Re-Os dating of pyrite from Giant Bayan Obo REE-Nb-Fe deposit

The giant Bayan Obo REE-Nb-Fe deposit is locatedat the northern margin of the North China Block, i.e. atlatitude 41.7° north and longitude 110.0° east. The depositis very special in the world because it is the largest LREEdeposit and the second largest Nb deposit in the world,and also a large iron deposit. Geological features, mineralassemblage and geochronology of the deposit have beenreported[1—6]. However, various dating methods gave dif-ferent mineralization ages, and discrepancie…     

Re-Os dating of gold-bearing arsenopyrite of the Maoling gold deposit,Liaoning Province,Northeast China and its geological significance

The Maoling gold deposit, one of the large gold deposits in eastern Liaoning Province, NE China, is an arsenopyrite-disseminated gold deposit with a resource of approximately 25 t Au and an average Au grade of 3.2 g/t. Six arsenopyrites closely related to Au mineralization of the Maoling gold deposit are dated by Re-Os technique and define a Re-Os isochron with an age of 2316±140 Ma, which suggests that the deposit was formed in the Paleoproterozoic era rather than in the Indosinian period as some early researchers suggested. High initial ^187Os/^188Os ratio of 1.32±0.48 indicates a crustal derivation of the ore-forming material of the deposit, which may be derived from rocks of the Gaixian formation of the Liaohe Group. Furthermore,the result also implies that the age of the Gaixian Formation in the Maoling district is older than 2316±140 Ma.     

Single grain Rb-Sr dating of euhedral and cataclastic pyrite from the Qiyugou gold deposit in western Henan, central China

The Rb-Sr isotopic dating of pyrite mineral from ore deposits can directly provide mineralization age. However, many geological factors may affect the Rb-Sr isotopic system,which baffles application of this method. Employing ultra-low procedural blank Rb-Sr method,we have dated pyrites separated from the No. 4 breccia pipe of the Qiyugou gold deposit,western Henan Province. Single grains of euhedral pyrite crystal with few microcracks yield an isochron age of 126 ± 11 Ma, which represents time of the main mineralization stage of the deposit. Pyrite grains of cataclastic type show nevertheless scattered Rb-Sr isotopic composition and no reasonable isochron can be defined. Crystal morphology and mineral inclusion studies reveal that Rb and Sr of pyrite mineral probably are preserved mainly in biotite, K-feldspar, and sericite mineral inclusions. The dating results likely suggest that cataclastic pyrite is not suitable for the Rb-Sr dating due to modification of the Rb-Sr isotopic system by later hydrothermal activity of fluid.     

Re-Os dating of Mo-bearing black shale of the Laoyaling deposit,Tongling, Anhui Province,China

Laoyaling is a typical stratiform deposit in the Tongling district and the molybdenum orebody is hosted by black shale of the Dalong Formation of the Upper Permian system. Eight black shale samples from the Laoyaling Mo orebody were dated by Re-Os technique using ICP-MS, which give an isochron age of 234.2±7.3 Ma with an initial 187Os/188Os ratio of 1.37±0.39. The apparent Re-Os age is a few million years younger than the depositional age of the Late Permian. The young isochron age may be caused by the later hydrothermal disturbance or mass fractionation during ICP-MS measurement. However, the obtained isochron age is close to the depositional age and far earlier than those of the Late Yanshanian intrusions. It suggests that the Mo ore of the Laoyaling deposit is sedimentary in origin and not related to the Late Yanshanian magmatism. Black shales of the Upper Permian are distributed widely in the Mid-Lower Yangtze region, our result is important for understanding the ore-forming processes in the regio     

Re-Os isotope dating of pyrite from the footwall mineralization zone of the Xinqiao deposit,Tongling, Anhui Province: Geochronological evidence for submarine exhalative sedimentation

The Xinqiao deposit is located in the Tongling area,Anhui Province.This deposit is dominantly composed of stratiform sulfide orebodies,which are restricted to the transitional zone from clastic rocks to carbonates at the base of the Late Carboniferous Huanglong Formation.There are discordant veinlets or networks of mineralization in the footwall rocks below the stratiform sulfide orebodies.The underlying discordant mineralization zones coexist with conformable stratiform sulfide orebodies,which are considered to be the most representative features of massive sulfide deposits formed by submarine exhalative sedimentation.This study reports a pyrite 187Re-187Os isotopic age of 319±13 Ma(MSWD=16) for the footwall mineralization zone.This isochron age is consistent with the interval of strata hosting the conformable stratiform sulfide orebody,and provides direct geochronological evidence for Carboniferous exhalative sedimentary mineralization.     

