甘肃临泽正北山凹凸棒石黏土矿物学及形成机制

甘肃省临泽县凹凸棒石黏土矿储量丰富，是重要的天然纳米矿物资源。本文采用X-射线衍射（XRD）、扫描电镜（SEM）以及透射电镜（TEM）等纳米矿物学的研究手段，对甘肃省临泽县正北山矿区凹凸棒石黏土矿床的矿物组成和微观形貌、结构特征进行了分析。结果表明，不同矿层的矿物成分相似，主要有石英、长石、白云石、方解石、石盐、石膏以及黏土矿物，其中黏土矿物以凹凸棒石和伊利石为主，含有少量的高岭石、绿泥石、蒙脱石以及伊蒙混层矿物。各矿层矿物含量差别较大，其中碎屑矿物石英含量介于12.35%~64.34%之间，凹凸棒石含量为10.31%~37.93%。根据主要矿物组合及含量将矿石划分为5种类型：凹凸棒石黏土、伊利石型凹凸棒石黏土、碳酸盐型凹凸棒石黏土、富石膏型凹凸棒石黏土以及石膏矿石。SEM和TEM观察发现矿层中普遍存在的凹凸棒石具有长、短纤维两种形态以及由其组成的束状和席状结构，且矿石中发育大量凹凸棒石覆盖或包裹的菱面体白云石和片状伊蒙矿物颗粒边缘外延生长的凹凸棒石微结构，表明凹凸棒石具水溶液沉淀以及前驱体转化等多种形成机制。本研究对甘肃省临泽县地区低品位凹凸棒石黏土资源的综合开发利用具有重要意义。

Mineralogy and formation mechanism of attapulgite clay in Zhengbeishan,Linze, Gansu Province

The Zhengbeishan attapulgite clay deposit is located at Linze County, Gansu Province in Northwest China, mainly hosted in Late Oligocene Baiyanghe Formation. In this paper, mineralogy and microstructure of attapulgite clay were investigated using powder X-ray diffraction(XRD), scanning electron microscopy(SEM)and transmission electron microscopy(TEM). Our results indicate that the mineral composition of the Zhenbeishan attapulgite clay ore is similar, mainly consisting of quartz, feldspar, dolomite, calcite, halite, gypsum and clay minerals. The clay ore has higher average concentration of attapulgite with ranging from 10.31% to 37.93% except detrital quartz with from 12.35% to 64.34% content. Illite together with little kaolinite, chlorite, smectite and illite/smectite mixed layer minerals dominates the <2 μm fraction. Based on mineral assemblage, the clay ore can be divided into five types including attapulgite clay, illite-bearing attapulgite clay, carbonate-bearing attapulgite clay, gypsum-bearing attapulgite clay, and gypsum ore. SEM and TEM investigations have documented co-occurrence of authigenic and detrital attapulgite. The detrital attapulgite shows relatively long fibers, occurring as bundles and mats aggregates in mixture other detrital quartz, feldspar or covering on the surface of plated particles. While authigenic attapulgite is present as straight fiber, formed on both surfaces of dissolved euhedral dolomite crystals and radiated from the margins of platy illite/smectite. These observations suggest that attapulgite in the ore has various formation processes including chemical precipitation in aqueous solution and precursor mineral solid-state transformation. The mineralogical study of attapulgite clay will provide valuable instruction for comprehensive utilization of the low content attapulgite-bearing clay ore in Linze region and Hexi Corridor mineralization belt.