Gold Belt Research Articles

Thermochronological constraints on the exhumation history of the Carboniferous Katebasu gold deposit, western Tianshan gold belt, NW China

Abstract The western Tianshan Gold Belt hosts numerous giant and large gold deposits that have been formed during the late Paleozoic amalgamation of the Tianshan orogen. However, little is known about their exhumation histories during the Mesozoic to Cenozoic intracontinental evolution of the orogen. The Carboniferous Katebasu orogenic gold deposit in northwestern China is a new gold discovery within the western Tianshan Gold Belt, and it shares many similarities with other orogenic gold deposits in the belt. In this contribution, new 40 Ar/ 39 Ar and (U–Th)/He ages were combined with previous geochronology and numerical modelling to quantify its post-Carboniferous cooling and exhumation history. The results revealed a three-phase cooling history and two phases of post-mineralization exhumation. We suggest that a large volume ( c. 0.8 km) of the mineralized roof parts of the Katebasu deposit might have been removed during uplift and erosion, whereas significant ore reserves could still exist at depth. The large erosion depth of the Katebasu gold deposit in the Nalati Range of the Chinese western Tianshan also signifies that shallow-emplaced porphyry and epithermal systems that formed prior to Permo-Triassic uplift might have been largely eroded.

Imaging the shallow crustal velocity structure of the Qingchengzi ore field on the Liaodong Peninsula, China, with a short-period dense array using ambient noise tomography

The Qingchengzi ore field, which is located in the middle of the Liaodong Peninsula, has a large number of Au, Ag, and Pb-Zn deposits owing to Mesozoic tectonic and magmatic-hydrothermal activities. To reveal the relationship between shallow crustal velocity and gold mineralization and provide constraints on deep ore prospecting (> 1.5 km), ambient noise tomography consisting of an experimental short-period dense array with 334 seismographs surrounding the study region, is adopted. Shallow crustal velocities at depths less than 5.0 km are obtained by a direct inversion method of Rayleigh wave phase velocity dispersion at a period of 0.5–3.0 s. We obtain the following results. (1) The Jianshanzi fault (JSZF) is well imaged at a depth of 5.0 km. Because ore-forming fluids and materials originated from adjacent concealed granite intrusions characterized by low-velocity anomalies, we infer that the JSZF contributed to mineralization. (2) The Baiyun gold alteration belt in the northern ore field has a high velocity and cuts through the surrounding low-velocity area, extending downward to approximately 0.9 km. This high-velocity belt may be a superposition of the marble of the Dashiqiao Formation and mineralization-alteration, which suggests that the depth of the belt may be of favorable prospecting potential. (3) Based on the obvious low-velocity intrusive anomalies beneath the southern Xiaotongjiapuzi gold belt, we deduce that the mineralization of the Xiaotongjiapuzi gold belt is controlled by unexposed granite intrusions and thus has high mineralization potential at great depths. (4) A geologically reasonable model of the distribution of possible concealed granite intrusions related to deep mineralization and two prospective mineralization areas is presented.

K–Ar geochronology of orogenic gold mineralization in the Vangtat gold belt, southeastern Laos: Effect of excess argon in hydrothermal quartz

AbstractThe Thongkai‐Ok gold deposit is one of several actively mined deposits in a newly discovered orogenic gold belt in southeastern Laos. At a district scale, gold mineralization occurs within the Vangtat shear zone, one of the tectonic structures of the Poko suture zone that marks the collision between the Indochina Terrane and the Kontum Massif in southern Laos‐central Vietnam. High grade gold mineralization is associated with quartz–pyrite–white mica veins and silicified zones up to 10 m thick, hosted by strongly deformed and sheared pelitic schist. Lower‐grade gold mineralization occurs in a graphite–carbonate–quartz–sulfide hydrothermal alteration envelope that grades into sub‐economic/barren altered pelitic schist. The objective of this study is to establish the age of mineralization in the Vangtat orogenic gold belt by K–Ar dating of hydrothermal white mica in the gold‐bearing quartz‐sulfide veins in order to better understand its spatial and temporal relation to other gold deposits in Southeast Asia and to regional tectonic events. Three‐white mica bearing quartz–pyrite samples were collected from the open pit at Thongkai‐Ok. The dominant white mica phase in the samples is 2M1 muscovite and the K2O content measured by electron microprobe techniques in individual white mica crystals ranged between 8.61 and 9.79 wt%. Two of the three vein samples were separated by gravity settling into four size fractions, <2, 2–4, 4–10, and 10–40 μm, respectively. The results of potassium measurements by flame photometry in the K–Ar sample aliquots show a range in potassium content which reflects the amount of quartz present in each sample as an impurity. With one exception, a correlation was observed between potassium concentration in the samples, including the size fraction separates, and the calculated K–Ar age. The large range of calculated ages, from 348 to 206 Ma, is interpreted to reflect excess argon contained in fluid inclusions in the hydrothermal quartz present in the analyzed samples. We interpret the youngest age of the quartz‐free samples, 206 ± 4 Ma, as closest to the age of mineralization in the Vangtat gold belt. The age could be as young as ~170 Ma if the age versus potassium content relation is extrapolated to the average potassium content of white mica in the samples analyzed.

