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Jinchang |
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Heilongjiang, China |
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Au Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Jinchang gold district is located ~30 km NW of Dongning, 425 km SE of Harbin and ~1200 km NE of Beijing in eastern Heilongjiang Province, NE China, ~20 km west of the Russian border.
(#Location: 44° 15' 27"N, 130° 48' 38"E).
The district is located in the northeastern part of the larger Yanbian-Dongning gold belt, which is well-endowed with epithermal and porphyry gold deposits. The Jinchang district comprises a cluster of deposits and mineralised occurrences distributed over an east-west elongated, ~5 x 2 km corridor, occurring as i). veinlet stockworks in pervasive hydrothermally altered (potassic, phyllic and propylitic) Mesozoic granitoids; ii). quartz-sulphide (mainly pyrite, chalcopyrite, pyrrhotite, galena and sphalerite) veins hosted by ring and radial faults; and iii). breccia pipes developed along major faults, mainly at cross-fault intersections.
Fluid-inclusion data from different orebodies within the cluster (Yu et al., 2017), suggest these styles originated from different levels of a major multiphase hydrothermal event (Cai et al., 2019) that included i). an early porphyry-style mineralisation inferred by high formation temperatures and high salinities (700 to 200°C; 0 to 70% NaCl) of veinlet style mineralisation in broad zones of alteration (Jia et al., 2005; Zhang et al., 2006, 2008); and ii). overprinting epithermal-style, based on the relatively low temperatures of formation and the low CO2 content of magmatic-hydrothermal auriferous quartz-sulphide veins (Zhu et al., 2003).
Regional Setting
The Jinchang gold district is located towards the easternmost extremity of the exposed Neoproterozoic and Phanerozoic Central Asian Orogenic Belt (Wu et al., 2011).
For detail of the regional setting of this part of the Central Asian and Palaeo-Pacific orogenic belts see the separate Manchuria Overview record that will be available soon.
Geology and Structure
Severe metamorphism and deformation in the region, particularly faulting, has made it difficult to define a stratigraphic sequence. The stratigraphy of the region surrounding Jinchang comprises a Neoproterozoic metamorphic basement of phyllite to granulite and marble overlain by Carboniferous to Permian successions. The Carboniferous comprises metaclastic/volcanic rocks, including, garnet-bearing two-mica schist and metasandstones, whilst the Permian sequence is mainly composed of terrestrial clastic and volcanic rocks, including siltstones-sandstones and basaltic-andesites (Zhao, 2013; Ma, 2014; Cai, 2017). Mesozoic volcano-sedimentary rocks are widespread, segmented by regional NE-trending faults, and include intermediate to felsic volcanic/pyroclastic/tuffaceous and volcaniclastic sedimentary rocks (Men, 2011). These are overlain by predominantly Tertiary vesicular olivine basalts and by minor Quaternary sediments (Xu, 2009). Four phases of multipulse Phanerozoic magmatism are recognised, two related to closure of the Palaeo-Tethys Ocean and two to Palaeo-Pacific subduction, namely: i). ~266 to 240 Ma in the Late Permian to Early Triassic; ii). ~229 to 213 Ma, in the Late Triassic; iii). ~206 to 168 Ma in the Early to Middle Jurassic; and iv). ~135 to 104 Ma in the Early Cretaceous. Intrusive rocks of the latter suite include predominantly diorite, tonalite, granodiorite, monzogranite and syenogranite (Wu et al., 2011; Xu et al., 2013; Ren et al. 2016), which in particular, appear to be both temporally and spatially related to the regional porphyry-epithermal Au-(Ag) mineralisation that occurred between 128 and 97 Ma.
The Jinchang district occurs at the boundary between the Laoheishan Depression/Graben and Taipingling Uplift/Horst which are to the SE and NW respectively and are separated by the NNE trending transcurrent Suiyang Fault. The Laoheishan Depression is mainly filled by 217 to 201 Ma (zircon U-Pb; Xu et al., 2009) Triassic volcanosedimentary rocks, predominantly the dacitic to rhyolitic lavas and tuffs of the 217 to 208 Ma (zircon U-Pb; Zhao, 2013; Xu et al., 2009) Luoquanzhan Group of Cai et al. (2019) (or Tuntianying Group of Li et al., 2019). The Taipingling uplift is mostly composed of Mesozoic granitoids and minor Mesozoic to Cenozoic volcanosedimentary rocks (e.g., Wu et al., 2005, 2011; Xu et al., 2009; Zhang et al., 2004; Zhou et al., 2010).
