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

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

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 ,化学成分 ,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 .0 1Al0 .0 1) 2 .0 2 O7(OH ) 2 .0 3·0 .88H2 O ,晶胞参数a =0 .8380 ( 4 )nm ,b =1.0 718( 7)nm ,c =0 .512 5( 6)nm。对异极矿矿物学特征的全面研究 ,丰富了国内的矿物学资料。该矿物是乐红铅锌矿床中次生的主要工业锌矿物 ,因此 ,具有现实的工业利用价值并对寻找原生铅锌矿体有重要的指示意义。

Hemimorphite has been found in the oxidized zone of the Lehong Pb_Zn deposit, Yunnan Province. 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: N g=1.637, N m=1.618, N p=1.615, (+)2V with optic angle of 45°. Chemical analyses show that the formula of this mineral is Zn 3.98 (Si 2.01 Al 0.01 ) 2.02 O 7(OH) 2.03 ·0.88H 2O, and X_ray powder diffraction data indicate that its unit cell parameters are a =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(HCO 3) 2] and zinc sulfate (ZnSO 4) under the strong acid oxidizing_leaching condition, whereas ZnSO 4 and Zn(HCO 3) 2 were 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 is not only the main economic secondary zinc mineral but also an important indicator for the prospecting of primary Pb_Zn deposits.