Qinling Gold Province - Yangshan, Liba, Maanqiao, Liziyuan, Shuangwang, Baguamiao, Pangjiahe, Daqiao, Huachanggou, Ludousou
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The Qinling Gold Province in the Qinling Mountains is located to the west of the Xiaoqinling gold province and is in Shaanxi and Gasnsu Provinces, central China. The province includes over 50 gold deposits (excluding placer accumulations) varying from the large Yangshan with a resource of 308 t Au, to small ones with resources of <1 t Au (Chen et al., 2004). It also inludes the Baguamiao, Maanqiao (Ma'naoke), Liziyuan, Shuangwang, Pangjiahe, Daqiao, Ludousou and Liba orogenic deposits and goldfields which together contain >500 t of Au (Zeng et al., 2012).
The ores of the gold province are confined to an ENE trending belt of highly-deformed and regionally metamorphosed Devonian and Carboniferous flysch separating the North China and Yangtze (South China) cratons. This belt of gold deposits extends from near Lixian in Gansu Province to Zhenan in Shaanxi Province, over a length of 600 km x ~200 km wide.
The Qinling Orogen can be divided by three major northerly dipping tectonic zones that are subparallel to the trend of the orogen. These tectonic zones are:
i). Palaeozoic Shangdan Suture to the north that separates the North Qinling Terrane from the South Terrane (Gao et al., 1996). The North Qinling Terrane, which consists of an early Palaeozoic arc that was accreted to the North China Craton at ~450 Ma along the Shangdan Suture (Zhang et al., 2000), hosts minor gold mineralisation (Mao et al., 2002).
ii). the Zhenan-Fengxian (Lixian-Shanyang, Mao et al., 2002) Thrust Zone, which divides the South Qinling Terrane into the central and southern domains. The central domain, which is included by Mei et al., (1999) in the northern zone of the South Qinling Terrane, is dominated by flysch and other clastic rocks that accumulated in a late Palaeozoic basin between the converging cratonic blocks. The southern domain is covered by Palaeozoic strata in the east and characterised by the easternmost exposure of Triassic turbiditic deposits in the west that are partly calcareous and form part of the immense Songpan-Ganzi Basin (Mao et al., 2002). Geographically, the South Qinling Terrane is arbitrarily subdivided into East and West Qinling Domains on either side of the Baoji-Chengdu railway (Zheng et al., 2010).; and
iii). the Mianlue Suture to the south, that forms the margin with the South China/Yangtze craton to the south and the main bulk of the Songpan-Ganzi Basin.
Plutons in the Qinling Orogen, range in age from Palaeozoic to Yanshanian (late Mesozoic) and include monzogranite, granodiorite and quartz diorite. Zhang et al. (2006) recognized two major distinct tectono-magmatic events in the orogen, which are late Ordovician (~450 Ma) and late Triassic (~220 Ma) in age. The late Ordovician granites are spatially constrained to the North Qinling Terrane (Zhang et al., 2000; Lu 2000; Zhang et al., 2002), and the late Triassic granites were emplaced into both the North Qinling Terrane (Wang et al., 2008) and the South Qinling Terrane (Sun et al., 2002). Early Triassic magmatism is also reported just south of the Shangdan Suture (e.g., the Xiahedong pluton, Jin et al., 2005, and Xianggou pluton, Zhu et al., 2009).
The late Ordovician tectono-magmatic event is interpreted to relate to the partial melting of thickened island-arc crust. This took place during the northward subduction of the palaeo-Qinling oceanic plate along the Shangdan Suture between the North Qinling and the South Qinling tectonic units. The late Triassic tectono-magmatic event is interpreted to relate to the break-off of a subducted oceanic plate during the continental collision between the North China and South China cratons (Sun et al., 2002). It is uncertain whether the second event was a post-collisional setting or volcanic arc setting (e.g., Chen et al. 2009).
For a more detailed description of the Qinling Orogen see the Regional Setting section of the Qinling Molybdenum Belt record.
The timing of gold mineralisation in the Qinling Orogen is loosely constrained between 338 and 234 Ma in age at the Pingding deposit (Liu et al., 1994). Mao et al. (2002) suggested that gold mineralisation took place between about 210 to 170 Ma. Chen et al. (2004) proposed a 220 to 100 Ma age with a peak at ~170 Ma. Zhang et al. (2002, 2004) argued the correlation of gold metallogeny with the oblique collision between the North China and South China Cratons during the Jurassic to Early Cretaceous. The large age ranges may be due to multiple events or the dating methods were not conducted precisely or accurately (Zeng et al., 2012).
