Huayong Chen

Metallogenesis of the Ertix gold belt, Xinjiang and its relationship to Central Asia-type orogenesis

The Ertix gold belt is located on the boundary of the Kalatongke arc and the Kelan back-arc basin of D-C1. Most scholars used to interpret the formation and distribution of the gold deposits in the Ertix tectonic belt in terms of the petrogenic and metallogenic models for active continental margins. However, enormous data of isotopic dating and geologic research show that the mineralization was obviously later than the oceanic subduction, whereas exactly simultaneous with the collisional orogenesis during C2-P, especially at the transition stage from collisional compression to extension. Based on study of metallogenic time, tectonic background, ore geology, ore fluid nature, ore material source, etc., we reveal that all the gold deposits possess the character of orogenic deposits formed in collisional orogenic system, and that their ore-forming materials mainly have derived from the stratigraphic terranes south to individual deposits. Accordingly, the theoretical tectonic model for collisional metallogenesis and petrogenesis is employed to explain the formation of the Ertix gold belt and to determine the gold exploration directions.

Mineralization and fluid evolution of the Jiyuan polymetallic Cu–Ag–Pb–Zn–Au deposit, eastern Tianshan, NW China

The newly discovered Jiyuan Cu–Ag–(Pb–Zn–Au) deposit is located in the southern section of the eastern Tianshan orogenic belt, Xinjiang, northwestern China. It is the first documented deposit in the large Aqikekuduke Ag–Cu–Au belt in the eastern Tianshan orogen. Detailed field observations, parageneses, and fluid inclusion studies suggest an epithermal ore genesis for the main Cu–Ag mineralization, accompanied by a complicated hydrothermal alteration history most likely associated with the multi-stage tectonic evolution of the eastern Tianshan. The Jiyuan Cu–Ag ore bodies are located along the EW-striking, south-dipping Aqikekuduke fault and are hosted by Precambrian marble and intercalated siliceous rocks. Early-stage skarn alteration occurred along the contact zone between the marble layers and Early Carboniferous diorite–granodiorite and monzogranite intrusions; the skarns are characterized by diopside–tremolite–andradite–pyrite–(magnetite) assemblages. Local REE-enriched synchysite–rutile–arsenopyrite–(clinochlorite–microcline–albite) assemblages are related to K–Na alteration associated with the monzogranite intrusions and formed under conditions of high temperature (310°C) and high salinity (19.9 wt.% NaCl). Subsequent hydrothermal alteration produced a series of quartz and calcite veins that precipitated from medium- to low-temperature saline fluids. These include early ‘smoky’ quartz veins (190°C; 3.0 wt.% NaCl) that are commonly barren, coarse-grained Cu–Ag mineralized quartz veins (210°C; 2.4 wt.% NaCl), and late-stage unmineralized calcite veins (140°C; 1.1 wt.% NaCl). Tremolite and Ca-rich scapolite veins formed at an interval between early and mineralized quartz veins, indicating a high-temperature, high-salinity (>500°C; 9.5 wt.% NaCl) Ca alteration stage. Fluid mixing may have played an important role during Cu–Ag mineralization and an external low-temperature Ca-rich fluid is inferred to have evolved in the ore-forming system. The Jiyuan auriferous quartz veins possess fluid characteristics distinct from those of the Cu–Ag mineralized quartz veins. CO2-rich fluid inclusions, fluid boiling, and mixing all demonstrate that these auriferous quartz veins acted as hosts for the orogenic-type gold mineralization, a common feature in the Tianshan orogenic belt.