Palaeozoic strata of the Huangsong Group are widely distributed in the region, both in the basement of the Laoheishan Depression and in the Taipingling Uplift, often occurring as screens between undeformed Mesozoic granitoids. They are mostly composed of mica schist, gneiss, amphibolite and marble, derived from clastic protoliths with intercalated calc-alkaline volcanic rocks.
Multiphase intrusive rocks are extensive within and surrounding the district, and include: i). Late Triassic fine-grained tonalite and pyroxene diorite stocks (Ma, 2014); ii). Early Jurassic, ~206 to 185 Ma granodiorites, monzogranites and syenogranites that are the principal hosts to Au (-Cu) mineralisation (zircon U-Pb; Lu et al., 2009; Ma, 2014; Han et al., 2017); and iii). Early Cretaceous, ~129 to 118 Ma diorite, ~114 to 110 Ma granite porphyry dykes, as well as monzonite and granodiorite, that intrude both Late Triassic and Early Jurassic granitoids (Qian et al., 2012; Zhao et al., 2012; Zhang et al., 2013; Lu et al., 2009; Ma, 2014; Han et al., 2017). The bulk of granitoids contain both hornblende and biotite as major mafic minerals, interpreted to indicate they are I-type granitoids (Wu et al., 2002).
Major structures within the district include NE trending transpressive, and cross-cutting NW-striking faults, the intersections of which are intensely brecciated. In addition, concentric ring and radial faults are also developed, many of which controlled the distribution of vein-type mineralisation.
The oldest intrusion in the immediate district is a large 209±1.4 Ma Late Triassic diorite stock (U-Pb; Zhao, 2013) in the middle of the deposit. A separate 202.1±3.0 Ma Later Triassic graphic granite stock (U-Pb; Lu et al., 2009) is located in the northern part of the district. A 192.1±5.8 Ma Early Jurassic granite stock (U-Pb; Zhang et al., 2007) is the largest intrusion and occurs in the southern part of the district. In addition, 127.9±2.6 Ma diorite porphyry (U-Pb; Xu, 2009) and 109±2.4 Ma granite porphyry dykes (U-Pb; Han 2010) are scattered throughout the district. A concealed 106.8±2.0 Ma granodiorite stock (U-Pb; Wang 2018) occurs at depth in the core of the ring and radial fractures structural complex in the eastern half of the district.
Mineralisation
Mineralization within the Jinchang gold district occurs in breccia pipes, ring, radial and linear faults, and in stockworks hosted by altered Mesozoic granitoids. Mineralisation in the western part of the district includes Au-Cu ores, the bulk of which is within the J0 crypto-explosive breccia pipe with grades of 11.34 g/t Au, 1.44% Cu), accounting for 5% of the known gold resources at Jinchang. In the remainder of the district, crypto-explosive breccia pipes, stockwork/disseminations and veins contain Au-only mineralisation (Cai, et al., 2019).
The J0 crypto-explosive breccia pipe is developed at the intersection of east-west and NW-SE (~320°) striking fault systems mostly at the contact between Late Triassic diorite and Early Jurassic monzogranite granites, but extending down into the interior of the diorite. It has NW-SE elongated plan dimensions of ~45 x 40 m, forming an extended cylindrical body plunging at 80 to 85°E. It is atypical of the breccia pipe mineralisation in the district, representing a transition between breccia pipe and wall rock alteration mineralisation. The J0 breccia pipe is composed of subangular monzogranite and diorite clasts closer to surface, but gradually changes with depth to angular monzonite clasts. At depth, mineralisation takes the form of disseminated molybdenite, pyrite and chalcopyrite in monzonite at the bottom of the pipe, whilst quartz-chalcopyrite-pyrite stockwork mineralisation on the pipe margin. The main breccia is cemented by ore and gangue minerals. The metallic minerals mainly comprise chalcopyrite and pyrite, with minor molybdenite and magnetite, with a gangue of quartz, K feldspar, epidote, chlorite and carbonate. The alteration is extensive and comprises K feldspar, epidote and chlorite in the
breccia pipe, and chlorite and carbonate with minor silica in the wall rocks (Cai, et al., 2019). Six molybdenite samples from this breccia yielded similar model ages of 113.0 to 113.6 Ma, and a well-fitting and consistent isochron age of 114.0±3.0 Ma is taken to reflect the timing of the Au-Cu mineralisation. This age is coeval (within error) with the concealed Cretaceous monzonite found at depth within the deposit (Cai, et al., 2019).
