic dykes observed at surface. The granite porphyry stock contains 30 to 40% phenocrysts of plagioclase, K feldspar, quartz and minor biotite. The matrix comprises fine-grained K feldspar, plagioclase, quartz and biotite, with minor sphene, zircon, apatite, magnetite and ilmenite.
The quartz porphyry, rhyolitic and granite porphyry dykes contain weak Mo mineralisation, although they are significantly above the main orebodies. Although the concealed granite porphyry dykes and stock are mineralised and hydrothermally altered, they only contain <1% of the calculated reserve. However, these magmatic rocks are surrounded by a broad hydrothermal alteration halo within the country rocks, zoned from a potassic alteration core, surrounded by an extensive concentric propylitic alteration halo, and an intermediate zone of phyllic alteration that strongly overprints the potassic zone. The potassic core, characterised by strong K feldspar alteration forms an elliptical shell surrounding and overlying the stock with a diameter of 1 to 1.5 km.
Hydrothermal alteration at the Qian'echong deposit includes the following assemblages (Yang et al., 2013):
• Potassic, predominantly as biotite and K feldspar, occurring in the granitic porphyry stock and in the surrounding schists and adjacent dykes;
• Silicification, both as pervasive alteration and as quartz sulphide stockworks or veinlets;
• Sericitisation/phyllic, replacement of feldspar and biotite, in association with disseminated pyrite and quartz-sericite veinlets;
• Argyllic, typified by the alteration of feldspar to kaolinite, generally associated with Mo-bearing quartz stockworks, rhyolitic to granitic dykes, and fractures in the feldspathic schists;
• Propylitic, occurring as an assemblage of epidote, chlorite, sericite and calcite as the predominant hydrothermal minerals;
• Carbonate, mainly as carbonate veinlets; and ;
• Fluorite, characterised by disseminated purple fluorite grains or veinlets.
The hydrothermally altered rocks host mineralisation with an outward and upward zoning from Mo → Cu-Mo → Pb-Zn-Ag.
Sheeted chalcopyrite- and molybdenite-bearing quartz veins are exposed at surface or at shallow levels in the potassic alteration zone. Sheeted Cu ±Mo veins are generally 0.5 to 2.5 m thick with lengths of 150 to 350 m, following WNW trending faults, with dips of 70 to 80°S, although some also dip steeply to the north. Grades in the veins are <0.03% Mo, although they contain 0.38 to 1.21% Cu at depths of 15 to 70 m. They become shorter, thinner, and merge into fine stockwork networks and disseminations in the main Mo orebodies at depth.
Three main Mo orebodies are hosted within the potassic altered schists, mainly at elevations between 150 m and 750 m below the surface, and immediately below the zone of sheeted Cu ±Mo veins, but above the Qian'echong granite porphyry stock. The largest of these orebodies is ~1500 x 400 to 1000 m in plan, and lenticular in shape. Ore minerals are mainly molybdenite and pyrite, with minor magnetite, chalcopyrite, galena and sphalerite. Gangue minerals include quartz, feldspar, epidote, biotite, sericite, chlorite, fluorite and calcite. Mineralisation occurs as veinlets and stockworks that are several to tens of millimeters thick, and as disseminations with flaky, replacement, idiomorphic to hypidiomorphic grains (Yang et al., 2013).
Pb-Zn-Ag mineralisation occurs as sulphide-quartz ±calcite veins in the propylitically altered schist following WNW and NNW trending faults. The largest vein has a NNW strike length of ~800 m, persists for 115 to 237 m down dip, and is 1.8 to 6.7 m thick, and dips 75 to 85°. The mineral assemblage in these veins includes sphalerite, galena and pyrite, with trace chalcopyrite, tetrahedrite, argentite and native silver, averaging ~1% Pb, ~1% Zn, ~50 g/t Ag, and <0.2% Cu. The three largest Ag-rich veins containing >60 g/t Ag are 150 to 330 m long, 0.7 to 1.1 m wide, with 60-170 g/t Ag, found to the east of the sheeted Cu ±Mo veins, and are focussed along the WNW trending faults, dipping at 70 to 80°S.
Hydrothermal alteration and mineralisation was introduced in four stages:
• Stage 1, characterised by zoned assemblages that include K feldspar, quartz, epidote, magnetite and pyrite. Magnetite is predominantly disseminated, coexisting with K feldspar, quartz and epidote. Pyrite occurs as idiomorphic to hypidiomorphic cubes or replaces magnetite, whilst minor molybdenite is disseminated within the porphyry. These minerals are zoned outward from potassic to silicic and then to a peripheral propylitic assemblage.
• Stage 2, was responsible for the bulk of the Mo mineralisation, and is characterised by quartz, molybdenite and pyrite. Molybdenite occurs as flakes, and is present in quartz-molybdenite ±pyrite stockworks or as fine-grained films coating fractures.