Triassic shoshonitic dykes from the northern North China craton: petrogenesis and geodynamic significance

Zircon U–Pb ages, major and trace element geochemistry and Sr, Nd and Pb isotope compositions of diorite and diorite porphyry dykes from the Jinchanggouliang (JCGL) gold ore field on the northern margin of the North China craton (NCC) were studied to investigate their sources, petrogenesis and geodynamic significance. LA-ICP-MS zircon U–Pb dating reveals three major age groups of 2500 Ma (n = 2), 253 ± 7 Ma (n = 5) and 227 ± 1 Ma (n = 9). The inherited ages of 2500 Ma, contemporary with the Archaean NCC continental growth, imply that crustal material was involved in the magma source. The igneous zircons with a concordia age of 227 ± 1 Ma may record the emplacement age of the JCGL dykes. Both diorite and diorite porphyry exhibit a wide range of SiO 2 and MgO contents and are characterized by high concentrations of Na 2 O+K 2 O and Al 2 O 3 , and low abundances of P 2 O 5 and TiO 2 . They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies, and depleted in high-field-strength elements; all are categorized as shoshonitic rocks. All samples show a narrow range of Sr isotope compositions with initial 87 Sr/ 86 Sr ratios from 0.70394 to 0.70592, variable e Nd ( t ) values (1.1 to −12.0) and T DM2 ages of 913–1972 Ma. Their Pb isotope compositions form continuous variation trends and plot in the fields between enriched mantle 1 (EM1) and lower continental crust (LCC). The above results suggest that the JCGL dykes studied could have been derived from mixing of lower crust, lithospheric mantle of the NCC and ascending asthenospheric melt in a post-orogenic extensional geodynamic setting. These shoshonitic dykes, together with the geochronological data of regional ENE-trending retrograded eclogites, ophiolites, continental arc magmatic belt, A-type granite, alkaline intrusions and metamorphic core complex from the northern NCC and Central Asian Orogenic Belt (CAOB) suggest that closure of the Palaeo-Asian Ocean (i.e. stage of pre-collision to collision) had completed during latest Permian to earliest Triassic time, and that the CAOB was subsequently tectonically dominated by post-orogenic extensional regimes. The involvement of asthenospheric melt in the magma source implies that the sub-continental lithospheric mantle (SCLM) of the NCC had been modified, and the onset of lithospheric destruction and thinning beneath the northern NCC may have occurred in Middle–Late Triassic time as a result of post-orogenic subducting slab detachment and lithospheric delamination.

Progress and records in the study of endogenetic mineralization during collisional orogenesis

To develop and perfect the theory of plate tectonics and regional metallogeny, metallogenesis during collisional orogenesis should be thoroughly studied and will attract increasing attention of more and more scientists. This paper presents the main aspects of research and discussions on metallogenesis during collisional orogenesis after the development of plate tectonics, and accordingly divides the study history into two stages, i.e. the junior stage during 1971–1990 and the senior stage after 1990. Beginning with the negation of mineralization in the collision regime by Guild (1971), the focus of study was put on whether there occurred any mineralization during collisional orogenesis at the junior stage. At the senior stage, which is initiated by the advance of metallogenic and petrogenic model for collisional orogenesis, scientists begin to pay their attention to the geodynamic mechanism of metallogenesis, spatial and temporal distribution of ore deposits, ore-forming fluidization, relationship between petrogenesis and mineralization in collisional orogenesis, etc. Abundance of typical collisional orogens such as Himalayan, China has best natural conditions to study collisional metallogenesis. Great progress in the study of metallogenesis during collisional orogenesis has been made by Chinese geologists. Therefore, we hope that the’ Chinese geologists and Chinese governments at various levels to pay more attention to the study of collisional metallogenesis. Some urgent problems are suggested to be solved so as to bring about breakthroughs in the aspects concerned.

Petrogenesis of the Permian Intermediate-Mafic Dikes in the Chinese Altai, Northwest China: Implication for a Postaccretion Extensional Scenario

