Instrumental neutron activation analysis as an analytical technique for gold exploration

Various methods are described for the analysis of Au and the Pt-group elements (PGE) using different geochemical media commonly collected by the exploration geochemist. The methods described utilize primarily the Instrumental Neutron Activation Analytical technique (INAA) in use at a commercial INAA laboratory.Rocks and soils are routinely analyzed by using a Pb fire-assay preconcentration on a 20-g sample and then analyzing the resultant Ag dore bead by INAA to a detection limit of 1 ppb. Growing rapidly in popularity is the analysis of a 30-g aliquot of sample for 34 elements including Au, solely by INAA. The elements included provide a wealth of information of a geological nature.Due to the very inhomogeneous nature of Au occurring in heavy-mineral concentrates it is imperative to analyze the whole concentrate. The only method which can provide a multielement analysis and still retain the sample intact is INAA.Biogeochemistry using either humus or vegetation as the sample media is rapidly becoming widely used. INAA provides a very sensitive means of determining Au and 34 other elements rapidly and at relatively low cost.These and other methods using the INAA technique for Au and the Pt-group will be described.     

关注地质分析文献，了解分析技术发展——地质分析综合性评述论文评介

现代地学已进入地球系统科学研究时代,它涉及到天、地、生的广阔研究领域,是一个综合性很强的学科[1]。地学理论的发展将越来越多地需要用高新技术所获取的高质量、海量观测和分析数据。海量地球化学数据就是其最重要的基础数据之一。地质体归根到底是由化学元素构成的,而且几乎包含了天然存在的所有元素。化学元素的组成、配比、迁移和演化都与一定的地质过程相关联。而要获取这些基础数据和信息,就需要现代地质分析技术的支持。因此当今越来越多的地学家关注着地质分析技术的发展。另一方面,现代地质分析技术已远不是过去的以化学法为主的…     

关注地质分析文献,了解分析技术发展——地质分析技术应用类评述论文评介

地质分析技术产生的数据是进行地质科学研究和矿产资源、地质环境评价的重要基础,是发展国土资源地质调查事业和地球科学的重要技术支撑。中国地质事业已经得到了空前的发展,地质分析文献迅速增加,迫切需要对文献进行整理、加工、综合、评价。为了解当前中国地质分析技术在各领域的应用状况和获得的成果,对国内科研人员20年来发表的地质分析应用类评述性论文作一评介,内容联系当今全球地质分析技术发展的新趋势,主要包括标准物质与标准方法,岩石矿物分析,地球化学调查(区域地球化学、多目标地球化学和生态地球化学调查)、地球化学填图样品分析,海洋地质样品分析,现场分析,贵金属分析,化学物相与元素形态分析,水分析,能源矿产和环境样品分析,稳定同位素和同位素地质年代学技术与应用10项分析技术领域取得的研究成果。阐述了国内地质分析技术新应用领域的进展、动态和发展前景。     

Rapid laboratory analysis by neutron activation: experience in bauxite exploration

The efficiency of neutron activation as an analytical technique has been evaluated for exploration of lateritic and karstic bauxites in Sierra Leone, Guinea, Australia (Gove), Philippines and Jamaica. The 10-g bauxite samples are prepared in the field and sent to a central laboratory. With the “Automatic Bauxite Analyzer” — equipped with an isotopic neutron source — a single Al and Si determination can be made in 5 minutes. For calibration, standards are required which are similar in composition to the samples to be analyzed. Using sample pairs and averaging the results of three subsequent determinations an accuracy of ±2% Al₂ O₃ and about ±0.6% SiO₂ can be obtained. Time requirements, accuracy and cost of this technique are compared with wet chemistry and X-ray fluorescence. For an exploration programme incorporating for example 15,000 drill core samples, a 50% reduction in expenditure for analytic determinations can be achieved by applying neutron activation instead of X-ray fluorescence alone.     

A neutron activation technique for the analysis for fluorine in fluorspar samples

This article explains the results of the feasibility study about using neutron activation technique via Deferred gamma rays, to analyze the fluorine content in a sample from a fluorspar concentration plant. The theoretical responses of 12 items, constituting the samples have been analyzed. 468 reactions have been obtained from the study with the database EXFOR of these elements with neutrons from an Americium Beryllium source of 1 Ci activity.The radioactive decay of 29 products, anticipated from such an activation, has also been analyzed. From these results, a prototype for neutron activation has been designed. The different criteria of the measurement procedure to enable the activation of the fluorspar samples and to record their spectra with minimal interference from the source have been adjusted. A mathematical model of the activation response has been created and validated. The activation method to determine the fluorine content in fluorspar samples proved to be scientifically and technically feasible and verified by the results obtained.     

