The Study Of Mantle Liquid And Uranium Metallogenesis

Nanling metallogenic belt locates Southeast of Eurasia, whose Southeast is Pacific Plate and Northwest is Jiangnan Orogen. It formes three Magmatic belt ,which are yuechengling-wanyangshan,qitianlling-zhuguangshan,huashan-dadongshan-east of guizhou province and who are controlled by regional discordogenic fault,and comes through many tectonic- magmatic activities since Paleozoic.Nanling metallogenic belt also discovers a lot of rare and non-ferrous metal belt which is one of the rare and non-ferrous metal assemble area and granital uranium ore assemble area.The uranium ore field of south zhuguang mountain lies in the mulriple part of Naling west-east tectogene and wanyangshan-zhuguangshan south-north tectogene,the mother body of uranium rock is composed of two parts:the west rock is formed by early Yanshanian rocks which are distributed as west-east and the east is composed of Indosinian rocks and a few of Yanshanian rocks,which are distributed as south-north.Many kides of dike rocks shch as aplite,quartz porphyry and granite porphyry ect.are discovered in the zhuguangshan rock..The relationship between basic dyke and uranium mineralization distributed in the rock is close.So,. The uranium ore field of south zhuguang mountain is the center of tectonic- magmatic activitie and thermal fluid,alteration of mantle fluild to rock,specially during lateCretaceous to tertiary,provides advantaged congdition to uranium ore field.in the study erea. The paper ,taking uranium ore field of south zhuguang mountain as study object and based on collection and coordination of geology,physical geography and geochemistry deta.,analyses the character of lithology geochemistry and isotope geochemistry of granite and basic dykite and studies the property of tectonic and mine liquid and its evolvement,the source and mechanism of mine liquid ,as well as the source and mechanism of basic dykite and its relationship to uranium mineralization,at the same time ,the paper also discusses manifestation geochemistry sign and position mark of mantle liquid metallogenesis. The paper gains these conclusion. (1) The subtle chronology study of zircon SHRIMP U-Pb.The results show that the age of Indosinian rock is 239 ~ 231Ma,which belongs to early Indosinian and the age of Yanshanian is 160 ~ 154Ma,which belongs to early Yanshanian, different basic dykite is the result of late Yanshanian.(2) The study of lithology geochemistry and isotope geochemistry of Indosinian rock shows that they are Indosinian collision,which are rich Si Al and high alkali K>Al.. The spider map of trace element shows positive Rb,Th and negative Ba,Sr,P,Ti,Nb,Ta,rich in U;∑REE is high, positive LREE and negative Eu, lowεNd(t),high (87Sr/86Sr)I and old Nd pattern age.Ale of these show Indosinian granite belong to lithosphere type or S type.The ratio of CaO/Na2O changes between 0.11 to 0.50,which shows the source is composed of arenite and argillaceous rock.which are admixture in definite ratio because of high Rb/Sr and Rb/Ba. The tectonic discrimination diagrams reflecte that the admixture source fusion,which is composed of argillaceous rock and arenite, forms the Indosinian granite.(3) The range of SiO2 content(69.47 ~77.50%),alkaline gross (6.46% ~ 10.07%),K2O/Na2O ratio (0.91 ~1.23) and ACNK (0.94~1.31)value from the Yanshanian granites is obviously wider. In the standard and modular diagram of trace element, the Yanshanian granites show moderate Rb and Th enrichment,Ba,Sr,P,Ti loss,moderate Nb and Ta depletion, obvious uranium enrichment;The granites display mew's wing REE patterns:lower and obvious change of REE content,negative Eu anomaly, light REE enrichment;However, The granites have a small rage of moderately negativeεNd(t) values(-12.6~-10.0), a great change of 87Sr / 86Sr ratio(0.70761 ~ 0.77651) and an old age of Nd mode (1763~1964Ma).Then It can be concluded that the Yanshanian granite belongs to crustal type or S-type granites category. (7) The CaO/Na2O (0.10~0.84), Rb/Sr (1.8~30.0) and Rb/Ba (53~232.0) ratio in these