Publications
Kenex co-founder Greg Partington and other members of the Kenex team have kept up an incredible track record of publishing papers in conference proceedings and scientific journals since Kenex was founded. You can read them here.
Domaining in Mineral Resource Estimation: A Stock-Take of 2019 Common Practice
Resource blocks estimated within a particular domain should only be informed by sample points from within that domain. If this fundamental principle of mineral resource estimation is not adhered to it may severely compromise the quality of the final resource estimate. Nonetheless, the repeated reminder of resource downgrades or even complete project devaluations as the consequence of poor domaining practice suggests that this principle is still not well-entrenched in industry practice. As many practitioners have warned and as documented in books, course materials and online blogs over the years: geology is important. It is good practice to base domains primarily on geological information derived from geological logging of drill core or chips, underpinned by an understanding of the structural geometry of the ore body and a well-understood genetic model of mineralisation. However, a sound statistical analysis of geochemical data that are accurate and precise is also required to evaluate the domains. Multi-element geochemistry from laboratory or portable XRF instruments combined with multivariate data analysis and machine-learning (ML), as well as core scanners and down-hole optical televiewers, and other recent technological advances are powerful tools that enable the proper delineation of domains. However, these tools are often underutilised as they require additional investment at a time in a project when their value can be hard to demonstrate. Unfortunately, the use of geological information to create domains is the exception rather than the rule. Our review of mineral resource estimates published since 2017 suggests that more than half of all estimation-constraining wireframes are built using grade cut-offs and are not informed by any primary geological information such as lithology or alteration. While using a grade cut-off may seem perfectly logical to delineate domains when detailed geological information is not available, if not treated with caution, this can lead to poor domain integrity. Books and courses on resource estimation clearly express the importance of domaining but offer few practical solutions or rules of thumb. There appears to be a lack of clear standards, a lack of a framework to distinguish good from bad domaining practice and there is a perpetuation of bad practice masked as common practice. Here we offer some recommendations to raise domaining standards across the industry and present a rules-based approach to improve domaining practices at the individual level.
Practical Implementation of Random Forest-Based Mineral Potential Mapping for Porphyry Cu–Au Mineralization in the Eastern Lachlan Orogen, NSW, Australia
With the increasing use of machine learning for big data analytics, several methods have been implemented for the purpose of exploration targeting using mineral potential mapping in a GIS environment. Random forests (RF) have been successfully applied to data-driven mineral potential mapping using relatively small numbers of input maps that have typically been pre-classified by a geologist familiar with the mineral system being targeted. However, it is useful to understand how well RF perform for mineral potential mapping when a large number of multi-class categorical or non-thresholded numeric input maps are used in the classification or when weighted or ranked training data are used. Four different implementations of RF are presented to examine how the results vary depending on the degree of intervention from an expert in the modeling process. A case study has been devised using data from the eastern Lachlan Orogen in New South Wales (Australia) for the purposes of targeting porphyry Cu–Au mineralization related to the Macquarie Arc. The results demonstrate that the use of a large number of multi-class categorical or non-thresholded numeric predictive input maps results in a poor mineral potential map outcome. An expert review to determine reclassifications or thresholds that produce geologically meaningful maps as proxies for the mineral system being targeted results in more effective RF-based mineral potential maps being produced. Weighting or ranking the deposits used as training data produces more narrowly defined prospective areas that may assist with targeting tier-one economic deposits. Comparison of the RF results to a standard weights of evidence analysis highlighted some significant differences in which predictive maps should be considered important for modeling, and in the extent of prospective area delineated from each output mineral potential map.
Mineral potential mapping as a strategic planning tool in the eastern Lachlan Orogen, NSW
The Geological Survey of New South Wales (GSNSW) is undertaking a statewide mineral potential mapping project driven by the need to provide justifiable land use planning advice to key government stakeholders and to highlight the exploration potential of the state’s major mineral systems at a regional scale. Following delivery of mineral potential data packages for the Southern New England Orogen (Blevin et al. 2017) in 2017, and the Curnamona Province and Delamerian Thomson Orogen (Ford et al. 2018) in 2018, the eastern Lachlan Orogen was selected as the next area for a review of key mineral systems and mineral potential.
