Cr-Zoning in pyroxene as a prospectivity indicator for magmatic Ni-Cu sulfide deposits

Schoneveld, Louise1; Barnes, Steve1, HV Makkonen5, M Le Vaillant1, D Paterson6, V Taranovic1, K-Y Wang2,3, Y-J Mao4

1CSIRO, Kensington, Australia, 2Chinese Academy of Sciences, China, 3University of Chinese Academy of Sciences, China, 4Chinese Academy of Sciences, China, 5Boliden FinnEx, Finland, 6Australian Synchrotron, ANSTO, Clayton, Australia

Small intrusions dominated by olivine- and pyroxene-rich cumulates are common in a variety of settings around the world, but only a very small proportion contain economically exploitable sulfides. We aim to provide a new tool for distinguishing these fertile intrusions from sparse exploration drilling.

Cumulate and poikilitic pyroxenes in strongly mineralised intrusions have complex grain-scale Cr zonation. We separate the zonations into three distinct types: 1) abrupt zoning; 2) sector zoning 3) oscillatory zoning. This combination of zoning patterns is likely to indicate high magma flux and fluctuating cooling rate that accompanies wall rock assimilation in the dynamic conduits where sulphide liquid forms and accumulates. As the diffusion of chromium is extremely slow, these zoning patterns can last thousands of years within hot terranes. 

We have investigated pyroxene-bearing samples from small intrusions containing magmatic sulphide deposits including the Noril’sk-Talnakh camp in Siberia, the Kotalahti Nickel Belt in Finland, Ntaka Hill in Tanzania, Nova-Bollinger in the Albany-Fraser Orogen and Savannah in the Halls Creek Orogen of Australia, Jinchuan in central China, Xiarihamu in Tibet and Huangshanxi in the east Tianshan Ni province of NW China. To compare, we analysed samples from the weakly mineralised or barren intrusions in four of these regions along with four mafic intrusions that are not associated with any economic sulfide mineralisation.

Cumulus orthopyroxene with a combination of abrupt zoning, sector zoning and resorbed olivine inclusions has so far only been detected in mineralised intrusions. Desktop XRF mapping instruments easily image this distinctive zoning pattern in large pyroxenes,which provides a useful fertility indicator for exploration of new magmatic Ni-Cu-(PGE) deposits.


Biography

Louise obtained her bachelors and honours in geology from James Cook University, Townsville and in 2018 graduated with a PhD from the Australian National University (ANU).  Currently she is focussed on investigating the trace element signatures in minerals as possible indicators for economic mineralisation.

Geoheritage significance of three contiguous Holocene wetlands 161, 162, & 163 in the Becher Wetland Suite, south-western Australia

Semeniuk, Christine1, Semeniuk, Vic1,2

1V & C Semeniuk Research Group, , , 2Notre Dame University, Fremantle, Australia

The Becher Wetland Suite comprises a series of wetland basins located in inter-dune depressions on a Holocene prograded beach-ridge plain.  With progradation, the wetlands formed by the regional water table naturally rising into the inter-dune depressions.  As beach-ridge progradation is westerly, the inter-dune depressions (becoming wetland basins) generally young towards the west, with the oldest basins some 4500 years old, and the youngest < 900 years old.  Through the Becher region, the insertion of wetlands on the prograded beach-ridge plain, through generally younging westwards, in detail, is staggered because of the uneven topography of the depressions along their length.  For instance, wetlands 161, 162, & 163, the subject of this paper, all occur along an inter-dune depressions located on the 4500-year beach-ridge isochron (the oldest part of the beach-ridge plain) and, as such, ideally should be the same age and show the same history. However, they have a staggered history, with wetland 161 commencing accretion some 4350 years ago, wetland 162 commencing 4110 years ago, and wetland 163 commencing 2920 years ago.  All three basins filled with calcilutite.  However, with different ages and longevity of accretional history, and subject to differing small-scale temporal climate changes (in the order o 100 years of less) they exhibit different sedimentary history in terms of thickness of calcilutite, the relationship of calcilutite to underlying sand, diagenetic effects (such as dissolution of underlying carbonate sand, dissolution of Chara and sponge spicules, and patchy cementation of calcilutite), and the responses to fire.  This sequence of wetlands illustrates the complexities of wetland basin sedimentation.   As such, the contiguous wetlands 161, 162, & 163 are a system of international geoheritage significance.