Acid mine drainage at the Bahia Gold Belt (Brazil): microbial isolation and characterization.

Acid mine drainage occurs due to the chemical and microbiological oxidation of sulfide minerals and can be a source of potentially toxic elements contamination of groundwater and surface water. The objective of this study was to identify microorganisms involved in sulfide oxidation in the tailings of a Bahia Gold Belt mine (Brazil). Samples of solids and water were collected at the mine tailings dam and characterized. The microorganisms were isolated after enrichment and subsequent purification. The major constituents of the tailings are Si, Fe, Al, S, and K. The sulfur content of the tailings is 0.98%. The major phases are quartz, muscovite, and clinochlore. Gravity concentrates of the tailings show several particles of pyrite, that is, the major sulfide phase. Molecular analysis identified the microorganisms isolated in the acid mine drainage process in this region. Five bacterium species were found: Acidithiobacillus spp., Acidithiobacillus ferrooxidans, Acidiphilium spp., Leptospirillum type II, and Sulfobacillus spp. No organisms of the archaea or eukaryote domains were found. The isolate was used in the bioleaching of copper sulfide ore, and the copper extraction was about 60% in 60days for ground ore.

Mesozoic mafic dykes in the North China Craton: magmatic evolution and implications for gold mineralization

ABSTRACT The North China Craton (NCC), which underwent multiple subduction and lithospheric destruction during the Mesozoic, is well known for hosting some of the world-class gold deposits. In many cases, Mesozoic mafic dykes are associated with the gold deposits, although there has been no systematic studies aimed to integrate the characteristics of these dykes in different regions of the NCC. Here we investigate diabase and lamprophyre dyke suites in the Xiaoqinling region along the southern margin of the NCC, and compile the published geochronological, geochemical and isotopic data for regional mafic dykes and gold deposits from the major gold belts including Jiaodong, Xiaoqinling and central NCC. Zircon U-Pb data show the mafic dykes in Xiaoqinling were emplaced in two episodes at 219–227 Ma and 121–137 Ma, and their εHf(t) values (ranging from −2.1 to 3.8 and −13.6 to 1.6 respectively) suggest increasing input of lithospheric materials in the Early Cretaceous dykes. The compiled geochemical data on the mafic dykes from different regions in the NCC show that the magmatic evolution involved olivine and clinopyroxene fractional crystallization with limited crustal contamination and subduction-related fluid metasomatism. The geochemical and isotopic signature suggests multiple sources for the parent magma of the mafic dykes ranging from convective asthenospheric mantle to ancient lithospheric mantle, with the magma source characterized by enriched mantle (EM2 or EM2+ EM1), and that signatures might be potential for gold mineralization. Further, most dykes are coeval and cospatial with gold deposits in the NCC. The geochronological data show that small amount of both Mesozoic dykes and gold deposits formed in Triassic whereas the peak formed in Cretaceous following slab roll back of the Pacific plate subducting from the east during 145–110 Ma. We envisage that the tectonic extension associated with Pacific slab subduction contributed to the magmatism and gold mineralization in the NCC.

