Analysis of Geochemical Reference Materials Using Simultaneous Multi-Element Atomic Absorption Spectrometry

Analytical data are presented for the determination of Ag, Bi, Cd, Co, Cu, Mn, Ni, Pb, Zn in 60 geochemical reference samples by simultaneous multi-element atomic absorption spectrometry with flame atomization. The samples include rocks, sediments, coal ash, Mn nodules and ores. Accuracy and precision of the analysis are evaluated statistically.     

A SELF-CONSISTENT COMPILATION OF ELEMENTAL CONCENTRATION DATA FOR 93 GEOCHEMICAL REFERENCE SAMPLES

Concentration data obtained by instrumental neutron activation analysis (INAA) are presented for up to 36 chemical elements in 93 geochemical reference samples, including some for which there are little previous data. Because all data are based on at least three independent analyses, and for many of the data the uncertainty associated with counting is an insignificant source of error, the values presented here are considered of higher precision than generally reported by INAA. Information on subsampling error (sample heterogeneity) is also presented.     

Using robust staged R-mode factor analysis and logistic function to identify probable Cu-mineralization zones in Khusf 1:100,000 sheets,east of Iran

Factor analysis method is a multivariate analysis technique that is widely used for the interpretation of stream sediment geochemical data. The purpose of factor analysis is describing the changes in a set of multi-element geochemical data by reducing the dimension of the data and variables to a number of factors that can present the hidden association between elements. Differences in mobility, physical, and chemical properties of the elements and the nature of the factor analysis method in which the matrix of all data is used cause paragenes elements not to be found on the output of factor analysis. In this research, to improve the output of factor analysis for deriving the best reagent multi-element mineralization, robust staged factor analysis method was used according to the close nature of geochemical data in order to identify the Cu-mineralization potential in Khusf 1:100,000 sheets located at the east of Iran. The robust staged factor analysis enhances the recognition of anomalous geochemical signatures and increases geochemical anomaly intensity and the percentage of the total explained variability of data. As indicated by the results of the study, few anomalous zones have been found in the study area. The observation of chalcopyrite and malachite mineralization in andesite and dacite–andesite rocks in a region during the field study confirms the effectiveness of the robust SFA technique. Such studies can be used by mine engineers and geologists for designing an optimum grid exploration on the next exploration steps.     

MULTI-ELEMENT ANALYSIS OF COASTAL MARINE SEDIMENT, AN IAEA PROPOSED REFERENCE MATERIAL (IAEA-356)

Proposed standard reference material, coastal marine sediment (IAEA-356) recently released under the IAEA Analytical Quality Control Services programme, has been analysed by instrumental neutron activation analysis technique. Up to 32 elements have been measured using the multi-element analysis approach. The precision of measurements varied from 1.3 to 12.5% with median value of 4.9%. The quality control of the data has been validated by analysing IAEA reference material of similar matrix which shows excellent agreement with IAEA values.     

Quantifying chemical changes in hydrothermally altered volcanic sequences — silica enrichment as a guide to the crandon massive sulfide deposit,Wisconsin, U.S.A.

A multi-element geochemical study of the wallrocks which host the large Precambrian Crandon deposit (≈ 70 million tons of zinc, copper ore) in Wisconsin, U.S.A. was carried out to identify pathfinder elements which significantly enlarge the size of the deposit as an exploration target. The Crandon deposit occurs in what appears to be a “normal”, subalkaline, intermediate to felsic volcanic sequence. The silica concentration of the wallrocks shows neither a systematic relationship to volcanic stratigraphy nor a distinctive pattern around ore.To determine if silica has been added to the host rocks, a regression analysis was performed on published data from 496 unaltered, subalkaline volcanic rocks from the Abitibi Subprovince of Canada, with silica as the dependent variable and the ratio of “immobile” elements Zr/TiO₂ as the independent variable. Based on the second degree regression curve and the associated standard error of estimate, predicted and residual silica values were calculated and plotted for the Crandon host rocks.The results show that massive sulfide ore was deposited in andesitic rocks with an original SiO₂ content of 52–62%, and that more than 7.4% SiO₂ was added to the rocks stratigraphically beneath the deposit and on strike with the deposit. Silica was added to the hanging wall rocks also, which confirms that hydrothermal activity at Crandon continued after cessation of massive sulfide ore deposition. In contrast to the pattern of silica enrichment at Crandon which significantly enlarges the size of the exploration target, two noneconomic prospects within ten miles of Crandon contain low to moderate levels of silica enrichment and corresponding low base metal values.Silica enrichment occurs in some systems unassociated with mineralization and is therefore not a specific signature of ore-forming processes. However, from the data presented on the Crandon deposit, if silica enrichment does exist in an exploration search area, the chances of finding a massive sulfide ore deposit are improved.     

