辽宁瓦房店金伯利岩中尖晶石族矿物种类划分及指示意义

摘要

晶体矿物学理论认为不同成岩环境金伯利岩中尖晶石族矿物由于形成物理化学条件不同，其晶体结构和化学成分会发生明显的变化，通过对无矿、贫矿、富矿金伯利岩岩管中的尖晶石族矿物晶胞参数和化学成分的测定，研究尖晶石族矿物化学成分和晶胞参数变化与无矿、贫矿、富矿金伯利岩的内在关系，可以提高金伯利岩型金刚石矿床找矿效率。为了确定辽宁瓦房店金伯利岩中的尖晶石族矿物种属，探讨辽宁瓦房店金伯利岩中尖晶石族矿物化学成分和晶胞参数与金伯利岩含矿性关系，本文运用电子探针波谱仪对50件尖晶石族矿物中的MgO、FeO、TiO2、Al2 O3、MnO及Cr2 O3进行微区化学成分分析，运用单晶X射线衍射仪对136个尖晶石族矿物晶胞参数进行测定。数据统计显示：瓦房店金伯利岩中尖晶石族矿物为铬铁矿和镁铬铁矿，以化学分子式中A、B组主要阳离子占位特征为基础，可把矿区的尖晶石族矿物划分为10个亚种；如果用尖晶石族矿物化学成分中Cr2 O3与（ Cr2 O3+Al2 O3）含量的比值Cr′来表示尖晶石族矿物与金伯利岩含矿性的关系，金伯利岩岩体含矿性由富矿→中等含矿→贫矿，相应岩体中尖晶石族矿物Cr′值分别为89.5%、83.4%~87.1%和70.2%，逐渐变低；从无矿金伯利岩岩体→贫矿和中等含矿金伯利岩岩体→富矿金伯利岩岩体，金伯利岩体中第一世代尖晶石族矿物晶胞参数分别为0.831~0.832 nm、0.834~0.836 nm、﹥0.837 nm，有逐渐变大的趋势。本文认为，辽宁瓦房店金伯利岩中第一世代尖晶石族矿物晶胞参数大小和Cr′参数可以作为判断辽宁瓦房店金伯利岩含矿性的指示标型。%According to crystal mineralogy theory,under the diagenetic environments with different physical and chemical conditions,crystal structure and chemical composition of spinel group minerals in kimberlite will be obviously different. Through the determination of the lattice parameters and chemical compositions of spinel group minerals from non-lean ore mines and Bonanza kimberlite pipe, the study of internal relations of chemical composition and lattice parameter changes in spinel group minerals among no ore,lean ore and bonanza kimberlite plays an important role for kimberlite diamond deposits prospecting. In order to determine the species of spinel group minerals,MgO,FeO,TiO2 ,Al2 O3 ,MnO and Cr2 O3 of 50 spinel group minerals were analyzed by using micro area chemical analysis with Electron Microprobe. The lattice parameters of 136 spinel group minerals were determined by single-crystal X-ray Diffraction. The results show that spinel group minerals in kimberlite Wafangdian of Liaoning province are magnesium-rich chromite. Based on the main cations occupying chemical formulae groups A and B,the spinel group minerals in mining can be divided into 10 subspecies. If the ratio of Cr2 O3/( Cr2 O3 +Al2 O3 )content( Cr′ values)in spinel group minerals represent the degree of mineralization of kimberlite ore-bearing deposit,the Cr′values in high-grade ore,medium-grade ore and lean ore of kimberlite rock in Wafangdian Liaoning are 89. 5%,83. 4% -87. 1% and 70. 2%,respectively. Lattice parameters of the spinel group minerals were 0. 831 -0. 832 nm,0. 834 -0. 836 nm and larger than 0. 837 nm from non-rock,lean ore rock,medium-grade ore and high-grade ore. A case that the spinel mineral lattice parameter of the first generation and Cr′value are the indicators of the ore bearing in Wafangdian kimberlite,Liaoning province is described.