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A4 heat-bound report of 8pp (ISSN 1749 8775)

Modelling of 3D domain boundaries using information from drill holes is a standard procedure in mineral exploration and mining. Manual logging of drill holes can be difficult to exploit as the results may not be comparable between holes due to the subjective nature of geological logging. Exploration and mining companies commonly collect geochemical or mineralogical data from diamond drill core or drill chips; however, manual interpretation of multivariate data can be slow and challenging; therefore, automation of any of the steps in the interpretation process would be valuable. Hyperspectral analysis of drill chips provides a relatively inexpensive method of collecting very detailed information rapidly and consistently. However, the challenge of such data is the high dimensionality of the data’s variables in comparison to the number of samples. Hyperspectral data is usually processed to produce mineral abundances generally involving a range of assumptions. This paper presents the results of testing a new fast and objective methodology to identify the lithological boundaries from high dimensional hyperspectral data. This method applies a quadrant scan analysis to recurrence plots. The results, applied to nickel laterite deposits from New Caledonia, demonstrate that this method can identify transitions in the downhole data. These are interpreted as reflecting mineralogical changes that can be used as an aid in geological logging to improve boundary detection.

Manually interpreting multivariate drill hole data is very time-consuming, and different geologists will produce different results due to the subjective nature of geological interpretation. Automated or semi-automated interpretation of numerical drill hole data is required to reduce time and subjectivity of this process. However, results from machine learning algorithms applied to drill holes, without reference to spatial information, typically result in numerous small-scale units. These small-scale units result not only from the presence of very small rock units, which may be below the scale of interest, but also from misclassification. A novel method is proposed that uses the continuous wavelet transform to identify geological boundaries and uses wavelet coefficients to indicate boundary strength. The wavelet coefficient is a useful measure of boundary strength because it reflects both wavelength and amplitude of features in the signal. This means that boundary strength is an indicator of the apparent thickness of geological units and the amount of change occurring at each geological boundary. For multivariate data, boundaries from multiple variables are combined and multiscale domains are calculated using the combined boundary strengths. The method is demonstrated using multi-element geochemical data from mineral exploration drill holes. The method is fast, reduces misclassification, provides a choice of scales of interpretation and results in hierarchical classification for large scales where domains may contain more than one rock type.

The chemistry of hydrothermal monazite from the Carrapateena and Prominent Hill iron oxide-copper-gold (IOCG) deposits in the IOCG-rich Gawler Craton, South Australia, is used here to define geochemical criteria for IOCG exploration in the Gawler Craton as follows: Monazite associated with IOCG mineralisation: La + Ce &gt, 63 wt% (where La &gt, 22.5 wt% and Ce &gt, 37 wt%), Y and/or Th &lt, 1 wt% and Nd &lt, 12.5 wt%, Intermediate composition monazite (between background and ore-related compositions): 45 wt% &lt, La + Ce &lt, 63 wt%, Y and/or Th &lt, 1 wt%. Intermediate monazite compositions preserving Nd &gt, 12.5 wt% are considered indicative of Carrapateena-style mineralisation, Background compositions: La + Ce &lt, 45 wt% or Y or Th &gt, 1 wt%. Mineralisation-related monazite compositions are recognised within monazite hosted within cover sequence materials that directly overly IOCG mineralisation at Carrapateena. Similar observations have been made at Prominent Hill. Recognition of these signatures within cover sequence materials demonstrates that the geochemical signatures can survive processes of weathering, erosion, transport and redeposition into younger cover sequence materials that overlie older, mineralised basement rocks. The monazite geochemical signatures therefore have the potential to be dispersed within the cover sequence, effectively increasing the geochemical footprint of mineralisation.

There is a need for rapid and reliable techniques for extracting geological information from geochemical data derived from exploration drill hole samples because geochemical data bases are becoming too large to interpret manually. Automated boundary detection techniques which use the continuous wavelet transform are a popular method for extracting multi-scale geological boundaries from drill hole signals. However, these boundary detection techniques do not distinguish between sharp and gradational boundaries, which may be an important factor when interpreting the geology of the subsurface or calculating resource estimates. This paper demonstrates how a scale-dependant measure of relative sharpness of the boundary can be extracted from the results of the continuous wavelet transform. The results of the automated method are compared against the interpretations of 15 geologists. The comparison demonstrates the need for alternative boundary selection methods when boundaries are not sharp. The results also demonstrate how the multi-scale nature of the sharpness measure allows for reliable gradient analysis in noisy signals.

