Short Wavelength Infrared (SWIR) Spectral Analysis of Hydrothermal Alteration Zones Associated with Base Metal Sulfide Deposits at Rosebery and Western Tharsis, Tasmania, and Highway-Reward, Queensland
Short Wavelength Infrared (SWIR) Spectral Analysis of Hydrothermal Alteration Zones Associated with Base Metal Sulfide Deposits at Rosebery and Western Tharsis, Tasmania, and Highway-Reward, Queensland
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DOI：
10.2113/gsecongeo.96.5.939
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发表时间：
2001-08
期刊：
影响因子：
5.8
通讯作者：
W. Herrmann;Michael Blake;Mark Doyle;D. Huston;J. Kamprad;Nick Merry;S. Pontual
中科院分区：
文献类型：
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作者：
W. Herrmann;Michael Blake;Mark Doyle;D. Huston;J. Kamprad;Nick Merry;S. Pontual
使用便携式红外矿物分析仪（PIMA）光谱仪通过短波红外（SWIR）分析对岩石样品进行光谱分析是一种相对较新的现场方法，在矿产勘探中有应用。该技术可以快速现场鉴定热液蚀变矿物和划分蚀变带。还可以确定矿物组成、结晶度和相对丰度的变化。层状硅酸盐，包括白色云母和云母，特别适合于短波长红外分析。这些是塔斯马尼亚州里德火山和北昆士兰州温莎山地区长英质火山岩中的重要蚀变矿物。它们作为成岩和变质产物具有区域性分布，局部存在于与火山岩型硫化物矿床有关的蚀变带中。对里德火山蚀变最小的岩石中的白色云母进行的地球化学和光谱研究表明，背景成分变化相当大。白色云母的范围从多硅白云母到中等钠白云母，SWIR光谱测量提供了其成分的可靠估计。在这些岩石中，亚氯酸盐的成分范围也很广。然而，短波红外光谱分析已被证明是不可靠的，在确定样品中的云母成分，其中云母存在的比例较低，相对于白色云母或在混合组合与绿帘石。Rosebery层状Zn + Pb存款矿床（塔斯马尼亚州）下盘蚀变带中的白色云母是白云母，类似于区域背景火山岩中的白云母。Rosebery上盘序列中相对未蚀变的火山灰砂岩单元在矿石透镜体附近含有异常钠质白云母。与西塔尔西斯（塔斯马尼亚州）和Highway-Reward（北昆士兰州）的浸染状至块状黄铁矿状Cu + Au矿床相关的白色云母的成分范围从多硅白云母到微钠白云母。在这些对称分带的蚀变系统中，白色云母的成分从外围带的多硅白云母到靠近矿石的近端带的轻微钠质白云母。在所有三种情况下，白色云母成分变化是一个矢量的矿石，有效地测量了短波红外光谱，特别是应用在远景规模的勘探。在Rosebery的绿泥石组合物是不严格的空间相关的矿石，但往往是最镁的高丰度区。在西塔尔西斯的外部蚀变带，有一个微弱的近端趋势，以富铁的绿泥石。然而，在这两种情况下，它都不代表一个定义良好的向量。试图通过光谱分析对混合样品中白色云母和云母的相对丰度进行定量估计，结果与地球化学得出的估计相比是不精确的。数据分散与分析的大多数样品中的低比例氯离子有关，导致弱选择性。在特定的蚀变或岩石地层领域，使用定制的光谱分解软件可能会获得更好的结果。这项调查表明，PIMA为基础的短波红外光谱法是一个有效的外地方法映射的组成变化，在白色云母，代表经验向量，至少有一些类型的火山主办的硫化物矿床。在叶蜡石、祖母绿、黄玉等具有成因意义和勘探意义的大型蚀变矿物的野外识别中，也显示了其有效性。
Spectral analysis of rock samples by short wavelength infrared (SWIR) analysis, using the portable infrared mineral analyzer (PIMA) spectrometer, is a relatively new field method with applications in mineral exploration. The technique allows rapid field-based identification of hydrothermal alteration minerals and delineation of alteration zones. Variations in mineral composition, crystallinity, and relative abundance may also be determined. Phyllosilicates, including white mica and chlorite, are particularly amenable to short wavelength infrared analysis. These are prominent alteration minerals in the felsic volcanic rocks in the Mount Read Volcanics, Tasmania, and the Mount Windsor subprovince, North Queensland. They have regional distributions as diagenetic and metamorphic products and exist locally in alteration zones associated with volcanic-hosted sulfide deposits. A geochemical and spectral investigation of white micas in the least altered rocks in the Mount Read Volcanics has shown considerable background compositional variations. The white micas range from phengite to moderately sodic muscovite and SWIR spectral measurements provide reliable estimates of their compositions. Chlorites also have a broad compositional range in these rocks. However, SWIR spectral analysis has proven to be unreliable in determining chlorite composition in samples where chlorite exists in low proportions relative to white mica or in mixed assemblages with epidote. White micas in footwall alteration zones of the Rosebery stratiform Zn + Pb deposit (Tasmania) are variably phengitic, similar to those in regional background volcanics. A unit of relatively unaltered volcaniclastic sandstone in the Rosebery hanging-wall sequence contains anomalous sodic muscovite in proximity to ore lenses. White micas associated with the disseminated to massive pyritic Cu + Au deposits at Western Tharsis (Tasmania) and Highway-Reward (North Queensland) range in composition from phengite to slightly sodic muscovite. In these symmetrically zoned alteration systems, white micas grade in composition from phengite, in peripheral zones, to slightly sodic muscovite, in proximal zones near ore. In all three cases, the white mica compositional variation is a vector to ore that is effectively measured by SWIR spectrometry, with particular application in prospect-scale exploration. Chlorite compositions at Rosebery are not strictly spatially related to ore but tend to be most magnesian in zones of high chlorite abundance. In the outer alteration zone at Western Tharsis, there is a faint proximal trend to iron-rich chlorites. However, it does not represent a well-defined vector to ore in either case. Attempts at quantitative estimation of the relative abundance of white mica and chlorite in mixed samples, by spectral analysis, have produced results that are imprecise in comparison to geochemically derived estimates. The data scatter relates to the low proportions of chlorite in the majority of the samples analyzed, resulting in weak chlorite absorptions. Better results may be obtainable, in specific alteration or lithostratigraphic domains, by use of customized spectral unmixing software. This investigation has shown that PIMA-based SWIR spectrometry is a potent field method of mapping compositional variations in white micas that represent empirical vectors to at least some types of volcanic-hosted sulfide deposits. It has also highlighted its effectiveness in field identification of megascopically difficult or indeterminate alteration minerals, such as pyrophyllite, zunyite, and topaz, which may have genetic implications and exploration significance.