Contrast between metamorphic and ore-forming fluids in the Ailaoshan belt, southeastern Tibet: New constraints on ore-fluids source for its orogenic gold deposits

The source of ore-forming fluids for orogenic gold deposits is still disputed with models ranging from derivation from metamorphism of continental crust to derivation from metasomatized mantle lithosphere. This dispute is addressed by this study of the Ailaoshan orogenic gold belt, southeastern Tibet, whose evolution involved intense metamorphism on the eastern side of the Ailaoshan shear zone. Both the regional metamorphic barren quartz veins and gold-related quartz veins in this belt are genetically related to movement on the Ailaoshan shear zone and thus formed over the same limited age span. Microthermometry, fluid compositions and stable isotope analyses conducted on both metamorphic fluids extracted from regional metamorphic quartz veins and ore-forming fluids collected from auriferous quartz veins at Zhenyuan and Jinchang gold deposits reveal significant differences. These include: (1) regional metamorphic quartz veins contain three types of fluid inclusions, including CO2-rich, aqueous-CO2 and aqueous types. The CO2-bearing inclusion types are more abundant than those in auriferous quartz veins; (2) those fluids from barren metamorphic veins with high CO2 content (up to 45 mol%) are typified by low-medium temperature (217–418 °C), low salinity (2–8 wt% NaCl) and variable pressure (28–440 MPa), and belong to the NaCl-CO2-H2O system. In contrast, the ore-forming fluids, which exhibit lower temperature (mainly 170–270 °C), higher salinity (mainly 5–13 wt% NaCl), and lower pressure (20–282 MPa and 14–44 MPa for Zhenyuan and Jinchang, respectively), belong to the NaCl-H2O-CO2 system; (3) the metamorphic fluids contain high Ca2+ and Mg2+ in liquids and CO2, N2 and CO in gases, whereas the ore-forming fluids are enriched in K+ in liquid and H2O, CO2, CH4 in gases; (4) the pyrites from regional metamorphic quartz veins have δ34S values ranging from 2.08 to 2.86‰ (mean = 2.50‰), indicating a single sulfur source of metamorphic fluids, thus contrasting with the broad range of δ34S values of ore sulfides. These distinctions negate a genetic relationship between crustal metamorphism and gold mineralization and demonstrate that ore-fluids that deposit orogenic gold deposits, at least in the Ailaoshan belt cannot be derived or evolved from crustally-derived regional metamorphic fluids. This provides a new line of evidence for the derivation of ore-forming fluids from a sub-crustal, metasomatized mantle lithosphere source for at least some orogenic gold deposits.

Geodynamic Emplacement Setting of Late Jurassic Dikes of the Yana–Kolyma Gold Belt, NE Folded Framing of the Siberian Craton: Geochemical, Petrologic, and U–Pb Zircon Data

We present the results of geostructural, mineralogic–petrographic, geochemical, and U–Pb geochronological investigations of mafic, intermediate, and felsic igneous rocks from dikes in the Yana–Kolyma gold belt of the Verkhoyansk–Kolyma folded area (northeastern Asia). The dikes of the Vyun deposit and the Shumniy occurrence intruding Mesozoic terrigenous rocks of the Kular–Nera and Polousniy–Debin terranes were examined in detail. The dikes had diverse mineralogical and petrographic compositions including trachybasalts, andesites, trachyandesites, dacites, and granodiorites. The rocks showed significant similarities in distributions of REE, and their concentrations of most HFSEs were close to the intermediate ones between ocean islands basalts and enriched middle ocean ridge basalts. We propose that the subduction that was ongoing during the collision of the Kolyma–Omolon superterrane with Siberia led to melting in the asthenospheric wedge and in the lithosphere, which formed a mixed source for the dike systems from both an enriched and a depleted mantle source. The U–Pb SHRIMP-II dates obtained for the dikes corresponded to the Late Jurassic interval of 151–145 Ma. We present a geodynamic model for the northeastern margin of the Siberian Craton for the Tithonian age of the Late Jurassic.

