Geochemical exploration: what is truly new?

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SRK News | Issue 57Exploration Geology: Keys to success

Hennie Theart, Corporate Consultant and Partner


Geochemical exploration has seen major advances, mainly driven by technological breakthroughs as laboratory and field equipment have improved -- but has our ability to interpret the results kept up? I have my doubts.

The biggest advances in the laboratory have been the maturing of ICP linked techniques for optical emission and mass spectrometry. This produced significantly lowered detection limits and simultaneous accurate multi-element analyses. Advances in x-ray fluorescence (XRF) spectrometry took place mainly in developing greatly improved algorithms for matrix corrections.

The biggest advances in field equipment came about through continuing improvements in the portable XRF, Infra-red and near Infra-red spectrometry, and x-ray diffraction tools. Although the latter method is used for mineral identification, it is ideal in detecting the alteration envelopes surrounding some mineral deposits. The biggest challenge with these tools lies with the advertisers that depict them as a revolver in the hands of today’s cowboy. However, if used responsibly, where the analyses are based on representative, appropriately prepared samples, such instruments can dramatically reduce turn-around time on sample analyses, rapid redirection of sampling programmes, target selection, and follow-up exploration.

The huge advances in robust portable computing facilities, gridding software and the linked geographic location technology all contribute to bringing geochemical exploration into real-time.

However, this is where the new has stopped. The greatest challenge facing the modern explorer is inadequate training and experience in processing and interpreting ever increasing sets of data and the operator’s limited understanding of sampling theory, geochemical associations and the chemical processes in the primary ore forming and secondary weathering environments.

For example, the plunge into multi-variate statistics as new methods provide us with multi-element analyses at no additional cost without considering:
  • Differences in the nature of the distributions of underlying populations;
  • More than one population sampled;
  • Auto correlation; 
  • The effect of closure; and
  • That the software packages used do not indicate the error or weakness in the results.

It seems like the same cowboys are now using sophisticated statistical operations and come to conclusions without considering the error or relevance of the underlying assumptions. The fact is that exploration for new discoveries becomes more challenging since the targets are no longer so easy to find.

I believe that the new advances discussed here are of huge significance if coupled with advanced sampling, sample preparation and data processing methods. Some of the historical methods used need to be re-discovered.

A few examples include:

  • Considering the ease with which major element analyses now become available, it is advocated to return to the traditional normative mineral calculations developed for major element geochemistry;
  • Conduct alteration studies using the isocon diagram, the boxplot and various alteration index formulas developed in the past;
  • Introduce methods to separate out different underlying populations in the data at the earliest stage, if not, at the onset of the interpretation, using tools such as the Probability Plot procedure of Sinclair; and
  • Calculate residuals for stream and soil samples to eliminate the effect of scavenger processes in the weathering environment.

Exploration geochemistry is at the dawn of a new day of discovery, and the role of the well-qualified, experienced geochemist is becoming even more important.

Hennie Theart: htheart@srk.co.za

 

SRK Latin America