Mineral Exploration Programs Research Articles

The Tichauer-DeTomi Matrix: a Tool for Assessment of Geological Uncertainty in Small-scale Mining

Mineral exploration is a critical step for success in mining. However, small-scale mining often ignores exploration best practices. This paper introduces the Tichauer-DeTomi Matrix, a tool for assessment of geological uncertainty in small-scale mining. This matrix, which measures the level of compliance of exploration programs in small deposits with industry best practices, has been applied to three small mining projects in Brazil: an artisanal gold mine in the Amazon, a small-scale manganese mining venture in the Northeast, and a small manganese deposit in the Southeast. The application of the matrix resulted in indexes that reflect the actual level of maturity of the mineral exploration program in each project. Therefore, the matrix has shown potential to be an effective tool for assessment of the geological uncertainty remaining in small-scale mineral projects, as well as to identify priority exploration activities for reduction of risks associated with the geological uncertainty. As a risk assessment tool, the Tichauer-DeTomi Matrix may be helpful in promoting investment and sustained development in and around small mines.

Application of Multi-Sensor Satellite Data for Exploration of Zn–Pb Sulfide Mineralization in the Franklinian Basin, North Greenland

Geological mapping and mineral exploration programs in the High Arctic have been naturally hindered by its remoteness and hostile climate conditions. The Franklinian Basin in North Greenland has a unique potential for exploration of world-class zinc deposits. In this research, multi-sensor remote sensing satellite data (e.g., Landsat-8, Phased Array L-band Synthetic Aperture Radar (PALSAR) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)) were used for exploring zinc in the trough sequences and shelf-platform carbonate of the Franklinian Basin. A series of robust image processing algorithms was implemented for detecting spatial distribution of pixels/sub-pixels related to key alteration mineral assemblages and structural features that may represent potential undiscovered Zn–Pb deposits. Fusion of Directed Principal Component Analysis (DPCA) and Independent Component Analysis (ICA) was applied to some selected Landsat-8 mineral indices for mapping gossan, clay-rich zones and dolomitization. Major lineaments, intersections, curvilinear structures and sedimentary formations were traced by the application of Feature-oriented Principal Components Selection (FPCS) to cross-polarized backscatter PALSAR ratio images. Mixture Tuned Matched Filtering (MTMF) algorithm was applied to ASTER VNIR/SWIR bands for sub-pixel detection and classification of hematite, goethite, jarosite, alunite, gypsum, chalcedony, kaolinite, muscovite, chlorite, epidote, calcite and dolomite in the prospective targets. Using the remote sensing data and approaches, several high potential zones characterized by distinct alteration mineral assemblages and structural fabrics were identified that could represent undiscovered Zn–Pb sulfide deposits in the study area. This research establishes a straightforward/cost-effective multi-sensor satellite-based remote sensing approach for reconnaissance stages of mineral exploration in hardly accessible parts of the High Arctic environments.

Fluid Inclusion Characteristics of Basemetal Mineralization in Southern Part of Aladahalli - Nuggihalli Schist Belt, Western Dharwar Craton, Karnataka, India

ABSTRACT Aladahalli-Nuggihalli Schist belt of Karnataka in Western Dharwar Craton is well known for its remobilized volcanic exhalative type base-metal mineralization. The schist belt comprises metamorphosed mafic-ultramafic rock assemblage, traversed by quartz veins. The study area belonging to the southern extension of the schist belt is chosen on the basis of bipolar aero-magnetic anomaly (magnetic high) and higher order EM channels (4th, 5th and 6th) along with favourable geological conditions for mineralization. Lithology of the area includes metabasics (dominant) and meta-ultramafics intricately associated with pegmatite dykes and quartz veins. Subsurface mineral exploration programmes carried out in Aladahalli belt shows a close link between the quartz veins and sulphide mineralisation. Fluid inclusion study has been carried out on quartz samples from these veins to characterise the composition and P – T condition of entrapment of fluid inclusions. Three contrasting types of fluid inclusions are reported suggesting moderate to low salinity hydrothermal fluid pertaining to shallow-level epithermal condition.

