THE VALUE OF ADVANCED GEOPHYSICAL TECHNOLOGY IN MODERN EXPLORATION

S.N. Sheard,

MIM Exploration Pty Ltd, Level 2, Boundary Court, 55 Little Edward St, Spring Hill, Qld, 4000

Key Words: geophysics, FALCON, MIMDAS, mineral exploration, environment, data interpretation

Introduction

Geophysics technology is an integral part of exploration life. We as explorers for example accept, and now are generally dependent on, a precise geographic fix. This is technology that we understand and has been a great boon to exploration. There is no need to argue the cost savings in the ability to get back within metres of where we went to that gossan or collected that geochemical sample for example. The value of this technology is enormous and acceptable.

The GPS phenomenon is however not accepted as a Geophysical Technological advance and still we hear the age old cries – to find an orebody you need “boots on the ground”? or a manager saying “I’ll fund geology picks but not another #bl!!#*! computer – as you’ll never find an orebody sitting behind a computer screen”. This single-minded approach to exploration is largely dying but does still exist in some explorers, who apparently use GPS technology!

Technology in exploration can be defined as the application of science to exploration. The aim is to assist explorers find orebodies in regions where “geology” cannot do it alone. In the geophysical branch the aim should basically be assisting the explorer to produce 3D physical property maps to reduce the drilling risk, and find orebodies.

Geophysics is only part of the equation as to do exploration properly and successfully requires an integrated approach. This paper however will only touch on geophysical application.

Advances in Technology

The advances in geophysical technologies have not really kept up with those in the geographic positioning areas as there has been limited money invested in these areas in the last 6 to 8 years. What little there has been is spread through all areas of geophysical applications – from application of current systems, advanced acquisition systems, to processing, and interpretation, generally with costs borne by exploration companies.

The “applicability” of geophysics is not always in the metal arena, for example, the use in geotechnical/ environmental studies. Here standard exploration systems have been used to great advantage with the use of high resolution surveys.

An example of the value of “standard” exploration geophysics applied to environmental areas is shown in Figure 1 where using an airborne electromagnetic system, a tailings dam containment policy was augmented by ensuring correct placement of pump back holes.

In this use a Humming Bird 5 Frequency (3 coplanar 2 coaxial) System was used. In Figure 1, the conductivity image shows that the flow from the tailing dam could be better controlled using additional pump back sites. A similar study at a later stage will show the effect of this containment policy using these sites.

The ability to undertake this detailed observation has come directly from exploration technologies and is being used in the ore finding industry but unfortunately with less success due to the complexity of the problem.

In ground acquisition systems, the advances are coming through recently developed technologies with specific aims of increased penetrability combined with better resolution for the production of 3D physical property models or increased coverage at lower cost. This is of value as in many parts of the globe (particularly those where you can reliably make money) it is becoming increasingly difficult to locate new orebodies which may have little or no surface expression. In Australia, the last documented major base metal find to become a producing base metal mine found directly from geophysics is Ernest Henry, North West Queensland (Webb 1995). Unfortunately, in Australia base metal finds using any technique are becoming rare.

Obviously, there are external causes such as native title that diminish the accessibility to prospective ground in Australia, particularly in the accepted producing belts. It is worth noting however, that two of the “Big Ones” (Broken Hill and Mt Isa) were found by prospecting and one (Olympic Dam) by an integrated use of data including geophysical data. Basically, technology contributed to finding that Mine which will contribute greatly to Australia’s GDP for the next 50 years. Elsewhere, for example Chile, vast tracks of prospective areas for huge copper porphyries are covered by gravels and caliche – a very resistive surface cover that makes IP surveys difficult to impossible for standard systems. This is where innovative technology will be exceedingly useful and uncover these orebodies.

MIM and other companies have realised this problem and by their own initiatives have developed or assisted in developing technology to arrest this “non-discovery” trend. BHP has assisted in creating FALCON (Van Leeuwen 2000) – an airborne gravity gradiometer, Normandy “a helicopter borne time domain system”, and MIM a distributed acquisition system MIMDAS for deep prospecting in difficult areas.

MIM perceived the need for undertaking this development seven years ago as current ground systems were inadequate. Data collected was erroneous due to many factors which contributed to poor interpretation and thus costly drilling and perhaps missed orebodies. MIMDAS was developed from scratch to produce a quantum leap in resolution, penetration and interpretability of data. Concurrently processing, interpretation and display systems were re-engineered to accept the quality data. This was achieved and the system is being continuously used to great advantage to assist in MIM Exploration’s exploration effort. Examples of this will be shown.

Apart from MIM, other groups are producing technological advances in the display and interpretation of data. Figure 2 (not available yet) gives an indication of these advances.

The advances in the presentation and interpretation areas are generally “backward compatible” – unlike most commercial software and computing operating systems! This old data can be re-interpreted and provide startling results often overlooked by earlier qualitative interpretation. Examples of this will be given.

At present these technological advances, although very useful have yet to be shown to be “orebody” generators. This could be because the systems do not work - this is wrong as numerous examples can be shown where deep, difficult, bodies can be detected. Perhaps, the answer is in the acceptance of technology. Explorers now need to rethink their strategies and drive the exploration assisted and sometimes driven by the technology. An integrated approach is still required with the geologist interpreting the 3D data and the geochemist integrating remote techniques into the overall interpretation. There is an overriding principle that “technologies will not discover orebodies if they are not there”. Thus, we need to be in the correct place to apply our technological advances. This is a problem for our project generators.

Conclusion

The lack of exploration success for base metals in the last 10 years in the conventional exploration areas, when combined with reduction in mining costs has made the search for, and exploration of deeper targets more feasible. To find these has required a greater use of technology in the exploration process. These have driven an advance in our technologies in acquisition systems, presentation and interpretation methodologies. These advances although not immediately successful will be the platforms for discovery in the future if they are applied in the correct areas.

References

Van Leeuwen, E., BHP develops world’s first airborne gravity gradiometer for mineral exploration, Preview, Issue 86, June 2000, 28-30.

Webb, M. & Rowston, P.A., The geophysics of the Ernest Henry Cu-Au Deposit (N.W.) Qld; Exploration Geophysics, Vol 26, No2/3, Jun/Sept 1995, 51-59.