An improved method for computer simulation of geochemical neutron activation experiments

A computer method has been developed that simulates gammaray spectra of geochemical thermal neutron activation experiments. The input for the simulation includes the designation of rock type, neutron flux, sample volume and density, irradiation time, time of detection start, duration of monitoring, and number of analyzer channels. The output of the simulation includes either two-or threedimensional computer drawn plots of the resulting (simulated) gammaray spectra. The threedimensional plots (energy vs counts per sec vs time of detection) allow the investigator to observe the apparent appearance and disappearance of photo peaks, annihilation peaks, and pair production peaks of the various isotopes as a function of time. Various combinations of irradiation, delay, and detection times result in various spectral patterns. The resultant patterns accurately simulate the real activation experiments run under the same time conditions. The simulated spectra are useful for identifying peaks obtained from real spectra, helping in radiochemical separation decisions, and, in general, in designing the neutron activation experiment.     

精确的定量和定年技术--中子活化技术

精确的定年技术是建立高精度层序地层时间序列的关键,而该项技术的核心是如何精确地确定地层中地层界面的年代和其他可从沉积物序列中分辨出的地质事件的年代,特别是对地层中高频沉积旋回的每个旋回上下界进行定年,并在可能的情况下恢复地层的沉积间断时间,计算地层的沉积速率和沉积周期[1,2]。我国新生代陆相湖盆由于封闭性较高,湖底沉积对气候变化的反映比较敏感,因此湖相沉积物常被当作古气候变化记录的良好载体。通过对湖泊发展史的准确恢复和对其所蕴含的古气候演变规律的深入分析,可为全球变化趋势研究提供可信的科学依据。     

The importance of second order activation in the determination of trace elements in geological samples by instrumental neutron activation analysis

This paper deals with the disturbance of INAA trace element determinations in rocks by second order activation. The degree of error in the determination of Gd by Eu in rocks is checked by experiments and compared with results of computer evaluations. The consequence of the Dy-interference for the determination of Ho was also calculated. Hints to avoid these interferences are given.     

标准物质的中子活化定值测试研究

用中子活化分析方法,定值测试了湖北岩矿测试中心研制中的GSS31~GSS35土壤底泥标准物质,测定了28个元素;定值测试捷克生物标准物质TY1~4,测定了12个元素,对谱干扰和U裂变干扰作了修正。这里列出了由国际地质分析协会(IAG)组织,有全球71个地球化学分析实验室参与测试的玄武岩BNV-1的平均值及本实验室的测试结果。     

Elemental composition of sediment cores from a mangrove environment using neutron activation analysis

The geochemistry of Sepetiba Bay was studied in four sediment cores using a multi-element approach. Two cores were sampled in the more contaminated eastern part of the bay and two cores were sampled in the western region. The aim was to determine whether less common elements like the rare earths or the actinides are associated with contaminant metals like zinc in the Bay. Samples were analysed by instrumental neutron activation analysis that permits the quantification of total concentrations of metals (Ba, Co, Cr, Cs, Fe, Hf, Rb, Sc, Zn), rare earth elements (Ce, Eu, La, Lu, Sm and Yb), actinides (Th, U), non-metals and semi-metals (As, Br). Organic carbon and total sulphur were also analysed. The results show very strong zinc contamination in the top layers (more than 1000 μg g⁻¹) and background concentrations in the bottom (15 μg g⁻¹). Elements like chromium which would be expected to be released by the heavy industries of Sepetiba Bay, did not show a contamination profile, and concentrations remained close to those of natural environments. No evidence of any association between the zinc and other potential contaminant elements could be identified in this work.     

砷的仪器分析方法新进展

砷是自然界中广泛存在的一种物质在工业，农业，医药等方面应用很广。笔者着重介绍了近几个来砷的仪器分析方法新进展，主要有光度法，电化学法，原子吸收法等。     

Some trace element data and their interpretation for several new reference samples obtained by neutron activation analysis

A number of problems associated with the geochemical application of instrumental neutron activation analysis are discussed. Particular emphasis is placed on the problems of preparing and using multi-element standard solutions and/or those associated with the accurate computer reduction of γ-spectral data. It is concluded that accurately and extensively analysed rocks and minerals best fulfil the requirements for multi-element standards in this type of analysis.In the second part of the paper instrumental neutron activation analysis data are presented for 26 international reference samples including 4 of the less well-analysed U.S.G.S. standard rocks. Some limited geochemical interpretations of the data are presented.     

