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Abstract
Bangbu gold deposit is located to the south of the east section of the Yarlung Zangbo tectonic suture zone in the southern Tibet. The gold orc bodies are controlled by the secondary fractures in the large-scale brittle-ductile shear zone. It is a proved large-scale primary gold deposit in Tibet. Microthermometric measurements and Laser Raman analysis show that auriferous quartz veins of the Bangbu gold deposit contain three types of fluid inclusions: liquid aqueous inclusions (type I) : CO2-bearing brine inclusions (type II), which can be subdivided into two-phase (type Ha) and three-phase (type lib) inclusions: pure gaseous hydrocarbon inclusions (type III). The CO2-bearing brine inclusions have salinity values of 2. 20% NaCl eqv ∼9. 45% NaCleqv, with a peak of 6.0% NaCl eqv ∼7.0% NaCleqv and an average of 6.25% NaCl eqv, homogenization temperature values of 166.7 ∼ 335. 8°C, with a peak of 210 ∼ 250°C and an average of 235. 4°C, and density values of 0.63 ∼ 0. 96g/cm3, with a peak of 0. 85 ∼ 0. 95g/cm3 and an average of 0. 87g/cm3, suggesting that the ore-forming fluids of the Bangbu gold deposit is characteristics by high content of CO2, low salinity, low to moderate homogenization temperature and low density, which are similar to those of typical orogenic gold deposits. Oxygen and hydrogen isotopic analyses show that δD and δ18O of the ore-forming fluids in the Bangbu gold deposit are-44. 4% ∼-105. 3% and 4.7% ∼ 9.0%, respectively, indicating that the ore-forming fluids is composed mainly of metamorphic fluid, with addition oi mantle-derived fluid Geologic and geochemical features show that the Bangbu gold deposit may be a Cenozoic orogenic gold deposit formed under continental collisional background.
... The Indus-Yarlung Zangbo suture zone (IYZSZ) is an important Cenozoic gold province (proven ore reserve: > 200 metric tonnes (t), highest grade: 32 g/t), extending across the southern Lhasa Terrane for over 1300 km from NW India via southern Tibet to NE India (Hou et al., 2015;Deng and Wang, 2016;Zhang et al., 2017;Wang et al., 2021). The Bangbu gold deposit is one of the largest orogenic gold deposits in the IYZSZ (gold reserves: 40 t) (Wei, 2011;Zhai et al., 2014;Pei et al., 2016;Sun et al., 2016;Zhao et al., 2020;Zheng et al., 2020). A significant amount of work has previously been performed to understand the oreforming processes of the Bangbu. ...
... Based on field geological observations, two types of mineralization styles with distinct characteristics are recognized in the orebody III, including the vein and disseminated mineralization styles , which contribute 70 % and ~30 % of the gold reserve, respectively (Wei, 2011). Both ore types show close associations with quartz veins, although their respective vein sizes are different (Fig. 4b, d). ...
... As shown in Fig. 12b, all generations of pyrite Co/Ni ratio in ores from same range between 1 and 0.1 indicating Py1-3 may have a sedimentary origin. However, this cannot rule out potential hydrothermal contribution, due to the hydrothermal sericite and quartz coexisting with Py1-3 that occurred under petrographic observations in vein and disseminated ores, and cannot be observed in the sedimentary host rocks without quartz veins (Wei, 2011). Adam et al. (2020) and Tan et al. (2022) suggested that in addition to the Co/Ni ratio, different mineral assemblages and redox reactions should also be considered when interpreting the pyrite origin because some hydrothermal pyrites can have Co/Ni ratios of less than 1 due to fluid-rock reactions. ...
Carbonaceous material (CM) is widely distributed at the Bangbu orogenic gold deposit in vein-hosted and disseminated ores, as well as wall rocks. Despite being closely ore-related, the CM nature and genesis, as well as its possible role in gold metallogeny, remain unclear. Hence, we investigate the role of five ore-related CM types (CM1-4 and methane, which coexist with three pyrite generations of Py1-Py3) by integrating petrographic observation, Raman spectroscopy, LA-ICP-MS, fluid inclusion microthermometry, and thermodynamic modeling. CM1 only occurs in disseminated ores and is overprinted by large euhedral Py1 with median 5.28 ppm Au. Raman spectroscopy analysis shows that CM1 has undergone high-temperature regional metamorphism (∼510 °C). Geochemical modeling shows that Au precipitation in Py1 can be attributed to the fluid-rock interactions of CM1 and Au-bearing ore fluids, which future leads to the host rock alteration and CM1 consumption. CM2 occurs with large subhedral Py2 and hydrothermal sericite in quartz veins, and gold exists as native gold and as Au⁺ solid solutions in pyrite. Py2 consists of Py2a with median 0.44 ppm Au and Py2b with median 49.80 ppm Au. Raman spectroscopy of CM2 experienced a temperature of ∼455 °C, much higher than the main ore stage fluid inclusion homogenization temperature (167–247 °C). Meanwhile, methane is commonly found in CO2-bearing fluid inclusions in the quartz closely associated with Py2 and CM2. Geochemical modeling shows that methane can be a more efficient reductant than CM2 and is capable of reducing Au-bisulfide to native gold. CM3 intergrows with fine Au-poor subhedral Py3 (median 1.00 ppm Au) in randomly-oriented “black sinuous” veins within vein-type ores. The CM3 formation temperature is calculated as ∼290 °C. During the sulfidation processes, H2S and CO2 from the ore fluids may have reacted with Fe-bearing minerals, precipitating CM3 and Py3. The loss of aqueous H2S would destabilize Au-bisulfide complexes, which is the secondary gold precipitation mechanism proposed for this deposit. CM4 occurs in the wall rocks and have similar structural features with structure-bound semi-graphite observed by petrology, indicating that the formation process is different from that of other CM types. This is supported by the Raman geothermometric results of CM4 (formation temperature ∼388 °C). Additionally, no spatial association was observed between CM4, auriferous sulfides, and native gold. In conclusion, our study proposed the most likely roles of CM in gold precipitation in this deposit, which bears important implications for better understanding of the processes that lead to the formation of high-grade ores.
... The southern Tibet Au\Sb metallogenic belt, in the Himalayan orogen to the south of the ITS, contains more than 50 gold-and/or stibnite-bearing vein deposits or occurrences, and associated placer gold deposits (Tibet Institute of Geologic Survey, 2003;Nie et al., 2005;Yang et al., 2009). Typical Au deposits including Mayoumu (or Mayum) ( Duo et al., 2009;Jiang et al., 2009;Wen et al., 2006), Bangbu (N20 t Au) ( Sun et al., 2010), and Zhemulang (Ai, 2007); Au\Sb include Mazhala ( Yang et al., 2009;Zhang et al., 2000) and Zhegu ( Nie et al., 2005;Yang et al., 2009); and Sb include Shalagang ( Li et al., 2002; Yang et al., 2000;Yang et al., 2009) and Chequnzhuobu ( Wu et al., 2008). Different opinions have been offered for the genesis of the lode deposits, including defining these as epithermal, or orogenic deposits, and suggesting a variety of ore fluid types including magmatic or mixed magmatic-meteoric. ...
... Its width is variable, from 100-300 m to 2-3 km ( Li et al., 1995). To the west, the large (N20 t) Bangbu deposit ( Sun et al., 2010) is hosted in the second-order faults or splays of the Juqu-Zhemulang shear zone (Fig. 1). ...
... The ore-forming fluids were suggested to evolve from magmatic water-dominated to me- teoric water-dominated outwards, and the mineralization was assumed to have been controlled by a hydrothermal convection system driven by the leucogranites, with the deposits generally showing characteristics of epithermal deposits ( Yang et al., 2009). On the basis of stable isotope, noble gas, and fluid inclusion evidence, the ore-forming fluid for Bangbu gold deposit was suggested to have derived from meta- morphic fluids, with some involvement of a mantle fluid ( Sun et al., 2010;Wei et al., 2010). ...
... Orebody III is the largest orebody, located in the center of the Bangbu gold deposit (Fig. 1b). The thick lode in orebody III strikes 218-255 • and dips 26-45 • to the southwest, with an average grade of 9.39 g/t Au and a reserve of 16.06 t ( Fig. 1c and 2a; Sun et al., 2010). Most of the host rocks are developed ductile deformation and the wall rock fracturing is weak. ...
The extreme fluctuations in pressure during earthquakes are widely regarded as responsible for gold mineralization in quartz-vein-hosted gold deposits. However, it is barely noticed that base metal sulfides can precipitate together with gold during these processes. Here we present the phenomenon and unravel the mechanism of the co-precipitation of Au and base metal sulfides during the fluid boiling via geological study and thermaldynamic modeling, respectively. The Bangbu deposit, a lode-type orogenic gold deposit in Tibet shows two mineralization substages of pyrite. The pyrite formed in the later substage is hosted in the wall rock selvages of laminated crack-seal quartz veins formed by the fault-valve processes. The pyrite grains are characterized by anhedral small crystals with a porous texture and abundant native gold, chalcopyrite, galena, and sphalerite inclusions. They also contain higher concentrations of Cu, Pb, Ag, Sb, and Au, and lower concentrations of Co and Ni, compared to the euhedral large-grained pyrite formed in the initial substage. The textural and trace element characteristics of the pyrite indicate that vigorous boiling occurred during fault-valve behavior, which decreased the solubilities of Au, Cu, Pb, and Zn in the ore fluid in Bangbu. The co-precipitation of Au and base metal sulfides triggered by fluid boiling have also been reported in other orogenic gold deposits worldwide.
