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Incorporating conceptual and interpretation uncertainty to mineral prospectivity modelling

Geoscience Frontiers 2019年第4期10卷 1383-1396页

作者： J.N.Burkin M.D.Lindsay S.A.Occhipinti E.-J.Holden centre for exploration targeting School of Earth SciencesThe University of Western Australia

Prospectivity analyses are used to reduce the exploration search space for locating areas prospective for mineral *** scale of a study and the type of mineral system associated with the deposit control the evidence layers used as proxies that represent critical ore genesis *** particular,knowledge-driven approaches(fuzzy logic)use a conceptual mineral systems model from which data proxies represent the critical *** typically vary based on the scale of study and the type of mineral system being *** analyses utilising interpreted data to represent proxies for a mineral system model inherit the subjectivity of the interpretations and the uncertainties of the evidence layers used in the *** the case study presented,the prospectivity for remobilised nickel sulphide(NiS)in the west Kimberley,Western Australia,is assessed with two novel techniques that objectively grade interpretations and accommodate alternative mineralisation *** targets are then identified and supplied with a robustness assessment that reflects the variability of prospectivity value for each location when all models are *** first technique grades the strength of structural interpretations on an individual line-segment *** are obtained from an objective measure of feature evidence,which is the quantification of specific patterns in geophysical data that are considered to reveal underlying *** structures are weighted in the prospectivity model with grading values correlated to their feature *** technique allows interpreted features to contribute prospectivity proportional to their strength in feature evidence and indicates the level of associated stochastic *** second technique aims to embrace the systemic uncertainty of modelling complex mineral *** this approach,multiple prospectivity maps are each generated with different combinations of confidence values applied

关键词： Prospectivity Confidence Uncertainty Multiple models Mineral exploration Nickel

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3-D geochemical interpolation guided by geophysical inversion models

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Geoscience Frontiers 2021年第3期12卷 132-145页

作者： Tom Horrocks Eun-Jung Holden Daniel Wedge ChrisWijns centre for exploration targeting.School of Earth Sciences University of Western AustraliaCrawleyWA 6009Australia

3-D geochemical subsurface models,as constructed by spatial interpolation of drill-core assays,are valuable assets across multiple stages of the mineral industry's ***,the accuracy of such models is limited by the spatial sparsity of the underlying drill-core,which samples only a small fraction of the *** limitation can be alleviated by integrating collocated 3-D models into the interpolation process,such as the 3-D rock property models produced by modern geophysical inversion procedures,provided that they are sufficiently resolved and correlated with the interpolation *** standard machine learning algorithms are capable of predicting the target property given these data,incorporating spatial autocorrelation and anisotropy in these models is often not *** propose a Gaussian process regression model for 3-D geochemical interpolation,where custom kernels are introduced to integrate collocated 3-D rock property models while addressing the trade-off between the spatial proximity of drill-cores and the similarities in their collocated rock properties,as well as the relative degree to which each supporting 3-D model contributes to *** proposed model was evaluated for 3-D modelling of Mg content in the Kevitsa Ni-Cu-PGE deposit based on drill-core analyses and four 3-D geophysical inversion *** the inversion models improved the regression model's likelihood(relative to a purely spatial Gaussian process regression model)when evaluated at held-out test holes,but only for moderate spatial scales(100 m).

关键词： Machine learning Gaussian process regression Kriging Geophysical inversion Interpolation

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Subaerial hot springs and near-surface hydrothermal mineral systems past and present,and possible extraterrestrial analogues

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Geoscience Frontiers 2020年第5期11卷 1549-1569页

作者： Franco Pirajno centre for exploration targeting(CET) The University of Western Australia35Stirling HighwayCrawleyWA6009Australia

