ASEG Extended Abstracts - 2nd Australasian Exploration Geoscience Conference: Data to Discovery, 2019

Lao PDR is a poorly developed country, with a large rural population which relies heavily on agricultural production. The Vientiane Plain is one of the most important and largest agricultural production areas with plans to expand the area under irrigated agriculture. Historically, surface water has been used because of its relative abundance with limited consideration to use groundwater. Where groundwater development has occurred for irrigation there is little or no management, and what little there is, is based on very poor hydrogeological information. A lack of knowledge of where to site wells has led to well failure and poor water quality.

This project was initiated through the Society of Exploration Geophysics - Geoscientists without Borders Program to: teach local scientists, both university-based, as well as from the government, about the latest in hydrogeophysical technology and how it can be used in the Lao PDR. Specifically we looked to apply hydrogeophysical techniques to characterise the hydrogeology of the Vientiane Plain; to evaluate the quantity and quality of groundwater that may be available; and to enhance the scientific knowledge of local resource users. Two field trips were undertaken in 2018 and 2019 to conduct workshops and training with in-country government department officials and students from the Laos University.

Results from the project identified and mapped highly conductive zones related to saline geological features which would be unsuitable locations for well locations for groundwater irrigation.

Microseismics – the detection and characterisation of mining-induced fracture events in the rockmass – is widely used to improve geotechnical understanding of the rockmass response to mining, and for hazard assessment of rockbursts and roof falls. These uses of microseismics require that the seismic events be accurately located, which can only be done using an accurate velocity model.

In sedimentary environments, seismic velocity is typically anisotropic, usually being somewhat faster in a horizontal direction than in the vertical direction. However, anisotropy is seldom taken into account when processing microseismic data, resulting in locations of seismic events which can be significantly in error.

This paper presents a technique for inverting a set of calibration shots with known location, along with a set of mining-induced seismic events, for an anisotropic velocity model. An example of the differences in event location is shown, illustrating the potential geotechnical significance.

The Weena Trough and the Milpera Depression in the SW Cooper Basin contains some unusually thick Permian coal seams. Their development is linked to the Late Carboniferous-Early Permian glacial palaeoclimates, the slow subsidence resulting from their flanking structural location, and the isolation of the peat swamps from the main fluvial drainage systems.

The very thick coals are sub-bituminous to bituminous and have high inertinite:vitrinite ratios with relatively large amounts of semi-fusinite and alginite macerals. This combination of thickness, maceral composition and rank makes them ideal for coal bed methane production notwithstanding their depth.

In this research a flexible electrode array's combination device is used for 2D/3D resistivity data acquisition. This system can be used for applying any possible array over a survey electrode network with no restriction on the array size in any direction. Despite similar systems which are limited in size of network and possibility of electrode configuration, this system can be used in a large scale 2D or 3D acquisition.

It not only enables acquiring a large collection of data, but also gives the ability to apply optimized electrode array in spite of other similar systems, hence it is suitable for 2D or 3D data acquisition. The data sets acquired with this device can be planned and used in optimized electrode array design. This can give better resolution while the data set inversion process. This equipment affects data interpretation with increasing of captured data quantity in which directly impact the interpretation quality.

Electrode array design can be chosen prior to the actual survey and with this equipment, it will be a full automated process. Another option is to let device decides and modify survey steps based on acquired survey acquisition.

To achieve this task effectively, the noble modeling technique is used with combination with a K-factor engine. As this new method has no singularity problem to solve a resistivity network, and it uses parallel programming technique to improve processing time, it makes it the best choice for forward modeling engine in the flexible electrode array's device.

The structural context and Australian versus Asian affinity of regional outcrop of Timor’s Lolotoi Metamorphic Complex are critical to the interpretation of hydrocarbon prospectivity but are obscured by complex geology and still strongly debated. Timor Resources and Geomage used Common-Offset Multi-Focus (CO-MF) processing to vastly improve imaging of legacy onshore seismic surveys. These are interpreted by integration with surface geology mapping, wells, offshore seismic and gravity data, providing the first geophysical insight and possible resolution of the Lolotoi conundrum. Beneath a bland zone interpreted as allochthonous Lolotoi lies reflectivity interpreted as faulted blocks within a large sub-allochthon anticline. Closure up to 90 km² occurs to a modest total depth around 2500 mSS, providing a viable drill target to test the sub-thrust reflectivity package.

Loupe is a new generation of time-domain electromagnetic (TEM) instrument designed for profiling and mapping in the near surface. It employs a two man backpack-mounted transmitter-receiver combination for rapid continuous data acquisition. In addition, a trailer-mounted version is under construction.

Interference from a range of sources is a significant problem for TEM systems. Problems are exacerbated when surveys are undertaken in urban areas.

This paper will present case histories from a range of applications including mapping buried rubbish, saline incursion, shallow sulphide exploration, graphite exploration and tailings dam assessment.

