Mapping the geology that matters – the role of Australia’s geological surveys in supporting mineral discovery in the 21st century

Yeats, Chris1

1Geological Survey of New South Wales, Department of Regional NSW, Maitland, Australia

During the late 20th century, Australia’s geological survey organisations (GSOs) completed 1:250,000 scale surface geological mapping of the continent. This work provided a framework for mineral exploration that led to the discovery of most of the surface and near-surface deposits in areas of outcropping basement that form the basis of the country’s current mineral production. From the 1970s, geological mapping was augmented by regional geophysical data and from the mid-1990s increased geochronological analysis, which supported a second generation of higher resolution mapping under the National Geoscience Mapping Accord into the early 21st century. However, this second wave of mapping, which often focused on areas of good quality outcrop with known mineral potential, did not lead to many significant discoveries and over 80% of the country’s current mineral production now comes from deposits discovered prior to 1980.

In order to provide a framework for mineral discovery in the 21st century, Australian GSOs need to change the search space and provide the exploration industry with the data they need to successfully explore deeper and step out into the 75% of the Australian continent where prospective basement is buried under younger, non-prospective cover. Essentially, GSOs must map “the geology that matters” – defining the structural architecture, temporal evolution and lithologies of potentially prospective geological terranes, regardless of whether they are exposed at the surface, or not.

This work has already started in New South Wales (NSW), with the NSW Seamless Geology providing an interpreted lithotectonic framework for the state, based primarily on surface mapping and potential field geophysical data. However, further geological data is required to support this model, particularly in undercover terranes. As participants in the ten-year MinEx CRC National Drilling Initiative (NDI), Australia’s GSOs will generate new precompetitive geoscientific data over several underexplored, undercover regions across the continent. Equally importantly, the NDI will support development of cheaper, faster drilling technologies, real-time sensing technologies and new concepts and decision-making tools that will aid mineral exploration in deep and/or covered terranes, thereby making large parts of the continent more accessible to mineral exploration.

Concurrently, Australia’s GSOs are deploying new technologies to augment existing national datasets. The ~55km-spaced stations of the collaborative Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) is delivering a lithospheric-scale conductivity model that can be used to define areas of anomalous fluid flow for further investigation. Completion of the AusAEM electromagnetic survey across Australia over the next four years will deliver a near-surface conductivity model that can be used to define depth to basement, as well as potential for mineral and groundwater resources. New geochemical and isotopic datasets are also being used to define fluid sources and crustal evolution at a continental scale.

As we enter the third decade of the 21st century, Australia’s GSOs face a watershed moment. We must and are transitioning from mapping the surface geology, to mapping prospective geology and delivering new types of data, to create a framework for the discovery of the new deposits needed to support Australia’s mineral industry into the second half of the century.


Biography

Chris was Executive Director of the Geological Survey of NSW from June 2015 to December 2020. Prior to this, he spent 17 years as a researcher and manager at CSIRO, where his work focussed on the formation of and exploration for gold and base metal deposits in ancient and modern terranes.

Application of indicator minerals in mineral exploration

Salama, Walid1; Le Vaillant, Margaux1; Schoneveld, Louise1; Schlegel, Tobias1; Anand, Ravi1

1CSIRO Mineral Resources, Kensington, Perth, Western Australia

Mineral exploration in weathered and covered terrains has given preference to geophysical and geochemical methods over mineralogical analyses. Airborne and ground geophysical surveys identify magnetic, electromagnetic and gravitational anomalies and allow the rapid delineation of exploration targets. However, the methods don’t indicate whether a target is mineralised or not. Geochemical surveying, based on the analysis of soils, vegetation, termites or calcrete are well-established techniques for locating and identifying variable types of mineralisation. However, their application in areas of deep cover is limited. Indicator minerals, useful for exploration in the weathered and covered terranes, are those that 1) resist chemical weathering in weathered profiles; 2) undergo chemical changes to form secondary minerals in the weathering profile; 3) precipitate within organic-rich sediments during diagenesis; and 4) resist physical weathering during erosion, transportation and deposition.