Comparison between the effectiveness of regional BLEG and −80# stream sediment geochemistry in detection of precious and base metal mineral deposits in Western Turkey

Stream sediments remain the preferred sampling media for regional mineral exploration programs in most parts of the world where there is a well-defined drainage system. In Au exploration the analysis of either BLEG (bulk leach extractable gold) or acid-extractable Au in the −80# (<180μm) stream sediment fraction are the two most common approaches. Western Turkey contains a variety of mineral deposit types and geological settings. Using a large geochemical database derived mainly from company exploration programs (5149 BLEG, 11,692 −80# stream sediment analyses and 7732 rock chip samples), a comparison is made between the efficiency of these two approaches in detecting the known mineral deposits or occurrences. There is only limited variation between the median or 95th percentile values for Au or Cu across the different lithologies, although Cu is higher in BLEG in basaltic areas and Au higher in the ultramafic and metamorphic dominated terranes. Element distributions were examined using both quantile-quantile (Q-Q) and concentration-area (C-A) multifractal plots to establish the major breaks between regional geochemical populations. The C-A fractal plots generated clearer breaks than the Q-Q plots between populations and lower thresholds to the dominant “background” populations (e.g. 2ppb Au for Q-Q and 0.9 ppb for C-A in BLEG). Overall geochemical patterns in the −80# delivered clearer spatial correlations with known mineral deposits and occurrences than BLEG. Comparing the observed population breaks with the distribution of catchments containing known mineralization, based on the proportion of “true positives” and “false negatives”, C-A was more effective at separating populations related to catchments containing Au or Cu mineralization with little difference between BLEG and −80# (~80% agreement) for Au but a superior response in the −80# fraction for Cu. Given ongoing improvements in analytical detection limits for most elements, the use of the −80# (or possibly finer fractions) is recommended over BLEG for regional reconnaissance stream sediment survey in terrains similar to Western Turkey.

Introduction to the thematic issue: analysis of exploration geochemical data for mapping of anomalies

The journal Geochemistry: Exploration, Environment, Analysis (GEEA) ‘focuses on mineral exploration using geochemistry…’ ( ). GEEA is well-known for geoanalysis, which involves development of techniques and methods for systematic measurements of the chemical properties of a variety of Earth materials (e.g. rocks, soils, sediments, waters, vegetation, etc.). The most common chemical property measured from every geochemical sample is the concentration of one or more elements. The task of analysing geochemical concentration data (or geochemical data in short) from mineral exploration programmes aims basically to identify and separate samples with anomalous chemical concentrations from samples with background chemical concentrations. GEEA has published at least 50 papers on exploration geochemical data analysis (Appendix 1), which represent roughly 10% of all papers published in GEEA since its first issue in 2001. To contribute to the achievement of GEEA's aim, this thematic issue contains eight papers on the development of methods and techniques for exploration geochemical data analysis. We thank Editor-in-Chief Kurt Kyser for agreeing to publish this special collection of papers in a thematic issue of GEEA. We are grateful to all the authors for the contributions, even to those who withdrew their papers after considering the reviewers’ comments and those whose manuscript were not acceptable to the reviewers. We deeply appreciate the support of the following individuals for the invaluable time they have given to review the submitted manuscripts, many of who graciously reviewed more than one manuscript indicated by numbers in parenthesis: Peyman Afzal (2), Monica Arias, Guoxiong Chen, Shishi Chen, David Cohen, Yuan Feng (2), Mario Goncalves (2), Eric Grunsky, Ardeshir Hezarkhani, Karel Hron (2), Yue Liu (2), Jennifer McKinley, Ahmad Reza Mokhtari (2), Charles Moon (2), Martiya Sadeghi, Ricardo Valls, Qingfei Wang, Wenlei Wang (2), Fan Xiao (2), Shuyun Xie, Douglas Yager, and Mahyar Yousefi (3). We also thank Jessica Pollitt, staff editor of GEEA, for assisting the authors, reviewers and ourselves regarding the use of the online manuscript submission and review system.