• Stage 3, produced the assemblage of quartz ±calcite and base metal sulphides. The sulphides, mostly sphalerite, galena, pyrite and chalcopyrite, are usually xenomorphic and occur within quartz and calcite in veins. Silicification and phyllic alteration are best developed in Stages 2 and 3.
• Stage 4, is represented by quartz-carbonate, carbonate, or/and carbonate-fluorite veinlets, with no or little sulphide, crosscut the earlier veins, stockworks and altered porphyry assemblages.
Fluid inclusion studies (Yang et al., 2013) indicate hydrothermal fluids evolved from initial high salinity and CO2-rich, to low-salinity and CO2-poor post-ore residues. Fluid inclusions in minerals of Stages 1, 2 and 3 homogenized at temperatures of 400 to 260, 340 to 200 and 300 to 160°C °C respectively. The estimated minimum trapping pressures are as much as 100 MPa in Stage 1 and 62 MPa in Stage 2, corresponding to an initial mineralisation depth of at least ~4 km (Yang et al., 2013). On the basis of the observed chalcopyrite, calcite and sylvite, but the absence of halite in solid-bearing inclusions, the same authors proposed that the Qian'echong hydrothermal system was NaCl-poor. This characteristic, together with the initial CO2-rich nature of the fluids and the widespread potassic alteration and fluoritisation, is consistent with a magmatic-hydrothermal systems that evolved in continental collision settings (e.g., Chen and Li, 2009; Mi et al., 2015).
Dating (206Pb/238U; zircon; Mi et al., 2015) from dykes of exposed quartz porphyry, rhyolitic porphyry and granite porphyry, and of concealed granite porphyry returned average ages of 128.9±1.1 Ma, 127.42±0.94 Ma, 127.44±0.98 Ma and 126.6±1.4 Ma respectively. The concealed granite porphyry stock yielded a weighted average age of 124.7±1.6 Ma, slightly younger than the exposed dykes, but within the error of tolerance for the concealed granite porphyry dyke. Five molybdenite samples from the ores yield ages of 123.31±1.02 to 128.49±1.40 Ma (Re-Os; molybdenite; Mi et al., 2015). This is consistent with the Mo being associated with the porphyry intrusion during the Lower Cretaceous.
The Qian'echong porphyry Mo deposit has a proved reserve of ~741 Mt of ore @ 0.081% Mo (Geological Survey Team 3 of Henan Bureau of Land and Resources, 2009; Yang et al., 2013; as quoted by Mi et al., 2015).
This summary is paraphrased from Mi et al. (2015).
Baoanzhai, Xinxian County, Henan Province.
The small Baoanzhai porphyry Mo deposit is located <10 km to the SE of Qian'echong. It is associated with a syenogranite porphyry intruding schists of the Xinyang Group, Nanwan Formation and gneisses of the Sujiahe Group, Xiaojiamiao Formation. Mineralisation includes molybdenite, chalcopyrite, pyrite and scheelite and is accompanied by potassic-propylitic and phyllic alteration zones. It has resources of <50 000 t of contained Mo metal (Chen et al., 2011). Dating of the host granite porphyry stock has yielded a date of 135.3±1.9 Ma (LA-ICPMS zircon U-Pb weighted average; Yang et al., 2010).
Dayinjian, porphyry-skarn Mo deposit, Henan Province (#Location: 31° 44' 44"N, 114° 40' 35"E).
The Dayinjian deposit is located <10 km SE of the Qian'echong deposit in the northwestern Dabie Mountains. The intrusive system associated with the deposit straddles the major Xiaotian-Mozitan Fault system which marks the boundary between the less deformed rocks of the North China Block and the UHP metamorphosed rocks of the Dabie Complex in the South Qinling Terrane. The rocks to the north of the fault belong to the Huwan Formation of the Sujiahe Group, and includes two lithologic members. The lower consists of gneisses with various proportions of biotite, hornblende, muscovite, plagioclase and quartz. The upper includes two-mica plagioclase gneiss, muscovite-plagioclase gneiss, migmatitic gneiss and marble. The rocks of the Dabie(/Tongbai) Complex UHP are mainly coesite bearing muscovite-plagioclase migmatitic gneiss, augen-like migmatite gneiss and plagioclase-hornblende gneiss, which were assigned to the Qijiaoshan Formation.
Intrusive rocks in the deposit area are mainly porphyritic monzogranite, granodiorite and granite porphyry dykes (Li et al., 2010, 2012). Porphyritic monzogranite is the principal intrusive phase associated with Dayinjian Mo deposit, occurring as an irregular NNE elongated stock covering an area of ~1.4 km2. It intrudes both the Qijiaoshan Formation of the Dabie Complex and the Huwan Formation of the Sujiahe Group, as well as the Xiaotian-Mozitan Fault which separates them. The porphyritic monzogranite has been dated at 124.9±1.3 Ma (LA-ICPMS zircon U-Pb weighted average; Li et al., 2012). It weathers to pale red, white to grey, and contains 40 to 45 vol.% perthite, 30 to 35 vol.% oligoclase, 28 to 30 vol.% quartz and 2 to 3 vol.% biotite, as well as accessory zircon, titanite, apatite and magnetite (Li et al., 2012).