Re-Os Dating of Galena and Sphalerite from Lead-Zinc Sulfide Deposits in Yunnan Province,SW China

Dating of lead-zinc deposits is of critical importance for better understanding of ore ge-nesis, but has long been a big challenge due to the lack of suitable minerals that can be unequivocally linked ...     

Zircon U-Pb dating of basement gneisses in the super-large Bayan Obo REE-Fe-Nb deposit,Inner Mongolia

Zircon U-Pb ages have been determined for basement gneisses in the Bayan Obo REE-Fe-Nb deposit. On the U-Pb concordia diagram data of three samples yield upper intercept ages of 1948-1917 Ma. Thus, these basement gneisses are of Paleoproterozoic. Rock association of these basement gneisses includes tonalite, syenite and paragneiss, not belonging to a sedimentary package. It is more appropriate to consider this association as a basement complex rather than a stratigraphic "Group".     

The Rb-Sr isochron of ore and pyrite sub-samples from Linglong gold deposit, Jiaodong Peninsula, eastern China and their geological significance

Here we report the first direct Rb-Sr dating of pyrites and ores using sub-sampling from lode gold deposits in Linglong, Jiaodong Peninsula, which is a supra-large lode gold deposit and propose this as a useful geochronological technique for gold mineralization with poor age constraint. The Rb-Sr data of pyrites yield an isochron age of (121.6±8.1) Ma, whereas those of ore and ore-pyrite spread in two ranges from 120.0 to 121.8 Ma and from 110.0 to 111.7 Ma. Studies of characteristic of gold deposit and microscopy of pyrite and quartz indicate that the apparent ages of ore and ore-pyrite are not isochron ages, only mixed by two end members, i.e. the primitive hydrothermal fluids and wall rocks, whereas the isochron age of pyrite sub-samples constrains the age of gold mineralization (121.6±8.1) Ma, i.e. early Cretaceous, which is in good agreement with the published SHRIMP zircon U-Pb ages.     

云南轮藻植物研究

云南共有轮藻植物５属４８种（包括变种和变型）．在种类组成中，丽藻属最多，轮藻属次之，其它３属的种类较少分布特点具有热带、亚热带性质；区系属于印度一马来西亚，但鸟巢藻属、拟丽藻属、松藻属的地理分布带有地中海沿岸区系的成分。云南轮藻某些种类在形态上存在的差异显示了系统发育的间断性，同时，它们在形态上所具有的一些共同点，反映了在其进化过程中的连续性．     

On emplacement ages of lamproites in Zhenyuan County, Guizhou Province, China

Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-Ar method. Intrusive activities of lamproites in the Sinantang area of Zhenyuan County, Guizhou Province, took place during the Late Cambrian, as indicated by the Sm-Nd isochron ages ( t ) = (503 ± 17) (2σ) Ma and by the Rb-Sr isochron ages ( t ) = (501.2 ± 4.6) (2σ) Ma. Intrusive activities of olivine lamproites at the Maping with Ⅱ-type diamond and Xitou in Zhenyuan County, Guizhou Province, took place from the Late Cambrian to the Early Ordovician, as evidenced by the Sm-Nd isochron ages ( t ) = (502 ± 27) (2σ) Ma and by the Rb-Sr isochron age ( t ) = (502 ± 27) (2σ) Ma. This suggests that the upwelling hot materials derived from the deep mantle were emplaced from the Late Cambrian to the Early Ordovician (503-497 Ma), while the time terminal of cooling of the geothermal event of magmatism-tectonism probably was at 442.64-435.54 Ma, as dated by the whole rock K-Ar method.     

山西辛庄金矿床成矿模式分析

对辛庄金矿的成矿地质条件、控矿因素及矿化富集标志进行研究;结合本区地质特征,总结辛庄金矿床的主要成矿要素,建立辛庄金矿床的成矿模式.研究结果表明:区内五台群金刚库组地层为矿床的形成提供了部分成矿物质;北西向区域性张性大断裂(龙山断裂和义兴寨断裂)及其强烈挤压下形成的北西向次级断裂是本区的主要控矿构造,为成矿物质的就位提供了有利的空间;燕山期的岩浆侵入活动为成矿提供了大量的成矿物质和热能,是成矿的首要因素;五台群金刚库组地层、北西向区域性张性大断裂、燕山期岩浆岩、以硅化、黄铁矿化以及绢云母化为主的围岩蚀变及主脉带与围岩之间的接触带是本区的关键控制因素;多金属硫化物阶段以及热液蚀变的广泛发育是其矿化富集标志.