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Chalukou |
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Heilongjiang, China |
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Mo Pb Zn
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Super Porphyry Cu and Au
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The Chalukou porphyry Mo deposit occurs in the Great Hinggan Range, ~120 km NW of the Duobaoshan deposit and 80 km north
of the city of Jiagedaqi in Heilongjiang Province, northern China.
(#Location: 51° 10' 14"N, 123° 55' 21"E).
Regional Setting
Chalukou, which is one of the largest molybdenum deposits in the world, was discovered in 2006. It lies near the western margin of the Xing'an Terrane, adjacent to the Xinlin-Xiguitu Suture Zone that separates that terrane from a downthrown wedge of the Mandalovoo Terrane that is, in turn, bounded by the Erguna Terrane to the NW. The Erguna and Xing'an terranes were amalgamated in the early Palaeozoic (Ge et al., 2005) accompanied by the magmatism of the Mandaloovo Terrane straddling their common boundary. The amalgamated terranes were composed of Palaeoproterozoic metamorphic rocks (Xinghuadukou Group), Neoproterozoic greenschist facies rocks (Dawangzi Formation), Cambrian, Ordovician and Silurian island arc clastic and volcanic sedimentary rocks (Tongshan and Duobaoshan formations). The boundary zone between the two terranes was subsequently affected by movement on the continental scale Irtysh/Derbugan Fault, a broad complex of faults that have been active since the Permian, with a mostly sinistral offset of several hundred kilometres. This structural reorganisation led to the juxtaposition of the Mandaloovo Terrane between the Erguna and Xing'an terranes. The other regional influences include the closure of the Mongol Okhotsk Ocean some 300 km to the NNW, subducting southward below the Xing'an and Erguna terranes between the Devono-Carboniferous and the Early-Mid Jurassic. Sequences associated with this period include Upper Palaeozoic continental volcanic sedimentary rocks (e.g., the Niqiuhe, Genlihe and Huaduoshan formations). Subsequently, following an up to ~40 m.y. hiatus, a major extensional event commenced over a large area accompanied by the deposition of the Great Xing'an Range Large Igneous Province during both the Late Jurassic from 160 to 150 Ma and in the Early Cretaceous from 141 to 122 Ma, separated by a distinct temporal gap (Chen et al., 2007; Guo et al., 2008). The sequence deposited during this event included basalts and basaltic andesites with some rhyolitic tuffs, overlain by variably developed 20 to 190 m thick sedimentary unit, followed by 100 to 1420 m of rhyolite and dacite and related volcani-clastic rocks, capped by 10 to 305 m of basalt and basaltic-andesite, with ophitic or vitrophyric textures.
Intrusive suites in the area were mainly emplaced during the Late Palaeozoic, between 350 and 260 Ma and Mesozoic from 200 to 100 Ma, with lesser phases in the Early Palaeozoic between 500 and 460 Ma. The latter includes granodioritic intrusions and are mainly confined to the eastern margin of the Xing'an Terrane immediately west of the Hegenshan-Heihe Suture Zone that separates it from the Songnen-Xilinhot Terrane to the SE. The Duobaoshan Copper deposit is hosted by these Early Palaeozoic intrusives. Mylonitized granites and mafic-ultramafic intrusions were predominantly emplaced during the Carboniferous to Permian along the Nenjiang-Xinkailing-Heihe fault zone (Ge et al., 2005; Wu et al., 2005, 2012; Liu et al., 2012). Extensive Mesozoic granite batholiths, accounting for ~40% of all the exposed rocks. Mesozoic volcanism is widespread and is subdivided into the Longjiang formation andesitic volcanic rocks and Guanghua formation rhyolitic volcanic rocks. The bulk of both the Mesozoic batholiths and volcaniclastic sequences belong to the Great Xing'an Range Large Igneous Province.