Faulting is are well developed in the surrounding area, with two main sets, NW parallel to the Xiaotian-Mozitan Fault system, and NE to NEE trending cross faults.
Mineralisation is predominantly associates with skarns in the outer contact zones between monzogranite and the upper member of the Huwan Formation (Xu et al., 2013). Orebodies occur as stratabound skarn mantos and lens with areal extents of 150 to 480 x 180 to 450 m and thicknesses ranging from 1 to 79 m. Molybdenite is found as disseminated flakes or fine stockworks, accompanied by pyrite, magnetite, chalcopyrite, scheelite and bornite. The principal wallrock alteration includes silicification, K feldspar, muscovite-sericite and fluorite in the inner contact zone, whilst skarn, silicification, chlorite and serpentinite are developed in the outer contact zone.
Four stages of hydrothermal alteration and mineralisation have been recognised in both the felsic intrusive and host rocks:
Stage 1 - K feldspar-quartz±molybdenite veins;
Stage 2 - quartz-molybdenite veins;
Stage 3 - quartz-polymetallic sulphide veins; and
Stage 4 - quartz-carbonate-fluorite veins.
Alteration of carbonates or calcareous schists resulted in a younging series of garnet-diopside and epidote-actinolite-magnetite skarns, crosscut by veinlets of quartz-molybdenite±magnetite, quartz-polymetallic sulphide and quartz-carbonate-fluorite.
Molybdenite has been dated at between 121.5±1.8 and 123.9±2.0 Ma (Re-Os; Luo et al., 2010) and 125.07±0.87 Ma (Re-Os isochron; Li et al., 2012).
Reserves comprise (Chen et al., 2013):
~40 Mt @ 0.05 to 0.06% Mo containing 0.0215 Mt of Mo metal.
Shapinggou and Gaijing, southwest of Jinzhai county, Anhui Province (#Location: 31° 35' 35"N,115° 40'30"E) .
The Shapinggou porphyry Mo deposit was discovered in 2006 after recognition and followup of a Mo-Pb-Zn-Ag geochemical anomaly in whole rock, soil and stream sediment chemistry.
The deposit is located ~100 km from Liu'an city, and 75 km ESE of the Qian'echong deposit in the western Dabie Mountains (Zhang et al., 2010). It is situated to the north of the final Triassic suture between the North China Craton and South China Block, marked by the NW-SE trending Xiaotian-Mozitan Fault, near its intersection with the NNE trending Shangcheng-Macheng cross fault. Several less prominent NNE and NW trending faults are also mapped in the immediate area of the deposit.
Structural trends in the region can be divided into three groups: i). NW-trending lithostratigraphic units, faults and compressional-shears; ii). NE to NNE trending extensional shears and faults, which were developed since the Jurassic, and are major regional fractures dividing the orogen into a series of stepped blocks; and iii). north-south faults. Yanshanian granitoids are widely distributed along the NW and NNE-trending structures or in their intersections, comprising both deeply seated granite batholiths and small stocks. Smaller Yanshanian granitic stocks at fault intersections are often associated with porphyry-type Mo mineralisation (Zhang et al., 2010).
The metamorphosed volcano-sedimentary country rocks of the Mesoproterozoic Luzhenguan Group occur as amphibole-plagioclase gneiss, biotite-plagioclase gneiss, granitic gneiss and/or mica schist in isolated blocks separated by more extensive intrusions (Xu et al., 2009; Zhang et al., 2012).
Yanshanian granitoids are extensively developed in the district, mostly monzonite, with lesser granite, granodiorite, diorite and quartz syenite. Cross-cutting relationships have shown that the early Cretaceous magmatism occurred in two stages (Ren et al., 2014; Wang et al., 2014):
• Early stage intrusions from 138 to 125 Ma are widespread, and comprise 136.3±1.6 Ma monzogranite (Ren et al., 2014), 127.5±2.9 Ma granodiorite (Ren et al., 2014), 138.5±1.5 Ma pyroxenite (LA-ICP MS zircon U-Pb, Wang, 2013) and 133.7±1.7 Ma amphibolite (LA-ICP MS zircon U-Pb, Wang, 2013). These early-stage intrusions are composed of K feldspar, quartz, plagioclase, biotite, hornblende and pyroxene with accessories that include zircon, apatite, sphene and magnetite.