Effects of heavy metal pollution on farmland soils and crops: A case study of the Xiaoqinling Gold Belt, China

ABSTRACT This paper focuses on the heavy metal enrichment and heavy metal pollution degree associated with mining activities in some crops and the soils of different parent materials in the Xiaoqinling Gold Belt. According to the geochemical analysis results of the soils observed in the gold belt, the soils are most highly enriched in Pb, followed by Cr, Cu, and Zn. Furthermore, they are relatively poor in Hg, Cd, and As. It is also shown that the heavy metals in all kinds of soils have the same geochemical characteristics in the gold belt. As for the crops (such as corn and wheat) in the gold belt, Zn and Cu are the most abundant elements, followed by Pb and Cr. Meanwhile, Hg, Cd, and As were found to have relatively low concentrations in the crops. The heavy metals in wheat and corn have the same geochemical characteristics in the gold belt in general. Compared to the aeolian loess soils and the crops therein, heavy metals are more enriched in diluvial and alluvial soils and the crops therein. As shown by relevant studies, the Hg, Pb, Cd, Cu, and Zn pollution are mainly caused by mining activities. Corn and wheat in the gold belt have a high tendency of risk exposure to heavy metal pollution since they are mostly affected by mining activities and feature high background values of heavy metal concentrations. Furthermore, wheat is more liable to be enriched in heavy metals than corn is grown in all types of soils. The Hg pollution in soils leads to Hg accumulation, increasing the risk of Hg uptake in crops, and further affecting human health. This study will provide a scientific basis for the control and management of heavy metals in farmland soils of mining areas.

Petrogenesis of Cretaceous granitoids in the Bengbu–Wuhe area, southeastern North China Craton: Implications for gold mineralization

Sinistral slip along the Tancheng–Lujiang Fault Zone (TLFZ) during the Mesozoic resulted in an offset of approximately 400 km between the Dabie and Sulu orogens. The Bengbu–Wuhe gold belt (BWGB) represents an extension of the Zhaoyuan–Yexian gold belt to the west of the TLFZ. Early Cretaceous intrusions are widely distributed throughout the BWGB. Gold deposits in the BWGB are commonly associated with intermediate acid dykes that are roughly contemporaneous with mineralization, and some orebodies are hosted in granitoids. This paper investigates granitoids within the BWGB to constrain their petrogenesis, tectonic setting, and metallogenic significance using systematic whole-rock elemental geochemistry, apatite geochemistry, zircon U–Pb dating, zircon Lu–Hf isotopes, and whole-rock Sr, Nd, and Pb isotopes. The timing of Au mineralization (134–113 Ma) in the area is consistent with the age of intrusive adakite-like rocks (130–115 Ma) and normal calc-alkaline granitoids (114–109 Ma). The adakite-like samples are characterized by pronounced enrichment in light rare earth elements (REE), depletion in heavy REE ((La/Yb)N = 30.5–66.2), an absence of Eu anomalies, high Sr contents and Sr/Y ratios, low Y and Yb contents, and fractionated REE patterns ((Dy/Yb)N = 1.22–1.69). They have relatively low Mg# values (38–42) and variable Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr(t) = 0.7083–0.7111; εNd(t) = −22.2 to −14.9; 206Pb/204Pb(t) = 17.219–18.010; zircon εHf(t) = −21.0 to −12.3). These features indicate that the parental magmas of the adakites were derived from partial melting of thickened lower crust of the South China Plate and/or the North China Craton. The normal calc-alkaline granitoids have low Sr/Y (6.0–40.5), La/YbN (6.8–24.7), and Dy/YbN (0.90–1.28) ratios, exhibit negative Eu anomalies, and have variable Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr(t) = 0.7082–0.7085; εNd(t) = −22.7 to −17.7; 206Pb/204Pb(t) = 16.686–16.713; zircon εHf(t) = −24.9 to −19.0), indicating they were derived from the middle to lower crust of the North China Craton. Compared with the normal calc-alkaline granitoids, the adakite-like rocks have higher zircon Ce4+/Ce3+, higher apatite SO3 and lower apatite MnO contents, lower and more variable zircon crystallization temperatures, and higher apatite molar OH/F and Cl/F ratios, indicating that the adakitic magmas were more enriched in volatiles and more highly oxidized. Taken together, field observations and geochemical data suggest that the adakite-like rocks related to the subducted South China Block are the ore-causative rocks.

Plasmonic refractive index sensor based on D-shaped photonic crystal fiber for wider range of refractive index detection

A surface plasmon resonance (SPR) sensor based on D-shaped photonic crystal fiber (PCF) for a wider range of refractive index (RI) detection is proposed in this paper. Two nanoscale gold belts as plasmonic material for SPR are deposited on the D-shaped PCF plane. Asymmetric core enhances birefringence and makes the coupling of the y-polarized mode stronger. Numerical results indicate that wavelength sensitivities of 1700–12,600 nm/RIU can be obtained in the sensing range of 1.15–1.36. The maximum sensor resolution reaches to 7.94 × 10−6 RIU. The proposed sensor is suitable for the detection of low RI analytes, bio-sensing and chemical analysis.

