Abstract:The Dongxi gold deposit is an important epithermal gold deposit in the Tongbai-Dabie orogenic belt, central China, with reserve of >5 tons(t) Au. It belongs to a suite of low-sulfidation epithermal systems associated with the volcanism. Gold mineralization is hosted in the Early Cretaceous andesite, and consists primarily of auriferous calcite-quartz veins that are confined to the NW-trending faults. The mineralization process is composed of two stages, i.e., coarse grained calcite veins (Stage Ⅰ) and quartz + calcite veins (Stage Ⅱ). Primary fluid inclusions in calcite include three types:monophase vapor, monophase liquid, and two-phase liquid-rich inclusions. The early-stage fluid inclusions have low homogenization temperature (128~172℃) and low salinity (0.35% to 0.92%), while the late-stage fluid inclusions have homogenization temperatures of 105~160℃ and salinities of 0.18%~0.92%. The temperatures and salinities of ore-forming fluids tend to decrease progressively. The ore-forming fluid seems to be the mixture of the magmatic and meteoric components. The crystallization age of the ore-bearing andesite has been fixed at 126.7±1.4 Ma (1σ, MSWD=0.95) according to U-Pb analysis of zircons by LA-ICP-MS. The Dongxi deposit might have been formed in a lithospheric extension and mantle upwelling setting, which provided abnormally high heat and fluid fluxes necessary for gold mineralization.

Abstract:The large area of the eastern section of the North Dabei Mountain lies in North Qinling orogenic belt with extensive exposed trachyte, which was formed in early Silurian, sandwiched in lower level carbonaceous silty slates of the Early Silurian Meiziya Group (S₁m) and spread from northwest to southeast. This trachyte is closely related to niobium mineralization. The Tianbao Nb deposit occurs in the middle to lower part of the volcanic sedimentary rhythm. The most important host rock is ignimbrite. The trachytes are alkali-rich, with high ∑REE and enriched LREE. High field strength elements such as Nb, Ta, Zr and Hf are enriched and Sr, P, and Ti are depleted, showing the characteristics of OIB. These characteristics of the trachytes indicate that trachyte magma originated from the evolution of mantle-derived basaltic magma. They are low pressure type trachytes formed in an intraplate rift tectonic environment. Compared with the barren trachyte, the ore-forming trachyte has lower SiO₂, higher Al₂O₃, K₂O, CaO, lower P₂O₅, higher high field strength elements(Nb, Ta, Zr, Hf)and light rare earth elements(La,Ce), stronger negative Eu anomalies, positive Ce anomalies, slightly strongly depleted in P and Ti, and higher volatiles(F, CO₂). Niobium-containing mineral is aeschynite, which was generated along the early mineral edge, cracks or late veins. The metallogenic stage was in the late stage of magmatsim. The enrichment process of element Nb was closely related to the migration and preservation of the volatiles (F, CO₂ etc.). This Nb deposit is a volcanic rare metal deposit, with the characteristics of magmatic type and magmatic hydrothermal deposits. The deposit type is different from that of Miaoya and Shaxiongdong rare earth deposits; nevertheless, they belong to the same mineralization series.

Abstract:Dahongshan area, located on the southern margin of the Tongbai-Dabie orogenic belt, has extensively exposed metamorphic gabbro-diabase. This dike intruded into the accretionary complex of the Dahongshan orogenic belt. In this paper, zircon U-Pb LA-ICP-MS dating method shows that the emplacement age of rock vein is 163±3 Ma. The age of this mafic dike is one of the earliest known records of Late Mesozoic magmatic activities after the collision in the Tongbai-Dabie orogenic belt, suggesting that the Late Mesozoic magmatic activities in the Tongbai-Dabie orogenic belt started in late period of Middle Jurassic, which is similar to the time of initial anatexis in northern Dabie orogenic belt, and is about 30 Ma earlier than the peak period of the Early Cretaceous magmatism (~130 Ma). The analytical results of Hf isotope from zircon show that εHf(t) is +5.8~+10.8 (with an average +9.7±0.7), and the corresponding single stage Hf model age t_DM1 is 387~595 Ma (mean value being 434±29 Ma), obviously larger than the age of diagenesis. These data show that the source of magma was derived from depleted mantle, resulting from the remelting of the Early Paleozoic partially melted depleted mantle basaltic rocks. All the data show that 163±3 Ma is one of the oldest magmatic rock records after the continent-continent collision of the Mesozoic Tongbai-Dabie orogenic belt, and this age is in agreement with that of root softening in Dabie orogenic belt. It possibly represents the conversion time of Dabie orogenic belt from compressional environment to extensional environment. It is therefore considered that the interval from root softening to large scale extensional collapse in Tongbai-Dabie orogenic belt is~30 Ma.

