In this paper, we summarise advancements in top-of-hole sensing achieved within the Deep Exploration Technologies Cooperative Research Centre (DET CRC). It was demonstrated that the drill fines, which were previously discarded, show high potential to act as a representative sample media of the lithologies intersected by the drill hole and can be successfully used for analysis in real time. The Lab-at-Rig(R) (LAR(R)) system was developed for prospecting rigs (diamond drilling in the first instance and coil tube drilling in the future) and encompasses sample capture, sample preparation and presentation to sensors. In the initial setup of the LAR platform, there are two sensors, a portable X-ray fluorescence (pXRF) and a portable X-ray diffraction, capable of delivering chemical and mineralogical data in near real time. Laser-induced breakdown spectroscopy was also explored as a potential additional sensor for future versions of the LAR system, as it can yield information on elemental composition including essential light elements not currently measured by air-based pXRF detectors (e.g. Li, Na and Mg at low levels) or other elements problematic by pXRF (e.g. Au). The LAR system implements X-ray diffraction (XRD) analysis from which mineralogical data (mineral identification and most importantly mineral quantification) must be obtained in near real time. The existing challenge with XRD is that any data processing and especially data interpretation with available software packages requires some expertise in the field and background in crystallography and is time-consuming. Hence, SwiftMin(R), the world's first algorithm for automated processing of XRD data, was developed. It provides mineral identification and quantification and performs all calculations and processing independent from a user. SwiftMin returns a result in seconds and is able to batch process hundreds of XRD patterns in a matter of minutes. The above means, that SwiftMin is a technology that allows processing of large amount of XRD data quickly, saving time, costs and labour. The overall concept and vision developed within the DET CRC in top-of-hole sensing by coupling chemical and mineralogical analyses of drilling materials is to provide an end-to-end solution that supports rapid decision making by a geologist, at the time-scale of drilling the hole.

Microanalysis can provide rapid, quantitative characterization of mineral systems that complements the field-and core-scale observations traditionally made in ore deposits. We review recent innovations in microanalytical procedures and their application to studies of ore deposits. Case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems. Synchrotron X-ray fluorescence shows centimetre-scale chemical variations associated with proximity to mineralization in samples from Sunrise Dam Gold Mine, Western Australia. Pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid-driven brecciation with very little shearing. Both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization. A second case study of sulphide mineralogy at the Mt Keith nickel sulphide deposit, Western Australia demonstrates how X-ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems. Large-scale interaction between silicate and sulphide melts, shown by homogenous palladium enrichment in pentlandite, leads to a large proportion of globular ores with a high nickel content. Increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro- and macroscale datasets.

The Emmie Bluff iron oxide, copper, gold (IOCG) prospect is located in the Olympic Dam district, South Australia, and hosts sub-economic 150-m-thick Cu–Au mineralisation associated with the hematite–chlorite–sericite alteration with chalcopyrite commonly replacing pre-existing pyrite at a depth of 800 m. With the use of cutting-edge synchrotron X-ray fluorescence microscopy and field emission gun-scanning electron microscopy, it is shown for the first time that sub-economic IOCG mineralisation in the Olympic Dam district was affected by a late fluid event, which resulted in partial dissolution of Cu mineralisation and transport of Cu in the form of chloride complexes. The porous chlorite–sericite matrix associated with the late alteration of chalcopyrite hosts a Cu–Cl–OH phase previously undescribed in IOCG rocks, which was identified as one of the polymorphs of the atacamite group of minerals, Cu2Cl(OH)3. Thermodynamic modelling shows that “atacamite” is produced during dissolution of chalcopyrite by an oxidised, Cl-bearing fluid. An acidic environment is produced within millimetres of the chalcopyrite grains during oxidation. This process drives chlorite recrystallisation that is recorded by compositional variation of chlorite proximal to chalcopyrite. The existence of the atacamite is discussed in the context of fluid evolution and interaction with IOCG-type mineralisation and its implications to ore preservation versus destruction and remobilisation.

