Circadian rhythm of dune-field activity

Gunn, Andrew1, Lancaster, Nicholas2, Edmonds, Douglas3, Ewing, Ryan4, Jerolmack, Douglas1

1University of Pennsylvania, Philadelphia, United States, 2Desert Research Institute, Reno, United States, 3Indiana University, Bloomington, United States, 4Texas A&M University, College Station, United States

Wind-blown sand dunes are both a consequence and a driver of climate dynamics; they arise under persistently dry and windy conditions, and are sometimes a source for airborne dust. Dune fields experience extreme daily changes in temperature, yet the role of atmospheric stability in driving sand transport and dust emission has not been established. Here we report on an unprecedented multi-scale field experiment at the White Sands Dune Field (New Mexico, USA), where we demonstrate that a daily rhythm of sand and dust transport arises from non-equilibrium atmospheric boundary layer convection. A global analysis of 45 dune fields, including those in Australia, confirms the connection between surface wind speed and diurnal temperature cycles, revealing an unrecognized land-atmosphere feedback that may contribute to the growth of deserts on Earth and dune activity on Mars.


Biography

Andrew Gunn is a PhD candidate in Earth & Environmental Sciences at the University of Pennsylvania advised by Prof. Douglas Jerolmack. His dissertation is on aeolian process geomorphology. He completed his undergraduate at the University of Melbourne in Applied Mathematics, and Honours at the University of Tasmania in Physical Oceanography.

Approaches to structural history in areas of weak to moderate upright folding

Durney, David W1

1Earth & Environmental Sciences, Macquarie University, Australia

A particular style of convergent deformation in upper crustal sedimentary basins in many parts of Australia is gentle to close upright folding on multiple trends, typified by dome-basin interference patterns. This style occurs widely in Siluro-Devonian continental back-arc sedimentary and volcanic strata of the Lachlan Orogen (LO) in New South Wales (NSW). Several hypotheses have been suggested for folding in that region, most notably up to four successive extensional and ‘orogenic’ events.

As conventional methods of structural analysis have limited applicability, the present talk aims to outline the basis of the approach used by Hood et al. at this conference in their analysis of this style in the mildly deformed Quidong Basin in NSW.

The basis is both geological and mechanical. It is geological in the sense that:

  • the area is one of very-low grade metamorphism where the geologically observable solution-transfer/pressure-solution deformation mechanism is known to be prominent in many sedimentary rocks, and
  • extensional deformation is acknowledged in the fromation of the basin.

It is mechanical the sense that:

  • the theoretical rheology of solution-transfer deformation is approximately linear-viscous, meaning slow deformation can occur under very low stress,
  • because of that, ductile rather than brittle deformation is prominent and
  • viscous buckling theory applies to layered strata under horizontal compression.
  • As a separate matter, equilibrium of horizontal forces is recognised as a constraint on likely structural combinations at any given time over broad regions of continental upper crust.

It is suggested that these points also limit the range structural hypotheses that are applicable to such regions.

Briefly, the methods have been selected to emphasise short-period incremental deformations: (1)identification of separate fold directions, (2) application of buckling theory to infer associated shortening directions and their relative timing in upright Ramsay Type 2 or ‘banana’ refolds, (3) correlation of incrementally sensitive mesoscopic spaced cleavages in limestones with the folds, (4) use of outcrop-scale kinematic indicators to establish the 3D character of the deformations, (5) use of buckling theory to explain “fault-related minor folds” and (6) application of force equilibrium to infer regional distribution.


Biography

David Durney began geology at London under John Ramsay (BSc 1965, MSc 1968, PhD 1972), has taught structural geology and mapping (Macquarie University 1973–92, 1993–2005; Barcelona 1992–93; UNSW 2008) and maintains an interest in geology of the Lachlan Orogen.