Precise determination of uranium in rocks and minerals by neutron activation analysis using 133I fission product

A radiochemical neutron activation technique for uranium determination in rock and mineral samples is presented. The method is based on an alkaline fusion, a selective oxidation of iodine by a sodium-nitrite solution, followed by an iodine distillation technique for the isolation of the ¹³³I produced in fission. The outlined scheme is rapid, sensitive and reliable. Determination of uranium in U.S. Geological Survey standard rocks (G-1, W-1, G-2, BCR-1, AGV-1, GSP-1), C.R.P.G. Nancy geochemical standards (GA, GH, BR, Mica-Fe, Mica-Mg), C.A.A.S. reference syenite rocks (SY-1, SY-2, SY-3) and other analysed rock samples are reported. These results are compared with those obtained by other methods.     

A study of Gd,Ce and Eu impurities in fluorite deposits by electron paramagnetic resonance and neutron activation analysis

In order to obtain a better understanding of fluorite deposits, rare earth impurities have been analyzed for a large number of samples taken from cross-sections of several low temperature hydrothermal veins. Two types of measurements have been used: Electron Paramagnetic Resonance (EPR) and Neutron Activation Analysis (NAA). For Gd, the ratio of spin concentrations to total concentration [Gd³⁺]/[Gd_total] is close to 1 in all the samples; on the other hand, the ratios [Eu²⁺]/[Eu_total] and [Ce³⁺ -F _? ⁱ ]/[Ce_total] exhibit large variations. The first result suggests that the major part of the lanthanides in the samples is incorporated in the crystal lattice and that clustering of lanthanides ions is not important. The behaviour of Eu and Ce is ascribed to charge state changes and symmetry state changes respectively.     

Preparation of Synthetic Standards For Use in Instrumental Neutron-Activation Analysis

An account is given of the formulation and preparation of synthetic standards suitable for the routine analysis of minerals, ores and ore concentrates by instrumental neutron activation. Fifteen standards were prepared, each containing from one to seven elements. The standards contain forty-four elements that produce isotopes with half-lives longer than 12 hours. An evaluation of the accuracy and precision of the method of preparation is given.     

Instrumental Neutron-Activation Analysis Of Uranium Reference Materials

This paper reports an investigation into the suitability of the neutron-activation method, by use of the reaction ²³⁸ U(n,γ) ²³⁹ U with detection of the gamma-rays from the daughter ²³⁹ Np, for the determination of uranium in 10 proposed reference materials. ¹⁸² Ta was used to monitor the neutron flux. The precision of measurement varied from 0.92 to 2.7 per cent. Results compare favourably with those obtained by other analytical procedures, and show that this established method can be used to yield useful and independent results in the preparation of uranium reference materials.     

The Na/K ratio of fluid inclusions in pegmatitic quartz and its genetic implications. A study by neutron activation analysis

Samples of quartz and its fluid inclusions (f.i.) from Black Hills pegmatites and from graphic granites were analyzed for Na, K, Rb and Cs by neutron activation analysis. The Na/K ratios of the whole quartz and its f.i. seem unrelated. The spatial locations for six samples from the Helen Beryl pegmatite were known. The Na/K ratios of their f.i. are mainly a function of their vertical positions in the pegmatite. The ratios of the central-core quartz f.i. seemingly indicate a much higher temperature than those closer to the upper wall. This is consistent with the theory of pegmatite genesis by Jahns & Burnham. The f.i. of quartz from two graphic granites give very different Na/K ratios, seemingly related to differences in their formation history.     

Instrumental Neutron Activation Analysis of Six Bulgarian Geostandards

Instrumental neutron activation analysis (INAA) was used for the determination of 25 elements (most of them in trace quantities) in six Bulgarian geostandards: Monzonite BV, Gabbro GV, Dolomite DM, Porphiry Copper Ore MrA, Fire Clay OgG and Lead-Zinc Sulphide Ore OZrO. Analyses were made independently in two laboratories and compared with available data.