The principal features,geotectonic settings and association with near-surface hydrothermal mineral systems of ancient and present subaerial hot springs,fumaroles and geysers are herein *** and geysers usually occur in volcanic craters and are in most cases,part and parcel of hot spring *** hot springs are characterised by siliceous-and carbonate-rich chemical sediments,such as sinters and travertines,*** are commonly enriched in various metalliferous *** springs surface discharges are also characterised by pools,which exhibit bright colours due to the presence of ***-day examples discussed in this paper,include the fumaroles and hot springs of the White Island volcano(New Zealand),the world-renowned Yellowstone caldera(USA)and the Afar region of the East African Rift *** Afar triangle,in the northern part of East African Rift System,provides a good example of hot springs associated with evaporative *** Tuli-Sabi-Lebombo triple junction rifts were formed during the^180 Ma Karoo igneous event in southern Africa,of which the Tuli arm is the failed rift(aulacogen),as is the Afar *** Tuli rift is effectively an unusual,if not unique,tectono-thermal setting,because it comprises Karoo-age hot springs systems and associated vein stockworks and breccias,which includes the Messina Cu deposit as well as currently active hot springs with sinter deposits probably due to post-Karoo *** pipes in ignimbrites of the Erongo Volcano-Plutonic Complex in Namibia are *** is followed by an example of banded chert rocks in the Killara Formation of the Palaeoproterozoic Capricorn Orogen(Western Australia),interpreted as hot spring chemical sediments,which also show evidence of"fossil"microbial *** paper ends with a brief overview of possible analogues of hot springs on planet Mars.

关键词： Subaerial hot springs Fumaroles Chemical sediments Hydrothermal systems Afar Erongo volcano-plutonic complex

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The giant Kalgoorlie Gold Field revisited

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Geoscience Frontiers 2016年第3期7卷 359-374页

作者： Noreen Mary Vielreicher David Ian Groves Neal Jesse McNaughton Department of Material Science and Physics University of Salzburg centre for exploration targeting University of Western Australia John de Laeter centre for Isotope Research Curtin University

The Neoarchaean Kaigoorlie Gold Field contains the giant Golden Mile and world-class Mt Charlotte deposits,which have been the subject of much research for over 100 *** Golden Mile deposit is a complex array of ductile to brittle vein and breccia lodes that are predominantly hosted in the highlyfractionated Golden Mile Dolerite *** Fimiston lodes comprise an array of narrow lodes that evolved broadly syn- to late-formation of the regional D2 NW-trending *** lodes are characterized by pyrite veinlets and disseminations,quartz veinlets and breccias,and banded quartz-carbonate veins with sericite,carbonate,and pyrite-dominated *** Green-Leader,or Oroya-style,lodes,with grades in excess of 1000 g/t Au,are similar to the Fimiston-style lodes,but are characterized by abundant visible gold,native tellurium and more abundant telluride minerals within roscoelitebearing alteration *** arguably structurally younger Mt Charlotte-style lodes are characterized by a pipe-shaped,coarse-grained quartz,carbonate and scheelite vein-stockwork with distinct verticallyzoned,carbonate-sericite-albite-pyrite ± pyrrhotite dominant alteration assemblages around veins within Unit 8 of the Golden Mile dolerite and porphyry *** network of steep- and gently-dipping extension and shear fracture-fill veins are associated with NE-trending fault se ts that cross cut the regional *** deposit area is intruded by swarms of porphyry dykes,including syn-volcanic mafic dykes,early and volumetrically most significant c.2.67 Ga feldspar-phyric porphyry dykes,as well as later c.2.66-2.65 Ga calc-alkaline hornblende-phyric dykes associated with younger c.2.65-2.64 Ga lamprophyre *** post-volcanic dykes have similar orientations to the Fimiston *** feldspar dykes are clearly overprinted by all styles of mineralization,although the relationship between hornblende-phyric and lamprophyre dykes and gold mineralization is more *** agree

关键词： Kalgoorlie Golden Mile Mount Charlotte Gold giant Orogenic gold Magmatic-hydrothermal gold

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Province-scale commonalities of some world-class gold deposits:Implications for mineral exploration

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Geoscience Frontiers 2015年第3期6卷 389-399页

