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The Mount Read Volcanics (MRV) of western Tasmania is a belt of Middle to Late Cambrian submarine volcanics and volcaniclastics and one of the major base and precious metal provinces within Australia. Exploration success in the MRV has been in decline in recent years due to a variety of challenges including intensely altered rocks with complex stratigraphy and lithofacies variation, and a lack of accessible outcrop. As a result, local and regional mapping of the MRV is often restricted to Group-level stratigraphy, rendering geological mapping ineffective for identifying decametre-scale mine stratigraphy. Surface rock chip and drill hole samples were collected and analysed using commercially available geochemical assays to create a regional geochemical dataset of the MRV, covering the entire province and all major stratigraphic units. From these data, a lithogeochemical methodology was developed, utilizing Ti/Nb and V/Sc systematics that effectively characterizes the samples according to composition and magmatic processes. This method is shown to be robust to biases due to alteration and lithofacies, eliminating the need for highly selective sampling or extensive data filtering. To demonstrate the utility of this method in an exploration context, data from the K-lens of the Rosebery polymetallic volcanic-hosted massive sulfide (VHMS) deposit was used as a case study. Using Ti/Nb–V/Sc systematics, a rock composition classification was developed that allowed for discrimination of the footwall, hanging wall and host stratigraphy of the Rosebery mine sequence. A geochemical fingerprint for the footwall stratigraphy to mineralization was developed, and by correlating this signature to the regional unclassified samples, geochemical analogues for the Rosebery footwall were readily identified. This approach rapidly reduces the exploration search space and provides valuable information for future mineral exploration. The methodology is applicable in other terrains; however, appropriate orientation studies are required to investigate potential biases due to lithofacies, alteration and mineralogical variability. [ABSTRACT FROM AUTHOR]

At the end of the 19th century, classical geochemistry arrived in Brazil through Henri Gorceix, being primarily used in his studies of mineralogy and petrology. Meanwhile, exploration geochemical arrives later, in the mid-20th century. But it was only in the late 1960s that systematic survey at the national level began, starting with the creation of CPRM - Geological Service of Brazil, culminating in over 50 years of uninterrupted activities, providing coverage of the entire country at various scales: global (7.3%), national (6.2%), regional (22.7%), and local (2.3%). Throughout this period, 681 projects were carried out and a variety of sample matrices were collected, such as stream sediment (226,792), soil (122,202), heavy-mineral pan concentrate (107,959), rock (56,807), among others (8,258), totaling 522,018 samples so far. All this collection has been progressively recovered, compiled, and organized into a robust public database (open access), developed by CPRM - Geological Service of Brazil. More recently, high-density geochemical surveys were conducted in partnership with the China Geological Survey with the aim of comparing analytical and sampling methodologies. For the future (until 2050), two main actions are planned: 1) an expectation of an increase in the coverage of high-density prospecting surveys, ranging from 951,386 km² (restrictive scenario: 11.2% of Brazilian territory) to 2,204,778 km² (favorable scenario: 25.9% of Brazilian territory); 2) a forecast of Brazil's participation in the Global Geochemical Baselines Program, where sampling will be subdivided by regions – North (736), Central-West (225), Northeast (305), and South-Southeast (343) – totaling 1,609 sampling cells.

Since the 1970s, till geochemical and indicator mineral methods for mineral exploration, provenance studies and environmental research in glaciated terrain have been developed, tested and refined. This review summarizes these methods, focusing on field and laboratory methods for till geochemical, indicator mineral and boulder surveys. This review of protocols is intended as a guide for the mineral exploration industry and publicly funded agencies. It summarizes till as a sample medium, and describes the formation of glacial dispersal trains, along with methods for till sample collection, sample processing, matrix geochemistry, indicator mineral analyses, quality assurance/quality control procedures and data reporting and interpretation. The methods described here can be used to conduct reconnaissance- to deposit-scale till sampling surveys to assess mineral resource potential and establish environmental baselines. Supplementary material: Appendix A – Photographs of till types described in text; Appendix B – Logistical and geological factors to consider in till sample survey design; Appendix C – Photographs of glaciate terrain types described in text; and Appendix D – Till sample processing and analysis flow charts are available at https://doi.org/10.6084/m9.figshare.c.6786087 Thematic collection: This article is part of the Reviews in Exploration Geochemistry collection available at: https://www.lyellcollection.org/topic/collections/reviews-in-exploration-geochemistry [ABSTRACT FROM AUTHOR]

Stream sediment surveys support early-stage reconnaissance mineral exploration and regional assessment programmes, enhanced by recent improvements in analytical method detection limits, continuously improving mineral chemistry, and new approaches to the interpretation of geochemical data. Sediment surveys may be used to predict catchment basin lithology, mineralization type based on pathfinder geochemistry, and geological features based on indicator mineral chemistry. Sediment surveys that target a finer-fraction sediment sample led to the discovery of the La Colosa gold deposit, Colombia. The Batu Hijau porphyry Cu–Au deposit in Indonesia was discovered based on an anomalous clay-sized fraction sample 12 km downstream. In an arid region with poorly developed drainages and minor topographic relief, the Ag-base-metal Navidad District in Argentina was discovered with clay-fraction sediment geochemistry. Heavy mineral concentrate (HMC) sediment surveys that include mineral chemistry determinations have led to global diamond discoveries. HMC surveys contributed to discovery of the Ring of Fire Ni–Cu–PGE and chromite district, Ontario, Canada. Discoveries and geochemical mapping can assist advancement of the application of stream sediment geochemistry in those global areas for which lithologies and deposits are exposed. Stream sediment surveys continue to be one of the most cost-effective geochemical methods for covering large areas for mineral exploration. Thematic collection: This article is part of the Reviews in Exploration Geochemistry collection available at: https://www.lyellcollection.org/topic/collections/reviews-in-exploration-geochemistry [ABSTRACT FROM AUTHOR]

