Optical dating: Recuperation after bleaching

Bleaching by sunlight results in rapid reduction of optically-stimulated luminescence, e.g. by a factor of 300 in 15 min for one of the several samples of quartz so far tried. However, if the bleached sample is stored before measurement the signal partially recovers, suggesting the possibility that the observed natural luminescence from a young sediment sample may contain a significant contribution from this component. Recuperation is accelerated if the sample is warmed during storage: after 5 min at 220°C the recuperation levels in the samples of quartz studied were equivalent to the order of one gray. Recuperative effects are also observed in zircon. We suggest that the effect is associated with phototransfer into shallow light-insensitive traps during bleaching, with subsequent thermal redistribution into the traps responsible for the initial luminescence. Investigation of recuperation gives a useful insight into the mechanisms upon which optical dating relies.     

中条山铜矿峪矿深部段矿石铜矿物粒度查定分析

通过对铜矿物嵌布料度特征的查定，预测选矿效果，确定合理选矿指标，合理配矿及指导深部中段开采方案设计，提供科学的地质依据。     

Thermoluminescence, electron paramagnetic resonance and optical absorption in natural and synthetic rhodonite crystals

Thermoluminescence, electron paramagnetic resonance and optical absorption properties of rhodonite, a natural silicate mineral, have been investigated and compared to those of synthetic crystal, pure and doped. The TL peaks grow linearly for radiation dose up to 4 kGy, and then saturate. In all the synthetic samples, 140 and 340°C TL peaks are observed; the difference occurs in their relative intensities, but only 340°C peak grows strongly for high doses. Al₂O₃ and Al₂O₃ + CaO-doped synthetic samples presented several decades intenser TL compared to that of synthetic samples doped with other impurities. A heating rate of 4°C/s has been used in all the TL readings. The EPR spectrum of natural rhodonite mineral has only one huge signal around g = 2.0 with width extending from 1,000 to 6,000 G. This is due to Mn dipolar interaction, a fact proved by numerical calculation based on Van Vleck dipolar broadening expression. The optical absorption spectrum is rich in absorption bands in near-UV, visible and near-IR intervals. Several bands in the region from 540 to 340 nm are interpreted as being due to Mn³⁺ in distorted octahedral environment. A broad and intense band around 1,040 nm is due to Fe²⁺. It decays under heating up to 900°C. At this temperature it is reduced by 80% of its original intensity. The pink, natural rhodonite, heated in air starts becoming black at approximately 600°C.     

Thermoluminescence dating of sediments

The potential for using the thermoluminescence behaviour of sediments for dating them was first recognized by Soviet scientists G.V. Morozov and V.N. Shelkoplyas, and for over a decade their TL dates, obtained from a variety of sediments, have appeared in the Soviet literature. Since 1977 TL sediment dates have been published by six additional groups using a variety of methods.In this review we describe the principles of TL dating, the various methods used, and contrast TL dating of sediments with the now well-accepted TL dating of pottery. We conclude that while TL dating has the potential to solve many sedimentary problems, more fundamental research needs to be carried out before such dates should be accepted. A set of criteria for acceptable dates is proposed.     

应用石英释光灵敏度溯源的研究现状和展望

应用石英释光灵敏度进行物源研究是释光技术发展的新方向。回顾了石英释光灵敏度在测年研究中的发展现状,对其产生的机制、实验中的影响因素及其在测年中对灵敏度的监测、矫正等进行了介绍,详细介绍了空间尺度上不同沉积物(冰碛物、风成沉积物、水成沉积物)石英释光灵敏度的差异和时间序列上风成沉积物释光灵敏度的变化特征。据现有的研究成果分析,沉积历史和母岩来源对沉积物中石英的释光灵敏度的高低有重要的影响,因此可用它来追溯石英的物源。探讨该技术在物源研究领域存在的问题,对其发展前景进行了展望。     

Thermoluminescence of carbonates from carbonatites

The Gejiu tin field in southern China consists of six major deposits and many minor ones containing more than 120 million tons (pre-mining resource) at 1% Sn and significant amounts of Cu, Ag, Zn, and Pb. It is one of the largest tin fields of primary deposits in the world. Mineralization is the result of the intrusion of granitic plutons into Permian and Triassic sedimentary rocks, which are dominantly limestone, dolomitic limestone, and dolomite. Five (mostly peraluminous) granitic intrusives (64-115 Ma) are present in the area. The largest orebodies are spatially and temporally related to the Laoka (principally), Beipaotai, and Marsong granites. Tin mineralization is mainly within greisens developed at the outermost zone of a skarn zonal sequence and are mineralogically dominated by fluorite, quartz, and micas.

