Peter Robert Milligan

ENRiT

The delineation of near-surface (0-300m) hydrostratigraphy and tectonic features is essential for successful characterisation of groundwater systems and subsequent hydrogeological modeling. While most remote sensing of such systems is commonly achieved using high-resolution airborne electromagnetic data, validated by drilling data, and complemented...

The Australian Government has recently provided Aus$100.5M to Geoscience Australia over 4 years (2016-2020) to manage the Exploring for the Future (EFTF) programme designed to increase investment in minerals, energy and groundwater resources, primarily in Northern Australia. The programme includes Aus$30.8M for groundwater-specific investigations,...

The Diamantina ∼120 km-diameter ring feature, a unique feature in western Queensland, is manifested by a near-360° circular drainage pattern, radial creeks and a coincident radiometric K–Th–U pattern. The structure has been studied in the context of an investigation of the nature and origin of Australian circular structures. Geophysical signatures,...

A new version of the World Digital Magnetic Anomaly Map, released last summer, gives greater insight into the structure and history of Earth's crust and upper mantle.

The Capel and Faust basins (northern Lord Howe Rise) are located in the SW Pacific between Australia, New Zealand and New Caledonia. New seismic, gravity, magnetic and bathymetry data and rock samples have enabled the construction of a three-dimensional geological model providing insights into the crustal architecture and basin stratigraphy. Multip...

Australia, via the efforts of the Government Geological surveys, has a program of releasing ever bigger, higher resolution, continental-scale datasets. The recently released isostatically corrected gravity data imagesmany deep and large-scale crustal features. This is a key dataset for understanding the primary structure of the deep crust across th...

Earth’s gravity and magnetic fields are used as natural reference frames in directional drilling. The azimuth of the bottomhole assembly is inferred by comparing the magnetic field measured-while-drilling (MWD) with a geomagnetic reference model. To provide a reference of sufficient quality for accurate well placement, the US National Geophysical D...

The Tilt-Depth method is investigated as a means to rapidly derive estimates of depth to basement from magnetic data. This method involves calculating the tilt angle from reduced-to-pole magnetic data. Magnetic sources are assumed to have simple contact geometry. The depth to these sources can be estimated from the distance between contours of the...

A deep seismic reflection profile and coincident refraction and magnetotelluric data were acquired across the northern Eyre Peninsula, Gawler Craton in 2008 to enhance the prospectivity of this region for uranium and geothermal energy, by establishing the crustal architecture and regional geodynamic framework. The seismic line crossed several tecto...

In 2008 Geoscience Australia acquired regional seismic reflection, wide-angle refraction/reflection, gravity, and magnetotelluric (MT) data along a 253km east-west transect across northern Eyre Peninsula, Gawler Craton in South Australia as part of the Australian Government’s Onshore Energy Security Program (OESP). These datasets provide complement...

In 2008, as part of its Onshore Energy Security Program, Geoscience Australia, in conjunction with AuScope, Primary Industries and Resources South Australia (PIRSA) and the Northern Territory Geological Survey, acquired 634 km of vibroseis-source, deep seismic reflection data and gravity data along a single traverse from about 25 km southeast of Er...

Geoscience Australia and the Australian State and Territory Geological Surveys have systematically surveyed most of the Australian continent over the past 40 years using airborne gamma-ray spectrometry to map potassium, uranium and thorium elemental concentrations at the Earth's surface. However, the individual surveys that comprise the national ga...

A global Earth Magnetic Anomaly Grid (EMAG2) has been compiled from satellite, ship, and airborne magnetic measurements. EMAG2 is a significant update of our previous candidate grid for the World Digital Magnetic Anomaly Map. The resolution has been improved from 3 arc min to 2 arc min, and the altitude has been reduced from 5 km to 4 km above the...

Magnetotelluric (MT) data have been acquired in 2008 and 2009 at 40 broadband (0.01 s to 500 s) and 12 long-period (10 s to 10 000 s) sites along the east-west deep seismic reflection transect (08GA-G1) of northern Eyre Peninsula, South Australia. The MT survey is a joint project between the University of Adelaide and Geoscience Australia and is fu...

We have improved magnetic anomaly map of the United States using National Uranium Reconnaissance & Evaluations (NURE) aeromagnetic surveys collected during the 1970s. Previous versions of these data processed using IGRF/DGRF do not mesh well at the survey boundaries because of leveling artifacts. Similarly, the U.S. component of the North American...