Geology
The rocks exposed in the deposit area include the Neoproterozoic metamorphic rocks of the Dawangzi Formation which extend in a NE direction, are weakly alterered with molybdenite developed within fractures; Lower Ordovician, flow banded altered felsic volcanic rocks, occurring as strongly altered rhyolite with small quartz phenocrysts in the central part of the deposit area; and Lower Cretaceous felsic volcanic rocks, mainly dacite and rhyolite, which occur on the periphery of the deposit and are cut by intrusive porphyries and Mo mineralisation (Duan et al., 2018).
The Chalukou Mo mineralisation is hosted by Jurassic fine-grained porphyry, granite porphyry, quartz porphyry, monzogranite and breccia pipes that intrude Lower Ordovician volcanic rocks comprising rhyolite, rhyolitic tuff, dacite and andesite. The principal hosts are the Ordovician volcanic rocks, which are intruded by the Jurassic porphyritic rocks detailed above, as well as Cretaceous diorite and monzonite porphyry dykes (Zhou et al., 2021).
The mineralisation has been divided into Eastern and Western zones, separated by the NW-SE Duobukuer River. The eastern zone contains the bulk of the resource and is the focus of the summary below. In addition to the Ordovician volcanics and Jurassic intrusions, the Eastern Zone contains Neoproterozoic quartz-chlorite schist, meta-sandstone, quartz-biotite schist and minor marble as well as Late Jurassic to Early Cretaceous rhyolite. The mineralisation is predated by a set of ring fractures centred on the late Jurassic to early Cretaceous rhyolite and is post-dated by NE- and NW-striking faults (Zhou et al., 2021).
The western zone predominantly comprises monzogranite and late Jurassic to early Cretaceous rhyolite and quartz diorite.
The intrusive suites have been divided into three distinct stages, namely:
• Pre-mineral monzogranite, dated at 162 ±2 Ma (U-Pb zircon, Liu et al., 2014), that occurs as a >80 km2 batholith, exposed to the NW and SE of the deposit (Nie et al., 2011; Liu et al., 2014; 2015). It has also been encountered at depths of >600 m below the southeastern part of the Chalukou deposit, where it intrudes Ordovician volcanic rocks and is cut by fine-grained porphyry and quartz monzonite porphyry that are not exposed at surface. It is generally massive and porphyritic, with mainly K feldspar phenocrysts that range from 1 to 2 cm in size. The matrix comprises ~40% K feldspar, ~30% quartz and ~20% plagioclase. Biotite is the major mafic mineral. Accessory minerals include zircon and titanite. It also contains variable 5 to 15 cm mafic 'microgranular enclaves', mainly composed of hornblende and plagioclase. Although pre-mineral, it is one of the main host rocks for Mo mineralisation in the Chalukou area (Liu et al., 2014a).
• Syn-mineral fine-grained porphyry, granite porphyry and quartz porphyry. The granite porphyry and quartz porphyry were intruded into the Ordovician volcanic rocks and monzogranite batholith as dykes or small stocks with widths that range from 3 to 80 m. These rocks are accompanied by crypto explosion breccias which occur in the central part of the deposit area. In contrast, the fine-grained porphyry intrusion, which is only found at a depth of 600 m below the surface, has a mushroom-shape that reaches a maximum width of 1000 m in the centre of the Ordovician volcanic rock unit (Zhou et al., 2021).
The granite porphyry, which has been variously dated at 148.8 ±1.1 Ma (U-Pb zircon, Zhou et al., 2021), 152.1 ±2.2 Ma (zircon LA-ICP-MS U-Pb, Zhang and Li, 2017) and 154 ±1 Ma (U-Pb zircon, Duan et al., 2018). It contains 2 to 5 mm phenocrysts that comprise ~12 vol.% smoky grey high-temperature quartz, ~10 vol.% K feldspar, ~4 vol.% plagioclase and minor biotite, set in a matrix of quartz and plagioclase that constitutes the remaining ~75 vol.% of the rock. Accessories include zircon, titanite and magnetite (Zhou et al., 2021).
