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

Mineral Resources and Reserves are not easy things to define. Qualified Persons (QP – NI43-101) and Competent Persons (CP – JORC, SAMREC etc.) exist to do difficult things independently and provide a level of comfort to investors, clients and regulatory authorities.

During the exploration and development of a mineral property, it is common (and good practice) for exploration or mineral companies to build a three-dimensional geology model before a resource estimate is required. Subsequently, independent QP/CPs are often engaged to estimate and sign off on the mineral resource to meet regulatory requirements.

Building a three-dimensional geology model to constrain the estimation domains takes time and costs money. In many instances, quite rightly, clients feel that they have a superior level of knowledge of the deposit and that the client can rely on the existing interpretation. In a depressed market, proposals look a lot more acceptable to clients, without the budget and hours needed to construct a three-dimensional geology model. Particularly if the client views such an exercise as at best a duplication of previous efforts. But sometimes clients do not have the knowledge or experience to provide a robust model.

By using the domain model provided by a client, the QP or CP is limiting the independence of the resource estimation process to populating a predetermined volume (tonnage) with grades from sampling data. Simply accepting a predetermined interpretation could have a very significant impact on tonnage and contained metal.

Before accepting any pre-existing domains for the estimation, it would be prudent for the QP/CP to safeguard the independent nature of his or her work (paraphrasing from CRIRSCO, 2012) by ensuring that;

  • data spacing and distribution is sufficient to establish the degree of geological and grade continuity appropriate to the resource category,
  • the level of confidence in (or conversely, the uncertainty of) the geological interpretation of the mineral deposit,
  • the nature of the data used and
  • any assumptions made and
  • the effect of alternative interpretations.

How this should be done, is at the discretion of the QP/CP. In the words of Harry Parker, “Check everything and trust no one!” .


Standard Definitions. 2012. CRIRSCO.

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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