Fractures and faults were extracted from a reverse time migrated 3D Vertical Seismic Profile (VSP) data acquired over a carbonate reservoir offshore Abu Dhabi in the United Arab Emirates. A specific workflow was used for the extraction of fractures and faults. The workflow was based on data preconditioning (i.e. noise attenuation), semblance based seismic attributes, binary filtering, and clustering. A complex network of fractures was extracted. The dominant strike direction of the extracted fractures showed a good correlation with the dominant strike direction of interpreted fractures from FMI (Fullbore Formation Microimager) and core data at three reservoir zones. A known fault in the area was also detected. The extracted fracture network was then used to compute fracture intensity maps. Fracture intensity maps give indications of zones with high fracturing that may be associated with greater porosity and permeability.

Divining has been used for centuries for groundwater and mineral prospecting. Historically, divining has been reliant on a rod, or pair of rods, accompanied by a particular individual. Recently, the use of fluid-bearing containers was cited as a viable water divining technique by a popular Indian ‘youtuber’. We numerically simulate the response from a coconut using an appropriate robust statistical method, similar to that deployed by the diviner in their videos. Coincidentally, a clear response in the rotation of the coconut is generated wherever the diviner desires. Our results indicate that divining is and remains at the whim of the practitioner. Unfortunately, this pseudo-science pervades in the modern day and discredits other methods of remote subsurface imaging.

The Paleoproterozoic Yerrida, Bryah and Padbury Basins are located on the northern margin of the Archean Yilgarn Craton, and are host to orogenic gold (Peak Hill, Fortnum and Horseshoe), volcanic-hosted massive sulfide (VHMS; Horseshoe Lights, Red Bore, Monty and DeGrussa) and epithermal copper deposits (Thaduna) ultramafic, shear hosted copper mineralisation (Forrest-Wodger), as well as economic amounts of talc and manganese.

Characterisation of the sulphur and lead isotope signatures of the different deposit types helps to distinguish the deposits types from one another (e.g. a DeGrussa-type VHMS deposit from a Thaduna-type Cu deposit), as well as the source of mineralising fluids in each deposit. With the exception of Horseshoe Lights, Pb isotopes have characteristically high μ values (10.8) throughout the Bryah Group. Combining this information with accurate geochronological information may provide guidance for exploration for gold and base metal mineralisation, not only in the Bryah and Yerrida, but also throughout the larger Capricorn Orogen.

The Geological Survey of New South Wales is building a statewide 3D geological model comprising a series of interlocking province-scale models and a 3D statewide fault network. The model is being developed in conjunction with the New South Wales Seamless Geology geodatabase and is constrained by mapped geology, interpreted geology, drillhole intersections, seismic sections and potential-field imagery and modelling. Detailed 3D models of mineral, hydrocarbon, coal and groundwater resources will be embedded within the framework provided by the statewide 3D model. The model will support land use management, mineral and energy exploration, scientific research, groundwater management, civil engineering and other applications.

World class gold discoveries are being made in the Yamarna Terrane, one of the least understood terranes of the Yilgarn Craton. Despite many and varied challenges, Gold Road are in the unique position of compiling and constructing the stratigraphic map for this immature exploration terrane allowing continual improvement to ongoing targeting and exploration programmes.

The key to successful exploration is the development of a regional stratigraphic and structural geological model through acquisition of new data, application of modern science, and integration of fundamental geological observation. Lithogeochemical classifications, geochronology, and development of mineralisation models are the three areas of focus Gold Road considers paramount to combine with the fundamental structure of the Yamarna Terrane. New geochronological data has implications for the understanding of the geodynamic evolution of the Yilgarn Craton, identifying some of the oldest rocks so far found in Eastern Goldfields Superterrane.

A case study is presented of the development in the understanding of the tectonostratigraphic evolution of the Yamarna Terrane to target for gold efficiently and effectively.

Understanding the mobility of individual elements in the oxidised environment is important for the accurate interpretation of geochemical data from regolith and weathered bedrock samples. In the weathered environment, immobile element geochemistry can reflect primary lithological and in situ mineralisation signatures, whereas mobile elements can help establish the degree and extent of weathering. Three exploration case studies are presented here to demonstrate the application of multielement geochemistry in the weathered environment:

1. An example from the Shorty Creek Project, Alaska (Freegold Ventures), highlights the importance of reviewing and understanding pathfinder elements in soil, weathered bedrock and fresh basement. Here, commodity elements Cu and Zn are highly mobile and relatively depleted in the soils and weathered zone over Cu-Au mineralisation, whereas Au, As, Bi and Sb are less mobile and highly anomalous in the oxidised bedrock and associated soils.
2. The Hermosa Deposit, Arizona (South32), where downhole geochemistry can help map the oxide-fresh rock boundary at the deposit scale. Subtle depletion in mobile elements allows the weathered zone to be identified in altered rhyolites, and Zn:S and Pb:S ratios in the mineralised zone helps distinguish Zn and Pb oxides from Zn and Pb sulphides.
3. A review of residual soils over a Ni-Cu-PGE prospect in Northern Queensland, where immobile elements are reliable discriminants of primary lithologies in highly weathered environments. Zirconium, Y, Th and Nb can be used to distinguish felsic from mafic bedrock, and variations in Cr, V, Al, Fe and Sc in soils confidently identify blind, compositionally distinct mafic-ultramafic bodies.