The quartz porphyry dated at 147.5 ±2.1 Ma (U-Pb zircon, Zhou et al., 2021), has a similar composition to the granite porphyry and comprises ~15 vol.% 1 to 3 mm phenocrysts, which are dominantly quartz (~10 vol.% of the rock) and lesser plagioclase, set in an ~85 vol.% matrix made up of quartz and minor plagioclase (Zhou et al., 2021).
The fine-grained porphyry, dated at 147.4 ±2.7 Ma (U-Pb zircon, Zhou et al., 2021), composed of 1 to 2 mm phenocrysts of K feldspar (~5 vol.%) and quartz (<1 vol.%) set in a groundmass that constitutes ~95 vol.% of the rock and is dominated by quartz with minor K feldspar and plagioclase. Accessory minerals are magnetite, zircon and apatite. Unidirectional solidification textures (USTs) are found in the apex of the intrusion, and are interpreted to record the transition from magmatic to hydrothermal conditions (Jin et al., 2014; Zhou et al., 2021).
• Post-ore quartz monzonite porphyry and diorite porphyry, which are not exposed on the surface, but cut across the ore body and wall rocks belwo the surface and represent the final stage of magmatic activity in the district (Zhou et al., 2021). The diorite porphyry has been dated at 138.9 ±2.3 Ma (U-Pb zircon, Zhou et al., 2021).
These intrusions are younger than the magmatism associated with closure of the Mongol-Okhotsk Ocean, but lie within the field of the magmatism of the Great Xing'an Range Large Igneous Province.
Alteration
Alteration covers an area of ~3 km2 at surface, which has expanded to 8 km2 at a depth of >600 m. Five alteration types have been recognised at Chalukou (after Zhou et al., 2021):
• Potassic, which is predominantly manifested by the replacement of plagioclase by K feldspar. It is developed in two zones, related to the emplacement of i). the granite porphyry at a depth of ~400 m and ii). the fine-grained porphyry at >600 m depth. Both zones of potassic alteration are developed both in the respective intrusions and in the intruded Lower Ordovician volcanic wall rocks, and both are associated with high-grade Mo mineralisation. The alteration assemblage occurs both as vein filling and disseminated in the wall rocks. In addition, in both zones, the alteration is most intense in the contact zone between the intrusive and the volcanic rocks. Potassic altered rocks are characterised by the assemblage K feldspar-quartz-molybdenite ±minor biotite ±magnetite ±anhydrite ±fluorite (Zhou et al., 2021). Intense to medium potassic alteration formed in the lower part of deposit occurs above and peripheral to the silicic alteration (Li et al., 2019).
• Silicic alteration is restricted to the apex of the fine grained porphyry intrusion which is composed of vein fillings of large volumes of quartz with minor K feldspar, fluorite and molybdenite (Zhou et al., 2021; Li et al., 2019).
• Sericite alteration which is developed above the potassic zone, occurs as a fine-grained assemblage of sericite-quartz-molybdenite ±pyrite ±minor fluorite, that occur as veins or are disseminated in the wallrocks (Zhou et al., 2021; Li et al., 2019).
• Intermediate argillic to argillic alteration is widely developed in the medium to shallow parts of the deposit characterised by the assemblage illite, quartz, fluorite, sphalerite ±pyrite with minor calcite, anhydrite, galena, hematite and chalcopyrite. It usually overprints the early sericitic and potassic zones, and illite sometimes completely replaces the secondary K feldspar in the potassic zone (Zhou et al., 2021; Li et al., 2019).
The sericitic and argillic alteration zones are extensive and accompanied the emplacement of the fine-grained porphyry. Both overprint potassic alteration.
• Propylitic alteration is relatively weak compared to the other alteration types, and was formed at distal outer and shallow levels, represented by the assemblage epidote-chlorite ±calcite and pyrite, mainly developed in the Lower Ordovician volcanic and Neoproterozoic metamorphic wall rocks.
