Geological Geochemistry Characteristics Of The Biotite In Granite-pegmatite-type Uranium Deposit In Danfeng

Danfeng area was located in the collision zone between Qinling orogenic belt and North China plate,and was the only area where granite-pegmatite-type uranium deposit be discovered in China.In this paper,the Chenjiazhuang and Guangshigou uranium deposits in Danfeng area were studied.On the basis of the study of the lithological and mineralogical,mineralogy of biotite was carried out both in uranium-bearing rocks and uranium-free rocks.Identied the mineral assemblages,distribution and chemical compositions of biotite,based on the chemical composition estimated by EPMA biotite was classified.The forming physicochemical conditions of the biotite were estimated through calculating the values and ratios of n(Fe2+)/n(Fe2++Mg2+),n(Mg2+)/n(Fe2++Mg2+),Al?,Al?et al.,and their interrelationships.Finally the geochemical characteristics of biotite from both uranium-bearing rocks and uranium-free rocks ware compared with each other.The research results were listed as below:(1)The uranium-bearing rocks was mainly composed of biotite granite pegmatite,but the uranium-free rocks was dominated by biotite pegmatite and biotite granite.Biotite was always one of the main rock-forming minerals both in uranium-producing rock and the uranium-free rocks.(2)The biotite in uranium-free rocks was distributed dispersedly,while in uranium-bearing rocks was distributed as crumby structure.The biotite in uranium-free rocks was inset in the crystals of quartz and feldspar,or distributed amongst them in the shape of flakes,and its pleochroism was obsered,but the biotite in uranium-bearing rocks were mostly flaky or clusters.(3)The results of electron probe analysis(EPMA)showed that the biotite belonged to iron biotite,but the biotite in ore was more biased towards magnesia biotite.Based the chemical composition of biotite,both the uranium-producing rocks and the uranium-free rocks belonged to peraluminous granite of S type.(4)The diagenetic environments of both deposits showed some similarities on high temperature and low oxygen fugacity.In comparison,the biotite from Guangshigou uranium deposit showed an environment of relatively lower temperature and oxygen fugacity The crystallization temperature of biotite in uranium-free rocks was between 650? and 710?,in uranium-producing rock was compared with between 630? and 705?.