Thermodynamic models are designed to acquire the predominant species and solubility of Au, Cu, Pb, and Zn in orogenic ore fluids under varied chemical conditions. The results show that Au, Cu, Pb, and Zn are dominantly transported as hydrosulfide complexes under lower mesozonal to epizonal deposit conditions. At temperatures of about above 350°C, Au hydrosulfide species still predominates, but the predominant Cu, Pb, and Zn species change from hydrosulfide to chloride complexes. A sudden decrease in the reduced sulfur concentration during fluid boiling may be the most important mechanism controlling the precipitation of Au, Cu, Pb, and Zn in lower mesozonal to epizonal deposits. The decrease of logfS2 during fluid boiling can increase the fluid pH, resulting in the decrease of solubilities of base metal chloride complexes and thus explain the co-precipitation of Au and base metal sulfides in hypozonal deposits.
... 40 Ar/ 39 Ar ages for hydrothermal sericite from auriferous quartz veins indicate that the Bangbu gold deposit likely formed at ~50-44 Ma (Sun et al., 2016b;Pei et al., 2016). Some geologists studied fluid inclusions and stable (C-D-O) and noble gas (He-Ar) isotopes at Bangbu and argued that ore-forming fluids were metamorphic fluid mixing with mantle fluid Sun et al., 2010Sun et al., , 2016bPei et al., 2016). Based on sulfur isotopes of bulk pyrite grains at Bangbu, some researchers suggested that sulfur was of mantle source (δ 34 S = 2.8-4.7‰; ...
The Bangbu orogenic gold deposit in the North Himalaya of the southern Tibet contains more than 40 t Au at an average grade of 7.0 g/t. In this deposits, gold-bearing quartz veins were controlled by nearly E–trending Qusong-Cuogu-Zhemulang shear zone and occurred within the secondary faults which crosscut Late Triassic greenschist- facies rocks. To further understand the sulfur source and ore-forming process, we have conducted a compressive study of in-situ SIMS sulfur isotopes and LA-ICP-MS trace element compositions of two stages of pyrite at Bangbu. Early-stage pyrite (Py1) is coarse-grained (mostly 0.2 - 2 mm) and euhedral, and has gold concentrations of less than 0.3 to 54 ppm (mean of 20 ppm) and δ³⁴S values of 1.6 to 5.1‰ (mean of 3.2‰). Late-stage pyrite (Py2) is generally fine-grained (mostly < 50 μm to 1 mm) and subhedral to anhedral, and has gold concentrations of 3.6 to 115 ppm (mean of 30 ppm) and δ³⁴S values of 0.9 to 5.2‰ (mean of 2.7‰). Gold occurs mainly as invisible refractory within Py1 and Py2, and to a lesser extent as native gold within quartz, pyrite, arsenopyrite and sphalerite. Sulfur for Bangbu gold mineralization was probably sourced from the Greater Himalayan crystalline complex. Release of ore-forming fluids was likely related to amphibolite-facies metamorphism during ∼50-45 Ma. Ore fluids deposited Au-rich pyrite during early and late mineralization stage and precipitation of native gold was probably related to fluid boiling and/or remobilization of invisible gold within pyrite.
... 2014). In the Tibetan Plateau, mineral exploration along the Yarlung-Zangbo suture led to discovery of the Bangbu and Mayum orogenic gold deposits (Jiang et al., 2009;Sun et al., 2010Sun et al., , 2013, showing the metallogenic potential for gold in southern Tibet. In central Tibet, numerous placer gold occurrences and old mining sites occur along the Bangong-Nujiang suture zone (Li et al., 2017), including large alluvial gold mines, such as Bengnazangbo (Wang et al., 2006), indicating gold mineralization in the drainage basin. ...
Shangxu is an orogenic gold deposit within the Bangong-Nujiang suture zone, central Tibet, China. It is hosted by turbidite sedimentary rocks of the Jurassic Mugagangri Group. The host rocks were metamorphosed to subgreenschist facies prior to being hydrothermally altered adjacent to mineralization. Hydrothermal minerals in wall rocks consist of muscovite, carbonate, sulfides and chlorite. Whole rock geochemistry indicates hydrothermal alteration is characterized by the introduction of K2O, CO2 and S, and leaching of Na2O. Increasing 3K/Al and decreasing Na/Al alteration indexes approaching the ore correlate to muscovitization. CO2 concentration reflects the degree of carbonation, which in conjunction with molar (Mn+Fe)/(Fe+Ca+Mg+Mn) and CO2/CaO can be used to distinguish siderite from ankerite in carbonate alteration. Mass transfer analysis shows gains in As, Au, CO2, W, Ca, Cd, Ni, Cr, Sr, Rb, K and losses in Na, Pb, Cu during hydrothermal alteration. In the muscovite alteration zone, muscovite within shear zones (Ms1) shows an increase in Fe, Mg and Na towards the ore, whereas metamorphic muscovite along cleavage planes and in pressure shadows (Ms2), and hydrothermal muscovite (Ms3) change in composition from phengitic (Mg, Fe) distal to mineralization, to paragonitic (Na) adjacent to gold. In carbonate alteration, the composition in carbonate phases changes from early magnesian siderite to ankerite, and then to calcite and dolomite during the evolution of the hydrothermal system. Siderite spots in host rocks and ankerite in veins, wall rock or its replacement of siderite are all enriched in Fe, Mn and depleted in Mg from proximal to distal alteration zones. Pyrite is a dominant mineral in sulfide alteration of the Shangxu deposit. The earliest framboidal pyrite (Py1) formed during diagenesis, and overprinted by Py2, which is recrystallized pyrite associated with burial metamorphism. Py3 rims and enlarges previous pyrite aggregates, or recrystallizes into cubic grains with cracks and quartz pressure shadows during deformation. Py4 is ore-related euhedral pyrite, disseminated near gold, and formed in hydrothermal stage. Vein pyrite (Py5) coexists with marcasite, and fills cracks in quartz veins. Hydrothermal alteration minerals form overlapping alteration haloes surrounding the main auriferous lodes. Distal muscovitization, carbonatization and proximal sulfidation constitute a progressive alteration front from gold. The alteration envelope is tabular in shape, following the strike and dip of the mineralization, and tends to be the widest around the thickest parts of the ore, such that the occurrence and thickness of the alteration envelope can be used as an approximate guide to the size of gold mineralization. Shangxu shares many diagnostic features with turbidite-hosted orogenic gold deposits, such as Bendigo, Reefton and Meguma districts, in deposit geology, alteration mineralogy and lithogeochemistry.
... In the northern part of Himalaya, over 50 gold deposits, consistently enriched in antimony, are scattered within the widespread mid-Miocene domes, which are intruded by Miocene leucogranites (Z.S. Yang et al., 2009). Due to inadequate geological exploration, most gold deposits so far are small, and different genetic models including orogenic, epithermal, or Carlin-like have been proposed for these deposits (Z.S. Yang et al., 2009;Sun et al., 2010). ...
We present a review of major gold mineralization events in China and a summary of metallogenic provinces, deposit types, metallogenic epochs and tectonic settings. Over 200 investigated gold deposits are grouped into 16 Au-metallogenic provinces within five tectonic units such as the Central Asian orogenic belt comprising provinces of Northeast China and Tianshan-Altay; North China Craton comprising the northern margin, Jiaodong,
and Xiaoqinling; the Qinling-Qilian-Kunlun orogenic belt consisting of the West Qingling, North Qilian, and East Kunlun; the Tibet and Sanjiang orogenic belts consisting of Lhasa, Garzê-Litang, Ailaoshan, and DaduheJinpingshan; and the South China block comprising Youjiang basin, Jiangnan orogenic belt, Middle and Lower Yangtze River, and SE coast. The gold deposits are classified as orogenic, Jiaodong-, porphyry–skarn, Carlin-like,and epithermal-types, among which the first three types are dominant. The orogenic gold deposits formed in various tectonic settings related to oceanic subduction and subsequent crustal extension in the Qinling-Qilian-Kunlun, Tianshan-Altay, northern margin of North China Craton, and Xiaoqinling, and related to the Eocene–Miocene continental collision in the Tibet and Sanjiang orogenic belts. The tectonic periods such as from slab subduction to block amalgamation, from continental soft to hard collision, from intracontinental compression to shearing or extension, are important for the formation of the orogenic gold deposits. The orogenic gold deposits are the products of metamorphic fluids released during regional metamorphism associated with oceanic subduction or continental collision, or related to magma emplacement and associated hydrothermal activity during lithospheric extension after ocean closure. The Jiaodong-type, clustered
around Jiaodong, Xiaoqinling, and the northern margin of the North China Craton, is characterized by the involvement of mantle-derived fluids and a temporal link to the remote subduction of the Pacific oceanic plate concomitant with the episodic destruction of North China Craton. The Carlin-like gold metallogenesis is related to the activity of connate fluid, metamorphic fluid, and meteoric water in different degrees in the Youjiang basin and West Qinling; the former Au province is temporally related to the remote subduction of the Tethyan oceanic plate and the later formed in a syn-collision setting. Porphyry–skarn Au deposits are distributed in the Tianshan-Altay, the Middle and Lower Yangtze River region, and Tibet and Sanjiang orogenic belts in both subduction and continental collision settings. The magma for the porphyry–skarn Au deposits commonly formed by melting of a thickened juvenile crust. The epithermal Au deposits, dominated by the low-sulfidation type, plus a few high-sulfidation ones, were produced during the Carboniferous oceaic plate subduction in Tianshan-Altay, during Early Cretaceous and Quaternary oceanic plate subduction in SEt coast of South China Block, and during
the Pliocene continental collision in Tibet. The available data of different isotopic systems, especially fluid D–O isotopes and carbonate C–O systems, reveal that the isotopic compositions are largely overlapping for different genetic types and different for the same genetic type in different Au belts. The isotopic compositions are thus not good indicators of various genetic types of gold deposit, perhaps due to overprinting of post-ore alteration or the complex evolution of the fluids.
