Characterization and distribution of adularia and other alteration minerals by X-ray diffraction analysis at the El Peñón Au-Ag epithermal deposit, northern Chile
Jorge E. Morales Leal, A. Menzies, H. Wilke, J. Zuluaga
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引用次数: 0
Abstract
The El Peñón low-sulfidation epithermal deposit, located in the Paleocene metallogenic belt in the Antofagasta region, northern Chile, consists of Au-Ag bearing veins and hydrothermal breccias hosted in volcanic rocks and surrounded by alteration haloes consisting of a series of minerals, such as adularia, K-micas, and clay minerals. They are the result of metasomatism generated by the passage of reduced, and near neutral pH, hydrothermal fluids, that transported gold through structures and its interaction with the host rock. we investigated the spatial distribution of these minerals (mainly adularia) in the wall rocks around the Aleste vein, in the northern part of the deposit, to establish their relationship with the Au-Ag ore and, thus, support the identification of new exploration targets. An X-ray diffraction technique to discriminate adularia from other K-feldspars in whole rock samples was developed by the detail study of the diffractogram patterns of an adularia standard. The study of an X-ray diffraction standard pattern allowed the recognition of this mineral by 4 secondary peaks. Our results indicated that adularia occurs in association with felsic volcanic rocks, and it is restricted in intermediate composition units. The spatial distribution of this mineral is correlated with the mineralized zones, being adularia semi-quantitative abundance in the range of 25 to 40% a good indicator of gold mineralization. Sericite and illite occur mainly where adularia is scarce or absent. The spatial distribution of these minerals showed the structural control in the evolution and flow path of the hydrothermal fluids toward the surface. Kaolinite is related to argillic alteration caused by steam-heated fluids, and the advanced argillic alteration associated with later supergene alteration. Chlorite usually is far from the mineralized areas; therefore, it could be a reliable indicator of the margins of the system. The characterization and spatial distribution pattern of the alteration minerals identified by the X-ray diffraction method in the veins of El Peñón deposit show the capability of this type of analyses in determining possible prospection targets.
El Peñón低硫化浅成低温热液矿床位于智利北部Antofagasta地区古新世成矿带,由含金银脉体和热液角砾岩组成,寄存于火山岩中,周围由一系列矿物组成的蚀变晕,如阿黄、k云母、黏土矿物等。它们是由还原的、pH值接近中性的热液流体通过构造及其与宿主岩石的相互作用将金输送到金矿所产生的交代作用的结果。通过对矿床北部Aleste脉周围围岩中这些矿物(主要为adularia)的空间分布特征的研究,建立了它们与Au-Ag的关系,从而支持新的找矿目标的确定。通过对一种阿杜石标准样品的衍射图进行详细研究,建立了一种区分阿杜石与其他钾长石的x射线衍射技术。通过x射线衍射标准模式的研究,可以通过4个次级峰来识别这种矿物。结果表明,阿杜里亚与长英质火山岩伴生,局限于中间组成单元。该矿物的空间分布与成矿带具有相关性,其半定量丰度在25 ~ 40%之间,是金矿化的良好指示物。绢云母和伊利石主要出现在少或无成虫的地方。这些矿物的空间分布显示了热液流体向地表演化和流动路径的构造控制。高岭石与蒸汽加热流体引起的泥质蚀变有关,晚期泥质蚀变与后期表生蚀变有关。绿泥石通常远离矿化区;因此,它可以作为系统边际的可靠指标。利用x射线衍射方法在El Peñón矿床矿脉中识别的蚀变矿物特征和空间分布规律表明,这种分析方法能够确定可能的找矿靶区。
期刊介绍:
This journal publishes original and review articles on geology and related sciences, in Spanish or English, in three issues a year (January, May and September). Articles or notes on major topics of broad interest in Earth Sciences dealing with the geology of South and Central America and Antarctica, and particularly of the Andes, are welcomed.
The journal is interested in publishing thematic sets of papers and accepts articles dealing with systematic Paleontology only if their main focus is the chronostratigraphical, paleoecological and/or paleogeographical importance of the taxa described therein.