Mineral Exploration Applications Research Articles

High‐resolution unmanned aerial vehicle aeromagnetic surveys for mineral exploration targets

ABSTRACTRecent advancements in geophysical exploration have been realized through reliably integrating unmanned aerial vehicle platforms with lightweight, high‐resolution magnetometer payloads. Unmanned aerial vehicle aeromagnetic surveys can provide a contemporary data product between the two end‐members of coverage and resolution attained using manned airborne and terrestrial magnetic surveys. This new data product is achievable because unmanned aerial vehicle platforms can safely traverse with magnetometer payloads at flight elevations closer to ground targets than manned airborne surveys, while also delivering an increased coverage rate compared to walking conventional terrestrial surveys. This is a promising new development for geophysical and mineral exploration applications, especially in variable terrains. A three‐dimensional unmanned aerial vehicle aeromagnetic survey was conducted within the Shebandowan Greenstone Belt, northwest of Thunder Bay, Ontario, Canada, in July 2017. A series of two‐dimensional grids (∼500 m × 700 m) were flown at approximate elevations of 35, 45 and 70 m above ground level using a Dà‐Jiāng Innovations multi‐rotor unmanned aerial vehicle (S900) and a GEM Systems, Inc., Potassium Vapour Magnetometer (GSMP‐35U). In total, over 48 line‐km of unmanned aerial vehicle aeromagnetic data were flown with a line spacing of 25 m. The collected aeromagnetic data were compared to a regional heliborne aeromagnetic survey flown at an elevation of approximately 85 m above the terrain, with a line spacing of 100 m, as well as a follow‐up terrestrial magnetic survey. The first vertical derivative of the gathered unmanned aerial vehicle total magnetic field data was calculated both directly between each of the different flight elevations, and indirectly by calculating the values predicted using upward continuation. This case study demonstrates that low flight elevation unmanned aerial vehicle aeromagnetic surveys can reliably collect industry standard total magnetic field measurements at an increased resolution when compared to manned airborne magnetic surveys. The enhanced interpretation potential provided by this approach also aided in delineating structural controls and hydrothermal fluid migration pathways (a pair of adjacent shear zones) related to gold mineralization on site. These structural features were not clearly resolved in the regional manned airborne magnetic data alone, further demonstrating the utility of applying high‐resolution unmanned aerial vehicle aeromagnetic surveys to mineral exploration applications. The conclusions and interpretations drawn from the unmanned aerial vehicle aeromagnetic data, coupled with historical data, were applied to make a new gold mineralization discovery on the site, assayed at 15.7 g/t.

Chemical weathering of garnet in Banded Iron Formation: Implications for the mechanism and sequence of secondary mineral formation and mobility of elements

Abstract The chemical weathering of rocks and minerals on the Earth’s surface leads to the mobilization and redistribution of elements and has (a) significant control on the chemistry of the soil-hydrosphere-atmosphere system, (b) a profound effect on the bioavailability and toxic effects of elements, and (c) applications in mineral exploration among others. In this study, we describe the sequential weathering of spessartine- and pyrope-bearing almandine garnet in metamorphosed banded magnetite quartzite from the Khetri Copper Belt, western India. Based on detailed microtextural relations the following sequence of garnet weathering is proposed: garnet → alumo-goethite1 → alumo-goethite2 → kaolinite ± (monazite + xenotime ± thorite) → haematite. Our study thus reports for the first time the presence of alumo-goethite, kaolinite, monazite, xenotime, and thorite in weathering assemblage of garnet. The sequential chemical weathering of garnet was both grain boundary-controlled and fracture-controlled. Tectonic fractures (developed during exhumation), reaction-induced fractures (developed due to volume expansion), and secondary porosity (developed due to volume reduction) collectively controlled the propagation of weathering. Integrating multiple lines of evidence, e.g., corrugated contact between the weathering phases, presence of pores, relative molar volume changes, and high mobility of most elements it is argued that the weathering progressed through an interface-coupled dissolution-precipitation process. In situ major and trace element measurements and mass balance calculations show that several major (Fe, Na, K, P) and trace elements (Cl, F, alkalis, alkaline earth elements, and first series transition and base metals) were added while Si, Al, Ca, Mg and Mn were lost during the garnet to alumo-goethite transformation. During kaolinitization, all the major elements except Si and Al were lost to the weathering fluid. The alkali and alkaline earth, first series transition elements, base metals excepting Cr were lost during this weathering stage. Phosphorous, REEs, and Th were locally immobilized as monazite, xenotime, and thorite. In the more advanced stages of weathering, kaolinite was replaced by haematite. This stage involved re-addition of several major (except Al and Si) and trace elements. It is seen that although alumo-goethite, kaolinite, and haematite can host significant quantities of several trace elements, alumo-goethite and haematite have a much better potential of immobilizing most trace elements including toxic ones compared to kaolinite in the weathering profile.