Although gold metallogeny in China was initiated in Cambrian and lasted until Cenozoic, it is mainly concentrated in four main periods. The first is Carboniferous when the Central Asian orogenic belt formed by welding of microcontinental blocks and arcs in Tianshan-Altay, generating a series of porphyry–epithermal–orogenic deposits. The second period is from Triassic to Early Jurassic when the current tectonic mainframe of China started to
take shape. In central and southern China, the North China Craton, South China Block and Simao block were amalgamated after the closure of Paleo-Tethys Ocean in Triassic, forming orogenic and Carlin-like gold deposits. The third period is Early Cretaceous when the subduction of the Pacific oceanic plate to the east and that of NeoTethyan oceanic plate to the west were taking place. The subduction in eastern China produced the Jiaodongtype deposits in the North China Craton, the skarn-type deposits in the northern margin (Middle to lower reaches of Yangtze River) and the epithermal-type deposits in the southeastern margin in the South China Block. The subduction in western China produced the Carlin-like gold deposits in the Youjiang basin and orogenic ones in the Garzê-Litang orogenic belt. The Cenozoic is the last major phase, during which southwestern China experienced continental collision, generating orogenic and porphyry–skarn gold deposits in the Tibetan and Sanjiang orogenic belts. Due to the spatial overlap of the second and third periods in a single gold province, the Xiaoqinling, West Qinling, and northern margin of the North China Craton have two or more episodes of gold metallogeny.
... Taken 2.7 g/cm 3 as the density of upper continental crust rocks (Shepherd et al., 1985), the estimated trapping pressures for the early-stage fluids are 1988-2829 bars, suggesting an alternating lithostatic-hydrostatic fluid system, controlled by fault-valve activity (see Drummond and Ohmoto, 1985) at a depth of 7.5 to 10.7 km (Table 2). These values along with oxygen isotopic signatures (δ 18 O fluid : +6.5 to + 10.2‰; this study and δ 18 O fluid : + 6.0 to + 11.2‰ for orogenic-type deposits, Yu et al., 1984;McCuaig and Kerrich, 1998;Bierlein and Crowe, 2000;Sun et al., 2010) agree with mesothermal P-T constrains estimated from the alteration and ore mineral assemblages and are consistent with the P-T conditions of regional greenschist facies metamorphism in the Zinvinjian deposit (Niroomand et al., 2011). Therefore, the Zinvinjian deposit was formed at a depth of 7.5-10.7 km (type-A; Table 2), formed at a level comparable with the depth of mesozonal orogenic deposits (~6-12 km; Groves et al., 1998Groves et al., , 2003Goldfarb et al., 2005;Chen, 2006). ...
The Zinvinjian polymetallic deposit occurs as veins controlled by a NW–SE trending–structure within the Cretaceous metamorphosed limestone and dolomite, schist, and metavolcanic rocks, northwest of Iran. The retrograde greenschist facies metamorphism was accompanied by large–scale transpressional faulting, crack–seal veins, infiltration of large volumes of hydrous fluid with high XCO2, and is largely overlapped by the main hydrothermal events. The metamorphism has resulted in two stages of mineralization in the Zinvinjian deposit. These are early–stage polymetallic sulfides–quartz and late–stage pyrite–quartz veins. The early–stage veins filled fractures and are undeformed, suggesting a tensional shear setting. The late–stage veins are also mainly open–space fissure–fillings that cut or replace earlier veins. Three types of fluid inclusions (FIs), including aqueous (type–I), mixed carbonic–aqueous (type–II), and carbonic (type–III), were identified in ore–related quartz veins. The early–stage quartz contained all three types of primary FIs homogenized at temperatures of range 197–300 °C and salinities of 2.5–15.2 wt% NaCl equivalent. In contrast, the late–stage quartz veins contained only type–I FIs with homogenization temperatures ranging between 192 and 210 °C, and salinities of 0.2–2.7 wt% NaCl equivalent. This indicates that the metallogenic system evolved from a carbonic–rich, metamorphic fluid to a carbonic–poor, one through input of meteoric fluids. All three types of FIs in the early–stage minerals displayed evidence of vein formation during an episode of fluid immiscibility. Quartz δ¹⁸O (+ 15.3 to + 19.0‰) and sulfide δ³⁴S (− 9.4 to + 11.6‰) indicate isotopic equilibrium with host metasediments (rock buffering) and a metasedimentary source of sulfur during early–stage. It is believed that ore mineralization is the result of a decrease in base–metal solubility during an episode of the fluid immiscibility. This study suggests that mineralization at the Zinvinjian deposit is metamorphogenic in style, probably related to a deep–seated orogenic system.
... It is one of the largest lode gold deposits in Tibet and is located to the east part of the Yarlung Zangbo terrane suture zone. Preliminarily investigations have focused on the local geology and a tentative genetic model (Lu, 2005;Lv et al., 2005; Geological Survey of Tibet Bureau of Geology and Mineral Exploration and Development, 2006;Sun et al., 2010;Wei et al., 2010), and stressed that Bangbu may be an epithermal gold deposit. However, a systematic study of geochemical features and geochronology, critical for understanding the genesis, was lacking. ...
Located along the southern part of the Yarlung Zangbo suture zone in southern Tibet, Bangbu is one of the largest gold deposits in Tibet. Auriferous sulfide-bearing quartz veins are controlled by second- or third-order brittle fractures associated with the regional Qusong-Cuogu-Zhemulang brittle-ductile shear zone. Fluid inclusion studies show that the auriferous quartz contains aqueous inclusions, two-phase and three-phase CO2-bearing inclusions, and pure gaseous hydrocarbon inclusions. The CO2-bearing inclusions have salinities of 2.2-9.5% NaCleq, and homogenization temperatures (Th) of 167-336°C. The δD, δ18O, and δ13C compositions of the Bangbu ore-forming fluids are -105.5 to -44.4‰, 4.7 to 9.0‰ and -5.1 to -2.2‰, respectively, indicating that the ore-forming fluid is mainly of metamorphic origin, with also a mantle-derived contribution. The 3He/4He ratio of the ore-forming fluids is 0.174 to 1.010 Ra, and 40Ar/36Ar ranges from 311.9 to 1724.9. Calculations indicate that the percentage of mantle-derived He in fluid inclusions from Bangbu is 2.7-16.7%. These geochemical features are similar to those of most orogenic gold deposits. Dating by 40Ar/39Ar of hydrothermal sericite collected from auriferous quartz veins at Bangbu yielded a plateau age of 44.8±1.0 Ma, with normal and inverse isochronal ages of 43.6±3.2 Ma and 44±3 Ma, respectively. This indicates that the gold mineralization was contemporaneous with the main collisional stage between India and Eurasia along the Yarlung Zangbo suture, which resulted in the development of near-vertical lithospheric shear zones. A deep metamorphic fluid was channeled upward along the shear zone, mixing with a mantle fluid. The mixed fluids migrated into the brittle structures along the shear zone and precipitated gold, sulfides, and quartz because of declining temperature and pressure or fluid immiscibility. The Bangbu is a large-scale Cenozoic syn-collisional orogenic gold deposit.
... Nevertheless, they did suggest that the mineralization in the region was related to the South Tibet Detachment System (STDS) and probably formed during the Miocene in a post-collisional setting. However, Sun et al. (2010b) and Zhai et al. (2014) suggested the Bangbu Au and Mazhala Sb-Au deposits to be orogenic-type based on the fluid inclusion studies. Recent researches have shown that the mineralization at Zhaxikang formed during two distinct phases: an early phase of Pb-Zn(− Ag) mineralization and a later Sb mineralization (Zheng et al., , 2014bLiang et al., 2013). ...
... Most deposits are hosted in Mesozoic strata, which compose mainly post-rift passive margin turbidites and underwent low-grade metamorphism during the Himalayan orogeny. The typical gold deposits include Mayoumu ( Duo et al., 2009) and Bangbu ( Sun et al., 2010), gold-antimony and antimony include Mazhala and Shalagang, these gold-and/or antimony deposits belong to typical epizonal orogenic mineral systems ( Zhai et al., 2014). From deep to shallow, gold, gold-antimony and antimony deposits compose a mineralization comtinuum. ...