The larger orebodies are located in the West and East Qinling Domains and the Southern Domain, localised by the intersection of NE and NW structures with the regional east-west to WNW striking fold and shear zones, mostly dipping 50 to 70°W.
Gold occurs in: i). small quartz stockworks and veinlets along major ductile shear zones (eg., Baguamiao); ii). disseminated in wall rocks along brittle fractures in hornfels zones (eg., Liba), iii). in large breccia zones (eg., Shuangwang), iv). in carbonaceous carbonaye rocks (e.g., Yangshan).
The Yangshan gold deposit, Wenxian county, Gansu province, contains 308 t Au with average grade of 4.74 g/t Au. It is a syn-collisional Carlin-like gold deposit, with orebodies controlled by an east-trending shear-zone and hosted in Devonian carbonaceous carbonate-phyllite-slate sequence or granite-porphyry dykes intruding into the Devonian strata. Isotopic ratios from fluid inclusions within quartz separates, suggest that the ore-fluids have been mainly sourced, through metamorphism and/or reworking, from the Devonian strata or/and similar lithologies which comprise carbonaceous phyllite, slate, chert and carbonate, with a significant input of meteoric water. In general, the ore-forming fluid-system varies from early, deep, metamorphic fluid to late, shallow, meteoric water (Chen et al., 2008). For more detail see the separate Yangshan record.
The sedimentary- and granite porphyry-hosted Pangjiahe gold deposit is located in the north belt of the South Qinling Orogen, with a proven reserve of 38 t of contained Au at an average grade of 6.3 g/t. The deposit is located in the NW corner of the Fengxian-Taibai graben basin. Gold mineralisation is predominantly
hosted in the Upper Devonian Dacaotan Formation, which locally comprises euhedral pyrite-bearing phyllite and sandstone. Euhedral, granular pyrite occurs in both altered and unaltered phyllite and sandstones of Dacaotan formation. The host sedimentary rocks were weakly metamorphosed to sub-greenschist facies
during the Triassic orogeny, when a number of approximately east oriented faults with localized shearing and the Pangjiahe anticline were developed. The Pangjiahe anticline (axial plane striking 75 to 85° and dipping <70 to 75°) is the principal structural feature in the mine. Five subsidiary
east-striking strike-slip faults are mapped in the mining area, hosting five gold ore bodies outcropping at surface and a sixth that is not exposed. The mineralised faults predominantly dip to the south with high angle (<65°to near vertical to the north). They range from between 170 and 360 m in length, and are 0.1 to 12.5 m thick. All six ore bodies are hosted by discrete zones of strongly foliated phyllite rocks, suggesting that mineralisation occurred either during or after deformation. Gold mineralisation predominantly occurs in veins of zoned auriferous pyrite and arsenopyrite that are parallel with the phyllite foliation. Pyrite and arsenopyrite within these veins do not show any evidence of deformation (Ma et al., 2018).
The Liushagou granite stock is situated 500 m west of the deposit, with two other intrusive phases recognised in the main deposit area, namely granite porphyry and dolerite dykes. The granite porphyry dykes are predominately in the western part of the deposit. They strike east-west and extend for between 20 and 300 m along strike, with widths of 1 to 10 m, and are normally parallel to the sediment hosted lodes. The granite porphyry dykes have sharp contact with the host rocks and are locally mineralised with up to 4 g/t Au, although this is only a minor component of the ore. The dolerite dykes are predominantly found in the eastern part of the deposit, and also strike east-west with lengths of between 5m and >100 m and widths of <<1 to 3 m. They cross the ore lodes and have sharp contacts and chilled margins (Ma et al., 2018).
Baguamiao, which contains >80 t Au @ 3.5 to 6 g/t Au, is one of the largest orogenic gold deposit in the Qinling Gold Province occurring as a main ore zone of about 1.7 km along strike, 50 to 160 m wide, and a 500 m down dip extent. The major ore minerals, comprising about 5% of the hydrothermal phases, are pyrrhotite, pyrite and secondary marcasite with lesser sphalerite, galena, tellurobismuth and gold. Alteration halos that surround the orebodies are characterised by a broad bleaching zone of white mica and ankerite, and a proximal zone of silicification with abundant sulphide minerals. Biotite, albite and tourmaline are locally developed.