Biography

Christine Semeniuk is a Director of VCSRG, a Research & Development Corporation.    Graduated from the University of Sydney in 1969, she was awarded a PhD from Murdoch University in 2003. Christine arrived in Western Australia 50 years ago, undertaking research into wetlands of Western Australia, and has over 30 peer-reviewed publications in wetland science and geoheritage, including the geoheritage values of wetlands of the Swan Coastal Plain. Christine is a founding member of the NGO the Wetlands Research Association inaugurated in 1999.

Patina: A microscopic feature of palaeo-environmental and geoheritage significance

Clifford, Penelope1, Semeniuk, Vic1,2

1Notre Dame University, Fremantle, Australia, 2V & C Semeniuk Research Group, ,

Patina is an ultra-thin crust of silica or silica and carbonate that is developed on glass and, while it best developed on anthropogenic glass, it provides important information on products and processes associated with weathering of glasses in general.  It is common in modern environments, though variable in expression dependent on environmental setting, and it has been recorded on pre-Mediaeval and Mediaeval artefacts.  Anthropogenic glass is geochemically unstable and, as such, it corrodes relatively rapidly (within years), generating a variety of weathering crusts of different thicknesses, and various internal structures.  The type of patina that is developed depends on the glass composition, the type of soil it is embedded in, the hydrochemistry of the soil water, climate setting, and whether the glass is located in an inland vadose zone or phreatic zone, a maritime coastal zone, or a submarine environment. The patina crusts are < 10 µm up to 100 µm, thickening with age. The solutional relationship of the patina to the glass varies from straight, undulating, irregular, to cuspate and, internally, shows structures of colloform to undulating lamination, parallel lamination, massive to mottled patterns, micro-brecciation, shrinkage cracks, and infiltrated dust-sized minerals, all reflecting and recording a history of solution and precipitation, and variation in climate. For vadose environments, the main agents in the patination is alternating wet and dry vadose conditions, and alternating acid and alkaline vadose conditions that result in precipitation of an amorphous silica ‘gel’ that forms silica laminae, its layer-parallel shrinkage, and the precipitation of calcite laminae.  While modern patina and historic patina have been documented from the various climate, hydrochemical, and pedogenic environments, the results are widely applicable to understanding and unravelling the weathering of natural materials such as obsidian, chert, and volcanic glasses – in this context, it conforms to the geoheritage category of ‘modern processes’ and provides a record of modern processes and products in the weathering of natural glass and glass-like materials.


Biography

Vic Semeniuk is a Director of VCSRG, a Research & Development Corporation. Awarded a PhD from the University of Sydney, a UWA Postdoctoral Fellowship, and the Queens Postdoctoral Fellowship in Marine Science, as a multi-disciplinary research scientist, Vic has over 160 peer-reviewed publications in the geology, geomorphology, and geoheritage, as well as in coastal science, environmental science, and conservation ecology (estuaries, mangrove, wetland, coastal dunes, soldier crabs). Vic arrived in Western Australia 50 years ago, initially with a position at The University of Western Australia, and continues to teach and supervise postgraduate students as an Adjunct Professor at the University of Notre Dame and Murdoch University. Vic is a founding member in 2019 of Geoheritage Australasia, and in 1999 of the Wetlands Research Association. Inc.

Recognising and preserving mineral diversity: An updated catalogue of type mineral specimens in Victoria’s State collections

Lindenmayer, Oskar1

1Museums Victoria, Melbourne, Australia

Type mineral specimens are designated by the International Mineralogical Association (IMA) as the physical standards by which newly discovered mineral species are defined. They represent the benchmarks against which the word’s mineral diversity can be recognised and studied. Each type mineral specimen is a globally significant element of movable natural heritage and forms an irreplaceable resource for researchers in the fields of mineralogy, crystallography and materials science. Despite their importance, the management of these specimens has historically lacked transparency.