In the Cloncurry District, several similar to 1530 Ma iron oxide-copper-gold (IOCG) deposits such as Ernest Henry, and the Merlin Mo-Re deposit, are hosted by polymictic hydrothermal breccias with textures implying fluidization. Similarly textured breccias, highly discordant yet barren, are found along fault arrays and junctions in specific corridors through the Cloncurry district. We generated geomechanical models of the stress and fluid pressure requirements for failure along the fault arrays thought to be active at the time of IOCG and Mo-Re mineralization. The richest mineralized breccias occur within corridors in areas of overlap of predicted highest rock failure potential for the two main structural events. Most barren breccias and some IOCGs without fluidized breccia occur in low to moderate failure potential sites of only one of the deformation events. We infer the mineralizing, high energy packages were structurally connected to mid-crustal metal + fluid sources (e.g. from intrusions) along deeper-penetrating and longer lived master structures. Barren, very high energy breccias, were connected, probably more transiently, to metal-poor fluid sources due to time/space differences in fluid release, or because more extreme overpressures failed to precipitate metals.

Transported overburden is a persistent problem for mineral exploration in Australia and elsewhere, with explorers not confident in the current understanding of where, when and how geochemical anomalies form (or don't form) in surficial materials and how to make the critical interpretive link to buried deposits. The recent discovery of the high-grade VHMS Cu-Au DeGrussa deposit on the margins of the Yilgarn Craton in the Bryah Basin of Western Australia highlights the value of effective exploration in these covered terrains. We investigated this deposit to understand the near surface geochemical signature from weathering and groundwater dispersion. Multiple sample media (soil, regolith, groundwater and vegetation) and analytical methods were used to examine metal migration. The DeGrussa (Cu-Au) ore body was successfully identified using organic soil, vegetation and groundwater with multi-element anomalies associated with the buried ore. Primarily, the anomalies are caused by weathering and vertical dispersion through thin (2 – 10 m) transported cover and vegetation cycling of Au and Cu located a few metres below the surface. Aqua regia extractions of soils and vegetation, and MMI-M extraction of soils were effective by providing strong, coherent multi-element anomalies at relatively close spacing (50 m). Conversely, portable XRF analysis was less effective at this site as the elemental concentrations were too low. Gold, As and Cu in groundwater were present in anomalous concentrations, but inconsistently so at larger sample spacing (100 s of metres). When compared to regional hydrogeochemistry (e.g. >1000 m spacing), Au, As, Cu, Pd and Pt element concentrations in the DeGrussa groundwater were elevated in a broad, general area along strike potentially identifying additional targets. Weathering, hydraulic lift by vegetation and hydromorphic dispersion are the mechanisms responsible for metal migration at the DeGrussa site.

The analysis of drill powders (drill fines) extracted from fluid that is returned during drilling can provide a sampling media that records cm-scale changes in the geochemistry of the rock being drilled through. In addition to being an ideal sample media (~78% of particles are <38μm; cf. conventionally pulverised samples where ~42% of particles are <38μm) that is ready for analysis once dried, diamond drill fines may produce a larger sample per meter drilled than recovered by the core itself, and thus be a better representation of the rock that has been drilled through. For an HQ hole size (for rocks with specific gravity=3100kg/m3), the mass of drill fines produced in 1m of drilling is 12.5kg, whereas, the mass of the 1m in length of core for the same interval is 9.7kg. In this contribution we compare high-spatial resolution geochemistry collected by portable X-ray fluorescence (pXRF) and mineralogy collected by portable X-ray diffraction (pXRD) from 12m of diamond drill core to the corresponding interval of drill fines to highlight the depth fidelity (at the cm-scale) that this sample source may record. We also demonstrate that the drill fines that were previously discarded show high potential to act as a representative sample media of the lithology intersected by the drill hole and can be successfully used for analysis in real time. The integrated pXRF-pXRD data can be used to constrain lithologies and contacts between various units, hydrothermal alteration and ore types.

Many ore deposits are hosted by metamorphic rocks, and metamorphic fluids have been invoked as a source for various deposits, especially gold deposits. Metamorphic fluid compositions reflect original sedimentary environment: continental shelf sequences yield saline metamorphic fluids with little dissolved gas while metasediments from accretionary and oceanic settings host less saline fluids with significant CO2 contents.The principal difficulty in reconciling ore deposits with a metamorphic origin is that many form quickly (c. 1 Ma), whereas metamorphic heating is slow (c. 10-20 degrees/Ma). Gravitational instability means that fluid cannot be retained. Metamorphic ores may nevertheless form by: (a) segregation leading to enrichment of pre-existing concentrations; (b) infiltration of water-rich fluids from schists into marbles at high temperature overstepping decarbonation reactions and allowing fast reaction that locally draws down temperature; and (c) rapid uplift driving dehydration reactions owing to pressure drop.Some orogenic lode gold deposits fit well with a purely metamorphic origin during rapid uplift, but others are problematic. At Sunrise Dam, Western Australia, anomalies in Sr-isotope ratios and in apatite compositions indicate a partial mantle/magmatic source. Low salinity, H2O-CO2 fluids commonly associated with hydrothermal gold reflect the effect of salt on gas solubility, not the origin of the fluid.