Predictive Mapping of Prospectivity in the Gurupi Orogenic Gold Belt, North–Northeast Brazil: An Example of District-Scale Mineral System Approach to Exploration Targeting

The Gurupi Belt hosts a Paleoproterozoic gold province located in north–northeastern Brazil, at the borders of Para and Maranhao states. It is considered to be an extension of the prolific West African Craton’s Birimian gold province into South America. Additionally, the belt has been the object of recent mineral exploration programs with significant resource discoveries. This study presents the results of predictive mapping using up-to-date mineral system concepts and recently finished regional-scale geological mapping, stream sediment and airborne geophysical surveys conducted by the Geological Survey of Brazil. We relate gold mineralization to an initially enriched crust, metamorphism, deep fluid pathways, structurally controlled damage zones and hydrothermal alteration. Prospective targets were generated using only regional public datasets and knowledge-driven targeting technique. This work did not incorporate any known gold deposits, yet it predicted the largest known deposits and their satellite targets. Besides, high prospective targets mapped almost 40% of known primary gold occurrences within 7% of the project area. This work allowed considerable search area reduction and identification of new target areas, thus collaborating on reducing costs, time and risk of mineral exploration. Results indicate that we achieved an efficient understanding of the geological processes related to the Gurupi Belt mineral system.

Chloritites of the Tocantins Group, Araguaia fold belt, central-northern Brazil: Vestiges of basaltic magmatism and metallogenetic implications

Chloritites from different localities (Arapoema, Couto Magalhães Velho, Juarina, Morro Grande, Morro do Jabuti, Morro do Pau Ferrado, Morro do Salto, Serra do Jacu, Serra do Quatipuru, Serra do Tapa, Serrinha) of the Araguaia fold belt, Tocantins geotectonic province, central-northern Brazil, have been investigated. Based on field work and petrographic, diffractometric, geochemical and mineral chemistry data, these rocks, commonly associated with metacherts and banded iron formations, have been interpreted as products of ocean-floor exhalative-hydrothermal activity on MORB basalts. Distribution patterns of rare earth elements and diagrams of relatively immobile components in the hydrothermal environment highlight not only the genetic link between the chloritites and the basaltic rocks that occur in the region (Serra do Tapa and Morro do Agostinho), but also some peculiar characteristics of the submarine environment. The rock association and anomalous contents of Cu, Zn, Ni, As, and Au are suggestive that the region was favorable to the formation of volcanogenic massive sulfide deposits, what makes it a potential target for mineral exploration programs.

Low density geochemical mapping and mineral exploration: application of the mineral system concept

The mineral exploration industry is used to very high sample densities (100s to 1000s of samples/km 2 ) for geochemical exploration in order to define drill targets. Lately, geoscience organizations in many countries have been geochemically mapping increasingly larger areas at progressively lower sampling densities (1 site/100 to 1 site/18 000 km 2 ). A single ore body is too small a target and cannot be expected to be discovered at such low sample densities; indeed numerous deposits could be hidden within a 100 × 100 km grid cell. However, mineral systems, which include all geological ingredients and processes necessary for the generation of mineral deposits, form much larger targets that could be identified even at such low sampling densities. Examples from some European low density geochemical surveys where patterns emerged that may have implications for mineral exploration are shown and discussed. It is concluded that low density geochemical mapping holds great promise in the early stages of mineral exploration programmes in guiding subsequent effort into the more fertile regions. Interpretation of these maps, however, may need a different approach than that used in classical, high density mapping exercises, where only ‘high values’ of certain metals are the traditional target.