Museums Victoria holds approximately half of the type mineral specimens in Australian institutions. The most recent edition of the global catalogue of type mineral specimens, prepared under the direction of the IMA Commission on Museums, lists 98 specimens as lodged with Museums Victoria, of which 45 are from Australian localities and 53 are from overseas localities. This catalogue also lists the whereabouts of 12 specimens from Australian localities as unknown. In contrast to the global catalogue, Museums Victoria’s internal catalogue includes 125 type mineral specimens, of which 59 are from Australian localities and 66 are from overseas localities. There are also a number of discrepancies between the two catalogues for specimens that appear on both, including type status (ie. whether the specimen is a holotype, cotype or neotype) and registration number.

To resolve these issues, a review of the information available in publications, Museums Victoria records and correspondence, and minutes from meetings of IMA Commissions has been undertaken for each specimen. Where necessary and practical, authors of new mineral descriptions have been contacted for further information. A methodology has been developed to identify legitimate type specimens and appropriately categorise them by their type status. In a departure from previous attempts to document type mineral specimens in Victoria’s State collections, areas of uncertainty or missing information for specimens are flagged and explicitly discussed.

The sources of the majority of the discrepancies between the global and internal catalogues were found to be either publically undocumented transfers from other institutions or incomplete information having been given in the original publications of new mineral descriptions. Amongst the discrepancies resolved was the identification of Museums Victoria as the lodging institution for five of the type specimens listed as having unknown whereabouts in the global type catalogue. In the absence of a formal mechanism for reviewing details or reporting transfers of type mineral specimens, periodical review and publication of catalogues by the institutions that hold them is necessary for the ongoing management of these most significant parts of mineral collections. It is hoped that by undertaking this review in a transparent manner, and making the results and methodology publically available, other institutions will be encouraged to do the same.


Biography

As Collection Manager, Geosciences, at Museums Victoria, Oskar is responsible for managing Victoria’s State collections of minerals, gemstones, rocks, meteorites, and tektites.

This involves preserving and organising the collection, maintaining and improving the digital collection database and facilitating access of the collections for the purposes of research, education, and exhibition.

A geoheritage treasure – a case study of the Hornsby Diatreme

Semeniuk T A1,2

1Western Sydney University, The College, Quakers Hill, Australia.  email: t.semeniuk@westernsydney.edu.au

The quarrying for bluestone at the Hornsby Quarry Site exposed a > 40 m-deep cross-section of a volcanic diatreme, showing a volcanic neck extruding through Sydney Basin sediments, complete with volcanic features visible at many scales, with post-volcanic features related to magma and gas extrusion at various depths, and with different host rocks. Globally, there are very few instances of such excellent exposure, revealing a full range of macroscale to microscale features in three dimensions. It is arguable that this exposure alone, makes it a site of international geoheritage significance.  Using the Geoheritage Tool-kit, applied at various scales shows that this diatreme is internationally to nationally significant.  For example, at the macroscale, there dish beds in all orientations of the quarry walls are visible, giving a three-dimensional picture of its structure, reflecting its volcanic accretion and later caldera collapse.  At the mesoscale, where breccia beds, bombs, and surge layers are visible, these show how the magma interacted with various host rocks and other post-volcanic processes that occurred prior to solidification.  Finally, at the microscale, lapilli (including accretionary lapilli), chilled margins and carbon-rich xenoliths are evident in hand specimen.  As such, this Quarry is a unique site worldwide. In fact, the Quarry, exposing the volcanic pipe of the Hornsby Diatreme, offers a snapshot in time of the Sydney Basin, preserving its volcanic and post-volcanic history on the quarry walls.


Biography

Trudi Semeniuk is a multidisciplinary scientist in the fields of general geology, metamorphic geology, geoheritage, wetland-, mangrove-, foraminiferal-, and tidal-flat sedimentology and ecology.  Her work experience is manifold ranging from fieldwork for VCSRG (a Research & Development Corporation), and a Research Officer for ANU, CSIRO, and Kings Park Botanical Gardens. More recently Trudi has focused on reviewing sites of geoheritage significance listed on, the now archived, Register of the National Estate (NSW) and work as a scientific editor.  Trudi was awarded a PhD from the Institute of Mineralogy and Petrography, ETH Zurich in 2003 in a study of Alpine mylonites, and completed a Postdoctoral Fellowship in 2004-2006 in aerosol chemistry at Arizona State University.  Trudi is active in Geoheritage, and is the co-convenor for the NSW Division for Geoheritage in the Geological Society of Australia.