The Liba goldfield in Gansu province, contains a gold resource of 87 tonnes (2.8 Moz), and is located to the NE of the Zhongchuan Granite of the West Qinling Orogen. The structurally controlled gold mineralisation is located ~2 km NE of the Zhongchuan Granite, and is hosted by Devonian metasedimentary rocks, comprising metamorphosed siltstone, sandstone, mudstone and shale, assigned to the Shujiaba Formation, which have been intensely deformed to phyllitic rocks that commonly trend ESE (Cheng and Zhang 2001). Others deposits in the region include the Jinshan and Maquan gold deposits that are located 2 to 5 km south of the 30 km diameter Zhongchuan Granite, and are hosted by the Devonian Xihanshui and Carboniferous Xiajialing groups respectively. The Shujiaba Group, referred to as the Liba Group by Li (1999), comprise a ~5000 m thick succession of clastic-dominant flysch deposits, including siltstone, slate, micrite, sandstone and quartzite (Zhang et al., 2004). By contrast, the Xihanshui Group, regarded as a lateral equivalent of the Liba Group, is a 5800 m thick succession of carbonate with interbedded clastic units, interpreted as a shallow continental shelf deposit (Jin and Li 1996).
The Devonian rocks are overlain by metamorphosed Carboniferous shale and siltstone to the NW and SE of the Zhongchuan Granite, and metamorphosed Cretaceous sandstone and conglomerate to the NE, SE and SW of the granite. The Jurassic and Carboniferous rocks in the SE are in fault contact. The Cenozoic successions form isolated outcrops in the east and SW where they comprise reddish terrigenous clastic units that total 2000 m in thickness. Up to 50 m thick Quaternary eluvial and alluvial sediments contain small placer gold deposits locally. Sedimentary rocks in the region have been regionally metamorphosed to greenschist-facies.
Mineralisation in the Liba Goldfiled is associated with silica-sericite-chlorite-carbonate alteration, which have also affected most of the dykes, suggesting that most of the dykes are pre- to syn-mineralisation.
Individual deposits include the: Zhaogou orebody is the northernmost ore zone delineated in the Liba goldfield. 50 t of gold has been delineated at grade of 1.5 g/t Au (Dragon Mountain Gold, ASX Announcement 2009); Wawugou orebody located in the Wawugou Fault, enveloped by breccia. WWG-1 has a northwest-trending lenticular shape that is over 900 m long and dips ~60°SW, with a thickness of 1 to 12 m, and average grade of 3.78 g/t Au (Zhang 2003). WWG-II is subparallel to WWG-I and located 60 m to the NE. The mineralised zone is steeply dipping, strikes 290°, and is over 400 m long and ~1 m wide; At the Magou orebody, 36 t of contained gold has been delineated at 1.8 g/t Au (Dragon Mountain Gold ASX Announcement, 2009) in two zones, the largest of which is >930 m long, averaging 5.78 g/t Au with an average thickness of 8 m (Shi 2001).
Two main styles of mineralisation are known on the goldfield: i). disseminated sediment-hosted and ii). quartz vein hosted types. Pyrite, arsenopyrite and arsenian pyrite are major gold carriers, while native gold grains and electrum are spatially associated with the sulphides. Numerous felsic/intermediate dykes have a similar structural distribution as the mineralisation, and their contacts with host rocks are considered to be favourable zones for mineralisation.
Three phases of deformation have been recognised in the area. The first deformation (D1) event had a broadly north-south orientation and was compressional. The D2 event was also compressional and orientated in a NE-SW direction, while D3 was post-mineralisation, associated with the emplacement of barren calcite and anhydrite veins. Compression related to D2 controlled the distribution of igneous dykes and gold mineralisation in the Liba goldfield. Both igneous and hydrothermal fluids preferentially focused along dilational jogs under local transtension, which took place during the late stage of D2. Precise dating with high-resolution ion microprobe (SHRIMP) U-Pb on zircon and 40Ar/39Ar on muscovite, biotite, hornblende and plagioclase of crosscutting pre-mineralisation granitic porphyry and diorite dykes have constrained the mineralisation age to after ~227 Ma. 40Ar/39Ar analysis of minerals formed in hydrothermal alteration zones associated with gold mineralisation indicates that there was a widespread ~216 Ma hydrothermal event that affected almost all lithologies in the area (Zhou et al., 2012).
