Beyond the ranges…

Photo of the “Three Sisters” range outside Hosmer, BC, Canada by Mike O’Brien.

Author: Mike O’Brien, Senior Principal Consultant, P.Geo., Pr.Sci.Nat.


In this extract from Rudyard Kipling’s The Explorer, a voice cries out to exploration geologists.

“Something hidden. Go and find it. Go and look behind the Ranges –
Something lost behind the Ranges. Lost and waiting for you. Go!”

Many things have changed in the exploration business since these words were written – notably technology and regulation.

But the message is still as clear as it was 120 years ago. Go and get it!

But…..  How big could it be? What is the chance it isn’t there at all?

Long before a mineral resource can be formally estimated and reported, it would be useful to have some idea of the ‘size of the prize‘. This is important to be able to prioritize business decisions and to assess whether there is some hope of obtaining a good ‘bang for the buck’ (or is it a the long, mournful cry for the loon[ie]?). For this reason, some of the reporting codes have defined ‘exploration targets’ and ‘targets’.

‘Ranges’ are not just distant lines of mountains. According to the various mineral resource and reserve reporting codes, exploration targets require ‘ranges’ to demonstrate uncertainty. The following extracts from JORC, PERC, SAMREC and International CRIRSCO (Template) Codes, specifically mention ‘ranges’ being required for exploration targets.  Understandably, this is a thorny issue – an exploration target is something which must never be confused with a mineral resource, but can be quantified with qualifications and which can be useful to the investor or the operator.

JORC 2012 Clause 17

It is recognised that it is common practice for a company to comment on and discuss its exploration in terms of target size and type. However, any such comment in a Public Report must comply with the following requirements.

Exploration Target is a statement or estimate of the exploration potential of a mineral deposit in a defined geological setting where the statement or estimate, quoted as a range of tonnes and a range of grade (or quality), relates to mineralisation for which there has been insufficient exploration to estimate a Mineral Resource.

PERC 2013 Clause 19

‘A Public Report which includes an Exploration Target must be accompanied by a Competent Person statement taking responsibility for the form and context in which the Exploration Target appears.

All disclosures of an Exploration Target should clarify whether the target is based on actual exploration results completed or on proposed exploration programs yet to commence. Where the Exploration Target statement includes information relating to ranges of tonnages and grades or qualities these should be represented as approximations. The explanatory text paragraphs should include a brief description of the process used to determine the grade or quality and tonnage ranges used to describe the Exploration Target.’

SAMREC 2009 Clause 20

It is common practice for a company to comment on and discuss its Exploration Results in terms of size and type. Any such information relating to exploration targets must not be expressed or misrepresented as an estimate of Mineral Resources or Mineral Reserves. The term Resource(s) or Reserves(s) must not be used in this context. Any statement referring to potential quantity, quality and content, as appropriate, of the target must be expressed as ranges and include a detailed explanation of the basis for the statement and a proximate statement that the potential quantity, quality and content, as appropriate, are conceptual in nature, that there has been insufficient exploration to define a Mineral Resource and that it is uncertain if further exploration will result in the determination of a Mineral Resource.

International CRIRSCO Template 2013 Clause 17

An Exploration Target is a statement or estimate of the exploration potential of a mineral deposit in a defined geological setting where the statement or estimate, quoted as a range of tonnes and a range of grade or quality, relates to mineralisation for which there has been insufficient exploration to estimate Mineral Resources.

The CIM Definition Standards and Guidelines do not include such a term (except for a very general use of the word ‘target’ in relation to coal). Perhaps the CIM guidelines should be updated to align this aspect to the other codes (or explicitly disallow such usage).


Note that PERC 2013 specifically requires a brief description of the process used to estimate the ranges. Explicit description of the logic and estimation assumptions would certainly go some way towards convincing investors that there is more to an exploration target than smoke and mirrors. The other codes might benefit from including as similar requirement in future updates.

What methods can be used to estimate quantitative ranges for exploration targets to satisfy the reporting codes? 

  •  Application of professional experience

plus,

  • Simulation of indicators to show the uncertainty of the spatial extents of domains,
  • Simulation of continuous variables to assist the range definitions for grades / metal and
  • Indicator Interpolation using implicit modelling methods (with P10 and P90 limits, but that’s another story….)

About Mike O’Brien

Senior Principal Consultant, P.Geo., Pr.Sci.Nat. ARANZ Geo Limited – Expert Services (formerly QG Consulting)

For three decades Mike has been making a difference to Mineral Resources and mines. On the technical front, he has extensive experience in Mineral Resource estimation and geological modelling. He has managed technical teams to achieve results in mining companies and in consultancies. While the majority of his experience has been in gold deposits, he has expertise in the uranium, base metals and multi-product environment. A qualified geologist and geostatistician, he has been a team member and reviewer of due diligence and feasibility exercises in South Africa, Brazil, Ghana, Namibia, DRC, Russia, Kazakhstan, Uzbekistan, Colombia, Peru and the United States. Specialties: Mineral Resource estimation, geostatistics, Mineral Resource classification, Mineral Resource reporting codes, SAMREC, JORC. 

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