In-situ Rb–Sr dating of Precambrian sediments

Subarkah, Darwinaji1, Blades, Morgan L1, Collins, Alan S1, Farkas, Juraj1, Gilbert, Sarah2, Lloyd, Jarred C1

1Tectonics and Earth Systems (TES) Group and Mineral Exploration CRC, Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia, 2Adelaide Microscopy, University of Adelaide, Adelaide, SA 5005,

Sedimentary rocks make up only 5% of the Earth’s crust and yet represents the primary archive of the planet’s biogeochemical cycles. As such, precise depositional age constraints of sedimentary sequences are critical to our understanding of how these systems have evolved through time. Here we present from a novel application of in-situ Rb‒Sr dating and elemental analyses using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS/MS) on a set of sedimentary rocks across the Precambrian under different geological settings. A reaction gas is introduced between two quadropoles in the system, allowing for the online separation of 87Sr and 87Rb. Three case studies were investigated using this method. Roper Group shale samples in proximity with the Derim Derim Dolerite intrusion were sampled from the UR5 drillhole in the Proterozoic McArthur Basin, northern Australia. These samples yielded ages extremely radiogenic initial 87Sr/86Sr values analogous to the dolerite sample taken from the same well. These time constraints are consistent with the crystallisation age of the igneous suite (ca. 1313 Ma) located elsewhere in the basin. We propose that these samples recorded an alteration event instigated by the intrusion that reset the Rb‒Sr chronometer and geochemistry of the surrounding sediments. On the other hand, a sample from the intrusion-absent UR6 borehole has been interpreted to reflect the depositional history of the Roper Group instead. Multiple analyses on glauconitic sediments from the Doomadgee Formation in the South Nicholson Basin gave two main outcomes. One set of results gave an age ca. 1300 Ma and retained a very high initial Sr isotopic ratio. On the other hand, another sample gave an age of 1607 ± 28 Ma, which overlaps with a tuff age interbedded within the same formation. Furthermore, this sample’s initial 87Sr/86Sr ratio was within error of contemporary seawater. Lastly, a calcareous shale from the Neoproterozoic Tapley Hill Formation in Arkaroola yielded an age of 664 ± 28 Ma with initial 87Sr/86Sr value overlapping with their coeval seawater during time of deposition. Together, our study demonstrates the capabilities of this technique to date Precambrian sediments and evaluate the nature of fluids that their isotopic system was in equilibrium with by coupling laser-derived Rb‒Sr and geochemical data. This approach thus allows for a rapid and accurate discrimination of depositional and alteration histories of sedimentary sequences and has potential to be a powerful dating tool for these archives through deep time.


Biography

I am an international PhD student from Indonesia in my second year of candidature at the University of Adelaide. My research interests focuses on using geochemical proxies from sedimentary rocks to reconstruct past palaeoenvironments and biogeochemical cycles through deep time.

Detrital Zircon Age and Provenance of the Tonian-Cryogenian of the Adelaide Superbasin

Lloyd, Jarred C.1,2; Van Der Wolff, Erica1; Blades, Morgan L.1; Virgo, Georgina M.2,1; Collins, Alan S.1; Amos, Kathryn J.2

1Tectonics and Earth Systems Group, Mawson Centre for Geoscience; and MinEx CRC, Adelaide, Australia, 2Australian School of Petroleum and Energy Resources, Adelaide, Australia

