Yuanchao Shen

Characteristics and genesis of Kanggur gold deposit in the eastern Tianshan mountains, NW China : evidence from geology, isotope distribution and chronology

Abstract The Kanggur gold deposit lies in East Tianshan mountains, eastern section of Central Asia orogenic belt. The gold mineralization occurs on the northern margin of the Aqishan–Yamansu island arc in the Tarim Plate. It is mainly hosted in Lower Carboniferous volcanic rocks, and controlled by syn-tectonic intrusions and the ductile shear zone. The host rock is a calc-alkaline volcanic rock series consisting of andesite, dacite, tuff and subvolcanic rocks. The gold ore bodies were distributed in transition zone from strong ductile deformation to weak deformation. Ore-controlling structure is EW-trending normal brittle–ductile shear zone. The gold ore bodies are composed of Au-bearing altered rocks and a few Au-bearing sulfide-quartz veins. The mineralization shows vertical zonation in which Au was enriched in the upper orebodies, Au–Pb–Zn were enriched in the middle and Au–Cu were enriched in the lower orebodies. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification, chloritization, pyritization and magnetization zone (major ore body); pyrite-phyllic rock and/or sericite alteration zone; and sericite–chlorite alteration zone. Five mineralization stages are identified on the basis of mineral assemblage and crosscutting relationship of veins. The δ 34 S values of sulfide in the ores range from −0.9‰ to +3.3‰, similar to those of the volcanic and subvolcanic rocks (−3.21∼+1.3‰), indicating that the sulfur isotope composition is characterized by unfractionated mantle sulfur. The lead isotope compositions of ores are between those of the volcanic rocks and subvolcanic rocks. The initial 87 Sr/ 86 Sr ratios of the ores vary between 0.7077 and 0.7106, similar to those of the host rocks (0.7079–0.7125). According to the Sr, S and Pb isotopic data, it is indicated that the ore-forming materials were derived from the surrounding volcanic rocks and feature deep source. The δ 18 O values of the ore fluids vary from +3.83‰ to −1.77‰ and the δ D values from −46‰ to −66‰. The δ 18 O vs. δ D and δ 18 O vs. 87 Sr/ 86 Sr diagrams indicate that ore fluids were derived from dynamic metamorphic water, magmatic water and meteoric water. The ore-forming ages of Kanggur gold deposit are determined by Rb–Sr and Sm–Nd isochron methods. The results show that the main ore-forming stages of Kanggur gold deposit are 290–282 Ma, secondary mineralization stages are 275–254 Ma. Studies on regional geology, ore geology, isotope geochemistry and ore-forming ages have proved that the Kanggur gold deposit was formed in the compression–extension transition stage during the latest Paleozoic continental collision, and is characterized by orogenic gold deposits.

Two geodynamic–metallogenic events in the Balkhash (Kazakhstan) and the West Junggar (China): Carboniferous porphyry Cu and Permian greisen W-Mo mineralization

This study focuses on the geochronology and elemental and Nd isotopic geochemistry of the Baogutu Cu deposit and the newly discovered Suyunhe W-Mo deposit in the southern West Junggar ore belt (Xinjiang, China), as well as the geology of the newly discovered Hongyuan Mo deposit in the southern West Junggar ore belt and the Kounrad, Borly, and Aktogai Cu deposits and the East Kounrad, Zhanet, and Akshatau W-Mo deposits in the North Balkhash ore belt (Kazakhstan). The aim is to compare their petrogenesis, tectonic setting, and mineralization and to determine the relationship between the southern West Junggar and North Balkhash ore belts. Based on our newly acquired results, we propose that the Kounrad, Borly, Aktogai, and Baogutu deposits are typical porphyry Cu deposits associated with calc-alkaline magmas and formed in a Carboniferous (327–312 Ma) subduction-related setting. In contrast, the East Kounrad, Zhanet, Akshatau, Suyunhe, and Hongyuan deposits are quartz-vein greisen or greisen W-Mo or Mo deposits associated with alkaline magmas and formed in an early Permian (289–306 Ma) collision-related setting. Therefore, two geodynamic–metallogenic events can be distinguished in the southern West Junggar and North Balkhash ore belts: (1) Carboniferous subduction-related calc-alkaline magma – a porphyry Cu metallogenic event – and (2) early Permian collision-related alkaline magma – a greisen W-Mo metallogenic event. The North Balkhash ore belt is part of the Kazakhstan metallogenic zone, which can be extended eastward to the southern West Junggar in China.

An Ordovician intra-oceanic subduction system influenced by ridge subduction in the West Junggar, Northwest China

We report elemental and Nd–Sr isotopic data for three types of Ordovician volcanic and gabbroic rocks from the Sharburti Mountains in the West Junggar (Xinjiang), Northwest China. Gabbros and Type I lavas occur in the Early Ordovician Hongguleleng ophiolite whereas Type II and III lavas are parts of the Middle Ordovician Bulukeqi Group. Gabbros and Type I lavas are tholeiites with a depleted light rare earth element (LREE) and mid-oceanic ridge basalt (MORB)-like signature with a crystallization sequence of plagioclase–clinopyroxene, suggesting formation at a mid-oceanic ridge. Type II lavas are Nb-enriched basalts (NEBs, Nb = 14–15 ppm), which have E-MORB-like REE patterns and Nb/Yb and Th/Yb ratios. They come from mantle metasomatized by slab melts. Type III lavas are further divided into two sub-types: (1) Type IIIa is tholeiitic to calc-alkaline basalts and andesites, with REE patterns that are flat or slightly LREE enriched, and with a negative Nb anomaly and Th/Yb enrichment, indicating that they were generated above a subduction zone; (2) Type IIIb is calc-alkaline basalts and andesites, which are strongly enriched in LREE with a marked negative Nb anomaly and Th/Yb enrichment, suggesting generation in a normal island-arc setting. The initial 87Sr/86Sr ratios of Type III lavas range from 0.70443 to 0.70532 and ϵNdt ranges from +1.5 to +4.5, suggesting that these melts were derived from mantle wedge significantly modified by subducted material (enriched mantle I (EMI)) above a subduction zone. Contemporary tholeiitic to calc-alkaline basalt–andesite and NEB association suggest that the NEBs erupted during development of the tholeiitic to calc-alkaline arc. We propose a model of intra-oceanic subduction influenced by ridge subduction for the Ordovician tectono-magmatic evolution of the northern West Junggar.