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.     

西藏撞多勒地区水系沉积物地球化学特征及其地质填图应用

西藏撞多勒地区位于班公湖—怒江缝合带西段南侧燕山晚期火山—岩浆弧带,经历了多阶段复合造山作用,各类地质体和构造形迹复杂多样。本文在总结1:5万水系沉积物地球化学特征及分布规律基础上,分析不同地质体中元素的背景值、标准离差、富集系数、变异系数。依据地球化学示踪作用原理,运用多元素背景值推断主要地质体的空间展布和构造形迹,制作As、Sb、Hg元素组合及Cr、Ni、Zn元素组合的衬值累加图分别解译构造和岩浆岩,厘清宏观地质体与微观元素之间的关系,进行地层划分、地质体圈定和断裂追踪,对区域地质填图起到了较好的辅助作用。     

Instrumental Neutron Activation Analysis Of 37 Geochemical Reference Samples

37 geochemical reference samples, issued mostly by the U.S. Geological Survey and the "Centre de Recherches Pétrographiques et Géochi-miques", have been analysed for more than twenty trace elements using instrumental neutron activation technique. The results are compared with published data; in most oases, the agreement is good.     

Incorporation of principal component analysis,geostatistical interpolation approaches and frequency-space-based models for portraying the Cu-Au geochemical prospects in the Feizabad district,NW Iran

Delineation of mineralization-related geochemical anomalies of stream sediment data is an essential stage in regional geochemical exploration. In this study, principal component analysis (PCA) was applied to 12 selected elements to acquire a multi-element geochemical signature associated with Cu-Au mineralization in Feizabad district, NE Iran. The spatial distribution of enhanced multi-element geochemical signature of the second component (PC2) was modeled by different geostatistical procedures including variogram calculation, ordinary kriging (OK) and inverse distance weighting (IDW) interpolation techniques. Concentration-area (C-A) fractal and U-spatial statistics models were then applied to the continuous-value interpolated models for delineation of geochemical anomalies. Quantitative comparison of results based on the known mineral occurrences in the study area was carried out using normalized density index and success-rate curves. All generated models represent a high positive relation with known Cu (±Au) deposits in the study area, although, comparison of the results revealed that the OK-based U-spatial statistics model was superior to the rest of models. Besides, the low, moderate and high-intensity anomalies are spatially associated with geological-structural features in the study area.     

西藏日喀则地区雅鲁藏布蛇绿岩地球化学特征及其源区性质

日喀则地区的蛇绿岩是西藏南部雅鲁藏布蛇绿岩带出露较好的蛇绿岩之一。对日喀则地区白朗蛇绿岩的主量、微量元素及Sr-Nd同位素研究表明,其基性岩石为钙碱性系列,主要氧化物具有低钛(0.6%~1.1%)和富镁(6.6%~8.7%)、高铝(15.3%~16.0%),以及烧失量普遍较高(2.8%~4.6%)的特征。岩石微量元素配分型式与N-MORB类似,又具有岛弧玄武岩的地球化学特征,表明蛇绿岩受到了俯冲作用的影响。Sr-Nd同位素特征表明源区为略富集的MORB型地幔。白朗蛇绿岩所代表的特提斯地幔域与印度洋地幔域具有相似的地球化学性质,进一步证实了现今的印度洋继承了特提斯地幔域的地球化学特征。     

Multi-Element Analysis of Fifty-Four Geochemical Reference Samples Using Inductively Coupled Plasma-Atomic Emission Spectrometry

Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) has been applied for simultaneous, multielement analysis of a diverse suite of igneous rocks and minerals, metamorphic and sedimentary rocks, coals and soils using a single matrix calibration procedure and a single sample preparation. Analytical results determined on 40 elements in 54 geochemical reference samples are presented. A sample analysis time of about three minutes allows the analyst to run several hundred samples per day, but does not include sample dissolution. The instrumental method described here provides the capability for rapid, simultaneous, multielement determination of the major (except silica), minor, and trace elements in rocks using a single sample preparation technique. Analytical data collected on the Geochemical Reference Samples (GRS) demonstrate the general utility of the method. Analytical results show an excellent agreement with previously published results for the major and minor elements. Of the 28 trace elements studied, 17 can be routinely determined in crustal rocks, but the concentration of several of the others can be determined only if present at concentrations several times above their crustal-abundance level.     