作者： David I.Groves M.Santosh centre for exploration targeting UWA State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences centre for Tectonics Resources and exploration Dept.of Earth SciencesUniversity of Adelaide Division of Interdisciplinary Science Faculty of ScienceKochi University

Discovery rates for all metals, including gold, are declining, the cost per significant discovery is increasing sharply, and the economic situation of the industry is one of low base rate. The current hierarchical structure of the exploration and mining industry makes this situation difficult to redress. Economic geologists can do little to influence the required changes to the overall structure and philosophy of an industry driven by business rather than geological principles, However, it should be possible to follow the lead of the oil industry and improve the success rate of greenfield exploration, necessary for the next group of lower-exploration-spend significant mineral deposit discoveries. Here we promote the concept that mineral explorers need to carefully consider the scale at which their exploration targets are viewed. It is necessary to carefully assess the potential of drill targets in terms of terrane to province to district scale, rather than deposit scale, where most current economic geology research and conceptual thinking is concentrated. If orogenic, IRGD, Carlin-style and IOCG gold-rich systems are viewed at the deposit scale, they appear quite different in terms of conventionally adop- ted research parameters. However, recent models for these deposit styles show increasingly similar source-region parameters when viewed at the lithosphere scale, suggesting common tectonic settings. It is only by assessing individual targets in their tectonic context that they can be more reliably ranked in terms of potential to provide a significant drill discovery. Targets adjacent to craton margins, other lithosphere boundaries, and suture zones are clearly favoured for all of these gold deposit styles, and such exploration could lead to incidental discovery of major deposits of other metals sited along the same tectonic boundaries.

关键词： Mineral exploration Gold deposits Tectonic settings Mining industry Discovery rate

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Source to sink zircon grain shape:Constraints on selective preservation and significance for Western Australian Proterozoic basin provenance

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Geoscience Frontiers 2018年第2期9卷 415-430页

作者： V.Markwitz C.L.Kirkland School of Earth ■ Environment The University of Western Australia Department of Applied Geology Centre for Exploration Targeting-Curtin NodeJohn de Laeter CentreInstitute of Geoscience Research (TIGeR)Curtin University

The effect of selective preservation during transportation of zircon grains on the detrital age spectrum is difficult to quantify and could potentially lead to systematic bias in provenance analysis. Here we investigate whether the shape of detrital zircon grains holds provenance information and if the grain shape can assist in understanding preservation. We applied multiple linear regression analysis to identify significant shape properties in detrital zircons from Proterozoic metasediments of the Capricorn and Amadeus basins and their Archean and Proterozoic sources in the Yilgarn Craton and the Musgrave Province in Western Australia. Digital images and isotopic data from 819 SIMS U-Pb dated zircons were examined for correlation between grain shape, age, U and Th content. Out of twelve shape descriptors measured, Minor Axis, the width of zircon grains perpendicular to the crystallographic c-axis, consistently shows the most significant correlation with isotopic age. In the studied population Archean grains are narrower than Proterozoic grains: the probability that grains wider than 75 μm are Archean is less than30%.Calculations of the proportions of source material in sedimentary rocks relative to the proportions of source material in the overall catchment area(erosion parameter 'K' calculated based on age spectra)produced values typical for mature river systems, with K = 6 for the Yilgarn-Capricorn and K = 5.5 for the Musgrave-Amadeus source-sink system. For the Yilgarn-Capricorn system, we also calculated 'K' based on Minor Axis, to determine whether grain width can be linked to age populations. Results of the shapebased K of 5.3 suggest a similarity between age-based and shape-based 'K' values, demonstrating that zircon grain width may be a useful discriminator of provenance. Contrary to commonly applied qualitative shape classifications, we found no consistent correlations between shape descriptors of magmatic zircons and the composition of their host rock. Wh

关键词： Zircon grain shape U-Pb geochronology Detrital Whole rock geochemistry Precambrian

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Geology and Lead-Sulphur Isotope Compositions of the Tongyu Volcanic-Hosted Massive Sulphide Copper Deposit in the Western Part of the North Qinling Orogen, China