Mineral explorers are interested in knowing the fertility of a mineral system, in minerals indicating the presence or absence of mineralisation and in vectors towards mineralisation. Within the CSIRO Discovery Program, research projects continue to focus on the identification and characterisation of indicator minerals. Examples of such studies are the potential use of trace element zoning patterns in pyroxenes as fertility indicators for magmatic Ni-Cu-Co-(PGE) deposits, white mica composition in hydrothermal alteration halo as a vector toward Au mineralisation, trace element composition of chromite and arsenide as exploration tools for Ni and Au deposits, and the REE composition of fluorite which reflect the fluid type involved in IOCG mineralisation.

In weathered terrains, rutile, gahnite and cassiterite with base metal sulfide inclusions are residually enriched in the leached and lateritic zone over the Scuddles massive sulfides forming Bi, Sb and Pb anomalies. The use of heavy indicator minerals is also a practical exploration tool in areas of Quaternary glacial till in Canada and Fennoscandia and in the Permian glacial diamictites in Australia. In Australia, the diamictites deposited immediately above the Permian unconformity are largely unweathered and contain detrital sulfides. The distance that indicator minerals disperse from the source depends mainly on the topography of the unconformity between the cover and the bedrock. In northeast Yilgarn Craton, the Permian diamictites were deposited on a rough topography and indicator minerals are expected to be derived from proximal source rocks. Iron, Cu, Zn, As, Ni and Co sulfides were identified at the base of the Permian cover above mafic-ultramafic rocks and used as vectors toward Au mineralisation at Agnew and Lancefield in Western Australia.

In summary, trace element contents of indicator minerals are used to vector toward mineralisation and the source fluids involved in its formation. Residual and supergene indicator minerals in weathered profiles can indicate mineralised bedrock underneath the cover. Detrital and diagenetic indicator minerals in transported cover are a potential vectoring tool for various types of mineral deposits.    


Biography

Walid Salama is a senior research scientist working for CSIRO Mineral Resources. He joined the regolith geoscience group as a postdoc fellow in 2012. His research focused on geochemical exploration of Au, base metals, Ni and Fe in the weathered and covered terrains in Western Australia, Queensland and Botswana.

Martian regolith: from cryolithosphere to atmosphere

Caprarelli, Graziella1

1Centre for Astrophysics, School of Sciences, University of Southern Queensland, Toowoomba, QLD 4350, Australia

Regolith is: “everything, from fresh rock to fresh air”1. The term indicates the layers of loose material that mantle bedrock, although there is disagreement among regolith experts between the camp that subscribes to the broad definition given above, and the camp that discriminates between the material formed in place as a product of weathering, and sediments formed elsewhere, transported and deposited on bedrock which was not the parent material2. We now know that regolith mantles the surface of all rocky bodies in the solar system: on many of these objects there are no geological processes leading to sedimentary erosion and deposition such as on Earth. Thus, here I use the term in its broader sense.

Mars is a hyperarid planet3, with water stored as ice in its polar caps and in the ground. The uppermost layers of the martian crust are thus termed the ‘cryolithosphere’. Meteoritic “gardening” since early Noachian times (~ 4.0 Ga) has produced the thick layer of broken rocky material covering Mars’s surface globally. Wind erosion and mass wasting also act on a global scale, while chemical processes have led to the deposition of hydrous minerals in the soil. The martian regolith thus comprises dust, sandy soils and sediments, pebbles, rocks, secondary minerals, and may include water ice at mid- to high latitudes, where permafrost landforms are observed4, and where additional disintegration of bedrock occurs owing to thaw/freeze cycles. Aeolian processes move solids across the martian surface: dust particles (< 10 mm) may remain in suspension indefinitely; dust and silt (< 60 mm) are lifted and may be deposited at great distance by atmospheric currents; sand particles (up to a few hundred mm) move by saltation, breaking into smaller fragments that may then be lifted; coarse grained material (1-5 mm in size) is dragged or accumulates as lag deposits. A way to study the distribution of these materials is through satellite thermophysical data: mapping based on thermal inertia and albedo classification5 shows links between type of material and geology.

My colleagues and I have investigated the spatial distribution and vertical composition of the martian cryolithosphere through impact processes6 and by ground penetrating radar7. Here, I show and discuss the main outcomes of our work in relation to: (a) the spatial distribution of the martian regolith and its composition; (b) ground ice and regolith; (c) the link between cryolithosphere and atmosphere. These aspects underpin part of the geological and climatological history of the planet, with far reaching implications about the selection of landing sites and possible future human missions to Mars.       