Yanshanian granite are change significantly. As shown in the plot Rb/Sr vs. Rb/Ba , datas are almost in the shale area, while these granite dates fall into collide granite area in the tectonic environment graph, which indicate they are the product of within-plate magmatic activity formed in stretched tectonic environment(4) The Cretaceous medium-basic dykes are significantly varied in their major elements concentration(SiO2,TiO2,Al2O3 and alkali gross);The standard and modular diagram of trace element,uplift at left and relatively flat at right,shows negative Nb,Ta trend;The REE pattern is a right distribution with higer LREE/HREE and (La/ Yb) N ratio,basic Eu value without loss. TheεNd(t) (8.2-4.3) and (87Sr / 86Sr) i value of Early Cretaceous diabase (0.70828 ~ 0.72338) change obviously, while their lead isotope composition has anomaly Dupal characteristic which reflects these diabases are derived from concerntratly inhomogeneous mantle source; Late Cretaceous diabase-porphyrites have a slight variation inεNd(t) value (-2.2~-0.9 ),(87Sr /86Sr) i value ( 0.71276 ~0.71312),206Pb / 204Pb (18.500 ~ 18.574) and 207Pb / 204Pb (15.718 ~ 15.790) ratios. In the Nd - Sr, Nd - Pb and Pb - Pb related diagram, the Early Cretaceous date fall into MORB,EMⅡand the Pacific Ocean deep-sea turbidite group, which reflects the mantle source of diabase enriched by the influence of fluids metasomatism caused by Pacific-Oceanic Plate subduction and sediment dehydration, Whereas the Late Cretaceous data locate between the MORB and EMⅡ,which indicates they derived from mantle source with mixing MORB and EMⅡmember according to a certain proportion. The enrichment reflect source, owing to fluid metasomasis between subduction zones and overlying mantle wedge.(5) Based on the study of hydrogen and oxygen isotopic composition in 302 metallic miner, we get some fluid date(δDH2O=-65 ~ -82‰,δ18OH2O=6.8 ~ 0.6‰for metallogenic epoch;δDH2O=-50 ~ -65‰,δ18OH2O=-0.8 ~ -7.1‰for late stage of metallogenic epoch). In theδDH2O-δ18OH2O diagram ,dates in metallogenic epoch mainly fall into the edge of evolution area of. These indicate fluid of metallogenic epoch is composed by mixing mantle fluid and atmospheric fall, while fluid in late stage of metallogenic epoch is mainly evolved from atmospheric fall. The homogenization temperature obviously shows positive correlation with salinity distribution of inclusions, indicating mantle fluid with high temperature and salinity mixed with low salinity atmospheric fall according to different degree, which also verify metallogenic epoch mixed by mantle fluid and atmospheric fall .(6) Ore-forming components with multiple source characteristics: calciteδ13C value (-0.84%~-0.53 %)mainly reflects the carbon from the mantle; (87Sr / 86Sr) i value of Fluorite (0.71474 ~ 0.71697) is between the diabase (0.70861 ~ 0.72473) and ore-rich granite (0.77152~0.73519) , reflecting strontium mainly from the mafic dikes or a mixture of mafic dikes and ore-rich rock. TheεNd (t) value (- 11.5 on average) and Nd age pattern (1787Ma on average) of detrital uraninite share similar with ore-rich granite(-13.2, 1945Ma forεNd (t), Nd in oil hole rock; -11.0,1787Ma forεNd (t), Nd in Yangtze rock), but obviously differ in diabase(-1.4 forεNd (t) ; 1770Ma for Nd) .(7) Because of basement metamorphic in the Nanling region with high content of uranium( 4 ~ 6×10-6) and ore-rich granite with high content of uranium (19.5 x 10-6 for Yangtze rock , 11.1 x 10-6 for oil hole rock) and obvious alkali metasomasis , the major uranium is from the crust, but not the mantle. When the fluid rich in CO2 reacts with uranium, especially activate uranium to produce stable UO2(CO3)22- or UO2(CO3)34-, which are transferred into the ore-forming fluid.According to the mineralization of mantle fluid, the 302 metallic belongs to the ore-forming processes of mantle fluid like Shi-tuling,Xianshi and Xiwang metallic, It is thereby confirmed that as other large and super-large metallics, mantle fluid has very vital significance in formation of large and super-large metallic deposit.