Geochemical evidence for contribution of ore-forming materials from peraluminous granite basement ―Taking Fucheng pluton and No. 6722 uranium deposit in southern Jiangxi Province as examples

摘要

Using the induced fission-track method, mobile uranium leaching and lead isotope analysis, this work obtianed geochemical features of the peraluminous Fucheng granite basement and the host rock (shoshonite) of the No. 6722 uranium deposit in southern Jiangxi Province, (ⅰ) Uranium contents of the leucocratic rock-forming minerals (0.18 μg/g for quartz, 0.36 μg/g for feldspar) are lower than the uranium content of the whole rock (4.6 μg/g). Biotite and some accessory mineral inclusions (zircon, monazite and uraninite) are the main uranium carriers of the Fucheng granite pluton. The fissure uranium in altered minerals (hydromica and chlorite) increased evidently, (ⅱ) Leachable rate of mobile uranium in the biotite granite is 10.4%, while that in the altered granite increased to 31%. (ⅲ) Caculation based on lead isotopes shows that during alteration the Fucheng granite lost uranium (ΔU = -37%—-65%), whereas the Caotaobei shoshonite gained uranium (ΔU = +37%—+58%). These features suggest that the ore-forming material of the No. 6722 uranium deposit was mainly derived from the altered peraluminous granite basement of Fucheng pluton.