Genetic Types, Spatiotemporal Distribution of Ore Deposits and Sources of Ore-forming Materials in the Xuancheng Area, Anhui Province

In recent years,several large and medium-sized ore deposits have been discovered in the shallow cover of Xuancheng,Anhui Province,indicating that this area has a productive metallogenic geological background and may be a potential prospecting region.Based on systematic investigation,the geological and mineralization characteristics of porphyry Cu-Au deposits and skarn Cu-Mo-W deposits in this region have been summarized.Zircon U-Pb dating(LA-ICPMS)of the Chating quartz-diorite porphyry and the Kunshan biotite pyroxene diorite yield concordia ages of 145.5±2.1 Ma and 131.8±2.1 Ma,respectively.Meanwhile,the Re-Os dating analyses for molybdenite from the Shizishan and Magushan skarn Cu-Mo deposits yielded 133.81±0.86 Ma and 143.8±1.4 Ma ages,respectively.When viewed in conjunction with previous studies,it is suggested that twostage(the early stage of 145-135 Ma and the late stage of 134-125 Ma)magmatism may have occurred during the Mesozoic in Xuancheng region.Early stage intrusive rocks are distributed along both sides of the Jiangnan deep fault(JDF).The intrusive rocks to the north of the JDF are mainly quartzdiorite porphyry and granodiorite(porphyry)rocks,related to porphyry Cu-Au deposits and skarn-type Cu-Mo-W deposits.These deposits belong to the first stage of the porphyry-skarn copper gold metallogenic belt of the Middle-Lower Yangtze Metallogenic Belt(MLYB),associated with the high potassium calc-alkaline intermediate-acid intrusions.The magmatic and ore-forming materials are mainly derived from the enriched lithospheric mantle.South of the JDF,the Magushan granodiorite is a representative intrusive rock of the first stage I-type granite,which hosts the Magushan Cu-Mo skarn deposit,similar to the W-Mo-Cu skarn deposits in the Eastern Segment of the Jiangnan Uplift Metallogenic Belt(ESJUB).The magmatic and metallogenic materials mainly came from the Neoproterozoic basement,with the possible participation of a small amount of mantle components.The late stage magmatism was dominated by volcanic rocks with a small amount of intrusive rocks,which were consistent with the limited volcanic-intrusive activities in the second stage of the MLYB.The H-O stable isotopes of ore deposits in the region indicate that the ore-forming hydrothermal fluids of the porphyry and skarn deposits were mostly of magmatic water for the ore-forming stage,the percentage of meteoric water obviously increasing during the late ore-forming stage.The ore-forming materials of the deposits are mainly from the deep magma with a few sedimentary wall rocks,according to the stable carbon isotopes of the carbonates in the ore deposits.Additionally,according to previous research,the molybdenite from the MLYB has a higher Re content than that of the ESJUB.The higher content of Re in the molybdenite from the Shizishan deposit is identical to that of MLYB rather than ESJUB,whereas Re characteristics in molybdenite of Magushan deposit are similar to that of ESJUB.The differences in Re characteristics indicate the different deep processes and ore-forming material sources(mainly mantle composition for the former and crustal materials for the latter)of these ore deposits on opposite sides of the JDF.

Multistage Carbonatization and Mineral Geochemistry of a Skarn-type Copper Deposit at Tongshan,Guichi

The Tongshan copper deposit at Guichi can be considered as a skarn-type copper deposit.Mul-ti-stage carbonatization was well developed in the skarn zone and copper-bearing orebodies,Mineralogy,mineral chemistry and stable isotope data allow it to be divided into five stages:(1)carbonatization of single calcite crystals in the skarn stage;(2)calcite carbonatization in the oxide stage;(3)carbonatization in the early sulfide stage;(4)carbonatization in the late sulfide stage;and (5)carbonatization in the post-sulfide stage.Carbonatization in the early sulide stage is ,among other things,closely related to copper mineralization and is one of the alteration indicators of copper mineralization of this type.C.O,Rb and Sr isotopic studies indicate that the cakites of skarn and oxide stages were formed from hydrothermal solutions predominated by magmatic water,and those of sulfide stage were formed from hydrothermal solutions mainly involving heated meteoric warer.The former was formed in the environment where ?o2(?o2>10^-33and 10^-33>?o2>10^-36)(pH=7-8)is high as compared with the latter(10^-35>?o2>10^-38;pH=5.7).

Geochronology and geochemistry of the W-Mo-ore-related granitic rocks from eastern Ningzhen,lower Yangtze river belt,eastern China