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Rare earth elements (REEs), a significant subset of critical minerals, play an indispensable role in modern society and are regarded as "industrial vitamins," making them crucial for global sustainability. Geochemical survey data proves highly effective in delineating metallic mineral prospects. Separating geochemical anomalies associated with specific types of mineralization from the background reflecting geological processes has long been a significant subject in exploration geochemistry. The processing of high-dimensional, non-linear geochemical survey data necessitates a systematic framework to address common issues, including missing values, the closure effect, the selection of appropriate multivariate analysis methods, and anomaly detection techniques in order to detect geochemical anomalies associated with mineral occurrences. The Curnamona Province in South Australia is considered an emerging REE province with significant REE mineralization potential. In this study, we use data from this region to evaluate the performance of a novel machine learning-based framework that incorporates data pre-processing, multivariate statistical analysis, and anomaly recognition to address challenges such as missing data, noise interference, data imbalance and high non-linearity. We utilize lithogeochemical data to map potential greenfield regions of REE mineralization. The primary advantages of our framework lie in its provision of an effective random forest-based data imputation method, utilization of isometric log-ratio transformation to eliminate the closure effect, and reduction of the impact of outliers on data interpretation through robust principal component analysis. Additionally, the framework utilizes a deviation network to learn anomaly scores from complex, non-linear data under imbalanced data conditions, identifying geochemical anomalies associated with REE occurrences by leveraging prior knowledge rather than those caused by data noise or anthropogenic factors. The anomalous areas identified by this framework delineate all known REE deposits and extend to the surrounding regions. Furthermore, a close spatial coupling relationship exists between these strongly anomalous areas and the felsic granite intrusions. The comprehensive workflow for processing geochemical data proposed in this study can effectively address common challenges in the geochemical exploration of critical minerals. The identified geochemical anomalies can provide important clues for subsequent exploration. • A novel framework designed to detect geochemical anomalies linked to REE mineralization. • An effective random forest-based method for data imputation, proficient in handling missing values. • Robust principal component analysis that minimizes the impact of outliers on data interpretation. • A deviation network approach that effectively identifies geochemical anomalies, even with imbalanced datasets. • Geochemical anomaly mapping that demonstrates a strong correlation with known REE mineral occurrences. [ABSTRACT FROM AUTHOR]

The Geological Survey of Canada carried out reconnaissance-scale to deposit-scale geochemical and indicator-mineral surveys and case studies across northern Canada between 2008 and 2020 as part of its Geo-mapping for Energy and Minerals (GEM) program. In these studies, surficial geochemistry was used to determine the concentrations of up to 65 elements in various sample media including lake sediment, lake water, stream sediment, stream water, or till samples across approximately 1 000 000 km2 of northern Canada. As part of these surficial geochemistry surveys, indicator mineral methods were also used in regional-scale and deposit-scale stream sediment and till surveys. Through this program, areas with anomalous concentrations of elements and/or indicator minerals that are indicative of bedrock mineralization were identified, new mineral exploration models and protocols were developed, a new generation of geoscientists was trained, and geoscience knowledge was transferred to northern communities. Regional- and deposit-scale studies demonstrated how transport data (till geochemistry, indicator mineral abundance) and ice-flow indicator data can be used together to identify and understand complex ice flow and glacial transport. Detailed studies at the Izok Lake Zn–Cu–Pb–Ag VMS, Nunavut, the Pine Point carbonate-hosted Pb–Zn in the Northwest Territories, the Strange Lake REE deposit in Quebec and Labrador as well as U–Cu–Fe–F and Cu–Ag–Au–Au IOCG deposits in the Great Bear magmatic zone, Northwest Territories demonstrate new suites of indicator minerals that can now be used in future reconnaissance- and regional-scale stream sediment and till surveys across Canada. [ABSTRACT FROM AUTHOR]

Investigation on the behavior of elements in the soil is important both in exploration and environmental geochemistry studies. Rare earth elements (REEs) are the most useful among all trace elements. REE studies have shown that they have important applications in igneous, sedimentary, and metamorphic petrology. This work aims to investigate the relationship of these elements with one another and the behavior of the major oxides and trace elements with REEs. Soil samples were obtained from the alteration site possibly related to mineralization and were analyzed for major oxides, trace elements, and REEs. The relationships between the major oxide–trace element/heavy metal and REE were investigated by statistical methods, such as descriptive statistics, correlation coefficient, and principle component analysis. According to the correlation coefficient matrix, light REEs (LREEs) showed weak to moderate negative correlation with MgO and MnO and moderately positive correlation with SiO2 and K2O. No association was detected between the heavy REEs (HREEs) and the main oxides, but a strong positive correlation with LREEs was observed. For the trace elements, LREE showed a weak positive correlation with Ba and Sn and moderate to strong positive correlation with As, Hf, Nb, Rb, Ta, Th, U, W, and Zr. They also displayed weak to moderate correlation with Sc, Co, Zn, Ni, and V. HREE showed weak to moderate positive correlation with Ni, Cs, Ga, Hf, Th, Zr, As, and LREE. Although REEs exhibited no direct correlation with Au and Ag, they showed a good correlation with some trace elements that are related to hydrothermally altered products. This study showed that REEs can also be used in exploration and environmental geochemistry studies by exploiting the relationship between REEs and other trace/heavy metal elements. [ABSTRACT FROM AUTHOR]

