Study On Wall Rock Alteration Zoning,the Source Of Ore-forming Fluid And Ore-forming Material Of The 302 Uranium Deposit In Northern Guangdong Province

302 uranium deposit in northern Guangdong province is in the southeastern part of the Zhuguangshan granite,which is located at the joint part of the later Caledonian apophysis in Fujian,Jiangxi and Guangdong and Hercynian-Indosinian depression in Hunan, Guangxi and northern Guangdong.In order to discuss the genesis of 302 uranium deposit,based on geological field work,we conducted systematical study on fresh granite, alteration zoning, alteration minerals and accessory minerals which is closely related mineralization by means of petrographic, geochemistry,LA-ICP-MS zircon U-Pb dating,electron probe qualitative and quantitative analysis, H-O isotope and Sr-Nd isotope.The research of rock geochemistry shows that the coarse grained mica granite in Changjiang granite has high SiO2 content(72.27-75.08 wt.%) and alkali content(Na2O+K2O= 7.68～8.10 wt.%) and belongs to the high potassium calcium alkali series,A/CNK value of rock is 1.03～1.05,which is belong to Weak peraluminous granite. Changjiang granite is rich in light REE.It has obvious Eu negative abnormal(δEu=0.14～0.30),apparent Rb,Th and U enrichment, strong Ba,Sr,and Ti deficit,slight Nb deficit. The results of LA-ICP-MS zircon U-Pb dating show that the age of the rock is 164±2 Ma (MSWD=6.3,N=13).The research of alteration zoning shows that altered rocks can be divided into 4 zones. From near to far, the alteration degree decreases,which can be summarized as silication+hematitization to sericitization to chloritization+alkaline feldspathization to weak alteration or normal granite. Silication and hematite is closely related to mineralization.Under complex construction background, alteration zoning is formed by water-rock exchange interaction which combine multi-stage fluid with wall rock.The chlorite of horizontal alteration zoning belong to chamosite and aphrosiderite which characterized by Si deficit and Fe enrichment. They belong to high-temperature hydrothermal alteration of period before mineralization.The research of accessory minerals of horizontal alteration zoning shows that the main accessory minerals are coffinite-thorite, zircon, xenotime, apatite, allanite and pyrite. Uraninite is the most important uranium enrich minerals.Zircon is the most common accessory mineral.The amount of xenotime and apatite is small. Allanite only can be finded in weak alteration or normal granite. From near to far, mineral assemblages can be summarized as coffinite-thorite+zircon+xenotime to zircon+ allanite+apatite.The research of H-O isotope of quartz shows that 818OH2O and δDH2O values of ore-forming fluids are ranging from-7.09%o to 3.24%o and from-105%o to-63‰, respectively, indicating that ore-forming fluids were mainly formed by deeply circulating meteoric water which have experienced water-rock interaction.The research of trace elements and Sr-Nd isotope of flurite shows that the εNd(t) value of fluorite(average-11.6) of metallogenic period is similar to Changjiang granite(average-10.9),is close to Youdong granite(average-13.2),and is obviously different from the εNd(t) values of mafic dikes(average 1.4). Rare earth elements distribution patterns of the fluorite are similar to those of the Changjiang granite but obviously different from those of the Youdong granite.The (87Sr/86Sr)i value of fluorite is between that of Changjiang granite and mafic dikes. In conclusion,above-mentioned may indicating that many constituent of ore forming fluid was mainly derived from the Changjiang granite by interaction of fluid and wall rock.Since the Cretaceous, the tectonic-magmatic activity of northern Guangdong is very strong. The continental crust of northern Guangdong is in extensional phase, oxidizing liquid derived from meteoric water infiltrate and circulate along the fault tectonic,which can be heated and evoluted into hydrothermal fluid.In the process of migration,the oxidizing hydrothermal fluid can leach out uranium and other elements of granite in the interaction with granite,and make uranium unloaded and form deposite under favorable physicochemical conditions and structural position.