The deposits are the result of volatile-rich ore solutions that evolved late in the plutonic crystallization history. The solutions produced metamorphic skarns as well as ore skarns, both of which later became “greisenized” skarns. Gejiu is the largest example of what has been, up to now, a style of mineralization reported only in minor amounts.     

Thermoluminescence of shock-loaded amethyst quartz

In natural amethyst samples subjected to shock pressures between 10 and 50 GPa (1 GPa=10⁹ Pa), thermoluminescence (TL) was observed after subsequent X-ray irradiation, in some cases even without high energy irradiation. The glow curves could be decomposed into at most five components of Gaussian shape, but no reliable activation energies could be determined from them, perhaps due to a wide distribution of trap depths. With increasing shock pressures traps of higher thermal stability were favored. Emission bands with maxima near 14000 cm^?1 were observed independent of shock pressure. They appear to be characteristic of defects created during the shock events, but it is uncertain whether the observed TL is connected with the iron impurities characteristic for amethyst. In natural amethyst samples of the same origin no TL could be observed, even after additional X-ray irradiation. It is concluded that TL in amethysts reported in the literature was actually caused by defects associated with aluminium impurities, not by destruction of Fe⁴⁺.     

海啸波作用下岸滩演变与床沙组成变化研究综述

从海啸波作用下岸滩演变、床沙组成变化、建筑物周围淘刷和数值模拟研究4个方面,总结分析了国内外的研究现状和最新进展,指出可控环境下的实验和数值模拟研究相对较少、床沙组成变化缺乏关注、建筑物周围局部冲刷机理认识不足、缺少多尺度数值模拟计算等是当前研究存在的主要不足。在特大型波浪水槽内开展实验研究、发展多尺度混合数学模型、完善海啸波作用下的泥沙输移计算理论等是未来研究取得突破的关键方向。     

王庄油田强水敏油藏粘土矿物危害研究

强水敏油藏指储层遇到外来流体后,渗透率的下降幅度超过70%的油藏.该类油藏由于渗透率的大幅下降,导致注水、注汽等地层能量补充困难,开发效果不理想.目前国内外对储层敏感性机理研究逐渐从试验走向实践,并形成了一套系统的储层敏感性试验研究方法,但敏感性油藏的开发始终未取得较大的突破,其重要原因就是粘土矿物伤害储层.笔者以王庄油田强水敏性油藏为例,对粘土矿物危害进行探讨.     

矿床保存变化研究的热年代学技术方法

成矿后矿床的保存与变化是矿床地质研究的重要组成部分,但研究程度不高,至今仍属于薄弱环节。矿床的保存与其隆升剥露密切相关,深入细致研究恢复矿区矿床的隆升和剥露历史,是揭示矿床保存变化的一种重要途径。本文重点论述研究矿床保存变化的技术方法,通过综合应用裂变径迹、（U-Th）/He、40Ar-39Ar年代学以及La-ICP-MS、锆石U-Pb定年等多种技术手段,研究成矿期次、构造活动期次以及二者间的联系,定量计算不同矿区、不同矿体、不同部位、不同时间的冷却隆升速率、隆升幅度、剥蚀速率和剥蚀量,探讨矿床保存深度与剥蚀量间的关系,总结不同时代、不同矿区矿床保存-变化过程,建立新的矿床地质-保存环境模型,完善矿床预测的综合示踪标志,最终预测不同矿区、不同地段隐伏矿床可能的产出深度,给出矿床可能已经被剥蚀殆尽的区段或地段,为深部找矿和区域成矿潜力评价提供依据。本文可为地质工作者的相关应用提供借鉴和手段。     

The use of microchemical analysis of alluvial gold grains in mineral exploration: experiences in Britain and Ireland