1Eggleton RA, Ed. (2001) CRC LEME, ISBN 0-7315-3343-7, 144 pp.

2Pain and Ollier (1996) AGSO J Austral Geol Geophys 16(3), 197-202. 

3Baker VR (2001) Nature 412, 228-236. 

4Lasue et al. (2013) Space Sci Rev 174, 155-212.

5Jones et al. (2014) Remote Sensing 6, 5184-5237.

6Jones et al. (2016) JGR Planets 121, 986-1015.

7Orosei et al. (2017) JGR Planets 122, 1405-1418.


Biography

Dr Graziella Caprarelli FAIG is Adjunct Research Fellow with the Centre for Astrophysics at the University of Southern Queensland, Adjunct Research Professor at the International Research School of Planetary Sciences (Italy), and member of MARSIS science team. She explores the martian subsurface geology looking for water.

Australia and Brazil: Contrasting Weathering and Erosion Histories but Similar Cratonal Landscapes

Paulo Vasconcelos1

1School of Earth and Environmental Science, the University of Queensland, Brisbane, Qld, Australia.

Australia is sparsely vegetated and the flattest, hottest, most tectonically stable but fastest latitudinally moving continent on Earth; it has migrated from high to low latitudes in ~50 Ma. In contrast, Brazil is a densely vegetated, wet, high relief cratonal terrane that has moved slowly longitudinally along the Equator for the past ~70 Ma. Despite these contrasting underlying geological and geographical characteristics, landscapes in these two regions are remarkably similar, share analogous ancient weathering histories, and are marked by plateaus surrounded by dissected plains that erode similarly and at equivalent rates.  In situ cosmogenic isotopes show that plateaus eroded at less than 2 m.Ma-1, while dissected plains erode at 5-20 m.Ma-1. Cosmogenic isotope concentrations in sediments show greater erosion rates, suggesting that erosion focusses preferentially along escarpments. 40Ar/39Ar geochronology on Mn-oxides and (U-Th)/He-4He/3He geochronology on goethite show that ancient weathering profiles blanketing plateaus in both continental areas are as old as ~90-70 Ma. These results are substantiated by in situ cosmogenic 3He concentrations in hematite. Geochronological results for the surrounding plains, on the other hand, indicate that the dissected areas are typically younger than ~30 Ma. Weathering profiles in both continental areas, on opposite sides of the planet, host supergene mineral populations that record analogous and often contemporaneous events of water-rock interactions through time. Importantly, these plateaus have been continuously emergent throughout their entire histories, hosting in the weathering profiles underneath minerals precipitated under contrasting climatic conditions through time. Interestingly, the analogous weathering histories of the two continental areas are mostly recorded in oxides, hydroxides, and clay mineral assemblages. The distribution and abundance of sulphates, carbonates, and silica-minerals, on the other hand, mark significant contrasts between the two landmasses. The most striking contrast is weathering under water deficient conditions in Australia while Brazil weathered under pronounced oversupply of rainwater. It is remarkable that such differences in climatic conditions produced such similar resulting landscapes. This is only possible because in Brazil, iron oxyhydroxides and ferricretes provided the landscape scaffolding that is provided in Australia by silica minerals and silcretes.


Biography

Paulo Vasconcelos is a geologist specialised in the development and application of novel geochronological tools for investigating earth and planetary processes.

Exploring for the Future: New Canning Basin geomechanics and rock property data

Bailey, Adam1, Jarrett, Amber1, Wang, Liuqi1, Dewhurst, David2, Esteban, Lionel2, Kager, Shane2, Monmusson, Ludwig2, Carr, Lidena1, Henson, Paul1

1Geoscience Australia, Canberra, Australia; 2CSIRO Energy, Perth, Australia

Exploring for the Future (EFTF) is an Australian Government initiative focused on gathering new data and information about potential Northern Australian mineral, energy and groundwater resources. Northern Australia is generally under-explored yet offers enormous potential for industry development, as it hosts many prospective regions and is located close to infrastructure and major global markets. In June 2020 a four year extension to the EFTF program was announced, expanding the scope to include the whole of Australia.

