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Makeng-Yangshan Skarn Fe Belt - Makeng, Dapai, Luoyang, Yangshan |
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Fujian, China |
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Fe Zn Pb Mo Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Makeng-Yangshan Skarn Fe Belt (or Southwest Fujian Iron Polymetallic Metallogenic Belt) covers a NE-SW elongated area of ~180 x 120 km in the southeastern Cathaysia Block in Fujian Province, China. It is defined by abundant iron ore deposits and occurrences, with or without significant Pb-Zn and Mo mineralisation, that include Makeng, Dapai, Luoyang, Yangshan, Pantian, Tangquan, and Zhongjia.
(#Location: Makeng - 25° 0' 14"N, 117° 4' 55"E).
Regional Setting
The Cathaysia Block is the southeastern half of the greater South China Block, which also includes the major Yangtze Craton to the NW, to which it was accreted at ~825 to 805 Ma in the Neoproterozoic. These two domains are separated by the ophiolite-bearing Neoproterozoic Jiangnan Fold Belt, which represents the Qinghang suture zone (Li and Zhao, 2020). Metamorphosed bimodal volcanic rocks within Fujian Province imply the Cathaysia Block underwent rifting between 800 and 750 Ma, contemporaneous with a wider rift-related magmatic event that extended over the majority of southern China (Zhang and Zuo, 2014). The South China Block was subsequently subjected to an early Palaeozoic Caledonian orogeny, forming pre-Devonian metamorphic sequences, before undergoing late Palaeozoic intracontinental extension between 405 and 270 Ma with associated deposition of submarine sedimentary sequences. The Mesozoic tectono-magmatic evolution of the South China Block is interpreted to be the result of the transition from tectonism dominated by Permian to Middle Triassic Palaeo-Tethyan activity along the southwestern margin of the block, to a regime associated with subduction between the Palaeo-Pacific Plate and the southeastern margin of the South China Block. This transition culminated in the northwest directed subduction of the Pacific Plate below the southeastern margin of the Cathaysia Block, initiated in the Late Triassic, and continued into the Cenozoic, punctuated by alternating periods of compressional advance, and roll-back induced extension (Jiang et al., 2015). The consequent development of the circum-Pacific metallogenic domains within it have included large-scale Cu, Mo, Fe, Au, Ag, Pb and Zn mineralisation. Major deposits in SE Fujian include the Zijinshan copper-gold and Makeng iron deposits. The Cathaysia Block is, in turn, subdivided into the eastern and western Cathaysia blocks by the major NE-SW trending Zhenghe-Dapu Fault. These two blocks have differing intra-crustal structures, petrochronology features and metallogenic characters (Zhang et al., 2021). The Zhenghe-Dapu Fault is more or less half way between the Jiangnan Fold Belt/Suture and the Pacific coast.
District Setting
The Makeng-Yangshan Skarn Fe Belt straddles the NE-SW trending Zhenghe-Dapu Fault within the southeastern Cathaysia Block. As such, the belt is located on the northwestern margin of the Palaeo-Pacific tectonic and metallogenic domain. The iron polymetallic ores of the belt are controlled by this regional trend, both in location and form, with a marked NE-trending distribution.
The regional stratigraphy in the southeastern Cathaysia Block comprises three main stratigraphic groupings: i). pre-Devonian rocks, mostly pre-Sinian and Sinian (i.e., 800 to 570 Ma) basement rocks; ii). Late Palaeozoic to middle Triassic clastic sedimentary and cap carbonate strata, and; iii). Late Mesozoic continental clastic and volcanic rocks (Wang et al., 2017; Zheng and Mao, 2023). Of these packages, the Early Carboniferous siliceous clastic rocks and Late Carboniferous to middle Permian limestones are the main hosts to the iron polymetallic deposits.
These volcano-sedimentary successions are intruded by extensive Mesozoic plutonic rocks, mainly I-type granitoids, dated between 145 and 86 Ma (zircon U-Pb). Based on their geochemical compositions, these granitoids are sub-divided into: i). 145 to 137 Ma granitoids with characteristics interpreted to indicate they were formed by partial melting of thickened continental crust of up to ~ 40 km, under a compressional regime, without obvious mantle involvement; and ii). 136 to 86 Ma granitoids with geochemical markers suggesting they were formed by partial melting of thinned continental crust of ~30 to 40 km, with obvious mantle involvement under an extensional environment.