The examination of populations of gold grains by SEM and EPMA generates a microchemical signature based upon the assemblage of opaque mineral inclusions within the gold and the concentration of minor alloying metals. Duplicate samples of alluvial gold from the same locality have yielded the same microchemical signature independent of the field worker who collected the sample, or the date of collection. A study of five separate alluvial localities yielded a microchemical signature consistent with the mineralogy of the adjacent host mineralisation. This result has permitted informed speculation on the styles and complexity of gold mineralisation contributing to the alluvial population of gold grains where the style of source mineralisation is unknown.The technique can yield information about several aspects of the source mineralisation of an alluvial population at an early stage in the exploration process. Distinctive microchemical signatures can be used to evaluate the dispersion of gold either by fluvial or glacial action. The technique can identify gold derived from separate mineralising events either within a region or along a watercourse, thereby allowing speculation on the magnitude of the source mineralisation. It is also possible to establish whether specific types of gold mineralisation of potential economic interest have contributed to an alluvial population. In areas subjected to glaciation, analysis of the microchemical signature of populations of alluvial gold may indicate whether the gold grains are of proximal or distal origin.The volume of information made available through the study of alluvial gold grains has contributed greatly to the understanding of regional gold mineralisation. Interpretation of microchemical signatures of populations of alluvial gold from about 130 localities throughout Great Britain and Ireland has facilitated characterisation of gold in terms of the style of the source mineralisation. This information has augmented that available from about ten bedrock gold localities and has permitted a more complete classification of gold occurrences throughout the region.Quantitative analysis of some minerals within the opaque inclusion assemblage can provide information on the chemistry of the mineralising fluid, which may be related to the capacity for gold transportation.In Devon, South West England, a model for the emplacement of gold mineralisation was developed from interpretation of the microchemical signature of alluvial gold grains. The selenide-rich inclusion suite containing no sulphides suggested that oxidising conditions prevailed during precipitation. The model of transport of gold in solution through the oxidising environment of Permian red beds and its subsequent precipitation in underlying rocks due to reduction in Eh was consistent with the observed distribution of gold in alluvial sediment, residential overburden and drill core. Using this model other targets for gold mineralisation were successfully predicted.     

The use of settling velocity in defining the initiation of motion of heavy mineral grains, under unidirectional flow

The results of critical threshold experiments on four commonly occurring heavy minerals are described. The data are presented, in conjunction with comparable quartz data, using the non-dimensional Shields’ Curve and the Movability Number (U*/w_s). The results indicate that critical shear stress for material of high density is overestimated by use of Shields’ Curve, under smooth boundary conditions. Grain settling velocity is found to be a good indicator for the critical shear stress for grains of a wide density range. A physical explanation for the results is proposed.     

Physico—Mechanical Property Changes Associated with mineral Phase Transition in Granite

Variations in elastic wave velocity, low-frequency internal friction and acous-tic emission in granite were experimentally studied as a function of temperature.It is found that the wave velocity and Young‘s modulus tend to decrease with temperature.In association with the α-β transition of quartz a sharp internal friction peak can be recognized accompanied by a drastic drop in wave velocity and modulus and by a second peak of acoustic emission rate.     

Thermoluminescence of meteorites and their terrestrial ages

A new technique is described in which the natural thermoluminescence (TL) in chondritic meteorites is normalized to the TL sensitivity of each meteorite. The relationship between the normalized TL level and a meteorite's terrestrial age is examined. The average normalized TL level measured in 45 ordinary chondrites of known terrestrial age decreases with increasing terrestrial age. There is a factor of ten variation in the TL levels of fresh falls which is primarily due to differences in orbital temperatures (Melcher, 1981). Nevertheless, it is possible to distinguish between recent falls and meteorites greater than a few hundred years old if they have been stored at the same temperature. The decay characteristics of the TL are studied by means of initial rise experiments and isothermal decay experiments at elevated temperatures. The TL levels of 11 Antarctic meteorites are compared with the results of ¹⁴C, ²⁶Al and ³⁶Cl studies of the terrestrial ages of these objects. There is a rough correlation between the low temperature TL levels and the radionuclide activities. Since the TL method is quick and requires as little as 10mg of material, it is most valuable as a rapid screening process to select samples appropriate for study by other techniques.     

湘西沃溪钨锑金矿床黄铁矿中发现Au-Sb矿物相

利用扫描电镜和电子探针等方法,对沃溪钨锑金矿床中产于(块状白钨矿-石英脉中的)黄铁矿微裂隙中的自然金和Au-Sb矿物相进行了较详细的观察和研究。结果表明,黄铁矿中Au-Sb矿物相除了有前人已经鉴定出的方锑金矿(AuSb2.13)外,还新发现有锑金矿(Au1.02Sb)矿物相。二者以显微颗粒的形式存在于黄铁矿显微裂隙中。黄铁矿微裂隙中Au-Sb矿物相的存在,指示矿床成矿在黄铁矿形成之后存在Au-Sb混溶的成矿流体。自然金、方锑金矿、锑金矿等矿物的沉淀析出可能是Au-Sb混溶流体从高温(高于350℃)向低温(250℃)演变的结果。此外,Au-Sb矿物相的发现对改进矿石冶炼中Au、Sb的分离技术有参考价值。     