The Other crypto-explosive breccia pipes in the central and eastern parts of the district account for a further 36% of the gold resources, occurring in more than 8 separate pipes (Yu et al., 2017; Zhao, 2013). The J1 pipe, which is representative of these, is developed within an Early Jurassic monzogranite, at the intersections of NE-SW (45°) and NW-SE (163°) striking fault sets. This pipe has an NE-SW (70°) elongated elliptical shape in plan with dimensions of 40 to 50 x ∼30 m. In three dimensions it has a cylindrical shape, plunging at 82° with an azimuth of 160°, containing an orebody that averages 8.1 g/t Au and extends for ~540 m down plunge with a thickness averaging !21 m. The breccia pipe has a sharp contact with the surrounding wall-rocks and is composed of sub-angular to rounded clasts that vary from centimetre-scale to a few metres across (averaging 0.1 to 0.5 m) of poorly sorted monzogranite, supported by a matrix of mainly sulphide minerals and hydrothermal alteration gangue minerals. Sulphide minerals include mainly auriferous pyrite with trace chalcopyrite and galena, occurring as dissemination, patches and veins. Gangue minerals, which mostly occur in the breccia matrix, include quartz, sericite and chlorite, and minor carbonate. A zoned alteration halo extends for several tens of metres laterally outward in the surrounding monzogranite, comprises and inner potassic or silicic-sericite (phyllic) selvage proximal to the orebody, surrounded and locally overprinted by more distal kaolinite-sericite/argillic, and surrounded by an outermost chlorite/propylitic zone (Chen, et al., 2000; Yu et al., 2017; Cai, et al., 2019). Fluid inclusion trapped in gold ores from these breccias yields a wide range of medium to high temperatures of 500 to 200°C and salinities (0 to 70%NaCl (Jia et al., 2005; Men et al., 2008; Wang et al., 2011). The bulk of the production from Jinchang has been from crypto-explosive breccia pipes. Auriferous pyrite Re-Os ages from the J1 breccia pipe yielded ages of 103±3 Ma (Cai, et al., 2019).
Vein-type Au mineralisation is responsible for ~39% of the gold resources (Yu et al., 2017), occurring as auriferous quartz-pyrite veins cutting the Late Triassic diorite and Early Jurassic monzonitic granite. It is hosted in the concentric ring, radial, and east-west striking faults. The ring complex has a diameter of ~1 km, with an outward dip of 40 to 50°. The radial faults are near vertical and perpendicular to the ring faults around the structure, varying from 130 to 220 m, but up to 780 m in length and ~1 m in thickness. The largest, the No. II vein cluster, which are representative of this mineralisation, are controlled by the NW-SE striking southwestern section of the ring faults. The cluster includes at least six ore veins which have average grades of 5.05, 2.11, 13.26, 9.00, 3.14 and 6.14 g/t Au respectively. The trends of the individual veins vary from NW-SE (136 to 160°) to east-west, and dip outward at 45 to 58°. Together they have a length of ~1600 m, are individually 0.2 to 1.4 m thick, and are developed to a depth of ~400 m down dip. The gold-bearing veins of this cluster locally cut the J1 breccia. Ore minerals are predominantly pyrite with minor galena, whilst the gangue minerals include quartz, carbonates, K feldspar and minor sericite. Extensive alteration in the diorite and monzogranite is zoned horizontally and comprises silica, sericite and K feldspar with increasing distance from the veins (Chen et al., 2000; Yu et al., 2017; Cai, et al., 2019). These ores had not been mined in 2013 (Zhang et al., 2013). Auriferous pyrite Re-Os ages from the No. XII radial vein yielded ages of 101±3 Ma (Cai, et al., 2019).