The paper completes our summary of literature data on the physicochemical parameters and characteristics of the chemical composition of mineralizing fluids at endogenous gold deposits. The average values and variation limits of the temperature (50–845°С, mean 290°C), pressure (20–3600 bar, mean 600 bar), and salinity (0.1–88.0 wt % equiv. NaCl, mean 13.1 wt % equiv. NaCl) of fluids of Cenozoic gold deposits are estimated. The inherent features of the gas composition of the mineralizing fluids of these deposits are
revealed. Parameters of mineralizing fluids at Cenozoic gold deposits are discussed in comparison with the analogous parameters of fluids at Archean, Proterozoic, Paleozoic and Mesozoic gold deposits. The chemical composition and parameters of mineral-forming fluids of gold deposits were determined to systematically evolve with time. Cenozoic gold deposits generally differ from older gold deposits in having a higher fluid temperature and salinity, lower pressure, and the highest value of the CO2/CH4 ratio. The decrease in fluid pressure from ancient gold deposits to younger ones may be associated with differences in the erosion depths of ancient and young mineralizing systems.
The Bangbu gold deposit is the largest Au deposit, and the only deposit in production, within an orogenic Au belt hosted by the Indus–Yurlung Zangbo suture zone in Tibet. Strontium isotopes, and in situ trace-element data from ore-related pyrite, quartz, and fluid inclusions were used to determine the composition of ore-forming fluids, the sources of ore components, and ore-forming processes. Arsenic, Se, and Ge are incorporated into Au-bearing pyrite by isomorphic substitution for S, while Co and Ni replace Fe in the pyrite lattice, and Au occurs either as lattice-bound or in the form of nanoparticles in pyrite. The individual fluid inclusions have Au contents of 0.59–4.41 ppm, with an average of 1.43 ppm. Single fluid inclusion analyses show a negative correlation between Au and Cl contents, indicating that Au did not complex with Cl ions and was probably transported as Au(HS)2⁻. Aluminum is positively correlated with Li and Ge in ore-related quartz, consistent with a contribution from magmatic hydrothermal fluids. The average ⁸⁷Sr/⁸⁶Sr ratio of fluid inclusions in quartz is 0.71577, which indicates a contribution from mantle-derived material. Gold is likely to have been sourced from fluids evolved from mantle-derived magma, rather than the surrounding rocks.
The Himalayan mineral field includes over 50 quartz-vein type Sb-Au deposits, and placer Au deposits. The poorly documented Laqiong deposit is a typical example of quartz-vein type Sb-Au mineralisation in Tethys Himalayan sequence. The orebody are controlled by shallow north-dipping normal faults and north–south trending faults. Magmatic zircons extracted from muscovitic leucocratic granite from the southern part of the Laqiong mine area yield a Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry U-Pb age of 14 ± 1 Ma (n = 12, MSWD = 0.9) that is similar to the ⁴⁰ Ar/ ³⁹ Ar age of ca. 14 Ma from hydrothermal sericite in auriferous sulphide-quartz veins. The ε Hf (t) values for the magmatic zircon rims range from −5.4 to −1.9, corresponding to two-stage Hf model ages of 1403–1214 Ma. Quartz from the mineralised veins has δ ¹⁸ O H2O-SMOW values varying from +4.97 to +9.59‰ and δD H2O-SMOW values ranging from −119.7 to −108.1‰. The δ ¹³ C V-PDB values for calcite from the ore Stage III range from −6.9 to −5.3‰, and calcite from Stage IV are −3.5 to −1.7‰. The δ ¹⁸ O V-SMOW values for calcite from Stage III are +20.3 to +20.6‰ and for Stage IV are −6.3 to −4.9‰. The stibnite and pyrite samples have ²⁰⁸ Pb/ ²⁰⁴ Pb ratios of 38.158 to 39.02, ²⁰⁷ Pb/ ²⁰⁴ Pb ratios of 15.554 to 15.698, and ²⁰⁶ Pb/ ²⁰⁴ Pb ratios of 17.819 to 18.681, and bulk and in-situ δ ³⁴ S V-CDT values for stibnite, arsenopyrite and pyrite range from −1.1 to +2.3‰. The calcite from the orebodies are enriched in MREE and depleted in LREE and HREE. Fieldwork, petrological, and geochemical data collected during our study leads to the following salient findings: the mineralising fluid is a mix of magmatic and meteoric fluids; and the deposit is closely related to the emplacement of Miocene granites originating from a thickened continental crust.
The Nianzha gold deposit, located in the central section of the Indus-Yarlung Tsangpo suture (IYS) zone in southern Tibet, is a large gold deposit (Au reserves of 25 tons with average grade of 3.08 g/t) controlled by a E–W striking fault that developed during the main stage of Indo-Asian collision (∼65–41 Ma). The main orebody is 1760 m long and 5.15 m thick, and occurs in a fracture zone bordered by Cretaceous diorite in the hanging wall to the north and the Renbu tectonic mélange in the footwall to the south. High-grade mineralization occurs in a fracture zone between diorite and ultramafic rock in the Renbu tectonic mélange. The wall-rock alteration is characterized by silicification in the fracture zone, serpentinization and the formation of talc and magnesite in the ultramafic unit, and chloritization and the formation of epidote and calcite in diorite.
The Jiapigou gold province, located in the eastern part of the northern margin of the North China Craton, includes the Erdaogou and Xiaobeigou gold deposits, which are hosted in amphibolites, amphibolitic gneisses, and tonalite-trondhjemite-granodiorite gneisses of the Jiapigou Group. The gold deposits occur as gold-bearing quartz veins and disseminated- and veinlet-type mineralization. Orebodies are strictly controlled by NW-SE -trending secondary faults. Four stages of mineralization have been identified in the Erdaogou gold deposit: (1) milky quartz, (2) pyrite-quartz, (3) native gold-quartz-pyrite, and (4) quartz-carbonate. In the Xiaobeigou gold deposit, five stages of mineralization have been identified: (1) milky quartz, (2) pyrite-sericite-quartz, (3) pyrite-quartz, (4) native gold-quartz-pyrite, and (5) quartz-carbonate. Three fluid inclusion populations have been identified in the deposits: CO2-H2O (C-type), aqueous (W-type), and pure CO2 (PC-type). C-type, W-type, and PC-type fluid inclusions are observed in the Erdaogou gold deposit, whereas C-type and W-type fluid inclusions are dominant in the Xiaobeigou gold deposit. Microthermometric data indicate that the fluid inclusions of the deposits homogenize at 128-370C (0.18-15.35wt.% NaCl equivalent). Pressures estimated from fluid inclusion data cluster into two populations at 140-165MPa and 60-80MPa, indicating that mineralization occurred at a depth of 5.1-8.0km. The O-isotope ratios (δ¹⁸OH2O) of ore-forming fluids in the Xiaobeigou gold deposit range from -1.84‰ to -1.14‰, with δD of -102‰, whereas late-stage fluids have δ¹⁸OH2O of -9.40‰ to -9.20‰, and δD of -78‰. Integrated C-H-O-S-Pb-isotope data suggest that the initial ore-forming fluids of the deposits consisted of magmatic water produced by the partial melting of lower crustal material containing a mantle component. Water-rock interaction occurred in the early mineralization stage. Fluid immiscibility resulted in rapid gold deposition. Regional and deposit geology, fluid inclusions, and stable isotopes indicate that the Erdaogou and Xiaobeigou gold deposits are mesothermal, related to subduction of the Paleo-Pacific plate. The Jiapigou gold province has significant potential for deep-seated mineralization, and should be the focus of future exploration.
The Bangbu gold deposit is a large orogenic gold deposit in Tibet formed during the Alpine-Himalayan collision. Ore bodies (auriferous quartz veins) are controlled by the E-W-trending Qusong-Cuogu-Zhemulang brittle-ductile shear zone. Quartz veins at the deposit can be divided into three types: pre-metallogenic hook-like quartz veins, metallogenic auriferous quartz veins, and post-metallogenic N-S quartz veins. Four stages of mineralization in the auriferous quartz veins have been identified: (1) Stage S1 quartz+coarse-grained sulfides, (2) Stage S2 gold+fine-grained sulfides, (3) Stage S3 quartz+carbonates, and (4) Stage S4 quartz+ greigite. Fluid inclusions indicate the ore-forming fluid was CO2-N2-CH4 rich with homogenization temperatures of 170-261°C, salinities 4.34-7.45 wt% NaCl equivalent. δ18Ofluid (3.98‰-7.18‰) and low δDV-SMOV (-90‰ to -44‰) for auriferous quartz veins suggest ore-forming fluids were mainly metamorphic in origin, with some addition of organic matter. Quartz vein pyrite has δ34SV-CDT values of 1.2‰-3.6‰ (an average of 2.2‰), whereas pyrite from phyllite has δ34SV-CDT 5.7‰-9.9‰ (an average of 7.4‰). Quartz vein pyrites yield 206Pb/204Pb ratios of 18.662-18.764, 207Pb/204Pb 15.650-15.683, and 208Pb/204Pb 38.901-39.079. These isotopic data indicate Bangbu ore-forming materials were probably derived from the Langjiexue accretionary wedge. 40Ar/39Ar ages for sericite from auriferous sulfide-quartz veins yield a plateau age of 49.52 ± 0.52 Ma, an isochron age of 50.3 ± 0.31 Ma, suggesting that auriferous veins were formed during the main collisional period of the Tibet-Himalayan orogen (∼65-41 Ma).
