陕西白河小东沟绿松石矿明矾石的矿物学及谱学特征

Mineralogical and Spectral Characteristics of Alunite From Xiaodonggou Turquoise Deposit,Baihe,Shaanxi

鄂豫陕地区是我国重要的绿松石产区,其中陕西白河位于秦岭东部,是绿松石的重要矿点之一。选取陕西白河县小东沟绿松石矿床的黄白色和绿色伴生矿样品,对其进行薄片观察、X射线粉晶衍射测试、红外光谱仪和拉曼光谱仪分析的矿物学和谱学研究。测试结果表明样品为明矾石,还含有少量磷铝矾和高岭石。可观察到其呈脉状结构产出,表明具有多期次形成阶段,后期结晶颗粒较好,具有典型假立方体状的菱面体的结晶特点;该矿物红外光谱谱带主要分布在3697~3488 cm^(-1)以及1638~433 cm^(-1)范围内,在3697和3620 cm^(-1)处具有高岭石中OH导致的弱红外吸收谱峰;明矾石的拉曼光谱谱峰由SO42-振动导致,此外在3700和3626 cm^(-1)处出现高岭石中OH的伸缩振动导致的峰位。结合该地区绿松石矿床风化淋滤特点,判断该区明矾石矿脉形成于低温富碱性环境下,当含矿溶液或围岩中形成绿松石所需成分不足时,趋向于形成明矾石,以脉状、块状形式产出,并共生有磷铝矾和高岭石矿物,为研究本区绿松石矿床特点提供依据。

The turquoise deposits in China are mainly distributed in Hubei,Henan and Shaanxi provinces,among which Baihe county,Shaanxi is one of the most important turquoise deposits.The yellow and green associated minerals collected from Xiaodonggou turquoise deposit in Baihe County,Shaanxi Province,were studied by a microscope,X-ray powder diffraction,infrared,and Raman spectroscopy.The results showed that samples were composed of alunite,and a small amount of hotsonite and kaolinite.Different shades of alunite were observed via microscope,suggesting different mineralization periods.The backscattering images showed that alunite formed later were well-developed particles with the typical false cube-like rhombohedron shapes.The infrared spectra of alunite had the bands related to PO3-4/SO2-4 in the range of 3697~3488and 1638~433cm^(-1),with additional bands at 3697and 3620cm^(-1)attributed to the hydroxyl group of kaolinite.The Raman spectra of green samples were characterized by SO2-4 of alunite.Moreover,the peaks of OH stretching vibration in kaolinite appeared at 3700and 3626cm^(-1).It was assumed that the alunite veins in this turquoise deposit are formed in low temperatures and a rich alkaline environment as the deposit was of weathering and leaching origin.When the essential components derived from ore-bearing solution or surrounding rock are insufficient to produce turquoise,alunite was preferred to be formed,occurring as veins and massive and associated with hotsonite and kaolinite.This paper provided valuable information on the origin of turquoise deposits.