马坑铁矿钻孔岩心红外光谱特征及蚀变分带特征研究

红外反射光谱技术可无损、快速、批量地识别出硅酸盐、硫酸盐、碳酸盐等矿物，近年来在矿物学研究、地质勘探与找矿、矿山选冶等方面取得了较显著进展。尤其是热红外波段（6000~14500nm）可识别出辉石、石榴子石、橄榄石等蚀变矿物以及长石、石英等造岩矿物，对于矽卡岩型、铜镍硫化物型以及石英脉型等矿床地质找矿、矿床成因研究等具有重要意义。本文通过对国家实物地质资料馆馆藏的马坑铁矿钻孔岩心进行短波-热红外反射光谱测量与分析，总结马坑铁矿各蚀变矿物光谱特征，并快速厘定了该矿床的蚀变矿物类型及组合特征。马坑铁矿蚀变矿物主要有石榴子石、辉石、碳酸盐、绿泥石、绢（白）云母、角闪石、绿帘石、蒙脱石、石膏等。石榴子石热红外光谱特征是在9199nm、9730nm、10500nm及11100nm处具有明显的反射特征，辉石热红外光谱特征主要是在11500nm和12150nm处具有明显的吸收特征。红外光谱分析表明蚀变矿物在空间上呈现出明显的分带性，蚀变矿物组合及分布严格受围岩岩性和热液交代的双重控制。通过红外反射光谱蚀变矿物组合特征研究，“石榴子石+辉石”可作为矽卡岩型矿床的标型矿物组合，蚀变分带特征也反映了主矿体从高温到低温的变化过程；结合矿床地质特征，推断出马坑铁矿为典型的层控矽卡岩型矿床。本研究可为矽卡岩型矿床的成矿规律认识和找矿勘探等方面提供科学支撑。

Study on the Characteristics of the Infrared Spectrum and the Alteration Zoning of Drill Core in the Makeng Iron Deposit

BACKGROUND: Silicate, sulfate, carbonate and other minerals can be identified by infrared reflectance spectroscopy which is a non-destructive and rapid batch method. In recent years, infrared reflectance spectroscopy has played an important role in mineralogical research, mineral exploration and prospecting, mining and metallurgy. Altered minerals such as pyroxene, garnet, olivine and rock-forming minerals such as feldspar and quartz can be identified rapidly with thermal infrared (6000-14500nm, TIR), which is important for mineralogical research, mineral exploration and prospecting of skarn type, copper-nickel sulfide type and quartz-vein type deposits.
OBJECTIVES: To quickly characterize the type and assemblage of alteration minerals.
METHODS: Shortwave-thermal infrared reflectance spectroscopy was used to analyze the drill cores of the Makeng iron deposit in the National Geological Archives. The spectral characteristics of the altered minerals in this deposit were summarized, the type and assemblage of alteration minerals were quickly determined.
RESULTS: The results showed that the altered minerals in Makeng include garnet, pyroxene, carbonate, chlorite, sericite, hornblende, epidote, montmorillonite and gypsum. There were significant reflections at 9199nm, 9730nm, 10500nm and 11100nm for garnet. For pyroxene, the significant reflections were mainly located at 11500nm and 12150nm. Infrared spectroscopy analysis showed that altered minerals displayed obvious zoning in space, and the assemblage and distribution of altered minerals were strictly controlled by the lithology of country rocks and hydrothermal metasomatism. Garnet+pyroxene can be used as the typical mineral assemblage of skarn deposits, and the characteristics of alteration zoning indicated a process from high temperature to low temperature.
CONCLUSIONS: Combined with the geological features, the Makeng iron deposit can be defined as a stratabound skarn deposit. This research can provide scientific support for the understanding of skarn-type deposits and related prospecting and exploration.