云南乐红铅锌矿床氧化带中异极矿的矿物学特征及其意义

云南乐红铅锌矿床氧化带十分发育，呈细脉或葡萄状产于氧化矿石中的白色矿物曾被认为是菱锌矿，笔者对该矿物作了物理、光学性质，化学发，Ｘ射线衍射，红外光谱及失重和差热分析研究，确定其为异极矿。其晶体化学式为Ｚｎ３．９８（Ｓｉ２．０１Ａｌ０．０１）２．０２Ｏ７（ＯＨ）２．０３．０．８８Ｈ２Ｏ晶胞参数ａ＝０．８３８０（４）ｎｍ，ｂ＝１．０７１８（７）ｎｍ，ｃ＝０．５１２５（６）ｎｍ。对异极矿矿物学特征的全面

Mineralogical Character of Hemimorphite from the Oxidized Zone of the Lehong Pb-Zn Deposit in Yunnan Province and Its Significance

Hemimorphite has been found in the oxidized zone of the Lehong Pb-Zn deposit, YunnanProvince. It occurs as veinlet-like or fine_grained botryoidal aggregates in fissures of cave walls within the oxidized ores. The mineral was studied by such means as physical and optical examination, chemical analysis, X_ray powder diffraction, IR spectral analysis, TG and DTA. Microscopic studies give the following optical data:Ng=1.637,Nm=1.618,Np=1.615,(+)2V with optic angle of 45°. Chemical analyses show that the formula of this mineral is Zn3.98(Si2.01Al0.01)2.02O7(OH)2.03·0.88H2O, and X-ray powder diffraction data indicate thatits unit cell parameters area=0.8380(4)nm,b=1.0718(7)nm,c=0.5125(6)nm. The mineral assemblage of the oxidized ore mainly includes limonite, goethite, hemimorphite, zinkspath and secondary carbonate. Studies show that most former zinkspaths were altered into zinc bicarbonate [Zn(HCO3)2] and zinc sulfate (ZnSO4) under the strong acid oxidizing-leaching condition, whereas ZnSO4and Zn(HCO3)2were combined with the silica gel in the oxidized zone to form hemimorphite. Therefore, it is considered that the development of hemimorphite depends on strong oxidizing-leaching process in the Pb-Zn deposit, that is to say,the stronger the process, the more favorable the formation of hemimorphite. Hemimorphite isnot only the main economic secondary zinc mineral but also an important indicator for the prospecting of primary Pb-Zn deposits.