• Late stage intrusions from 118 to 111 Ma, comprising 117.2±1.2 Ma syenite (Ren et al., 2014), 116.1±2.2 Ma quartz syenite porphyry (Chen et al., 2013), 112.2±1.2 Ma granite porphyry (Ren et al., 2014) and 111.89±0.31 Ma diorite porphyry (LA-ICP MS zircon U-Pb; Ren et al., unpublished). These intrusions are composed of K feldspar, quartz, plagioclase, biotite, muscovite and hornblende with accessory zircon, apatite, sphene and magnetite.
Molybdenum mineralisation is predominantly hosted by the late stage granite porphyry and syenite. Virtually all of the economic mineralisation is contained within the main ellipsoidal ore body that has an areal extent of ~1000 x 800 m, and vertical dimension of ~600 m. It is centred on the upper sections of a concealed vertical stock of granite porphyry which is nested within a 2 x 1.5 km plug of diorite porphyry, which, in turn, intrudes a much more extensive mass of monzogranite. The monzogranite surrounds blocks of country rock that are hundreds of metres to a few kilometres long and intrudes a large granodiorite (Ren et al., 2018).
Explosive breccias are found in the northwestern section of the diorite porphyry, on the opposite end to the deposit. This breccia is exposed over an area of 500 m2 and contains a mixture of different rock types, particularly granite, syenite, metavolcanic and metasedimentary rocks. A series of NE, NNE-trending tensile fracture systems are developed at the top and around the breccia (Zhang et al., 2014).
The small Gaijing deposit is hosted within the explosive breccia. Mineralisation occurs as veins and a pipe in the porphyry-breccia and contact zone, containing molybdenite, pyrite, galena, sphalerite, bismuthinite, chalcopyrite, hematite and magnetite in a gangue of quartz, K feldspar, plagioclase, sericite, biotite, fluorite, chlorite and calcite. It contains <20 000 t of Mo metal at grades of 0.02 to 0.32% Mo ± Pb and Zn
Mineralisation occurs as veins, veinlets, stockworks and disseminations (Ren et al., 2015). Shapinggou is almost solely an Mo deposit, with very low associated Cu levels, generally <10 ppm, with Mo/Cu ratios of >50, but has high Rb (217to 483 ppm) and Nb (75 to 167 ppm). Molybdenite, the only Mo-bearing mineral. Flakes ranges from 0.02 to 0.16 mm across and comprises 59.70 to 60.75% (average 60.23%) Mo, 38.56 to 40.25% (average 39.67%) S, with 0 to 0.16% (average 0.043%) Re (Zhang et al., 2012).
In addition to molybdenite, the metallic minerals present are pyrite, with minor or trace magnetite, hematite, ilmenite, galena, sphalerite, chalcopyrite and pyrrhotite. Gangue minerals include K feldspar, quartz, plagioclase and fluorite, with minor biotite, muscovite, anhydrite and gypsum, and trace phlogopite, chlorite, epidote and calcite (Chen et al., 2017).
Four hydrothermal alteration types have been recognised in the deposit (Chen et al., 2017): i). Early silicic and potassic, comprising K feldspar and biotite; ii). propylitic, with weak chlorite-epidote; iii). phyllic, characterised by strong quartz-sericite-pyrite; and iv). argillic (Ren et al., 2015).
The ore-forming stagres that accompanied these alteration stage can be divided into (Chen et al., 2017):
Stage 1 - quartz-K feldspar, deposited at 550 to 340°C, from fluids with 7.8 to 16.9 wt.% NaCl equiv.;
Stage 2 - quartz-molybdenite, deposited at 450 to 240°C, from fluids with 34.1 to 50.8 wt.% NaCl equiv.;
Stage 3 - quartz-sericite, deposited at 345 to 220°C, from fluids with 32.9 to 39.3 wt.% NaCl equiv. and ;
Stage 4 - quartz-fluorite-gypsum, deposited at 330 to 177°C, from fluids with 0.7 to 65 wt.% NaCl equiv..
Molybdenite is deposited in the first three stages but predominantly in the second (Ren et al., 2015). Hydrogen and oxygen isotopes indicate ore-forming fluids of the first two stages are of magmatic origin whereas those associated with the last two stages incorporated meteoric water (Huang et al., 2013; Ni et al., 2015). The sulphur and lead isotopic compositions suggest that the ore materials are related to the granite porphyry (Ni et al., 2015).
Dating of molybdenite samples have yielded the following: 110.2±1.7 to 113.8±3.6 Ma (Re-Os; 7 samples; Zhang et al., 2011); 112.2±1.7 to 113.9±1.7 Ma (Re-Os; 9 samples; Huang et al., 2011); 100.0±1.8 to 113.6±1.7 Ma (Re-Os; 5 samples; Meng et al., 2012).
Ore reserves comprise (Zhang et al., 2010):
~1300 Mt @ 0.17% Mo containing 2.2 Mt of Mo metal (at a cutoff grade of 0.03% Mo);
at a cutoff grade of 0.06% Mo, the reserve is reduced to 1.6 Mt of Mo metal.