Structure of the Silurian Quidong Basin: New observations on a microcosm of Eastern Lachlan Orogen tectonic and metallogenic problematica

Hood, David I. A.1, Durney,Dr David W.2, Parkes, Dr Ross A.2

1R&D Dept., Ardex Australia, Seven Hills, Australia, 2Earth & Environmental Sciences, Macquarie University, , Australia

The Quidong Basin is a small (~20 km2) structural basin made up of sediments of Wenlock to Ludlow age within the in-faulted Ordovician–Silurian Tombong Block in the Delegate area of far south-eastern New South Wales. It is a true microcosm of several contested tectonic and metallogenic problems that are common to other parts of the Lachlan Orogen of New South Wales. (1) It displays an angular unconformity with older Silurian sediments attributed to a localised convergent orogeny: the “Quidongan Orogeny”.  (2) There have been competing syngenetic and thrust-related models for the origin of stratbound and faultbound massive sulphide mineralisation in the Basin. (3) It is affected by complex superposed folding and cleavage development whose sequence has not been resolved in the published literature.  (4) Interpreted time relations between folding and prominent faulting in the area have been ambivalent.  (5) The area lacks a direct time constraint on the age of the convergent fold deformation.

A better understanding of the deformational structures and how the unconformity may have formed is also important for palaeogeogrphical reconstruction and stratigraphical correlation of fossil horizons in the faulted and folded sediments. It was for this purpose that DH carried out field observations and analysis of structures at selected sites in the area in support of palaeontological and sedimentalogical work by Ross Parkes for his PhD study at Macquarie University in the early 2000s.

We have since reviewed the structural data of DH to examine their implications for the broader questions listed above. These data have the benefit of being observational and detailed.  The methods of analysis  are well known but not often used in rocks of similar age elsewhere in the Orogen: domain analysis of fold directions and whether a time sequence can be determined in individual superposed folds, and incremental strain-axis analysis of kinematically significant minor fault, vein and stylolite associations.  We also describe a new type of structure—incoherent fault-related folds (DD)—which provides unambiguous criteria to determine the time relation between sub-parallel faults and minor folds.

From these observations and analyses we report (a) the time relation between at least two of the three known fold systems in the area, (b) the same three fold systems above and below the unconformity, which argues against a convergent deformation origin of the unconformity, (c) minor thrust and wrench kinematic data consistent with sinistral wrench reactivation of prominent NNW faults, (d) pre-fold normal movement on the prominent NNW faults, (e) a pre-fold or syngenetic origin of the massive-sulphide mineralisation, (f) no detected map-scale thrusts or inversions and (g) regional correlations which suggest a post-Late Devonian or Kanimblan age of the multiple folding.


Biography

David Hood obtained Hons in Earth Sciences at Macquarie University (1996), specialising in multiple deformations.  Employment includes James Hardie and ARDEX Australia as an Industrial Chemist.

David Durney taught structural geology and geomechanics at Macquarie University to 2006.

Ross Parkes obtained Hons then PhD (2005) in Palaeontology at Macquarie University

Evolution of the Lachlan Orogen in the East Riverina region, NSW: Insights from 100 new SHRIMP dates

Bodorkos S1, Gilmore PJ2, Eastlake MA2, Bull KF2, Blevin PL2, Trigg SJ2, Campbell LM2 and Waltenberg K1

1Minerals, Energy and Groundwater Division, Geoscience Australia (GA), 2Geological Survey of New South Wales (GSNSW), Department of Regional NSW

The southern part of the central Lachlan Orogen in NSW is prospective for intrusion-related tin-tungsten (e.g. Ardlethan), porphyry-style copper-gold, and orogenic gold mineralisation; however, the regional geological framework has long been poorly understood. GSNSW’s 2014–2018 East Riverina mapping project (spanning the area between West Wyalong and the Murray River, east to Cootamundra and Adelong, and west to Narrandera and the Murray Basin) updated large areas of 1960s–1990s geological mapping, to support mineral prospectivity studies. The project included a collaborative GA–GSNSW geochronology program that generated nearly 100 new U–Pb SHRIMP zircon dates, to establish a regional chronology of felsic and intermediate magmatism, and to understand the depositional history of the intervening basin successions. Some highlights include:

  1. Sheared 493 Ma and 489 Ma granites of the Belimebung Igneous Complex confirm previous LA-ICPMS dating of the first Cambrian igneous rocks identified within the Gilmore Fault Zone. They were intersected in drillcore beneath the early Silurian Gidginbung Volcanics north of Barmedman, and indicate a possible latest Cambrian age for NW-trending magnetic lineaments near the Gilmore Fault.
  2. The propylitically-altered 439 Ma Cooba Monzonite southeast of Junee extends the known distribution of ‘Phase 4’ Macquarie Volcanic Belt rocks (prospective for porphyry copper mineralisation) to the south.
  3. Tholeiitic andesites of the 432 Ma Junawarra Volcanics and related rocks host gold mineralisation at Dobroyde, northeast of Junee. These are geochemically distinct from, and significantly younger than, the shoshonitic 439–436 Ma Gidginbung Volcanics to the northwest, and establish two separate associations of Silurian gold-bearing volcanic rocks in the region.
  4. More than 20 S-type plutons of the 432–427 Ma Koetong Supersuite have been dated, as far north as Nymagee, east to Young and Tumut, and west under Murray Basin cover to Barellan and Howlong.
  5. The predominantly mid-Silurian ‘Wagga Batholith’ is transected and flanked by NW-trending belts of Early Devonian (420–412 Ma) plutonic rocks linked to intrusion-related mineralisation. S-type granites associated with tin-tungsten mineralisation include the 418 Ma Burrandana Granite and the de-silicated 417 Ma Ryan Granite in the south, and fractionated 415–413 Ma granites near Ardlethan in the north. Contemporaneous I-type rocks include the cassiterite-bearing Yithan Rhyolite at Ardlethan, diorite associated with gold mineralisation at Mount Adrah, and intrusions east and south of Tarcutta and Holbrook.
  6. Regional Early Devonian volcanism encompasses the expanded 419–416 Ma Gurragong Group in the Cargelligo-Ardlethan area, and the newly-defined Culcairn Group (comprising the 415–413 Ma S-type Budginigi Ignimbrite and the 413–411 Ma Wallandoon Ignimbrite and Hickory Hill Diorite) in the Culcairn-Henty-Walbundrie area. These volcanic units constrain the timing of pre-eruptive siliciclastic sedimentation and influence the detrital signatures of post-eruptive sediments.
  7. I-type plutonism is youngest in the southwestern East Riverina. Early Devonian (414 Ma and 411 Ma) Leeton Igneous Complex granites stitch the unexposed northwestern extension of the Kancoona Fault. Northeast and north of Albury, the 407–402 Ma Mullengandra Monzodiorite and Jindera Granite appear to be associated with Central Victorian granites of similar age.

Biography

Simon Bodorkos has worked in Geochronology at Geoscience Australia since 2007, and has conducted the U-Pb SHRIMP dating program supporting the Geological Survey of New South Wales’ East Riverina project since 2013. His co-authors include GSNSW’s East Riverina mapping team and mineral systems specialists.

Apatite as as indicator of porphyry fertility in the Northparkes district

Wells, Tristan1, Meffre, Sebastien1, Cooke, David R,1,2, Steadman, Jeffrey A.1, Goemann, Karsten

1CODES. Centre for Ore Deposits and Earth Sciences, University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australia. 2ARC Industrial Transformation Research Hub for Transforming the Mining Value Chain – TMVC, Private Bag 79, University of Tasmania – Hobart, Tasmania, 7001. 3Central Science Laboratory, University of Tasmania, Hobart Tasmania, 7001

The resistate nature of apatite in the weathering profile, combined with its potential to record physical and chemical information about magmatic and hydrothermal systems, makes it a useful mineral for assessing magmatic fertility. Magmatic apatite trace element compositions can reflect the degree of fractionation, sulphur content and oxidation of the host rock, whereas hydrothermal or recrystalised apatite also has the potential to record hydrothermal fluid evolution.