Whole rock lithogeochemical data from the andesite rocks which host low-sulfidation epithermal gold veins in the Waihi district, New Zealand have been used to interpret hydrothermal alteration processes that variably altered the andesite rocks. The andesite host rocks are interpreted to have similar primary chemical compositions throughout the Waihi area, as reflected in similar ratios of immobile elements (eg Zr, Ti and other high field strength elements). The geochemical data reveal that elevated K/Al ratios occur in rocks proximal to low-Au–Ag deposits, reflecting adularia alteration in the host rocks associated with the upflowing hydrothermal fluids. Silicification of host rocks is achieved both by the addition of SiO2, as well as the destruction of plagioclase (reflected in the loss of CaO and Na2O). The rocks have been variably altered, with calcite and pyrite abundance reflecting the addition of carbon and sulphur. Pathfinder element (eg As, Sb) concentrations are variable across the district, with high pathfinder element concentrations interpreted to reflect proximity to hydrothermal fluid flow. Together, the results provide a district-scale overview of hydrothermal alteration at Waihi, and emphasise the utility of lithogeochemistry for classifying and quantifying hydrothermal alteration that can then be used to interpret hydrothermal processes and assist mineral exploration. [ABSTRACT FROM AUTHOR]

As a cross-disciplinary scientific domain, a great deal of research on landscape geochemistry has been conducted since its establishment. However, the used methods lack the ability of revealing the relationships of landscape geochemistry with other sciences, and the obtained knowledge is thus fragmented and isolated. In this study, the state-of-the-art regarding the applications of relatively new geospatial technologies including fractal theory, geographic information system and remote sensing to landscape geochemistry was reviewed and analyzed to provide deep insights of current research and a roadmap for furthering the development of landscape geochemistry as a cross-disciplinary discipline. The results showed that substantial research on the applications of fractal theory, GIS and RS technologies for analyzing the processes and data of landscape geochemistry has been conducted by using the advantages of the geospatial technologies. However, the great challenges still exist when the geospatial technologies were individually utilized due to the limitations of the technologies themselves and the complexity of landscape geochemistry. In the end, opportunities and challenges for advancing the further studies of landscape geochemistry were discussed in detail and new directions of studying landscape geochemistry using multidisciplinary or integrated approaches to enhance understanding the relationships among the relevant disciplines were suggested. [ABSTRACT FROM AUTHOR]

Local singularity analysis (LSA) has been proven to be an effective tool for identifying weak geochemical anomalies. The common practice of grid-based LSA is to firstly interpolate irregularly distributed observations onto a raster map by using either kriging or inverse distance weighting (IDW). The inherent nature of the weighted moving averaging of these methods typically subjects the interpolated map to a smoothing effect. Additionally, the traditional procedure did not allow for uncertainties on the values of geochemical attributes at unsampled locations. As such, these two aspects might affect LSA results. This paper presents a hybrid method, which combines sequential Gaussian simulation and grid-based LSA to identify geochemical anomalies. A case study of processing soil samples collected from the Jilinbaolige district, Inner Mongolia, China, further illustrates the hybrid method and helps compare the results with those from kriging-based LSA. The findings indicate that (1) the uncertainties of values at unsampled locations could affect the results of grid-based LSA, and (2) singularity exponents from kriging-based LSA roughly represent the trend (median) of singularity exponent distributions from simulation-based LSA, but the latter can also provide a measure of uncertainty of singularity exponent propagated from the uncertain values at unsampled locations, and (3) the procedure combining simulation-based LSA and analysis of distance is a feasible way for identifying geochemical anomalies with uncertainty being considered. The anomaly probability map obtained can provide a more generalized perspective than interpolation-based LSA to delineate anomalous areas. [ABSTRACT FROM AUTHOR]

The study presents data from a geochemical till survey conducted in the Oppdal/Berkåk area of Central Norway. Using a 1 × 2.5 km grid, 877 samples were taken to cover a 2000-km2 survey area (one site per 2.2 km2). The samples were air dried, sieved to <2 mm and analysed for 51 elements following an aqua regia extraction. A number of geochemical anomalies, related to lithology, a prominent fault zone, mineralization or environmental processes, are delineated for a large number of elements. Four main anomalies are outlined. A large, elongated (40 km long) multi-element anomaly is associated with normal faults and adjacent rhyolitic-andesitic rocks occurring in the area. Elements associated with gold (As, Sb) form an anomaly on the central high-altitude area just to the east of the fault related anomaly. Two further areas that display high concentrations for many elements are located around Orkelsjøen and Soknedal. Climatic/topographic conditions have a strong influence on the Hg and Se distribution. Several areas that display geochemical anomalies, where more detailed studies could be conducted were also identified. [ABSTRACT FROM AUTHOR]