The Daqiao epizonal orogenic gold deposit is located ~60 km SE of Liba and ~160 km west of Baguamiao. It is hosted in organic-rich Triassic pumpellyite-actinolite facies metamorphosed turbidites. It is characterised by high grade hydraulic breccias that overprint an earlier tectonic breccia.
The deposit is structurally controlled by the Zhouqu-Chengxian-Huixian fault, hosted in the Middle Triassic Huashiguan Formation turbidite sequences of siltstone, siliceous, calcareous, and pelitic slates, with lesser pyritic carbonaceous slates and thin- to thick-bedded limestone. These rocks are in fault contact with Carboniferous limestone to the SE. Structurally, the deposit occurs on the northwestern flank of an inferred anticline (You and Zhang, 2009), the core of which is occupied by Carboniferous limestone, with Triassic clastic rocks in both limbs. Gold mineralisation is found on the northern limb. A number of NE and less commonly east-west or north-south striking reverse faults cut the deposit. The Carboniferous limestones and Triassic turbidites are separated by the secondary Yaoshang-Shixia (or F9) fault, part of the regional Zhouqu-Chengxian-Huixian fault system. Both the anticline and reverse faults are regarded to be due to Mesozoic deformation (Dong et al., 2011; Dong and Santosh, 2016).
A number of intermediate to silicic composition dykes intrude the Carboniferous and Triassic sedimentary rocks in the deposit area. Within the Daqiao deposit, granodiorite dykes have a close spatial relationship to gold orebodies and to strongly silicified zones. NE or NW striking, 2 to 10 m thick dykes extend for several tens to a few hundred metres along strike, are weakly deformed and have been variably altered by silica, sericite, sulphides and carbonates with occasionally weak gold mineralisation. These dykes were emplaced between 215 and 212 Ma (LA-ICP-MS zircon U-Pb; Gansu Geological Survey, unpub. report, 2017).
Host rocks of most gold mineralisation are siliciclastic breccias that are mainly localised between the Triassic slate and Carboniferous limestone units, as well as interlayered structures within the Triassic slates, and regarded to be tectonic breccias of the Huashiguan Formation (Gansu Geological Survey, unpub. report, 2011). The hydrothermally altered and mineralised tectonic breccias are developed along NE-striking reverse faults in the southern part of the deposit, whilst NW-striking faults are more important in the north. The F6-F8 faults, which strike NE and dip 55 to 70°SE, are the major structures in the deposit area and host the largest gold orebody. Other gold orebodies are cut by these faults, indicating fault reactivated during and after gold mineralisation (Gansu Geological Survey, unpub. report, 2011).
The Daqiao gold deposit comprises >100 'orebodies', with additional resources indicated at depth and surrounding areas (Gansu Geological Survey, unpub. report, 2017). Gold mineralisation is mainly hosted in the highly competent and permeable Triassic silicified breccias and, less commonly, silicified slates (Figs. 2–4, 5C-H). The upper limits of gold orebodies are mostly concealed at depths of 50 to 120 m below the current surface, although the uppermost parts of some orebodies in the southern section of the deposit are exposed and intensely oxidised to form supergene ores. The hypogene sulphide ores have an average grade of 3 to 4 g/t Au, although high-grades of up to 30 g/t are not uncommon in the extensively silicified fault gouge (Gansu Geological Survey, unpub. report, 2011). The supergene ores are generally 20 to 50 m thick and together contain ~9 t of Au at 7 to 9 g/t Au. The ores also contain 2 to 50 g/t Ag, locally with maximum grades of 370 g/t Ag. There is mostly a positive correlation between Au and Ag display (You and Zhang, 2009). Based on milling and flotation of the past to 2018, about 70% of gold in the hypogene ores can be recovered.
The largest orebody, I-1, has a strike length of ~2 km, with an average thickness of 12 m, and extends over a maximum vertical interval of 525 m from 1127 to 1652 m above sea level. The other more significant orebodies are 60 to 300 m long, 2 to 30 m thick and persist for 40 to 355 m downdip (Gansu Geological Survey, unpub. report, 2011). These orebodies are effectively stacked over a thickness of ~400 m within the Triassic turbidite sequence, enveloped by thicker and more extensive stratabound zones of silicification.
