Paul Lusty

Reconnaissance-Scale Prospectivity Analysis for Gold Mineralisation in the Southern Uplands-Down-Longford Terrane, Northern Ireland

The Southern Uplands-Down-Longford Terrane in southeast Northern Ireland is prospective for Caledonian-age, turbidite-hosted orogenic gold mineralisation with important deposits at Clontibret in the Republic of Ireland and in Scotland. Geochemical and geophysical data from the DETI-funded Tellus project have been used, in conjunction with other spatial geoscience datasets, to map the distribution of prospectivity for this style of mineralisation over this terrane. A knowledge-based fuzzy logic modelling methodology using Arc Spatial Data modeller was utilised. The prospectivity analysis has identified several areas prospective for turbidite-hosted gold mineralisation, comparable to that at Clontibret and gold occurrences in the Southern Uplands of Scotland. A number of these either coincide with known bedrock gold occurrences or with areas considered prospective and targeted by previous exploration work, validating the predictive capability of the exploration model devised and its translation into a GIS-based prospectivity model. The results of the modelling suggest that as in other parts of the Southern Uplands the coincidence of regional strike-parallel structures and intersecting transverse faults are highly prospective, as these are likely to create zones of anomalous stress for fluid flow and deposit formation. Those areas in which there are no known gold occurrences are considered to be favourable targets for further exploration and should be followed up.

Challenges to global mineral resource security and options for future supply

Abstract Minerals are vital to support economic growth and the functioning of modern society. Demand for minerals is increasing as global population expands and minerals are used in a greater range of applications, particularly associated with the deployment of new technologies. While concerns about future mineral scarcity have been expressed, these are generally unfounded and based on over-simplistic analysis. This paper considers recent debate around security of mineral supply and technical, geosciences-based options to improve utilization of the resource base and contribute to replenishing reserves. History suggests that increasing demand for minerals and higher prices will generally lead to technological and scientific innovation that results in new or alternative sources of supply. Recent assessments of global mineral endowment suggest that society should be optimistic about its ability to meet future demand for minerals, provided that there is continued innovation and investment in science and technology. Reducing energy consumption and breaking the current link between metal production and greenhouse gas emissions are among the greatest challenges to secure a sustainable mineral supply. However, widespread adoption of low-carbon mineral extraction technologies, underpinned by multidisciplinary research, and increased global utilization of low-carbon energy sources will allow these challenges to be met.

Ore Deposits in an Evolving Earth

Ore deposits form by a variety of natural processes that concentrate elements into a volume that can be economically mined. Their type, character and abundance reflect the environment in which they formed and thus they preserve key evidence for the evolution of magmatic and tectonic processes, the state of the atmosphere and hydrosphere, and the evolution of life over geological time. This volume presents 13 papers on topical subjects in ore deposit research viewed in the context of Earth evolution. These diverse, yet interlinked, papers cover topics including: controls on the temporal and spatial distribution of ore deposits; the sources of fluid, gold and other components of orogenic gold deposits; the degree of oxygenation in the Neoproterozoic ocean; bacterial immobilization of gold in the semi-arid near-surface environment; and mineral resources for the future, including issues of resource estimation, sustainability of supply and the criticality of certain elements to society.

Gold potential of the Dalradian rocks of north-west Northern Ireland: prospectivity analysis using Tellus data

Abstract The Dalradian terrane in the north-west of Northern Ireland is prospective for orogenic vein-hosted gold mineralisation with important deposits at Curraghinalt and Cavanacaw. New geochemical and geophysical data from the DETI-funded Tellus project have been used, in conjunction with other spatial geoscience datasets, to map the distribution of prospectivity for this style of mineralisation over this terrane. A knowledge-based fuzzy logic modelling methodology using Arc Spatial Data Modeller was utilised. Four main groups of targets were identified, many close to known occurrences in the Lack – Curraghinalt zone and others in prospective areas identified by previous investigations. Additional targets are located along west-north-west trending linear zones at the eastern end of the Newtownstewart Basin and to the north of the Omagh-Kesh Basin. These zones may be related to major structures linked to a westward extension of the Curraghinalt lateral ramp which is regarded as an important control on the location of the Curraghinalt deposit.