An important step in mineral resource estimation process is the grouping of drill hole samples into domains that reflect zones of homogeneous properties for accurate grade estimation and practical exploitation purposes. In practice, this challenging task is performed through a subjective, time-consuming manual interpretation of the mineral deposit. Therefore, various interpretations are possible. The definition of domains can be viewed as a clustering problem consisting of grouping samples into clusters, herein called domains, so that samples belonging to the same cluster are more similar than those in different clusters. Several methods exist for this purpose; however, groups of samples created through traditional clustering tend to show poor spatial contiguity. Alternatively, spatially contiguous clusters can be obtained through geostatistical clustering where the spatial dependency between samples is considered. This paper is devoted to the application of geostatistical clustering to support do...

A 3D geology model is a simplified version of the true geology, designed to give a visual summary of the geometry and distribution of major geological elements in a specified region. Drill holes provide detailed data of the subsurface that can be classified into geological units that are the fundamental elements of the 3D model. Due to software limitations, upscaling (‘lumping’) is usually required to reduce the number of geological units in the drill holes prior to model building. Upscaling is a subjective process, which means that different geologists will group in different ways and will typically not record the rationale behind their decision; this means the “experiment” is not reproducible. In our study we use a method of upscaling geological units, in this case based on assay data, using the continuous wavelet transform (CWT) and tessellation methods. This method reduces subjectivity and can easily be repeated (e.g. on an updated or new drill hole) by using the same parameters, ensuring that the upscaling process is consistent over all drill hole data. We apply this technique to a large assay database (>90,000 samples) from the Kevitsa Nickel-Copper-Platinum group element (PGE) deposit in Finland. The Kevitsa Ni-Cu-(PGE) disseminated sulfide orebody is hosted in a Proterozoic layered intrusion in northern Finland. Internal geological subdivision and correlation within the intrusion is very difficult to do consistently using lithological observations, owing to general homogeneity of rock types and an overprint of alteration, but distinct variability is evident in Ni and PGE sulfide tenors. In its raw form, the tenor variation dataset appears noisy and unsystematic. We have applied the tessellation method to classifying ore types based on tenor variations, consistently and objectively reducing the number of units in each drill hole to create a simplified 3D model of the orebody. Our results reveal shallow inward dipping cryptic layering defined by sulfide composition, which are interpreted as reflecting an increase in Ni and PGE tenor with time during emplacement of the sulfide-bearing cumulates. We interpret this as a progressive increase in silicate-sulfide mixing efficiency (R factor) as the intrusion developed from an interconnected sill sediment-complex choked with country rock inclusions into a freely convecting magma chamber. Based on this case study, we show that the tessellation method can add considerable value by distinguishing the wood from the trees in large 3D geochemical databases. The method may be widely applicable in other Ni-Cu-PGE deposits where tenor variations appear, at first sight, to be chaotic and uninterpretable.

In the Knobby mine area near Mary Kathleen northwest Queensland, a sequence of calc-silicate rocks of the Corella Formation have been intruded, multiply deformed and metamorphosed. Three metasomatic episodes have been recognised and associated with phases of intrusion and tectonic activity. An analysis of the style and geometry of complex fold outcrops reveals the presence of a previously undocumented major deformation phase, FI, with recumbent and upright folds at both mesoscopic and macroscopic scales. These are overprinted by a major, regional deformation event, F2, and minor conjugate monoclinal folds, F3. Variations in refolded fold patterns involving FI and F2 are largely due to the variability in dip and orientation of FI axial planes. The variability in orientation of the FI folds is considered to be partly due to heterogenous strain around pretectonic intrusives, but mostly reflects the structures associated with a proposed thrusting environment. Recent mapping throughout the Mary Kathleen region has uncovered areas of FI thrust duplexes and nappes. Correlation of FI structures in the study area with zones of thrusting in adjacent areas, and comparison with similar thrust belts elsewhere in the world, have shown that FI is consistent with deformation in a thrust and nappe environment. The proposed direction of thrust movement for the study area is similar to that postulated for the nearby Deighton and Mitakoodi areas, but dissimilar to that proposed for the adjacent, structurally underlying, Wonga Belt, suggesting a complex history of pre-F2 sub-horizontal movement.

Manual interpretation of data collected from drill holes for mineral or oil and gas exploration is time-consuming and subjective. Identification of geological boundaries and distinctive rock physical property domains is the first step of interpretation. We introduce a multivariate technique, that can identify geological boundaries from petrophysical or geochemical data. The method is based on time-series techniques that have been adapted to be applicable for detecting transitions in geological spatial data. This method allows for the use of multiple variables in detecting different lithological layers. Additionally, it reconstructs the phase space of a single drill-hole or well to be applicable for further investigations across other holes or wells. The computationally cheap method shows efficiency and accuracy in detecting boundaries between lithological layers, which we demonstrate using examples from mineral exploration boreholes and an offshore gas exploration well., 20 pages, 10 figures, submitted to Computers & Geosciences, 2019