Apatite from the Northparkes district, NSW were analysed by colour cathodoluminescence, scanning electron microscopy, electron micro-probe and laser ablation inductively coupled mass spectrometry. Colour cathodoluminescent imaging of apatite from Northparkes highlights complex zonation and differing luminescent colours that are linked to variations in mineral trace element abundance and crystal origins. At Northparkes, magmatic apatites have a lavender or blue luminescent colour, whereas apatites that have complex internal geometries and a yellow-green to brownish luminescent colour are associated with hydrothermal alteration and proximity to mineralised centres. Magmatic and hydrothermal apatite have similar crystal forms, making them virtually indistinguishable from each other without the aid of colour cathodoluminescence. Depletion of light rare earth elements in apatite is associated with hydrothermal alteration across the Northparkes district. Hydrothermally altered apatite from the mineralising intrusions at the Endeavour 26 deposit have pronounced LREE depletion and MREE enrichment, concurrent with a strong positive Eu anomaly. The detection of apatite with these characteristics can be used to infer the proximity to mineralization in porphyry systems in the Northparkes district.


Biography

Tristan is a part-time PhD student researching the fingerprint of magmatic fertility in the Northparkes district and broader Macquarie Arc. His research uses a combination of whole rock and mineral chemistry to define the signature of fertile porphyry intrusions and vectors towards them.

Scale reduction magnetotelluric survey in the East Tennant region, Northern Australia

Jiang, Dr Wenping1, Duan, Jingming1, Schofield, Anthony1, Brodie, Dr Ross1, Clark, Andrew1

1Geoscience Australia, canberra, Australia

Geoscience Australia has undertaken a series of integrated studies to identify prospective regions of mineral potential using new geological, geophysical and geochemical data from the Exploring for the Future (EFTF) program, together with legacy datasets. Data from the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) have been used as first-order reconnaissance survey to resolve large-scale lithospheric architectures for mapping areas of mineral potential in northern Australia. The resistivity model derived from the newly-acquired AusLAMP data has mapped deep lithospheric-scale conductivity anomalies in highly endowed mineralised regions and in greenfield regions where mineralisation was not previously recognised. For example, the model reveals a conductivity anomaly extending from the Tennant Region to the Murphy Province, representing a potential fertile source region for mineral systems. This conductive feature coincides with a broadly northeast-southwest-trending corridor marked by a series of large-scale structures identified from preliminary interpretation of seismic reflection and potential field data. This under-explored region, referred to as East Tennant, is, therefore, considered to have significant mineral potential.

We undertook a higher-resolution infill magnetotellurics survey to investigate whether the deep conductivity anomaly is linked to the near surface by crustal-scale fluid pathways. Broadband MT (BBMT) and audio-MT (AMT) data were acquired at 131 stations with station spacing of ~2 km to ~15 km in an area of approximately 90 km x 100 km. The 3D resistivity model revealed two prominent conductors in the resistive host whose combined responses result in the lithospheric-scale conductivity anomaly mapped in the AusLAMP model. The resistivity contrasts coincide with major structures preliminarily interpreted from seismic reflection and potential field data. Most importantly, the conductive structures extend from the lower crust to the near surface. This observation strongly suggests that the major faults in this region are deep-penetrating structures that potentially acted as pathways for transporting metalliferous fluids to the upper crust where they could form mineral deposits. This result indicates high mineral prospectivity for iron oxide copper–gold deposits in the vicinity of these major faults. We then used AMT data to estimate cover thickness to assist with drill targeting for the stratigraphic drilling program which, in turn, will test the models and improve our understanding of basement geology, cover sequences and mineral potential. This study demonstrates that integration of geophysical data from multiscale surveys is an effective approach to scale reduction during mineral exploration in covered terranes with limited geological knowledge.

