摘要
位于湘西雪峰山中段的渣滓溪钨锑矿床是我国典型的脉状充填型锑矿床。本文利用高精度的LA-ICP-MS对该矿床中白钨矿的稀土元素进行了原位分析。研究表明,渣滓溪白钨矿中的稀土元素分布存在强烈的不均一性:不同白钨矿颗粒、甚至同一颗粒不同部位,其稀土元素含量和配分模式,均可相差很大。该矿床白钨矿中的稀土元素配分模式大体可分为MREE富集型、MREE亏损型和REE平坦型三种;这三种配分模式既可独立存在、也可分布于同一薄片中,甚至于同一矿物颗粒中。上述3种REE配分模式在同一白钨矿颗粒中的存在,可能揭示了成矿热液体系一个完整的动力学演化过程:早期热液中MREE优先进入白钨矿晶体;这种富MREE白钨矿的沉淀,会明显改变成矿流体中的稀土元素组成,形成一种贫MREE的流体;这种经演化而贫MREE的流体导致晚期沉淀的白钨矿MREE亏损,而LREE和HREE相对富集。本研究表明,传统利用块样分析稀土元素的做法需谨慎小心,以免得到一些错误的信息和结论。
The Zhazixi W—Sb deposit, located in the Xuefeng Range, western Hunan, is a typical one of the vein-filled hydrothermal deposits. Scheelite is a widespread mineral in this hydrothermal deposit. In the present contribution, the REE in-situ analyses have been performed by laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） on scheelite samples collected from the Zhazixi mining district. It is revealed there is obvious REE inhomogeneity among the scheelite samples analyzed in this study. REE concentrations and chondrite-normalized patterns can change abruptly among different scheelite grains in the same thin section, even in different part of the same grain. The chondrite-normalized REE distribution patterns of scheelite from the Zhazixi deposit can be classified into the MREE-enriched type, MREE-depleted type and REE-flat type; these three REE patterns can exist independently or co-exist in certain scheelite sample. Even in the same scheelite mineral grain in some thin sections, the above three REE patterns can simultaneously appear, probably revealing a complete dynamic evolution process that reflects this scheelite formed as follows： MREE in the early ore-forming fluid are incorporated into scheelite, the precipitation of this MREE-rich scheelite will significantly alter the composition of hydrothermal fluid and produce a MREE-depleted fluid, which results in the subsequent formation of MREE-flat and MREE-depleted scheelite. Therefore, LA-ICP-MS method may be a potential tool to identify the dynamic process of ore-forming hydrothermal fluids. In addition, cautions have been taken for traditional REE analyses of bulk samples, lest some mistaken information or conclusions should be obtained.
出处
《地质论评》
CAS
CSCD
北大核心
2010年第6期810-819,共10页
Geological Review
基金
国家自然科学基金资助项目(编号41073036
40673021
40472053)的成果