The energy component of EFTF aims to improve our understanding of the petroleum potential of Australian frontier basins. The Kidson Sub-basin, located within Western Australia’s Canning Basin, is an EFTF primary area of interest. A large, underexplored depocentre, it is likely that the proven petroleum systems of the Canning Basin extend into this frontier region. Geoscience Australia and partners recently acquired significant new data over the Kidson Sub-basin, including the L211 Kidson Sub-Basin 2D Seismic Survey and the deep stratigraphic borehole, Waukarlycarly 1.

This study brings together the geomechanical studies undertaken in the Canning Basin, including the Kidson Sub-basin, as part of EFTF. This includes interpretation of the regional stress regime and its context within the Australian continent, detailed analysis of present-day stress magnitudes, and geomechanical rock testing undertaken by CSIRO-Energy on samples recovered from Waukarlycarly 1.

Wireline log data, including wellbore image logs, were interpreted from open-file petroleum and stratigraphic wells to define stress orientations and magnitudes across the Canning Basin. A NE-SW regional present-day maximum horizontal stress orientation is interpreted from observed wellbore failure in image logs, and is in broad agreement with both the Australian Stress Map and previously published earthquake focal mechanism data. A strike-slip faulting stress regime is interpreted through the basin, however, when analysed in detail there are three distinct stress zones identified: 1) a transitional reverse to strike-slip faulting stress regime in the top ~1.0 km of the basin, 2) a strike-slip faulting stress regime from ~1.0 km to ~3.0 km depth, and, 3) a transitional strike-slip to normal faulting regime at depths greater than ~3.0 km. Detailed mechanical earth models demonstrate a variable present-day state of stress within the Canning Basin. Significant changes in stress within and between lithological units, due to the existence of discrete mechanical units, form numerous inter- and intra- formational stress boundaries that are likely to act as natural barriers to fracture propagation.

Rock testing targeted potential reservoir-seal pairs and intervals with identified unconventional hydrocarbon potential, characterising mechanical and petrophysical properties through unconfined compressive stress (UCS) tests, desktop ultrasonic testing, mercury injection capillary pressure (MICP), road-ion-beam milling and scanning electron microscopy (BIB-SEM), and gas porosity and permeability experiments. Hence, conventional and unconventional reservoir rock properties are characterised.

These data provide geomechanical and petrophysical insights into intervals with identified or potential hydrocarbon prospectivity and allow for extrapolation of rock properties. Although the Kidson Sub-basin is underexplored, these results demonstrate that should Canning Basin petroleum systems extend into the Kidson Sub-basin, geomechanical properties are likely to be favourable for the development of shale resources.


Biography

Adam Bailey graduated with a PhD in 2016 from the Australian School of Petroleum and currently works with the Onshore Energy Systems team at Geoscience Australia and has expertise in petroleum geomechanics, structural geology and basin analysis. Adam is currently working on the flagship Exploring for the Future Program.

Geodynamic influences on volcanological, paleoenvironmental and tectonic evolution of the Archean Kalgoorlie Terrane LIP, Western Australi

Cas RAF1, Hayman PC2, Squire RJ3, IH Campbell IH4, Wyche S5, Sapkota J6, Smithies H7

1School of Earth, Atmosphere and Environment, Monash University, Vic, 3800, Australia 2Queensland University of Technology, Brisbane, QLD, 4074, Australia 3School of Earth, Atmosphere and Environment, Monash University, Vic, 3800, Australia 4Research School of Earth Sciences, Australian National University, ACT, 4074, Australia 5Geological Survey of Western Australia, Perth and Kalgoorlie, WA, Australia 6Geological Survey of Western Australia, Perth and Kalgoorlie, WA, Australia 7Geological Survey of Western Australia, Perth and Kalgoorlie, WA, Australia

The stratigraphy of the late Archean (>2.7 Ga to 2.658 Ga) Kalgoorlie Terrane Large Igneous Province, in the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia, preserves an evolution of magmas, eruption processes paleo-environments, sediment provenance, and deformation that are inconsistent with a plate tectonic setting. An initial, deep submarine LIP komatiite and basaltic succession several kms thick (Stage 1 ~2.72-2.69 Ga) of lavas, hyaloclastite breccia and sills, with intercalated chert, black mudstones and minor felsic volcanics, extends > 600km along strike. It represents a widespread mantle plume event during regional extensional (D1) rift volcanism. Eruptions occurred in an open, anoxic, deep-water setting with no evidence of nearby emergent continents. Hydrostatic pressure suppressed all explosive activity.