Age Dating from Electron Microprobe Analyses of U, Th, and Pb: Geological Advantages and Analytical Difficulties

Electron microprobe analysis of U, Th, and Pb in naturally occurring minerals can indicate their age. Where the Pb is entirely due to the radioactive decay of U and Th, the time since mineral formation or equilibration can be calculated. Uraninite (UO2), monazite (REE PO4), zircon (ZrSiO4), and xenotime (YPO4) have been used, the latter containing U and/or Th in minor proportions. Any stable U- or Th-bearing phase can be considered. Careful analysis is required with attention to interferences, background measurement, detection limits, and Pb-free sample preparation. Extended counting times (600 s) at a probe current >200 nA are recommended. Ages can be determined from uraninite older than 2 Ma for a Pb detection limit of 0.02% and up to 700-1,000 Ma, after which Pb can be lost from the structure. The youngest monazite ages permitted by the Pb detection limit are 50-100 Ma and ages greater than 3,000 Ma have been determined. The method does not provide the detail of isotopic methods, but results can be obtained more readily. Examples show dating of cheralite ((Ca,Ce)(Th,Ce)(PO4)2), a rock containing primary and secondary UO2, and a suite of detrital uraninite grains that formed a part of a mineral exploration program.

Identificação dos padrões espectrais da alteração hidrotermal da Mina Uruguai, Caçapava do Sul (RS), utilizando espectros de reflectância experimental

Uma série de análises espectrais foi efetuada em amostras de rochas sedimentares eopaleozoicas afetadas por alteração hidrotermal associada às ocorrências de cobre na Mina Uruguai (Minas do Camaquã, RS). A base de dados contemplou espectros na faixa do visível e infravermelho próximo (350 a 2500 nm) obtidos através de leituras em um espectrorradiômetro portátil ASD FieldSpec-3 High-Resolution. A interpretação mineralógica das assinaturas espectrais foi efetuada com o apoio do software The Spectral Geologist (TSGTM Pro) que permitiu a discriminação das fases minerais presentes por comparação das feições de absorção no espectro analisado com feições similares de minerais de uma biblioteca espectral de referência. A partir da análise espectral das amostras da área de estudo, puderam ser identificados os seguintes minerais principais: caulinita, ilita, clorita, hematita e goetita. As assembleias minerais identificadas se mostraram consistentes com alteração hidrotermal sob condições epitermais de baixo enxofre descrita em estudos anteriores na região. Os resultados obtidos reforçaram o potencial de utilização da espectroscopia de reflectância em programas de exploração mineral, especialmente nas fases iniciais, mesmo em áreas com condições fisiográficas pouco favoráveis.

Data fusion and porphyry copper prospectivity models, southeastern Arizona

Mineral exploration programs commonly use a combination of geological, geophysical and remotely sensed data to detect sets of optimal conditions for potential ore deposits. Prospectivity mapping techniques can integrate and analyse these digital geological data sets to produce maps that identify where optimal conditions converge. Three prospectivity mapping techniques – weights of evidence, fuzzy logic and a combination of these two methods – were applied to a 32,000km2 study area within the southeastern Arizona porphyry Cu district and then assessed based on their ability to identify new and existing areas of high mineral prospectivity. Validity testing revealed that the fuzzy logic method using membership values based on an exploration model identified known Cu deposits considerably better than those that relied solely on weights of evidence, and slightly better than those that used a combination of weights of evidence and fuzzy logic. This led to the selection of the prospectivity map created using the fuzzy logic method with membership values based on an exploration model. Three case study areas were identified that comprise many critical geological and geophysical characteristics favourable to hosting porphyry Cu mineralisation, but not associated with known mining or exploration activity. Detailed analysis of each case study has been performed to promote these areas as potential targets and to demonstrate the ability of prospectivity modelling techniques as useful tools in mineral exploration programs.

