新疆白杨河大型铍铀矿床成矿流体特征及矿床成因初探  

Geochemical characteristics of the ore-forming fluid and ore genesis of the Baiyanghe Be-U deposit,Xinjiang, China

作　　者：张鑫[1,2] 张辉[1] 

机构地区：[1]中国科学院地球化学研究所,贵州贵阳550002 [2]中国科学院大学,北京100049

出　　处：《地球化学》2013年第2期143-152,共10页Geochimica

基　　金：国家重点基础研究发展计划(2007CB411303);国家科技部支撑计划"305"项目(2007BAB25B01)

摘　　要：新疆和布克赛尔县白杨河大型铍铀矿床是亚洲最大的铍矿床，其矿体产出于晚石炭世微晶花岗斑岩与上泥盆统塔尔巴哈台组（D3t）中酸性火山岩的接触带上，该矿床为典型的热液矿床。萤石作为白杨河铍铀矿床中与成矿作用密切相关的脉石矿物，发育大量气液包裹体。通过对萤石中流体包裹体的显微测温，获得了其主成矿期包裹体的均一温度，为237～372℃（n=40），平均为308.5℃，反映该矿床为中高温热液矿床。萤石以相对富集中稀土（MREE）（（La／Yb）N=3.18-3.55），强烈亏损Eu（diEu=0.01），REE分布模式呈“V”字型为特征。萤石锶钕同位素数据显示出较高的锶同位素初始比值（0.7106），以及正^εNd（t）值（3.50～2.95），相似于微晶花岗斑岩的锶钕同位素组成（（^87Sr／^86Sr）=0.7143～0.7466，^εNd（t）=4.06-5.29），由此提出成矿流体主要来自微晶花岗斑岩岩浆分异的晚期热液。主成矿期的萤石包裹体显示高温、低盐度的特征，推断成矿流体源于微晶花岗斑岩晚期岩浆热液与大气降水的混合。Xinjiang Baiyanghe Be-U deposit is the largest Be deposit in Asia. The deposit is typical hydrothermal in origin, characterized by veinlet disseminated and mainly developed on the contact zone between a Late Carboniferous granite porphyry and Late Devonian intermediate-acidic volcanic rocks. Fluorite, as the main gangue mineral of the deposit, is rich fluid inclusions. The homogenization temperature of the primary inclusions ranged from 237 to 372℃ （n = 40）, with an average of 308.5℃, suggesting that the Baiyanghe Be-U deposit is a kind of intermediate-high temperature hydrothermal deposit. The chondrite-normalized REE diagram of the fluorite is characterized by enrichment of MREE （（La/Gd）N = 0.60-0.66）, with strong negative Eu anomalies and V-shaped pattern. Similar to isotopic compositions of the granite porphyry （（^87Sr/^86Sr）i = 0.7143-0.7466, ^εNd（t） = 4.06-5.29）, fluorite shows high initial Sr isotope ratio （0.7106） and positive ^εNd（t） values （2.95-3.50）, indicating the ore-forming fluid was possibly late magmatic-hydrothermal differentiated from the granite porphyry. As characterized by high temperature and low salinity of the primary fluid inclusions in fluorite, it is deduced that the ore-forming fluid was probably originated from mixing of magmatic hydrothermal and meteoric water.

关 键 词：流体包裹体 锶钕同位素 萤石 白杨河铍铀矿床 西准噶尔 

分 类 号：P59[天文地球—地球化学] P611.11[天文地球—地质学]