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OREAS Certified Reference Materials - Frequently Asked Questions

GENERAL:-

1) Who is Ore Research & Exploration (ORE)?

ORE is an Australian company whose core business is the manufacture of OREAS and Custom Certified Reference Materials (CRMs) for the global mining industry. Since 1988, as one of the longest established producers, we've forged a proud history of innovation with many industry firsts, including the introduction of:

  • guaranteed homogeneity for gold and platinum CRMs from all ore types.
  • durable, single-use unit packaging using flexible wallpouches (capacity of up to 50,000 pouches/day).
  • inert gas packaging as routine for all sulphide-bearing CRMs.
  • an accurate method for gold homogeneity quantification via the reduced analytical subsample method (see item 12 below) to demonstrate an unparalleled level of homogeneity in all our naturally derived gold CRMs.
  • low cost single use 10 gram packaging for non-precious metal CRMs.
  • SuperCRMs® featuring complete ICP-OES and ICP-MS suite certification (up to 179 analytes per CRM) by a range of analytical methods, suitable for pathfinder and lithogeochemical applications.
  • gold CRMs in batch sizes of 5 tonnes.
  • acid-soluble copper certification.
2) What sort of CRMs do you produce?

We stock a comprehensive range of ready-to-use CRMs covering gold, platinum, silver, copper, nickel, iron, zinc, lead, uranium, rare earth elements, tin, tungsten, manganese, etc. We also specialise in preparation of matrix-matched (custom) CRMs from client-supplied materials.

3) Are you a major producer?

We have the largest dedicated CRM production facility in the world with 171 different OREAS CRMs and over 160 tonnes of CRM stocked and ready to ship to our 1300 clients located across 105 countries.

4) Who are your clients?

All the major international mining houses (e.g. BHP Billiton, Vale, Anglo American, Rio Tinto, Glencore, Newmont, Barrick, Freeport, Gold Fields, Gold Corp, Polymetal, B2Gold, MMG, Newcrest, Harmony, etc.), the major commercial laboratory groups (e.g. ALS, SGS, Bureau Veritas and Intertek) and numerous mid-tier and junior miners.

5) Are you ISO accredited and do you follow ISO guidelines in the manufacture and certification of CRMs for the mining industry?

Yes, we are accredited to ISO 9001:2008 for our Quality Management System including development, manufacturing, certification and supply of CRMs. We adhere to and in many instances exceed the recommendations in ISO Guides 30, 31, 32, 33, 34, 35, 3207 and 5725.

6) What are the most important attributes of a CRM?

The accuracy of the certified values, low but realistically achievable standard deviations, homogeneity of the certified elements, packaging durability and quality of documentation.

7) Why is packaging durability important?

Many ores contain sulphides that oxidise in air. For that reason we package all sulphide-bearing CRMs under nitrogen in single-use laminated foil pouches. This robust packaging ensures a shelf life in excess of 10 years for all ore types, including highly reactive massive sulphides.

8) What packaging units do you offer?

Our standard packaging units are:

  • single-use 10g for non-precious metal CRMs
  • single-use 60g and 100g for gold (and platinum) CRMs
  • 0.5 to 1.0 kg jars for laboratory use

We also offer custom packaging into any size unit on request.

9) Why offer both 60g AND 100g units for gold?

Some geologists standardise on a 25-30g fire assay charge weight where a 60g unit is appropriate while others prefer a 50g charge weight and require 100g. Laboratories should be given sufficient sample to allow for one repeat assay. Having a 60g unit available minimises wastage and provides a cost saving to the user.

10) I've heard you now offer SuperCRMs®. What are they?

OREAS SuperCRMs® enable control over a range of analytical methods for complete ICP-OES and ICP-MS element suites within a single CRM:

  • 4-acid digestion (up to 49 elements)
  • aqua regia digestion (up to 44 elements)
  • fusion - borate and peroxide (up to 44 elements)
  • borate fusion XRF majors and traces (up to 22 elements)
  • infra-red combustion furnace (C and S), Loss On Ignition

Some of our SuperCRMs® are certified for up to 179 analytes. The comprehensive range of analytical methods and certified elements makes them extremely versatile and useful for pathfinder and lithogeochemical programs.

TECHNICAL:-

11) How can I determine the quality of a CRM?

High quality products contain certified values with negligible or no sampling error. This will be apparent by well constrained 95% tolerance intervals (a direct measure of homogeneity), 95% confidence intervals and low standard deviations. Only then can the user confidently apportion error seen in QC data as laboratory measurement error. Otherwise the user is fraught with uncertainty as to the origin of the error. Certificates of Analysis should be clear and transparent with tabulation of statistical parameters (Certified Values, 95% Confidence Intervals, Standard Deviations and Tolerance Intervals) and include a list of the participating laboratories, a description of analytical methods used to determine the Certified Values and full tabulation of all laboratory data generated in the round robin program. ORE only uses data generated from similar analytical methods to determine Certified Values and Standard Deviations. If data from different analytical methods are combined then there will always be a bias in comparison with your laboratory results.