Tangjiaping, Henan Province (#Location: 31° 31' 25"N, 115° 20' 30"E).
The Tangjiaping porphyry Mo deposit is located in the southern Dabie Shan, ~ 20 km WSW of the Shapinggou depsoit. It associated with the syn-mineral Tangjiaping granite porphyry which intrudes the UHP metamorphosed rocks of the Dabie Complex south of the Xiaotian-Mozitan Fault. In the deposit area, the Dabie Complex comprises biotite- and hornblende-plagioclase gneisses, which have been partially altered. Faults that control the emplacement of the host porphyry also control the distribution of mineralisation. Rocks within and adjacent to these fault zones are mostly brecciated, silicified and kaolinised (Yang et al., 2008; Chen and Wang, 2011; Wang et al., 2016).
The Tangjiaping granite porphyry has an outcrop area of ~0.34 k m2, and has subsurface, north-south elongated dimensions of ~100 x 200 to 500 m. It comprises ~10 vol.% phenocrysts, made up of 5 vol.%K feldspar, 3 vol.% quartz and 2 vol.% plagioclase. The matrix has 20 to 56 vol.% K feldspar, 10 to 30 vol.% plagioclase and 10 to 25% quartz, with minor biotite and muscovite. Accessory minerals include magnetite, hematite, zircon, titanite, monazite and rutile. Dating of the granite porphyry yielded ages of 121.6±4.6 Ma (LA-ICPMS zircon U-Pb concordia; Wei et al., 2010) and 118.1±0.8 Ma (LA-ICPMS zircon U-Pb weighted average; Wang et al., 2016).
The porphyry stock surrounds enclaves of andesitic country rock (Chen and Wang, 2011; Wang et al., 2016).
The deposit occurs as a lens like cap in the roof of the granite porphyry, straddling the contact with the Dabie Complex, with dimensions of ~1120 x 960 x 250 m, dipping at ~20°SW (Chen et al., 2017).
Tangjiaping is a molybdenum-only deposit, with no other metals recovered as by-products (Chen and Wang, 2011; Wang et al., 2016). The main metallic minerals include molybdenite, pyrite, magnetite and hematite, with minor sphalerite, chalcopyrite and galena. The principal gangue minerals are quartz, feldspar, sericite, and muscovite, with lesser biotite, chlorite and epidote.
Molybdenite occurs as:
• Coarse-grained radial aggregates disseminated in K feldspar-quartz stockworks filling fissures;
• Aggregates and scaly, sparse disseminations in the altered granite porphyry; and
• Small grains and aggregates or films, associated with quartz and pyrite, forming millimetre-thick, fine-grained, quartz-pyrite-molybdenite stockworks.
Limonite is evident in the weathered zones.
From the core of the deposit, outward to the periphery of the system, three alteration zones have been recognised:
i). potassic-silica core, which is pervasive and extensive, persisting into the metamorphic wall rocks. It is characterised by the assemblage K feldspar, biotite and quartz;
ii). An outermost concentric propylitic halo, which is extensive and comprises an assemblage of predominantly epidote, chlorite and calcite (Chen and Wang, 2011).and
iii). A weakly developed intermediate zone of phyllic alteration that overprints the potassic-silica and propylitic assemblages, typified by the replacement of feldspar and biotite by sericite with disseminated pyrite and quartz-sericite veinlets.
Mineralisation can be divided into the following stages based on crosscutting relationships, mineral assemblages and hydrothermal alteration:
• Stage 1 is characterised by the assemblage of K feldspar, quartz, pyrite, magnetite ±molybdenite. Magnetite is mostly disseminated, and coexists with K feldspar and cataclastic quartz. Pyrite occurs as hypidiomorphic to idiomorphic cubes, and the minor flakes of molybdenite. The associated alteration is K feldspar, silicification and propylitic.
• Stage 2 is closely realted to the Mo mineralisation, characterized by stockworks of quartz-pyrite-molybdenite±chalcopyrite. Molybdenite occurs as flakes, disseminations in veins or as fine-grained films coating veins or fractures, whilst pyrite always coexists with muscovite.
• Stage 3 is characterised by a quartz-calcite-polymetallic sulphide assemblage. Sulphide include pyrite, chalcopyrite and galena. They occur as xenomorphic grain in veins and coexist with quartz and sericite with minor calcite and chlorite. Silicification and phyllic alteration are most conspicuous in Stage 2 and 3.
• Stage 4 is quartz-carbonate veins or carbonate veinlets with little or no sulphides, cross-cutting the earlier veins, stockworks and altered granite porphyry (Chen and Wang, 2011).
Dating of molybdenite yielded ages of 113.5±1.8 to 118.5±1.9 Ma (Re-Os; 5 samples; Yang, 2007) and 119.7±2.1 Ma (Re-Os weighted average; 3 samples; Luo et al.l., 2010).