A multi-sensor logger for rock cores: Methodology and preliminary results from the Matagami mining camp, Canada

Diamond drilling typically constitutes a major part of costs in advanced mineral exploration programs. This generates thousands of meters of rock cores during major exploration campaigns, but the cores are not currently utilized to their full potential. They could supply three-dimensional information on physical properties, geochemistry and mineralogy; such data could be used to model the geology or physical properties in 3D, characterize hydrothermal alteration, or provide chemo-stratigraphic constraints, for example. But measuring all the parameters one by one at high spatial resolution by traditional methods would be impractical due to cost or time considerations and, for some parameters, it would destroy the core (e.g. geochemistry).In this paper we describe a multi-sensor core logger and its use on rock cores from exploration diamond drill holes. This semi-automated system can measure near-simultaneously, non-destructively and at high spatial resolution, the following parameters: (1) volumetric magnetic susceptibility; (2) density using gamma-ray attenuation; (3) several chemical elements through energy-dispersive X-ray fluorescence spectrometry; and (4) visible/near infrared spectrometry, which allows numerous minerals to be detected and characterized. The logger also acquires a continuous image of the core using a line-scan camera, which allows the user to compare other properties with the visual aspect of the core and creates a complete virtual archive. The aim of this mostly methodological paper is to describe the logger as a whole and then each instrument or sensor separately, outlining the numerous tests that have been performed to assess and improve data quality. We also present preliminary results from the Matagami mining camp of Canada, a base metal district.

Exploring and appraising the oldest gas accumulations in Australia

In early 2012, Armour Energy set out to evaluate the Middle-Proterozoic formations in the Batten Trough, McArthur Basin, NT. The Batten Trough holds a massive potential shale gas play in the Barney Creek Formation, and recent gas discoveries in the overlying Lynott and Reward formations, and underlying Coxco Dolomite. The Lawn Supersequence, Isa Superbasin, Queensland, is another Middle-Proterozoic shale gas play with overlying and underlying conventional and unconventional oil and gas accumulations. Exploratory drilling between the 1980s and 1990s showed gas and oil shows across the Isa Superbasin, Queensland. Egilabria–1, ATP 1087, exhibited 390 gas units while drilling with mud, highlighting the prospectivity of this area. In both areas, the Barney Creek and Lawn Hill formations are proven source rocks and are significantly older than North American shale reservoirs. In 2012, an innovative exploration program was designed and implemented in the NT to maximise the capture of drilling data while integrating data from previous mineral and petroleum exploration programs. This resulted in gas discoveries at Cow Lagoon–1, EP 176, and in the Glyde–1 and Glyde–1 ST lateral wells in the Glyde Sub-basin in EP171. In both cases, air drilling was instrumental in aiding drilling penetration rates, gauging gas influx while drilling, and allowing geologists to rapidly obtain and assess drill cuttings. The authors first discuss the details of the formation evaluation methods used in Armour’s successful 2012 program and how these methods are extended to Armour’s 2013 program in the Isa Superbasin, northern Queensland. Next, an outline of the strategy for further delineation of the Batten Trough is provided. Finally, the authors summarise the exciting potential of the Lawn Supersequence in Queensland.

Geologia e ocorrências de ouro do Terreno Granito-Greenstone do Tocantins, TO: síntese do conhecimento e parâmetros para exploração mineral

The Paleoproterozoic Tocantins Granite-Greenstone Terrane is composed of granite-gneissic domes and narrow intervening greenstone belts. Tholeiitic metabasalts and calc-alkaline metatonalites have chemical composition characteristic of subduction tectonic environment. The main gold concentrations occur in iron-rich amphibolite, banded iron formation and granitic rocks. It is suggested that the Tocantins Granite-Greenstone Terrane gold occurrences and deposits were formed by dominantly metamorphic hydrothermal fluids during the Brasiliano Orogeny, with granitic contribution. Guide lines for mineral exploration programs for gold in the Tocantins Granite-Greenstone Terrane are presented.

