摘要
白钨矿是钨矿床中主要的载钨矿物,其独特的晶体结构使其富含微量元素,被广泛用于示踪钨成矿过程与流体源区。本文对南岭地区氧化型矽卡岩、还原型矽卡岩、黑钨矿-石英脉型、白钨矿-石英脉型、(矽卡岩-)云英岩型、(石英脉-)云英岩型钨矿床中白钨矿开展矿物组合和X-射线单晶衍射分析,实验结果显示:(1)白钨矿晶体结构存在一定差异,矽卡岩型钨矿中白钨矿Ca-O键长变化较大(0.0043 nm),石英脉型钨矿中白钨矿次之(0.0035 nm),云英岩型钨矿中白钨矿最小(0.0034 nm);(2)Ca-O键长的差异对最优替代稀土元素影响较大,氧化型矽卡岩钨矿中白钨矿从成矿早期到晚期,最优替代稀土元素从Pr-Nd(进变质阶段)、Pr-Sm(退变质阶段)转变为Nd-Sm(石英-方解石-萤石阶段),而(石英脉-)云英岩型钨矿中白钨矿呈现以Sm^(3+)为中心(Nd-Gd)的最优替代元素;(3)矽卡岩型和云英岩型钨矿中白钨矿,稀土元素主要通过Nb^(5+)耦合替代和空位替代进入白钨矿晶格,石英脉型钨矿的白钨矿中,稀土元素主要通过空位替代和Na+耦合替代进入白钨矿晶格。此外,岩浆流体中稀土特征、共生矿物沉淀、氧化还原环境、外来流体加入、水岩交代作用等对白钨矿中微量元素替代与稀土元素配分型式也具有较大影响。综合分析认为,矽卡岩型钨矿中白钨矿稀土元素配分型式主要受石榴子石等共生矿物沉淀控制,(矽卡岩-)云英岩型钨矿中白钨矿主要继承了岩浆流体的稀土元素配分型式,(石英脉-)云英岩型钨矿中白钨矿稀土元素配分型式主要受晶体结构影响,石英脉型钨矿中白钨矿经历了多阶段流体演化,稀土元素配分型式显示凸起—平坦—凹陷的变化。
Scheelite is the main W-bearing mineral in tungsten deposits.Its unique crystal structure is enriched in trace elements,and it is widely used to implicate mineralization processes and fluid sources.In this research,the mineral assemblage and single-crystal X-ray diffraction analysis of scheelite from oxidized skarn,reduced skarn,wolframite-quartz vein,scheelite-quartz vein,greisen(-skarn)and greisen(-quartz vein)types W deposits related to granite intrusions in Nanling metallogenic belt are presented.The experimental results show that:①there are some differences in the scheelite crystal structure.The difference in Ca-O bond length data of scheelite in skarn(0.0043 nm)is greater than that of scheelite in quartz vein(0.0035 nm)and greisen(0.0034 nm);②the difference in Ca-O bond length has little influence on trace elements substitution,but has a great influence on the optimal substitution of REEs.The scheelite in oxidized skarn is developed in multiple stages,and there is a transition from Pr-Nd(prograde skarn stage)to Pr-Sm(retrograde skarn stage)to Nd-Sm(quartz-calcite-fluorite stage)as the optimal substitution of REEs from early to late.The scheelite in greisen(-quartz vein)type deposit presents the REE distribution pattern of the optimal(Nd-Gd)substitution element centered on Sm^(3+);③in scheelite from skarn type and greisen type deposits,REEs enter scheelite lattice mainly through Nb^(5+)coupling substitution and vacancy substitution mechanism.In scheelite from quartz vein type deposit,REEs enter scheelite lattice mainly through vacancy substitution and Na+coupling substitution mechanism.In addition,the characteristics of REEs in the parent fluid,the precipitation of associated minerals,the redox environment,the addition of foreign fluids,and the fluid-rock interaction also have a great impact on the substitution of trace elements in scheelite.After all,the scheelite in skarn type deposit is mainly controlled by the precipitation of garnet and other associated minerals.The scheelite in greisen(-skarn)mainly inherits the REE distribution pattern of magmatic fluid.The crystal structure of scheelite in greisen(-quartz vein)has the greatest impact on REEs.However,the scheelite in quartz vein type deposit underwent the multi-phase hydrothermal fluid evolution,showing the changes of bulge-flat-depression MREE types REE distribution pattern.
作者
吴锟言
刘飚
WU Kunyan;LIU Bia(Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Ministry of Education,Changsha,Hunan 410083,China;School of Geosciences and Info-Physics,Central South University,Changsha,Hunan 410083,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2023年第10期3314-3325,共12页
Acta Geologica Sinica
基金
湖南省自然科学青年基金项目(编号2021JJ40722)
国家重点研发计划项目(编号2018YFC0603902)联合资助的成果。
关键词
白钨矿
晶体结构
稀土元素
替代机理
南岭成矿带
scheelite
crystal structure
REE
substitution mechanism
Nanling metallogenic belt