Structure, Isotopes, and 40Ar/39Ar Dating of the Pengjiakuang Gold Deposit, Mesozoic Jiaolai Basin, Eastern China

The Pengjiakuang gold deposit, located on the northeastern margin of the Mesozoic Jiaolai basin, eastern Shandong Province, China, is controlled by a low-angle detachment fault. Three economic ore bodies and more than 10 mineralized bodies have been proved in recent years. The main ore bodies are made up of gold-bearing breccia, cataclastic rocks, and sulfide-quartz veins in lenses and veins. Gold ores are typically brecciated, veinlet, and disseminated. Lamprophyre dikes are spatially and temporally associated with the gold ore bodies. The isotopic analysis indicates that the δ34S range (6.5-12.89‰) of sulfides in the Pengjiakuang gold deposit is consistent approximately with that of metamorphic rocks, Mesozoic granites, and the Jiaojia and Linglong gold deposits in eastern Shandong. However, there are wide ranges of compositions of δ34S and lead isotopes in the Pengjiakuang ore except for lower 206Pb/204Pb ratios. Analyses of sulfur and lead isotopic compositions suggest that the ores have a multiple origin. Unlike the Jiaojia and Linglong deposits, the oxygen and hydrogen isotopic compositions of fluid inclusions in the Pengjiakuang deposit show a mixed source: dominant meteoric water, and subordinate magmatic water. The Ar-Ar method was adopted to date the Au-bearing quartz. Brecciated ore yields a 40Ar/39Ar age of 118.42 ± 0.25 Ma and an isochron age of about 117.03 ± 0.13 Ma. Veinlet ore yields a 40Ar/39Ar age of 118.70 ± 1.40 Ma and an isochron age of 117.33 ± 0.15 Ma. The results indicate that the Pengjiakuang gold deposit was formed at ∼117.3-118.4 Ma. Biotite from a lamprophyre dike gives an age of 117.49 ± 0.25 Ma and an isochron age of 116.83 ± 0.36 Ma. Clearly, the formation of both lamprophyre dikes and gold mineralization are coeval products of tectonic-magmatic activity. The consistency in metallogenic age between the Pengjiakuang gold deposit, located on the margin of a Mesozoic pull-apart basin, and gold deposits of the northern uplift area in eastern Shandong suggests that both can be ascribed to the same the metallogenic event.

Oxidation Conditions of Granitic Magmas Associated With Porphyry Copper Deposits in the Central Asian Orogenic Belt

Porphyry copper deposits are associated with oxidized felsic magmas (Sillitoe, 2010). Such oxidized magmas are considered to supply metals and S to ore deposits (Hedenquist and Lowenstern, 1994; Hattori and Keith, 2001; Cooke et al., 2005). Ce is 4+ in oxidized conditions and readily incorporated into zircon, which produces positive Ce anomalies. Previous studies show that the Ce/Ce ratios in zircon can be used as a proxy for oxygen fugacity of magmas (e.g., Trail et al., 2012). The ratios successfully discriminate fertile igneous rocks from barren rocks (Ballard et al. 2002; Liang et al., 2006; Qiu et al., 2013; Han et al., 2013). The Central Asian Orogenic Belt (CAOB) hosts porphyry-type deposits with significant range in size including largeand intermediatesize deposits (Figure 1). The CAOB, therefore, presents an opportunity to evaluate the relationship between the oxidation condition and metal-fertility of granitic magmas.

Sulfur, helium and argon isotopic features of gold deposits in the Sawuershan region, Xinjiang, NW China

Two gold deposits (Kuoerzhenkuola and Buerkesidai) have been discovered, explored and mined in the Sawuershan district, Xinjiang, NW China. Gold mineralization at Kuoerzhenkuola deposit occurs within Carboniferous andesite and volcanic breccias. Gold mineralization at Buerkesidai deposit occurs within Carboniferous siltstones. δ34S‰ values of pyrite separates of ores and altered andesite from Kuoerzhenkuola deposit variy from 0.25‰ to 1.3‰ and 1.5‰ to 2.44‰, respectively. δ34S‰ values of pyrite separates of ores and altered albite porphyry from Buerkesidai deposit vary from 0.44‰ to 0.84‰ and 1.1‰ to 2.81‰, respectively. He isotope data from fluid inclusions in pyrites formed during mineralization stage of Kuoerzhenkuola and Buerkesidai gold deposits show that the 40Ar/36Ar and 3He/4He ratios of fluid inclusions are respectively in the range of 282–525 and 0.64–9.48 R/Ra, suggesting that mantle fluids may have played an important role in the ore-forming processes. On the basis of S, He and Ar isotope data, we conclude that the ore-forming materials may be derived from the mantle and the ore-forming fluid may be a mixture of mantle-derived fluid with the meteoric water.