Major advances in exploration geochemistry, 1998–2007

ABSTRACT Exploration geochemistry continues to be a major contributor to mineral exploration programs at all scales. The decade has spanned a complete economic cycle in the minerals industry, during which there has been a change in exploration emphasis from the dominance of Au and diamonds to the addition of a range of base metals and the recent revival of U exploration. Increasing metal prices and the development of new geochemical techniques have allowed exploration activity to expand in previously under-explored terrains, including those characterized by thick, transported regolith cover. There has been significant evolution and refinement of geochemical dispersion models for transported regolith, especially processes associated with oxidizing sulphide mineralization. These models have prompted further developments in sampling methods, analytical techniques and approaches to anomaly detection. The routine measurement of fundamental soil and groundwater properties, such as pH, has been demonstrated to assist in detecting geochemical and mineralogical effects of buried mineralization on regolith. New lithogeochemical techniques have been developed for terrane selection and early discrimination of potentially mineralized units. The production of regolith-landform maps, including 3-D models, and more detailed techniques for differentiating the origin and nature of regolith materials now underpins the design of exploration programs in a number of terrains. Various exploration techniques, such as biogeochemistry and soil gas, have been revitalized by the application of new technologies. Ongoing improvements to detection limits and the reliability of multi-element analytical methods have permitted development and routine application of a wide range of selective geochemical extraction methods aimed at detecting subtle geochemical haloes developed in transported regolith cover. The results from a plethora of selective extraction orientation studies have, however, indicated the reliability of such methods to be uncertain, especially in arid terrains. Low-density geochemical mapping of large regions has been undertaken by government agencies for a variety of resource, environmental and health purposes, including attracting mineral exploration. Such maps typically demonstrate the dominance of underlying geology on regional geochemical patterns in regolith, even in industrialized regions. Philosophical and numerical approaches to defining and detecting geochemical anomalies continue to be reviewed. There is a need to supplement classical parametric outlier-detection approaches, routinely applied to geochemical data, with statistical techniques that reflect a recognition that subtle, multivariate patterns related to the geochemical effects of mineralization may emanate from within the main data cloud and not outlying or distinct clusters.

Structural mapping under cover with airborne EM

The drive to explore under cover necessitates methods of geological or geochemical mapping that can ?see through? the masking cover rocks. Magnetic data are routinely collected for this type of structural mapping in various terranes. In Mali, magnetic data have been of very limited use to Resolute Mining?s mineral exploration programs - magnetically featureless cover rocks hide almost all structural expression in the basement. Airborne EM has proven invaluable in tracing lithological contacts, subtle stratigraphic horizons, and intrusive bodies through conductive weathering up to 100m deep. Helicopter time domain systems with high transmitter moments penetrate deep enough to escape contamination by surficial conductivity features such as drainage patterns. The results under basin cover in Mali are particularly impressive in their ability to provide a clean picture of basement geological structure.

Predictive targeting in Australian orogenic-gold systems at the deposit to district scale using numerical modelling

3D numerical models of coupled deformation and fluid flow provide a useful tool for exploration in orogenic-gold systems. Numerical modelling of ore-forming processes can lead to a reduction in targeting and detection risk, thus improving the value proposition of mineral exploration. Hydrothermal mineralisation arises from a complex interplay of deformation, fluid flow, conductive and advective heat transport, solute transport and chemical reactions. Coupled simulation of all of these processes represents a significant computational challenge that cannot be solved within the time-scale of a mineral exploration program. However, the problem can be simplified by identifying a subset of processes representing the first-order controls on mineralisation at the scale of interest. For most orogenic-gold systems, it is argued that the first-order controls on mineralisation at the camp to deposit scale are deformation-induced dilation, fluid flow and fluid focusing. Hence, numerical models of coupled deformation and fluid flow can provide a quantitative insight into the localisation of ore-forming fluids in this type of system. In two case studies, known deposits were modelled in order to determine the critical deformation and fluid-flow-related factors controlling the localisation of mineralisation in these systems. The quantitative results from the forward models were then used as a basis for constructing predictive models that were applied to regional targeting, prospect ranking and selecting the choice of detection methods. Both case studies show that numerical modelling is capable of reproducing the distribution of known anomalism, and that it can predict anomalies that were not expected or accounted for by purely empirical analysis.

