新疆白杨河铀矿区白色云母短波红外光谱及电子探针成分特征

Short-wavelength infrared spectroscopy and EPMA of white mica from Baiyanghe uranium district in Xinjiang

铀是我国战略性关键金属资源之一,对科技发展和国家安全具有重要意义。新疆白杨河铀矿床是我国重要的热液型铀矿床,铀成矿过程中广泛发育白色云母。已有研究表明,白杨河铀矿床白色云母短波红外光谱蕴含着丰富的地质信息,记录了其形成热液环境及其与矿化的关系,但其短波红外光谱变化规律及其地质影响因素研究依然薄弱。因此,运用短波红外光谱技术和电子探针微区分析等分析方法对矿床白色云母进行分析研究。研究表明:白杨河铀矿床白色云母Al-OH特征吸收峰波长在2190和2220 nm之间漂移变化,电子探针化学组分表明其发生了明显的Tschermak(契尔马克)替换,Al-OH特征吸收峰波长直接受Mg和Fe含量以及Fe/(Fe+Mg)比值的影响,也受围岩成分的影响。Al-OH特征吸收峰波长较短的白色云母反映了相对高温的热液流体环境,而Al-OH特征吸收峰波长较长的白色云母则代表了相对低温的热液流体环境。白杨河铀矿床铀矿化点附近白色云母具有相对较短的Al-OH特征吸收峰波长、较大的ISM(伊利石光谱成熟度)值和较低的FWHM 2200(半峰宽)值。综合白色云母的Al-OH特征吸收峰波长、ISM值和FWHM2200值的空间变化规律,可以推断白杨河铀矿床的热液矿化中心位于杨庄花岗斑岩与上泥盆统火山岩的北部接触带。这不仅对完善白杨河铀矿床成因和深部与外围勘探具有重要的实际意义,对其他热液型金属矿产勘查亦具有重要的参考价值。

Uranium is one of the critical metals in China,and it is of great significance to the development of science and technology and national security.The Baiyanghe uranium deposit is an important hydrothermal uranium deposit,and white mica is widely developed in the process of uranium mineralization.Studies have shown that the shortwave infrared spectra of white mica contain rich geological information,recording its formation environment and its relationship with mineralization,however,systematical variation rules to shortwave infrared spectral parameters of white mica and geological influencing factors are still poorly known.In this paper,we use shortwave infrared spectroscopy and electron probe analysis to study the white mica from Baiyanghe uranium deposit.The results indicate that white mica with Al-OH absorption wavelengths from the Baiyanghe uranium deposit range from 2190 nm to 2220 nm,and the geochemical compositions indicate an obvious Tschermak substitution in white mica and suggest that variations in the Al-OH wavelengths of white mica are mainly affected by the Fe and Mg content and Fe/(Fe+Mg)ratios in addition to the wall rock composition.The white mica exhibiting a shorter Al-OH absorption wavelength indicates a relatively high-temperature hydrothermal environment,while the white mica with a longer Al-OH absorption wavelength suggests a relatively low-temperature hydrothermal environment.In addition,it is found that the white micas close to the uranium mineralization in the Baiyanghe uranium deposit,have shorter Al-OH wavelengths,greater ISM values,and lower FWHM 2200 values than those with features unlike those near the uranium mineralization.The spatial distributions and variations in the Al-OH wavelengths,ISM values,and FWHM 2200 values for white mica suggest that a hydrothermal mineralization center may be located in the northern contact zone between the Yangzhuang granite porphyry and the Devonian intermediate-acid volcanic rocks of the Baiyanghe uranium deposit.This study is of great practical significance for improving the genesis and for deep and peripheral exploration in Baiyanghe uranium deposit,and also has important reference value for the exploration of other hydrothermal metal minerals.