The Naozhi Au–Cu deposit is located on the continental margin of Northeast China, forming part of the West Pacific porphyry–epithermal gold–copper metallogenic belt. In this paper, we systematically analyzed the compositions, homogenization temperatures, and salinity of fluid inclusions as well as their noble gas isotopic and Pb isotopic compositions from the deposit. These new data show that (1) five types of fluid inclusions were identified as pure gas inclusions (V-type), pure liquid inclusions (L-type), gas–liquid two-phase inclusions (W-type, as the main fluid inclusions (FIs)), CO2-bearing inclusions (C-type), and daughter-mineral-bearing polyphase inclusions (S-type); (2) W-type FIs in quartz crystals of early, main, and late stage are homogenized at temperatures of 324.7–406.7, 230–338.8, and 154.6–308 °C, with salinities of 2.40–7.01 wt% NaCleq, 1.73–9.47 wt% NaCleq, and 6.29 wt% NaCleq, respectively. S-type FIs in quartz crystals of early stage are homogenized at temperatures of 328.6–400 °C, with salinities of 39.96–46.00 wt% NaCleq; (3) Raman analysis results reveal that the vapor compositions of early ore-forming fluids consisted of CO2 and H2O, with H2O gradually increasing and CO2 being absent at the late mineralization stage; (4) fluid inclusions in pyrite and chalcopyrite have 3He/4He ratios of 0.03–0.104 Ra, 20Ne/22Ne ratios of 9.817–9.960, and 40Ar/36Ar ratios of 324–349. These results indicate that the percentage of radiogenic 40Ar* in fluid inclusions varies from 8.8 to 15.5 %, containing 84.5–91.2 % atmospheric 40Ar; (5) the 206Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of sulfides are 18.1822–18.3979, 15.5215–15.5998, and 38.1313–38.3786, respectively. These data combined with stable isotope data and the chronology of diagenesis and metallogenesis enable us suppose that the ore-forming fluids originated from the melting of the lower crust, caused by the subduction of an oceanic slab, whereas the mineralized fluids were exsolved from the late crystallization stage and subsequently contaminated by crustal materials/fluids during ascent, including meteoric water, and the mineral precipitation occurred at a shallow crustal level.
Zhaxikang antimony polymetallic ore deposit, the first super large deposit discovered in northern Himalayan metallogenic belt (NHMB) and first SEDEX discovered modified by hot spring type Mn-Fe-Sb-Pb-Zn-Ag deposit in China, is the marked prospecting breakthrough in the youngest and great southern Tibetan detachment system (STDS). Many detailed field surveys and comprehensive researches have been made to seek evidence of SEDEX and hot spring mineralization, including the ferromanganese carbonate formation, lamellar structure, dalmatianite structure, concentric rings, paleo-spout, hot water eggs, hydrothermal breccia, hot spring hole, (Pb+Zn) concentration much higher than Cu, Ga concentration much higher than In, as well as the higher concentrations of Mn, Fe, Ba and B. These indicate that Zhaxikang is the SEDEX modified by hot spring type deposit. The innovation of ore-forming prospecting theory method plays an important role in the prospecting breakthrough of Zhaxikang deposit. Based on the analysis of characteristics of ore deposit and its genetic type, the discovery process and exploration advance were introduced, which is of great significance both in the prospecting theories and practices, and in the exploration and evaluation, scientific research, and theory innovation in NHMB.
The Shalagang antimony deposit is the most representative antimony deposit of gold-antimony ore-forming belt in southern Tibet, China. A microthermometric study using infrared microscopy was performed on fluid inclusions hosted in stibnite and symbiotic quartz, in order to directly characterize physicochemical conditions of ore-forming fluid from Shalagang antimony deposit. Results of infrared microthermometric measurement show that fluid inclusions hosted in stibnite have homogenitation temperatures values of 134.9-221.9°, with a peak of 160 ∼ 190°C, salinity values of 1.65% ∼ 7.25% NaCleqv, with a peak of 5.0% ∼ 6.0% NaCleqv, and density values of 0.879 ∼ 0.958g/cm, with an average of 0.934g/cm3; fluid inclusions hosted in symbiotic quartz have homogenitation temperatures values of 142.5 ∼ 205.6°C, with a peak of 160 ∼ 190°C, salinity values of 2.31% ∼ 6.96% NaCleqv, with a peak of 4.0% ∼ 6.0% NaCleqv, and density values of 0.910 ∼ 0.947g/cm3, with an average of 0.929g/cm3. Comparative study indicates that stibnite and symbiotic quartz from Shalagang antimony deposit formed in the same physicochemical conditions and capture the same ore-forming fluids. With Laser Raman analysis of fluid inclusions hosted in symbiotic quartz, it shows that the ore-forming fluids of the Shalagang antimony deposit is a NaCl-H2O fluid system which is characterized by low homogenization temperature, low salinity, low density and trace CO2, N2 and H4 gases. The boiling of ore-forming fluid is the dominant factor for stibnite deposition.
Bangbu gold deposit is located to the south of the east section of Yarlung Zangbo tectonic suture zone in the Southern Tibet. Ore bodies are controlled by the secondary fractures in the large-scale brittle-ductile shear zone. Its geological and geochemical characteristics show that it is an orogenic gold deposit. In this study, He-Ar-S isotopic compositions of ore-forming fluids in pyrites collected from the Bangbu auriferous quartz veins were analyzed, and the results show that 3He/4He ratio is 0.174 to 1.010R a, 40Ar/39Ar ratio ranges from 311. 9 to 1724. 9, and δ34S is 2. 8% ∼ 4. l%, averaging 3. 6%: whereas pyrite collected from country rocks has 3He/4He ratio of 0.01137Ra, 40Ar/36 Ar of 1709.7, and δ34S of 6.5%, suggesting that the ore-forming fluid of the Bangbu gold deposit was a mixture of crust fluid and mantle-derived fluid, and the former is predominant. The ration of mantle-derived He is 2. 7% ∼ 16.7%. Crust-mantle interaction and the subsequent injection of mantle-derived fluids might have played an important role in the mineralization of the Bangbu gold deposit. During collision between India plate and Asia plate, large-scale vertical lithospheric shear zones were formed, and the subsequent mantle-derived fluid went up through the shear zone, mixing with the lower crust derived CO2-rich fluid. The mixed ore-forming fluids migrated to the secondary brittle structures in the shear zone, and finally precipitated auriferous sulfide quartz ores because of decline of temperature and pressure and subsequent boiling of the ore-forming fluids.
The study of fluid inclusions from the Laowangzhai gold deposit shows that the types of fluid inclusions in auriferous quartz veins are mainly NaCl-H 2Oinclusions and CO2H2O inclusions; that in the pre-metallogenic stage ( I ), the homogeneous temperature of fluid inclusions is concentrated in 300. 0̃350. 0°C; the salinity (mass fraction of NaCl) is 9. 209% ̃ 9. 856%, the metallogenic pressure varies is 82. 7 ̃108. 4 MPa and the emplacement depth is about 3. 18 ̃4. 17 km; that in the metallogenic stage ( II ), the homogeneous temperature is concentrated in 195. 0 ̃225. 0°C ; the salinity is 4. 495% ̃ 4. 650%, the metallogenic pressure varies is 71. 1 ̃ 73. 6 MPa and the emplacement depth is about 2. 73 ̃ 2. 83 km, and that in the metallogenic stage( III ) , the homogeneous temperature is concentrated in 106. 8 ̃ 171. 1°C , the salinity is 2. 737%̃4. 650%, the metallogenic pressure varies is 41. 0 ̃ 46. 0 MPa and the emplacement depth is about 1. 58 ̃ 1. 77 km. The measurements of the noble gas isotopes display that the average of 3 He/4 He ratios of the ore-forming fluids is 0. 4614 Ra, which is higher than the crustal eigenvalue and lower than the mantle eigenvalue, that the average of 40Ar/36Ar ratios and 38Ar/36Ar ratios is 341. 8 and 0. 20675 respectively, which are higher than air's, and lower than MORB's or OIB's, and that the 129̃136Xe/130Xe ratios all show surplus characteristics compared with air's. The combined study of noble gas isotopes and the characteristics of the fluid inclusions from the gold deposit reveals that the CO2-bearing deep hydrothermal solution with higher temperature and pressure carries metallic elements from deep to superficial part and companying with the temperature and pressure decreasing and CO2 escaping, the solution is supersaturated, thus, gold and pyrite and other sulfides are precipitated to form the deposit, from the pre-metallogenic stage ( I )→ the metallogenice stage ( II )-→-the post-metallogenic stage ( III ), and the mineral-laden fluid presents the continuous evolution characteristics that temperature, pressure and salinity decrease and emplacement rises. Meanwhile, the deep fluids derived from mantle are mixed with the crustal fluids at varying degrees, resulting in the mixture of crust-mantle materials to be favourable for mineralization.