In the last thirty years, portable X-ray fluorescence (pXRF) has grown from prototypes to being a key technique for field geochemical analyses, especially for mining and environmental applications. This technology provides real-time or near real-time decision support for operational field decisions (exploration, mining, site remediation or waste management), provides a cost-saving alternative to classical laboratory analysis programs, and deals efficiently with remote or harsh field conditions. The ability to rapidly collect a large number of samples and replicate analyses facilitates acquisition of higher data density compatible with geostatistics. pXRF can be used profitably for sample screening and selection tasks, dynamic sampling plans based on field observations and measurements, grid mapping of a site and determining relative element abundance. In waste management and remediation, pXRF is used to identify unknown waste composition, and verify waste loads before disposal or treatment. In all applications, having robust QA/QC plans and systematic laboratory controls on selected samples are essential for ensuring reliable measurements. The best overall results are usually achieved through a clever combination of field (pXRF) and lab data, with pXRF providing the bulk of the data at low cost, on larger data sets and potentially with better reliability than lab-based campaigns based on a limited number of samples. [ABSTRACT FROM AUTHOR]

This paper presents and validates a workflow that provides for the rapid collection of reliable and robust portable X-ray fluorescence (pXRF) data in a regolith-dominated exploration setting. The analysis of regolith material by pXRF is challenging because of its variable Fe content (e.g. 0 to >70 wt%) that results in large matrix effects, which can be mitigated with appropriate standards. Here, we present a dataset from the Western Mount Isa Inlier, Queensland, Australia, comprising soil, lag, rock and rotary air blast (RAB) samples. In the soil dataset, comparison of the laboratory and pXRF datasets for Cu, Pb and Zn haveR2> 0.9, and Cu and Zn fall within 2% of the laboratory data, while Pb is 77% less than the corresponding laboratory analyses. Iron, Al, K and Ca by pXRF perform reasonably well when compared with the laboratory data (R2= 0.59 for Al,R2> 0.9 for Fe, K and Ca, <25% variation from the laboratory data), while Mn, Rb and Sr have very good correlations (<8% variation) withR2> 0.94. Titanium, Zr, Ni, Cr and As have poorer comparisons. Overall, the RAB dataset shows similar trends with Cu overestimated by 17%, Zn underestimated by 4% and Pb overestimated by 69%;R2for all elements is >0.92. Since no suitable standards are available, the solid rock dataset was uncorrected; despite this limitation, the dataset shows good correlations with the laboratory data for many elements, and Cu is overestimated by 9.8% with anR2= 0.87. The poor analytical performance of Pb in all datasets is associated with erroneous Bi concentrations being reported by the pXRF unit. When high Fe and Pb amounts are present in a sample, erroneous Pb and Bi concentrations are reported, owing to a pile-up of the Fe Kαpeak (6.405 keV) at ∼12.8 keV, which is proximal to the Pb Lβ(12.614 keV) and Bi Lβ(13.023 keV) peaks. Despite the care that is required in validating data, by using pXRF there is substantial opportunity for dynamic exploration campaigns in regolith-dominated terranes with rapid turnaround times, additional elements that may not otherwise be analysed for and low analytical costs. Decisions to stop, continue or infill drill holes while the drill rig is present can be made in near-real time, and not after laboratory results are available and the drill rig has left the area. [ABSTRACT FROM AUTHOR]

Results of the project "Mongol Altai-50"of the Czech Development Cooperation with Mongolia, were successfully defended before the Mongolian Stratigraphic Commission in September 2016, in Ulan Bator. The project was carried out during 2013-2016, and experts from four countries participated in its implementation. The project was located in western Mongolia in the Hovd Department and the districts (soums) of Munhkhairkhan, Mankhan, and Zereg (Fig. 1). The western part of the Mongolian Altai Range has a mostly character of stepped plateaus, some of which rise above 4000 m a.s.l. There is a different morphology in the lower and peripheral parts of the mountain rejuvenated by deep faults or in places with former glaciation. Rocky ridges and deep gorges and canyons originated due to intensive feedback erosion (Figs. 2a-h). Five base geological maps at a scale of 1 : 50,000 (sheets L_46_28V, L_46_28G, L_46_29V, L_46_29G and L_46_30V) covering an area of 1770 km2 were compiled during the project implementation. The field-work in Mongolia was realised during three main campaigns in 2013-2015, each year 2-3 months long (Figs. 3 a-d). The project also had an educational significance, which involved training of 19 young Mongolian geologists in the field (Figs. 4 a-d). The Final Report (Žáček et al. 2016a) presents 43 new geochronological data, new insights into petrology, geochemistry, mineralogy, structural geology, sedimentology and palaeontology, and also includes a chapter on economic geology, and 50 applied maps showing results of exploration geochemistry. A set of geological maps represents an instructive E-W profile across an area on the contact of Lake, Altai and Hovd terranes (zones), which are part of the Central Asian orogenic belt (CAOB, Badarch et al. 2002), Fig. 5. These terranes are a collage of Lower Palaeozoic volcanic arcs, accretionary wedges, and back-arc basins separated from one another by deep-seated faults. The generally NW-SE trending and relatively steeply dipping lithological contacts, deformational fabrics and morphological pattern are common geological feature of a western Mongolian Altai. Structural record in the rocks is a result of polyphase development of three ductile deformational phases portrayed in varying intensity. The youngest deformation phase is associated with penetrative hydrothermal event, which produced abundant epidote and chlorite, ubiquitous in whole research area. Previous maps of the area on the scale 1 : 200,000 were given by Luvsandanzan et al. (1999) and Baatarhuyag and Gansukh (1999), general and local stratigraphy by Ariunchimeg et al. (2012). The Lake Zone in the E of the research area is formed by mid-Cambrian volcano-sedimentary Baatar Formation. It is intruded in several stages by the Togtokhinshil Igneous Complex, the age of which was newly determined to be Middle Ordovician (gabbros and diorites), and Upper Devonian (granites), Soejono et al. (2016). Thick sequence of folded Lower Palaeozoic sediments prevails in the Hovd and Altai zones. The sediments are ascribed to Zuun Nuruu (Ordovician), Tsetseg (Silurian) and Sagsai (Lower Devonian) formations (see Fig. 5). The age of these sediments decreases generally westwards, but the stratigraphic record is complicated by strong deformation when the same part of the sequence may be repeated. The sediments occur in several developments: deep basinal (shales), common flysh, shallower calcareous flysh, minor volcano-sedimentary, and shallow psammitic. Fossils are rare and poorly preserved, and usually indicate a broader age. The following groups of fossils were found: Graptoloidea, Anthozoa, Crinoidea, Brachiopoda, Bryozoa, Cephalophoda and abundant ichnofossils.(...) [ABSTRACT FROM AUTHOR]