Borehole magnetics navigation: An example from the Stratmat Deposit, Bathurst, New Brunswick

Information acquired from studies of borehole core or from borehole geophysical logs form an integral part of all mineral and oil exploration programs. Yet, as is the case of any survey, the value of that information is dependent upon how well the location of each observation point is known. Location information becomes especially critical when the resource target has limited depth extent. For example, a location error of 10 m when evaluating a 5-m thick gold vein can make the difference between an economic and noneconomic deposit. The trajectory of a borehole is commonly computed using an array of data points that are acquired progressively with increasing distance along the borehole. Depending on the type of survey employed, observation points may be sparse (static readings at a limited number of points) or redundant (dynamic surveys where the distance between observation points is less than the length of the rigid probe). At each observation point, three parameters are normally acquired: (a) inclinatio...

Backward elimination procedure for a predictive model of gold concentration

In mineral exploration campaigns, concentrations of the element(s) sought and pathfinder elements are determined in order to delimit targets that may lead to the discovery of hidden mineral deposits. The pathfinder elements for epithermal Au deposits commonly include Ag, As, Sb, and Hg. Traditionally, contours of anomalous concentrations of these pathfinder elements are superimposed in map form as a means of assessing the Au potential of a target area. However, the information generated is more qualitative than quantitative. This paper proposes a statistical modeling approach that quantitatively predicts Au concentration from the known concentrations of the aforementioned pathfinder elements. Element concentration data from the Florida Canyon deposit, Nevada (USA), a large disseminated epithermal gold deposit, were used to develop and examine the validity of this predictive model. A geologically constrained data set of 115 data points and 575 elemental concentrations obtained from a total of 28 vertical and inclined drill holes located in a restricted area of the deposit formed the basis for model development and validation. A backward elimination procedure was pursued starting with a cubic regression model excluding all higher order (> 2) interaction terms to arrive at a suitable predictive model. After seven steps of factor elimination, a quadratic model including several two-factor interaction terms was obtained with an adjusted R 2 value of 0.994 and F-ratio of 1665.5. The model was validated with another 112 geologically constrained data points (560 elemental concentrations) obtained from 13 additional drill holes in the same area of the deposit. Further analysis highlighted the effects of individual and combined pathfinder element values on predicted Au concentrations in the Florida Canyon deposit. Although the model developed herein is deposit specific, the statistical approach can be applied to other disseminated epithermal Au deposits and deposit types where the model constraints are satisfied (e.g., geological homogeneous domain). Such an approach may be utilized in mineral exploration programs to predict gold concentrations in undersampled areas of a deposit, optimize the number of pathfinder elements required for the efficient detection of the element of interest, and evaluate geochemical data sets generated by different laboratories or analytical techniques.

Spinifex biogeochemical expressions of buried gold mineralisation: The great mineral exploration penetrator of transported regolith

A major challenge for mineral explorers is to efficiently detect mineralisation beneath the weathered cover that extends across the landscape. Determination of the elemental composition of plants (biogeochemical exploration) can aid in the detection of buried ore deposits due to their root penetration through the weathered cover. At the coyote prospect in Western Australia a range of plant species were sampled traversing a buried Au orebody. Here it is shown that the soft spinifex (Triodia pungens) accumulated important pathfinder elements related to the mineralisation, which produced a multi-element surficial expression of the underlying ore deposit. Spinifex grasses are one of the most widespread grasses over the Australian continent and have vertical root systems that can extend for many 10s of metres through sedimentary cover and interact with buried mineral deposits and alteration zones in the underlying substrate. Spinifex biogeochemistry therefore has potential to be a low cost, low environmental impact, sampling medium for mineral exploration programs across large parts of arid Australia. The examination of similar grasses from other semi-arid and arid regions from around the world therefore also warrants further investigation.