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    热液型矿床白色云母短波红外光谱特征及其在地质找矿中的应用

    Shortwave infrared spectral characteristics of white mica in hydrothermal deposits and its application in geological exploration

    • 摘要:
      研究目的 白色云母是热液型矿床最为广泛发育的蚀变矿物,其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。研究热液型矿床白色云母短波红外光谱变化规律及地质影响因素,这不仅可为高光谱矿物填图技术的深入找矿应用提供重要理论支持,还可以进一步完善蚀变矿物勘查标识体系。
      研究方法 本文系统整理、总结了热液型矿床白色云母短波红外光谱特征,剖析了白色云母化学组分和含量,热液流体温度、酸碱性、压力等地质因素与其短波红外光谱特征的关系。
      研究结果 白色云母短波红外光谱吸收特征与其结构中主要的两种含氢基团Al−OH和H2O 有着密切的关系,主要的两个特征吸收峰位分别位于2200 nm(主要吸收峰)和2350 nm(次要吸收峰)附近。白色云母Al−OH特征吸收峰位受到热液流体温度、压力、酸碱性等地质因素影响,主要发生Tschermak(契尔马克)替换VIAl3+ + IVAl3+νIVSi4+ +VI (Fe2+, Mg2+, Mn2+),Si、Al、Fe、Mg、K、Na等离子含量产生变化,致使其Al−OH特征吸收峰位在2180 nm和2230 nm之间发生漂移变化。原岩组分、其他蚀变矿物、流体组分、岩石渗透率和水/岩比值等地质因素也会影响白色云母Al−OH特征吸收峰位波长的变化。
      结论 白色云母Al−OH特征吸收峰波长与矿化的关系会因地质环境的不同而呈现出正相关或负相关关系,在利用Al−OH特征吸收峰波长变化规律圈定矿床热液矿化中心时需要综合考虑矿床地质特征。白色云母的伊利石成熟度或结晶度(ISM或SWIR−IC)在不同的热液矿床系统中则呈现出一致性,即靠近矿床热液矿化中心,伊利石成熟度值相对较大,远离矿床热液矿化中心则相对较小。未来应加强白色云母光谱特征的精细、定量化星空(卫星和航空)高光谱遥感反演研究,建立典型热液矿床成矿热液特征的高光谱遥感反演应用示范,以推进星空高光谱遥感矿物填图技术的深入地质应用。

       

      Abstract:
      This paper is the result of mineral exploration engineering.
      Objective White mica is widely developed in the hydrothermal deposits, and the shortwave infrared spectrum of white mica contains rich geological information, recording the hydrothermal environment it formed and its relationship with mineralization. Analyzing the variation patterns and geological influencing factors to short wave infrared spectra of white mica in hydrothermal deposits not only provides important theoretical support for the in−depth exploration and application of hyperspectral mineral mapping technology, but also further improves the identification system for exploration of altered minerals.
      Methods This paper systematically summarizes the characteristics of the short wave infrared spectral changes of white mica in hydrothermal deposits, and analyzes the relationship between the chemical composition and content of white mica, and geological factors such as hydrothermal fluid temperature, acid−base properties, pressure, and their shortwave infrared spectral characteristics.
      Results The absorption characteristics of shortwave infrared spectra in white mica are closely related to the two main hydrogen containing groups Al−OH and H2O in its structure, and the two main characteristic absorption peaks are located near 2200 nm (main absorption peak) and 2350 nm (secondary absorption peak), respectively. Since the Al−OH characteristic absorption−peak positions of white mica are influenced by geological factors such as hydrothermal fluid temperature, pressure, acidity and alkalinity, white mica mainly undergoes Tschermak substitutionVIAl3+ + IVAl3+νIVSi4+ +VI (Fe2+, Mg2+, Mn2+), resulting in changes in the content of Si, Al, Fe, Mg, K, and Na plasma, which results in a shift in the Al−OH characteristic absorption−peak position varying between 2180 nm and 2230 nm. Geological factors, such as original rock components, other altered minerals, fluid components, rock permeability, and water/rock ratios, can also affect the changes in the wavelength of the Al−OH characteristic absorption peaks of white mica.
      Conclusions The relationship between the Al−OH characteristic absorption peak wavelength of white mica and mineralization may exhibit a positive or negative correlation depending on the geological environment, therefore, when delineating the hydrothermal mineralization center, it is necessary to comprehensively consider the geological characteristics of the deposits. The illite maturity or crystallinity (ISM or SWIR−IC) of white mica is consistent in different hydrothermal deposit systems, that is, the maturity values of illite near the hydrothermal mineralization center are relatively large, while the maturity values of illite far away from the hydrothermal mineralization center are relatively small. In the future, in order to promote the in−depth geological application of satellite and airborne hyperspectral remote sensing mineral mapping technology, it should strengthen the fine and quantitative satellite and airborne hyperspectral remote sensing inversion researches on spectral characteristics of white mica, and establish a demonstration of hyperspectral remote sensing inversion application for mineralization hydrothermal characteristics of typical hydrothermal deposits.

       

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