From ~2.69 to 2.67 Ga (Stage 2) felsic TTG magmatism was dominant, represented by submarine lavas, hyaloclastite, monomictic tuffaceous megaturbidites, polymictic volcanogenic turbidite and conglomeratic mass flow deposits, and contemporaneous high-level granitoid intrusions. A major mafic event at ~ 2.80 Ga indicates mantle heat likely caused felsic crustal magmatism. The felsic volcanics and volcaniclastics represent marine intra-basinal felsic volcanoes (lava domes, stratovolcanoes?), some of which grew into shallow water and became emergent, were explosive under low ambient pressures, and produced the submarine tuffaceous megaturbidites. The Stage 2 volcanic conglomerates, including some granitoid clasts, were not generated by orogenic deformation and uplift, but were derived exclusively from the intra-basinal volcanic centres and sub-volcanic plutons, and from Stage 1 komatiite and mafic stratigraphy that was up-domed by diapiric granitoids. Ongoing plume buoyancy and contemporaneous local granitoid diapirism caused regional and local uplift (D2’) and shallowing of basins during ongoing regional extension (D1).

From ~2.67 Ga a transition into more widespread subaerial paleoenvironments is represented by felsic tuffaceous volcanic sediments deposited in fluvial braid-plain, alluvial fan, shallow marine, and local deep-water settings (Stage 3A). At < 2.658 Ga “late basin” polymictic, alluvial fan – fan delta conglomerates and sandstones represent major, regional crustal compression, uplift (D2/D4’, depending on scheme), emergence of large landmasses, and far-field sediment provenance (Stage 3B). There is no geological evidence of a plate tectonic regime prior to 2.658 Ga (i.e. no ophiolites, accretionary prisms, blueschist belts, uplifted orogenic belts, mountainous continents). A long-lived mantle plume caused partial melting of thick metasomatized mafic crust causing uprise of TTG plutons, leading to plutonic diapiric updoming, and changing paleoenvironments and eruption styles from Stages 1 to 3 (~ 50 Myr). Widespread TTG magmatism does not signify a subduction setting, but widespread anatexis of a lid-like crust/lithosphere.


Biography

Ray Cas has interesets in all aspects physical volcanology, including (paleo)environmental influences on eruption styles, geodynamic settings of volcanism, associated mineralisation and Archean paleovolcanology. He leads an annual professional shortcourse on these topics hosted by Monash U, UTasmania and Queensland University of Technology.

Characterising the hyperspectral SWIR features of tourmaline from two western Tasmanian granites

Cassady L. Harraden1, Wei Hong2,3, Cari Deyell-Wurst1

1Corescan Pty Ltd, Vancouver, BC, Canada, V6E 2E9 2Centre for Ore deposit and Earth Sciences (CODES), University of Tasmania, Hobart, TAS, Australia, 7001 3Department of Earth Sciences, School of Physical Sciences, The University of Adelaide, Adelaide, SA, Australia, 5005

Western Tasmania is one of the most important resource suppliers for Sn and W production in Australia and is host to numerous world-class high-grade deposits. The Heemskirk Granite, a highly productive batholith in this terrane, is associated with numerous skarns and greisens, which together have yielded a total of more than 104,000 tons of Sn. The nearby Pieman Heads Granite is of similar age (365-360 Ma; Hong et al., 2017) and has similar geochemical and mineralogical characteristics, but has not been associated with any known mineralisation. Both plutons contain abundant tourmaline in a variety of forms including magmatic hydrothermal veins, cavities, orbicules. This study compares the geochemical and spectral features of the tourmaline in both plutons to identify potential indicators of fertile magmatic systems.

Tourmaline samples were previously analysed by Hong et al. (2017) using Electron Microprobe (EMPA) and Laser-Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) to quantify the major and minor element compositions. Results showed that tourmalines are dominated by schorl varieties with a narrow range of chemical compositions (enriched in Fe and Al, moderately enriched in Mg, and poor in Ti, Li and Zn). Some systematic increases in Fe, Al and Li, and decreases in Mg and Ti are recognised from early- to late-stage tourmaline occurrences.