Ore reserves comprise (Chen et al., 2017):
~375 Mt @ 0.063% Mo containing 0.235 Mt of Mo metal (at a cutoff grade of 0.02% Mo).
Huangjiagou, Hubei Province.
The Huangjiagou molybdenum deposit is located ~30 km south of Tongbai in Hubei Province. It lies within the Dabie-Tongbai Complex, with country rocks comprising marble, gneiss, amphibolite and sandstone intruded by leptite and diorite to granite. The sandstone belongs to the unconformably overlying Mesozoic Hugang Formation, whilst the marble is the upper layer of the Neoproterozoic Qingshanzhai Formation. The amphibolite and leptite are thought to be parts of Tongbai Complex. The gneiss is composed of dolomite-quartz gneiss, dolomite-albite gneiss and dolomite-albite-quartz gneiss of the Mesoproterozoic Liulin Formation. However, granites dominate in he deposit area.
Mo mineralisation occur as small quartz-molybdenite veins and disseminations in leptite or amphibolite lenses enclosed within the Huangjiagou granite. Three granite varieties occur in this region, namely fine-, medium- and coarse-grained granites. The Huangjiagou granite is coarse grained, and has a subhedral granular texture. It is mainly composed of ~ 55% feldspar, ~ 40% quartz, ~ 4% hornblende and ~1% biotite, with accessory titanite. The medium-grained granite comprises feldspar, quartz and biotite without hornblende. A diorite dyke was also present. The amphibolite and leptite lenses within the Huangjiagou granite are interpreted to be members of the Wudang Group that belongs to the Tongbai Complex and have igneous protoliths with a Neoproterozoic 701±9.1 Ma age (zircon U-Pb age, our unpublished data quoted in Chen et al., 2017). Five discrete Mo bodies have been delineated in the deposit. While some molybdenite is disseminated in the amphibolite and leptite, the bulk occurs in quartz veins. The alteration related to Mo mineralisation includes potassic and silica assemblages, occurring in both leptite and granite.
Molybdenite from the veins yields an age of 137.0±8.1 Ma (Re-Os isotope dating), which is consistent with the 137.6±1.6 Ma age of the Huangjiagou granite (LA-ICP-MS zircon U-Pb), suggesting a coincident relationship between the granite and mineralisation, with the mineralisation associated with a phase within the larger granitic body. Geochemical data indicate the Huangjiagou granite is high-K calc-alkalic to shoshonitic and weakly peraluminous with relatively low Mg contents. The host rocks are enriched in LREE and depleted in HREEs. The (La/Yb)N ratios vary from 24.39 to 40.37, and no significant Eu anomalies have been identified. The rocks also show enrichment in large ion lithophile elements (LILE; e.g., Pb, Ba) and depletion in high field strength elements (HFSE; e.g., Nb, Ti). The Hf isotopic compositions of zircons from the granite indicate εHf(t) variations from -17.3 to -22.1 (average -19.8±0.5) with two-stage model ages (TDM2) from 2.26 to 2.56 Ga (average 2.42 Ga).
These data imply that the Huangjiagou granite was likely derived from partial melting of a thickened lower crust that mainly contained garnet and clinopyroxene without feldspar. The abundance of Re in the molybdenites also indicates that the Mo may be derived from the thickened crust with possible minor mantle material mixing (Chen et al., 2017).
Ore reserves comprise (Chen et al., 2017):
~120 Mt @ 0.03 to 0.87%, averaging 0.084% Mo, containing 0.1 Mt of Mo metal.
Tianmugou, Henan Province.
The Tianmugou porphyry Mo deposit is located in the northwesternmost Dabie Shan, close to the Luanchuan Fault, and is hosted within the Tianmushan granite batholith. This batholith, which intrudes schists of the Erlangping, Kuanping and Luanchuan groups, is exposed over an area of ~60 km2, and is largely composed of five main phases.
• Phase 1 is fine-grained K feldspar granite, occurring as a narrow remnant outermost rim to the batholith.
• Phase 2 is medium-grained K feldspar, exposed at the SW and NE sections of the batholith. This phase has similar mineralogical constituents to phase 1, comprising 45 vol.% K feldspar, 20 vol.% plagioclase, 25 vol.% quartz and 5 vol.% biotite, with 5 vol.% accessory minerals, mainly sphene and zircon.
• Phase 3 is a coarse-grained biotite monzogranite, largely surrounded by Phase 1. It comprises 30 vol.% coarse-grained quartz, 30 vol.% K feldspar, 30 vol.% plagioclase and 5 vol.% biotite, with accessory sphene, zircon, magnetite and ilmenite.
• Phase 4 is a porphyritic granite with 10 to 25 vol.% quartz and K feldspar phenocrysts set in a matrix of K feldspar, plagioclase, quartz and biotite.
• Phase 5 is also a fine-grained K feldspar granite, forming the core of the batholith.
