Logo Earthworks
Show/Hide Menu


The scientific basis of resource exploration

Systematic resource exploration starts with geological reconnaissance. Geological mapping was therefore a priority in many countries in the first half of the 20th century, underpinned by heroic campaigns of field mapping, supported in due course by the interpretation of aerial photography and then of satellite imagery in the second half of the century. The sheer size of areas to be covered in places like Africa is daunting and the problems of tedious land access are compounded by the paucity of bedrock exposure over large parts of most continents. The offshore continental margins, with their potential for oil and gas, offer virtually no conventional exposure.
Aeromagnetic surveys
Since about 1950, airborne magnetometer surveys have shown their ability to offer fast geological reconnaissance of large areas at low cost, regardless of conditions on the ground. Such surveys evolved in their technological sophistication and had been joined by high resolution gamma-ray spectrometry by the 1990s. Airborne gravity has also gained its place amongst the most pertinent technologies to explore what lies at depth below large areas. The economic importance of extending geological mapping into these areas devoid of outcrop – and into the third dimension everywhere – is probably still underestimated by the earth science community at large. 'Geophysical mapping' is relevant at scales from a map sheet to a continent. The procedures of geophysical mapping are at the heart of Earthworks’ experience. An introductory text-book, Aeromagnetic Surveys: Principles, Practice and Interpretation was released by Geosoft in 2005.
Thorough, intelligent and informed inventory of solid mineral and hydrocarbon prospectivity on land and at sea is essential both to the commercial resource sector and to national and international authorities. Despite their key economic role in this, many national geological surveys - in Africa, for example - are still starved of resources. Aid programmes attempting to compensate for decades of under-performance have routinely turned to airborne geophysical surveys to accelerate the national resource mapping process by providing pre-competitive baseline data to release to the exploration sector. Colin has been active in this sector for more than 50 years.
National gravity survey of Botswana

A half-century of geophysical mapping and interpretation

His approach has been to face up to this challenge squarely, starting with the initial forays into the geology hidden below the sands of the Kalahari in Botswana. This evolved over many years into a focus on the key role of national geological surveys in collating, understanding and disseminating basic geological knowledge for their territories. Many international aid projects have supported economic exploration in this way. Wherever possible within these programmes Earthworks has sought to assist in institutional strengthening and capacity building. We argue that this starts with adopting a management strategy that is suited to the era of information and communication technology (ICT). ICT must now be at the core of any public sector survey organisation that is to remain effective as the custodian of the national geoscience database. We have repeatedly used management consultants versed in ‘the management of change’ to help achieve this within our projects.
The post-Karroo dyke swarm in Botswana
The interpretation of regional geophysical surveys is a specialist skill that demands experienced practitioners. Pre-existing geological maps and knowledge must be the foundation of the work, but geophysical techniques always reveal hidden structures (such as the Okavango dyke swarm in Botswana, illustrated) that not only allow interpolation and extrapolation of known geology into covered areas but also add the third dimension to hidden structures everywhere. The interpreter’s skill involves developing geological ideas that not only fit the observed geology but also make defensible arguments about what lies below, embracing the geophysical anomalies. It is fundamental to exploration programmes that such ideas suggest locations that can be tested in more-detailed exploration work at local scales.
At the other end of the scale spectrum, from the broad perspective afforded by experience with national survey programmes in many countries of central, southern and eastern Africa, it is evident that geological correlations at continental scale drawing on these new national-scale insights are under-developed. There is no continent-wide geological mapping authority in Africa to match the performance of, for example, Geoscience Australia, the Geological Survey of Canada or the USGS. With hands-on experience in so many countries of sub-Saharan Africa, this is one focus of the current endeavours of Earthworks. A better appreciation of the broader features of continental geology for Africa, in turn, allows the continent to be fitted more elegantly into larger assemblages of Precambrian terranes such as Gondwana, Pangea and Rodinia.
Combined magnetic and radiometric image

The hidden two-thirds of the Earth

Most of our planet is covered by the water of the deep oceans. Their geological history was virtually unknown until the theory of plate tectonics brought a new dimension to earth science as a whole in the 1960s. Then, in 1997, satellite altimetry started to deliver images of sea-floor topography of startling resolution worldwide. The detail revealed was sufficient to interpret with confidence the processes of ocean creation within the guidelines of plate tectonic theory.
In combination with spherical geometry, the paths by which the continents dispersed from the Paleozoic entity of Gondwana could be traced over time with new accuracy. Making use of this data required the adoption of paleo-reconstruction software and postulating and evaluating continental movements that followed logical rules to produce models that were also satisfactory when viewed in animation. Slowly, satisfactory models of the dispersion of Gondwana were developed that bridged the Cretaceous Quiet Zone, devoid of the marine magnetic anomalies used universally to time ocean growth, and extended accurate reconstructions back into Lower Cretaceous and Jurassic times where the story of Gondwana disruption is rooted. This work is ongoing.
Gondwana at the base of the Albian
With the luxury of a supply of available quality time, priority is now being given to these curiosity-driven research activities, including support to the new Geological Map of Gondwana (IGCP-628). Earlier contributions to basic research have included, for example, the Magnetic Anomaly Map of the World, contributions to two scientific encyclopaedias and many workshops and training programmes. We are now particularly interested in cooperating with others with expertise, experience and non-confidential data (particularly in Africa) that can be shared with the wider earth science community to promote scientific knowledge of the geological past in the southern hemisphere.
The global thinker
Last update: 2021 June 16