12) How does a CRM producer demonstrate homogeneity, as I understand this can be a real issue with gold CRMs?

The only valid way to do this is by quantifying sampling error. For 19 years at ORE we have been demonstrating homogeneity at the 0.5 to 1g level in every gold CRM we produce using high precision neutron activation analysis and the reduced analytical subsample method. By validating homogeneity at this level, we can be confident that for a typical 25 to 50g fire assay charge all errors originate in the analytical process with no contribution from the CRM. Importantly, we are the only gold CRM producer applying this rigorous test and can confidently claim to have the most homogeneous gold CRMs commercially available.

13) How can I evaluate the accuracy of a CRM?

Accuracy can be defined as the closeness of the certified value to the true value (which is unknown). A measure of accuracy is given by the 95% Confidence Interval or the Expanded Uncertainty, where the smaller the interval generally the more reliable the Certified Value. These intervals should not be used as control limits for laboratory performance. It is important that a critical number of world class laboratories are employed in the certification program. They should include all the major laboratory groups and where feasible, be geographically representative.

14) What is the Standard Deviation?

The Standard Deviation provides the Control Limits to which laboratories under test should perform. Plus or minus two Standard Deviations from the Certified Value is generally considered acceptable. Note that each laboratory has its own inherent SD (for a specific concentration level and analyte-method pair) based on the analytical process and this SD is not directly related to the round robin program. This ‘one size fits all' approach may require revision at the discretion of the QC manager concerned following careful scrutiny of QC control charts.

15) You mention ANOVA studies in your certificates, what do these tell us?

Analysis of variance is a powerful statistical method used to validate the homogeneity across the entire prepared batch of CRM. It is a relative test to confirm that all packaged units of a CRM are identical in composition (the variance both within and between units is equal). The ANOVA test should not be done in isolation, however, as a CRM can be uniform across the batch and therefore pass this test but still possess a significant sampling error. It should be combined with the reduced analytical subsample method, described in 12) above, that quantifies absolute homogeneity and hence sampling errors.

16) Can quality gold CRMs be produced using a typical laboratory preparation mill?

Being highly malleable, gold tends to form gold leaf inside a ‘puck and bowl' milling environment. If a candidate gold CRM is ground to a specification simulating a sample prepared in an analytical laboratory (nominally 85% passing 75 microns), then an acceptable level of homogeneity can only be achieved if gold in the source material is extremely fine grained (<10 microns). Consider that a single gold grain of 75 microns in a 30 gm subsample will add 0.27 g/t gold to the assay, significantly impacting results. Few gold ores have consistently fine gold and the nugget effect in the source material will be carried through to the finished CRM. It then becomes impossible to differentiate between poor quality assay results and poor sample homogeneity in the CRM. The only way a homogeneous gold CRM can be prepared with total confidence is by grinding to a fine particle size and destroying the nuggetty grains in the process. All OREAS gold CRMs are prepared to this high standard.

The ‘gold nugget' problem is nicely illustrated by the Golden Grove VMS deposit in Western Australia. Here the gold occurs in zinc-rich ores as electrum inclusions in sphalerite. We prepared 5 tonnes of this zinc-rich ore and 2 tonnes of copper-rich ore from the same deposit by grinding to 90% passing 75 microns followed by homogenisation. Check assays of the homogenised zinc ore illustrate the persistence of gold nuggets under conventional grinding with a whopping 133% RSD (Relative Standard Deviation) on 42 fire assay splits. Individual assays ranged from 0.67 to 17.9 g/t gold. Following further grinding to 100% minus 30 micron and destruction of the nuggets we combined the zinc and copper ores to produce a suite of 5 CRMs. Homogeneity test work on these CRMs produced RSD's between 0.36 to 1.02% for gold (calculated for a typical 30g fire assay charge weight determined from 20 x 1g NAA results and the Sampling Constant).

17) Are OREAS CRMs natural or synthetic?

All OREAS CRMs are made from natural ores and geological materials and cover a broad range of mineralisation styles, e.g. epithermal, orogenic and Archean greenstone-hosted gold, porphyry and IOCG copper-gold-moly, epithermal silver-gold, polymetallic VMS, BHT and SEDEX silver-lead-zinc, etc.

18) Why don't you make synthetic gold CRMs like some of your competitors?

The problem with synthetic gold CRMs, often made by adding gold ‘dust' to barren rocks, is that the robustness of the fire assay method is not tested. Unlike natural ores, all the gold is liberated in a synthetic CRM, regardless of the efficacy of the fire assay process. It is easy for laboratories to assay for gold when it is already liberated but this does not evaluate the laboratory's performance for gold occluded in quartz associated with sulphides, tellurides and other minerals. The laboratory may report acceptable gold assays for synthetic CRMs but there could be an undetected low bias due to a fusion problem with your samples.