This abstract is published with the permission of the CEO, Geoscience Australia


Biography

Dr Wenping Jiang is a senior geophysicist working in Mineral Systems Branch in Geoscience Australia.

dh2loop 1.0: An open-source python library for automated processing and classification geological logs

Joshi, Ranee1,2, Madaiah, Kavitha1,2, Jessell, Mark1,2 and Lindsay, Mark1,2

1Centre of Exploration Targeting, School of Earth Sciences, University of Western Australia, 35 Stirling Highway, Crawley 6009 Western Australia,2Mineral Exploration Cooperative Research Centre (MinEx CRC), School of Earth Sciences, University of Western Australia, 35 Stirling Highway, Crawley 6009 Western Australia

Exploration and mining companies rely on geological drill core logs to target and obtain initial information on the composition and size of mineralized zones and/or a potential ore deposit. The drilling data is also used as inputs to 3D geological modelling to allow better visualization and understanding of the geology in a local and/or mine scale. With the amount of legacy drilling data available in geological surveys, extraction and processing of these data will allow for better shallow subsurface constraints for semi-regional and regional 3D geological models. These models will be helpful in designing mapping programs and more efficiently targeting sustainable new discoveries.

In this contribution, we focus on the processing and classification of lithological logs from the Geological Survey of Western Australia Mineral Exploration Reports Database in the Yalgoo-Singleton Greenstone Belt (YSGB) region. We refer to lithological logs as the component of a geological log that contains the dominant rock type in a specific downhole interval. Inevitably, lithological drill core logging is subjective and plagued with uncertainty, particularly as at a regional scale it is likely to have been conducted by tens to hundreds geologists, all of whom would have their own personal biases. It can also be difficult to recognize lithology with confidence and to establish subtle variations or boundaries in apparently homogeneous sequences. Given that we are dealing with geological legacy datasets, a large amount of important data are recorded in an unstructured textural form using varying geological drill core logging forms and formats depending on the company, logging geologist, investigation method, investigated materials and/or drilling campaign.

To resolve these challenges and unlock the vast information store in legacy drilling datasets, we developed dh2loop (github.org/Loop3D/dh2loop), an open-source python library that provides the functionality to extract and standardize drill hole data and export it into readily importable interval tables (collar, survey, lithology). dh2loop addresses the subjective nature and variability in nomenclature of lithological descriptions within and across different drilling campaigns by integrating published dictionaries, glossaries and/or thesaurus that were built to improve resolution of poorly defined or highly subjective terminology and idiosyncratic logging methods. Furthermore, lithological data is classified into multi-level groupings that can be used to systematically upscale and downscale drill hole data inputs for multiscale 3D geological modelling. dh2loop also provides drill hole desurveying and log correlation functions so that results can be plotted in 3D for analysis and comparison. dh2loop formats legacy data bridging the gap between utilization and maximization of legacy drill hole data and drill hole analysis functionalities available in existing python libraries (lasio, welly, striplog).

Keywords: drill core logging, legacy data, subsampling, Yalgoo-Singleton Greenstone Belt

We acknowledge the support of the MinEx CRC and the Loop: Enabling Stochastic 3D Geological Modelling (LP170100985) consortia. The work has been supported by the Mineral Exploration Cooperative Research Centre whose activities are funded by the Australian Government’s Cooperative Research Centre Programme. This is MinEx CRC Document 2020/41.


Biography

Ranee is a PhD candidate in the Centre for Exploration Targeting working with Mark Jessell, Mark Lindsay, Nicolas Thebaud and Tim Ivanic. She works on developing subsampling workflows to be able to automate multiscale 3D geological modelling. This project is a collaboration between the Loop and MinEx CRC consortium.

