铜陵新桥矿田褐铁矿矿物组成及成因

Mineralogy of the limonite ore from the Xinqiao sulfide iron deposit in the Tongling ore concentration area of Anhui Province and its implications

褐铁矿是铁帽型金矿和铁矿的重要矿产类型,但目前对其从矿物学的微观角度研究较少。本文采用粉晶X射线衍射(XRD)以及场发射扫描电镜(SEM)矿物学研究手段,对铜陵矿集区新桥矿田褐铁矿的矿物组成、微结构进行研究。根据矿物组成及微结构将新桥褐铁矿分为两种成因类型:Ⅰ型褐铁矿,该类型褐铁矿主要起源于黄铁矿矿石,矿石多具蜂窝状构造。主要组成矿物为针铁矿,次要矿物为赤铁矿,含有少量石英,针铁矿晶体长度一般介于500 nm^2μm,长度/半径比值(长径比)较大;Ⅱ型褐铁矿,由原生菱铁矿矿石风化而成,矿石多具肾状构造。矿物组成主要为针铁矿,其次为赤铁矿、锰氧化物和伊利石等粘土矿物,针铁矿晶体长度一般小于500 nm,具有较小的长径比。褐铁矿矿物学和微结构不仅可以初步确定原生矿物和矿石类型,而且对寻找铁帽金矿床也具有重要指示意义。

Limonite is an important ore of the gossan-type gold deposit and the iron deposit; nevertheless, the microstructure of limonite has not been investigated in detail. For the purpose of probing into morphological characteristics and microstructures of limonite ore, the authors investigated 70 samples from the Xinqiao sulfide iron deposit using X-Ray Powder Diffraction （XRD） and Scanning Electron Microscope （SEM）. The limonite ore can be divided into two groups based upon the components and microstructures. Limonite （Ⅰ） with honeycomb structure was mainly sourced from the weathering of pyrite ore. The major minerals identified are represented by goethite with a minor amount of hematite and quartz. The particle sizes of goethite is in the range of 500 nm2 μm with a higher ratio of length/diameter. Limonite （Ⅱ） with kidney structure was derived from the weathering of siderite ore. Goethite is also the major mineral, and the secondary minerals include manganite, hematite and illite. The length of goethite is less than 500 nm, with a lower ratio of length/width. The information on the mineralogy and microstructure of limonite not only can be used to infer the type of the primary minera but also is of important indicating signicance in search for gold deposits in gossans.