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.