The iron ores of the Makeng-style skarn altered iron polymetallic deposits are accompanied by Mo-, Pb- and Zn-mineralisation. However, whilst the molybdenite was emplaced between 135 and 130 Ma (Zhang et al., 2018; Zhang et al., 2012), unlike the magnetite, it is only found within the granite bodies and in the fracture surface cutting both wall rocks and ron ores, with no direct evidence to suggest the molybdenite and magnetite are contemporaneous (Wang et al., 2023). However, Wang et al. (2023) report nine U-Pb dates of garnet skarn samples from these deposits suggesting the Makeng-style iron
polymetallic deposits mainly formed during 137 and 130 Ma, which is consistent with the zircon U-Pb and molybdenite Re-Os ages.
Makeng Deposit
The Makeng deposit has been the largest exploited magnetite skarn deposit in Southern China. The principal strata exposed in the deposit area are Carboniferous to Permian limestone and sandstone, and Permian shale. The 133 to 125 Ma (U-Pb zircon; Zhang 2012) Juzhou granite intrudes the Carboniferous to Permian strata immediately below the magnetite bodies. Several dolerite dykes dated at ~303 Ma or ~64 Ma also intrude the sequence (Zhang 2012).
The main iron orebodies and skarn alteration at Makeng are hosted by the Carboniferous to Permian limestone and sandstone, whilst minor mineralisation and skarn alteration is also spatially associated with the dolerite dykes. The deposit comprises the main Fe orebody, which comprises the bulk of the resource, and some relatively small-scale magnetite-skarn lenses, and is now mined underground at depths of from 80 to 600 m below the surface with ore grades ranging from 28 to 45% Fe. The main Fe orebody dips at ~30 to 45°NW and has has a length of ~3800 m and is generally 20 to 50 m, but is locally up to 200 m thick, whilst the smaller satellite lenses are tens of metres in length and <10 m thick. The main orebody has a marked variation in dimensions in different locations due to the control of folds and faults (Zheng and Mao, 2023; Wang et al., 2023).
The main ore mineralisation was formed at the contact zone between Early Carboniferous clastic rocks and the Late Carboniferous to Middle Permian carbonate sequence. Magnetite is the major metal-bearing mineral, with lesser hematite, pyrite, molybdenite and sphalerite. As indicated above, molybdenite appears to be a late mineral, filling fractures in wall rocks and cutting iron ores as veins and scattered enclaves of various shapes. The Fe ores are both massive and disseminated and are mainly composed of magnetite, garnet and pyroxene. Magnetite veining is also often present within the mineralised bodies, and is always accompanied by skarn minerals. Other minerals in the Fe ores include chlorite, amphibole, epidote and fluorite. Garnet and diopside are the primary gangue minerals within the magnetite ore, with the garnet being dark reddish brown, typical of andradite. The iron minerals mainly exhibit a semi-euhedral to euhedral, medium to coarse granular texture, with lesser metasomatic texture. More than 70% of the magnetite ore within the Makeng deposit has a dense massive structure. However, despite its extensive dimensions, and the wide variety of skarn minerals, there is no obvious zonation of skarn observed within the mine (Zheng and Mao, 2023; Wang et al., 2023).
Garnet from two Fe skarn ore samples in the Makeng deposit yielded two U-Pb ages of 132.9 ±0.9 and 131.4 ±1.2 Ma (Zheng and Mao, 2023).
The Makeng deposit is estimated to have comprised an original resource of 430 Mt @ 41.60% Fe. In addition to the Fe ores, Makeng also contains a separate resource of 80 Kt of Mo ore (quoted by Zheng and Mao, 2023 after Zhang, 2012).