Twenty Years of ASTER Contributions to Lithologic Mapping and Mineral Exploration

The Advanced Spaceborne Thermal Emission and Reflection Radiometer is one of five instruments operating on the National Aeronautics and Space Administration (NASA) Terra platform. Launched in 1999, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) has been acquiring optical data for 20 years. ASTER is a joint project between Japan’s Ministry of Economy, Trade and Industry; and U.S. National Aeronautics and Space Administration. Numerous reports of geologic mapping and mineral exploration applications of ASTER data attest to the unique capabilities of the instrument. Until 2000, Landsat was the instrument of choice to provide surface composition information. Its scanners had two broadband short wave infrared (SWIR) bands and a single thermal infrared band. A single SWIR band amalgamated all diagnostic absorption features in the 2–2.5 micron wavelength region into a single band, providing no information on mineral composition. Clays, carbonates, and sulfates could only be detected as a single group. The single thermal infrared (TIR) band provided no information on silicate composition (felsic vs. mafic igneous rocks; quartz content of sedimentary rocks). Since 2000, all of these mineralogical distinctions, and more, could be accomplished due to ASTER’s unique, high spatial resolution multispectral bands: six in the SWIR and five in the TIR. The data have sufficient information to provide good results using the simplest techniques, like band ratios, or more sophisticated analyses, like machine learning. A robust archive of images facilitated use of the data for global exploration and mapping.

Electrode array and data density effects in 3D induced polarization tomography and applications for mineral exploration

Synthetic resistivity and chargeability models are employed to study the electrode array and data density effects in inversion resolution for 3D induced polarization tomography. Results from the inversion tests with different electrode arrays illustrate that the inversion resolution for electrical resistivity tomography (ERT) and induced polarization tomography (IPT) data with the dipole–dipole array perform better than the pole–pole array and pole–dipole array. In addition, the anomalous bodies with high impedance and high chargeability are hard to be reconstructed. In contrast, the ones with low resistivity and high chargeability can be well established. Results from the inversion tests with different data densities illustrate that the higher data density will yield better inversion resolution for the ERT and IPT data. We firstly employ the sensitivity analysis method and depth of investigation (DOI) index method to evaluate the inversion results. Then, we present the observation-to-parameter ratio (OPR) and model-drift ratio (MDR) for discussing and evaluating the quality of the inverted maps, and the result shows that the correlation can reach to the limit when the data density reaches a certain OPR value of 44. Results from the synthetic inversion tests generally provide reference and guidance for employing the measuring electrode with a suitable arrangement and reasonable number in the field ERT and IPT surveys. Lastly, IPT method with dipole–dipole array has been employed in the mining area with the better prospect of mineral exploration northwest of Gansu Province, China. Moreover, the inverted maps reveal three ore bodies with high resolution.

Review of the Role of Remote Sensing Applications in Mineral Exploration and Sustainable Development in Oman

Applications of remotely sensed satellite data are wide and unique in the mapping of different lithologies, mineral resources, and ore deposits. Satellite images are capable in discriminating rock types useful for geological applications and significantly used in the identification of mineral resources. The techniques are low-cost and save time in mapping and exploration of such resources and are well-suitable and applicable to the arid region. Oman has the potential occurrence of the industrial minerals and ore deposits which mostly occur in inaccessible mountains and desert regions where it is difficult to do conventional geological mapping. Thus, understanding the capability of the techniques to map and ex­plore such potential resources by geologists is highly important. The absorption characters of spectral bands of Advanced Spaceborne Thermal Emission and Re­flection Radiometer (ASTER) and selected imaging processing methods namely decorrelation stretching, band ratios, linear spectral unmixing (LSU), and Mixture Tuned Matched Filtering (MTMF) demonstrates the sensor capability of ASTER to map several mineral deposits and different rock lithologies in Oman, which in­cludes limestone, marl, listwaenites, carbonatites, metamorphic zones, caves, karst, springs, vegetation’s, rock fall and slide, Moho, copper, chromite, awaruite, manganese, and gold deposit in different parts of the Sultanate of Oman. It demonstrates the spectral sensitivity of such rocks for simple interpretation over satellite data and describes and distinguishes them based on the absorptions of hydrous minerals in the spectral bands of ASTER for mapping and exploration studies.