Abstract:In this paper, the authors systematically performed zircon LA-ICP-MS U-Pb dating and studied rock geochemistry for Xiadian magmatic rock body in Western Dabie orogenic belt. The study shows that the rock body has characteristics of richer silicon and higher alkali, and poor Ca, Mg and Al. The rock body is characterized by enrichment of LREE, depletion of HREE, obvious fractionation between LREE and HREE, and strong depletion of Eu. The rocks are enriched in LILE (Rb, K, Th, etc) and Pb elements, and are depleted in HFSE (Ta, Nb, Ti, etc) and Sr and Ba elements. The rock body belongs to A-type granite in rock type. LA-ICP-MS zircon U-Pb dating yielded a ²⁰⁶Pb/²³⁸U weighted average age of 130.0±1.8 Ma for Xiadian magmatic rock body, which represents the crystallization age of the rock body, suggesting the Early Cretaceous magmatism product. A-type granites of Xiadian magmatic rock were formed in a post-orogenic environment, which indicates that the Tongbai-Dabie orogenic belt entered the plate evolution stage.

Abstract:In this paper, the authors discussed the relationship between the Wudang block and the Yangtze continental nucleus (the Kongling area) and the evolution of the Northern Yangtze Craton during the Neoproterozoic, based on the collection of published detrital zircon U-Pb data from the Neoproterozoic sedimentary rocks in this area. Through the comparison between the data from the two regions, two major age populations (~710 Ma and~2.5 Ga) were found for the Wudang block, meanwhile, the absence of old ages (>3.0 Ga) is obvious, indicating that the sedimentary source might not have come from the Yangtze continental nucleus. The Wudang block might have been a microcontinent, which was separated from the Yangtze continental nucleus (represented by the Kongling area) before the Neoproterozoic, and then collided with the latter again during the middle Neoproterozoic to form a complete body.

Abstract:The Simianshan garnet-bearing migmatitic granite, which is located at the northern foot of the Dabie Mountain, is mainly composed of monzonitic granitoids. In this paper, the petrological and geochemical characteristics of the granitoid were studied to constrain the petrogenesis. The result shows that these granites are rich in silica, with high content of alkali (Na₂O+K₂O). Overall, they are metaluminous to peraluminous granites and belong to the high-K calc-alkaline series, with locally inhomogeneous migmatization. The granitoids are characterized by enrichment of Ba, Th, K and depletion of Nb, Sr, P, Ti. The abundance of ΣREE varies in the range of 115.05×10^-6~430.85×10^-6. Their LREE is enriched compared with HREE and the δEu values fail to show obvious abnormal phenomena. The preliminary results of this study show that the granitic magma was derived from the partial melting of mid-lower crust, which was triggered by delamination or underplating.

Abstract:The Goujiahe gold deposit is located in the western Wudang Mountain of South Qinling, which is controlled by ductile slip-shear belt and occurs in sericite chlorite-quartz schist and metamorphic quartz sandstone. The mineralization type is mainly composed of fracture alteration type and quartz vein type mineralization, in which the former formed the main orebody. The main fracture alteration type orebody is distributed in nearly NS-trending fault in stratoid or lenticular form, and the secondary orebodies were filled in NW_and NE-trending secondary faults, forming quartz vein ore bodies. Three metallogenic phases were recognized:the early quartz-sulfide stage, the middle quartz-sulfide-gold and silver stage and the late quartz-carbonate stage. The fluid inclusions of the quartz-sulfide-gold and the silver stage and the quartz-carbonate stage of the main orebody were observed and measured, the D, O, C isotope analysis of different stages of quartz and calcite and dolomite was conducted. The results show that most of fluid inclusions are enriched in liquid primary inclusions in crowded ran-dom distribution. The homogeneous temperature peak is mostly 220℃ and 170℃, the salinity is 1.40% to 14.46% and 1.34% to 7.31%, the density is 0.60~0.97 g/cm³ and 0.86~0.96 g/cm³ for the quartz-sulfide-gold and silver stage and the quartz-carbonate stage respectively. The hydrogen and oxygen isotope study of the two phase yielded 12.9‰~14.5‰ and 11.9‰~13.8‰, and the carbon and oxygen isotope study of calcite and dolomite yielded the values of δ¹³C_V-PDB=-12.4‰~-12.0‰, δ¹⁸O_V-PDB=-18.4‰~-18.1‰, suggesting that the original ore-forming fluids were metamorphic in genesis, characterized by mesothermal and low-salinity nature. Geological and fluid features and metallogenic tectonic background suggest that the Goujiahe gold deposit may be of the orogenic-type mineralization system.