These analysed samples were also scanned using the Corescan Hyperspectral Core Imaging (HCI-3) system to obtain high resolution hyperspectral imaging data between 450nm and 2500nm (representing the visible to near-infrared (VNIR) and short-wave infrared (SWIR) regions). Characteristic absorption features in the SWIR are attributed to BOH, AlOH, and MgOH stretching vibrations: ~2200nm (AlOH), ~2250nm (BOH), ~2320nm (MgOH), and ~2360nm (BOH) (Hunt et al., 1973; Clarke et al., 1990; Bierwirth, 2004). Results show very little variation in individual wavelength values across samples for all four major SWIR absorptions. However, using combination of spectral features and specialised imaging capabilities, differences in tourmaline spectra between the two plutons are apparent. Tourmaline from the Pieman Heads Granite has relatively high ~2375nm wavelength positions while the ~2200nm and ~2250nm wavelengths are shifted to lower wavelengths. The Heemskirk Granite tourmalines display mid-range wavelength positions for all three absorption features. Additionally, variations in specific reflectance ratios in the SWIR region highlight zoning patterns that could reflect small-scale Fe variations.

Distinguishing between the barren Pieman Heads and fertile Heemskirk Granites has implications for Sn exploration activities in Western Tasmania. The major-element compositions of the tourmalines in these two granites are very similar but discrete variations in key SWIR absorption feature relationships are apparent using high resolution hyperspectral imaging. This demonstrates the potential to apply hyperspectral imaging techniques to differentiating compositionally similar intrusive bodies with different mineral potential for mapping and exploration activities in the region and beyond. 


Biography

Cassady’ current work with Corescan is focused on developing new geometallurgical and geotechnical applications using data collected from hyperspectral imaging technology. This was also the focus of her PhD research. Before completing her PhD she worked as an exploration geologist in Alaska, Colorado, Nevada, Utah, and Arizona.

The isotopic footprint of a submarine mineral system: Cr and Sr isotopes in the Iheya North hydrothermal field, Okinawa Trough (IODP expedition 331)

Lucy McGee1, Thomas Burke1, Juraj Farkas1, Bradley Cave1, Chris Yeats2

1Department of Earth Sciences, University of Adelaide, Adelaide, Australia 2Geological Survey of New South Wales, Department of Regional NSW, Maitland, Australia

‘Black smokers’, or submarine hydrothermal vents, represent sites of intense hydrothermalism. Such chimneys transport metals into the ocean where they precipitate as Fe, Pb, Zn and Cu sulfide minerals. However, the spatial footprint of these high-temperature processes transporting metals in marine environments is not well constrained. Legacy material from the 2011 IODP expedition 331 to the Iheya North hydrothermal field in the Okinawa Trough provide a unique opportunity to investigate the isotopic footprint of key metals in the hydrothermal system. The sample set is based on the analysis of four cores: one situated at the foot of an actively forming massive sulfide mound, one drilled at a background site located 1km away from the hydrothermal vents and two cores sampled between these sites, representing a high temperature vent and a lower temperature vent. Samples taken at various depths from the four cores represent a wide range of material, from unaltered distal marine clays, through hydrothermally altered clays and volcanic material, to massive sulfides.

Bulk digestions on 30 samples give a suite of trace element analyses which show large variations, particularly in transition metal element concentrations. SEM-MLA mapping of key samples show important interactions between sulfide phases and the presence of gypsum/anhydrite shows oxidation and reduction in the same sample. The large variation between magmatic and seawater endmembers in 87Sr/86Sr isotopic ratios provide an excellent opportunity to investigate the magmatic ‘footprint’ of the metalliferous hydrothermal system in marine settings and how far into the background this can be detected. Stable Cr isotopes have the potential to show important redox interactions during anticipated oxidation of hydrothermal Cr(III) species in marine settings into oxidised Cr(VI), and possible back-reduction to Cr(III).


Biography

Lucy is a high temperature geochemist with a background in volcanology and igneous geology. She enjoys using isotopes to constrain Earth System processes related to magmas and is currently interested in the processes of metal transport in active systems.

