白竹峪铀多金属磷块岩矿床地球化学特征

Geochemical Characteristics of Baizhuyu U-Polymetallic Phosphorite Deposit

湘西北下寒武统铀多金属磷块岩由于富含多种矿产元素,受到国内外地质学者的越来越多的关注,但成因认识仍然众说纷纭。文章在对湘西北黑色岩系非常规铀资源开展地质和放射性调查的基础上,选取下寒武统牛蹄塘组铀多金属磷块岩露头较好的白竹峪矿床开展地质调查、岩石地球化学测量、系统的采样和分析测试,结果表明铀多金属磷块岩主量元素与上地壳所含的对应元素相比,只有CaO和P_(2)O_(5)富集,富集系数分别为9和204。此外,铀多金属磷块岩微量元素U(平均含量为1 350×10^(-6))、Ni(平均含量为6 822×10^(-6))和Mo(平均含量为2 104×10^(-6))均达到相应矿床的工业品位,且Re、Tl和V达到铀矿床综合利用指标。上震旦统灯影组白云岩、下寒武统牛蹄塘组铀多金属磷块岩和黑色碳质泥质页岩及板岩的δU、V/Cr、Ni/Co和δCe值均指示这3种地层形成于缺氧沉积环境,铀多金属磷块岩北美页岩配分曲线显示热水沉积特征,δEu大于1,结合主量元素和微量元素R型聚类分析结果推测铀多金属磷块岩在正常海相沉积的基础上发生了热液的改造作用。

The Lower Cambrian U-polymetallic phosphorites in northwestern Hunan has attracted more and more attention of the geologists due to the enrichment of diversiform minerals.However,there are still different views on its genesis.This paper focused on the geochemical characteristics of Baizhuyu deposit.The results of geochemical analysis showed that the U-polymetallic phosphorites of the deposit contain 38.4%CaO and 30.6% P_(2)O_(5) on average.The average grade of U,Ni and Mo are 1350×10^(-6),6822×10^(-6)and 2104×10^(-6),respectively,all of them beyond the industrial grade of the corresponding metals.Besides,the average grades of Re,Tl and V reach the target of comprehensive utilization.The values ofδU,V/Cr,Ni/Co andδCe of dolomite in the Dengying Formation of the Upper Sinian,and U-polymetallic phosphorite,black carbonaceous argillaceous shale and slate in the Niutitang Formation of the Lower Cambrian indicate that these strata was formed in anoxic sedimentary environment.The NASC-normalized REE patterns of U-polymetallic phosphorites are nearly horizontal or slightly inclined to the left.The LREE/HREE ratio is small.The total amount of REE is high.TheδEu values of U-polymetallic phosphorite are larger than 1.It was presumed that the U-polymetallic phosphorite in Baizhuyu deposit had undergone hydrothermal transformation.