Abstract:Intense alkaline magmatism and related Nb-REE mineralization occurred during the Silurian in the South Qinling belt, forming igneous rocks including syenites, carbonatites, trachytes and alkali basalts. The alkaline magma erupted during 450~430 Ma, at the same time with intense ultramafic and mafic activities in the region. These alkaline rocks were formed through fractional crystallization from mantle-derived magmas. The magma sources were likely composed of dominated HIMU mantle and minor EMI and EMⅡ mantle. The high values of alkali (K₂O+Na₂O) and protracted fractional crystallization constituted important geodynamic controls on the Nb-REE mineralization. The Silurian alkaline magmatic activities were generated in an intensive lithospheric extension and mantle upwelling setting, while the enriched lithospheric mantle was metasomitized by slab melts related to the subduction system.

Abstract:On the basis of zircon U-Pb dating and rock total analysis of Laoshanzhai rock mass, the authors hold that chemical components of Laoshanzhai rock mass have ultra-acid, alkali-rich and peraluminous characteristics, thus belonging to ultra-acid, alkali-rich and high-K calc-alkali series. The data indicate that Laoshanzhai rock mass is characterized by enrichment of LILE (Rb, K), HFSE (Hf, Th, U,) and LREE, and depletion of HREE, with moderate negative Eu anomaly. Rare earth element distribution curve is higher on the right side and flat on the left side, exhibiting light REE enrichment. Major trace elements show that magma of rock mass was mainly from lower crust source, and was probably mixed with a small amount of mantle materials. Zircon LA-ICP-MS U-Pb dating shows that ²⁰⁶Pb/²³⁸U weighted average age value of rock mass is 133±2 Ma (n=21, MSWD=3.1), which represents the emplacement age of Laoshanzhai rock mass as the product of magmatic activities of Early Cretaceous period. Laoshanzhai rock mass was formed by tectonic regime transition and the extension mechanism of Qinling-Dabie orogenic belt in Mesozoic, during which the lower crust had not yet been delaminated, the lower crust of high pressure granulite that contained plagioclase, pyroxene, hornblende and garnet was subjected to partial melting, and experienced upward migration along deep faults, then experienced consolidation diagenesis in the shallow crust.

Abstract:The Niangniangding tungsten-beryllium mining area in Dawu County of Hubei Province is located in the middle of the Tongbai-Dabie orogenic belt between the North China plate and the Yangtze plate. Proterozoic strata outcropped in the area are widespread, magmatic activity is frequent, and the bleak structure is developed, which exhibits a multi-periodic characteristic in the area. The ore deposit occurs along the granite rock contact zone and has close relationship with the late Yanshanian Niangniangding and Jigongshan rock bodies. Based on an analysis of characteristics of metallgonenic geological setting, geological characteristics of the deposit and the two geochemical anomalies in the Niangniangding tungsten-beryllium ore deposit in this area, the paper puts forward the key ore-prospecting orientation, which points to areas of the contact zone between the late Yanshanian granite and strata, rock mass and tectonic fracture zone area. This study not only fills the blank of tungsten-beryllium deposits in Wudang-Tongbai-Dabie metallogenic belt and describes the geological features of beryllium deposit for the first time so as to supply material for the research but also provides a certain theoretical basis and guiding significance for the study area and even for the whole Dabie region so as to help further tungsten-beryllium minerals exploration.

Abstract:The Laowan gold deposit is one of the typical shear zone type gold deposits in Tongbai area, Henan Province. The characteristics of fluid inclusions suggest that the ore-forming fluid is a K⁺_Na⁺-Cl^-SO₄^2- system which indicates medium-low temperature, low-salinity and CO₂-containing nature. The study of hydrogen oxygen isotopes shows that, in the early stage of the deposit, magmatic water was dominant, and in the late stage, meteoric water was the dominant one. The authors thus hold that the Pb source of the deposit was related to the Guishan Formation Complex and the Laowan granite, and was close to the granite, showing its deep source characteristics. These results provide evidence for the magmatic origin of the ore-forming fluids.