The Mo mineralisation is predominantly hosted within the Phase 4 porphyritic granite to the south of the Luanchuan Fault (Li, 2008). The bulk of the contained Mo mineralisation occurs as thin molybdenite-bearing pegmatite dykes, or as numerous hydrothermal veins, including quartz-molybdenite and molybdenite-only veins. The principal ore minerals molybdenite, pyrite and chalcopyrite. Molybdenite hosted by the thin mineralised pegmatite dykes coexists with coarse-grained quartz and K feldspar, occurring as 0.3 to 0.5 × 1 to 2 mm flakes, usually as aggregates. The molybdenite in the quartz-molybdenite vein is usually disseminated and scaly with 0.2 × 1 mm flakes. The main gangue minerals are quartz, K feldspar, biotite, sericite, fluorite and calcite. Hydrothermal alteration types at Tianmugou include:
• Potassic, predominantly biotite and K feldspar developed within the porphyritic granite;
• Silicic, particularly associated with quartz-sulphide stockworks or veinlets;
• Sericitic, replacing feldspar and biotite, accompanied by disseminated pyrite and quartz-sericite veinlets;
• Propylitic, characterised by epidote, chlorite, sericite and calcite; and
• Fluorite, represented by disseminated purple fluorite grains or veinlets.
Zircon crystals from the biotite monzogranite yielded a weighted average age of 123.0±0.8 Ma, (206Pb/238U; Yang et al., 2017) but those from the porphyritic granite do not yield a good age because of their high contents of Th, U and Pb. Seven molybdenite samples from the ores gave individual isotopic ages of 120.5±1.7 Ma to 122.5±1.9 Ma (Re-Os; Yang et al., 2017).
Tianmugou is a relatively small resource with <0.01 Mt of contained Mo at grades of 0.03 to 0.70% Mo.
Xiaofan, Henan Province (#Location: 31° 57'27"N, 114° 12'26"E).
Xiaofan is a porphyry molybdenum deposit in the Dabieshan of Luoshan County, Henan Province. Mineralisation occurs as stockwork veins containing molybdenite and pyrite in a gangue of quartz, K feldspar and biotite, hosted by granite porphyry which intrudes two-mica and quartz-feldspar
schists, of the Nanwan Formation of the Devonian to Triassic Xinyang Group. The deposit is located near the intersection of the regional, NW-SE Tong-Shang and near north-south Dawu faults. The deposit occurs as a lens at the contact between the porphyry and country rocks that is ~1000 x 440 to 573 to a depth of 270 m. Alteration includes silicic, potassic, phyllic and propylitic assemblages (from Chen et al., 2017; Mao et al., 2013).
The Xiaofan pluton that hosts the Mo mineralisation is mainly a porphyritic granite. It is exposed over an area of 0.039 km2, elongated north-south, and has been dated at 139.3±0.64 Ma (zircon U-Pb; Yang et al., 2015). The granite has a porphyritic texture with phenocrysts of subhedral, granular, twinned, plagioclase, subhedral K feldspar, irregular, granular quartz and biotite, set in a fine-grained matrix is composed of similar minerals as phenocrysts, with accessory zircon, titanite, apatite and magnetite, with lesser allanite (Liu et al., 2018).
Analyses by Liu et al. (2018) showed that it has high SiO2 contents of 74.29 to 76.07 wt.% (average: 75.18 wt.%), Al2O3 contents of 11.66 to 12.83 wt.% (average: 12.13 wt.%), and K2O contents of 5.37 to 7.90 wt.% (average: 6.86 wt.%) and low MgO (0.06 to 0.16 wt.%), TiO2 (0.09 to 0.10 wt.%) and P2O5 (0.047 to 0.103 wt.%) contents. It is enriched in Rb, U, K and Hf but depleted in Ba, Nb, Ta, Sr and Ti. These authors conclude that geochemical and mineralogical data, suggest the Xiaofan granites belong to A-type type granite and are dominantly sourced from the crust and that the Xiaofan Mo deposit may have formed in a post-collision extensional setting.
Reserves are ~150 Mt @ 0.045% Mo, 0.064% Cu for a total of 0.0715 Mt of contained Mo (Chen et al., 2017).
Mushan, Luoshan County, Henan Province (#Location: 31° 59' 29"N, 114° 19' 57"E).
The Mushan porphyry Mo deposit is located ~40 km WNW to NW of Qian'echong. It is associated with a granite porphyry intruding quartz-feldspar schist, gneiss and
plagioclase amphibolite of the Xinyang Group, Nanwan Formation. Mineralisation includes molybdenite, chalcopyrite and pyrite and is accompanied by potassic-propylitic and phyllic alteration zones. It has a resource of ~130 Mt @ 0.044% Mo, for 58 900 t of contained Mo metal (Xu 2011; Yang et al., 2011). Molybdenite from Mushan has yielded an age of 155.7±5.1 Ma (Re-Os; Li et al., 2013), while the host stock has been dated at 142.0±1.8 Ma (LA-ICPMS zircon U-Pb weighted average; Li et al., 2013).