Multi-robot coverage path planning using hexagonal segmentation for geophysical surveys

SUMMARYThe field of robotics has received significant attention in our society due to the extensive use of robotic manipulators; however, recent advances in the research on autonomous vehicles have demonstrated a broader range of applications, such as exploration, surveillance, and environmental monitoring. In this sense, the problem of efficiently building a model of the environment using cooperative mobile robots is critical. Finding routes that are either length or time-optimized is essential for real-world applications of small autonomous robots. This paper addresses the problem of multi-robot area coverage path planning for geophysical surveys. Such surveys have many applications in mineral exploration, geology, archeology, and oceanography, among other fields. We propose a methodology that segments the environment into hexagonal cells and allocates groups of robots to different clusters of non-obstructed cells to acquire data. Cells can be covered by lawnmower, square or centroid patterns with specific configurations to address the constraints of magneto-metric surveys. Several trials were executed in a simulated environment, and a statistical investigation of the results is provided. We also report the results of experiments that were performed with real Unmanned Aerial Vehicles in an outdoor setting.

The use of hyperspectral remote sensing for mineral exploration: a review

The hyperspectral remote sensing technology has been available to the research community for more than three decades. Since in its first steps the hyperspectral technology was also promoted as a tool for mineral exploration. Numerous mineral exploration applications of hyperspectral remote sensing have been reported. This paper provides an up-to-date and focused review of the applications of the hyperspectral remote sensing to mineral exploration. The ore deposits are grouped based on major processes of formation (magmatic, hydrothermal, sedimentary, supergene). The review shows that the hyperspectral remote sensing technology has found application to the study and exploration of a number of ore deposits including kimberlites (host-rocks of diamonds), carbonatites (host-rock of rare earth elements deposits), porphyry deposits, epithermal gold and silver deposits, skarn deposits, volcanic-hosted massive sulfide (VHMS) deposits, orogenic gold deposits, Carlin-type gold deposits, SEDEX Pb-Zn-Ag deposits. On the other hand, the possibilities of the hyperspectral technology remain still underexplored for the study and exploration of chromite deposits, Ni-sulfide deposits in mafic and ultramafic rocks, rare-metal pegmatites, greisen and related deposits, Mississippi Valley-type (MVT) Pb-Zn deposits, Kupferschiefer deposits and uranium deposits in sedimentary basins, iron ores in banded-iron formations, laterites and bauxites. A special attention has been paid in this review to the applications in mineral exploration of the emerging airborne hyperspectral thermal infrared technology. In addition, the possibilities and limitations of spaceborne hyperspectral imagery of moderate spatial resolution for detailed characterization and detection of mineralized systems are discussed for each major deposit type. The spatial resolution of the hyperspectral data is noted to be a key factor on the success of a hyperspectral exploration project. By providing a full up-to-date picture of the applications and contribution of the hyperspectral imagery to the exploration and characterization of ore deposits this review paper should be useful to the interested geological remote sensing researcher and practitioner, and to the mineral exploration manager as well.

Dendrochronology in mineral exploration: developing tools to see through anthropogenic impacts