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Acta Geologica Sinica(English Edition) 2017年第5期91卷 1767-1777页

作者： GONG Hujun ZHU Laimin LI Ben XIONG Xiao DING Lele State Key Laboratory of Continental Dynamics Department of Geology Northwest University centre for exploration targeting ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS)School of Earth and Environment The University of Western Australia

The Tongyu copper deposit, located in the western part of the North Qinling Orogen, China, is one of several volcanic-hosted massive sulphide（VHMS） deposits with industrial value and is also a typical example of mineralization related to the subduction and metallogenesis during the Caledonian orogeny. We conducted systematic lead-sulphur isotope geochemical analyses of the Tongyu deposit to understand the possible ore-forming material sources and tectonic settings. Twenty-six sulphide samples yielded clustered δ^34SCDT values of 1.13‰-3.36‰, average 2.22‰, and show a tower-type distribution,implying that the sulphur of the Tongyu copper deposit mainly originated from a mantle source. The Pb isotope compositions of sulphides（^206Pb/^204Pb = 17.59225-18.56354, average 18.32020; ^207Pb/^204Pb =15.51770-15.69381, average 15.66217; ^208Pb/^204Pb= 37.99969-39.06953, average 38.52722） are close to the values of the volcanic host rocks（^206Pb/^204PbPb= 18.10678-18.26293, average 18.21158; ^207Pb/^204PbPb =15.63196-15.68188, average 15.65345; ^208Pb/^204PbPb= 38.43676-38.56360, average 38.49171）, thus consistent with the Pb in ores and volcanic host rocks having been derived from a common source that was island-arc Pb related to oceanic crust subduction. The northward subduction of the Palaeo-Qinling oceanic crust triggered dehydration of the slab, which generated a large amount of high-oxygen-fugacity aqueous hydrothermal fluid. The fluid rose into the mantle wedge, activated and extracted metallogenic material and promoted partial melting of the mantle wedge. The magma and ore-forming fluid welled up and precipitated, finally forming the Tongyu VHMS copper deposit.

关键词： VHMS-type copper deposit ore-forming material source S-Pb isotope island arc environment

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The tectonics and mineral systems of Proterozoic Western Australia:Relationships with supercontinents and global secular change

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Geoscience Frontiers 2018年第2期9卷 295-316页

作者： A.R.A.Aitken S.A.Occhipinti M.D.Lindsay A.Joly H.M.Howard S.P.Johnson J.A.Hollis C.V.Spaggiari I.M.Tyler T.C.McCuaig M.C.Dentith centre for exploration targeting The University of Western AustraliaPerthWestern AustraliaAustralia The Geological Survey of Western Australia Department of Mines and PetroleumPerthWestern AustraliaAustralia BHP Billiton 125 St Georges TerracePerthAustralia ARC centre of Excellence for Core to Crust Fluid Systems Centre for Exploration TargetingSchool of Earth SciencesThe University of Western AustraliaAustralia Resource Potentials PerthAustralia Department of Geology The Ministry of Mineral ResourcesGreenland GovernmentGreenland

The cratonisation of Western Australia during the Proterozoic overlapped with several key events in the evolution of Earth. These include global oxidation events and glaciations, as well as the assembly,accretionary growth, and breakup of the supercontinents Columbia and Rodinia, culminating in the assembly of Gondwana. Globally, Proterozoic mineral systems evolved in response to the coupled evolution of the atmosphere, hydrosphere, biosphere and lithosphere. Consequently, mineral deposits form preferentially in certain times, but they also require a favourable tectonic setting. For Western Australia a distinct plate-margin mineralisation trend is associated with Columbia, whereas an intraplate mineralisation trend is associated with Rodinia and Gondwana, each with associated deposit types. We compare the current Proterozoic record of ore deposits in Western Australia to the estimated likelihood of oredeposit formation. Overall likelihood is estimated with a simple matrix-based approach that considers two components: The "global secular likelihood" and the "tectonic setting likelihood". This comparative study shows that at least for the studied ore-deposit types, deposits within Western Australia developed at times, and in tectonic settings compatible with global databases. Nevertheless, several deposit types are either absent or poorly-represented relative to the overall likelihood models. Insufficient exploration may partly explain this, but a genuine lack of deposits is also suggested for some deposit types. This may relate either to systemic inadequacies that inhibited ore-deposit formation, or to poor preservation. The systematic understanding on the record of Western Australia helps to understand mineralisation processes within Western Australia and its past connections in Columbia, Rodinia and Gondwana and aids to identify regions of high exploration potential.