Geophysical Data Optimisation for Modelling: Data collection in a value-of-information framework

Lindsay, Mark1,*, Pirot, Guillaume1, Jessell, Mark1,*, Giraud, Jeremie1, Scalzo, Richard2,*, Cripps, Edward3,*, Aitken, Alan1

1Centre for Exploration Targeting, School of Earth Sciences, The University of Western Australia, Perth, Australia, 2School of Mathematics and Statistics, The University of Sydney, Sydney, Australia, 3Department of Mathematics and Statistics, The University of Western Australia, Perth, Australia

* ARC Centre for Dare Analytics for Resources and Environment

Crustal 3D models provide an understanding of the tectonic history of a region and its mineral endowment. As mineral resources are now mostly discovered under sedimentary cover, geophysical data are necessary to guide exploration. Recent developments in modelling 3D uncertainty with optimisation techniques are combined to guide data acquisition to image mineral systems and identify prospective regions. Most mineral systems are difficult to image with individual geophysical techniques so it is important to understand which data combinations are most effective for each system component (architecture, fertility, depositional trap, geodynamic throttle, preservation). In the course of these model-driven studies, there are often competing choices to be made around which data should be collected in order to reduce geological uncertainty. The “GDOM” project – “Geophysical Data Optimisation for Modelling” – seeks to determine what and how much geophysical data is worth collecting, the best processing methods and application in the most economically efficient manner. The intention here is to guide government policy and industry data collection practices. The workflow aims to inform how geophysical datasets can be best used to constrain geoscientific concepts and models to reduce uncertainty and more reliably answer geological questions. Recent advances in 3D model analysis helps to place focus where required and be used within a value-of-information (VoI) proposition to help us decide where and what data to collect. Two important parameters used in a VoI calculation are the estimate of “gain” from data collection and the probability of that gain. “Gain” may be the increase in value through deposit discovery, or finding prospective mineralisation amongst a portfolio of prospects and results. Both gain and the its dependence on critical system parameters are also uncertain, and have a large influence on the VoI analysis and estimating the risk involved in an exploration project. The cost of data collection is likewise critical information for decision-makers, especially if hierarchical scenarios where additional data reduces the cost of drill targeting are considered.  We propose a method that places these parameters into a hierarchical Bayesian framework to give us a clearer understanding on the uncertainties around VoI analyses, and helps us to determine the relative utility of collecting different geophysical data.

We acknowledge the support of the MinEx CRC and the Loop: Enabling Stochastic 3D Geological Modelling (LP170100985) consortia. The work has been supported by the Mineral Exploration Cooperative Research Centre whose activities are funded by the Australian Government’s Cooperative Research Centre Programme. This is MinEx CRC Document 2020/xx.


Biography

Mark is a geoscientist and Senior Research Fellow at the University of Western Australia, specialising in integrated geoscientific and 3D modelling and understanding the value of geoscientific information. He also has research interests that include investigating complex mineral systems and their representations.

Using gases for mineral exploration through cover: Importance of microbial activity

Plet, Chloe1, Siegel, Coralie1, Noble, Ryan1

1CSIRO Mineral Resources, Kensington WA 6151, Australia

In Australia, the presence of a thick transported cover on ~70 % of the continent has hindered the discovery of new world-class mineral deposits. To overcome this challenge, novel approaches are developed. Gases, with their high mobility, are thought to hold great potential as pathfinders for mineral exploration through cover. Previous investigations of gases detected at the soil surface have shown varying degrees of success in revealing the presence of buried mineralisation.

Here we investigate gases produced during laboratory weathering of sulfides. The experiments were run under sterile and non-sterile conditions. Carbon dioxide (CO2) and carbon disulphide (CS2) were the most abundant gases detected in all experiments. Non-sterile experiments produced more abundant gases than their sterile equivalents highlighting the importance of microbes in the weathering of sulfides.

In addition, the results of sterile experiments were compared to equilibrium thermodynamic predictions. In all experiments, as predicted, CO2 was the most abundant gas detected. However, some sulfur gases predicted by thermodynamic modelling were not detected in the laboratory (e.g. S2, H2S, CH3SH and C2H6S). Moreover, the most abundant sulfur gas predicted, carbonyl sulfide (COS) was only detected at trace levels. These results indicate that the experiments did not reach equilibrium.