SUMMARY Public domain total magnetic intensity (TMT) airborne data covcring thc Australian contincnt havc bccn collated into a new database of grids. The cell resolution of each grid is optimal with regard to the original survey flight-linc spacing. Data for all the grids havc bccn matched in one inverse operation by using the statistics of data di...

SUMMARY The Euler method of automating depth to source from potential field data has undergone resurgence in popularity, with several new extensions to the method developed. Perhaps the most revolutionary of these provides a solution of the structural index as part of the inversion process. Previously, structural index was a required input paramete...

Ocean swells have a magnetic signal, caused by the motional induction of sea water moving in the steady main magnetic field of Earth. To check the character of such signals at the sea surface, a magnetometer has been set free from a ship to float unrestricted on the surface of the ocean for periods of several days. The path of the floating magnetom...

The distribution of kimberlite, lamproite and related alkaline volcanism in Australia can be broadly related to the structure of the Australian continent and lithosphere. Diamondiferous kimberlites and lamproites, with the apparent exception of the weakly diamondiferous Orrorro kimberlites in the Adelaide Fold Belt, lie within the large Precambrian...

Working interpretation of the integration process between the GA deep seismic through Olympic Dam, gravity and magnetic models, and the newly release magnetotelluric data from Rob Gill's PhD project. This presentation caused quite a stir, as it highlighted an interpretation bias in the GA team, causing them to subsequently revise their interpretat...

Edge detection and automatic trend analysis using potential field gradients are methods for producing unbiased estimates of sharp lateral changes in physical properties of rock packages. Where the points lying on the maximum horizontal gradients of potential field data show a lateral continuity, they can be mapped as “strings”. These strings may be...

Regional compilations of airborne magnetic data are becoming more common as national databases grow. Grids of the magnetic survey data are joined together to form geological province‐scale or even continental‐scale compilations. The advantage of these compilations is that large tectonic features and geological provinces can be better mapped and int...

There is now a comprehensive coverage of magnetic and gravity potential-field datasets for the Australian region. Onshore government regional airborne magnetic surveys and ground gravity surveys commenced about fifty years ago, and these datasets now cover the whole continent. Marine magnetic and gravity data have been acquired over the same period...

We used automatic trend analysis with filtered gravity and magnetic data and multi-scale edge analysis ("worming") to produce rose diagrams of structural variations in different tectonic domains and at different crustal levels. Milligan P R, Direen N G, Lyons P, Peljo M & Dance F, 2002, Analysis and 3d visualisation of new compilations of potential...

Explores the geophysical (magnetic) signature of faulting around the Olympic Dam deposit, and the magnetic expression of the alteration in possible source rocks for the Cu and Au enriched in the ore body assuming transport by crustal fluids found in the regional alteration assemblage. Using simple mass balancing, we can show that repeated fluid cyc...

Induction arrows are a traditional output of magnetovariational experiments, and represent transfer functions used quantitatively in the inversion of geomagnetic depth sounding data to give Earth electrical conductivity structure. In this paper, a technique is tested in which ‘total-field’ variations are combined with horizontal-field data recorded...

Abstract This work presents a "snapshot" of research into the crustal architecture around the Olympic Dam Iron Oxide Cu-Au deposit, and makes some preliminary inferences on the fault architecture and alteration systems on the basis of filtering, interpretation, modelling ad inversion of public domain potential field datasets. At the time of present...

This paper describes an investigation of the use of aeromagnetic crossover misfits as a source of geological information. The misfits occur when, at a crossover point of an aeromagnetic survey, the separate measurements of the Earth's magnetic field are not the same. Misfits are mainly the result of time-dependent field changes and, in this paper,...

Seafloor and land magnetotelluric (MT) data were collected in the SWAGGIE (Southern Waters of Australia Geoelectric and Geomagnetic Induction Experiment) project in April-May 1998, from 30 seafloor and 23 land sites. The principal objective of the experiment was to delineate the strike and depth of a zone of high electrical conductivity, known as t...

In the CICADA97 experiment a line of simultaneously-recording stationary vector magnetometers was deployed from inland NSW, across the east Australian coast, and into the Tasman Sea. The purpose of the experiment was to investigate the effect of electrical conductivity structure near a coastline on natural time-variations in Earth?s magnetic field....

Summary The Euler method of automated depth estimation from potential field data has been extended to permit solution for the structural index as part of the inversion process. Examples across several areas of Australia are discussed. A more concentrated D model of Broken Hill using 3DWEG also makes use of Euler. The Euler method generates many sol...