These orebodies are characterised by well-developed auriferous breccias. Breccia ores have been divided into tectonic and hydraulic types, with the best mineralisation associated with the latter, carrying grades of between 1 and 12 g/t Au, although tectonic breccias with relatively low gold grades of <4 g/t Au, also hosts significant amounts of gold due to their larger mass and volume. The tectonic breccias roughly occurs along the contact zone of the Triassic and Carboniferous sedimentary rocks and are composed of in situ siltstone, slate and limestone clasts, which are cemented by fault gouge, hydrothermal microcrystalline quartz and very fine grained sulphides. These breccias were subsequently further brecciated and cemented by chalcedony and sulphides to form intensely silicified hydraulic breccia, known as 'breccia B'. 'Breccia C', a second hydraulic breccia classification, resulted from repeated hydraulic fracturing of breccia B in proximity to the contact zone between the Triassic and Carboniferous strata, containing hydrothermal cements dominated by calcite, sulphides and minor chalcedony.
The dominant ore minerals of the hypogene ores are arsenian pyrite and marcasite, with associated minor to trace amounts of stibnite, chalcopyrite, sphalerite, galena, arsenopyrite, pyrrhotite, unidentified uranium oxides and platinum group element minerals. The gangue consist of quartz, calcite, sericite, kaolinite and carbonaceous material, with accessory apatite, rutile, and monazite. Gold is predominantly invisible, occurring in arsenian pyrite and marcasite, although free gold grains are abundant in the oxidised ores, ranging from 1 to 70 µm in width (You and Zhang, 2009), found as irregular, tabular or dendritic inclusions in limonite or as stringers filling fractures in quartz.
The sulphide minerals occur as disseminations or thin veinlets within the alteration zones, with a variety of crosscutting relationships and textures. Four sulphides stages are recognised:
S1. Layered or nodular pyrite aggregates, which are attributed to the pre-ore stage and occur in the black shale or carbonaceous layers within the Triassic turbidites;
S2. The early ore stage, which mainly consists of fine-grained euhedral pyrite cubes, pyritohedrons, columnar marcasite and irregular sulphide aggregates with abundant inclusions of apatite, chalcopyrite, galena, carbonaceous material and silicates. These sulphides are mainly hosted by the tectonic breccias and, less commonly, by minor quartz-pyrite veinlets typically parallel to the bedding of altered calcareous slate;
S3. The main ore stage sulphides are dominated by fine-grained pyrite aggregates that occur in milky quartz in breccia B and medium- to coarse-grained colloform pyrite or marcasite veinlets in breccia C;
S4. The late ore stage, which is characterised by widespread coarse-grained carbonate and marcasite veinlets in deformed pelitic slates close to the orebodies. The marcasite, which is characterised by a strong anisotropy with yellowish-brown to greyish-blue polarization colours, is only distinguished from the surrounding pyrite using optical microscopy. Detailed microscopic, scanning electron microscopy (SEM), and EBSD observations, show that marcasite accounts for approximately 0%, 20 to 35%, 15 to 25%, and 70 to 85% of total sulphides in the pre-, early, main, and late ore stages, respectively.
Carbonaceous material is widespread in the silicified black tectonic breccia ores at Daqiao, commonly occurring as sparse to dense disseminations that are 10 to 200 µm wide. Some carbonaceous material is enveloped by S2 stage irregular porous pyrite aggregates, with boundaries occupied by irregular or curvilinear interfaces. Fine-grained carbonaceous material also occurs as intergrowths with aggregates of porous pyrite and euhedral marcasite. No carbonaceous veinlets are observed in the hydrothermal cements of auriferous breccia types B and C.
The principal alteration assemblages at Daqiao include silica, sulphides, sericite and carbonates with no clear zonation. Multistage silicification is the most pervasive alteration type, controlled by the porosity and permeability of the immediate host rocks. It mainly occurs within the calcareous siltstone, siliceous slates and complex breccias that are characterised by high permeability.
Early penetrative silicification formed narrow selvages of a few µm of quartz in the granodiorite dykes, as well as quartz-sulphide veinlets, and more widespread microcrystalline quartz in the altered slate through replacement of pre-existing wall rock plagioclase and carbonate. Silicification is also broadly coeval with the formation of disseminated S2 sulphides in the tectonic breccias. The second stage of silicification mainly produces milky to chalcedonic microcrystalline quartz, precipitated with coeval irregular aggregates of fine-grained pyrite in the cements of hydraulic breccia B. Late, relatively weak silicification occurs as minor chalcedony, intergrown with calcite, and pyrite or marcasite aggregates and is associated with the breccia C hydraulic fracturing event.