Translating expressions of intrusion-related mineral systems into mappable spatial proxies for mineral potential mapping: case studies from the Southern New England Orogen, Australia
An understanding of the modelled mineral system and high-quality data that accurately map this system are prerequisites for producing geologically meaningful mineral potential maps. Critical to this is the translation of the targeted mineral system components into mappable targeting criteria and their spatial proxies. This paper presents a workflow that illustrates this translation process, also highlighting that, if done well, mineral potential mapping can produce statistically valid, geologically meaningful, and practically useful results that not only predict the location of known mineralisation but also identify new target areas. An important ingredient of the workflow described herein is what we call a mineral systems atlas. This compendium includes (1) a spatial data table detailing the translation of the modelled mineral system, (2) the predictive maps that capture the mappable components of the targeted mineral system, and (3) the final mineral potential maps. A case study implementing and illustrating this workflow is presented for intrusion-related Au and Sn +/- W mineral systems in the Southern New England Orogen, New South Wales, Australia. Importantly, the mineral potential maps generated as part of this study succeeded in identifying areas of known intrusion-related Au and Sn +/- W mineralisation and new areas with high potential for discovery.
3D mineral potential modelling of gold distribution at the Tampia gold deposit
A 3D mineral potential model was developed for the Tampia Gold Project in Western Australia to help constrain resource estimation, understand the distribution of gold grades from the resource estimation techniques with respect to geological and physiochemical continuity, and predict the location of new gold mineralisation for future exploration drilling to expand the gold resource at Tampia. The 3D mineral potential model was generated using predictive maps based on a local granulite-facies orogenic gold mineral system model. These were generated from regional scale data and data collected during a 40 m by 40 m resource drilling programme, and included lithology, structure, rock property data and geochemical data. The predictive capacity of each map was tested for the spatial correlation with training data from high grade gold drill intersections, using the weights of evidence technique. There were 44 predictive maps created that can be used as proxies to map the physical and chemical processes active in the orogenic mineral system at Tampia. Of these, 11 were chosen for the final model that had the highest spatial correlation with the training data and did not duplicate map patterns. A closely spaced infill drilling programme was subsequently undertaken over an area where the post probability results indicated high and continuous probability for gold mineralisation, while the resource model estimated less continuous and lower grade gold mineralisation. This infill drilling aimed to compare the gold continuity at a 10 m by 10 m drill spacing with the resource estimate gold grades and post probability distribution developed from 40 m by 40 m spaced resource drilling. The results from the 10 m by 10 m spaced drilling were thereby used to test the performance of both the resource and prospectivity models, and assess the utility of mineral potential modelling for use in developing geological domains to constrain resource estimation. Results from the first phase of infill drilling, which only covers 4% of the total model area, confirm the continuity of the post probability values and suggests that the mineral potential model predicts the location and distribution of gold mineralisation within the area drilled. The results were also better and more continuous than predicted by the resource estimate. Importantly, these results confirm that geological and physiochemical controls on gold mineralisation can be numerically measured and mapped at the scale of an orebody. This allows mineral potential modelling to be considered as an option to constrain and help inform the results of geostatistical techniques used in resource estimation.
Targeting Lithium Mineralisation in the Taupo Volcanic Zone, New Zealand
Mineral potential mapping of porphyry targets at the Bundarra Cu-Au project, Queensland
Mineral Potential Mapping for Pre-Competitive Data Delivery in NSW Zone 54
A collaborative project between the Geological Survey of New South Wales (GSNSW) and Kenex Pty Ltd was undertaken to evaluate the mineral potential of MGA Zone 54 in NSW as a continuation of GSNSW’s ongoing program of mineral potential mapping across the state, which commenced in the southern New England Orogen in 2017. The results of the Zone 54 project will deliver a pre-competitive geoscience data package that will be used to guide mineral exploration and land-use planning in the region. Prior to modelling, the available datasets were reviewed and updated by GSNSW to ensure accuracy and that relevant attribute information was present. Using a mineral systems approach, models were developed for Broken Hill Type Pb-Zn-Ag and IOCG mineralisation in the Curnamona Province, and Orogenic Au and VHMS mineralisation in the Delamerian-Thomson Orogens. The component processes in the mineral system models were translated into mappable targeting criteria. The key predictive variables, mapped using geological, geochemical, and geophysical datasets, were determined using spatial statistics. Mineral potential maps were generated for each mineral system using a weights of evidence approach. Area-frequency analyses show model efficiencies between 88-99%, which indicate almost all training points used to represent evidence of the mineral system being targeted are predicted within a small area. A comprehensive spatial data table outlining the details of the mappable targeting criteria and the results of the spatial data analysis, and maps of the key predictive variables were delivered, along with the mineral potential maps as a pre-competitive dataset for public release.
