Exploration Geochemists Research Articles

Identifying porphyry-Cu geochemical footprints using local neighborhood statistics in Baft area, Iran

Identifying geochemical anomalies related to ore deposition processes facilitates the practice of vectoring toward undiscovered mineral deposit sites. In district-scale exploration studies, analysis of dispersion patterns of ore-forming elements results in more-reliable targets. Therefore, deriving significant geochemical footprints and mapping the ensuing geochemical anomalies are of important issues that lead exploration geologists toward anomaly sources, e.g., mineralization. This paper aims to examine the effectiveness of local relative enrichment index and singularity mapping technique, as two methods of local neighborhood statistics, in the delineation of anomalous areas for further exploration. A data set of element contents obtained from stream sediment samples in Baft area, Iran, therefore was applied to illustrate the procedure proposed. The close relationship between anomalous patterns recognized and known Cu-occurrences demonstrated that the procedures proposed can efficiently model complex dispersion patterns of geochemical anomalies in the study area. The results showed that singularity mapping method is a better technique, compared to local relative enrichment index, to delineate targets for follow-up exploration in the area. We made this comparison because, as pointed out by exploration geochemists, dispersion patterns of geochemical indicators in stream sediments vary in different areas even for the same deposit type. The variety in the dispersion patterns is due to the operation of post-mineralization subsystems, which are affected by local factors such as landscape of the areas under study. Therefore, the effectiveness of the methods should be evaluated in every area for every targeted deposit.

Constraining the distribution of elements and their controlling factors in the Zhaojikou Pb–Zn ore deposit, SE China, via fractal and compositional data analysis

The distribution of elements in soil is affected by various natural processes, and therefore, it is essential that exploration geochemists are able to recognize whether an elemental concentration is related to mineralization or other processes. This research aimed to recognize the elemental distribution and its controlling factors around the Zhaojikou Pb–Zn ore deposit, SE China, via fractal and compositional data analysis. Firstly, histograms over the raw data and log-ratio transformations were used to check whether the concentration data followed a normal distribution or not. The concentration distribution maps of elements were then generated via spretrum–area fractal plot to show the spatial relationships. Afterward, the inter-relationships among different elements were studied through robust principal component analysis based on compositional data theory. The factors controlling the distribution of elements were discussed and geochemical indices were proposed for future exploration. Finally, a comprehensive anomaly map was generated to show important prospecting areas. Results showed how the interpretation of distributions of elements was enhanced due to the application of data log-ratio transformation in univariate and multivariate analysis compared to the use of raw data. The histograms based on isometric log-ratio performed best among the three log-ratio transformations. The concentration distribution maps showed three anomalous areas at the surface. It clearly allowed identifying the relationships between the elements and their possible source patterns. Area I with anomalous assemblage of Pb–Zn–Ag–Cu–Cd corresponded to the current known ore deposits, while Area II with anomalous assemblage of Pb–Zn–Ag–Cu–Cd may indicate the occurrence of new potential base metal (Pb–Zn) ore bodies, and Area III with anomalous assemblage of W–As–Sb may indicate the occurrence of new potential Au mineralization/ore occurences. The robust biplot of PCA shows that the distributions of elements of interest were generally controlled by three geological processes: Pb–Zn ore-forming process, Au mineralization and weathering. Lead, Zn, Ag, Cu, and Cd, were affected mainly by Pb–Zn ore-forming processes; W, Sb, and As were affected mainly by Au mineralization, whereas Al2O3, K2O, Rb, Ba, Sr, Na2O, CaO, MgO, and SiO2 were affected to a greater extent by weathering processes. Sulphur, a mineralizing agent, was controlled by the ore-forming processes, being affected greatly by weathering. Finally, we proposed Pb > 160 ppm, Zn > 120 ppm, Ag > 193 ppb, Cu > 50 ppm, Cd > 210 ppb, W > 5 ppm, As > 25 ppm, Sb > 3.5 ppm, and S > 120 ppm as geochemical indices based on concentration-area fractal model analysis for future surficial geochemical prospecting in the Zhaojikou District.