The introduction of sulphides was in the four main stages detailed above, and was associated with multistage silicification. Sulphide veinlets occur in the black silicified silty slate, whilst fine-grained disseminated or irregular sulphide aggregates occur in the tectonic breccia as well as in the cements of hydraulic breccias B and C. Sericite is widespread as an alteration product of plagioclase and K feldspar, and is commonly intergrown with disseminated sulphides, occurring both in the altered granodiorite dykes and breccia-type ores. Carbonate minerals are most extensive in the main and late ore stages, mainly occurring as cements in hydraulic breccia C, or in veins of coarsely crystalline calcite associated with marcasite in the weakly silicified slates.
This description of the Daqiao deposit is drawn from Wu et al. (2018).
The smaller Huachanggou gold deposit is located in Lueyang County, ~300 km SW of Xi'an in Shaanxi Province, China. It has a contained gold reserve of ~10 tonnes with a grade of 2 to 10 g/t Au (Li et al., 2014). The deposit is controlled by a 15 km long by ~2 km wide WNW-striking ductile-brittle shear zone within the Mianlue suture zone. The deposit is developed in spilite, limestone and phyllite in the Mid to Lower Devonian Sanhekou Group. Three ore zones, denoted as I, II and III make up the Huachanggou deposit. These zones are subparallel to the strike of the host sequence, only partially overlapping laterally and are found within different units at three levels within 200 m of the stratigraphic sequence. Altered spilite hosts gold mineralisation in ore zone I where five NW-striking orebodies dip at 55 to 65°N, with grades ranging from 2 to 6 g/t and locally as much as 36.8 g/t Au. Ore zone II is in the NE part of the district, extending over an interval of ~1.8 km, hosted by bedded crystalline limestone and silty sericite phyllite. Gold orebodies dip at 60 to 80°N with grades varying from 2 to 10 g/t, up to 38.2 g/t Au. Ore zone III is in the SE of the district, developed over a strike length of ~2 km. Mineralisation is hosted within a sequence of microcrystalline limestone and silty sericite phyllite as WNW-trending orebodies which dip at 40 to 75°N. Grades vary from 2 to 8 g/t, locally up to 30.7 g/t Au.
Ores occur as either altered spilite-type and carbonate-quartz vein type. The former contain an assemblage of pyrite, chalcopyrite and native gold in a gangue of quartz, albite, calcite and ankerite. Pyrite occurs as disseminations. The carbonate-quartz vein type ores in zones II and III have higher gold grades, and are characterised by banded quartz veins. The bulk of metallic minerals are pyrite, chalcopyrite and native gold, with minor galena and sphalerite. Gangue minerals are quartz, albite, calcite and ankerite. Pyrite occurs as disseminations.
Pyrite is the main gold-bearing mineral, and the native gold is either visible or microscopic. Visible gold is mainly in quartz veins and varies from ~3 mm. Microscopic gold is mainly interstitial, as minor inclusions and as fissure fill.
Gold mineralisation is accompanied by intense hydrothermal alteration, which includes silica, carbonate, sericite, chlorite and epidote. Silicification is widespread and has a close relationship with mineralisation in the form of quartz veinlets infilling schistosity and fissures in the wall rocks. Carbonates developed after silicification and generally occur as pyrite-quartz-carbonate veining. Gold is best developed where silicification is most intense and pyrite is disseminated in the silicified haloes.
This description of the Huachanggou deposit is drawn from Liu et al. (2016).