Here we present zircon U–Pb–Hf and wholerock major and trace element studies of eastern Ningzhen W-Mo-ore-related magmatic rocks,Yushan and Longwangshan granitic rocks,to constrain their form timing,magma sources,and tectonic settings.The results showed that the two plutons were formed in the Early Cretaceous with;Pb/;U ages of 107.8±1.2 and 105.2±1.5 Ma(;Pb/;U),respectively.The trapped/residual zircons are mainly distributed in 2.0–2.5 Ga.The two intrusions are characterized by high silicon(68.60–73.99%),high aluminum(13.56–15.02%),high Mg#(47–55),high Sr,Sr/Y,LaN/YN,and low Yb,falling into high Mg#adakitic rock region.The zirconεHf(t)values of the two intrusions range from-24.8 to-13.2,indicating an ancient continental crust in their magma sources.The average Ti-inzircon temperature is 689°C,slightly higher than those of other high-Mg adakitic rocks in the lower Yangtze River belt,but lower than those of high-Mg adakitic rocks in the Southern Tanlu Fault(STLF).Zircon Ce;/Ce;show low oxygen fugacity(LWS-1:3–400,average 92;sample ZYS-4:9–382,average 93).These geochemical features indicate a thickened lower continental crust in the Eastern Ningzhen region in a subduction setting.Comparing the geochemical characteristics of the eastern Ningzhen to the western Ningzhen and other areas in the Lower Yangtze River Metallogenic Belt(LYRMB)and the high-Mg ore-barren adakitic rocks of the STLF,we propose that the magmatic rocks from eastern Ningzhen may be mainly from a thickened lower continental crust that hybridized with a very small part of mantle sources,while the west Ningzhen magmatic rocks may have experienced a higher degree of mantle contaminations in their source.The metallogenic differences between the eastern(W–Mo)and western(Cu–Fe–Pb–Zn)parts of Ningzhen also indicate different proportions of crustal materials in their magma source.

Deep Mineralization Background and Metallogenic Regularity of the Tongling Ore District

Based on the geological conditions and characteristics of mineralization present,three-dimensional geological modelling is used in conjunction with previous deep research results,in order to discuss the process of deep mineralization in the Tongling ore district.The structural analysis shows that surface deformation is strong,deep deformation is weak,the surface has mainly experienced brittle deformation,with the possibility of a large number of deep ductile deformations.There is a thrust nappe between the Tongling uplift and the Nanling basin,that is the boundary of the Tongling block,which has resulted in the southwest uplift of the Tongling block.Combined with the deep exploration data,the threedimensional shape of the main rock masses is interpreted,with three-layer structures in the deep magma chamber.The spatial distribution of magmatic rocks is mainly controlled by the structure.The movement of magmatic hydrothermal fluid is dominated by mesoscale seepage in the deep part and'dike'type upwelling in the shallow part.There is a certain coupling relationship between the ore-forming rock mass and the surrounding rock.The ore-forming age is dominated by the Yanshanian period.Based on the distribution,types and metallogenic characteristics of the deposits,the metallogenic model of'layer coupling'in the Tongling ore district is summarized,with the'one body,two belts and a multilayer metallogenic system'is established,which is significant for the future direction of deep prospecting in the Tongling area.

Evolution of the historical polder landscape in the ancient Danyang wetland,lower Yangtze River,China,during the last 3000 years

Polder is a type of irrigation field unique to the lower Yangtze River of China.It is a product of long-term and ingenuous human modifications of wetland landscapes.In the pre-Qin Period,3000 years ago,the poldered area of eastern Wuhu city was once a large lake called the ancient Danyang wetland.The introduction of agricultural civilization and polder technology to the area during the Wu and Yue Kingdoms period gradually transformed it into an agricultural area.With an accelerating rate of land reclamation under a changing late-Holocene regional climate,the ancient Danyang wetland became an aquatic system strongly influenced by intensifying anthropogenic activities.In this study,based on field survey data,historical documents,and remote-sensing and archaeological data,we reconstructed the spatial distribution of the polder landscape over the last 3000 years and identified their structural diversity.We found that polder landscapes began to emerge in the Spring and Autumn Period,land reclamation intensified in the Three Kingdoms and developed rapidly in the Song Dynasty before eventually reaching the peak from the Ming and Qing Dynasties.The relocation of historical sites to low-altitude areas also marked the expansion of poldered fields from the center of the wetland to the southeast and northwest.The development and evolution of the polder landscape are related to regional climate conditions,changing social and economic statuses,and the development of agricultural technology in the Song Dynasty and succeeding periods.

PROVENANCES OF LOW GRADE METAMORPHIC AND SEDIMENTARY ROCKS FROM SOUTHERN ANHUI PROVINCE: EVIDENCE OF Nd ISOTOPE COMPOSITIONS

Nd isotope model ages of clastic sedimentary rocks are useful for tracing provenances of sediments and reconstructing evolutionary history of sedimentary basins as well as estimating the average age of the continental crust. In this report we present the Nd isotope ratios and model ages determined for the low grade metamorphic and sedimentary rocks from southern Anhui.

Discovery of the Early Proterozoic Basement in the Middle-Lower Reaches of Yangtze River and Its Significance

The middle-lower reaches of the Yangtze River are a famous copper-ironmetallogenic belt, but many vital basic geologic problems about lithogenesis andmineralization are hard to be solved, since the metamorphic basement has not beendiscovered. Although Dongling Group metamorphic rock series outcrops in Huaining,Anhui Province, and Huangxu System metamorphic rock series outcrops in NingzhenMountain in Jiangsu Province, they are generally considered to be of the Sinian, dueto their low metamorphism and the lack of convincible isotopic age data.

The Basic Structure of Dabie Collisional Orogen

The continental dynamic research has focused on the theory and model of collisional orogenic belts. As the joining zone between the southern and northern China massives, Dabie orogen has attracted many geologists from China and abroad, for its various distinctions, especially the exposed root profile, which rarely occurs in the world, of the orogenic belt. At present, however, the collision process, structure and deep geology of the orogen are not well known. The magnetotelluric prospecting profile from Lu’an,