This paper briefly reviews the application of geoinformatics in exploration geochemistry from the perspective of spatial analysis and visualization, and demonstrates the advantages of geoinformatics in exploring geochemical patterns and identifying geochemical anomalies. In particular, the application of geoinformatics to geochemical mapping, recognition of geochemical anomalies and simulation of geochemical patterns are discussed. The benefits of geoinformatics include: (1) overlay of geochemical data on a geological map, which helps geochemists to understand spatial geochemical patterns and visualize geochemical anomalies; (2) local neighbourhood spatial analysis, which considers the local spatial structure of geochemical patterns, as a powerful tool to identify weak geochemical anomalies; and (3) geochemical patterns simulation based on geological constrains, which helps to understand geological processes. Future researches should focus on development and application of various functions for processing geochemical data in a GIS to promote the progress of geoinformatics in both geochemical exploration and environmental studies. [ABSTRACT FROM AUTHOR]

The regolith in the Mt Isa region of Queensland consists of a variety of saprolites and duricrusts developed on Proterozoic basement rocks and fresh to weathered Mesozoic, Tertiary and Quaternary cover, all of which has impeded base metals exploration. This paper presents an overview of some of the regolith-geochemical work conducted in the Mt Isa region as part of an industry-supported three year CRC LEME/AMIRA Project. A complex weathering and landscape history has produced a landscape of (a) continuously exposed and exhumed basement rocks that have undergone varying intensities of weathering and partial stripping; (b) weathered and locally eroded Mesozoic cover sequences and (c) areas with younger transported cover concealing basement and Mesozoic cover. Various regolith sample media have been evaluated at a number of prospects and deposits which represent different regolith-landform terrains and landscape history. Geochemical dispersion processes and models are presented and false anomalies explained. Where ferruginous duricrust or ferruginous nodular gravel are preserved on weathered bedrock on an eroded plateau, they exhibit large (> 500 m) multi-element (As, Pb, Sb) dispersion haloes and are useful sampling media. Dispersion haloes in truncated profiles on weathered bedrock covered with colluvium are restricted, are limited to tens of metres from subcrop of the source, and contrast to the extensive anomalies in ferruginous duricrust and nodules. Geochemical exploration in covered areas depends on the possible presence of dispersion through the sediments or leakage along faults or fractures, but may be complicated by high metal backgrounds in the sediments themselves. Some of the most prominent anomalies occur in ferruginous materials and soils representing emergent residual terrain developed on Mesozoic sediments. These are largely due to weathering of sulfide mineralization that continued during submergence in a marine environment, with hydromorphic dispersion into the sediments as they accumulated. Multi-element (Cu, As, Zn, Sb, Au) anomalies occur in basal sediments and at the unconformity, due to a combination of clastic and hydromorphic dispersion and represent a useful sample target. Metal-rich horizons in weathered sediments, higher in the sequence, can also be targeted, particularly by specifically sampling ferruginous units and fragments. However, these are less certainly related to mineralization. Zinc and Cu, concentrated in Fe (and Mn) oxides at redox fronts, may be derived by leaching from the sediments with concentration in the sesquioxides, and be unrelated to any proximal basement mineralization. In all these regolith-dominated terrains, a clear understanding of local geomorphology, regolith framework, topography of unconformities and the origins of ferruginous materials is essential to sample medium selection and data interpretation. [ABSTRACT FROM AUTHOR]