Ludousou (#Location: 35° 5' 30"N, 102° 59' 30"E)
The Ludousou deposit is located ~18 km NE of Hezuo City in Gansu Province, China. It is dominantly hosted by metasedimentary rocks of the Lower Permian Daguanshan Formation, comprising a SW-dipping greenschist facies sequence mainly composed of metalimestone, metasiltstone, metasandstone and metaconglomerate of greenschist facies. This sedimentary sequence was covered by rhyolitic tuff eruptions of the Gari volcanic rocks, and intruded by the calc-alkaline to high-K calc-alkaline Dewulu intrusive complex stock (Qiu and Deng, 2017; Sui et al., 2017). Hornfels are developed along the contact between the stock and the metasedimentary rocks (Chen et al., 2007). In the deposit area, the Gari volcanic sequence contains glassy fragments, quartz and fine-grained scoriae with plagioclase and biotite. The quartz grains commonly have crescent, sickle, biconcave or rounded shapes. The Dewulu intrusive complex contains quartz diorite porphyry, quartz diorite and numerous mafic microgranular enclaves hosted by the quartz diorite. Phenocrysts within the grey-white coloured quartz diorite porphyry are mostly 0.5 to 2mm in diameter, comprising 30 to 50 vol.% plagioclase, 30 to 50 vol.% biotite and 5 to 10 vol.% amphibole set in a groundmass that is mainly composed of quartz and plagioclase. Accessory minerals include zircon and apatite. The quartz diorite is grey and is mainly composed of 40 to 50 vol.% plagioclase, 15 to 30 vol.% amphibole, 10 to 15 vol.% quartz and ~5% biotite with accessory apatite and zircon. More than 80% of the mafic microgranular enclaves hosted within the quartz diorite range from 10 to 30 cm in diameter, with ellipsoidal to spherical shapes and are dioritic with a porphyritic texture. The contacts between enclaves and host rocks are sharp and some are chilled. Phenocrysts within these enclaves comprise 10 to 15 vol.% and 0.1 to 0.7 mm diameter amphibole, 5 to 10 vol.% and 0.3 to 2.0 mm diameter plagioclase, 5 vol.% and 0.5 to 1.3 mm diameter quartz and 3 vol.% and 0.1 to 0.8 mm diameter biotite. The matrix comprises 45 vol.% plagioclase, 20 vol.% biotite and 10 vol.% amphibole. Quartz megacrysts surrounded by amphibole are commonly found in these enclaves. Accessory minerals are zircon and acicular apatite with length to width ratio of about 30:1.
Most of the Ludousou deposit resources are restricted to the two largest orebodies, referred to as the tourmaline-rich Au-Cu orebody and the Au3 fault and breccia related Au-Sb orebody, which represent two different styles of ore. Most of the Au-Cu orebodies are hosted in the upper part of the intrusive complex (i.e., the 3250 to 3220m level (Yang and Qian, 2017). In contrast, the Au-Sb orebodies are mainly hosted in disseminated breccias within reverse fault zones, within laminated quartz-sulphide lodes.
Locally, Au-Sb mineralisation crosscuts the tourmaline-rich ores and cement the tourmaline breccia. The tourmaline-rich Au-Cu ores contribute ~30% of the gold endowment (Yang and Qian, 2017) and are characterised by ~30% tourmaline, occurring as massive, vein, euhedral disseminated and nodular tourmaline that postdate the emplacement of quartz diorite porphyry. The disseminated and nodular tourmaline commonly occurs as tourmaline-enriched domains in host quartz diorite porphyry. Vein tourmaline commonly occurs along joints in the host rocks, whilst massive tourmaline usually cements granite breccia with strong silicification, sericitisation and sulphidation. The sulphides are pyrite, arsenopyrite and chalcopyrite. Pyrite and arsenopyrite generally occur as coarse-grained subhedral or euhedral crystals.
The fault and breccia related Au-Sb ores contribue ~70% of the gold endowment. Structures hosting the orebodies are irregular, varying from 0.2 to 3 m in width. These faults dip at 15 to 30°S, SE and SW. Mineralisation-related alteration patterns are structurally controlled by faults with the same strike and dip, and including sulphidation (pyrite and arsenopyrite), sericitisation, silicification and carbonatisation. The extensive carbonate halos are ~30 cm thick. Pyrite, arsenopyrite and stibnite are the dominant sulphide minerals with minor to trace amounts of chalcopyrite, sphalerite and galena. Invisible gold occurs in solid solution and/or as nanoparticles within pyrite and arsenopyrite.
This description of the Ludousou deposit is drawn from Yu et al. (2020).
The resources contained within other deposits in the Qinling Gold Province (Zeng et al., 2012) were: Yangshan (>300 t Au @ 4.74 g/t Au); Ma'anqiao (20 t Au @ 5 g/t Au); Shuangwang (60 t Au @ 3 g/t Au); Pangjiahe (>40 t Au @ 6 g/t Au); Daqiao (>105 t Au @ 3 to 4 g/t Au); Baguamiao (>106 t Au; Liu et al., 2015); Zaozigou (142 t Au; Sui et al., 2017); Huachanggou (>10 t Au @ 2 to 10 g/t Au; Liu et al., 2016); Ludousou (>8 t Au @ 3.8 to 5.5 g/t Au; Yu et al., 2020).
The most recent source geological information used to prepare this summary was dated: 2020.