The Central Asian Orogenic Belt is a long-lived accretionary orogen, and the late Paleozoic has been considered to be a critical period for the terminal amalgamation of its three tectonic collage systems. However, the exact timing of amalgamation and the geological process of such a huge accretionary orogenic belt are poorly understood. This study presents new geochronological and geochemical data for Permian intermediate-mafic dikes in the Chinese Altai, a key region between the Mongolian and the Kazakhstan collage systems. According to mineral assemblages and petrographic textures, the intermediate-mafic dikes can be categorized as gabbronorite and quartz diorite. The gabbronoritic and quartz dioritic dikes have zircon U-Pb ages of 276.7 ± 2.9 and 273.2 ± 4.3 Ma, respectively. The gabbronorites are characterized by low SiO2 (47.1–51.3 wt%) and high MgO (5.33–8.46 wt%), together with medium Cr (71.2–95.7 ppm) and Ni (80.6–192 ppm) contents. Geochemical modeling indicates that the parental magma was possibly contaminated by 4%–12% crustal materials. Zircon εHf(t) (+13.2 to +16.7) and whole-rock εNd(t) (+4.9 to +6.1) values as well as moderate Sm/Yb ratios (1.75–1.89) imply that the parental magma might have originated from a depleted mantle source dominated by spine lherzolite. In contrast, the quartz diorites exhibit higher SiO2 (57.3–58.3 wt%) and lower whole-rock εNd(t) (∼+2.5) and zircon εHf(t) (+9.1 to +14.4) values, implying that they have a magma source unlike the depleted mantle of the gabbronorites. The parental magma may be derived from mafic lower crust. The quartz diorites have high Y (>39.8 ppm) and heavy rare earth element (e.g., Yb >3.64 ppm) concentrations as well as low Sr/Y (<12) ratios, consistent with geochemical fingerprints of a magma reservoir at shallow depths (<10 kb). Major element compositions of the quartz diorites are comparable to those of intermediate liquids generated by ∼40% partial melting of alkali-enriched basaltic rocks at conditions of T = 1050°–1100°C and P = 8 kbar. Such a high geothermal gradient is inferred to be a consequence of intraplating and/or underplating of hot basaltic magmas in an extensional setting, which may shed light on the ubiquitous tectonic scenario after amalgamation of tectonic collages.

Isotope Geochemistry of the Weishancheng Stratabound Gold-Silver Ore Belt, Tongbai County, Henan Province, China

The Weishancheng ore belt is located in Tongbai Mountains and consists of three stratabound deposits (Yindongpo large gold deposit, Poshan super-large silver deposit, and Yindongling large silver-dominated poly-metallic deposit) and some small ore spots. The orebodies are strictly hosted in carbonaceous strata of the Neoproterozoic Waitoushan Formation. The H-O-C isotopic system of the fluid inclusions from each deposit indicates that the fluids in the early and middle ore-forming stages came from the metamorphic devolatilization, and in the late stage, considerable meteoric water entered the fluid system. The C-S-Pb isotope geochemistry suggests that the metallogenic materials are derived from the rocks from the Waitoushan Formation. The K-Ar and 40Ar-39Ar dating results show that the metallogenesis of the Weishancheng ore belt occurred during 100–140 Ma, when a tectonic setting changed from collisional compression to extension. The Weishancheng gold-silver ore belt belongs to a typical stratabound orogenic-type metallogenic system in terms of the ore-forming fluid, metal source, and geologic characteristics. The ore-forming process took place under the continental collision setting between Yangtze and North China plates.

Comparisons on Alteration and Mineralization Paragenesis between the Qiaoxiahala and the Laoshankou Fe‐Cu‐Au Deposit

