利用电子探针和X射线衍射研究准噶尔盆地风城组淡钡钛石矿物学特征

刘金; 王剑; 王桂君; 张晓刚; 尚玲

doi:10.15898/j.cnki.11-2131/td.202108190101

利用电子探针和X射线衍射研究准噶尔盆地风城组淡钡钛石矿物学特征

Analysis of Mineralogical Characteristics of Leucosphenite from the Fengcheng Formation in the Junggar Basin by Electron Probe Microanalyzer and X-ray Diffractometer

摘要

摘要: 淡钡钛石为含硼硅酸盐矿物，晶体结构属二轴晶单斜晶系，是典型的热液成因矿物。产于中国准噶尔盆地风城组页岩中的淡钡钛石尚未开展矿物学研究，其成因尚不明确。本文选取了该地玛页1钻井岩心中的淡钡钛石，采用电子探针(EPMA)、X射线能谱(EDS)和X射线衍射(XRD)分析其矿物成分和晶体结构特征。结果表明：风城组淡钡钛石晶体大小为微米级，形态呈板状或短柱状，与硅硼钠石共生。矿物主要元素组成为：BaO 12.64%，TiO₂ 13.47%，Na₂O 10.69%，SiO₂ 53.46%，B₂O₃ 10.11%；d=4.22(-220)、d=8.45(-110)、d=3.37(-112)对应的三个晶面最发育。风城组淡钡钛石元素组成及晶体衍射特征与国外发现的淡钡钛石相吻合，但更富硼元素。由于热液流体中硼含量与盐度呈明显正相关，因此风城组淡钡钛石形成于更高盐度热液流体中，深部热液流体侵入到风城组页岩中依次形成硅硼钠石、淡钡钛石。该研究结果为准噶尔盆地风城组淡钡钛石矿物学的进一步研究提供了基础资料。

Abstract:
BACKGROUND Leucosphenite, a borosilicate mineral with a biaxial monoclines crystal structure, is a typical hydrothermal mineral. The mineralogy of leucosphenite in the shale of the Fengcheng Formation in the Junggar Basin in China has not been studied, and its genesis is not clear.
OBJECTIVES To understand the mineralogical characteristics of leucosphenite in the Fengcheng Formation and its genesis.
METHODS Electron probe microanalysis (EPMA), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used to analyze the mineral composition and crystal structure.
RESULTS The crystal size of the leucosphenite in the Fengcheng Formation is at micron scale, and the morphology is plate-like or short columnar. Leucosphenite is associated with reedmergnerite. Leucosphenite is composed of 12.64% BaO, 13.47%TiO₂, 10.69% Na₂O, 53.46% SiO₂, and 10.11% B₂O₃. Crystal planes corresponding to d=4.22(-220), d=8.45(-110), d=3.37(-112) are the three most developed planes.
CONCLUSIONS The element composition and crystal diffraction characteristics of leucosphenite in the Fengcheng Formation are consistent with that found abroad, but the former is richer in B. Due to the obvious positive correlation between B content and salinity in the hydrothermal fluid, the leucosphenite of the Fengcheng Formation was formed in the hydrothermal fluid with higher salinity. Deep hydrothermal fluids intruded into the shale of the Fengcheng Formation, forming reedmergnerite and leucosphenite in turn.

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