The information in this summary was drawn from Zheng and Mao, 2023 and Wang et al., 2023
Dapai Deposit
The Dapai deposit in Yongding County is located ~15 km southwest of the Makeng Deposit. The surrounding stratigraphic sequence is dominated by carbonate rocks of the middle Carboniferous Jingshe, upper Carboniferous Chuanshan and lower Permian Qixia formations, and by clastic rocks of the Wenbishan and Tongziyan formations. Both the geology and mineralisation of the deposit have been affected by a suite of NE-SW trending thrusts and NW-SE-trending detachment faults. Whilst magmatic rocks are not extensively exposed, significant intrusive bodies are present at depth. These predominantly comprise 127.0 ±1.8 Ma granodiorite porphyry, monzogranite and granodiorite (Zhao et al., 2016). The granodiorite porphyry is grey, and contains generally 1 to 3 mm phenocrysts that make up ~42 vol.% of the intrusion. These phenocrysts are ~20 vol.% plagioclase, ~9 vol.% K feldspar, ~5 vol.% quartz and ~8 vol.% biotite, and are set in a fine-grained, generally 0.1 to 0.4 mm groundmass, composed of a 55 vol.% quartz-feldspar-amphibole assemblage, with accessory apatite, titanite, magnetite, fluorite and zircon. The plagioclase and K feldspar are weakly or locally altered to sericite, whilst biotite is generally altered into chlorite and pyrite. The monzogranite is light pink and fine to medium grained, composed of variable, but generally ~35 vol.% K feldspar, ~30 vol.% plagioclase, ~30 vol.% quartz, ~3 vol.% biotite and ~2 vol.% muscovite, commonly with accessory apatite, tourmaline, zircon and rutile. The plagioclase of the monzogranite is generally altered to chlorite, epidote and sericite, whilst K feldspar is locally converted to sericite.
Some 34 polymetallic orebodies have been delineated within the Dapai deposit (Ni, 2011), most of which are hosted by Carboniferous to Permian carbonate rocks, although some minor ore mineralisation is hosted in mudstone of the Wenbishan Formation. The dominant ore minerals in the deposit are magnetite, sphalerite, galena, chalcopyrite and molybdenite, which are generally vertically zonation from lower Fe + Mo → middle Pb-Zn-Cu + Mo → upper Pb-Zn.
The Pb-Zn-Cu mineralisation generally occurs at depths of 100 to 400 m below the surface as stratabound galena-sphalerite-chalcopyrite orebodies within the carbonate sequence. This mineralisation occurs within subordinate fractures that dip at between 5 and 35°, and are associated with NE-SW trending faults F1 and F4 in the western part of the deposit. The main hydrothermal alteration associated with the Pb-Zn-Cu mineralisation is silicification and marble development.
The Fe mineralisation is also generally stratabound, associated with epidote-actinolite-tremolite skarn alteration, occurring as endo- and exo-skarn along the contact zone between granodiorite porphyry and the surrounding carbonate rocks, locally overprinting the stratabound Pb-Zn-Cu mineralisation. The Fe-mineralised endoskarn has a relatively high ratio of garnet:pyroxene compared to the un-mineralised granodiorite porphyry and wall rocks, and is zoned successively outward from fresh granodiorite porphyry → a garnet-pyroxene assemblage → the stratabound Fe-mineralised pyroxene-epidote assemblage → the Fe-mineralised actinolite-tremolite-chlorite assemblage → the surrounding carbonate rocks.
The Mo mineralisation is predominantly hosted by monzogranite, but locally extends outward into the surrounding rocks along faults or subordinate structures for hundreds of metres from the intrusive contact zone. Spatially, the Mo mineralisation is closely associated with propylitic alteration, mainly epidote and chlorite. Some proximal vein-disseminated Mo has also overprinted the Fe mineralised skarn.