Epithermal Mineralization in the Busang Southeast Zone, Indonesia: New Insight into the Au Prospect at the Center of the Bre-X Fraud

The Busang mineral prospect in Kalimantan, Indonesia, was reported to host a large Au resource until 1997 when it was revealed that drill core samples had been deliberately and systematically contaminated (“salted”) with extraneous Au to falsify resource estimates. One month before the fraud was uncovered, Dr. G. Milligan, then professor emeritus of geology, visited the site to collect a suite of core samples for academic study that was deemed representative of the host rocks, alteration, and mineralization of the Busang Southeast Zone. These samples were re-examined here by optical microscopy, electron microprobe (EMPA), whole-rock geochemistry, and fluid inclusion microthermometry to characterize the subsurface geology and hydrothermal mineralization, and to assess reasons why the system is of uneconomic character. The host rocks were variably altered calc-alkaline porphyritic subvolcanic diorites, typical of the lithological units along the mineralized trend in the Kalimantan Gold Belt. Early hydrothermal mineralization with quartz-sulfide (pyrite, chalcopyrite, Cu-sulfosalts) stockwork veinlets associated with pervasive phyllic and propylitic alteration was overprinted by crudely banded quartz-carbonate-sulfide/sulfosalt (pyrite, sphalerite, chalcopyrite, galena, tennantite-tetrahedrite, bournonite-seligmannite) veins. The stockwork veins were associated with up to 140 ppb bulk rock Au, some of which was hosted by Cu-sulfosalts. Microthermometry on quartz-hosted aqueous fluid inclusion assemblages (FIA; n = 13) and single inclusions (non-FIA; n = 20) in quartz-carbonate-sulfide/sulfosalt veins yielded an overall range in homogenization temperatures (Th) between 179 °C and 366 °C and bulk salinities between 1.1 wt.% to 8.6 wt.% NaCl equivalent, with much smaller data ranges for individual FIA (e.g., FIA 3; 239.1 °C to 240.5 °C and 0.5 wt.% to 1.4 wt.% NaCl equivalent). Primary FIA along growth zones in quartz were identified, providing constraints on fluid characteristics at the time of quartz growth. Carbonate-hosted FIA (n = 3) and single inclusions (non-FIA; n = 3) in the same veins yielded Th between 254 °C and 343 °C and bulk salinities of 1.1 wt.% to 11.6 wt.% NaCl equivalent. Likewise, data ranges for individual FIA were much smaller. Many of the geological characteristics of the Busang Southeast Zone were compatible with a telescoped, intermediate-sulfidation epithermal system, having formed from diluted magmatic fluids that precipitated weak base metal mineralization. However, the system was unproductive with respect to Au and Ag, at least within the studied area. Of note, vein textures and fluid inclusion characteristics indicative of boiling or efficient fluid mixing—processes both considered critical for the formation of economic lode gold deposits—were absent in the samples.

PHALERAE THE DECORATION OF HORSE HEADGEAR FROM BARROW 1 ON ZUBOVSKI KHUTOR

The reasons for the alternative attribution of seven gold belt plates from the Sarmatian burial of the barrow 1 near Zubovski Khutor at the Kuban river region (1st century BC — 1st century AD) are proposed in the paper. During the period from the moment of excavations of this barrow (1899) three variants of the interpretation for these findings have been offered: as the belt decorations (К. Е. Dumberg, I. I. Gushchina, I. P. Zaseczkaya, M. B. Shchukin, V. I. Mordvintseva, etc), and as the fibula-brooch (М. I. Rostovczev, N. V. Anfimov, М. P. Аbramova) or phalerae for ceremonial horse harness (А. P. Маnczevich, М. Yu. Treister, А. V. Simonenko).
 The barrow was excavated by amateur and the methodic level of this work was poor. Due to the circumstances it seems inappropriate trust the data from the first publication of the findings. The belt plates version has no parallels among findings and materials from various Sarmatian burial assemblages since 1899. We There were no findings of plates decorating the belt. The interpretation of these items as fibula-brooch proves to be false as the plates did not equipped with pins and spring devices at their backsides.
 The correct interpretation for the plates seems to be phalerae of the horse headgear. This version is proved with well documented findings of horse equipment of the 1st—2nd centuries AD which contains from 6 to 12 phalerae of the similar size. It is also known the horse equipment containing just seven phalerae which decorate the headgear — from the burials in Kosika (Lower Volga region) and in Yashkul (Kalmykia). The important factor seems to be the way of fixing of these items to the straps of horse equipment. One can see the laminar wirers on the back of one phalera founded in the barrow 1 near Zubovski Khutor.