Analysis and mapping of geochemical anomalies using logratio-transformed stream sediment data with censored values

There is lack of research and documentation of actual (as opposed to theoretical) benefits (e.g., mineral deposit discovery) of developments in compositional data analysis and imputation of censored values to mineral exploration geochemistry. In the present study, analyses of logratio- and ln-transformed stream sediment geochemical data containing ca. 30% of samples with censored values of a pathfinder element for the mineral deposit-type of interest yielded the following findings. Exclusion of those samples supports interpretation of multi-element anomalies reflecting the presence of mineralization. However, the multi-element anomaly maps obtained by exclusion of those samples are barely better than the multi-element anomaly maps derived by inclusion of those samples after replacing the censored values with 1/2 of detection limit or with imputed values. Logratio (i.e., alr, clr, or ilr) transformation, compared to ln-transformation, of stream sediment geochemical data does not improve mapping of pathfinder element anomalies reflecting the presence of mineralization. However, stream sediment geochemical data, excluding or including censored values (replaced with 1/2 of detection limit or with imputed values), should be clr- or ilr-transformed to enhance recognition of anomalous multi-element associations reflecting the presence of mineralization. The anomaly maps of multi-element associations derived from ilr-transformed data are better, albeit slightly, than the anomaly maps of multi-element associations derived from clr-transformed data. In the present study, the main benefit of either clr- or ilr-transformation, compared to either ln- or alr-transformation, of stream sediment geochemical data is the enhancement of anomalous multi-element associations reflecting the presence of mineralization. This is an important benefit because variations in trace element concentrations in regional-scale stream sediment geochemical data are mostly due to lithology and other factors (or processes) unrelated to mineralization. Further investigations of various exploration geochemical data are needed to demonstrate and document the actual (as opposed to theoretical) benefits of developments in compositional data analysis and imputation of censored values to mineral exploration.     

DETERMINATION OF MINOR AND TRACE ELEMENTS IN FOUR CANADIAN IRON FORMATION STANDARD SAMPLES FER-1, FER-2, FER-3 AND FER-4 BY INAA AND ICP-MS

Analytical data on samples FeR-1, FeR-2, FeR-3 and FeR-4 obtained by instrumental neutron activation analysis and by inductively coupled plasma mass spectrometry are presented. The applied methods are described, and the analytical problems associated with their use are discussed. The accuracy of the two methods is demonstrated by comparing the results with the recommended values of the iron formation reference sample, IF-G. For the four FeR samples a set of values summarizing all data obtained by the two analytical methods is also given.     

河北省金的矿源层和地球化学块体

以区域化探岩石和水系沉积物测量成果为依据,讨论河北省范围内Au矿源层的地球化学判别、岩浆热液型金矿成矿过程的地球化学推导、Au的地球化学块体以及水系沉积物区域地球化学异常特征等问题.地层标准剖面和典型侵入体系统的岩石地球化学调查表明,在Au矿源层和非矿源层之间,w(Au)差异很小,以其作为判别标准是不可行的,但H2O ,CO2,S,Cl,F,Hg等组分却存在显著差异,据此提出一个新的矿源层--中新元古界碳酸盐岩.Au的区域地球化学背景研究显示,密云-青龙、怀安-崇礼-赤城、平泉和阜平-赞皇等地区存在着地球化学块体,而水系沉积物地球化学异常分布与这些块体基本一致,相互对应.     

