浙西衢州市仙洞大理岩矿稀土元素地球化学特征及成矿环境分析

REE Geochemistry of Marble Ore in the Xiandong Deposit,Quzhou,Western Zhejiang Province and Its Implications for Metallogenic Environment

衢州市衢江区地处赣杭构造带上,接近于扬子板块和华夏板块的构造结合部位,区内石炭系中统黄龙组及附近地层中分布大量大理岩,并形成矿床。研究区仙洞大理岩矿床灰岩、大理岩化灰岩和大理岩三类矿石中,依大理岩化程度,方解石呈现出不同程度的典型方解石式解理面,表面平滑程度也依次增加。地球化学研究表明这类矿石稀土元素ΣREE为5. 9×10^-6~2 027. 28×10^-6(均值为266. 52×10^-6,n=37),LREE/HREE为1. 35~36. 16(均值为9. 8,n=37),(La/Yb)N为0. 64~33. 59(均值为4. 2,n=37),轻重稀土分异较为明显,δEu为0. 46~33. 77(均值为9. 38,n=37),呈现正异常,稀土元素配分曲线呈平缓右倾型。综合数据讨论认为,研究区大理岩原岩为典型的沉积型碳酸盐岩,非岩浆成因的碳酸岩,成岩于氧化还原交替的浅海沉积环境,部分样品数据暗示可能有来自海底喷气热液影响,而大理岩化作用会对岩石内活动元素产生影响。

Qujiang District of Quzhou City is located in the Gan-hang tectonic belt,which close to the suture belt between Yangtze plate and cathaysia plate. A large number of marble are distributed in the middle Carboniferous Huanglong Formation and adjacent stratums of study area. The limestone,marblized limestone and marble ores in the Xiandong deposit could appear the typical calcite cleavage plane on the base of marmarization,and the smoothing degree of surface also increase by degrees. The REE analytical test of different carbonate ores from Xiandong deposit are carrried out,data show that the contents of ΣREE,LREE/HREE and( La/Yb) N are 5. 9 × 10^-6~2027. 28 × 10^-6,1. 35 ~ 36. 16 and 0. 64 ~ 33. 59. And the average values of them are 266. 52 × 10^-6,9. 8 and4. 2. The calcites are characterized by obvious fractionation between LREE and HREE,positive Eu anomalies( the contents of δEu is 0. 46 ~ 33. 77. The average values is 9. 38) and gently right-inclining NASC-normalized patterns. Based on the above discussion,the study found that the sedimentogenic marbles were formed in the alternation of oxidation-reduction of shallow sea sedimentary environment,with little influence of submarine hydrothermal. And the marmarization may be a diagenesis process of removal above active rare element.