By Mike O’Brien


10% and 90% Probability Shells for a Model of a Kimberlite Pipe
10% and 90% probability shells for a model of a Kimberlite Pipe

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. (But not as much as drilling it) 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
  • Any assumptions made
  • 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).

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