The Mazhala Deposit is the most representative gold-antimony deposit in the gold-antimony ore-forming belt in southern Tibet, China. Microscopic observation and microthermometric study were performed on fluid inclusions hosted in gold-bearing mineral (stibnite and quartz), in order to directly characterize the physicochemical conditions of ore-forming fluid and investigate the genetic type of the deposit, source of ore-forming fluids and metallogenic mechanism of Mazhala antimony-gold Deposit. The results of microscopic observation show that the fluid inclusions hosted in stibnite and quartz are nearly the same and can be divided into four types: i-e. two-phase aqueous, three-phase CO2-H2O, pure CO2 and pure H 2O inclusions, respectively. Infrared microthermometric study show that the homogenization temperature (Th) values of the fluid inclusions hosted in stibnite peak at 180-210°C, the salinity values peak at 2. 5 ∼3. 4% NaCleqv, and density values peak at 0. 895 ∼0. 915g/cm 3, and that the Th, salinity and density of the fluid inclusions hosted in quartz show triple peaks at 270-300°C:, 225-255°C: and 180-210°C:, 4. 3% ∼4. 9%NaCleqv, 3. 4% ∼4. 0% NaCleqv and 2. 8% ∼3. 4% NaCleqv, and the 0. 895 ∼0. 915g/cm3, 0. 835 ∼0. 855g/cm3 and 0. 775 ∼0. 795g/cm3, respectively. Comparison of the microthermometric measurements shows that the Th, salinity and density of the fluid inclusions hosted in stibnite match with the lower T h and salinity and higher density values of inclusion hosted in the late stage of quartz, indicating that quartz was deposited from the ore-forming fluid before stibnite, also suggesting the input of low temperature and low salinity while high density fluids during stibnite precipitation. The δ5DH2o of the fluid inclusions hosted in stibnite and quartz is -68. 1%o ∼-108%o, and their δOH2o is -2. 2%o ∼12. 2%o, projected near metamorphic fields in the δD-δ18 O diagram, occasionally near meteoric line, indicating that ore-forming fluid is the mixture of metamorphic and meteoric waters. The δ13 C of fluid inclusion hosted in quartz is - 2. 9%o ∼-3. 5%o, with an average of -3. 1%o, which falls within the range of mantle-derived carbon(δ 13 C = -5%o ∼-1%o), indicating C02 is probably mantle-derived. Moreover, the δ13 C of fluid inclusion hosted in stibnite is - 12. 6%o, which is significantly smaller than the mantle-derived carbon, suggesting a considerable amount of organic carbon was involved in ore-forming fluid during stibnite deposited. The ore-forming fluids of the Mazhala gold deposit is characteristics by high content of CO2, low salinity, low to moderate Th and low density, which are similar to those of typical orogenic gold deposits. Geologic and geochemical features show that the Mazhala goldantimony deposit may be a Cenozoic orogenic gold-antimony deposit formed under continental collisional background.
The Zhemulang gold deposit is located to the south of the east section of the Yarhing Zangbo tectonic suture zone in the southern Tibet The gold ore bodies are controlled by the secondary brittle fractures of the large-scale brittle-ductile shear zone. Microthermometric measurements and Laser Raman analysis show that auriferous quartz veins of the Zhemulang gold deposit contain three types of fluid inclusions: NaCl-H 2O inclusions (type I) ; CO 2 brine inclusions (type II) , which can be subdivided into two-phase (type IIa) and three-phase (type lib) inclusions; Pure gaseous inclusions (type III). The NaCl-H 2O inclusions have salinity values of 2.31% - 7.39% NaCleqv, with a peak of 4.0% - 7.0% NaCleqv and an average of 5.33% NaCleqv, homogenization temperature values of 164.5 - 273. 1°C, with a peak of 220 - 240°C and an average of 221.0°C , and density values of 0.82 - 0.93g·cm -3, with a peak of 0.84 - 0.90g · cm -3 and an average of 0.88g cm -3, suggesting that the are-forming fluids of the Zhemulang gold deposit is characteristics by high content of CO 2, low salinity, low to moderate homogenization temperature and low density, which are similar to those of typical orogenic gold deposits. H-O-C isotopic analyses show that δD H2O = -36.7‰ - -107.5‰, δ 18O H2O = 4.1‰ - 5.5‰, δ 13C = -9.6‰ - -11.5‰ in Zhemulang gold deposit, indicating that the ore-forming fluids is composed mainly of metamorphic fluid, with addition of mantle-derived fluid. Geologic and geochemical features show that the Zhemulang gold deposit may be an orogenic gold deposit formed under continental collisional background.
Liyuan Gold Deposit is located at the Taihang Mountain tectonic-magma-polymetallic metallogenic belt. Ore bodies mainly occur in the NNE-trending structural zone. The hydrothermal process can be divided into four stages, namely, A stage (quartz vein stage), B stage (quartz-pyrite stage), C stage (quartz-polymetallic sulfide stage) and D stage (quartz-carbonate stage). Three types of fluid inclusions are developed in B, C and D stages: aqueous inclusion (type I), CO2-aqueous inclusion (type II) and pure CO2 inclusion (type III). All three types of inclusions, mainly type I inclusions present in stage B, with homogenization temperatures ranging in 230-350 ℃, and salinities ranging from 1.82% to 12.63%. In addition to development of type I inclusions, type II and III inclusions increase significantly in stage C, with homogenization temperatures ranging from 200 ℃ to 330 ℃, salinities ranging in 1.82%-9.71%. Type I inclusions relatively develop in stage D, with homogenization temperatures concentrating in 140-170 ℃, and salinities ranging from 1.16% to 9.58%. High density of CO2 and CH4, H2 and N2 are found as gas compositions in the inclusions. Liquid phase of fluid is mainly composed of Ca2+, Na+, K+, SO42-, Cl-, F-. The calculated metallogenic pressures are in the range of 68-114 MPa, corresponding to capture temperature of 200-430 ℃, and the maximum estimated mineralization depth is 4.3 km. To sum up, the mineralization fluid of Liyuan Gold Deposit may be late magmatic hydrothermal fluid, belongs to low salinity, medium-low temperature, CO2-rich Ca2+(Na+, K+)-SO42-(Cl-, F-)-H2O-CO2 system. Liyuan Gold Deposit formed in intracontinental orogeny belongs to magmatic hydrothermal altered rock type gold deposit controlled by fracture zone. ©, 2015, Central South University of Technology. All right reserved.
The Dachang gold ore field, one of the super large ore field in the Sichuan-Shanxi-Gansu boundary region, is located in the Kekexili-Songpanganze in Late Palaeozoic-Mesozoic turbidite basin and fold and fault belt. It is controlled by an NW-trending structural and altered belt, and hosted in the Triassic carbonaceous sand stone-slate of flysch deposition. The main ore minerals are pyrite, arsenopyrite and stibnite, and gangue minerals are quartz, feldspar and calcite. The gold occurred as grained gold. Microthermometric measurements show that auriferous quartz veins in the Dachang gold ore field have three types of fluid inclusions: NaCl-H2O inclusions (type W):CO2 brine inclusions (type C) and pure gaseous inclusions (type PC). The salinity values of NaCl-H2O inclusions have a peak of 2% ∼5%NaCleqv, homogenization temperature values with a peak of 180 ∼200°C and metallogenic depths are 1.9 ∼12.3km. The pure gaseous inclusions are dominanted by N2, CO2, O2, H2O, with minor H2S. Liquid phase composition are Ca 2+, Na, Li+, K + and SO42-, CI, NO3-, F, with minor Mg2 +. They suggest that the ore-forming fluids of the Dachang gold ore field are characterized by low salinity, low to moderate homogenization temperature. H-0 isotopes analyses show that δD = -62%o ∼-106%o, δOH 2o =3. 1%o ∼10. 5%o, indicating that the ore-forming fluids are composed mainly of devolatilization of organic matter, with meteoric water. Geological and fluild features and metallogenic mechanism suggest that the Dachang gold ore field may be Carlin-like gold deposit.
Ailaoshan gold deposit belt formed during Himalayan orogenisis in Yunnan Province is one of the most important gold deposits belts in China, within which the Laowangzhai gold deposit is the biggest one. Fluid inclusion microtheimometry, Laser Raman analysis and carbon, hydrogen and oxygen isotope measurements are carried out in fluid inclusions of auriferous quartz veins from Laowangzhai gold deposits. The fluid inclusions are mainly NaCl-H 2O and CO 2-H 2O types. Microthermometric measurements show that the homogenization temperatures range from 102°C to 302°C, with peak values of 160 - 180 °C , the salinities are 2.5% NaCleqv to 12.9% NaCleqv, with peak values of 6.0% ∼7.5% NaCleqv,indicating that the ore-forming fluids are characterized by low salinity and mid-low temperature. Isotopic analyses show that δD h2o and 8 18O 1120 of the ore-forming fluids are - 115%o-90% e and 5. 2% o ∼ 6. 8% o, respectively, implying that the ore-forming fluids are mainly composed of magmatic fluid, with isotope interference of organic sediments. Carbon isotopic composition of the fluid inclusions lays within the range of mantle-derived carbon, suggesting that CO 2 in the ore-forming fluids was probably derived from the deep crust, even the upper mantle. Geologic and geochemical features show that the Laowangzhai gold deposit is an orogenic gold deposit formed during the Himalayan orogenisis.
Based on the petrological studies of wall rocks, mineralized rocks, ores and veins from the Laowangzhai gold deposit, it is discovered that with the development of silification, carbonation and sulfidation, a kind of black opaque ultracrystalline material runs through the space between grains and amphibole cleavages, which is the product of fast condensing consolidation with magma mantle fluids turning into hydrothermal crustal fluids in the process of mineralization and alteration. It is thought that the water in ore-forming fluids mainly derived from magmatic water through research on H-O isotopes, and C as well as S isotopic compositions, has clear mantle-derived characteristics, and rock (mine) stones contain high 87Sr/86Sr ratios, low 143Nd/144Nd ratios and high 206Pb/204Pb ratios, which also reflects the ore-forming fluids were derived from the metasomatically enriched mantle. In combination with the features of H-O-C-S isotopes and Sr-Nd-Pb isotopes described above, the ore-forming fluids of the Laowangzhai gold deposit in the northern part of the Ailao Mountains were derived mainly from the deep interior of the mantle, and their properties were transformed from magma fluids to hydrothermal fluids in the course of metasomatism and alteration, which initiated crust-mantle contamination simultaneously to be in favor of mineralization.