The deposit has a consistent, large-scale alteration zoning pattern that comprises a potassic-silicate zone, a sericite-quartzite zone, an argillic zone and a propylitic zone from the ore-hosting porphyry outwards. The strong silica and potassic-alteration occurs mainly in granite-, quartz- and fine-grained porphyry. The sericite-quartzite alteration and the argillic alteration are mainly developed in the altered rhyolite and monzogranite. The propylitic alteration is well developed in the metamorphic rocks, the altered rhyolite and in the monzogranite. The Mo mineralisation is spatially closely associated with potassic and sericitic alteration of the granite porphyry and fine-grained porphyry.
Mineralisation and Veining
Zhou et al. (2021) have divided the molybdenum mineralisation into a thin, upper low-grade zone of <0.06 wt.% Mo and a lower, high-grade zone containing between 0.08 and 0.53 wt.% Mo at depths of generally >500 m (Nie et al., 2011; Zhang and Li, 2017). The molybdenum mineralisation passes upward into a zone of subordinate epithermal vein-type Pb-Zn mineralisation. Li et al., quote the orebody dimensions as 2600 m long, with a width ranging from 360 to 1260 m and a thickness of ~200 to 900m thick after Meng et al., 2011).
Duan et al. (2018) note that two separate stages of Mo mineralisation and more than 10 distinct vein types have been recognized in the Chalukou deposit. The two Mo mineralising events comprise i). an early stage related to the emplacement of the granite porphyry; and ii). a later main stage associated with the emplacement of the fine-grained porphyry. These two stages were both succeeded by the Pb-Zn mineralisation and a late hydrothermal stage characterised by carbonate ±fluorite ±quartz veining (Jin et al., 2014; Li, Z., et al., 2019).
The veining evolution at Chalukou may be summarised as follows, from oldest to youngest (after Zhou et al., 2021, who applied the A, B and D vein nomenclature of Gustafson and Hunt 1975, and Sillitoe 2010):
Early veining event, or Stage I, associated with the granite porphyry - mineralisation from this event has been dated at between 153.96 ±0.08/0.63/0.79 Ma and 148.67 ±0.07/0.62/0.77 Ma (molybdenite ID-N-TIMS Re-Os, Zhou et al., 2021). This stage only led to the deposition over an ~5 m.y. period of minor Mo mineralisation, accounting for <10% of the overall Mo budget of the deposit (Zhou et al., 2021). These molybdenum mineralisation ages overlap those of the granite porphyry as detailed above. High-salinity and high pressure (>220MPa) fluid inclusions exist in quartz veins of this event, characterised by homogenisation through halite dissolution at temperatures of 517 to 324°C (Xiong et al., 2015). The veins from this event, from earliest to latest, include:
• A1 veins are the earliest formed. They are barren, 0.5 to 3 mm quartz veins with irregular or straight walls, composed of quartz and K feldspar. They largely occur within granite porphyry and felsic to intermediate volcanic-sedimentary rocks at shallow depths of <400 m and are cut by other veins.
• B1 veins, which are also largely hosted by granite porphyry and are the dominant vein type in the shallow section of the deposit. They are thin, 2 to 10 mm veins composed of quartz, molybdenite, pyrite and K feldspar with K feldspar halos. Molybdenite is usually concentrated at the margins of the veins. They cut the A1 veins described above, and are truncated by A2 veins, as detailed below.
• A2 veins, which are 1 to 5 mm thick with straight walls. They are composed of quartz, pyrite, K feldspar and minor disseminated molybdenite, with K feldspar halos and are found at shallow levels in association with the granite porphyry where they cut B1 veins.
• B2 veins, which are 1 to 3 mm thick with straight walls, and are Mo-dominant with minor quartz. They are the most abundant Mo-bearing veins of the early veining event, and are composed of molybdenite, quartz and sericite with sericite selvages and commonly occur within the granite porphyry forming dense stockworks. They are also, but only rarely found as molybdenite-sericite veins. Both the A1 and A2 veins are truncated by B2 veins, although crosscutting relationships between B1 and B2 veins were not observed by Zhou et al. (2021).