Ore Forming Fluids of Several Gold Deposits in the Irtysh Gold Belt, Xinjiang, China

The metallogenic environment of the Irtysh gold belt in Xinjiang is studied in detail. The metallogenic geological background, metallogenic conditions and ore-controlling factors of the gold deposits in eastern, central and western regions of the metallogenic belt are compared. The metallogenic structure of the Irtysh tectonic belt has the characteristics of diverging to the west and converging to the east. Composite ore controlling by ductile shearing and magmatic activity in Irtysh gold belt result in zoned and segmented distribution of gold mineralization. Through the fluid inclusion research and H-O-S isotope analysis, the evolution regularity of gold ore-forming fluids in the region was analyzed. Synchrotron radiation X-ray fluorescence was used to analysis the concentration of metal elements in a single fluid inclusion, explaining the occurrence and migration process of Au in hydrothermal fluid. The source of ore forming minerals in western gold deposit is more closely related to magmatic activity, and the structural metamorphism of eastern gold deposit has greater influence on mineralization. Metallogenic fluids of gold deposits are characterized by metamorphic water (and magmatic water) in the early stage and mixed with meteoric water in the late stage. And the metallogenic elements are enriched in CO2 rich fluid. The Au is mainly activated, migrated and enriched with the mixed fluid of magmatic hydrothermal, metamorphic hydrothermal and atmospheric precipitation in the medium-low temperature, shallow to medium-deep environment.

Petrogenesis of Paleogene lamprophyres in the Ailaoshan tectonic belt, western Yangtze Craton: Implications for the mantle source of orogenic gold deposits

The Ailaoshan tectonic belt, western margin of Yangtze Craton, is an important orogenic gold belt with ore source derived from mantle. The Paleogene lamprophyre dykes are temporally and spatially associated with gold ore bodies in this belt. Here we research the geochemical features of lamprophyres aiming to better understand the features of mantle source for the orogenic gold deposit. These lamprophyres are characterized by enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs), high (87Sr/86Sr)i (0.7061–0.7093) and negative εNd(t) (−5.60 to −0.44). These features indicate arc-like geochemical signatures, collectively pointing to the derivation of lamprophyre magmas from an enriched lithospheric mantle. The low range of Nb/U (1.55–6.53), elevated ratios of Ba/La (13.95–62.94), and limited values of Th/Yb (5.25–9.94) suggest this enriched mantle source was metasomatized by subducted slab-derived fluids. Moreover, the lamprophyres exhibit light Mg isotopic compositions (δ26Mg = −0.44 to −0.26‰), low Ti/Ti* (0.11–0.27) and Fe/Mn (47.45–66.65), and high Na2O + K2O (6.01–9.38 wt%), further indicating the mantle was metasomatized by carbonate-rich melts. The Mg-Sr isotope binary mixing modeling highlights the metasomatism of clastic sediments. This study has demonstrated that the mantle source for the orogenic gold deposits has been modified by diverse metasomatic agents to develop the potential to produce a metal-bearing and CO2-rich aqueous fluid.

