The occurrence of gold in hydrothermal sulfide at Southwest Indian Ridge 49.6°E

Massive sulfide precipitates found in the Southwest Indian Ridge(SWIR) 49.6°E hydrothermal field are enriched in gold.Here,the mineralogy and mineral chemistry of these massive sulfides to constrain the process of gold precipitation were studied.Sulfide samples in this field include lowertemperature Zn-rich sulfides and relative higher-temperature Fe-rich sulfides.Zn-rich sulfides are dominated by sphalerite-pyrite-chalcopyrite assemblages,with concentrations of gold ranging from 9.08 to 17.0 μg/g.Fe-rich sulfides consist mainly of pyrite-marcasite-isocubanite assemblages,with gold concentrations from 2.17 to 3.79 μg/g.The significant enrichment in gold within the lowertemperature Zn-rich sulfides and the effective separation of Zn and Fe in hydrothermal precipitates at the surface of this field are here interpreted to reflect the strong temperature dependence of gold transportation and deposition within the sulfides.In Zn-rich samples,large amounts of isolated native gold grains were identified.They were found mainly as inclusions up to 8 μm in diameter,occupying porous cavities in sphalerite or in the elevated iron content rim of sphalerite.The fineness of the gold ranged from 810 to 830.Unlike previously published results on other hydrothermal fields,these data show a low gold fineness values in SWIR 49.6°E.The FeS content of sphalerite associated with gold grains ranged from 3.2 mole % to 18.9 mole %.This was higher than in other fields,indicating that the sulfur activity is relatively low during the gold precipitation process and that sulfur activity may be one of the main factors affecting gold fineness in the SWIR 49.6°E hydrothermal field.Evidence regarding gold fineness and sulfur activity suggests that gold was quite likely transported as AuHS0 rather than as a Au(HS)-2 complex.     

广东某地高岭土的特征研究

通过光学显微镜、X射线衍射（XRD）、X射线荧光光谱（XRF）、电子探针和扫描电镜（SEM）等手段,对广东某高岭土进行了系统研究。研究表明,该高岭土淘洗率为71%。石英和钾长石在+0.045 mm粒级中富集;白云母在+0.030 mm粒级富集;高岭石（埃洛石）在-0.045 mm粒级中富集。各粒级烧成白度较高,-0.010+0.005 mm粒级烧成白度最高,达到85.69%。目的矿物高岭石为片状和叠片状,埃洛石为管状。高岭土中Ti含量较低,为0.051%,Fe含量较高,为1.009%,主要以表面铁和晶格铁形式存在。     

新疆阿尔泰钾长石矿物学特征及开发利用

阿尔泰钾长石是新疆优势非金属矿产资源之一，主要赋存在花岗伟晶岩矿脉、钾长花岗岩和碱性花岗岩中，钾长石资源储量大、品位高，易采易选，但尚未很好开发利用。通过阿尔泰钾长石矿物的物理特征、光学性质、化学成分以及工艺矿物学特征的研究，阐述了钾长石资源在工农业中的应用状况和应用范围，经与国内同类型矿种对比，指出新疆阿尔泰钾长石开发利用有着广阔的前景。     

南海多金属结壳(核)铁锰矿物/海水界面效应与成矿元素的富集

海底铁锰结壳和结核是重要的海底矿产资源,蕴含着丰富的金属元素并且具有巨大的经济价值。本文主要以南海多金属结壳（核）为研究对象,采用X射线粉晶衍射（XRD）、激光拉曼光谱、红外光谱分析（FTIR）以及X射线光电子能谱对铁锰矿物的矿物学和谱学特征进行了系统的分析和研究。粉晶衍射和拉曼光谱分析结果表明,南海多金属结壳的矿物组成为水羟锰矿、石英和长石,结核的矿物组成为钡镁锰矿、水羟锰矿、石英和长石,铁相矿物均为无定形铁氧化物/氢氧化物,并且锰相矿物和铁相矿物的结晶程度均较差。红外光谱分析结果显示多金属结核和结壳中的铁锰矿物具有大量表面羟基,这些含质子表面羟基官能团,可为海水中各成矿元素的络合提供丰富的活性位点。XPS分析表明多金属结核和结壳中铁锰矿物表面以Fe、Mn和O元素为主,其中Fe呈正三价态,Mn以正四、正三价为主,可能还含有少部分正二价态。对比南海多金属结壳（核）与太平海山结壳,南海多金属结壳（核）具有更为显著的表面羟基氧（-OH）含量,而太平洋海山结壳则以晶格氧（O^2-）为主,表明太平洋海山结壳铁锰矿物结晶程度较南海多金属结壳（核）高。综合研究表明,在海底铁锰结壳和结核中（氢）氧化锰/铁矿物与海水之间界面效应对金属离子的富集机理主要有：（1）金属离子与矿物表面羟基进行络合反应,形成以配位键相连的羟基络合物,或与表面的质子交换生成稳定的内层络合物;（2）矿物的带电表面与金属离子通过静电作用形成双电层,生成外层络合物;（3）金属离子与矿物结构中的Mn、Fe离子同晶置换而成为结构阳离子。     