关键词： Mineral systems Tectonics Australia

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The conjunction of factors that lead to formation of giant gold provinces and deposits in non-arc settings

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Geoscience Frontiers 2016年第3期7卷 303-314页

作者： David I.Groves Richard J.Goldfarb M.Santosh centre for exploration targeting UWA State Key Laboratory of Geological Processes and Mineral Resources China University of Geosciences U.S.Geological Survey Denver Federal Center centre for Tectonics Resources and exploration Dept. of Earth SciencesUniversity of Adelaide Division of Interdisciplinary Science Faculty of ScienceKochi University

It is quite evident that it is not anomalous metal transport,nor unique depositional conditions,nor any single factor at the deposit scale,that dictates whether a mineral deposit becomes a giant or not.A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc *** giant orogenic,intrusion-related gold systems（IRGS） and Carlin-type gold deposits and iron oxide-copper-gold（IOCG） deposits,there are common factors among all of these at the lithospheric to crustal *** are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or,in the case of most Phanerozoic orogenic giants,define the primary suture zones between tectonic *** provinces of IRGS,IOCG,and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant *** IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids,whereas the association of such melts with Carlin-type ores is more indirect and *** orogenic gold provinces show no direct relationship to such *** from metamorphic fluids,but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order *** contrast to their province scale similarities,the different giant gold deposit styles show contrasting critical controls at the district to deposit *** orogenic gold deposits,the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits,with resultant geometrical and lithostratigraphic complexity as a guide to their *** are few giant IRGS due to their inferior fluid-flux systems relative to orogeni

关键词： Giant gold deposits Orogenic gold Carlin deposits Iron oxide-copper-gold deposits Intrusion-related gold systems Lithosphere

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CO2 degassing and melting of metasomatized mantle lithosphere during rifting-Numerical study

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Geoscience Frontiers 2019年第4期10卷 1409-1420页

作者： Weronika Gorczyk Christopher M. Gonzalez University of Western Australia Centre for Exploration TargetingSchool of Earth SciencesARC Centre of Excellence for Core to Crust Fluid SystemsPerthWestern AustraliaAustralia School of Earth Atmosphere and EnvironmentMonash University ClaytonMelbourneVICAustralia

:Reactivation of metasomatized mantle lithosphere may occur during continental extension,which is an important component of plate *** lower most part of the metasomatized domains in the subcontinental mantle lithosphere can be locally enriched in ***,partial melting of these metasomatized domains may play a crucial role in the global carbon ***,little is known about this process and up until now few numerical constraints are *** we address this knowledge gap and use a 2-D high resolution petrological-thermomechanical model to assess lithospheric ***2 degassing and *** test 4 lithospheric thicknesses:90,110,130 and 200 km with a 10 km thick metasomatized layer at the base using CO2 of 2 wt.%in the bulk *** carbonate enriched layer is stable below^3 GPa(>110 km)for a temperature of 1300℃;therefore,we only observe degassing patterns for lithospheric models that are 130 km and 200 km *** metasomatized layer for the 130 km thick lithosphere mostly comprises carbonatite melting,whereas in the 200 km thick scenario propagation of melt development from kimberlites to carbonatites occurs as the metasomatic mantle is exhumed during *** numerical models fit well into natural rifting zones of the European Cenozoic Rift System for young(shallow)and of the North Atlantic Rift for old(thick)lithosphere.

关键词： Rifting Mantle CO2 degassing Carbonate melting

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