The Maia large solid-angle detector array and imaging system is capable of collecting high-resolution images of up to ∼100 M pixels in size with dwell times of less than 0.2 ms per pixel and thus it is possible to document variation in textures associated with trace element chemistry by collecting quantified elemental maps of geological samples on the scale of entire thin sections in a short time frame (6–8 hr). The analysis is nondestructive and allows variation to be recognised on a centimetre scale while also recognising zonations at the micron scale.

Alteration reactions associated with gold mineralisation can be used to elucidate the nature of the fluid that transported gold into a deposit. At the Junction gold deposit, Kambalda, Western Australia, gold is hosted in a metamorphosed and hydrothermally altered dolerite. Mineralisation at the deposit scale is associated with zones of K, CO2 and S metasomatism, as is common in many greenstone hosted gold deposits. However, at the thin-section scale gold is not closely associated with sulphide minerals but within zones of carbonate metasomatism and K-loss where pre-existing biotite has reacted to produce chlorite, muscovite and Fe–Mg carbonates. Gold precipitation is intimately associated with biotite breakdown where calcite is locally absent. Quantified mineral modes from detailed microstructural mapping are used to balance reactions describing the breakdown of biotite in the presence and absence of calcite. Using the basic assumption that Al is immobile during metasomatism the reactions are successfully balanced, even in a manifestly open system. Modelling of fluid–rock reactions using HCh constrains the fluid composition (0.11<X(CO2)<0.13) and fluid–rock ratios (<12:1) that can produce the observed mineral assemblage. Additional modelling of solid solution mineral phases using thermocalc estimates alteration conditions of 390°C, 4kbar and also suggests a fluid X(CO2)~0.1. Both these models show that the observed muscovite and chlorite compositions can be produced primarily through the removal of K from the measured precursor biotite. We show that it is not possible to transport and deposit all the gold observed in the alteration zone with the low fluid–rock ratios obtained from modelling of silicate alteration and inferred gold concentrations in these fluids. We suggest that this is typical of greenstone hosted gold deposits and that mechanisms other than aqueous solution, which can transport higher gold concentrations, must be considered.

The common practice in current exploration diamond drilling campaigns is to drill a hole, collect the core, log the core, split the core and send samples from selected intervals for analysis in a commercial lab. This results in a turnaround time of a few weeks or months, and the data obtained is a conventional assay data on a number of chemical elements. Rarely, if ever, a few samples are analysed by some other techniques, for example X-Ray Diffraction (XRD). Powders produced during diamond drilling show high potential to act as a representative sample media of the lithology intersected by the drill hole. The drilling powders are transported back to the surface by the drilling fluid providing an opportunity of being sampled and analysed in real time at a resolution defined by a geologist on site. Moreover, this novel sample media requires little or no sample preparation before it can be analysed.

Portable X-ray fluorescence (pXRF) technology can be used to collect large amounts of multi-element data rapidly at relatively low cost and has been widely embraced within the minerals industry. However, to date, it has been difficult to compare data-sets collected by different users or at different times because there is no standardized approach to the collection of these data. The absence of information on standardization and calibration procedures raises concerns about a lack of internal consistency within these data-sets and precludes comparison of different data-sets. This paper seeks to address this issue by developing a workflow for the collection of pXRF data in an exploration or mining setting. Two case studies highlight the robustness and possible applications of pXRF data collected following QA/QC protocols. A good correlation between conventional laboratory analyses and pXRF data is demonstrated through comparison of analysis methods for a drill-hole at the Plutonic Gold Mine, Western Australia, and fine-scale lithostratigraphic variation is recognized in pXRF data collected on grade control pulps from a drill fan at the Agnew Gold Mine, Western Australia. The Agnew data precision is sufficient to distinguish alteration signals from background lithology, and to discern which alteration signals are associated with gold mineralization.