Seven stages of mineralisation have been differentiated at the Dapai deposit, as follows:
i). Stratabound Pb-Zn-Cu mineralisation, - comprising banded, stratabound, galena-sphalerite-chalcopyrite-pyrite-pyrrhotite-chlorite-quartz aggregates that are interbedded with marble after carbonate protoliths. Calcite grains generally fill fissures within the Pb-Zn-Cu mineralisation. The minerals of these orebodies have been subjected to shear deformation and in some cases have occur as breccia. A substantial amount of the minerals formed during this stage have been overprinted or cross-cut by skarn alteration assemblages and magnetite of later stages, e.g., chalcopyrite is locally altered to bornite, and the fragmented assemblage is cross-cut or superposed by magnetite. Similarly, sphalerite is locally overprinted by diffuse tremolite-actinolite assemblages and occurs as small chains of isolated remnant grains. A pyrite and sphalerite Rb-Sr isochron age of 175.5 ±3.3 Ma represents the mineralisation age of the Pb–Zn–Cu deposit, supported by the ~184 Ma age of six inherited zircons from the ore-related granodiorite porphyry (Vatuva et al. 2023). The same authors present an argument and supporting data that suggest the Pb-Zn-Cu mineralisation was emplaced between 185 and 160 Ma, from ore-forming fluids related to mainly crust-derived granitic melts with the addition of a minor mantle component, and the pene-contemporaneous Mo was derived mostly from a mixed crustal-mantle source.
ii). Prograde skarn, - which marginally pre-dates the main Fe mineralising stage, and is represented by anhydrous skarn minerals, mainly garnet and pyroxene. These garnet-pyroxene skarn zones are generally situated along the contact between granodiorite porphyry and surrounding carbonate rocks, occurring as endoskarns. Garnet is generally red to brown in color, 0.5-3 mm in size, and subhedral-euhedral (Fig. 5f-h) and is locally anisotropic with oscillatory zoning. Pyroxene is usually light greyish green and 0.2 to 1.5 mm across, and typically overprints garnet.
iii). Retrograde skarn and Fe mineralisation, - represented by an epidote-actinolite-tremolite-chlorite-magnetite assemblage that overprints, cross-cuts, or infills fissures within the anhydrous skarn. This retrograde skarn stage produced a large amount of the magnetite of the Dapai deposit. Massive and veined magnetite aggregates typically occur in the proximal cupolas of the Fe-mineralised granodiorite porphyry, whilst disseminated and veinlet-disseminated magnetite aggregates generally cross-cut both older Pb-Zn-Cu mineralisation and skarns distal to the granodiorite porphyry contact. Granodiorite porphyry from the Dapai deposit yields a weighted mean 206Pb/238U age of 146.6 ±2.3 Ma, which represents the time of Fe mineralisation (Vatuva et al. 2023). The same authors present an argument and supporting data that suggest the Fe-Mo mineralisation was emplaced between 150 and 140 Ma by a porphyry–skarn system, and the ore-forming fluids were supplied by intermediate to felsic melts that were derived from a mixed crust–mantle source.
iv). Quartz-sulphide-sulphate formation, - as quartz-sulphide-anhydrite veins that generally cut or infill fissures in the preceding skarns assemblages.
v). Calcite formation - during the waning stages of skarn-forming hydrothermal activity, occurring as veined aggregates of calcite, generally cross-cutting earlier skarn alteration assemblages.
vi). Propylitic alteration, which pre-dates Mo mineralisation, and is represented by the formation of a large amount of hydrosilicate minerals, such as epidote and chlorite, especially within monzogranite and toward the marble replacement front; and
vii). Quartz-molybdenite mineralisation - occurring as veins that generally cut propylitic-altered monzogranite or extend outward to overprint the banded Pb-Zn-Cu mineralisation and Fe-mineralised skarn. Fibrous molybdenite aggregates generally infill fissures within early-formed rocks. Re-Os molybdenite dating analyses suggest that the main Mo orebodies formed at 130 to 135 Ma and are genetically related to coeval porphyry-skarn Mo systems, which have produced economically important Mo orebodies elsewhere in the region and involved a dominantly mixed crust-mantle source (Vatuva et al. 2023).
The Dapai Fe polymetallic deposit contains a reserve of (after Vatuva et al. 2023 quoting Ni, 2011):
4.71 Mt of contained Fe with an average grade of >35% Fe (equating to 13.5 Mt of ore);
1.1 Mt of Pb + Zn with at average combined grade of 4.89% Pb + Zn (equating to 22.5 Mt of ore);
2.10 Kt of Mo with an average grade of 0.297% (equating to 0.707 Mt of ore);
24.00 Kt of Cu with an average grade of 0.18% (equating to 13.5 Mt of ore).
The information in this summary was drawn from Vatuva et al., 2023.