A microorganism of the Marinobacter genus capable of Fe-oxidation at near-neutral pH, both in the presence and absence of oxygen, was found at a depth of 1.4 km in proximity to a Cu-Zn Volcanogenic Massive Sulphide (VMS) deposit, within the Triple 7 mine, Flin Flon, Manitoba, Canada. The microorganism was isolated from saline groundwater emanating from boreholes at that depth, which contained a small microbial community consisting of only two organisms. To examine biogeochemical trace metal cycling in this deep subsurface setting, incubation experiments were carried out with the Marinobacter isolate and mineralized (metal-containing ore) material in batch and column flow-through settings. The activity of the Marinobacter isolate resulted in an increase in the mobilization of major elements (Fe, S) and trace metals (Cu, Zn) from the solid ore material. These results indicate that Fe-oxidation may be an important biogeochemical process in the deep subsurface, which affects the mobilization of Fe and trace elements from buried mineralization. [ABSTRACT FROM AUTHOR]

The response in elemental concentrations and Pb isotopes in various surface media from the Cigar West unconformity-type uranium deposit located at a depth of 450 m were measured to ascertain if element migration from the deposit can be detected at the surface. The media included clay-size fractions separated from the A2, B and C soil horizons, and tree cores and twigs from black spruce ( Picea mariana ) and jack pine ( Pinus banksiana ) trees. Lead isotopes were used to trace any effect on the surface media from the deposit at depth because the 207 Pb/ 206 Pb ratios in the ore are < 0.1, whereas the background values in the basin are > 0.7 and modern anthropogenic Pb from aerosols are near 0.9. The tree cores record their lowest and therefore most radiogenic 207 Pb/ 206 Pb ratios of < 0.7 near the surface projection of the deposit and associated structures, particularly in tree rings that predate any exploration and drilling activity in the area. The median 207 Pb/ 206 Pb ratios increase in the order C, B soil horizon clays, tree cores, A2 soil clays and twigs because of the increasing contribution of common Pb with high ratios from anthropogenic sources that affect the shallowest media the most. Although this anthropogenic Pb as well as that from the background dominates the composition of all media at the surface and the contribution from the deposit at depth is diminished toward the surface, ore-related Pb is still present as a few percent of the composition of pathfinder elements and Pb isotopes. [ABSTRACT FROM AUTHOR]

The Quesnel terrane in the Interior Plateau of British Columbia, Canada, is highly prospective for locating new porphyry deposits; however, the bedrock in this region is obscured by a nearly continuous blanket of till, making mineral exploration challenging. Located within the Quesnel terrane is the Mount Polley deposit. It is an alkaline, silica-undersaturated, Cu-Au porphyry deposit mined by Imperial Metals Corporation. Eighty-six basal till samples were collected for geochemical and mineralogical analyses in the region of this deposit. Ore elements (Ag, Au and Cu), as well as pathfinder element (Hg and Zn) contents in till reflect detrital glacial dispersal from the Mount Polley deposit. The distribution of anomalous mineral counts of andradite garnet, apatite, chalcopyrite, epidote, jarosite and native gold also reflect glacial dispersal from the deposit. Outcrop-scale ice-flow indicators indicate a dominant ice-flow event to the NW that was preceded by a southwestward glacial advance. The element and mineral signatures of the Mount Polley Cu-Au porphyry deposit are dispersed in sub-glacial surface tills up to 12 km in the down-ice (NW) direction. We demonstrate that till geochemistry and mineralogy can serve for mineral exploration of Cu-Au porphyry mineralization in drift covered areas. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides a history of the development of exploration geochemistry in China. Over the past 60years, geochemists in China have made great efforts to develop geochemical exploration methods to cover large areas and even all of China or the whole world, as well as to more elements with emphasis on high sensitivity and accuracy. The new innovative exploration concept and strategies established by the Chinese geochemists have greatly contributed to discoveries of the mineral deposits and to the environmental regulations. [Copyright &y& Elsevier]

Abstract: Robust neighborhood statistics, such as median, median absolute deviation (MAD), and local relative enrichment index (LREI), were used to model spatial variations of geochemical landscapes and to recognize weak geochemical anomalies in covered terrane by means of a case study from the Chaobuleng Fe polymetallic district covered by grassland, in Inner Mongolia (China). The results of this study show that: (1) the robust neighborhood statistics of median and MAD can well discriminate between different geochemical landscapes (with outcrop areas characterized by high values of Fe2O3, and the covered areas linked with a low value of Fe2O3) and delineate the boundaries between the outcrop and covered areas; (2) the LREI can reduce the effects of covers such as soils and grassland on geochemical mapping and identify the weak geochemical anomalies caused by decaying and masking effects of covers; and also (3) the resulting neighborhood statistics are influenced by the size of neighborhood. [Copyright &y& Elsevier]

The solubilities of brandholzite, [Mg(H2O)6][Sb(OH)6]2, and bottinoite, [Ni(H2O)6][Sb(OH)6]2, at 25 °C in water have been measured. Solubilities are 1.95(4) × 10-3 and 3.42(11) × 10-4 mol dm-3, respectively. The incongruent dissolution of romeite, Ca2Sb2O7, and bindheimite, Pb2Sb2O7, at 25 °C in 0.100 mol dm-3 aqueous HNO3 was also investigated. Equilibrium dissolved Sb concentrations were 3.3 ± 1.0 × 10-7 and 7.7 ± 2.1 × 10-8 mol dm-3, respectively. These values have been used to re-evaluate the geochemical mobility of Sb in the supergene environment. It is concluded that the element is geochemically immobile in solution and in soils. This was in part validated by an orientation soil geochemical survey over the Bayley Park prospect near Armidale, New South Wales, Australia. Anomalous soil Sb levels are confined to within 100 m of known stibnite mineralization. [ABSTRACT FROM AUTHOR]

