Sampling theory and practice – Tips and Intel from Ian Glacken – Director of Geology

Ian Glacken, our Geology Director, has put together some 30 Second blast Tips and Intel about sampling theory and practice.

Here they are!

Should you use Aircore samples in your resource estimate?  If carried out to high standards, Aircore samples can approach RC in their level of representivity, although it is not suitable for all commodities and lithologies.  It is always worthwhile looking at the relationship between Aircore and other sampling types (RC or DD) within an area where there is more-or-less equal representivity of both sample types; there should be no bias over the range of reasonable ‘ore-grade’ values.

Remember that some sampling errors cannot be eliminated, but they can be minimised:  In addition to the Fundamental Sampling Error, which is the subject of Gy’s theory and its derivations, the Grouping and Segregation Error (GSE) is a function of the size, nature and constitution of the particles, among other factors.  The GSE certainly can be reduced through judicious practice, but there are circumstances where the GSE can swamp other errors – you need to be aware of these.

What is the sampling contribution to the nugget effect?  Remember that the sampling error can influence the nugget effect of an orebody, but that the nugget effect, as inferred from a variogram can have more than one component; the inherent nugget, which is a fundamental of the mineralisation and its uniformity (or lack thereof), and poor sampling practice, which can amplify and even swamp the ‘natural’ nugget.

Multi-tier riffle splitters can add to sampling error:  While Jones riffle splitters can give a statistically correct sample split, this is less likely with a multi-tier splitter and unlikely with a rig-mounted multi-tier riffle splitter.  Things to watch out for are the flow of the sample into the splitter (even and continuous), the orientation of the splitter (centred and vertical) and of course the presence of moisture in the sample – even a small amount of water can invalidate the splitting.

Be sure to check the orientation of the cone splitter daily:  While a cone splitter should and generally will give a matched (equiprobable) pair of field duplicates, the orientation of the splitter is all-important in determining this.  The long axis of the splitter needs to be vertical and the widest part of the splitter, i.e. the join between the cone and the chute, needs to be horizontal.  This should be checked daily with a magnetic clinometer.

Some background info about Ian:

Ian Glacken BSc (Hons) (Geology), MSc(Mining Geology), DIC, MSc(Geostatistics), Grad Dip Computing, FAusIMM(CP), FAIG, MIMMM, CEng

Ian is a geologist with postgraduate qualifications in geostatistics, mining geology and computing who has more than 30 years’ worldwide experience in the mining industry.

Ian’s skills are in resource evaluation, quantitative risk assessment, strategic advice, geostatistics, reconciliation, project management, statutory and competent person reporting and mining geology studies.

If you’d like to contact Ian, his contact details are:
Tel +61 (0)8 9215 0016 Email iglacken@snowdenoptiro.com