Geological Interpretation of Aeromagnetic Data
The Australian Society of Exploration Geophysicists (ASEG) has released a new e-book “Geological Interpretation of Aeromagnetic Data” by Dave Isles and Leigh Rankin.
This book aims to help geologists to extract maximum value from aeromagnetic survey data. It shows how to integrate these data with geological data to build an interpretation that matches the objectives of your project. The book is written by two consulting geoscientists who deal with complex geophysical and geological interpretation problems in their day-to-day work.
The authors have prepared the book in response to the frequently cursory analysis of high-quality aeromagnetic data, usually caused by the absence of geologists’ active participation in the integration and interpretation process. They have seen the value of many datasets seriously eroded by under-use. Surveys costing $500 000 or more sometimes attract only a handful of days of interpreter time for assessment. Aeromagnetic data contain a wealth of geological information that may be overlooked if the analysis is con-strained to the ‘geophysical’ aspects and confined to geoscientists with predominantly geophysical training and a focus on the physics and mathematics of the data. The examples in this book show the level of geological detail and consequent exploration value that can be gained from adequate, well-focused time spent analysing aeromagnetic data.
Dave Isles is a geophysicist by training who has spent most of his 40-year career using aeromagnetic data (and many other geophysical tools) to facilitate mineral explora- tion programs. His grasp of geology has grown through the need to fully understand the geological environ- ment of each new exploration project. Leigh Rankin is a geological mapper with specialist structural skills. He began using aeromagnetic data in South Australia during the 1980s when he discovered that just beneath the vast expanses of sand dunes, swamps and alluvial plains, there were rocks with readily measurable mag- netisation. Beneath the paddocks of wheat and sheep, these rocks could be mapped both individually and collectively by using aeromagnetic data, thus aiding the assembly of geological interpretations at all scales.
The authors emphasise that the main ingredients in a high-quality interpretation are astute use of the geoscientist’s brain and adequate time, not only to digest diverse clusters of data, but to integrate these into a working map that drives our project forward. The rewards for this (usually modest) effort and time can be substantial – a resource discovery, a quantum leap in understanding of local geological evolution or a new direction and momentum in exploration, to name a few.
The book has evolved from a short course created to address the demand from exploration geologists who, faced with an explosion of high-resolution aeromagnetic data in the Australian gold and base-metal prov- inces in the early 1990s, recognised the need to take ownership of the interpretation function on their project areas. Simply put, there were too few suitably experienced geoscientists then, to assist with the exciting task of integrating this wealth of new data into exploration programs. Hence the book has its roots mainly in gold exploration in Australia (as reflected in much of the imagery used in the examples), but the authors have since expanded the methodology to embrace the interpretation of aeromagnetic surveys in a wide range of ‘hard- rock’ and ‘soft-rock’ applications. The methodology described in the book is considered to be appropriate for mineral and hydrocarbon explorers, as well as groundwater explorers, and in fact all those involved in producing and using integrated geoscientific maps.
The book stresses the value of data integration; not only of geological and aeromagnetic data, but also radiometric, satellite imagery, aerial photo, gravity, electromagnetic and of course seismic reflection data where these are accessible for the project. Because of the diverse and consistent range of geological information it provides, our prime focus in this book is on ‘aeromagnetics’.1 We stress, however, that all available data should be considered when compiling a working interpretation. The cornerstones of the integration process are formed by the wonderful GIS, imaging and modelling tools at our disposal for enhancing and cross-referencing datasets, but the diligent and experienced human brain is the tool that shapes the end result and determines its quality. The tasks of observation, integration and interpretation that we describe in this book involve mostly simple and qualitative steps, using much more geological reasoning than heavy-duty physical or numerical analysis.
Click here to view the book’s Contents pages. An order form for the book is available here.
7 Feb 2013