40Ar/39Ar geochronology constraints on formation of the Tuwaishan orogenic gold deposit, Hainan Island, China

The Tuwaishan deposit is an orogenic gold deposit that is structurally controlled by the NE-trending Gezhen shear zone in the western part of Hainan Island, south China. It is part of a belt of numerous similar deposits hosted in Mesoproterozoic granitoids and lesser Paleoproterozoic to Mesoproterozoic schists. The Tuwaishan gold orebodies comprise auriferous quartz veins and disseminated gold in sulfidized granitic mylonite. The veins consist of early quartz-pyrite-arsenopyrite-pyrrhotite with minor gold, middle stage quartz-gold-base metal sulfides, and barren late quartz-carbonate. New 40Ar/39Ar dating of muscovite from wallrock schists yielded a minimum age of 356.8 ± 0.9 Ma, suggesting the youngest possible age estimate for amphibolite facies regional metamorphism of the Baoban Group country rocks. The 40Ar/39Ar dating of sericite from auriferous quartz veins yielded a weighted mean age of 243.4 ± 2.3 Ma, representing the ore-forming age of the Tuwaishan gold deposit. The formation of the shear-hosted gold deposits along the Gezhen gold belt was likely related to the Early to Middle Triassic convergence between the Indochina and South China Blocks. Based on the widely accepted metamorphic devolatilization model for orogenic gold deposit formation, most Au tends to be released into the ore-forming fluid in the source region when country rocks were firstly metamorphosed from greenschist to amphibolite facies. Therefore, it is highly unlikely that the immediate country rocks of the Baoban Group, which were at amphibolite facies by early Carboniferous, were the source for fluids and metals along the Gezhen shear zone.

Geology and geochronology of the Shijia gold deposit, Jiaodong Peninsula, China

The Shijia gold deposit, classified as a Linglong-type (quartz vein-type) gold deposit, is located in the north of Qixia-Penglai gold belt in the Jiaodong Peninsula. The orebodies predominantly occurring as quartz-sulfide veins are hosted in the Early Cretaceous Guojialing amphibole-bearing monzogranite and strictly controlled by NNE- to NE-striking high-angle faults. Hydrothermal minerals include K-feldspar, quartz, sericite, pyrite, sphalerite, galena, chalcopyrite, calcite and fluorite. Based on the mineralogical, textural and field cross-cutting relationships, the mineralization process can be divided into three stages: (I) quartz-sericite-pyrite stage, (Ⅱ) quartz-sulfide-gold stage and (III) quartz-calcite-fluorite stage. Field investigation shows that the orebodies have undergone several times of deformation after their formation, resulting in the deformation and discontinuity of the orebodies. Early Cretaceous dykes, including granite pegmatite, lamprophyre, diabase and granite porphyry, are developed in the Shijia gold deposit. The crosscutting relationship between orebodies and various mafic-felsic dykes shows that their formation sequence is granite pegmatite, Au orebody, lamprophyre, diabase and granite porphyry. LA-ICP-MS zircon U-Pb dating shows that the emplacement ages of granite pegmatite, lamprophyre, diabase, and granite porphyry are 129.7 ± 1.6 Ma, 129.3 ± 1.4 Ma, 128.3 ± 1.3 Ma and 120.0 ± 1.1 Ma, respectively. These dating results are consistent with the crosscutting phenomenon observed in the field, indicating that the mineralization time of the Shijia gold deposit is between 129.7 Ma and 129.3 Ma. The timing of gold mineralization at Shijia coincides with the large-scale thinning of the lithosphere in the North China Craton during the Early Cretaceous, indicating that the formation of the deposit is mainly controlled by extensional tectonics. Because the gold mineralization was predated the emplacement of lamprophyre and diabase dykes, there might be not a direct genetic relationship between the gold mineralization and the mafic dykes in the Shijia gold deposit.

New zircon fission track analysis constraints on tectonic-mineralization epochs in the Ganzi-Litang gold belt, eastern Qinghai-Tibet plateau

The Ganzi-Litang gold belt, as a part of the Sanjiang Tethys orogen, is located between the Yidun block and Songpan-Ganzi Block/Terrane in the eastern Qinghai-Tibetan plateau and experienced oceanic slab subduction, continent-arc collision and intracontinental convergence since the Indosinian orogeny. A series of gold ore deposits have been found within the region. This paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track (FT) thermochronology. A total of 15 zircon FT analysis results were obtained that can be divided into four age groups (217–213 Ma, 190–160 Ma, 155–93 Ma and 72–67 Ma) representing four distinct episodes of gold mineralization, of which the middle two episodes predominate. Eruption of the auriferous volcanic rocks that comprise the belt started at 217–213 Ma when the Ganzi-Litang Meso-Tethys ocean began to subduct. The mineralization episode at 190–160 Ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional-convergence of the Ganzi-Litang belt. Finally, the episodes at 155–93 Ma and 72–67 Ma are respectively related to the closing times of the Bangong-Nujiang and Yarlung Zangbu oceans, corresponding to tectonic quiet episodes.