belt, which is located in the Sawur Late Paleozoic island arc at the northern margin of the Junggar Terrane and hosted by the Middle Devonian Beitashan Formation volcanic and sedimentary rocks, currently incorporates the Fe-Cu-Au mineralization at Qiaoxiahala (1.44 Mt at 43% ~ 53% Fe, 0.55% ~ 2.21% Cu and 0.13 ~ 2.4 g/t Au) (Li, 2002; Wei, 2002) and at Laoshankou (3.26 Mt at 33.5% ~ 36.42% Fe, 9800 t at 0.19% ~ 0.41% Cu, 1400 t at 0.49 ~ 1.31 g/t Au) (Cheng, 2004; Lv et al., 2012). The Qiaoxiahala deposit is located 30 km to the southeast of Fuyun county, Xinjiang, China, and geologically on the southern margin of the Irtysh Fault. Alteration types mainly include garnetization, amphibolization, epidotization, chloritization, k-feldspathization, silicification and carbonatization. Based on field observations and micro-petrography, the paragenetic sequence can be established as (Fig. 1a): (1) early skarn, (2) late skarn, (3) magnetite stage, (4) magnetite-pyrite stage, (5) Cu (-Au) mineralization stage, and (6) late veins. The Laoshankou deposit is located 41 km to the southwest of Qinghe county and at the intersection between the Irysh Fault and Ertai Fault. Although the wall-rock alteration is similar to Qiaoxiahala, a slightly different paragenetic sequence was identified as (Fig. 1b): (1) early skarn, (2) late skarn, (3) magnetite-epidote stage, (4) pyrite-epidote stage, (5) Cu (-Au) mineralization stage, and (6) late veins. At Qiaoxiahala, the typical skarn alteration minerals, such as garnet and amphibole, are more widely present before magnetite mineralization compared with those in Laoshankou, at which the early skarn alteration is characterized by dominant Hypersthene. Magnetite at Qiaoxiahala is associated with quartz, apatite, sphene and K-feldspar in stage Q-III and with pyrite in stage Q-IV, respectively. However at Laoshankou, magnetite is closely associated with epidote in stage-L-III but not in sulfide mineralization stages. Chalcopyrite, probably associated with Au mineralization, usually replaced early-stage magnetite and pyrite in both Qiaoxiahala and Laoshankou, indicating a possible different hydrothermal fluid system.

Alteration and Mineralization Paragenesis of the Bailingshan Fe (‐Cu) Deposit in Eastern Tianshan

Hami (Tu-Ha) basin and the central Tianshan belt, is a part of the Tianshan Orogenic Belt (TOB) and can be subdivided into several subunits by nearly EW-trending deep faults (Hou et al., 2014). It’s composed of DananhuTousuquan arc belt, the Kanggur shear zone and the Aqishan-Yamansu volcanic belt from north to south. The Aqishan-Yamansu volcanic belt is bounded by the Yamansu fault to the north and by the Aqikeduke fault to the south, respectively. Numerous Fe (-Cu) deposits in this belt have been discovered, such as Aqishan, Hongyuntan, Bailingshan, Yamansu, and Shaquanzi from west to east (Mao et al., 2005). Among these deposits, the Bailingshan Fe deposit contains a reserve of 13.065 Mt iron with average grade of 44.94%. The orebodies are hosted in the andesitic tuff breccia of the Matoutan Formation consisting of the Late Carboniferous dacite tuff, andesitic tuff breccia, andesitic to dacitic tufflava and andesitic tuff-andesitic tuff breccia from the bottom up (Wang et al., 2005). Many granitoids, such as the granodiorite, moyite and granite porphyry, intruded the above layer. Ore minerals at Bailingshan are dominated by magnetite, hematite, pyrite, chalcopyrite, and specularite, with garnet, clinopyroxene, amphibole, epidote, chlorite, quartz, and calcite as the dominated gangue minerals. The ore textures are mainly massive and disseminated. Based on the handspecimen and petrographic observation, seven stages of alteration and mineralization are identified at Bailingshan. It contains the early skarn stage, late skarn stage, main mineralization stage, late amphibole stage, quartz-sulfide stage, late veins stage and oxidation stage (Fig. 1). The earliest stage I (early skarn stage) comprises aggregates of coarse-grained garnet and fine-grained clinopyroxene. In the subsequent stage II, metasomatism occurred throughout the garnet and clinopyroxene, represented by amphibole and minor pyrite. Stage III, main mineralization stage, which formed the massive iron orebodies, comprises a variety of opaque and gangue minerals. Major mineral assemblages assigned to stage III are magnetite-epidote and magnetite-chlorite (±epidote). In stage IV and V, minor amphibole (different from those in stage II) and intense quartz-sulfide veins cut the stage III magnetite-epidote assemblages (Chen et al., 2010; Chen et al., 2011; Duan et al., 2013). Meanwhile, massive quartz-pyrite aggregates, sometimes with chalcopyrite, have void filling with magnetite. In stage VI, numerous late veins, such as quartz (without sulfide), hematite, specularite, and calcite-barite, cut the magnetite-epidote or quartz-sulfide assemblages. Oxidation (stage VII) commonly developed on magnetite and sometimes on the surface of chalcopyrite to form bornite and azurite. The characteristics based on the field and petrographic studies imply that the Bailingshan Fe deposit is a metasomatic deposit in the Eastern Tianshan belt.