Abstract:The alkali feldspar syenite in Zhuxi Manjinggou, which is located in the south Qinling orogenic belt, intruded into the disbase body in small lenticular form. Locally, it intruded into Early Paleozoic strata. A study of its petrological characteristics and geochemical characteristics reveals the followings characteristics:the alkali feldspar syenite in this area is potassic alkaline syenite with high total alkali (Na₂O+K₂O); the Mg^# in the rock is obviously lower than that in the original magma, which indicates that the magma experienced a high degree evolution; the REE in the body is high, and exhibits LREE enrichment and HREE depletion. The trace element diagrams show that the syenite in this area originated from early continental rift environment in the Early Silurian.

Abstract:The authors conducted mapping in the mining area on the basis of detailed field geology and, in combination with the previous research results, fully analyzed gold ore-controlling structures and genesis of the Daleishan deposit. It is held that the ore-guiding and matching structures of the gold deposit belongs to a new type, and both structures are not fault, but belong to the formation of shear zone formed by upward migration of the Daleishan granite dome caused by magmatic activity during the Yanshanian epoch, which provided the channel for late ore-guiding structure and matching structure; Neoproterozoic gneissic monzogranite provided the gold with higher gold element background values for the gold deposit, and magmatic activities not only caused the activation migration of gold element but also provided the gold metallogenic material source. The gold ore deposit was a post-magma low temperature magmatic hydrothermal deposit. According to the geological feature that the gold quartz vein fills in the crack of lamprophyre, the authors used LA-ICP MS zircon U-Pb dating and obtained a lamprophyre diagenetic age of 126.8±2.0 Ma, which confined the mineralization age of the Daleishan gold deposit.

Abstract:The Lüshigou pluton is located in the Qiongheba ore concentration area in East Junggar. This pluton intruded into the host rock of the Lüshigou copper deposit. LA-ICP-MS U-Pb dating of zircons from this pluton yielded an early Carboniferous age of 354±1 Ma. The main rock type of the pluton is quartz-monzonite with many mafic-ultral mafic enclaves inside. These quartz-monzonites have high SiO₂ (62.31%~65.31%), Al₂O₃ (15.44%~16.29%), CaO (3.71%~4.89%) and K₂O (2.85%~3.54%) contents, exhibiting high-K calc-alkaline and metaluminous characteristics (A/CNK=0.93~0.99,A/NK=1.68~1.96), and belonging to I-type granite. The total REE values of them are low (90.82×10^-6~111.36×10^-6) with relative enrichment of LREE and Eu negative anomaly (δEu=0.68~0.87). The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE (K, Rb, Ba, Sr) and depletion of the HFSE (Nb, Ta, P, Ti). The quartz-monzonite has high Ba (758×10^-6~1 113×10^-6), Sr (401.8×10^-6~512.5×10^-6) values with high (La/Yb)_N, Sr/Y ratios, distinct Nb, Ta and Ti depletion, and are comprehensively called high Ba-Sr granitoid. These characters indicate that the Lüshigou pluton was probably formed by the magma-mixing of the mantle-derived mafic magma and crustal partial melting magma during the tectonic transition period from subduction to post-orogenic setting in the late Paleozoic.

Abstract:Paleocene-Eocene thick evaporites are developed in Kuqa depression, especially in the western part, with many salt spots. In this paper, the authors studied potash minerals and potassium-bearing salt minerals of Paleocene-Eocene evaporites so as to analyze potash-forming trend of Paleocene-Eocene evaporites in Kuqa depression. Glaserite mineral exists in potash-forming layer sectionⅠ; original sylvine, potassium gypsum and potassium-bearing halite gypsum occur in potash-forming layer section Ⅱ, indicating that ancient salt lake had reached potash deposition phase. Borehole chemical composition analysis shows that, from borehole bottom to the top, the shallower the depth, the higher the K⁺ concentration, with a maximum of 1.273%. In combination with characteristics of ions content, the potassium-to-chlorine ratio, the magnesium-to-chlorine ratio, the lithium-to-chlorine ratio and the strontium-to-calcium ratio, the authors determined two potash-forming trends during ancient salt lake evolution, and initially hold that potassium layer section Ⅰ and Ⅱ have the potential to form potash, with layer section Ⅱ having larger potential to form potash.