红色粘土型金矿成因矿物学特征

红色粘土型金矿是表生湿热气候条件下含金基岩经不彻底的红土化作用而形成的一种新类型金矿床。以云南上芒岗、贵州老万场和湖北蛇屋山金矿为例 ,对红色粘土型金矿的成因矿物学特征进行了研究。结果表明 ,表生成因的高岭石 +伊利石 +针铁矿 +自然金组合可作为该类型金矿的标型矿物组合 ;高岭石的 ( 0 0 1 ) X射线衍射峰半高宽可作为标型特征反映介质的酸性程度和硅、铝的饱和程度 ,进而指示金的富集部位 ;针铁矿中的铝置换率可反映红土化程度和粘土中的含水量 ,进而指示古潜水面的位置 ;金的粒度、形态和赋存状态可反映金的迁移富集程度和富集机制。     

卓资孔兹岩系成因矿物学研究

内蒙古卓资一带孔兹岩系中的辉石、角闪石、石榴石、黑云母均形成于麻粒岩相条件。二辉石地质温度计和石榴石—黑云母地质温度计和压力计计算结果表明,孔兹岩系岩石的变质温度为750—850℃,变质压力为800—920 MPa,变质地温梯度为26.2—28.5℃/km,属中压麻粒岩相。     

电子探针在工艺矿物学中的应用

文章简述了电子探针分析的原理,并以湖南宝山西铅锌银矿床为例在研究Ｐｂ,Ｚｎ,Ａｇ的赋存状态的基础上,着重探讨了电子探针在矿物命名,矿物形貌特征和组成元素的赋存状态等工艺矿物学方面的应用。     

西南天山东德沟地幔楔环境异剥钙榴岩的形成过程

中国西南天山昭苏县东德沟地幔楔环境的斜长角闪岩与蛇纹岩接触带中发现了异剥钙榴岩.按异剥钙榴岩化程度,可将研究的岩石分为三种类型:斜长角闪岩、异剥钙榴岩化斜长角闪岩和异剥钙榴岩,它们的矿物组合分别为:角闪石+中长石+石英+榍石+磷灰石±次透辉石;角闪石+钙长石+透辉石+斜黝帘石+绿泥石±方解石;斜黝帘石+钙铝榴石+透辉石+绿泥石+方解石.异剥钙榴岩化岩石的矿物化学及主量元素特征反映出交代流体中富Ca、Al.与洋底变质环境和俯冲带中发生的异剥钙榴岩化作用相比,此处的异剥钙榴岩化岩石中的流体有限.质量平衡计算也表明斜长角闪岩在富Ca、Al流体的交代下形成异剥钙榴岩,这一过程中,早期有Mg元素加入,而晚期异剥钙榴岩形成时,Mg又大量流失.     

Triassic palaeosols in the upper Narrabeen group of new South Wales. part I: Features of the palaeosols

The sea‐cliffs north of Sydney expose a complex of Triassic palaeosols, pedoliths, and sedimentary rocks.

The most obvious and diagnostic features of the palaeosols are fossil roots in place and markedly leached or reddened, relatively massive, clay‐rich strata. Associated coaly layers and fossil plant remains in adjacent sediments show varying degrees of decomposition. The A horizons of some of these palaeosols have been silicified by plant opal and contain abundant insect, earthworm, and larger animal burrows, cradle knolls, and basket podzols. Many of the palaeosols have well‐preserved peds and their upper horizons slake more readily in water than their lower horizons. Their B horizons may consist of extensive layers of siderite nodules or red claystone with tubular grey mottles around old root channels.

Less mature palaeosols show some relict sedimentary bedding and ripple marks within their profiles. More mature palaeosols, which appear massive in the field, may show anomalous grainsize variation in thin section, remaining from sedimentary bedding.

Soils can be eroded and deposited as pedoliths. Conglomerates of palaeosol clay pebbles and siderite nodules are easy to recognize as pedoliths. Finer‐grained pedoliths have the distinctive mineralogy and some of the small structures, but not the larger structures and field relations, of palaeosols.

Siderite crystals and nodules developed in the gleyed organic and A horizons of some of the clayey palaeosols shortly after they were covered by sediment and subsided below base level. With further compaction and dewatering, the ferric‐oxide minerals became redder by inverting to hematite, mineralized joints developed in some massive B horizons, some peds were accentuated by slickensides, and some root channels and coal cleat were filled with copper minerals.     

Tracing the emerald origin by oxygen isotope data: the case of Sandawana,Zimbabwe

Given the wide range of oxygen isotopic composition of emerald from all over the world (δ¹⁸O between +6.2 and +24.7‰), the δ¹⁸O_V-SMOW values of emeralds from the Sandawana mines in Zimbabwe (δ¹⁸O‰=+6.6 to +8.0), are relatively constant, among the lowest ever measured. These consistently low values can be explained by host-rock buffering in a very narrow emerald-bearing reaction zone between ultrabasic greenstones (metamorphosed komatiites) and albitised pegmatites. δ¹⁸O values of Sandawana emeralds overlap those of emeralds from Brazil, Austria, Australia and Madagascar, a fact indicating that, in these cases, oxygen isotope composition alone is not sufficient to determine the geographic origin of commercially available emeralds. However, stones with overlapping δ¹⁸O values may eventually be identified using a combination of physical properties, inclusion characteristics and chemical composition. To cite this article: J.C. Zwaan et al., C. R. Geoscience 336 (2004).