Luoyang Deposit
The Luoyang deposit lies within the central section of the Makeng-Yangshan Fe skarn metallogenic belt, adjacent to the regional Zhenghe-Dapu fault, and is ~50 km NE of Makeng. The deposit is hosted within a sequence that includes Carboniferous to Permian limestone, Permian sandstone and shale and Jurassic tuff, with ~131 Ma (U-Pb zircon; Zhang et al., 2012) granite being the main intrusive rock (Zheng and Mao, 2023; Wang et al., 2023).
The principal orebodies and skarn alteration are hosted by the Carboniferous to Permian limestone, Permian sandstone, and are spatially associated with the granite. The deposit has been sub-divided into the north and south domains, with the southern accounting for >70% of the known resource. Most of the iron orebodies range from 266 to 400 m in length, and are from several to near 48 m thick, composed of massive and disseminated mineralisation, mostly magnetite with a garnet and pyroxene gangue. Other minerals include pyrite, hematite, actinolite, tremolite, and chlorite (Zheng and Mao, 2023; Wang et al., 2023).
Garnet from the Luoyang Fe skarn deposit yielded ages of 130.7 ±0.7 and 131.8 ±1.4 Ma (Zheng and Mao, 2023).
The Luoyang deposit is estimated to have comprised an original resource of 14.4 Mt @ 42.44% Fe Total plus minor Mo and Zn resources (quoted by Zheng and Mao, 2023).
The information in this summary was drawn from Zheng and Mao, 2023.
Yangshan Deposit
The Yangshan skarn altered iron deposit is located ~40 km northeast of Luoyang. The host stratigraphy comprises Carboniferous to Permian limestone and Permian sandstone, and granite is the principal intrusive rock. The known resource is distributed over 44 separate orebodies, the largest of which is No. 37, with a strike length of ~1000 m, average thickness of 2 m and average grade of 41.29% Fe.
The iron mineralisation and skarn alteration are mainly located within or near the Carboniferous to Permian limestone. The ore grade mineralisation is both massive and disseminated, and is locally banded, mainly composed of magnetite, hematite, garnet and pyroxene. Other minerals include pyrite, ilvaite and fluorite.
Garnet from two Fe skarn ore samples in the Yangshan deposit yielded two U-Pb ages of 130.0 ±1.2 and 132.8 ±0.9 Ma (Zheng and Mao, 2023).
The Yangshan deposit is estimated to have comprised an original resource of 37.1 Mt @ 42.82% Fe Total (quoted by Zheng and Mao, 2023 after Li 2003), but unlike the Makeng and Luoyang deposits, no associated economic Mo mineralisation has been recognised.
The information in this summary was drawn from Zheng and Mao, 2023,
The most recent source geological information used to prepare this decription was dated: 2023.
This description is a summary from published sources, the chief of which are listed below.
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Makeng
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Selected References:
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Vatuva, A.,He, X., Zhang, X., Zhang, D., Feng, H., Yuan, Y., Wang, S., Yi, J. and Di, Y., 2023 - Genesis of Makeng-type Fe-polymetallic deposits in SE China: New constraints by geochronological and isotopic data from the Dapai-Makeng metallogenic system: in Geoscience Frontiers v.14, 24p. doi.org/10.1016/j.gsf.2023.101614.
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Wang, S., Cao, K., Zhang, D., Yi, J.-J., Hu, B.-J., Yang, J., Cai, M.-Y., Zhang, Y.-Y., Yuan, Y. and Pan, T.-W., 2023 - Mineralization age and genesis of the makeng-style iron deposits in the Paleo-Pacific tectonic domain of South China: In situ LAICPMS garnet U-Pb chronological and geochemical constraints: in Frontiers in Earth Science, Jan 2023, 22p. doi: 10.3389/feart.2022.1027620
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Zheng, J. and Mao, J., 2023 - Recognition of a ca. 130 Ma Makeng-Yangshan iron skarn belt in the Southeastern China: evidence from garnet in situ U-Pb geochronology: in Mineralium Deposita v.58, pp. 925-937. doi.org/10.1007/s00126-023-01164-0.
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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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