Further soil gases experiments should include characterisation of the microbial communities. These would permit to gain a better understanding of the processes by which microbes impact the gases and improve the reliability of both techniques in the search for buried mineral deposits.


Biography

Chloe Plet obtained her PhD in organic and isotope geochemistry at Curtin University in 2017. In 2018 she joined CSIRO Mineral Resources, where her work largely focuses on investigating the potential of soil gases as a medium for mineral exploration.

New strato-tectonic model and geochemical tool for revitalised IOCG targeting

Anderson, John1

1Austrike Resources Pty Ltd, Glenalta, Australia

The combination of a new strato-tectonic model for the Olympic Metallogenic Event (OME) and zircon-based geochemical tool is a significant step-change for ore vectoring for a spectrum of IOCG and coeval deposit styles in the Gawler Craton.

Minerals exploration by Aberfoyle Resources, MIM Exploration and Investigator Resources resulted in the recognition of the Nankivel advanced argillic cap in the nineties and resulting discovery of the 42Moz Paris silver deposit in 2011. Paris is interpreted as an intermediate sulphidation epithermal associated with Nankivel and Helen copper gold silver magnetite skarn, all within a 100km2 sericite pyrite lithocap. The mineralisation is hosted in part by 1620Ma subduction monzodiorites with the Paris-Nankivel mineralisation dated within 2Ma of the 1590Ma Olympic Dam mineralisation.

The revised model proposes the Paris-Nankivel epithermal-porphyry belt is formed at the same time as Olympic Dam on the margins of a super caldera filled with upper Gawler Range Volcanics (GRV). Prior subduction tectonics produced precursor epithermal-porphyry conditions on the southern shoulder of the caldera, whereas IOCGs formed on the northern and eastern margins with haematite- or magnetite-dominated systems respectively forming on the shoulder or in hotter more reduced conditions under the GRV blanket within the caldera.

The epithermal/porphyry and IOCG belts are both fluorine-anomalous and connected by a conductive magneto-telluric (MT) corridor possibly representing a fossil transfer fault and metal source along the mantle interface.

Variations of a mid-GRV stratigraphic marker of the caldera collapse and OME are interpreted as the Bitalli Rhyolite at Paris, Nankivel palaeosurface and as lateral ferruginous sediments and volcanogenic conglomerate facies that collapsed into the IOCG systems preserved under the Stuart Shelf. Drill logs indicate the overlying Pandurra Formation is transitional in places with the mid-GRV marker, so the cover role of that unit needs reassessment with implications for deposit preservation and exploration.

The Zircon Alteration Index (ZAI = 40 – Zr/Hf) is a robust search tool that is universally applicable to the OME spectrum of deposit styles and hosts. Compared with other pathfinder applications, ZAI is a simpler, more reliable and far-seeing proximity tool requiring less assay samples in less drill holes for future targeting. The exclusive association of Hf with Zr in zircon enables wholerock analysis of the Zr/Hf ratio to measure the amount of hydrothermal overprinting of the inherited volcanic or detrital zircon in a host rock and hence proximity to a mineral target. Downhole variations of ZAI and comparisons with lithologies enables lateral or vertical target vectors to be often added to the proximity measure.

The ZAI tool and strato-tectonic vectoring have been validated for the Stuart Shelf IOCG systems with a comprehensive study of 35 holes with the requisite Zr and Hf analyses in varying proximities to known IOCG deposits. Preliminary target ranges are assigned to the ZAI values. Combined with the approach of structural and MT targeting, ZAI identified ten drilled prospects recommended for reconsideration by the tenement holders. The mineral systems targeting approach is also recommended to select areas elsewhere in the Gawler Craton for ZAI target analysis.


Biography

Geologist by training and mineral explorer seeking research developments with applications to discovery. Formerly Aberfoyle, MIM Exploration and founding Managing Director of Investigator Resources responsible for several mineral discoveries and subsequent mines. Current Chair of Advisory Board for the Institute of Mineral and Energy Resources at the University of Adelaide.

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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.