Abstract: The regolith studied here is located at the defunct Areachap mine and the newly discovered Kantienpan Cu–Zn volcanic-hosted massive sulfide (VHMS) deposit, located in the Areachap Group of the eastern part of Mesoproterozoic Namaqua Metamorphic Province. This area is highly prospective for further VHMS discoveries. Paleo and recent weathering of the upper most parts of massive sulfide deposits led to the formation of a gossan zone. Due to semi-arid climatic conditions during the late Cretaceous, affecting the African Land surface, the lowermost units of the Kalahari Group and the underlying floor rocks were calcretized. An approximately 6 m thick calcrete layer formed above the gossan zone and this was later covered by eolian Kalahari sand. Samples were collected from the eolian sand cover in the study areas to determine the best analytical method that would enable recognition of the concealed ore deposits and detect the widest secondary dispersion halo. Mobile metal ions from the finest fraction of the eolian sand samples (<75 μm) were extracted with a NH4EDTA (EDTA) solution. The solution was analysed for Cu, Zn, Pb and Mn by inductively coupled plasma mass spectrometry (ICP-MS). The same grainsize fraction of the original samples was also analysed for comparison purposes by means of X-ray fluorescence (XRF). Results indicate that the ore zone in both areas may be recognized by both partial and total analyses of the eolian sand samples collected, although the calcrete layer, below the sand cover, acts as a partial geochemical barrier. The recognition of the ore zone depends on the regolith forming processes and the thickness of the eolian sand cover. In the Areachap area, with a relatively thick sand cover (in excess of 1 m) above the calcrete layer, the detectable geochemical halo is related to the distribution of the mobile metal ions, and partial extraction (EDTA solution) results define a larger dispersion halo than that, that could be detected by total analysis (XRF). Whereas, in the Kantienpan area with a very thin sand cover (<50 cm) dispersion appears to be related more to the secondary redistribution of gossaniferous clasts released by recent weathering out of the calcrete, than to dispersion of mobile metal ions on the surface of sand particles. In this area, the XRF results reveal a wider dispersion of the elements of interest. [Copyright &y& Elsevier]

Abstract: Focused-microwave heating was used in combination with simultaneous multielemental detection through ICP-TOFMS (inductively coupled plasma time-of-flight mass spectrometry) at a higher leaching flow rate than had been used with ICP-HRMS (ICP with high resolution mass spectrometry) to speed up the continuous leaching of soils. Compared to leaching at room temperature under otherwise identical conditions, heating the mini-column to 90 °C using focused-microwave energy significantly enhanced the release of several analytes from three mono-mineralic samples (pyrolusite, hematite and malachite), a 1:1:1 artificial mixture of the three, and a sandstone sample, by up to an order of magnitude. Furthermore, the resulting leaching profiles more closely resembled those obtained by ICP-HRMS at room temperature than those obtained at the same temperature by ICP-TOFMS. This indicates that the enhanced dissolution kinetics achieved through microwave heating compensated for the faster leaching flow rate. Thus, the whole fractionation study could be performed within about 16 min, which is substantially shorter than the several hours that are required for continuous leaching with ICP-HRMS. Although ICP-MS (with either TOF or quadrupole) is susceptible to spectroscopic interference, which could preclude the identification of some elements, it could nonetheless be used as a work horse for screening samples i.e. identify those that should be submitted to continuous leaching with ICP-HRMS for confirmation. [Copyright &y& Elsevier]

Abstract: A new method for multivariate outlier detection able to distinguish between extreme values of a normal distribution and values originating from a different distribution (outliers) is presented. To facilitate visualising multivariate outliers spatially on a map, the multivariate outlier plot, is introduced. In this plot different symbols refer to a distance measure from the centre of the distribution, taking into account the shape of the distribution, and different colours are used to signify the magnitude of the values for each variable. The method is illustrated using a real geochemical data set from far-northern Europe. It is demonstrated that important processes such as the input of metals from contamination sources and the contribution of sea-salts via marine aerosols to the soil can be identified and separated. [Copyright &y& Elsevier]

Regional geochemical data for 39 elements from several millions of stream sediment samples were obtained in China''s national geochemical mapping program. This program was carried out over a 24-year period and covered more than 6 million km2 of China. By examining this large data set, broad geochemical patterns other than dispersion halos and dispersion trains can be discerned. These broad geochemical patterns, such as geochemical regions, geochemical provinces, geochemical megaprovinces and geochemical domains, are the surface expressions of large blocks of rock with higher metal contents. These large “geochemical blocks” are the net results of the earth''s original heterogeneity and the distribution and redistribution of metals during the evolution of earth. Large geochemical blocks will provide large metal endowments necessary for the formation of large to giant ore deposits. The geochemical block concept has the capacity to change mineral exploration strategy and methodology in China, providing a powerful tool for global mineral potential assessment and inspiring new ideas for exploration geochemistry, ore-genesis and metallogeny. [Copyright &y& Elsevier]