Main veining event, or Stage II, associated with the fine-grained porphyry, - veins of this event are surrounded by potassic alteration envelopes. The bulk, i.e., >90% of the Mo in the deposit, was emplaced in ~0.65 m.y. between 147.67 ±0.10/0.60/0.76 and 147.04 ±0.12/0.72/0.86 Ma
(molybdenite ID-N-TIMS Re-Os, Zhou et al., 2021), coincident with the emplacement of a fine-grained porphyry at 147.4 ±2.7 Ma (zircon LA-ICP-MS U-Pb ages, Zhou et al., 2021). The coexistence of all fluid inclusion types were only observed at pressures of 218 to 150 MPa and temperatures of 375 to 352°C, with two salinity clusters of 0.9 to 16.6 wt.% NaCl equiv. and 56 to 37 wt.% NaCl NaCl equiv. (Xiong et al., 2015). The veins from this event, from earliest to latest, include:
• Unidirectional Solidification Texture (UST) veins which are thin and sinuous, generally 2 to 6 mm thick, predominantly composed of quartz with lesser K feldspar. They are found at a depth of >800 m in the apex of the fine-grained porphyry, cut by the main veining event A and B veins. These veins are interpreted to represent a magmatic-hydrothermal transition between the early and main events.
• A veins that are thicker than those of the early veining event. They are generally 1 to 15 mm thick with irregular or straight walls, and are predominantly composed of quartz with magnetite, hematite, pyrite, fluorite and K feldspar, enclosed by potassic alteration envelopes. These veins occur at depth, associated with the fine-grained porphyry. They cut numerous UST veins, but are, in turn, cut by B1 and B2 veins of the main stage.
• B1 veins of the main stage are principally quartz-molybdenite veins with associated pyrite. They are 2 to 10 mm thick and have K feldspar selvages. The molybdenite is usually concentrated along the margins of the thicker veins or as very thin, <2 mm Mo dominant fractures. They are most commonly hosted within the fine-grained porphyry and volcano-sedimentary wall rocks.
• B2 veins of the main stage are fine, 1 to 5 mm thick, containing more molybdenite than quartz, with associated pyrite and K feldspar and a halo of the latter. Some contain breccia fragments of granite porphyry. B2 veins are frequently found in the fine-grained porphyry at depths up to 1200 m.
Stage III quartz-polymetallic sulphide veins (after Xiong et al., 2015):
• D veins, which are late stage, crosscutting all of the veins above, and as such postdate the main stage Mo mineralisation. They are 5 to 40 mm thick and have straight walls, and are predominantly composed of euhedral pyrite intergrown with ±quartz ±fluorite, accompanied by minor chalcopyrite, molybdenite, sphalerite and galena, with well-developed sericitic alteration halos. In most cases, some polymetallic sulphide such as pyrite and chalcopyrite can be observed by the naked eye in these veins, whereas other sulphides such as sphalerite and galena can be discriminated under the microscope. There are >30 such Pb-Zn-Ag D veins or vein clusters distributed in shallow and peripheral parts of the deposit, crosscutting the main Mo mineralisation. Individual veins zones are controlled by faults and are 100 to 3220 m in length, 1.5 to 3.6 m cumulative thickness, striking at 30 to 70° and dipping at 30 to 45°NW. Fluid inclusions from these veins have homogenisation temperatures of 365 to 158°C and minimum pressures of 98 to 10 MPa. The estimated trapping pressure of the Main veining event and Stage III are interpreted to suggests an alternating lithostatic-hydrostatic fluid-system caused by fluid boiling (Xiong et al., 2015).
Stage IV carbonate ±fluorite ±quartz (after Xiong et al., 2015; Li et al., 2019)
Veins are composed of one to three phases of quartz, carbonate and fluorite (e.g. carbonate, calcite-fluorite and calcite-fluorite ±quartz veins), which cross-cut the earlier veins, stockworks and altered porphyries. Alteration assemblages include montmorillonite, fluorite, chlorite and carbonate (calcite). Fluid inclusions from these veins have homogenisation temperatures of 287 to 121°C (Xiong et al., 2015).