Eion Matheson Cameron 1933–2014

On May 30th of 2014 we lost a truly gifted and outstanding geochemist, pioneer, loyal friend, co-founder of the Association of Applied Geochemists (then the Association of Exploration Geochemists, AEG, and now AAG), and founder of the Association’s first journal, the Journal of Exploration Geochemistry (JGE): Eion M. Cameron. Most of Eion’s long and illustrious career was spent at the Geological Survey of Canada (1966–2000) as both a research geochemist and as Head of the Applied Geochemistry Subdivision, comprising some 32 scientists and technical staff. A major emphasis of Eion’s research was on the development, testing and application of new and improved methods of detecting ore deposits both at surface and buried at depth. His accomplishments in this area are diverse. For example, he established lake sediment and water geochemistry as an effective mineral exploration tool in Canada’s north. In 1972, Eion carried out the first regional-scale geochemical survey in Canada, sampling lake sediments and waters over 93 000 km2 of the Northwest Territories in only six weeks with three choppers and one float plane. Some of the discoveries, as a result, are the Yava and Hackett River VMS deposits. This survey paved the way for Canada’s National Geochemical Reconnaissance Program. Still in the 1970s, he led the first GSC multi-disciplinary multi-agency …

Future research directions in exploration geochemistry

ABSTRACT Although there have been some major breakthroughs in the field of exploration geochemistry over the past ten years, there is still much work to be done to advance the understanding of geochemical processes in different environments and proper application of exploration geochemistry in mineral exploration. Some future research directions in exploration geochemistry include: (1) detailed mechanistic studies of processes affecting the mobilization, transport and fixation of metals that result in patterns of soil geochemistry, gas compositions and other indicators of concealed mineral deposits; (2) further developments in heavy mineral indicator techniques, starting with cheaper and more effective separation methodologies, to evaluate both their distribution and, in particular, their mineral chemistry to determine elemental signatures for an expanded range of deposit types; (3) assessment of survival rates of minerals, in particular sulphide minerals, dispersed through various types of surficial materials associated with a variety of mineral deposit types in differing geological, surficial and climatic regimes globally; (4) evaluation of the usefulness of isotopes of various elements such as Pb, Se, Cu and Hg which could potentially help determine the transport mechanisms for elements released from bedrock to sites of surface accumulation; (5) further examination of the application of groundwater, and other types of water, to determine geochemical signatures for different mineral deposit types in order to establish the potential, the limitations, and the workable protocols for these methods; (6) development of field portable instrumentation for multielement and multispecies analysis of waters and soil gases; and (7) further refinement and development of visualization and interpretation techniques, particularly within a GIS context. There also needs to be a return to the application of fundamental regional reconnaissance scale geochemical surveys and an increasing awareness of the role that geochemical data can play as environmental baseline data. The biggest problem in the immediate future, however, will be the survival of ‘exploration geochemists’ due to the aging of the small population of existing geochemists and the global decline in opportunities for the education, development and training of young exploration geochemists.

Effective exploration for uranium in South Australian palaeochannels

Analysis of groundwater is a powerful tool for regional exploration for uranium when the target is much smaller than the potential host. Such is the case with the reduced sediments in South Australian palaeochannels. Detailed analyses of multi-element data are required to interpret the uranium data properly. Analyses by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry can provide quality groundwater datasets and, along with commercial software and better thermodynamic databases of uranium aqueous species in saline waters, make accurate solution chemical modelling available to the exploration geochemist. Lead isotopes, measured by inductively coupled plasma-mass spectrometry, can be used to confirm the groundwater interpretations. Palaeochannels containing uranium deposits in South Australia have neutral, moderately saline groundwaters whereas others may be characterised by saline and often acidic waters. Such waters readily mobilise radium, a daughter product of the uranium, and exploration methods based on uranium-daughters such as radon at the surface or the use of down-hole gamma-logging, may be ineffective. Recent studies on reduction of U4+ by bacteria and observation of enhanced U in saline ponds suggests that bacterial reduction maybe an alternative mechanism for formation of U deposits in palaeochannels. Such a model may assist to focus exploration into more favourable areas.

Molecular Geomicrobiology.: J. F. BANFIELD, J. CERVINISILVA, AND K. M. NEALSON, EDITORS. 294 Pp. Mineralogical Society of America, Reviews in Mineralogy and Geochemistry. Volume 59. 2005. ISBN: 093995071-5. US$40.00.

