Trace Element Determination by ICP‐AES and ICP‐MS: Developments and Applications Reported During 2006 and 2007

This review describes developments in trace element determination using inductively coupled plasma‐atomic emission spectrometry (ICP‐AES) and inductively coupled plasma‐mass spectrometry (ICP‐MS) that were reported in 2006 and 2007. It focuses on the application of ICP techniques to geological and environmental samples; fundamental studies in ICP‐MS and ICP‐AES instrumentation have largely been ignored. New advances in ICP‐MS and ICP‐AES were incremental over this period, partly because both techniques are now well‐established. A continuing shift towards the hyphenation of low‐flow separation techniques has sparked activity in the development of appropriate low‐flow interfaces, and papers discussing interference removal also contribute significantly to the volume of research for both ICP‐AES and ICP‐MS. Whereas the majority of new ICP publications concerned advances in ICP‐MS analysis rather than ICP‐AES, development for ICP‐AES still occurs in almost all areas, particularly in sample introduction and hyphenated techniques.     

云南香格里拉普朗铜矿蚀变与矿化关系

普朗斑岩铜矿床是近年来发现的一个重要印支期铜矿床.含矿岩体为普朗复式斑岩体,由全岩铜矿化的石英二长斑岩、石英闪长玢岩及花岗闪长斑岩组成,其中矿化较好者主要与石英二长斑岩关系密切.矿区蚀变矿物有伊利石、镁绿泥石、多水高岭石、硬石膏、蒙脱石、黑云母、铁镁绿泥石、白云母、阳起石、金云母、方解石等,蚀变类型主要有钾长石化、黑云母化、钠长石化、硅化、绢云母化、钠黝帘石化、泥化.并且由中心向外依次为硅化核—硅化钾化带—绢英岩化带—青磐岩化带—角岩化带的面型蚀变特征.其中硅化钾化、绢英岩化蚀变带与铜矿关系密切.     

油砂组分遥感光谱响应特征及意义

基于油砂组分的吸收光谱物理响应机理,通过对比矿物基团平均吸收深度,建立主要蚀变矿物ASTER多光谱遥感数据异常提取模式以识别油砂分布.研究表明,与传统的烃类微渗漏遥感研究手段相比,该模式可以更有效地指示油砂的分布.利用油砂组分基团光谱平均吸收深度与孔隙度及渗透率进行相关分析,研究了油砂光谱与所处地质背景环境中储层物性之间的关联关系.结果表明,表征粘土矿物含量的粘土基团吸收深度与孔渗值呈负相关关系,指示含油性的烃类基团吸收深度与孔渗值呈显著正相关关系.     

桂阳台子上蚀变岩体型锡矿床地质特征及找矿意义

该矿床赋存于大义山复式岩体中侏罗纪三江口序列花岗岩最晚期次的介头单元中心部位。矿体呈似层状，中心部位隐伏，NE端长约500m，宽400m，平均厚15．30m，Sn平均品位0．5%；南西段长400m，宽240m，厚4－25m，Sn平均品位0．7％。矿区有蚀为细粒花岗岩型和云英岩型两类锡矿。矿石矿物主要是锡石，次有黑钨矿、辉钼矿、铌钽铁锰矿等，脉石矿物 主要是长石、云母、石英等。围岩蚀变发育、类型多样，其中云英岩化、黄玉化、萤石化和褐铁矿化是重要的找矿标志，岩浆上的前锋位置且多组节理，裂隙的交 汇处，是有利的储矿空间。介头单元等晚期岩体的顶盖及其前锋部位，是寻找该类型锡矿的有利地段。     

Correlation, alteration, and origin of hydrocarbons in the GCA, Bahar, and Gum Adasi fields, western South Caspian Basin: geochemical and multivariate statistical assessments

Geochemical as well as multivariate statistical analyses (PCA) were carried out on 20 crude oil samples from ‘Middle’ Pliocene Production Series (MPPS) of Guneshli-Chirag-Azeri (GCA), Bahar, and Gum Adasi fields in the western South Caspian Basin (SCB). PCA analysis employed to source-specific biomarkers distinguishes the oils into two types one being divided into two sub-types; Type 1 (GCA oils), Type 2A (Bahar field oils) and Type 2B (Gum Adasi field oils). Indirect oil-to-source rock correlations to available source rock data from previous studies suggest that Type 1 oils, located in the Apsheron-Balkhans uplift area, are derived from basinal shales of the Oligocene-Lower Miocene Middle Maikop Formation. Type 2A and 2B oils, located in the Gum-deniz-Bahar-Shakh-deniz trend area, are more likely derived from shelf-edge shales of the Upper Maikop Formation and the Middle-Upper Miocene Diatom Suite, respectively.Biomarker maturity study reveals that Type 1 oils (mean %Rc=0.78) are more mature than Type 2 oils (mean %Rc=0.71). Source rocks, which generated these oils, were at generation depth interval between 5200 m (112 °C) and 7500 m (153 °C) at the time of expulsion. This indicates that the western SCB oils experienced significant long-range vertical migration along the deep-seated faults to accumulate in the MPPS reservoirs. Post-accumulation biodegradation process was only observed in the Guneshli field where bacterial alteration (level 4) began between 4.2 and 2.6 mybp and stopped with the deposition of the overlying impermeable Upper Pliocene Akchagyl Formation. Subsequent light hydrocarbon (C₁–C₁₆) charge into the Guneshli fields caused precipitation of asphaltenes, which is evidenced by high resin to asphaltene ratios for the present-day Guneshli oils. Evaporative-fractionation examined using the scheme of [Thompson, 1987] showed high correlations of the ‘aromaticity’ B parameter (=toluene/n-C₇) and ‘parafinicity’ F parameter (=n-C₇/MCH with the %Rc (maturity) and C₂₇/C₂₉ sterane ratio (organic matter type). This implies that Thompson's approach should be used with caution in the SCB. Among the several mechanisms, rapid and thick deposition of Pliocene sediments and subsequent high heating rate on the Maikop Formation and Diatom Suite is probably the most plausible way of explaining the origin of light hydrocarbons in the Guneshli and Bahar fields.     