New 40Ar/39Ar Data of Gold Mineralization in the Ailaoshan Gold Belt, Yunnan Province, China

New ⁴⁰Ar/³⁹Ar Data of Gold Mineralization in the Ailaoshan Gold Belt, Yunnan Province, China

Fluid Inclusion Study of the Penjom, Tersang, and Selinsing Orogenic Gold Deposits, Peninsular Malaysia

Ore-forming fluids in the auriferous district of the Central gold belt in Peninsular Malaysia were studied for their temperature, salinity, and relationship to the surrounding geology. Microthermometric analysis carried out showed homogenisation temperatures range from 210 to 348 °C (Tersang), between 194 and 348 °C (Selinsing), and from 221 to 346 °C (Penjom). Salinities range from 2.41 to 8.95 wt % NaCl equiv (Tersang), between 1.23 and 9.98 wt % NaCl equiv (Selinsing), and from 4.34 to 9.34 wt % NaCl equiv (Penjom). Laser Raman studies indicated that at the Tersang gold deposit, most inclusions are either pure or nearly pure CO2-rich (87–100 mol %), except for one inclusion, which contains CH4 gas (13 mol %). In addition, at Selinsing, most inclusions are CO2-rich (100 mol %). However, an inclusion was found containing CO2 (90 mol %), with minor N2 and CH4. Additionally, at the Penjom gold deposit, most fluid inclusions are CO2-rich (91–100 mol %), whereas one fluid inclusion is N2-rich (100 mol %) and another one has minor N2 and CH4. At a basin scale, homogenisation temperatures against salinity suggests an isothermal mixing of fluids. Most fluids are CO2-rich and are interpreted to be of metamorphic origin. The evidence further indicates involvement of magmatic fluids that is supported by the association of sandstone and carbonaceous black shales with magmatic rocks, such as rhyolite, rhyolite-dacite, and trachyte-andesite at the Tersang and Penjom orogenic gold deposits.

Geology, geochronology, and S-Pb-Os geochemistry of the Alastuo gold deposit, West Tianshan, NW China

The Alastuo gold deposit, located in the Narati region of the Chinese West Tianshan, is a newly discovered gold deposit within the world-class Tianshan gold belt. The gold mineralization is hosted by an Early Carboniferous granodiorite intrusion and controlled structurally by subsidiary faults of the transcrustal North Narati Fault. The deposit consists of auriferous alteration assemblages and minor vein ores. Field relations and petrographic data suggest four stages of mineralization with gold precipitated coevally with quartz, chlorite, epidote, pyrite, and galena during the second and third stages that are characterized by tectonic transformation from ductile shearing to brittle deformation. The temperature range of gold precipitation is estimated to be 280–330 °C using chlorite geothermometry. Ten auriferous pyrite samples yielded a well-defined Re-Os isochron age of 325 ± 3 Ma and two sericite samples yielded plateau-like 40Ar/39Ar ages of 321.7 ± 3.0 Ma and 321.2 ± 2.8 Ma. These consistent ages suggest that the gold mineralization in the Narati region was emplaced in a transitional regime from subduction to continental collision between the Tarim block and Middle Tianshan terrane (325–310 Ma), rather than during the post-collisional stage as in most part of the Tianshan gold belt. Gold-bearing pyrite has an initial Osi value of 0.7 ± 0.1 and lead isotopes ratios of 17.897 to 18.723 for 206Pb/204Pb, 15.474 to 15.643 for 207Pb/204Pb, and 37.522 to 38.299 for 208Pb/204Pb, while samples of pyrite, galena, and sphalerite have 34SV-CDT of +1.9 to +7.8‰. The isotope data suggest that the sulfur and metals are most likely derived from mixed mantle and crustal sources including metamorphic devolatilization of subducted oceanic slab and overlying sedimentary rocks. The mineralization styles, structural controls, metal and sulfur sources, and the timing of gold mineralization with respect to the orogenic event all suggest that the Alastuo gold deposit represents an orogenic type deposit. This newly recognized Carboniferous orogenic gold mineralization event calls for a re-evaluation of the gold metallogeny in the Middle Tianshan.