We present the application of a new synchrotron-based technique for rapid mapping of trace element distributions across large areas of the CV3 meteorites Allende and Vigarano. This technique utilizes the Australian Synchrotron X-ray Fluorescence Microscopy (XFM) beam line with its custom designed and built X-ray detector array called Maia. XFM with Maia allows data to be collected using a 2 mu m spot size at very low dwell times (similar to 0.1-0.5 ms), resulting in maps of entire thin sections in similar to 5 h. Maia is an energy dispersive detector system with a large collection solid-angle, which allows full spectral acquisition and high sensitivity. Hence, there is no need to constrain the elements of interest a priori.We collected whole section maps (similar to 2 cm x 1 cm) from 3 thick sections of Allende and a single map (2 cm x 1.5 cm) from a thick section of Vigarano. Our experimental conditions provide data for elements with 20 <= Z <= 40 (K-shell, Ca through Zr) and the L-emissions of Os, Ir, Pt, Au, and Pb. We illustrate the unique capabilities of this technique by presenting observations across myriad length scales, from the centimeter-scale down to the detection of sub-micrometer particles within these objects. Our initial results show the potential of this technique to help decipher spatial and textural variations in trace element chemistry between CAIs, chondrules, matrix, and other chondritic components. We also illustrate how these datasets can be applied to understanding both nebular and parent-body processes within meteorites. (C) 2014 Elsevier Ltd. All rights reserved.

Chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fluid from which the minerals precipitate. In fluid-buffered systems, zoning of mineral compositions is expected to reflect directly the evolution of fluid composition. Here we show that during rapid fluid-rock reactions, ultra-local equilibrium can form complex mineral zoning patterns, even when the overall system is highly fluid buffered. We reacted cleaved calcite single crystals with aqueous arsenate-phosphate solutions with molar ratios of As/(As + P) between 0.01 and 0.15 at 250 degrees C and water-saturated pressure. We find that complex zoning patterns and solid solution between hydroxylapatite-and arsenate-bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours, and these zoning patterns were destroyed within days during secondary reactions. We propose a two-stage reaction process in the formation of the final reaction product. (1) On an hour time scale, calcite is dissolved and replaced by compositionally heterogeneous apatite. The thin reaction-interface fluid layer becomes extremely enriched in arsenic at an ultra-local scale as the reaction removes phosphate faster than the interface fluid can re-equilibrate with the bulk fluid. (2) The heterogeneous apatite is replaced by homogeneous apatite that reflects the bulk fluid composition over a longer (days) time scale through interface-coupled dissolution-precipitation. This paper highlights the complexity that can arise from ultra-local fluid composition variations due to rapid fluid-rock interaction in a short-lived fluid flow event, for example during a seismic cycle. Subsequent interpretation of complex zoning patterns as reflecting the evolution of bulk fluid would be erroneous.

Motivated by the challenge of capturing complex hierarchical chemical detail in natural material from a wide range of applications, the Maia detector array and integrated real-time processor have been developed to acquire X-ray fluorescence images using X-ray Fluorescence Microscopy (XFM). Maia has been deployed initially at the XFM beamline at the Australian Synchrotron and more recently, demonstrating improvements in energy resolution, at the P06 beamline at Petra III in Germany. Maia captures fine detail in element images beyond 100 M pixels. It combines a large solid-angle annular energy-dispersive 384 detector array, stage encoder and flux counter inputs and dedicated FPGA-based real-time event processor with embedded spectral deconvolution. This enables high definition imaging and enhanced trace element sensitivity to capture complex trace element textures and place them in a detailed spatial context. Maia hardware and software methods provide per pixel correction for dwell, beam flux variation, dead-time and pileup, as well as off-line parallel processing for enhanced throughput. Methods have been developed for real-time display of deconvoluted SXRF element images, depth mapping of rare particles and the acquisition of 3D datasets for fluorescence tomography and XANES imaging using a spectral deconvolution method that tracks beam energy variation.

In high-nugget gold ore bodies, samples taken from drill core for gold assay are typically too small to allow for the extreme spatial variability in grade and are a poor representation of the underlying distribution of mineralisation. The GQ North lode at the Sunrise Dam Gold Mine in Western Australia is a good example of an orebody which has a very strong nugget effect (coefficient of variation >20) and that has proved very problematic to model. Gold is hosted in vein stockworks and shear zones and although there is a clear spatial relationship between mineralisation and alteration, high vein density and well-developed foliations, the relationship is best defined statistically because the association between high gold grades and various combinations of these features is non-trivial. We present a method for automating the inclusion of geological data (proxies for gold mineralisation) into the prediction of mineralised rocks, using conditional probability. The method uses the gold assays and the logged geological data to calculate the probability that rocks with particular geological features will be mineralised. The ore body can then be modelled automatically using interpolation software with isosurfaces indicating the regions with highest probability of gold mineralisation. A good understanding of the geological features associated with mineralisation and consistent geological logging are important prerequisites for successful conditional probability modelling of drill hole data.