安徽省大黄山假象绿松石矿物学特征与成因

Mineralogical features and genesis of the pseudomorphic turquoise in the Dahuangshan area, Anhui Province, China

对安徽大黄山假象绿松石和磷灰石进行了详细的显微镜、背散射图像(BSE)观察,在此基础上,对假象绿松石和磷灰石进行了电子探针原位化学分析和岩石地球化学分析。研究表明,大黄山假象绿松石具磷灰石晶体形态,致密微晶-鳞片状、不规则球粒紧密堆积状和球粒状变胶结构,BSE背散射图像显示大黄山假象绿松石和磷灰石中均含有细小独居石矿物包裹体。全岩化学分析和电子探针原位分析表明大黄山假象绿松石为磷铜铁矿端元-富铝端元固溶体矿物。P2O5为大黄山假象绿松石和磷灰石共同的主要化学成分,F、Cl、S为二者共同的次要化学成分,且含量接近,大黄山假象绿松石和磷灰石微量元素原始地幔标准化蛛网图和稀土元素球粒陨石标准化配分型式图分布趋势相同,绿松石主要成矿物质来源于磷灰石。根据磷灰石中稀土元素特征值(δEu=0.25~0.28,δCe=1.20~1.27)和大黄山假象绿松石稀土元素特征值(δEu=0.33~0.47,δCe=0.80~1.88),综合分析判断大黄山假象绿松石为热液蚀变交代磷灰石成因。

In this study,detailed observation by using microscopic and backscattered images(BSE)of the pseudomorphic turquoise and apatite in the Dahuangshan area,Anhui province,were conducted.Based on the study above,the in-situ electron probe microanalysis(EPMA)and chemical analysis of major and trace elements of the pseudomorphic turquoise and apatite were carried out.The results show that the Dahuangshan pseudomorphic turquoise has cone-like crystal form of apatite,with compact microcrystalline scaly,irregular spheroidal compact packing,and spheroidal gelatinous structures.The BSE images shows that the Dahuangshan turquoise and apatite both contain very fine rare earth mineral inclusions of monazite.The chemical analysis of major and trace elements and the in-situ EPMA analysis show that the Dahuangshan pseudomorphic turquoise is a solid solution mineral of the phosphorus-copper-iron-rich(chalcosiderite)end-member and aluminum-rich end-member.The Dahuangshan pseudomorphic turquoise and apatite are similarly composed of major P2O5 and minor F,Cl,and S elements,with similar primitive mantle-normalized distribution patterns of the trace elements and similar chondrite-normalized distribution patterns of rare earth elements.Thus,it is believed that chemical composition of the pseudomorphic turquoise was mainly originated from the apatite.Based on characteristics of rare earth elements of the apatite(δEu=0.25-0.28,δCe=1.20-1.27)and pseudomorphic turquoise(δEu=0.33-0.47,δCe=0.80-1.88),it is comprehensively discriminated that the Dahuangshan pseudomorphic turquoise was formed by the hydrothermal metasomatism of the apatite.