Disseminated (or 'Alteration-type') Au mineralisation accounts for ~20% of the gold resources in the district (Yu et al., 2017). These orebodies are characterised by veinlets and stockworks within hydrothermally altered rocks and are mainly found at depth below the ring fault complex that dominates the eastern half of the district. They are concentrated in a granodiorite porphyry plug and intensely altered dioritic and granitic wall rocks in the underlying core of the outward dipping ring fault complex. A representative example of this style is the underground No. 18 cluster of at least 4 orebodies which have respective grades of 15.79, 4.19, 3.17 and 3.46 g/t Au. These bodies are mainly hosted by Late Triassic diorites and Early Jurassic monzogranites. Individual orebodies have strike lengths of up to 800 m by up to 6.65 m in thickness, averaging 0.83 m (Yu et al., 2017). These higher grade zones enveloped by a gold mineralised halo that may be 30 to >100 m wide with various grades of >0.5 g/t Au (Zhang et al., 2013). They strike at ~140° and dip at ~47°SW, persisting to depths of 160 to 490 m (Cai, et al., 2019). Other 'alteration type' zones are recorded as having strikes that vary from west to east from 165 to 160° and corresponding dips from 64 to 56°. Extensive associated pervasive alteration within the porphyry, diorite and monzogranite is dominated by K feldspar overprinted by silica lower in the system and then upwards by sericite, with propylitic assemblages towards the periphery and top (Li et al., 2009). Sulphide minerals are dominantly pyrite with rare chalcopyrite, minor sphalerite, galena, pyrrhotite, arsenopyrite, molybdenite, stibnite, magnetite, specularite, native gold and electrum. These sulphides occur as veinlets and disseminations, mainly in the sericite alteration zone. Gangue minerals include quartz, sericite, K feldspar, chlorite and epidote, as well as minor kaolinite, biotite, chlorite, calcite, epidote and adularia. These ores had not been mined in 2013 (Zhang et al., 2013). Auriferous pyrite Re-Os ages from the No. 18 vein cluster yielded ages of 102±3 Ma (Cai, et al., 2019).
Paragenetic studies indicate the gold mineralisation in the Jinchang district can be divided into five hydrothermal stages (Zhang et al., 2013): i). quartz-chalcopyrite; ii). quartz-sericite-pyrite; iii). pyrite-quartz; iv). quartz-polymetallic
sulphide; and v). pyrite-calcite stages.
Yu et al. (2017) and Cai, et al. (2019) conclude that the deposits of the Jinchang gold district formed as a result of the superposition
of epithermal gold mineralisation on an earlier low grade porphyry gold system. Cai, et al. (2019) suggest the Jinchang gold-rich porphyry/epithermal deposit has experienced two mineralisation phases: i). an early Au-Cu 'porphyry-style' phase at ∼113 Ma that was spatially and temporally related to a 115±3 Ma Cretaceous monzonite, and ii). a late Au-only epithermal phase at ~103 to 101 Ma which was likely related to the 107±2 Ma concealed Cretaceous granodiorite porphyry. Both the monzonite and granodiorite porphyry are metaluminous and I-type. Their geochemical features, include LREE- and LILE-enrichment, and P, HREE- and HFSE-depletions, and negative Nb-Ta anomalies (Cai, et al., 2019).
Resources and Production
Production from Jinchang to 2013 amounted to 40 t of gold @ an average grade of 8 g/t Au, which would equate to an ore tonnage of 5 Mt (Zhang et al., 2013). Cai, et al. (2019) quote a resource of 76 t of Au @ 11.28 g/t Au for the high grade ores, which would equate with an ore tonnage of 6.75 Mt. Shi et al., 2018 reports an endowment of >80 t of contained gold.
The most recent source geological information used to prepare this decription was dated: 2019.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Jinchang (centre of system)
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Cai, W.-Y., Wang, Z.-G., Li, J., Fu, L.J., Wang, K.-Y., Konare, Y. and Li, S.-D., 2019 - Zircon U-Pb and molybdenite Re-Os geochronology and geochemistry of Jinchang porphyry gold-copper deposit, NE China: Two-phase mineralization and the tectonic setting: in Ore Geology Reviews v.107, pp. 735-753
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Li, S., Zhang, X. and Gao, L., 2019 - Ore Genesis at the Jinchang Gold-Copper Deposit in Heilongjiang Province, Northeastern China: Evidence from Geology, Fluid Inclusions, and H-O-S Isotopes: in Minerals v.9, 24p. doi:10.3390/min9020099.
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Shi, K., Wang, K., Yu, H., Wang, Z., Ma, X., Bai, X. and Wang, R., 2018 - The 40Ar/39Ar dating of quartz: new insights into the metallogenic chronology of the Jinchang gold deposit and its geological significance: in Scientific Reports, v.8:13879, 8p. DOI:10.1038/s41598-018-32242-3.
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Yu, B., Zeng, Q., Wang, Y., He, H. and Su, F., 2017 - The Sources of Ore-forming Fluids from the Jinchang Gold Deposit, Heilongjiang Province, NE China: Constraints from the He-Ar Isotopic Evidence: in Resource Geology v.67, pp. 330-340.
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Zhang, H.-F., Li, S.-R., Santosh, M., Liu, J.-J., DiWu, C.-R. and Zhang, H., 2013 - Magmatism and metallogeny associated with mantle upwelling: Zircon U-Pb and Lu-Hf constraints from the gold-mineralized Jinchang granite, NE China: in Ore Geology Reviews v.54, pp. 138-156.
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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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