Reserves and Resources
Variable resource estimates have been published, including the following:
Duan et al. (2018) - 2.46 Mt of molybdenum @ 0.11 wt.% Mo, which would equate to 2.24 Gt of ore;
plus - 0.37 Mt of Pb+Zn @ an average 1.27% Pb+Zn, which would equate to 29 Mt of ore;
Zhou et al. (2021) - 2.46 Mt of molybdenum @ 0.087 wt.% Mo, which would equate to 2.83 Gt of ore;
Liu et al. (2014); Li et al. (2019) - 1.78 Mt of molybdenum @ 0.087 wt.% Mo, at a 0.06% Mo cut-off, which would equate to 2.05 Gt of ore;
plus - 0.68 Mt of molybdenum @ 0.048 wt.% Mo (between 0.06% and 0.03%), which would equate to 1.42 Gt of ore.
The most recent source geological information used to prepare this decription was dated: 2021.
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.
Chalukou
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Selected References:
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Duan, P., Liu, C., Mo, X., Deng, J., Qin, J., Zhang, Y. and Tian, S., 2018 - Discriminating characters of ore-forming intrusions in the super-large Chalukou porphyry Mo deposit, NE China: in Geoscience Frontiers v.9, pp. 1417-1431. doi.org/10.1016/j.gsf.2018.04.003.
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Li, Z.-Z., Qin, K.-Z., Li, G.-M., Ishihari, S., Jin, L.-Y., Song, G.-X. and Meng, Z.J., 2014 - Formation of the giant Chalukou porphyry Mo deposit in northern Great Xingan Range, NE China: Partial melting of the juvenile lower crust in intra-plate extensional environment: in Lithos v.202-203, pp. 138-156.
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Li, Z.-Z., Qin, K.-Z., Li, G.-M., Jin, L.-Y., Song, G.-X. and Han, R., 2019 - Incursion of meteoric water triggers molybdenite precipitation in porphyry Mo deposits: A case study of the Chalukou giant Mo deposit: in Ore Geology Reviews v.109, pp. 144-162. doi.org/10.1016/j.oregeorev.2019.04.011.
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Liu, J., Mao, J., Wu, G., Wang, F., Luo, D. and Hu, Y., 2014 - Zircon U-Pb and molybdenite Re-Os dating of the Chalukou porphyry Mo deposit in the northern Great Xingan Range, China and its geological significance: in J. of Asian Earth Sciences v.79, pp. 696-709. doi.org/10.1016/j.jseaes.2013.06.020.
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Shu, Q. and Chiaradia, M., 2021 - Mesozoic Mo Mineralization In Northeastern China Did Not Require Regional-Scale Pre-Enrichment: in Econ. Geol. v.116, pp. 1227-1237.
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Xiong, S., He, M., Yao, S., Cui, Y., Shi, G., Ding, Z. and Hu, X., 2015 - Fluid evolution of the Chalukou giant Mo deposit in the northern Great Xingan Range, NE China: in Geological Journal v.50, pp. 720-738. doi:10.1002/gj.2588.
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Zhang, C. and Li, N., 2016 - Geochronology and zircon Hf isotope geochemistry of granites in the giant Chalukou Mo deposit, NE China: Implications for tectonic setting: in Ore Geology Reviews v.81, Part 2, pp. 780-793. doi.org/10.1016/j.oregeorev.2016.05.003.
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Zhao, Q., Zhai, D., Mathur, R., Liu, J., Selby, D. and Williams-Jones, A.E., 2021 - The Giant Chalukou Porphyry Mo Deposit, Northeast China: The Product of a Short-Lived, High Flux Mineralizing Event: in Econ. Geol. v.116, pp.1209-1225. doi:10.5382/econgeo.4818.
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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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