Surface lithogeochemical studies about a distal volcanogenic massive sulphide occurrence at Limerick,New South Wales

The results of a surface rock chip sampling study over a small distal volcanogenic massive sulphide deposit at Limerick, N.S.W., Australia are presented and compared with drill core and soil geochemical patterns. Major element halos are narrow in comparison to the pervasive patterns reported from major proximal deposits. Narrow zones of Mg and K enhancement are associated with sulphide mineralization. High levels of Na occur in these rocks in contrast to the regularly described pattern of Na depletion. Weathering, particularly in the presence of sulphides, has resulted in the leaching of Ca, Na and, to a lesser extent, K from surface rock chip samples, whereas Fe, Pb and Zn contents are enhanced compared to those in fresh rocks. Despite the problems of sample heterogeneity, variable weathering and the limited extent of alteration halos which exist in this environment, surface lithogeochemical methods in comparable situations may be useful in the confirmation and interpretation of soil geochemical anomalies.     

Neutron Activation Analysis for Trace Element Determination in Geostandards

The advantages of neutron activation analysis as applied to geological material are discussed. Analytical work performed in the authors' laboratories is described, and preferred values from this work for 38 elements in some USGS standard rocks are presented and compared with literature data.     

Application of multi-element relationships in stream sediments to mineral exploration: a case study of Walawe Ganga Basin,Sri Lanka

This study on the application of multi-element relationships in stream sediments to mineral exploration in the Walawe Ganga Basin presents one of the first of its kind in Sri Lanka. In order to determine the nature of these sediments, multi-element analysis of selected grain size (<63 μm, 63–125 μm, 125–177 μm and 177–250 μm) fractions was undertaken. The chemical composition of these fractions were compared with those of the upper continental crust.Some elements, notably Zr, Hf, Th, U, Ce and La, show very high enrichment factors (e.g. 54 for Zr) as compared to the upper crustal abundance. These are presumably associated with heavy minerals such as zircon, rutile and monazite found in abundance in the stream sediments of the Walawe Ganga Basin.Principal Component Analysis (PCA) of the geochemical data show that multi-element relationships could be effectively used to delineate target areas for mineral exploration. With the use of PCA, this study reveals that areas with associations of calc-silicate/marble and charnockitic rocks are probable source regions for mineral occurrences, particularly in the axial regions of anticlines.     

Comparison of Major and Trace Element Analyses by ICP, XRF, INAA and ID Methods

Element concentration data for a set of silicate igneous rocks have been determined by four independent analytical methods: inductivelycoupled plasma emission spectroscopy (ICP), instrumental neutron activation analysis (INAA), x-ray fluorescence (XRF), and isotope dilution mass spectrometry (ID). The results show excellent agreement among elements determined by more than one technique, and demonstrate the suitability of commercially available ICP instrumentation for the routine analysis of geologic material compared to other standard methods.     

Factor and discriminant analysis to lithogeochemical prospecting in an area of central Sweden

Alteration zones in host rocks surrounding mineral deposits have long been used as indicators of ores, and recent studies have stressed the importance of the chemical distribution patterns or haloes. These may be more pronounced than mineral alteration and therefore detectable over greater distances.There are, however, several problems involved in this type of prospecting. One is the possible presence of several geochemical populations in the analyzed samples. Only some of these populations reflect the haloes which one wants to detect, while others only disguise the haloes. One solution is to use multivariate statistical analysis to discriminate between the different populations.In the Stollberg orefield, central Sweden, these prospecting methods are presently in use. Here, located within Precambrian volcanic rocks, several small and large stratiform zinc-, lead- and iron ores are situated in the same stratigraphic zone and within 6 km of each other. Drifts in the area go down to 575 m. Approximately 3000 rock samples collected from outcrops, drill cores and drifts were analyzed for 35 elements by XRF and IDES (Image Dissector Echelle Spectrometer). These samples represent an area of 3 × 9 km to a depth of 600 m.Due to the presence of several geochemical populations, the raw data are difficult to interpret. After reducing the skewness of the data, factor analysis was performed and, in general, distinct multi-element zonations were detected. Factor scores were used as the input for discriminant analysis. In this manner chemical haloes were obtained which have an extension of more than one kilometer in all directions around the various ore types in the area. The ores can thus be detected at considerable distances. On the basis of these findings, some promising new prospects have been discovered.     

Silver Content of Some USGS Standard Rocks

The state of the art for silver determination in silicate rocks is discussed on the basis of available data on geostandards. A neutron activation procedure for silver in rocks is briefly described, and data on seven new USGS standard rocks are presented and discussed.