Mineralization epochs of the Daping gold deposits are divided into three stages: the early stage or scheelite-bearing quartz vein stage, the major stage or massive polymetallic sulphide typed auriferous quartz vein stage and the late stage or carbonate-quartz stage. Fluid inclusions in the various ore veins were studied by using a cooling/ heating stage and a Laser Raman spectroscopy, and the results show that the fluid inclusions are dominated by liquid CO2 inclusions and CO2-H2O inclusions with variable ratios of CO2/H2O. A lot of gaseous CO2-rich inclusions are found in the early stage scheelite-bearing quartz veins, liquid CO2 inclusions are dominanted in the major stage auriferous massive polymetallic sulphide ores, and aqueous inclusions are found only in the late stage carbonate-quartz veins. The gaseous phases in the fluid inclusions are nearly pure CO2, with a little N2 at the early stage. CO2-H2O inclusions in the early stage have salinity of 6.37%-14.64%NaCl with a peak of 9%-10.5%NaCl, homogenization temperature of 299.4-423. 7°C with a peak of 320-380°C entrapped pressure of about 190-440MPa, and CO2 inclusions density of 0.352-0.798g/cm3 with a majority of 0.64-0.71g/cm3. CO2-H2 O inclusions in the major mineralizing stage possess salinity of 3. 70% - 14. 64% NaCl with a mode of 7. 2% - 9. 0% NaCl, homogenization temperature of 279. 0-406. 5°C with a mode of 320-360°C, entrapped pressure of 133. 5 -340. OMPa with corresponding metallogenic depth of about 5.1-12.9km, and CO2 inclusions density of 0.591-0.843g/cm3. The fluid inclusion characteristics indicate that the ore-forming fluid of the Daping mine is a nearly critical CO2-H2 O-NaCl system with high-CO2 content (CO2 ≥, H2 O) and low to moderate salinity. Boiling or phase separation without fluid mixing might has occurred during gold mineralization. The Daping mine is a ductile shear zone controlled mesothermal deposit, which was formed by rapid decompression and subsequent boiling and deposition. Combined with other evidences, it is believed that the ore-forming fluid in the Daping gold deposit was a mixture of mantle-derived fluid and the lower crust-sourced CO2-rich fluids. The gold was probably transported by [HS] complexes in the CO2-rich fluid, and the auriferous sulfides deposition was probably caused by phase separation.
Bangbu gold deposit is located to the south of the east section of Yarlung Zangbo tectonic suture zone in the Southern Tibet. Ore bodies are controlled by the secondary fractures in the large-scale brittle-ductile shear zone. Its geological and geochemical characteristics show that it is an orogenic gold deposit. In this study, He-Ar-S isotopic compositions of ore-forming fluids in pyrites collected from the Bangbu auriferous quartz veins were analyzed, and the results show that 3He/4He ratio is 0.174 to 1.010R a, 40Ar/39Ar ratio ranges from 311. 9 to 1724. 9, and δ34S is 2. 8% ∼ 4. l%, averaging 3. 6%: whereas pyrite collected from country rocks has 3He/4He ratio of 0.01137Ra, 40Ar/36 Ar of 1709.7, and δ34S of 6.5%, suggesting that the ore-forming fluid of the Bangbu gold deposit was a mixture of crust fluid and mantle-derived fluid, and the former is predominant. The ration of mantle-derived He is 2. 7% ∼ 16.7%. Crust-mantle interaction and the subsequent injection of mantle-derived fluids might have played an important role in the mineralization of the Bangbu gold deposit. During collision between India plate and Asia plate, large-scale vertical lithospheric shear zones were formed, and the subsequent mantle-derived fluid went up through the shear zone, mixing with the lower crust derived CO2-rich fluid. The mixed ore-forming fluids migrated to the secondary brittle structures in the shear zone, and finally precipitated auriferous sulfide quartz ores because of decline of temperature and pressure and subsequent boiling of the ore-forming fluids.
Being one of the largest gold deposits in the Ailaoshan gold belt in Yunnan Province, the Daping gold mine occurred in a strongly mylonitized and sericitized Caledonian diorite batholith, and is a typical ductile shear zone-controlled gold deposit. 40Ar/39Ar dating was performed on hydrothermal sericite collected from mylonitized and sericitized diorite around rock of the Daping gold deposit, which yielded a set of age data, i. e., plateau age of 33.76±0.65 Ma, inverse and normal isochronal ages of 33.55±0.74 Ma and 33.57±0.74 Ma, respectively. These age data are very similar to ages (33-34 Ma) of the lamprophyre dykes, which are extensively distributed in the Ailaoshan gold belt, suggesting that gold mineralization of the Daping mine was closely related to the Cenozoic lamprophyre dykes, which were generated by partial melting of the upper mantle. From early of the Cenozoic Era, upwelling of the Moho and partially melted upper mantle caused by crustal extension and strong ductile deformation resulted in formation and intrusion of large amounts of lamprophyre dykes. The mantle-derived fluids formed by the upper mantle degassing and the CO2,-riching fluids from the lower crust released by dehydration and roasting triggered by the rising hot mantle magma's heat mixed and migrated up along micro-fractures in the shear zone, and reacted with the mylonitized and sericitized diorite around rock, and finally deposited the ore minerals in the brittle structures of the shear zone because of water-rock interaction and boiling.
The south Tibetan detachment system, located at the convergence belt between Indian and Asia continents, is one of the most important antimony and gold metallogenic belt in southern Tibet. The belt is composed of more than 50 antimony and gold deposits and occurrences, and parallel to the metamorphic core complex belt extending west - east. Based on the metallogenic characteristics of several deposits, three main types of deposit can be recognized as follows: (1) Shalagang type antimony deposit: orebody is quartz-stibnite vein filling in the NS-strike normal fault and EW-strike bedding fault with weakly wall-rock alteration; (2) Mazhala type antimony-gold deposit: orebody consists of gold containing quartz-stibnite vein swarm filling in fault, cleavage and joint with wall-rock alteration of silicification, sericitization, chloritization and carbonatization: (3) Langkazi type gold deposit: lenticular orebody is composed of quartz vein and altered rock with strong wall-rock alteration of silicification, chloritization and sericitization, and controlled by detachment fault and normal fault along the margin of the metamorphic core complex. Microthermometric results of fluid inclusions in quartz from Shalagang type antimony deposits and Mazhala type antimony-gold deposits show low homogenization temperature (peak value of 200°C and low salinity (1.23-6.16 NaCl%). Hydrogen- and oxygen- isotopic compositions of quartz indicate that the fluid of Shalagang type antimony deposit δD between -166‰ and - 140‰, δ18 OH2O between -11.5‰ and 12.3‰) is similar to the geothermal waters in southern Tibet, whereas the fluid of Mazhala type antimony-gold deposit (δD between -108‰ and -73‰, δ18 OH2O between 5. 4‰ and 11. 2‰) is likely to be the mixture of magmatic and meteoric waters. The regional distribution of deposit from the metamorphic core complex to the outside is in turn from Langkazi type gold deposit, to Mazhala type antimony-gold deposit, and finally to the Shalagang type antimony deposit, suggesting a close relationship between the ore-forming process and the geothermal system driven by the metamorphic core complex.
Noble gases isotopic composition of fluid inclusions in scheelites, which were collected from auriferous quartz veins in Daping gold mine, was analysed by using a high vacuum gas mass spectrum. The results are shown as follow. The 3He/4He ratios are (0.988-1.424) × 10-6 with an average of 1.205 × 10-6, and the corresponding R/Rare 0.706∼1.018, averaging 0.898. The 40Ar/36Ar ratios are 1801.8-2663.8, much higher than that of the air. 20Ne/ 22N and 21Ne/22Ne are 9.600∼11.56 and 0.028∼0.0467 respectively. The respective 134Xe/ 132Xe and 136Xe/132 Xe are 0.394-0.692 and 0.301-0.462, all higher than their corresponding values of the air. He-Ar, Ne and Xe isotopic compositions suggest that the ore-forming fluid of the Daping gold mine were composed mainly of mantle-derived magmatic fluid and crustal fluid, and air-saturated water was nearly absent. Genesis of the Daping mine might have a close relationship with crust-mantle interaction in the Ailaoshan metallogenic belt: during the early Himalayan, tectonic extension resulted in ascent and degassing of mantle magma and the mantle-derived fluids. Meanwhile, the lower crust released crustal fluid riching in CO2, 40Ar, 134Xe, 136Xe and 4He during dehydration and roasting triggered by the rising hot mantle magma's heat. The mixed fluids migrated up along micro-fractures in the shear zone, reacted with the diorite around rocks, and finally deposited the ore minerals in the brittle structures of the shear zone because of water-rock interaction and boiling. Thus, the Daping is a shear zone controlled mesothermal gold deposit.
