浙江外岗银多金属矿床热液蚀变短波红外光谱分析及找矿指示

Short-wave infrared spectroscopy analysis and prospecting indication of hydrothermal alteration of Waigang silver polymetallic deposit in Zhejiang, China

中国东南沿海浙闽交界地区发现大量银多金属矿床,这些矿床以石英脉状矿化为主,并伴有明显的热液蚀变作用,关于其成因和控矿因素尚不清楚。文章以其中的外岗银多金属矿床为研究对象,开展了短波红外光谱测量(SWIR),提取蚀变矿物种类、组合信息,划分蚀变矿物分带,分析矿化强度与蚀变矿物组合及分带的关系。短波红外光谱测量识别出的蚀变矿物主要有多硅白云母、伊利石、白云母、高岭石、铁绿泥石、铁镁绿泥石,这些矿物及其组合在水平方向上,自矿体由内而外形成了硅化带→青磐岩化带→泥化带的分带。通过对伊利石反射光谱特征参数的计算发现,伊利石结晶度(Illite crystallinity value,简称"IC值")和Al-OH 2200 nm特征峰吸收峰位值(Pos2200)在矿区内出现系统性的变化规律,即越靠近热液/矿化中心,IC值逐渐增大(>1.5),Al-OH 2200 nm吸收峰位值有减小的趋势(Pos2200≈2208 nm),将二者叠加的区域即可作为外岗地区勘查该类矿床的找矿重点区域。作者认为短波红外光谱技术可以有效地指导矿产勘查评价、降低勘查成本,在未来同类矿床找矿方面有良好的应用前景。

A large number of silver polymetallic deposits have been recently discovered in the border between Zhejiang and Fujian Provinces in China. These deposits are dominated by quartz vein-like mineralization, accompanied by obvious hydrothermal alteration. The genesis and ore-controlling factors are still unclear. Taking the Waigang silver polymetallic deposit as the research object, short-wave infrared spectroscopy analysis was carried out to extract the types and assemblage information of altered minerals, divide the zoning of altered minerals, and analyze the relationship between mineralization intensity and altered mineral assemblage and zoning. The altered minerals identified by short-wave infrared spectroscopy measurement mainly include phengite, illite white mica, kaolinite,prochlorite, and brunsvigite. In the horizontal direction, these minerals and their combination form a zoning feature of silica →prophylitic→ argillic zone from the inside of the ore body. Through the calculation of illite reflection spectral characteristic parameters, it is found that illite crystallinity(Illite crystallinity value, referred to as“IC value”) and Al-OH 2200 nm characteristic peak absorption value(Pos2200) have a systematic change rule in the mining area. Near the hydrothermal/mineralization center, the IC value increases gradually(>1.5), and the absorption peak value of Al-OH at 2200 nm has a decreasing trend(Pos2200≈2208 nm), which can be used as prospecting mark of this type of deposit. The authors believe that short-wave infrared spectroscopy technology(SWIR) can effectively guide the evaluation of mineral exploration, reduce the cost of exploration, and has a good application prospect in future prospecting in this area.