Using gravity to target gold at Tampia Hill, Western Australia
The discovery of the Tampia Hill orogenic gold deposit in the wheatbelt of Western Australia has sparked interest in this under-explored region of the state. The deposit is hosted within a granulite facies greenstone belt, with mineralisation mostly hosted in mafic gneiss, which has been intruded by undeformed and unmetamorphosed granite. A lack of outcrop in the project area has meant that geophysics has been vital for interpretation of the geology. A recent gravity and magnetic survey has allowed the most detailed interpretation of the underlying lithology and structures to date, and has highlighted previously unknown areas of mafic gneiss, with a similar signature to that at Tampia Hill. In order to extract the most useful information from the survey, spatial statistical analyses were conducted on the gravity survey data. The analyses over the project area map features within the gravity data that can be used to identify areas of known gold mineralisation. The results confirm that the gravity data not only provides critical geological information, but will also allow the identification of high priority targets for future exploration using spatial data modelling techniques.
Downhole Logging in 3D Geology and Mineral Potential Modelling
Logging of drillholes using wireline tools is an emerging methodology in mineral exploration that adds valuable data to exploration drilling. RC drilling is relatively cheap and quick, but it comes with the price of lost sample integrity and structural coherence. Wireline logging can cover this loss, by facilitating structural interpretations based on borewall imagery. Rock property data can also be recovered below the sampling resolution, such as optical televiewer (OTV) imagery, density, magnetic properties, natural gamma radiation and acoustic properties on cm and even mm scale. In the field, wireline logging will add just a few days to the drilling programme. A team of wireline technicians run their wireline down a recently completed drillhole using an assortment of tools depending on the requests of the client, at a cost amounting to only a few dollars per metre. The tools are oriented with magnetometers and accelerometers, enabling directional logging of geological features the drilling passed through. Combined with on-site logging of lithology and data from tools used in the field, wireline logging will enable exploration to take a significant step towards complete understanding of the prospect geology. In this paper we show downhole logging results from Tampia Hill, Western Australia, and how this work has been used to establish a structural framework and guide the creation of 3D geological and mineral potential models
The Southern New England Orogen Mineral Potential Project
The Southern New England Orogen (SNEO) in the northeastern part of New South Wales (NSW) is prospective for intrusion-related tin-tungsten, intrusion-related gold-bismuth-molybdenum-silver and orogenic goldantimony mineral systems. An initiative by the Geological Survey of NSW to conduct mineral potential modelling for these mineralisation styles in the SNEO has resulted in a comprehensive account of the mineral resource potential of the region. The Geological Survey of NSW has a successful strategy of providing high quality pre-competitive data that has been complemented and enhanced by the mineral potential mapping approach. Datasets including seamless basement geology, detailed attribution of faults, and igneous fertility that were created by the survey prior to modelling enabled an extensive number of variables be tested for relevance to each mineral system. The feedback from the data processing and spatial analysis allowed improvements to be made to the data and provided information on the relevance of the datasets to mineral exploration in the region. The outputs of the models are mineral potential maps that map the geological potential of the SNEO for each mineralisation style. The models will be used for land planning and advice purposes, technical resources for improved mineral system studies including global endowment estimations, and for promoting exploration in the SNEO through the generation of prospective targets. Due to the richness of the geological datasets in NSW it is likely that the technique, including the creation of high-quality datasets combined with mineral potential modelling, can be successfully applied to other mineralised regions within NSW.
Bullabulling goldfield
The Bullabulling goldfield straddles the Great Eastern Highway, 25 km west of Coolgardie and 70 km south-west of Kalgoorlie in Western Australia at -31.02 deg, 120.90 deg. Gold was first discovered and mined in the late 1980s at Gibraltar, which is late in the history of gold discoveries in the Yilgarn. The Bullabulling goldfield is atypical in the eastern Yilgarn because gold at Bullabulling is not associated with greenschist facies metamorphic rocks or brittle-ductile higher-grade narrow quartz vein arrays or shear zones; instead it has similarities with high-tonnage low-grade gold deposits more commonly found in the US or Canada. Recent structural analysis and 3D geological mapping of the Bullabulling gold deposit clarified the understanding of controls on gold mineralisation, and identified new areas for exploration within the Bullabulling gold deposit and regionally. Subsequent drilling of the Bullabulling gold deposit produced a sevenfold increase of the gold resource, transforming the goldfield in terms of future production potential. Gold endowment of the Bullabulling goldfield is 122 t Au.