Record last updated: 11/8/2020
This description is a summary from published sources, the chief of which are listed below.
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Deng, J. and Wang, Q., 2016 - Gold mineralization in China: Metallogenic provinces, deposit types and tectonic framework: in Gondwana Research v.36, pp. 219-274.|
Dong, Y., Yang, Z., Liu, X., Sun, S., Li, W., Cheng, B., Zhang, F., Zhang, X., He, D. and Zhang, G., 2016 - Mesozoic intracontinental orogeny in the Qinling Mountains, central China: in Gondwana Research v.30, pp. 144-158.|
Liu, C., Liu, J., Carranza, E.J.M., Yang, L, Wang, J., Zhai, D., Wang, Y., Wu, J., and Dai, H., 2016 - Geological and geochemical constraints on the genesis of the Huachanggou gold deposit, western Qinling region, Central China: in Ore Geology Reviews v.73, pp. 354-373.|
Liu, J., Liu, C., Carranza, E.J.M., Mao, Z, Wang, J., Wang, Y., Zhang, J., Zhai, D., Zhang, H.,Shan, L., Zhu, L. and Liu, R., 2015 - Geological characteristics and ore-forming process of the gold deposits in the western Qinling region, China: in J. of Asian Earth Sciences v.103, pp. 40-69.|
Ma, J., Lu, X., Escolme, A., Li, S., Zhao, N., Cao, X., Zhang, L. and Lu, F., 2018 - In-situ sulfur isotope analysis of pyrite from the Pangjiahe gold deposit: Implications for variable sulfur sources in the north and south gold belt of the South Qinling orogen: in Ore Geology Reviews v.98, pp. 38-61|
Mao, J., Qiu., Y., Goldfarb, R.J., Zhang, Z., Garwin, S. and Fengshou, R., 2002 - Geology, distribution, and classification of gold deposits in the western Qinling belt, central China: in Mineralium Deposita v.37, pp. 352-377.|
Wang, X., Wang, T. and Zhang, C., 2013 - Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process: in J. of Asian Earth Sciences v.72, pp. 129-151.|
Wu, Y., Li, J., Evans, K., Fougerouse, D. and Rempel, K., 2019 - Source and possible tectonic driver for JurassiceCretaceous gold deposits in the West Qinling Orogen, China: in Geoscience Frontiers, v.10, pp. 107-117.|
Wu, Y.-B. and Zheng, Y.-F., 2013 - Tectonic evolution of a composite collision orogen: An overview on the Qinling-Tongbai-Hongan-Dabie-Sulu orogenic belt in central China: in Gondwana Research v.23, pp. 1402-1428.|
Wu, Y.-F., Li, J.-W., Evans, K., Koenig, A.E., Li, Z.-Ke., O Brien, H., Lahaye, Y., Rempel, K., Hu, S.-Y., Zhang, Z.-P. and Yu, J.-P., 2018 - Ore-Forming Processes of the Daqiao Epizonal Orogenic Gold Deposit, West Qinling Orogen, China: Constraints from Textures, Trace Elements, and Sulfur Isotopes of Pyrite and Marcasite, and Raman Spectroscopy of Carbonaceous Material: in Econ. Geol. v.113, pp. 1093-1132.|
Wu, Y.-F., Li, J.-W., Evans, K., Vasconcelos, P.M., Thiede, D.S., Fougerouse, D. and Rempel, K., 2019 - Late Jurassic to Early Cretaceous age of the Daqiao gold deposit, West Qinling Orogen, China: implications for regional metallogeny: in Mineralium Deposita v.54, pp. 631-644.|
Yu, H.-C., Qiu, K.-F., Nassif, M.T., Geng, J.-Z., Sai, S.-X., Duo, D.-W., Huang, Y.-Q. and Wang, J., 2020 - Early orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean - Constraints from the Ludousou gold deposit, central China: in Ore Geology Reviews v.117, 15p. doi.org/10.1016/j.oregeorev.2019.103217|
Zeng Q, McCuaig T C, Hart C J R, Jourdan F, Muhling J and Bagas L, 2012 - Structural and geochronological studies on the Liba goldfield of the West Qinling Orogen, Central China: in Mineralium Deposita v.47 pp. 799-819|
Zhou, T., Goldfarb, R.J. and Phillips, G.N., 2002 - Tectonics and distribution of gold deposits in China - an overview: in Mineralium Deposita v.37, pp. 249-282.|
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