This paper also highlights the importance of collecting high quality, multi-element geochemistry with low detection limits at every stage of exploration.

There is an Indian proverb that goes: “Tell me the truth and I’ll believe it for a while. But tell me a story and it will stay with me forever.”

This paper outlines a Finite Element modelling workflow using the software package ‘Underworld’ that is applied to sedimentary basin undergoing multiple rifting events. The evolution of the resulting strain rate, viscosity structure, temperature field, and sedimentary structures can be tracked. Application to the Ceduna Sub-basin is discussed.

Onshore 3D seismic data is often acquired with rich azimuth coverage by utilising orthogonal shooting (or cross-spread) layouts. This means that azimuthal anisotropy, if present, can be readily observed and its effects on the data can be quantified and accounted for as part of the processing and imaging flow.

In this example from the Canning Basin, the data appeared initially to be exhibiting the effects of azimuthal anisotropy. However, with careful handling and honouring of the azimuths of the acquired data during the PreSDM velocity model building, it was possible to correct for most of the variation simply with a laterally variable velocity model, without the need to invoke the presence of azimuthal anisotropy.

The towed streamer market is moving towards the widespread use of multicomponent streamers. This type of streamer contains hydrophones and particle motion sensors which are used to carry out receiver-side deghosting of the data. The main source of noise on the particle motion sensors is streamer transverse vibration, and it can be challenging to obtain a high enough signal to noise ratio to use this data in the de-ghosting process. In this paper, we study how the characteristics of transverse vibration noise are affected by the choice of the streamer mechanical platform. To compare the implications of design options we built different streamer sections with dense single sensor sampling, identical electronic backbones and MEMS sensors. We towed them together under different tensions in a field experiment and observed that, as expected, the transverse vibration noise was the dominant noise mode, with dispersion characteristics depending on the streamer bending stiffness. We also found that the noise amplitude and maximum frequency (under the same towing conditions) depends on the mechanical properties of the cable, and that they could be reduced by using a new type of gel optimized to dampen vibration.

As a result of theoretical modelling and these field observations we propose a new approach to streamer noise attenuation which involves optimising the mechanical characteristics and using non-uniform single sensor sampling in the design of the cable. This avoids some of the compromises we incur using analog arrays and the high cost of single sensor, uniform Nyquist sampling.

In this paper, we present an algorithm based on the sensitivity of the data to the model space to reduce the large amount of data commonly collected during 3D DC/IP surveys to only those most relevant and important to the model space. The sensitivity-based data reduction (SBDR) algorithm is demonstrated using both synthetic and field data examples. The results indicate that the SBDR recovered models are valid solutions to the full inversion problem but require a fraction of the computation time and resources, providing a geologic solution in a much shorter time than required to solve the full inversion problem.

Electrical methods have been applied to the search for porphyry copper and IOCG deposits since the early 1950s. While there is a generally accepted model of disseminated sulfides giving rise to a chargeability response, no clear association has been attached to what EM surveys may be responding to. Work in the early 1990s (Nickson 1993) showed the well-developed supergene blankets over a porphyry copper could be conductive; this observation was however, never applied formally to generally accepted porphyry targeting models. The presence of other conductive zones associated with porphyry copper deposits is even less well studied. On the geological side, while there is a vast body of literature describing porphyry copper deposits and how to discover them, in very few cases do these studies even speculate if anomalous concentrations of sulfides could be conductive. On the geophysical side, observations of unexpected conductivity associated with porphyry systems is sometimes noted but these observations typically stop short of suggesting that there could be a more general observation made that a new class of geophysical feature should be defined. The present study is felt to have gathered a sufficient number of case studies which show that a significant number of porphyry copper deposits posse a mineralogical character which can be identified with EM techniques. This thesis can have significant implications as to how porphyry copper are explored for, especially those at depths >500 m, a generally accepted cut-off for IP techniques.

Total Organic Content (TOC), one of the most important parameters for sweet spot mapping of unconventional plays is estimated using a RockEval Pyrolysis technique. This process being expensive and time-consuming, the sampling rate per well is very low. In this paper, we use Machine Learning to develop a model that can use conventional wireline logs to estimate TOC data. This model is based on wells in the Canning Basin, Western Australia.