The field of geomicrobiology is rapidly expanding as both geoscientists and biologists have come to recognize the importance of both disciplines for understanding nature’s complexities. Bacteria and other microorganisms are extremely important in their direct and indirect effects on geochemical cycling of metals and organic matter throughout Earth history. Indeed, classically trained microbiologists are currently being hired by geoscience departments, which will ensure future beneficial collaborations in the field of geomicrobiology. Southam and Saunders (2005) reviewed much of the recent geomicrobiology literature in Economic Geology , trying to highlight important advances that might impact ore-forming processes and, perhaps, even geochemical prospecting techniques. No doubt, bacteria are directly responsible for forming a number of types of low-temperature ore deposits such as roll-front uranium deposits and Superior-type iron formations. In addition, bacteria have produced reduced sulfur for some types of higher-temperature deposits such as sediment-hosted Zn-Pb deposits. Bacteria have even been found as fossils in sulfide minerals. Thus, there are many aspects of bacterial metabolism that warrant understanding by economic geologists. Furthermore, as we explore for more deeply buried mineral deposits below the water table, exploration geochemists are going to have to factor in the effects of microbial processes in controlling dispersion of metals away from ores …

Association of Exploration Geochemists (AEG)

Association of Exploration Geochemists (AEG)

Evolution and remediation of acid sulphate water associated with mining

When the Association of Exploration Geochemists (AEG) was organized in 1970, the world of mining geochemistry was all about finding and understanding mineral resources. At that time, relatively little attention was placed by society at large on the geochemical impacts of mining. Where noted, such impacts were generally considered an unfortunate, but unavoidable, consequence of extraction. Now in 2001, times have certainly changed. The growth and maturation of the AEG has been paralleled by an international emergence of environmental awareness and values. This movement has changed the face of the minerals industry and …

Element mobilities and the Australian regolith - a mineral exploration perspective

Much of the Australian regolith ranges from Palaeogene to Late Cretaceous in age or even older, contrasting with the relatively young landscapes of the Northern Hemisphere. Hence, many imported geochemical exploration methods are unsuitable for Australian environments; this has led to successful homegrown innovation. Exploration geochemistry seeks to track geochemical anomalies arising from concealed ore deposits to their source. Much is known about element associations for different types of ore deposits and about observed patterns of dispersion. Element mobility in a range of Western Australian environments is discussed, drawing on field examples from the Mt Percy and Boddington gold mines and the Yandal greenstone belt, with reference to the effect of modern and past weathering regimes and the influence of groundwater on element mobility. Soil biota and vegetation affect Au mobility in the regolith, but specific processes, scale and environmental factors are unknown. Possible future synergies between biogeochemical or environmental research and regolith exploration geochemistry include determining the fundamental biogeochemical processes involved in the formation of geochemical anomalies as well as environmental concerns such as regolith aspects of land degradation. Exploration geochemists must study the work of biogeochemical and environmental researchers, and vice versa. There should also be collaborative research with regolith scientists and industry.

Reproducibility of overbank sediment sampling in Greece and Norway

Reproducibility of overbank sediment sampling was tested in twenty-nine floodplains in Europe, ten in Greece and nineteen in Norway, by the collection of duplicate pairs of samples. Distances between duplicate sites in Greece were 60 to 100 m, and in Norway 100 to 200 m. In Norway the same nineteen floodplains were sampled by a second team for the purpose of investigating differences in sampling variability and technique. Total element contents were determined in all samples. Paired samples were compared by calculating Spearman's rank correlation coefficient on the raw analytical data, and one-way analysis of variance on the log-transformed data. Pairs of overbank sediment samples collected from different floodplains by the Hellenic team and the first Norwegian team showed high rank correlations and low within-basin variability (sampling and analytical variance). Statistical results of the second Norwegian team were comparatively poorer; both Spearman's rank correlation coefficient and one-way analysis of variance, showed very low positive to negative correlations and high within-basin variation, suggesting a non-uniform distribution of elements in the Norwegian overbank sediment sequences and differences in the sampling technique of the two teams. Nevertheless, careful location of sample sites, as has been done by the Hellenic and the first Norwegian teams, reduces considerably the sampling variability, and the overall sampling reproducibility for most elements is very good for distances up to 100 m in Greece and 200 m in Norway, provided correlated overbank sediment sequences are sampled. The implication of this study for multinational regional geochemical mapping is that overbank sediment sampling must be carried out by well-trained professional teams of exploration geochemists, and where possible by one sampling team for the whole country.