The Adelaide Superbasin is a vast Neoproterozoic to middle Cambrian sedimentary basin in southern Australia that initiated due to the break-up of central Rodinia and, evolved into the Australian passive margin on edge of the Pacific Basin. We present over 2000 new detrital zircon analyses from more than 20 Tonian–Cryogenian formations of the central Adelaide Rift Complex of the Neoproterozoic–middle Cambrian Adelaide Superbasin. These new data focus on understudied formations from within the Burra and Umberatana Groups that were identified in Lloyd et al. (2020, Precambrian Research, 10.1016/j.precamres.2020.105849). Building on the >7,500 data previously published we now consider that we are getting an adequate idea of the spatial variation of detrital zircon populations for time-equivalent formations within this large basin. The same statistical method of Lloyd et al. (2020) is applied to this dataset. Samples of Burra and Umberatana Groups from the Mount Lofty Range region in the south of the superbasin, preserve local sources (Barossa Complex/Gawler Craton, ca. 2500–1560 Ma), suggesting local derivation. This contrasts time-equivalent formations from the north of the of basin (central and northern Flinders Ranges), where zircon sources include distal regions (Musgrave Orogen ca. 1550–1050 Ma) and suggest axial transport through the Willouran Trough. Samples in the south then show increasing zircon source diversity up sequence, similar to, although not as pronounced as, the progression seen in the north of the basin. All areas are then punctuated by the Sturtian Cryogenian ice-transported deposits. Post-Sturtian glacial deposits preserve younger zircon sources (ca. <1000 Ma), potentially from southern sources (Antarctica?). Notably ca. 980–950 Ma zircon populations are more common in the samples from the south of the basin than in the north of the basin. These observations and interpretations are suggestive of a progressive southward opening of the Superbasin, consistent with the current interpretation of lithostratigraphy.


Biography

Jarred Lloyd is a PhD student at the University of Adelaide with a passion for the evolving Earth system during the Neoproterozoic, South Australian geology,  education, and outreach.

Redefining the Basement Architecture of the Southern Mount Isa Inlier

Brown. D.D. 1 , Bultitude,R.J1., Simpson,J.M, Purdy,D.P1., Connors, K.A.2, Sanislav,I.V. 3.

1Geological Survey Of Queensland, 2University of Queensland, 3James Cook University

The Paleoproterozoic Kalkadoon-Leichhardt belt (KLB) forms the major basement block to a series of Paleoproterozoic Superbasin sequences of the Mount Isa Inlier. The basement sequences of the Mount Isa Inlier have a broad two-fold division comprising: 1) the Leichhardt Volcanics and the Kalkadoon Granodiorite (~1865Ma) formed during the Barramundi Orogeny and 2) a series of pre-1870Ma units which are restricted in distribution to the KLB and margins of the Western Succession (Kurbayia Metamorphic Complex, Yaringa Metamorphics, and Saint Ronans Metamorphics).

The eastern portion of the KLB is overlain by and complexly faulted with the Mary Kathleen Domain (MKD). The MKD is dominantly comprised of calcareous and siliciclastic metasedimentary units belonging to the Paleoproterozoic Leichhardt Superbasin (~1790 – 1740 Ma) and igneous rocks of the Wonga and Burstall suites (~1740 Ma). At the southern outcropping extent, several intrusive units had previously been included in either the Burstall Suite (Saint Mungo Granite), Wonga Suite (Birds Well Granite, Bushy Park Gneiss) or correlated with ~1740 Ma magmatism (Tick Hill Complex) and thus included in the Mary Kathleen Domain.

New SHRIMP and LA-ICP-MS U-Pb geochronology shows that some units in the southern MKD are much older and form part of the basement (KLB). The Bushy Park Gneiss and Birds Well Granite form part of the KLB with crystallisation ages consistent with the Barramundi portion of the KLB. Hafnium isotope studies indicate these units to have εHf which closer to CHUR whereas the previously analysed Barramundi portion of the KLB has uniform εHf values of ~ -4 which indicates some heterogeneity in the southern portion of the inlier.

This is confirmed by interpretation and reinterpretation deep seismic lines CF3 and M6, which reveal an extensive basement package in the subsurface of the Southern Mount Isa inlier and throughout the Eastern Sub province. This package appears to be a controlling factor for deformation and basin development from 1865 Ma.


Biography

Dominic Brown has worked on the geology, geochemistry, geochronology and geophysics of Queensland for 15 years at the Geeological Survey of Queensland across a diverse suite of projects.

