Characteristics And Uranium Of Migmatite Rocks In The Mouding Area In Yunnan Province

Mouding in Yunnan province is located in the central-southern Kangdian geological axis which is sit in western margin of the Yangtze Block,.Kangdian geological axis has complex rock types,strata and structures,and has always been the focus of regional mineral resource researches.As one of the key directions of years’exploration,the uranium mineralization types of Mouding is variable.Based on the scientific studies and analyses of petrology,gecchemistry and geochronology of Mouding 1101 uranium mineralization occurrence,we have had a basic understanding pertinent to petrological characteristics,geochemical and geochronological characteristics of major elements,trace elements and REE of the migmatite in study area,as well the relationships between migmatite and the epoch of uranium mineralization as well as uranium metallogenic regularities:（1）The rocks being mixed at Mouding 1101 uranium occurence mainly consist of mica schist,pegmatite,diabase,plagioclase amphibolite,granitic mylonite and granitic gneiss;the lithology of ore rockes are plagioclase amphibole schist,hornblende plagioclase gneiss,mica quartz schist and so on;the metasomatic textures caused by migmatitization are developed（sodic alkali metasomatism）;（2）Geochemical characteristics of migmatite in the uranium mineralization area in Monding 1101 occurence show aluminous,calc alkaline series rock nature,and the migmatite belongs to granite,monzonite and syenite.the content of SiO2 is51.2%⁷9.55%,Na>K in most samples which may caused by sodic alkali metasomatism and be opposite to nature of the granite in this area.The contents of Al₂O₃,CaO,Na₂O,K₂O,MgO changing along with SiO₂ do not show the trend of granitic magma,and it is products of migmatization.Chondrite-normalized spider diagram of trace elements show the magma concentrate large ion lithophile elements like Rb、K、La,while has deficits of Ba、Ce、Eu and Y,and the characteristics correspond to the magma.With the decreasing content of Be,K,Ce,the content of Rb,Rb/Sr and Rb/Ba ratios grow linerly at the same time,showing the characteristics of A-type granite.REE pattern show high LREE and Low HREE and obvious europium negative anomaly.（3）By the combination of this paper and the previous data of chronometers,we think the migmatitzation of the uranium mineralized migmatite at Mouding 1101 uranium occurence formed in the late Mesoproterozoic to early Neoproterozoic,especially about 1050Ma,the same time of Jinning movement.The author consider the formation of migmatite has a inextricable affinity with Jinning movement.Since the Th/U ratio is lessthan 0.5 and Th and U is positively related,we reckon the zircon has a magmatic origin.（4）There are there uranium mineralization types at Mouding 1101 uranium occurence:sulfide-bearing quartz veins and quartz-carbonate veins related uranium mineralization;Felsic veins and tectonic fractures related U-Th anormaly,pegmatite related uranium mineralization.Pegmatite comprises feldspar,quartz,mica,tourmaline,and a small amount of uranium-bearing rare earth ilmenite.Uraninite and its wall rock contain little Ba but relatively high Pb,this characteristic may facilitate the formation of uraninite.The LREE contents of uraninite and the wall rock kd5-4have too much difference,it concluded that uraninite mineralization fluid is not entirely from the surrounding rock,there may be deep fluid participation.By the macro analysis of uraninite at Mouding 1101 uranium occurence,we found the contents of Si,CaO and FeO are all lessthan 2%,demonstrating there is no further fluid alteration after the formation of uraninite.Comparing the U-Pb chronomerer ages of wall rock kd5-4 with the uraninite kd-03,the age of migmatitization of the wall rock is 1052±10Ma,and the formation age of uraninite is 1050⁸50Ma,almost during the same time,namely late Mesoproterozoic to early Neoproterozoic.As far as author concerned migmatitization may facilicate the formation of uraninite.（5）The tectonic structures and hydrothermal have certain control effection on the uranium mineralization.Uranium mineralization and anormaly spread along north-east trend tectonic zone,and there are silicification and hematitization at the surface exposures which are the evidences of hydrothermal activities.The roughly formation sequence of metal minerals is:pyrite-chalcopyrite,epiboulangerite,heterolite;hydroheterolite,goethite and lepidocrocite（limonite）;At the early stage,uranium minerals consist of uranium-bearing rare earth ilmenite or/and uraninite,the later stage mainly comprise uraninite,at the supergene stage uranium hydroxide and uranyl become predominant.The improtant conditions mainly include Julin Group metamorphic rocks,magma activities,tectonic movements and hydrothermal fluids.The strata,magma,tectonic movements and hydrothermal fluids are the main research objects and are all the integral parts for a comprehensive understanding to the area.