南极普通球粒陨石风化等级的重新厘定

在南极格罗夫山普通球粒陨石的风化等级划分中出现了和Wlotzka(1993)标准矛盾的现象。部分普通球粒陨石的金属和陨硫铁氧化不足20%,然而硅酸盐却发生了蚀变。如果考虑金属的氧化量,这种风化程度应为W1,如果考虑硅酸盐的蚀变,这种风化程度应为W5。对于存在如此大的差异本文给出了折衷的解决办法——对金属和硅酸盐同时进行风化等级划分。金属的风化等级划分为W_m0-W_m4五个,硅酸盐风化等级划分为W_s0-W_s3四个。依据新方案,GRV 021588、021636、021772和021957等4块无法用Wlotzka(1993)标准来确定风化等级的陨石的风化等级均为W_m1-W_s1。而陨石GRV 023312的风化等级为W_m3-W_s0,其相当于Wlotzka(1993)标准中的W3。     

Textural,mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke,Zimbabwe and the precious metals zone of the Sonju Lake Intrusion,Minnesota, USA

Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type.     

Evaluation of the effects of alteration and leaching on Sm–Nd and Lu–Hf systematics in submarine mafic rocks

Nd and Hf isotope systematics of oceanic basaltic rocks are often assumed to be largely immune to the effects of hydrothermal alteration. We have tested this assumption by comparing Nd and Hf isotope data for acid-leached Cretaceous oceanic basalts from Gorgona and DSDP Leg 15 with unleached data on the same rocks. Hf isotope values and Lu/Hf ratios are relatively unaffected by leaching, but ¹⁴³Nd/¹⁴⁴Nd values of leached samples are significantly higher than those of unleached fractions of the same sample in most cases. Furthermore, the Sm/Nd ratios of the majority of leached samples are 10–40% greater than those of unleached samples. X-ray diffraction studies indicate that selective removal of secondary minerals, such as smectite, during the acid leaching process is responsible for the fractionation of Sm/Nd ratios. These results have implications for interpretation of the Hf–Nd isotope systematics of ancient submarine rocks (older than ~ 50 Ma), as (1) the age-corrected ¹⁴³Nd/¹⁴⁴Nd ratio may not be representative of the primary magmatic signature and (2) the uncertainty of the age-corrected ε_Nd value may exceed the assumed analytical precision.     

Application of mineral equilibria modeling to constrain T and X CO2 conditions during the evolution of the Magdala gold deposit, Stawell, Victoria, Australia

Mineral equilibria modeling involving solid solution calculations has been combined with mineral assemblage information from the alteration zones associated with gold mineralization to determine the T and X _CO2 conditions for the formation of the Magdala gold deposit at Stawell, Victoria, Australia. Economic gold mineralization is primarily hosted within the stilpnomelane alteration zone of the Stawell Facies that is adjacent to the Magdala Basalt. Evolution of the Magdala gold deposit involved at least three fluid infiltration events: (1) a CO₂-bearing fluid during the D₂ deformation event produced carbonate spots throughout the chlorite zone; (2) a CO₂–S–K-bearing fluid, accompanied the D_3–4ab deformation and produced a muscovite zone and siderite rims on ankerite; and (3) a CO₂–K–S–Au-bearing fluid during the D_4c deformation event produced the stilpnomelane zone of the Stawell Facies, the proximal and distal alteration zones within the Magdala Basalt, and the main economic gold mineralization. Mineral equilibria modeling constrains the temperature of formation of the Magdala deposit to T = 345–390°C at 3kbar, substantially lower than indicated by other previous classical thermobarometry methods. Furthermore, this method has allowed the characterization of the mineralizing fluid and constrained its composition to X _CO2 < 0.08 at 3kbar. The timing and composition of the mineralizing fluids are similar to that of metamorphic fluid generated from devolatilization of a greenstone pile with peak of metamorphism occurring earlier and at deeper levels in the crust.