This paper introduces a new method, the element concentration–distance (C–D) model, for separating geochemical anomalies from background based on a fractal approach. The method is derived from Mandelbrot''s radial-density law by replacing the density with concentration, which in turn follows the power-law of fractals. The variability of the element concentration as a function of distance from sample sites reveals two different fractal distributional patterns acting within two scale ranges. Therefore, this model can be used to effectively separate geochemical anomalous areas from background. The method has been tested on three data sets from Zhejiang Province in China, two from stream sediment samples (n=3815) and one from lithogeochemical samples (n=329). We compared the anomalous area created using thresholds from various methods on the same data against the known deposits and occurrences, and found that the C–D model is superior to the other methods. [Copyright &y& Elsevier]

The chemistry of hydrothermal monazite from the Carrapateena and Prominent Hill iron oxide-copper-gold (IOCG) deposits in the IOCG-rich Gawler Craton, South Australia, is used here to define geochemical criteria for IOCG exploration in the Gawler Craton as follows: Monazite associated with IOCG mineralisation: La + Ce > 63 wt% (where La > 22.5 wt% and Ce > 37 wt%), Y and/or Th < 1 wt% and Nd < 12.5 wt%; Intermediate composition monazite (between background and ore-related compositions): 45 wt% < La + Ce < 63 wt%, Y and/or Th < 1 wt%. Intermediate monazite compositions preserving Nd > 12.5 wt% are considered indicative of Carrapateena-style mineralisation; Background compositions: La + Ce < 45 wt% or Y or Th > 1 wt%. Mineralisation-related monazite compositions are recognised within monazite hosted within cover sequence materials that directly overly IOCG mineralisation at Carrapateena. Similar observations have been made at Prominent Hill. Recognition of these signatures within cover sequence materials demonstrates that the geochemical signatures can survive processes of weathering, erosion, transport and redeposition into younger cover sequence materials that overlie older, mineralised basement rocks. The monazite geochemical signatures therefore have the potential to be dispersed within the cover sequence, effectively increasing the geochemical footprint of mineralisation. [ABSTRACT FROM AUTHOR]

The U.S. Department of Energy National Uranium Resource Evaluation Program is collecting stream sediment samples at a nominal density of one per 13 km from two-degree quadrangles throughout the United States. Each sample has been analyzed for from 14 to 43 chemical elements and other variables. We describe new methods of statistical map analysis, which we have applied to the regional distribution of multielement data from four two-degree quandrangles in the southeastern United States including parts of the southern Appalachian Mountains and the Coastal Plain, with particular reference to uranium distributions. Patterns of uranium distribution are clearly related to the geological provinces and also to individual geologic belts, plutons, and smaller stratigraphic subdivisions. Our work developed several anomalies, some of which were followed up by additional field sampling in 1979 and 1980. [ABSTRACT FROM AUTHOR]

A simple mathematical procedure is described for a first numerical analysis of regional geochemical stream sediment and peat samples. The treatment is based on the correlation matrix. The purpose is to reduce the relations between the element concentrations based on the background observations, which are supposed to describe very general geochemical relations of no interest for prospecting purposes. Anomalous observations are identified and temporarily isolated during the calculation of the background relations in order to get as good a description as possible of the background observations. The reduction for one element is carried out by means of an iterative process taking into account all other elements until the partial correlation coefficients go below a level chosen in advance. The convergence is rapid. This procedure gives the geochemist a good insight into the geochemical properties of the observations as a basis for the interpretation. Some brief examples are given and the results of the calculations are discussed. [ABSTRACT FROM AUTHOR]

Exploration geochemistry is viewed in a resource appraisal framework and the various general methods are discussed in terms of their applicability at different stages of the appraisal exercise. The direct nature of geochemical exploration is emphasized and the various types of data that the surveys yield are discussed together with their modes of interpretation. It is shown how the data may be simply reduced to a probability form which will allow data from many sources to be utilized. The limitations of exploration geochemistry in resource appraisal are also discussed so that unnatural expectations may not be fostered and that geochemistry be placed correctly, and complementarity, with the other geoscience techniques of resource appraisal. [ABSTRACT FROM AUTHOR]

Detection of chemically identifiable hydrocarbon (oil and gas) seepage is an important tool in offshore exploration. Generated and/or trapped oil and gas can leak to near-surface sediments and ocean in detectable concentrations. The seepage surface expression is controlled by hydrocarbon generation, regional pressure regimes, and migration pathways. The migrated hydrocarbon concentration and composition varies due to seepage rates and near-surface physical and biological processes that can alter the signal. A seepage continuum exists from large volume oil and gas seeps, known as macro-seepage, to lower volume seeps, known as micro-seepage, only detectible with special sampling and analysis. Understanding the impact of migrated hydrocarbon concentration relative to in-situ organic material and locally derived microbial hydrocarbons is critical. This paper describes factors that control the near-surface geochemical signal as well as the challenges in deciphering the migrated hydrocarbon signature to evaluate subsurface hydrocarbon generation and entrapment. • Seepage activity and type impacts seep concentration. • Sample location, depth, and extraction impact on results. • Importance technically sound seabed geochemical survey. • Recognition background versus migrated hydrocarbons. [ABSTRACT FROM AUTHOR]