Cold dissolution method for the determination of uranium in various geological materials at trace levels by laser fluorimetry

A cold dissolution procedure for the determination of uranium in various geological materials like rocks, minerals, soils etc., has been described. Samples are allowed to react with HF and HNO 3 at room temperature overnight. Boric acid is added to complex excess fluoride ions. From the clear solution thus obtained, uranium is determined directly in laser fluorimeter after the addition of fluorescence enhancing reagents. The results of few standard reference materials analysed by the present method agree with the certified values. This methodology does not require platinum or teflon ware, exhaust system and time consuming solvent extraction step. Hazardous acid vapours are not left in air, so there is no air pollution. Chemicals consumption is minimal. Therefore the method is economical. The method can be employed for high sample throughput which is the prerequisite for exploration geochemists.

Analysis of Metals in Condensates and Naphtha by Inductively Coupled Plasma Mass Spectrometry

Condensates and naphtha are petroleum samples with largely gasoline-range components (C5–C10). Metal organic complexes are source inherited components of oils which are associated with the polar components and asphaltenes of oils. Because of the very low levels of biomarkers such as hopanes and steranes in condensates, they present a special correlation problem. Geochemically significant metals, such as V and Ni, can be measured in some condensates using conventional Meinhardt–Scott chamber inductively coupled plasma mass spectrometry (ICP-MS). In order to increase the sensitivity and the range of condensates which can be analysed, the Cetac U-6000 AT Ultrasonic nebuliser–desolvation system was tested. The Cetac system improved the sensitivity for V and Ni by a factor of about 40. Valuable information for relating these difficult samples to each other and to heavier oils in a basin can thus be supplied to exploration geochemists. The influence of organic matrix on the analytical signal was investigated. Matrix effects are more pronounced for the Cetac system than for the conventional ICP-MS system. For both systems, the use of an In internal standard was found to be necessary for compensating for differences in nebulisation and combustion behaviour caused by variations in the nature of the sample. The use of ICP-MS for the analysis of toxic metals such as Hg and Pb in condensates and naphthas is also discussed. The results are compared with those obtained using electrothermal atomic absorption spectrometry and cold vapour atomic absorption spectrometry in an interlaboratory study of naphthas. Conventional Meinhardt–Scott chamber ICP-MS provided good accuracy and precision of analysis compared with the other techniques during this study. Volatile species such as Et4Pb and Me2Hg were lost in the desolvation unit when using the Cetac system. Volatilisation effects were not observed when using the conventional Meinhardt–Scott chamber ICP-MS system.

National geochemical mapping and environmental geochemistry — progress in China

The Regional Geochemistry-National Reconnaissance (RGNR) Project of China was initiated in 1978. The aim of the project is to sample systematically various types of surface materials, determine the contents of 39 elements in the samples by multi-element, multi-method analytical systems and present the spatial variation of the elements as geochemical maps of different scales. This project was originally mineral-exploration oriented, but the voluminous data set can also be utilized to provide an overview of the environmental problems in China by identifying problem areas quickly and at low cost. An extension of the project comprises systematic mapping of large alluvial plains totalling more than 1 million km 2 and detailed mapping of urban districts in China using the mapping techniques developed during these twelve years by Chinese exploration geochemists. The lack of communication between environmental geochemists and exploration geochemists is now being rapidly amended. The geochemical maps, now covering 4.6 million km 2 of Chinese territory, serve as a basis for new cooperative research by scientists of different disciplines.

Effects of refinery processes on biological markers

Concentrations of biomarkers remaining in straight-run refinery products of crude oil feedstock are mainly controlled by relative volatility. Thermal cracking exerts a second-order control on biomarker compositions of these products. Factors controlling biomarker concentrations and distributions in processed materials are more complex and include volatility, thermal stability, generation from heavier precursors, and the effects of catalysts and hydrogen pressure. Differential volatility of compounds within each biomarker class and sharp temperature gradients defining each distillation cut complicate interpretation of source- and maturation-dependent biomarker parameters used by petroleum exploration geochemists