The origin and distribution of critical metals (Pd, Pt, Te and Se) within the Skouries Cu–Au porphyry deposit, Greece

Component Analysis was used to reduce noise from spurious pixels associated with high water content in peat. These spurious pixels were subsequently removed using a supervised classification (Minimum-Distance). The data were standardised to zero mean and equal variance. An unsupervised classification (K-means) was used to automatically and objectively classify the remaining data in 9-dimensional space (based on the input variables). Six classes were found to be optimum for delineating geochemical variations within the granites. Here, we present this new classification of the granites using continuous data covering the whole batholith. We also consider how to incorporate ground-based geochemical and satellite multispectral (Landsat) data into the classification.

Ore deposits in an evolving Earth: an introduction

Abstract Ore deposits form by a variety of natural processes that concentrate elements into a small volume that can be economically mined. Their type, character and abundance reflect the environment in which they formed and thus they preserve key evidence for the evolution of magmatic and tectonic processes, the state of the atmosphere and hydrosphere, and the evolution of life over geological time. This volume presents 13 papers on topical subjects in ore deposit research viewed in the context of Earth evolution. These diverse, yet interlinked, papers cover topics including: controls on the temporal and spatial distribution of ore deposits; the sources of fluid, gold and other components in orogenic gold deposits; the degree of oxygenation in the Neoproterozoic ocean; bacterial immobilization of gold in the semi-arid near-surface environment; and mineral resources for the future, including issues of resource estimation, sustainability of supply and the criticality of certain elements to society.

Fe-rich cap lithologies in the TAG hydrothermal field: implications for the preservation of extinct seafloor massive sulphide deposits

ning of a thin section for bright PGM, following scan lines at a certain magnification, and are a time-consuming process. This is especially problematic in highly mineralised samples, (>8 g t total PGE), where it may take >8 h to manually record all the PGMs in a 1 cm area of a thin section. The demand by the mining industry for faster analyses and complete ore characterisation for metallurgical and liberation purposes has led to the development of various mineral liberation analysis (MLA) software products by FEI and MINTEK e.g. (van der Merwe et al. 2012) and (Voordouw et al. 2010). Contrastingly, the method outlined here utilises the widely available Oxford Instruments AZtecEnergy software on a Zeiss (NTS S360) Sigma HD FEG-SEM, fitted with two 150 mm EDS detectors at Cardiff University. The results of a comparative study whereby the manual method and the newly developed automated approaches are applied on the same thin section are presented here. By combining the data, an assessment of the accuracy and effectiveness of both approaches as well as an indication of any bias can be achieved. The data was collected using the AZtecFeature function. The hypothesis behind this methodology is that a thin section can be ‘screened’ for PGM based on their characteristic brightness, as described above. Greyscale threshold values can be applied to highlight grains of this specific brightness once a BSE image of a sample has been acquired, this typically takes 20 min. These threshold values are set for each sample and require one PGM to be found manually first as a ‘benchmark’. The highlighted grains are linked to the SEM so that the slide is easily navigated to these sites to confirm their composition and textural setting; the grain size (area) is calculated automatically. Early indications suggest that there are limitations and benefits of the automated technique. Automation improves search times by 98% (i.e. the time it takes to find all the PGM in the sample) although we have not yet fully automated PGM identification from other high density minerals. There are two main problems with relying on BSE intensity alone: (1) Galena has the same brightness as the PGM and (2) Laurite is duller than other PGM, leading to overand under-representation in the automated dataset, respectively.

Using radioelement distributions to classify a composite granite batholith in the South West England Orefield

The South West England Orefield is well-known for its polymetallic magmatichydrothermal mineralisation associated with the composite Cornubian granite batholith. The mineralisation contains elevated concentrations of a range of metals (e.g. W, Sb, Bi, As, Be, Cd, Ga, Ge, In, Li, Nb, Ta) used in high-technology and clean energy applications and for which security of supply concerns exist [1,2,3]. Exploration for these elements requires improved understanding of the spatial distribution of granite types and their relationship to the different mineralisation styles and parageneses. Previous granite classifications defined granite types based on mineralogical and/or textural observations from field sampling [e.g. 4]. However, these divisions over simplify mineralogical variation (e.g. micas), and the sample density is inadequate to reflect the heterogeneity of the batholith. Classifications based on whole-rock geochemistry, provide a more objective classification method [e.g. 5] and can guide mineral exploration, particularly in poorly exposed areas.