Oxygenation of Mesoproterozoic Ocean and its Consequences for Eukaryotic Evolution

 Zhu, Dr Xiangkun1, Wang, Dr Xun1, Zhang, Dr Kan1, Sun, Dr Jian1, Poulton, Dr Simon2

1Institute Of Geology, Chinese Academy Of Geological Sciences, China, 2School of Earth and Environment, University of Leeds, UK

The Mesoproterozoic Era (1,600-1,000 million years ago; Ma) has long been considered a period of relative environmental stasis, with persistently low levels of atmospheric oxygen, and sluggish biological evolution. There remains much uncertainty, however, over the evolution of ocean chemistry during this time period, which may have been of profound significance for the early evolution of eukaryotic life. Here, we present multiple geochemical proxies, including rare earth element, iron speciation, Fe-, Ca- and Sr isotopes to investigate the redox evolution, and its relationship with tectonics, and effects on bio-essential elements,  of the 1,600-1,550 Ma Yanliao Basin, North China Craton. These data confirm that the ocean at the start of the Mesoproterozoic was dominantly anoxic and ferruginous. Significantly, we find evidence for a progressive oxygenation event starting at ~1,570 Ma, immediately prior to the occurrence of complex multicellular eukaryotes in shelf areas of the Yanliao Basin. Interestingly, the onset of the oxygenation is coincident with the transition from rift to drift of the North China Craton. Moreover, the oxygenation is most likely progressive rather than a short-lived pulse, which resulted in depletion of bio-essential elements such as P. Our study thus demonstrates that oxygenation of the Mesoproterozoic environment was far more dynamic and intense than previously envisaged, and establishes an important link between rising oxygen and the emerging record of diverse, multicellular eukaryotic life in the early Mesoproterozoic. Furthermore, It sheds significant light on the reason of the sluggish evolution of eukaryotes during the protracted period.


Biography

Dr Xiangkun Zhu obtained a Ph.D. from Cambridge University. His researches mainly focus on isotopes of transitional metals and their implications in geochemistry, cosmochemistry and biogeochemistry.

The Impact of Snowball Earth Glaciation on Ocean Water δ18O Values

Defliese, William F.1

 1School of Earth and Environmental Sciences, The University of Queensland, St Lucia, QLD, Australia

It has been long recognized that glacial episodes can affect the δ18O value of ocean water, where preferential storage of 16O in ice changes the 18O/16O ratio of the ocean.  However, these effects are generally thought of as transient, as Cenozoic glaciation has had neither the magnitude nor duration to cause long-term change with ocean water buffered to values close to 0±2 ‰ VSMOW by tectonic processes.  The Snowball Earth glaciations of the Cryogenian have the potential to cause much larger changes in ocean water δ18O values due to their increased ice volume and long duration relative to Cenozoic glaciation, but these effects have not been previously investigated. 

Here, I use a numerical box model to investigate ocean water δ18O values over the Proterozoic and Phanerozoic.  The model simulates various temperature and tectonics dependant fluxes of 18O, while also incorporating a zero-dimensional climate model and ice volume component to model glacial cycles.  Monte Carlo simulations of the Sturtian and Marinoan glaciations reveal that these had the potential to alter ocean water δ18O values for hundreds of millions of years after the termination of glaciation, providing a mechanism for secular change in the δ18O value of ocean water.  This occurs as a very large volume of ice (presumably, but not necessarily 18O depleted) is sequestered from the ocean, causing the ocean to become enriched enough in 18O for exchange at mid-ocean ridges to remove 18O from the ocean and slowly change the overall ocean water δ18O value.  If Snowball Earth ice volumes were as large as proposed (~28-32% of ocean volume), present day values of ice δ18O would cause significant secular change in ocean water δ18O extending into the Phanerozoic.  An additional finding of this work is that the duration of the Sturtian glaciation required a very low CO2 degassing rate on the order of ~2 Tmol/year, significantly less than that estimated from most other mass balance approaches for the Phanerozoic.


Biography

Dr. William Defliese is Lecturer in Geochemistry in the School of Earth and Environmental Sciences at UQ.  His research interests include stable isotope geochemistry, clumped isotope geochemistry, carbonate sediments, basin analysis, and paleoclimatology.  He joined UQ in 2019 after postdocs at UCLA and Texas A&M University.

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About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.