The Sudbury Igneous Complex (SIC) and its associated mining camp is one of the largest Cu, Ni, PGE ore systems in the world. Due to a long history of mining (>100 years), the SIC has been extensively explored making the discovery of new surface deposits difficult. This study explored the use of dendrochemical analysis as an economic means to locate deposits concealed by overburden. Tree cores combined with soil samples were collected and analyzed from two sites to provide a comparison between a known deposit (Broken Hammer) and a known contamination location (downwind site). Samples were collected from both White Pine (Pinus Strobus) and Scots Pine (Pinus Sylvestris) species, however White Pine proved to have a stronger affinity for the uptake of ore-associated metals (i.e., Cu, Ni, Fe, Co, Hg, Cd, Pb, Sb, S). Analyses of tree-core intervals revealed clear anthropogenic effects in the samples from both sites; however, due to the age of the trees the magnitude of these effects compared to pre-mining conditions could not be determined. The concentrations of S, Cu, Ni, Fe, Al, Pb and As in the downwind samples increased over time. On average, S increased from 6.37 to 8.98 ppm, Cu from 0.503 to 0.908 ppm, Ni from 0.605 to 1.18 ppm, Fe from 124 to 273 ppm, Al from 4.38 to 6.60 ppm and As from 0.008 to 0.012 ppm. Conversely, the concentrations of Cu, Fe, Ni, Al, S and As in the samples from Broken Hammer decreased over time. Copper decreased from 0.84 to 0.55 ppm, Fe from 2.45 to 1.19 ppm, Ni from 1.02 to 1.18 ppm, Al from 6.81 to 4.96 ppm, S from 7.62 to 7.57 ppm and As from 0.014 to 0.002 ppm. The total Pb concentration decreased over time in all samples from both sites. There were no trends in the Pb isotopic ratios with the exception of the 207 Pb/ 206 Pb. A comparison of the samples from each location revealed unique trends in the distribution of the data, which could suggest two sources. Soil (Ah and B horizon) collected proximal to the sampled trees near Broken Hammer showed the metal concentration increasing with depth. Copper averaged 33.6 – 187.9 ppm, whereas Ni had an even steeper trend, increasing from an average of 22.4 ppm–234.5. Sulphur and Hg also displayed a similar trend, however the difference was not as substantial. The highs and lows in concentration levels in the tree cores correspond to various historical events. During WWII (1939 – 1945), the Korean War (1950 – 1953) and the Vietnam war (1964 – 1973), the demand for Ni increased resulting in increased smelting activities and a spike in contamination levels. Conversely, the recession in the late 1970s early 1980s and the INCO strike in the late 1990s resulted in a decrease in Ni production and a drop in contamination levels. The distribution of metal concentrations at Broken Hammer indicates a lack of surface contamination and therefore a non-contaminated B-horizon. The higher concentrations in the B-horizon are anomalous to other studies in the Sudbury area suggesting a possible subsurface source. This is encouraging and the potential remains to develop a method for mineral exploration applications utilizing tree core samples, even in heavily mining impacted areas like the Sudbury.

Passive seismic surveying for depth to base of paleochannel mapping at Lake Wells, Western Australia

Goldphyre Resources Limited (Goldphyre) undertook a passive seismic survey over parts of the Lake Wells project using Tromino 3G seismometers. Modelling of the passive seismic survey data has defined the depth to bedrock and location of a deep, E-W trending paleochannel system occurring beneath a broad salt lake playa, where underlying Cainozoic paleochannel deposits likely form a reservoir system for potash brines. Drilling by Goldphyre supports these findings. A total of 180 readings were acquired along six survey line traverses over the salt lake, spaced 1,200 m to 2,100m apart on average, using four Tromino seismometers and 20 minute recording times. The passive seismic data were analysed using the H/V spectral ratio (HVSR) method, whereby the spectral ratio of the horizontal and vertical component data are assessed to determine a resonant frequency of an upper softer layer having low S-wave velocity sitting above a high S-wave velocity bedrock. The depth of the upper layer is related to the resonant frequency and S-wave velocity by a simple formula: f0 = Vs/(4h), where f0 = peak frequency in Hz, Vs = shear wave velocity in m/s and h = thickness in m. The modelled passive seismic survey depth to bedrock estimation has delineated a paleochannel system over 20 km long, up to 4 km wide and up to 170 m deep. In addition, the paleochannel system was found to branch to the northwest and southwest, and remains open in these directions. A paleochannel of these dimensions can potentially provide significant high-grade sulphate of potash (SPO) mineralisation hosted in the paleochannel brines. The passive seismic method is commonly used for seismic hazard mapping, and has not been used extensively for mineral exploration up to now, as very broadband seismometers have typically been used in array configurations that take significant time to setup and record data. The Tromino seismometers are self-contained, lightweight, portable and very simple to use. The HVSR method of analysis allows the user to quickly estimate the thickness of softer sediment cover over hard basement rocks ranging from 0 to 500m. This method has many applications for mineral exploration, and it may become a standard survey tool to predict thickness of cover deposits and reduce drilling costs.