Workshop report: Design and interpretation of geochemical surveys

The purpose of the workshop was to review central issues concerning geochemical exploration program planning and execution. One and one-half days were devoted to the workshop, prior to the 13th IGES. Approximately 25 registrants attended, representing a broad spectrum of background from students to professional exploration geochemists. The meeting was more a short course than a true workshop. Most of the scheduled time was allocated to prepared presentations and discussion more commonly took place at breaks or the end of sessions. S.J. Hoffman (Prime Geochemical Methods, Vancouver), O.P. Lavin (Newmont Exploration, Denver) and L.G. Closs (Colorado School of Mines, Golden ) were the speakers. The topics addressed were: ( l ) design of geochemical surveys--an overview, (2) chemical analysis, (3) basic statistical data interpretation, (4) sampling and sampling design, (5) multivariate statistical applications, (6) microcomputer applications, (7) modeling and models, (8) budgeting--case histories and (9) summary--future trends. Design and planning concepts, including the problem solving approach, were reviewed in the context of the objective of exploration-discovery (Closs). This provided a framework for assessing project constraims, discriminating practicar' vs theoretical geochemistry based upon their relationship to exploration objectives, and focusing on end results, rather than means. Most agreed that much of this was motherhood but acknowledged that it was valuable to revisit these concepts as fuzzy thinking and/or violation of fundamental assumptions constitute the single greatest controllable sources of project failure. Chemical analysis was considered in its broadest context, from definition of survey objectives through to interpretation and presentation of results (Hoffman). The audience was asked how many used multi-element data and how many plotted all their data? Few responded affirmatively. Hoffman pointed out the advantage of full utilization of multi-element data packages, which included contribution to basic geological mapping, confident elimination of ground, as well as the traditional anomaly identification. Full utilization of the expanded trace-element suites cost-effectively available today will require both greater reliance on computers to efficiently present data and a

Novel Applications of Light Hydrocarbons Chemistry in Petroleum Exploration

The light hydrocarbons in petroleum are products of a kerogen-specific catalytic process. The catalysts are believed to be the transition metals entrained in kerogen. The process is controlled by the metals in the active sites and the kerogenous organic structures surrounding the active sites. Different catalytic sites are suggested to yield distinct distributions of light hydrocarbons. The author recognizes three dominant (primary) distributions, with all other distributions adequately represented by some linear combination of the three primary distributions. Three catalytic sites, therefore, can be associated with the generation of light hydrocarbons. He introduces a simple and inexpensive procedure using cross plots of various product ratios to correlate oils and source rocks. It has proven to be a remarkably articulate and powerful tool for deconvoluting diverse oils into genetic groups. The light hydrocarbons are also indicators of oil-generation temperature and other physical parameters associated with oil generation. The analysis of light hydrocarbons from this perspective is new. It provides the exploration geochemist with a novel technique for gaining insight into the fundamental chemistry of petroleum generation.

Association of exploration geochemists student paper competition

Association of exploration geochemists student paper competition

Instrumental neutron activation analysis as an analytical technique for gold exploration

Abstract 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.

S. J. Hoffman. Writing Geochemical Reports: Guidelines for Surficial Geochemical Surveys Rexdale, Ontario (Assoc. Exploration Geochemists: Special Vol. No. 12), 1986. 29 pp. Price $ (US) 5.00 or $ (Cdn) 7.00 including postage (from Assoc. Explor. Geochemists, PO Box 523, Rexdale, Ontario M9W 5L4, Canada).

S. J. Hoffman. Writing Geochemical Reports: Guidelines for Surficial Geochemical Surveys Rexdale, Ontario (Assoc. Exploration Geochemists: Special Vol. No. 12), 1986. 29 pp. Price (Cdn) 7.00 including postage (from Assoc. Explor. Geochemists, PO Box 523, Rexdale, Ontario M9W 5L4, Canada). - Volume 52 Issue 367

I. L. Elliott B. W. Smee, Eds. Geoexpo/86: Exploration in the North American Cordillera (Association of Exploration Geochemists), 1987. Rexdale, Ontario x+220 pp. Price (Post free from A.E.G., P.O.B. 523, Rexdale, Ontario, M9W 5L4 Canada). $ Canadian 45.00

I. L. Elliott B. W. Smee, Eds. Geoexpo/86: Exploration in the North American Cordillera (Association of Exploration Geochemists), 1987. Rexdale, Ontario x+220 pp. Price (Post free from A.E.G., P.O.B. 523, Rexdale, Ontario, M9W 5L4 Canada). $ Canadian 45.00 - Volume 52 Issue 367