Doupo, Luoshan County, Henan Province.
The Doupo porphyry Mo deposit is located ~20 km WSW of Qian'echong. It is associated with a porphyritic monzogranite of the Lingshan granite pluton, intruding gneiss and schist of the Sujiahe Group, Huwan Formation. Mineralisation includes molybdenite, pyrite, galena, sphalerite, chalcopyrite, magnetite, pyrrhotite and bornite and is accompanied by potassic-propylitic and phyllic alteration zones. The deposit is regarded as small. Molybdenite from Doupo has yielded an age of 140.5±8.2 Ma (Re-Os; Li et al., 2013).
NOTE; Reserves/resources quoted in the descriptions above are Chinese estimates quoted in academic papers and may not be compliant to JORC, NI 43-101 or equivalent conventions. Resources quoted in the original sources are as tonnes of contained metal and average grade. Ore tonnages quoted above have been back calculated from these figures assuming no recovery criteria are included in estimation of the contained metal reserves.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this summary was dated: 2017.
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.
Chen, Q.-Z., Jiang, S.-Y. and Duan, R.-C., 2017 - The geochemistry, U-Pb and Re-Os geochronology, and Hf isotopic constraints on the genesis of the Huangjiagou Mo deposit and related granite in the Dabie region, Hubei Province, China: in Ore Geology Reviews v.81, pp. 504-517.|
Chen, W., Xu, Z., Qiu, W., Li, C., Yu, Y., Wang, H. and Su, Y., 2015 - Petrogenesis of the Yaochong granite and Mo deposit, Western Dabie orogen, eastern-central China: Constraints from zircon U-Pb and molybdenite Re-Os ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes: in J. of Asian Earth Sciences v.103, pp. 198-211.|
Chen, Y.-J., Wang, P., Li, N., Yang, Y.-F. and Pirajno, F., 2017 - The collision-type porphyry Mo deposits in Dabie Shan, China: in Ore Geology Reviews v.81, pp. 405-430.|
He, T., Yang, X., Deng, J., Zhang, H., Zha, S., Li, C. and Zhang, H., 2016 - Geochronology, geochemistry and Hf-Sr-Nd isotopes of the ore bearing syenite from the Shapinggou porphyry Mo deposit, East Qinling-Dabie orogenic belt: in Solid Earth Sciences, v.1, pp 101-117.|
Mao, J., Pirajno, F., Lehmann, B., Luo, M. and Berzina, A., 2014 - Distribution of porphyry deposits in the Eurasian continent and their corresponding tectonic settings: in J. of Asian Earth Sciences v.79, pp. 576-584.|
Mao, J.W., Pirajno, F., Xiang, J.F., Gao, J.J., Ye, H.S., Li, Y.F. and Guo, B.J., 2011 - Mesozoic molybdenum deposits in the east Qinling-Dabie orogenic belt: Characteristics and tectonic settings: in Ore Geology Reviews v.43, pp. 264-293.|
Mi, M., Chen, Y.-J., Yang, Y.-F., Wang, P., Li, F.-L., Wan, S.-Q. and Xu, Y.-L., 2015 - Geochronology and geochemistry of the giant Qian echong Mo deposit, Dabie Shan, eastern China: Implications for ore genesis and tectonic setting: in Gondwana Research v.27, pp. 1217-1235.|
Mi, M., Li, C.-Y., Sun, W.-D., Li, D.-F. and Zhu, C.-H., 2017 - Yaochong Mo deposit, a low-F porphyry Mo deposit from the Qinling-Dabie orogenic belt: in Ore Geology Reviews v.88, pp. 188-200.|
Ni, P., Wang, G.-G., Yu, W., Chen, H., Jiang, L.-L., Wang, B.-H., Zhang, H.-D. and Xu, Y.-F., 2015 - Evidence of fluid inclusions for two stages of fluid boiling in the formation of the giant Shapinggou porphyry Mo deposit, Dabie Orogen, Central China: in Ore Geology Reviews v.65, pp. 1078-1094.|
Wang, G.-G., Ni, P., Yu, W., Chen, H., Jiang, L.-L., Wang, B.-H., Zhang, H.-D. and Li, P.-F., 2014 - Petrogenesis of Early Cretaceous post-collisional granitoids at Shapinggou, Dabie Orogen: Implications for crustal architecture and porphyry Mo mineralization: in Lithos v.184-187, pp. 393-415.|
Yang, Y.-F., Wang, P., Chen, Y.-J. and Li, Y., 2017 - Geochronology and geochemistry of the Tianmugou Mo deposit, Dabie Shan, eastern China: Implications for ore genesis and tectonic setting: in Ore Geology Reviews v.81, pp. 484-503.|
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