Effective Mineral Exploration Under Cover: Addressing the Challenge Using Passive Seismic Methodology

Passive seismic methodology is becoming a popular tool for estimation of cover depth, cover velocity structure and basement topography for mineral exploration applications. Analysis of passive seismic array data gives information on wavefield characteristics and constrains shear-wave velocity structure. Single station techniques are useful as a tool to rapidly estimate cover thickness but require further information from drill holes or array techniques for robust interpretation. The combined use of array and single station techniques provides an effective cover depth mapping methodology and allows for highly flexible survey design, adaptable for a range of applications. This paper provides a summary of relevant passive seismic techniques and overview of their effective use with several example mineral exploration scenarios.

Out‐of‐plane effects in 2D borehole‐to‐surface resistivity tomography and applications in mineral exploration

ABSTRACTIn this paper, we discuss the effects of anomalous out‐of‐plane bodies in two‐dimensional (2D) borehole‐to‐surface electrical resistivity tomography with numerical resistivity modelling and synthetic inversion tests. The results of the two groups of synthetic resistivity model tests illustrate that anomalous bodies out of the plane of interest have an effect on two‐dimensional inversion and that the degree of influence of out‐of‐plane body on inverted images varies. The different influences are derived from two cases. One case is different resistivity models with the same electrode array, and the other case is the same resistivity model with different electrode arrays. Qualitative interpretation based on the inversion tests shows that we cannot find a reasonable electrode array to determine the best inverse solution and reveal the subsurface resistivity distribution for all types of geoelectrical models. Because of the three‐dimensional effect arising from neighbouring anomalous bodies, the qualitative interpretation of inverted images from the two‐dimensional inversion of electrical resistivity tomography data without prior information can be misleading. Two‐dimensional inversion with drilling data can decrease the three‐dimensional effect. We employed two‐ and three‐dimensional borehole‐to‐surface electrical resistivity tomography methods with a pole–pole array and a bipole–bipole array for mineral exploration at Abag Banner and Hexigten Banner in Inner Mongolia, China. Different inverse schemes were carried out for different cases. The subsurface resistivity distribution obtained from the two‐dimensional inversion of the field electrical resistivity tomography data with sufficient prior information, such as drilling data and other non‐electrical data, can better describe the actual geological situation. When there is not enough prior information to carry out constrained two‐dimensional inversion, the three‐dimensional electrical resistivity tomography survey is the better choice.

The effect of dielectric permittivity on the fields radiated from a radio-frequency electric dipole in a homogeneous whole space

The radio imaging method (RIM) is an electromagnetic cross-borehole method with applications in mineral exploration, as well as in the coal industry, where it is used across mine drives. Attenuation of the signal from conductive regions may indicate areas of mineralization, and these conductive effects in general dominate the response. In an effort to better understand the effect of a material’s dielectric permittivity on the response of the RIM, we have developed a simple program to model an electric dipole in a homogeneous whole space. When increasing the dielectric permittivity, the amplitude peak broadened and increased, whereas the phase peak sharpened and shifted negatively. To showcase the effect of dielectric permittivity on RIM data, data recorded from two transmitter positions in a moderately homogeneous zone in the Sudbury Basin were curve fit, and we concluded that despite the stronger effect that conductivity has on the signal, RIM is still sensitive to dielectric permittivity, and appropriate values must be used when developing conductivity tomograms. In addition, we found that for the given situation and frequencies used, an increase in either the conductivity or dielectric permittivity could be accounted for by a decrease of approximately the same factor in the other variable. However, the low-conductivity, high-permittivity case seemed to fit the shape of the amplitude and phase curves better. For the sulfide impregnated crystalline rocks at our field site, relative dielectric constants of 26.4 and 31 at 1250 and 625 kHz, respectively, were inferred.

Turbodrill Design and Performance Analysis

Turbodrill (turbine down hole motor) has been recently proposed by the authors as the preferred drive mechanism with high rotation speed for hard rocks drilling for deep mineral exploration applications. Turbodrill is a type of hydraulic axial turbomachinery in which turbine motor section has multistage of rotors and stators that convert the hydraulic power provided by the drilling fluid to mechanical power with diverting the fluid flow through the stator vanes to rotor vanes. This paper presents a methodology for designing multistage turbodrills with asymmetric rotor and stator blades configurations. The numerical simulation approach and the simulations results carried out using computational fluid dynamics (CFD) code for the proposed small size model of turbodrill stage with different drilling fluid (mud) types and various mass flow rates are presented. As a result optimum operational parameters are proposed for gaining the required rotation speed and torque for hard rocks drilling.