Contrasting growth of the Pilbara and Yilgarn cratons from hafnium and neodymium isotopes

Kemp, Dr Tony1

1University Of Western Australia, , Australia

Long-lived radiogenic isotope systems such as 147Sm-143Nd and 176Lu-176Hf suggest that large volumes of the Earth’s continental crust formed in the Archean Eon (> 2.5 Ga). The onset of substantial continent stabilization in the geological record is marked by the distinctive ‘granite-greenstone’ terranes that are the hallmarks of Archean crustal blocks. Yet, to what extent generation of the buoyant, silica-rich (i.e. continental) components in these terranes involved the re-melting of pre-existing, primordial crust as opposed to rapid differentiation of new mantle additions, remains uncertain. Establishing the composition of the mantle source from which early crust was extracted, and comparing this with the compositions of felsic crust, is key to this question. The geochemical signatures of ancient, unambiguously mantle-derived rocks are, however, susceptible to modification by later metamorphism. Here, hafnium and neodymium isotope data are reported for well preserved mafic-ultramafic and felsic igneous rocks of the Pilbara and Yilgarn Cratons, Western Australia. Comparing the mantle and crustal records of Archean continent formation in these cratons reveals a striking isotopic link that endured over 500 million years. In the Pilbara Craton, this linkage is interpreted to reflect the efficient transformation of new mafic inputs from the mantle into felsic continental crust throughout the history of the craton. In contrast, broadly coeval rocks in the Yilgarn Craton formed by remelting older rocks, although the crustal evolutionary records of both cratons converge in the Neoarchean. The possible reasons for the cratonic contrasts are considered.


Biography

Currently in the School of Earth Sciences at the University of Western Australia

Validation of spectral data: A critical step towards accurated prediction

Ramanaidou, Erick1

1Mineral Resources – Discovery | CSIRO, Kensington, WA, Australia

The last three decades have seen the emergence of spectral mineralogy as a valued tool for the exploration and mining companies. From the past luggable GER IRIS and portable PIMA we now have access to an extended suite of small, fast, light and accurate field spectrometers such as the ASD and Spectral Evolution spectrometers covering the visible, near infrared and short-wave infrared – VNIR-SWIR 380 to 2500 nm range. In parallel, automated systems to scan diamond cores and drill chips have been developed such as the hyperspectral point analyser, the HyLogging System™, the hyperspectral imaging spectrometers, the Corescan™ Core Imager Mark III, SpecIm SisuROCK, Neo Hyspex and HCIS Terracore are commercially available for use by the exploration and mining companies. As well as VNIR-SWIR, the thermal infrared -TIR range (8 to 14 µm) is now available with the HyLogging System™ 3 providing the detection minerals such as quartz, felspar, olivine, pyroxene and garnet. Large volumes of diamond cores and drill chips have been measured by the exploration and mining companies and the spectral geologist research community has responded by providing automated ways of processing large number of spectra. The CSIRO- developed the spectral geologist or TSG™ offers two ways of processing the spectra (1) through the automated spectral analysis program or The Spectral Assistant (TSA) or through customised scripts, algorithms that use depth and minimum wavelength of absorptions to uniquely identify specific minerals. The TSA is applied for HyLogging System™ spectra on measured areas on around a few cm2 where mineral mixture is likely. On the other hand, the hyperspectral imaging Corescan™ Core Imager Mark III captures many pure pixels at a resolution of 500 µm and the mineral mapping processing is performed using a dedicated expert system program.

Reflectance spectra acquired using these systems are often the complex results of many absorptions embedding not only mineralogical but also particle size information. Although quite powerful, the processing methods previously mentioned require validation by more classical methods such as x-ray diffraction, Raman spectroscopy, X-ray fluorescence (XRF) and µXRF mapping to improve prediction.

Through examples selected from the iron ore and nickel laterite industries, it will be demonstrated that complementary and cross validated methods are essential to ensure that validation of spectral data is undertaken as a critical step towards accurate mineralogical prediction and that it is good to have redundant information.


Biography

Dr. Erick Ramanaidou is the Commodity Research Leader for iron ore and nickel laterite. He has been involved in spectral research for the last 25 years and has concentrated his effort to the understanding of the spectral properties of iron oxides and gangue minerals in iron ores.

About the GSA

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