Systematic temporal variations in the distribution of several important groups of metal deposits reflect the cyclic aggregation and breakup of large continents. In particular, metal deposits that form in continental basins or are associated with anorogenic magmatism were extraordinarily abundant in the Middle Proterozoic (2.0 to 1.4 Ga), corresponding to the assembly of the first large continents. It is important to note that peaks in the abundance of continental metal deposits also coincide with the postulated Late Proterozoic supercontinent (1.0 to 0.8 Ga) and the near maximum extent of Pangea. In contrast, metal deposits that form, or are preserved, in convergent-margin orogens were most abundant in the late Archean (2.9 to 2.6 Ga), corresponding to a period of high global heat flow and rapid stabilization of continental crust, and the past 200 my, which corresponds to the present tectonic cycle. Similar mineralization was also present, albeit less abundant, in Early Proterozoic orogens, as well as in Late Proterozoic and Phanerozoic orogens. -from Authors
Equilibrium constants for oxygen isotope exchange between quartz and
water have been measured from 195°C (1000 ln α = 12.0) to
750°C (1000 ln α = 0.4). Over limited temperature ranges the
behavior of fractionation with temperature can be approximated by 1000
ln α = 3.38 (106 T-2) - 3.40 for
200°-500°C and by 1000 ln α = 2.51 (106
T-2) - 1.96 for 500°-750°C. The results of
measurements in the quartz-water system can be combined with analogous
results from other mineral systems to make mineral-pair isotopic
thermometers for application to problems of petrogenesis.
The Donlin Creek gold deposit, southwestern Alaska, has an indicated and inferred resource of approxi-mately 25 million ounces (Moz) Au at a cutoff grade of 1.5 g/t. The ca. 70 Ma deposit is hosted in the Late Cre-taceous Kuskokwim flysch basin, which developed in the back part of the arc region of an active continental margin, on previously accreted oceanic terranes and continental fragments. A hypabyssal, mainly rhyolitic to Corresponding author: email, Goldfarb@usgs.gov
Located in western Tibet, China, the Mayum orogenic gold deposit was discovered in 2002 with estimated resources of > 80 tonnes gold. The gold mineralization is hosted by Neoproterozoic–Cambrian schists, and is controlled by nearly parallel E–W trending bedding-concordant fracture zones. The Au orebodies are composed of auriferous quartz veins and altered rocks, with the Au grades ranging from 2.23 g/t to 69.56 g/t, and containing < 3 vol.% sulfides.The δ34S values of 18 separates of sulfides from auriferous quartz veins show a large variation from − 0.2 to + 16.8‰. The lead isotope compositions of sulfides from the gold ore are characterized by highly radiogenic values and very wide ranges of ratios: 18.324 to 20.819 for 206Pb/204Pb, 15.679 to 15.856 for 207Pb/204Pb, and 38.401 to 41.204 for 208Pb/204Pb. These data indicate that lead and sulfur in the quartz veins have multiple sources, and were derived from the different wall rocks as the fluid flowed through them.Fluid inclusions indicate that the ore fluid was CO2-rich, with salinities mainly between 1 and 6 wt.% NaCl equiv, and homogenization temperatures predominantly ranging from 260 to 280 °C. The δ18O values for quartz from auriferous veins range from 13.7 to 16.3‰, and the calculated δ18OH2O values in equilibrium with quartz vary from 5.54 to 9.48‰. It suggests that the ore fluid may be derived from deep, metamorphic deep-crustal gold-transporting fluids, although a contribution from magmatic source cannot be ruled out.40Ar/39Ar age dating on the sericite from the alteration associated with the auriferous quartz veins in the Mayum gold deposit gives a plateau-like age of 59.34 ± 0.62 Ma, later than the onset of the Indo-Asian collision. It is believed the gold mineralization was related to the Indo-Asian collision, and was formed during the early stage of orogenesis.
The Daping gold deposit contains one of the largest resources in the Ailaoshan gold belt, the most economically significant Cenozoic gold belt in China. Most previous researchers considered Daping to be a reworked type gold deposit, and the ore-forming fluid to have been a mixture of magmatic and meteoric water. Ore-forming materials were considered to be derived mainly from the diorite host rocks or metamorphic basement by water-rock interaction. Detailed observation and in-situ laser Raman analyses discovered a large amount of fine-grained, highly-crystallized graphite in the auriferous sulfide quartz veins with obvious O peaks and very weak D peaks in the laser Raman spectrum, which suggests that those graphite grains were formed under granulite facies conditions. Isotope analyses show that the (87Sr/86Sr)0 and εNd(0) of the Daping scheelite, the earliest precipitated ore mineral in the paragenesis, vary between 0.7088 and 0.7112 and − 8.43 and − 6.20, respectively, and were projected in the lower crust field on a (87Sr/86Sr)0 versus εNd(0) diagram. Noble gases isotopic compositions of fluid inclusions in Daping scheelites were performed by a high vacuum gas mass spectrum, and the results show that the 3He/4He ratios are (0.988–1.424) × 10− 6 with an average of 1.205 × 10− 6, corresponding to R/Ra values of 0.706–1.018, with an average of 0.898. The 40Ar/36Ar ratios are between 1801.8 and 2663.8, much higher than that of the air (295.5); 20Ne/22Ne and 21Ne/22Ne are 9.600 to 11.56 and 0.028 to 0.0467, respectively, and the respective 134Xe/132Xe and 136Xe/132Xe are 0.394 to 0.692 and 0.301 to 0.462, demonstrating that ore-forming fluids and materials of the Daping mine derived mainly from the transitional zone between the lower crust and upper mantle. The δD compositions of fluid inclusions in Daping gold deposit are − 60.0‰ to − 85‰, with an average of − 74.5‰, whereas δ18OH2O are 2.39‰ to 7.59‰, averaging 5.68‰, indicating that the ore-forming fluids consist predominantly of metamorphic fluid, with contributions from mantle-derived primary magmatic fluids. The δ13C compositions of CO2 in fluid inclusions of Daping gold deposit lie between − 3‰ to − 6.5‰, suggesting that most of the CO2 in the ore-forming fluids was mantle-derived, and part came from the lower crust in the Ailaoshan gold belt. In addition, primitive mantle normalized platinum group elements (PGE) patterns for the auriferous ores are similar to that of the Cenozoic lamprophyre dykes in the gold deposit, but quite different from that of the diorite host rocks, also implying that the ore-forming materials in the Daping deposit derived mainly from the lower crust or even the upper mantle.The new data imply that crust–mantle interaction may have played an important role in the mineralization of the Daping deposit. At around 33 Ma, the middle and lower crust in the Daping area suffered high-temperature and high-pressure metamorphism because of ductile deformation and upwelling upper mantle magmas. The ore-forming fluids enriched in CO2, 3He, 20Ne and 130Xe, generated by granulite facies metamorphism and baking by upwelling upper mantle magmas, were transported to the middle to upper crust along the ductile shear zone along with highly crystallized graphite grains, and finally precipitated auriferous sulfide-quartz veins in brittle structures because of declining temperature, pressure, and subsequent boiling. Daping is a typical ductile shear zone controlled orogenic gold deposit.
Orogenic gold deposits have formed over more than 3 billion years of Earth's history, episodically during the Middle Archean to younger Precambrian, and continuously throughout the Phanerozoic. This class of gold deposit is characteristically associated with deformed and metamorphosed mid-crustal blocks, particularly in spatial association with major crustal structures. A consistent spatial and temporal association with granitoids of a variety of compositions indicates that melts and fluids were both inherent products of thermal events during orogenesis. Including placer accumulations, which are commonly intimately associated with this mineral deposit type, recognized production and resources from economic Phanerozoic orogenic-gold deposits are estimated at just over one billion ounces gold. Exclusive of the still-controversial Witwatersrand ores, known Precambrian gold concentrations are about half this amount.
The so-called `mesothermal' gold deposits are associated with regionally metamorphosed terranes of all ages. Ores were formed during compressional to transpressional deformation processes at convergent plate margins in accretionary and collisional orogens. In both types of orogen, hydrated marine sedimentary and volcanic rocks have been added to continental margins during tens to some 100 million years of collision. Subduction-related thermal events, episodically raising geothermal gradients within the hydrated accretionary sequences, initiate and drive long-distance hydrothermal fluid migration. The resulting gold-bearing quartz veins are emplaced over a unique depth range for hydrothermal ore deposits, with gold deposition from 15–20 km to the near surface environment.On the basis of this broad depth range of formation, the term `mesothermal' is not applicable to this deposit type as a whole. Instead, the unique temporal and spatial association of this deposit type with orogeny means that the vein systems are best termed orogenic gold deposits. Most ores are post-orogenic with respect to tectonism of their immediate host rocks, but are simultaneously syn-orogenic with respect to ongoing deep-crustal, subduction-related thermal processes and the prefix orogenic satisfies both these conditions. On the basis of their depth of formation, the orogenic deposits are best subdivided into epizonal (<6 km), mesozonal (6–12 km) and hypozonal (>12 km) classes.
The Palaeozoic western Lachlan Orogen in Victoria (SE Australia), the Buller Terrane (western South Island, New Zealand) and the Meguma Terrane (Nova Scotia, Canada) are remarkably similar in regard to their geological age and history, structural make-up, and the setting and formation of orogenic lode-and disseminated-style gold deposits within these fold belts. A comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities, but it also reveals several major geological, structural, tectonic, geochemical, and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts. Aspects that stand out as potentially playing a critical role in the generation of a Phanerozoic world-class orogenic gold province include (1) the presence of a hydrated, oceanic-character substrate that can provide a fertile ‘source’ rock for both fluids and metals, (2) asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting, (3) the existence of a number of near-vertical, deep-seated faults, (4) substantial transcurrent movement, and (5) evolution of an accretionary-subduction system that promotes development of an extensive fore-arc system with prolonged fluid generation and circulation. Quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits, and also have the potential to enable discrimination between more and less gold-favourable orogens, and parts of orogens.