黔东松桃地区凉风坳锰矿床的矿物学特征及其成因分析

摘要

黔东松桃地区凉风坳锰矿床是我国较为典型的"大塘坡式"锰矿床之一,由于矿物组成复杂,锰矿物晶形较差且粒度细小,对其矿物学的认识程度较低,矿床成因方面尚存在较大争议.野外地质调查和矿物学的研究表明,凉风坳锰矿床的锰矿层,主要产出于含锰岩系的菱锰矿-碳质页岩组合和菱锰矿-含锰碳酸岩-碳质页岩组合中,矿石类型有致密块状、条带状、角砾状和含方解石脉4种,主要锰矿物为菱锰矿和钙菱锰矿.矿物化学研究表明,由致密块状锰矿石→条带状锰矿石→角砾状锰矿石→含方解石脉锰矿石,锰矿物的MnCO 3、MgCO 3和FeCO 3总体上具逐渐减少,而CaCO 3具逐渐增多趋势;Mn/Fe比值变化范围为22.7~84.9,MnO 2+FeO与CoO+NiO呈极差的负相关关系.综上表明,凉风坳锰矿床形成于一个地堑式同沉积断陷盆地中,形成过程中处于较强的还原沉积环境,锰矿物为成岩成因类型,Fe、Mn两种元素的沉积受到强烈的陆源和火山活动等影响.%Liangfeng'ao manganese deposit in Songtao of eastern Guizhou is one of the typical "Datangpo type"manganese ore deposits in China.Because of its complex mineral composition,poor manganese mineral crystal with small particle size,poor understanding of the mineralogy,there's great controversy around the genesis of ore deposits.Field geological survey and mineralogical study showed that the manganese ore layers mainly occurred in the rhodochrosite-carbonaceous shale combination and rhodochrosite-manganese-bear-ing carbonate rocks-carbonaceous shale combination inside the manganese bearing rock series of Liangfeng' ao manganese deposit,and the ore types could be classified as massive,banded,brecciated and calcite-bear-ing forms.The main manganeseminerals include Rhodochrosite and greinerite.The mineral chemical study indicated that the content of MnCO 3 ,MgCO 3 and FeCO 3 generally decreased and CaCO 3 increased gradually while comparing manganese ores in massive,banded,brecciated and calcite-bearing forms.The variation range of Mn/Fe was within 22.7 to 84.9,and the value of MnO 2 +FeO was poorly in negative relation with the value of CoO+NiO.The results listed above suggested that Liangfeng'ao manganese deposit was formed in a graben-like synsedimentary garben basin in the strong reductive environment.The manganese minerals were diagenesis genesis type and the sedimentation of Fe and Mn were severely affected by terrigenous and volcano activities.