BIOGEOCHEMICAL CHARACTERISTICS OF EGGS OF BACKYARD POULTRY FROM BARITE MINERALIZATION, ANDHRA PRADESH, INDIA

In the present study an attempt has been made for biogeochemical studies involving elemental distribution and interactions in backyard poultry eggs from Vemula barite mineralized area to determine their indicator characteristics and of their possible application in applied environmental geoscience. The samples of backyard poultry eggs of hen were collected systematically. Their physical properties like moisture, organic matter and ash content are determined which shows wide variations. Trace element analysis of these samples was carried out for Ba, Sr, Cu, Pb, Zn, Mn, Ni, Co, Cr, Fe Mg, and Al. the parameter Coefficient of Apparent of Organic Binding (CAOB) is calculated for each element for the eggs. Wide variations are observed in the distribution of chemical elements in backyard poultry eggs. Ba occupies first position in the sequence in all parts of the raw eggs both on ash weight and dry weight bases. The enrichment of Ba concentration in backyard poultry eggs may be due to the presence of barite mineral. Therefore backyard poultry eggs may ideally be used as tools for their possible application in mineral exploration. This study has given greater scope in biogeochemical orientation surveys, and in environmental studies.

Research on Inversion Resolution for ERT Data and Applications for Mineral Exploration

This paper presents the effects of two factors on electrical resistivity tomography (ERT) resolution using numerical simulations. The results obtained from the first group of synthetic resistivity model numerical simulations with different electrode configurations illustrate that the inversion resolution can be improved if the current electrodes and potential electrodes are installed at a subsurface depth. The results obtained from the second group of synthetic resistivity models with different mesh densities illustrate that the inversion resolution can be improved if the mesh grid density is increased. The increased number of degrees of freedom necessary to fit the data to a prescribed target misfit leads to the inverted imagery deviating from the true resistivity model. Throughout the literature the inversion procedure is implemented in the conjugate gradient relaxation method and the model calculation speed is enhanced using the parallel processing mode. ERT surveys were employed for mineral exploration at Chifeng in Inner Mongolia, China. The inverted image clearly describes the vein behavior down to 200 m in depth in the prospect area and is consistent with the drilling data results.

ALLUVIAL AND ELUVIAL PLATINUM-GROUP MINERALS FROM THE BUSHVELD COMPLEX, SOUTH AFRICA

The present work provides an initial description of detrital platinum-group minerals (PGM) collected from alluvial sediments of rivers draining the Bushveld Complex, and from eluvial concentrations at the Onverwacht platiniferous pipe. During a field campaign, sediments were sampled at nine localities around the Bushveld Complex, and heavy mineral assemblages were investigated using optical and scanning electron microscopy (SEM) as well as microprobe analysis (EPMA) of PGM. All concentrates from the alluvial samples contain discrete PGM grains with grain sizes in the range from ~50 to 150 μm (maximum 600 μm). The overall PGM proportions are: native Pt, Pt-Pd and Pt-Fe alloys (together 54%), sperrylite (33%), cooperite/braggite (11%), and stibiopalladinite (2%). This PGM assemblage distinctly contrasts to the suite of PGM in the pristine, sulfide-bearing mineralization in the Merensky, UG-2 and Platreef, the assumed sources of the detrital PGM. Specifically, PGE-bismuthotellurides and -sulfarsenides, common in the primary ores, are missing in the assemblage of detrital PGM in the fluvial environment. Nearly all detrital PGM (98%) are Pt minerals, corroborating earlier findings that Pd-dominated PGM are unstable and are dissolved in the supergene environment, and that PGE-bismuthotellurides and -sulfarsenides, common in the PGM assemblages of the pristine ores are unstable during weathering and mechanical transport. The eluvial material collected at Onverwacht contained ca. 150 PGM grains with sizes mainly in the range 100 to 300 μm range (maximum 1.87 mm). The PGM assemblage comprises grains of Pt-Fe alloys (66%), sperrylite (14%), and many rarer PGM including stibiopalladinite, hollingworthite, laurite, PGE arsenides and PGE sulfides. The suite of eluvial PGM observed is similar to the PGM assemblage described previously from the Onverwacht pipe proper, including the type locality minerals genkinite, irarsite and platarsite, as well as some additional and possibly new PGM. Most of the relatively rare PGM detected in the suite of eluvial grains from Onverwacht were also reported in the detrital PGM assemblage from the Moopetsi river, farm Maandagshoek (Oberthur et al., 2004), indicating that many of the latter grains originate from platiniferous pipes and not from the Merensky or UG-2 reefs. Detrital PGM can be expected to be present in rivers draining PGE-bearing layered intrusions, and economic placers may form under particular sedimentological conditions. Therefore, this work also highlights the fact that the nowadays somewhat neglected field methods and basic techniques have their merits and value in mineral exploration, especially if they are combined with modern micro-analytical methods. The systematic recovery of PGM from stream sediments, soils and till should regain wider application in mineral exploration as these tools can provide useful indicators of platinum mineralization.

