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Chemical and short-wave infrared characteristics of white mica associated with the Gajah Tidur porphyry copper system at the deep Grasberg Cu—Au—(Mo) deposit, Indonesia
Resource Geology ( IF 1.1 ) Pub Date : 2022-07-29 , DOI: 10.1111/rge.12296
Reza Al Furqan 1 , Yasushi Watanabe 1 , Antonio Arribas 2 , Clyde Leys 3 , Takuya Echigo 1 , Rici Anggun Putri 4 , Renanda Sevirajati 5
Affiliation  

The Grasberg Cu—Au—(Mo) deposit comprises the shallower Main Grasberg porphyry Cu—Au and the deeper Gajah Tidur (GT) porphyry Cu—Mo—(Au) systems. The GT porphyry preserves various types of white mica whose geochemical variations provide insights into the white mica-dominated alteration of porphyry systems. The white mica assemblages within the GT porphyry system comprise: (1) muscovite-anhydrite-chlorite (MAC), (2) muscovite-chlorite-anhydrite (MCA), and (3) muscovite-quartz ± pyrophyllite (MQP). These assemblages display zonation from central and deep parts of the system to its shallower and peripheral parts. The MAC alteration white micas are characterized by high Na, Fe, Ti, and V concentrations, and with short-wave infrared Al—OH absorption wavelengths of 2203–2208 nm. The MCA white micas have higher Mg content than the other two GT white mica assemblages but similar Al—OH absorption wavelengths to the MAC white micas. The MQP alteration white micas have low Na, Fe, Mg, and Ti, but relatively high Si, Al, and F, and Al—OH absorption wavelengths are largely shorter than 2202 nm. We interpret that the high Fe and Ti content of the MAC white micas is due to inheritance of these elements from mafic minerals they replaced. The higher Fe content of these white micas explain their longer wavelength Al—OH absorption positions relative to the MQP white micas. In contrast, lower Fe content and shorter Al—OH wavelengths of the MQP white micas are caused by their higher Si and Al content, which reduces iron occupancy in the white mica crystal structure. White micas in this assemblage formed at lower temperature and probable lower pH condition that may have led to a replacement of Fe by Al. The short-wave infrared Al—OH position of white mica together with the associated hydrothermal assemblage can be used as a proximitor for porphyry Cu hydrothermal centres. White mica associated with chlorite, anhydrite, and chalcopyrite, which commonly occur overprinting or adjacent to the potassic alteration center, are characterized by Al—OH absorption positions at 2200–2215 nm. By contrast, white mica associated with quartz-pyrite are characterized by Al—OH wavelengths shorter than 2202 nm. In the distal part of porphyry Cu system, white micas may be associated with chlorite and have Al—OH absorption positions longer than 2204 nm.

中文翻译:

印度尼西亚 Grasberg Cu-Au-(Mo) 矿床深部 Gajah Tidur 斑岩铜系白云母的化学和短波红外特征

Grasberg Cu-Au-(Mo) 矿床包括较浅的 Main Grasberg 斑岩 Cu-Au 和较深的 Gajah Tidur (GT) 斑岩 Cu-Mo-(Au) 系统。GT 斑岩保留了各种类型的白色云母,其地球化学变化提供了对以白色云母为主的斑岩系统变化的见解。GT斑岩系统中的白云母组合包括:(1)白云母-硬石膏-绿泥石(MAC),(2)白云母-绿泥石-硬石膏(MCA),和(3)白云母-石英±叶蜡石(MQP)。这些组合显示了从系统的中心和深层部分到其较浅和外围部分的分区。MAC变质白云母的特点是Na、Fe、Ti和V浓度高,短波红外Al-OH吸收波长为2203-2208 nm。MCA 白色云母的 Mg 含量高于其他两种 GT 白色云母组合,但 Al-OH 吸收波长与 MAC 白色云母相似。MQP蚀变白云母Na、Fe、Mg和Ti含量较低,但Si、Al、F相对较高,Al-OH吸收波长大大短于2202 nm。我们认为 MAC 白色云母的高铁和钛含量是由于这些元素从它们所取代的镁铁质矿物中继承而来。这些白色云母中较高的铁含量解释了它们相对于 MQP 白色云母的更长波长的 Al-OH 吸收位置。相比之下,MQP 白色云母的 Fe 含量较低和 Al-OH 波长较短是由于其较高的 Si 和 Al 含量造成的,这降低了白色云母晶体结构中铁的占有率。这种组合中的白色云母在较低温度和可能较低的 pH 值条件下形成,这可能导致铁被铝替代。白云母的短波红外 Al-OH 位置以及相关的热液组合可用作斑岩铜热液中心的促进剂。与绿泥石、硬石膏和黄铜矿伴生的白色云母,通常出现在钾蚀变中心的叠印或附近,其特征在于 2200-2215 nm 的 Al-OH 吸收位置。相比之下,与石英-黄铁矿相关的白色云母的特征在于 Al-OH 波长短于 2202 nm。在斑岩Cu系的远端,白色云母可能与绿泥石伴生,Al-OH吸收位置长于2204 nm。白云母的短波红外 Al-OH 位置以及相关的热液组合可用作斑岩铜热液中心的促进剂。与绿泥石、硬石膏和黄铜矿伴生的白色云母,通常出现在钾蚀变中心的叠印或附近,其特征在于 2200-2215 nm 的 Al-OH 吸收位置。相比之下,与石英-黄铁矿相关的白色云母的特征在于 Al-OH 波长短于 2202 nm。在斑岩Cu系的远端,白色云母可能与绿泥石伴生,Al-OH吸收位置长于2204 nm。白云母的短波红外 Al-OH 位置以及相关的热液组合可用作斑岩铜热液中心的促进剂。与绿泥石、硬石膏和黄铜矿伴生的白色云母,通常出现在钾蚀变中心的叠印或附近,其特征在于 2200-2215 nm 的 Al-OH 吸收位置。相比之下,与石英-黄铁矿相关的白色云母的特征在于 Al-OH 波长短于 2202 nm。在斑岩Cu系的远端,白色云母可能与绿泥石伴生,Al-OH吸收位置长于2204 nm。黄铜矿多为叠印或邻近钾蚀变中心,其特征是Al-OH吸收位置在2200~2215 nm。相比之下,与石英-黄铁矿相关的白色云母的特征在于 Al-OH 波长短于 2202 nm。在斑岩Cu系的远端,白色云母可能与绿泥石伴生,Al-OH吸收位置长于2204 nm。黄铜矿多为叠印或邻近钾蚀变中心,其特征是Al-OH吸收位置在2200~2215 nm。相比之下,与石英-黄铁矿相关的白色云母的特征在于 Al-OH 波长短于 2202 nm。在斑岩Cu系的远端,白色云母可能与绿泥石伴生,Al-OH吸收位置长于2204 nm。
更新日期:2022-07-29
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