Magnetic field fluctuations have been recorded by an array of portable three-component magnetometers at 60 sites across the Eyre Peninsula in South Australia between December 1993 and March 1995. An additional 54 magnetometer data records, collected prior to 1989 and described by Milligan (1989) and Milligan, White & Chamalaun (1989), were included...

Interpretation of aeromagnetic data in areas of limited outcrop requires the use of all relevant data enhancement techniques for accurate positioning of geological boundaries and magnetic sources. Where no outcrop calibration exists, magnetic sources must be characterised by physical adjectives relating to their form, depth and relative magnetisati...

Airborne geophysical data can be enhanced by a range of linear and non-linear filtering algorithms which selectively enhance the anomalies due to one group of geological sources relative to anomalies due to other groups of geological sources. Mathematical enhancement techniques are complemented by a range of imaging routines which can be specified...

The Australian Geological Survey Organisation acquires and maintains extensive databases of airborne magnetic and radiometric surveys, digital elevation models and gravity measurements. These data can be accessed and processed to present information ranging from continental scale to detail at 1:25 000 scale. When data relating to the Broken Hill ar...

A high-resolution aeromagnetic survey was undertaken by the Australian Geological Survey Organisation (AGSO) across the Bendigo 1:250 000 map sheet area during February to April 1994. For part of this period, high-resolution ground magnetometers were also deployed to test for the way that short-period variations of the geomagnetic field (including...

Aeromagnetic data from the highly structured and metamorphosed geology of the Highland Rocks 1:250 000 map sheet of the Arunta Block of the Northern Territory is virtually impossible to interpret in its original form by virtue of complexity due to the inclination of the Earth's magnetic field, interference between anomalies, regional effects and an...

Image enhancement consists of raising subtle trends above the detectability threshold usually either by increasing the relative amplitude or by emphasising the continuity of the feature. Images of the vertical magnetic gradient are in themselves an enhancement of the shallow source anomalies present in total magnetic intensity data. Even in the gra...

The integration of high resolution, image-processed aeromagnetic data with regional geological, magnetic, gravity and seismic data-sets has provided new insights into the structural architecture, rifting history, and petroleum potential of the western onshore and offshore Otway Basin, south-eastern Australia.Three principal structural directions ar...

Interpretation of new seismic, gravity and aeromagnetic data sets from the western Otway Basin has contributed signif­icantly towards a better understanding of the regional tectonic framework of the basin's evolution. Geosat data from the Southern Ocean and gravity data onshore have defined what is here termed the Otway-Sorell microplate, a triangu...

Airborne magnetometers now have resolutions of typically less than 0.1 nT, and the location of sub-1 nT crustal anomalies is becoming increasingly important, particularly for the delineation of weak intrasedimentary magnetic sources in prospective petroleum provinces. Natural time-variations of the geomagnetic field, with periods ranging from fract...

Digital images are an invaluable aid to the study of large spatial data-sets. With the advent of the National Geoscience Mapping Accord (NGMA) between the Bureau of Mineral Resources, Geology and Geophysics (BMR), and the State Geological Surveys, large quantities of high-resolution airborne magnetic and gamma-ray spectrometric data, and gravity da...

The Bureau of Mineral Resources has been routinely acquiring airborne magnetic surveys over the land area of Australia since 1951 to record and map anomalies in the earth's magnetic field attributable to geological structures and lithologies. In forty years, over four million line kilometres of survey data have been flown, while the technology of s...

Twenty-two digitally recording fluxgate magnetometers measuring short-period natural time variations of the geomagnetic field were deployed during 1988 at 54 sites to define the northward extension of the Eyre Peninsula Conductivity Anomaly (EPCA). The southern portion of this zone of high electrical conductivity was initially mapped during the ear...

Time variations of the earth's geomagnetic field, with periods of a few seconds to the daily variation, can introduce errors of up to tens of nanoteslas into magnetic survey data (Lilley 1982; Riddihough 1971). These errors may be removed either by rapid looping methods similar to those used in gravity surveys, or, as is more usually the case, by s...

A systematic study of the coast effect in South Australia (White & Polatajko 1978, 1985: White & Hopgood 1979) revealed the existence of a conductivity anomaly on Eyre Peninsula. Significant deflections of the transfer function vectors at periods around 1 h indicated a telluric current concentration flowing SW?NE up the peninsula. This prompted a m...