3D full tensor gradiometry and Falcon Systems data analysis for iron ore exploration: Baú Mine, Quadrilátero Ferrífero, Minas Gerais, Brazil

The use of airborne gravity gradiometry (AGG) has undergone rapid increase in mineral exploration in recent years. The performance and final results, however, are affected by many factors, including the acquisition system, acquisition parameters, quality control procedures, and the ruggedness of the terrain. We studied repeat surveys using 3D full tensor gradiometry and Falcon AGG systems under identical survey-design parameters over the Baú Mine Site, Quadrilátero Ferrífero, State of Minas Gerais, Brazil. We also evaluated the planning and quality control procedures adopted for acquisition through these systems. We also studied the results from the two systems in terms of signal-to-noise ratio, power spectral analysis, and correlation with the local geology. We aimed to evaluate the information from repeat surveys using identical parameters but different systems to facilitate the understanding of this new type of geophysical data and their application in mineral exploration.

Thermal inertia mapping and its application in mineral exploration: results from Mamandur polymetal prospect, India

Thermal inertia mapping and its application in mineral exploration: results from Mamandur polymetal prospect, India

Predicting regolith thickness in the complex weathering setting of the central Mt Lofty Ranges, South Australia

We describe a model to predict regolith thickness in a 128,000ha study area in the central Mt Lofty Ranges in South Australia. The term regolith encompasses soil (A and B horizons) and highly weathered bedrock (C horizon). The thickness of the regolith has a major control on water holding capacity for plant growth and movement of water through the landscape, and as such is important in hydropedological modelling and in evaluating land suitability, e.g. for forestry and agriculture. Thickness estimates also have direct application in mineral exploration and seismic risk assessment.Geology and landscape evolution within the study area is complex, reflecting the variable nature of bedrock materials, and the partial preservation of deeply weathered profiles as a consequence of weathering processes dating to the Cenozoic, or possibly older. These characteristics, together with strong climatic gradients, make the study area an ideal location to understand environmental and landscape evolution controls on weathering depth. The area also features weathered landscape analogues to many parts of southern Australia. We use a digital soil mapping rules based approach to develop a model to predict regolith thickness. This model uses statistically-based relationships established between 714 regolith thickness measurements and 29 geographic environmental covariates including geology, geochemistry, terrain and climate themes, and with a ground resolution of 10m. Accuracy testing based on a 75:25% training:test data split on the resulting map established a correlation R2 of 0.64. This result is encouraging and is a significant advance over regolith depth mapping by traditionally-based regolith-landscape mapping methods. Finally, it leads the way towards a nationally consistent regolith thickness map for landscape scale environmental simulation modelling and decision support.

Coiled Tube Turbodrilling: a proposed technology to optimise drilling deep hard rocks for mineral exploration

The need to drill deep boreholes more efficiently for mineral exploration has raised the attention to investigate the feasibility of recent drilling technologies for such applications. The two principal methods of Reverse Circulation (RC) and diamond core drilling are usually used in combination by mine operators are subjected to certain limitations and inefficiencies. Considering that delivering large volume of reliable samples from deep zones to the surface in shortest possible time is of paramount importance in mineral exploration, then drilling small size holes as fast as possible and delivering the small chip samples to the surface would be a good alternative with several advantages over conventional drilling methods. As a result, the Coiled Tube (CT) turbodrilling technology is proposed here followed by presenting detailed calculations for the system required power and hydraulics and also Bottom Hole Assembly (BHA) selection suitable for hard rocks mineral exploration applications.