Gold distribution in vein-hosted hydrothermal ore deposits is commonly nuggety (i.e. occurs as very localised concentrations of gold). In these cases samples for gold assay from diamond drill core may be too small to model the underlying heterogeneity of gold distribution and result in poorly constrained ore body models and underestimated gold resources. Hence, it is common practice to use more spatially continuous proxies for mineralisation to help define the boundaries of mineralised regions. We present a method for automating the use of geochemical proxies for nuggety gold ore bodies. Sunrise Dam Gold Mine, in Western Australia, is a world-class gold deposit with a very high nugget effect. Multi-element geochemical data has been collected at this site in order to improve prediction of mineralised regions. Suitable proxy elements have been selected from this data set, in particular, those that are spatially related to gold mineralisation but do not display nuggety distribution, such as Sb, Rb and Cr. We applied a probabilistic approach to the problem of quantifying the relationship between gold assay values and geochemical elements. It is shown that a kernel density estimator and Bayes conditional probability can provide an effective method for calculating the probability of a sample having elevated gold content and that this measure will be more spatially continuous than gold assay values if the appropriate geochemical proxies are selected. Using conditional probability and suitable cut-off values, we reclassified approximately 27% of samples as mineralised which returned low Au assay results. When plotted on drill holes conditional probability values provided a much more spatially continuous guide to mineralised regions than Au assay values alone.

(2007). The Secret Life of Textiles: Six Pattern Book Archives in North West England, Philip Anthony Sykas. TEXTILE: Vol. 5, No. 1, pp. 98-101.

Sections from a sedimentary succession can be simulated using a process which includes both probabilistic and deterministic information. The inclusion of both of these types of information allows the production of geologically realistic simulations which contain the required level of heterogeneity. The process uses syntactic pattern recognition techniques and is based on the formal description of a geological model using a grammar. The simulations can be conditioned on well data.

We show that mapping data from a bounded region onto a toroidal surface prior to running the DR (Dog-Rabbit) clustering algorithm greatly increases the rate of success of finding all the clusters in the region.

The D'Entrecasteaux Islands in eastern Papua New Guinea are composed of a number of active metamorphic core complexes which have been intruded by granodiorite plutons during their formation. The plutons do not appear to have been intruded by diapiric processes as previously suggested. Late, relatively undeformed plutons form flat-lying bodies which crosscut structural boundaries and are strongly discordant to core complex shear zones. Granodiorite magmatism and the development of the metamorphic core complexes have occurred in a linear zone which coincides with a zone of thick crust and rugged topography. It is proposed that plutonism facilitated deformation in ductile extensional shear zones which resulted in tectonic exhumation of deep crustal rocks and formation of the metamorphic core complexes. The source of the plutons is thought to be related to a linear zone of mantle upwelling beneath the islands related to the propagation of the Woodlark seafloor spreading center into continental crust. It is suggested that a localized heat source of this type, which can provide heat and magmatic material to the crust, is essential for the development of metamorphic core complexes.

OPHTHALMOLOGY RESEARCH has identified a relationship between human placenta and eye tissue. Placental amniotic membrane provides structural healing properties that help restore vision in patients with ocular disease that has been unresponsive to medical treatment. THE PATHWAY from donor placenta retrieval to amniotic membrane transplantation (AMT) involves perioperative nurses from obstetrics and ophthalmology departments who are well versed in federal regulations and eye or tissue bank standards. PERIOPERATIVE NURSES can promote recycling of placentas for preservation and facilitate optimal surgical outcomes for patients undergoing AMT, as well as provide these patients with emotional support and education. AORN J 88 (November 2008) 731–742. © AORN, Inc, 2008.

As lithospheric plates are subducted, rocks are metamorphosed under high-pressure and ultrahigh-pressure conditions to produce eclogites and eclogite facies metamorphic rocks. Because chemical equilibrium is rarely fully achieved, eclogites may preserve in their distinctive mineral assemblages and textures a record of the pressures, temperatures and deformation the rock was subjected to during subduction and subsequent exhumation. Radioactive parent-daughter isotopic variations within minerals reveal the timing of these events. Here we present in situ zircon U/Pb ion microprobe data that dates the timing of eclogite facies metamorphism in eastern Papua New Guinea at 4.3 +/- 0.4 Myr ago, making this the youngest documented eclogite exposed at the Earth's surface. Eclogite exhumation from depths of approximately 75 km was extremely rapid and occurred at plate tectonic rates (cm yr(-1)). The eclogite was exhumed within a portion of the obliquely convergent Australian-Pacific plate boundary zone, in an extending region located west of the Woodlark basin sea floor spreading centre. Such rapid exhumation (1 cm yr(-1)) of high-pressure and, we infer, ultrahigh-pressure rocks is facilitated by extension within transient plate boundary zones associated with rapid oblique plate convergence.

Summary We present an algorithm that improves the detection of minor anomalies and patterns in potential field maps. Its use in conjunction with standard edge detection algorithms provides a tool for visual estimation of depth-to-the-source in gravity and magnetic maps.