淡—咸水界面切换中矿物表面吸附性变化研究

实验研究表明,当电解质离子浓度从有低上升到极高时,矿物吸附金属离子的普遍下降,例外的仅有石英、水云母、ＣａＣＯ３和三水铝矿对Ｐｂ＾３＋、Ｚｎ＾３＋离子的吸 云母对Ｃｕ＾２＋的吸附和石英对Ｃｒ＾３＋的吸附。理论研究表明,一方面,电解质ＮａＣｌ的加入,使矿物表面Ｓｔｅｎ的层电位发生变化,△ψ（ψ０－ψβ）的绝对值增大,提高了矿物表面吸附离子的能力;另一方面,由于Ｎａ离子的竞争吸附和Ｃｌ离子与深液中金     

Irradiation records in regolith materials. I: isotopic compositions of solar-wind neon and argon in single lunar mineral grains

We have applied a stepwise pyrolytic extraction technique to eleven individual lunar regolith grains to investigate the compositions of light noble gases embedded in grain surfaces by solar wind irradiation, with emphasis on the rather poorly known isotopic composition of solar-wind argon. Results are intriguing: average ²⁰Ne/²²Ne ratios observed in early pyrolytic releases from ilmenite grains separated from lunar soils 71501, 79035 and 10084 agree very well with both direct measures of the solar wind neon composition in the Apollo foils and with values obtained in first releases from acid-etched ilmenites by the Zürich laboratory, whereas these same pyrolytic and acid-etch fractions carry argon isotopic signatures that significantly disagree—average ³⁶Ar/³⁸Ar ratios near 5.8 for thermal extraction compared to 5.4–5.5 for chemical etching at Zürich. Consideration of the isotopic and elemental data from these grains in the context of first-order diffusive modeling calculations points to gas release at low temperatures, without significant isotopic or elemental fractionation, from isolated grain-surface reservoirs of solar wind composition. The physical nature of these reservoirs is presently unknown. In this interpretation the preferred solar wind ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios deduced from this study are respectively 13.81 ± 0.08 and 0.0333 ± 0.0003, both within error of the Zürich acid-etch values, and ³⁶Ar/³⁸Ar = 5.77 ± 0.08. It may be possible to reconcile the discrepancy between the acid-etch and pyrolytic estimates for the solar wind ³⁶Ar/³⁸Ar ratio in the context of arguments originally advanced by Benkert et al. (1993) to account for their He and Ne isotopic compositions. At the other, high-temperature end of the release profile from one of these grains there are clear isotopic indications of the presence of a Ne constituent with ²⁰Ne/²²Ne close to the 11.2 ratio found at Zürich and attributed by these workers to a deeply-sited component implanted by solar energetic particles.     

Thermoluminescence dates of Weichselian sediments in western Norway

Thermoluminescence dating has been carried out on feldspar sand grains from the distal sandur of the Godøya Formation and correlated sediments at Sunnmøre, western Norway. The accumulated dose was determined by the regeneration method. The Godøya Formation, which was earlier assumed to be of Middle Weichselian age, was dated to 105–130 ka and is now assumed to postdate immediately the Eemian interglacial. Dates of sediments previously correlated to the Godøya Formation yielded ages in the ranges of 70–90 and 40–50 ka, thus indicating at least three Weichselian ice-free periods predating the Ålesund interstadial in the area.     

Thermoluminescence dating of Dimlington Stadial deposits in eastern England

The loess component of a solifluction deposit of the Dimlington Stadial exposed at the inland site of Eppleworth in eastern England gave a thermoluminescence date of 17.5 ± 1.6 × 10³ years. The solifluction deposit is overlain by a slightly weathered till correlated with the Skipsea Till of coastal exposures. which lies between organic horizons with radiocarbon dates of 18,500–18,240 B.P. and 13,045 B.P. Although the till must have been deposited during the Dimlington Stadial (after 18,240 B.P. at Dimlington and after 17,500 B.P. at Epplcworth), it gave apparent TL dates of 42.1 ± 3.6 × 10³ years at Eppleworth and 102 ± 9 × 10³ years at Dimlington, indicating that the components of the till were not exposed to light immediately before deposition.