Alteration and Mineralization Paragenesis of the Heijianshan Fe-Cu Deposit in the Eastern Tianshan, Xinjiang

Eastern Tianshan belt between the Junggar Basin and Tarim Basin, about 150 km south of Hami City, Xinjiang, NW China. Regional E-W-trending crust-cutting deep faults act as major boundaries of the Late Paleozoic geological unites in the Eastern Tianshan (Mao et al., 2005). The Heijianshan deposit lies between the Yamansu Fault and the Aqikuduke Fault, belonging to the AqishanYamansu volcanic belt, which hosts many high-grade iron ore deposits, such as Yamansu, Kumutag, Bailingshan, and Hongyuntan (Hou et al., 2014). The strata of the Heijianshan mine is mainly composed by the Upper Carboniferous Matoutan Formation, consisting of tuff in the lower part overlain by basalt. Orebodies are commonly hosted by tuff and brecciated tuff. Four alteration and mineralization stages at Heijianshan, including epidote alteration, magnetite stage, polymetallic sulfide stage and late veins, have been recognized largely based on the megascopic and microscopic textural relationships and mineral assemblages (Fig. 1). Stage I—Epidote alteration: Fine-grained epidote was widely distributed to replace surrounding rocks and cut by veins of magnetite and actinolite. Coarse-grained and euhedral epidote locally is intergrown with calcite. Stage II—Magnetite stage: Magnetite has different forms of texture, such as granular, brecciated, and massive; nonetheless, magnetite is closely associated with amphibole. Fine-grained magnetite and associated amphibole commonly replaced country rock and previous epidote, clinozoisite, and calcite. Locally, quartz, Kfeldspar, and titanite closely coexist with magnetite and amphibole. A hematite sub-stage, now mainly replaced by magnetite (i.e., “mushketovite”), may occur before the main magnetite mineralization. Stage III—Polymetallic sulfide stage: The main minerals in stage III are quartz, pyrite, chalcopyrite, and chlorite, with minor pyrrhotite and electrum. Magnetite was commonly replaced or cut by Stage-III pyrite and chalcopyrite. Pyrite, locally coexisting with pyrrhotite, was also fractured by chalcopyrite with electrum in veinlets. Chalcopyrite was closely associated with chlorite. Stage IV—Late veins: Late-stage hydrothermal veins are abundant in the Heijianshan deposit, but their mutual age relationship are not very clear. The veins of epidote and calcite are widely distributed to cut wall rock and other mineral assemblages; whereas the veins of quartz, hematite, clinozoisite, chlorite, and albite are only locally distributed. Specularite veins occur locally and postdate magnetite and pyrite. Supergene alteration: The supergene alteration is very common at Heijianshan, which had been recognized as an oxidizing deposit (Zhang et al.,2012). Hematite and limonite after magnetite; digenite, bornite, and malachite replacing chalcopyrite have been commonly observed. Other supergene Cu minerals, such as atacamite and chrysocolla also locally occurred. Based on the preliminary paragenesis study, we conclude that the Heijianshan Fe-Cu deposit was formed by hydrothermal metasomatism and the Cu mineralization may be separate from previous magnetite stage.

Alteration and Mineralization of the Shaquanzi Fe‐Cu Deposit, Eastern Tianshan Orogenic Belt, NW China

The Eastern Tianshan Orogenic Belt (ETOB), located in NW China, is separated into four main tectonic units (the Dananhu-Tousuquan arc belt, the Kanggurtag belt, the Aqishan-Yamansu belt and the Central Tianshan belt) from north to south by several approximately E–Wtrending faults (Kangguer Fault, Yamansu Fault and Aqikekuduke-Shaquanzi Fault) (Huang, Qi et al. 2013). Our study area, located at the eastern part of the AqishanYamansu belt, host an important cluster of Fe-Cu deposits.