河南南泥湖矽卡岩型钼矿石地表风化产物初探

Preliminary study on secondary minerals in supergene weathered skarn-type molybdenum ore in Nannihu district,Henan Province

钼尾矿风化过程中钼元素释放会带来严重的环境污染问题,为了探究钼矿石在地表风化过程中含钼次生矿物形成对于钼元素在表生环境中迁移的影响,对南泥湖矽卡岩型钼矿石风化样品进行了系统的矿物学研究,探讨了次生矿物的形成机制以及钼矿石风化过程中Mo的赋存和迁移形式,进而评估其对环境的影响.矿石中的原生矿物主要为辉钼矿、黄铁矿、石英、方解石,检测到的次生矿物主要为钼钙矿、赤铁矿、针铁矿、石膏.辉钼矿在风化过程中表面破碎、层面卷曲,在辉钼矿与不同矿物接触界面,辉钼矿氧化形成的次生矿物有明显差异.辉钼矿与方解石接触处主要生成石膏和钼钙矿,钼钙矿呈半自形晶形,大小为2μm,方解石溶解消耗辉钼矿氧化生成的H^+,提高了局部的pH并且产生Ca^(2+),促进钼钙矿和石膏沉淀;在辉钼矿与黄铁矿接触处,主要生成赤铁矿、针铁矿,见少量钼钙矿,铁氧化物吸附重金属元素Mo.在pH为中性的环境中,含有辉钼矿、方解石、黄铁矿的钼矿石风化产物序列以钼钙矿-铁氧化物-石膏为主,Mo会被固定在钼钙矿中或者吸附在铁氧化物表面,从而减轻Mo释放带来的环境污染.

The release of molybdenum through the weathering of molybdenum ore imposes severe risks of heavy metal contamination.By using many spectrometric methods and SEM observation,the surface changes of skarn-type molybdenum ore sampled from the Nannihu distict and the secondary minerals formed during weathering have been investigated.The migration and valance change of molybdenum in supergene environments has been revealed.The primary minerals in molybdenum ore are dominantly molybdenite,calcite,pyrite,quartz and chlorite.Powellite,gypsum,goethite and hematite have been formed in the weathering process as secondary minerals.During the oxidation process,molybdenite breaks and curles.There exist different secondary mineral assemblages on the interfacesbetween molybdenite and other minerals.Powellite and gypsum mainly form on the molybdenite-calcite interface,powellite has a subhedral crystal and its size is about 1-2μm.Iron oxide is the main secondary mineral formed on the interface of molybdenite and pyrite,and it adsorbs molybdenum slightly.No ferrimolybdite formed in the two cases.In neutural environment,molybdenum is fixed in powellite or adsorbed onto iron-oxide,thus reducing the effect of the releasing element Mo to the environment.