下庄铀矿田方解石的谱学特征研究

下庄铀矿田是我国最大的花岗岩型铀矿田，其中的沥青铀矿-方解石型矿化类型是近年来新发现的一种富矿类型。系统采集了该矿田中不同成矿期、不同颜色的方解石样品．进行了粉晶X射线衍射、电子顺磁共振波谱及反射光谱学研究。电子顺磁共振波谱揭示成矿期方解石中普遍含有Fe^3 和Mn^2 色心离子，而成矿期后和远矿样品中则一般只含有单独的Fe^3 或者Mn^2 色心离子，说明矿田中唯一的工业矿石矿物．沥青铀矿可能是在氧化-还原过渡环境下沉淀的，强氧化和强还原环境均不利于矿石的沉淀。反射光谱学研究揭示不同成矿期方解石的光谱学特征不同，反映了它们在特征元素、含水性等方面均存在差异，成矿期方解石以890nm和400nm两个波长处Fe^3 氧化物的吸收为特征，而成矿期后的方解石则分别在1922nm和1400nm呈现明显的水的吸收。利用反射光谱测定可以定量计算矿物在不同光波波段的吸收性强弱，并得到色度值。研究表明红度较灰度和亮度能更好地定量表示本区方解石的颜色，这也许是由于研究区的方解石大多呈现不同程度的红色和白色所致。

SPECTROGRAPHIC CHARACTERISTICS OF CALCITE FORMED AT DIFFERENT MINERALIZATION STAGES IN XIAZHUANG URANIUM ORE FIELD

The Xiazhuang uranium ore field is the biggest granitic-type uranium ore field in China,and the pitchblende-calcite mineralization type is a new type of high-grade ores. Calcites of different mineralization stages and various colours were sampled based on the field work. Crystal powder X-Ray diffraction,electron paramagnetic resonance and reflectance spectroscopic analyses were profermed in this study. The results included: 1)EPR results showed that the calcites formed during the mineralization stage consist of both Fe~(3+)and Mn~(2+), while the calcites formed after the mineralization stage consist only of Fe~(3+)or Mn~(2+). It might be inferred that pitchblende,the exclusive ore mineral in the Xiazhuang uranium ore field, was precipitated in a redox environment; whereas oxidation or reduction environment did not favor the precipitation of pitchblende; 2)The calcites formed in different mineralization stages displayed different reflectance spectroscopic characteristics in minor elements and aquosity, the calcites formed during the mineralization stage had an absorbility of Fe~(3+)at 890 nm and 400 nm wavelengths, respectively, the calcites formed later than the mineralization stage had an absorbility of H_(2)O and OH at 1922 nm and 1400 nm, respectively; 3) Reflectance could be used as a proxy of the (mineral's) colour in VIS wavelength. In our case redness was more suitable to be used as the proxy for the colour of calcite than grayness and brightness.