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CRM is used in any QC program (8 replies)

Ace Levy
8 months ago
Ace Levy 8 months ago

When including CRMs to monitor accuracy in a drill sampling programme the recommendation is to use more than one CRM - but what about when there are multiple variables to monitor (like sulphur and carbon). What's the best cost-effective strategy here - prepare your own?

Paul Morrow
8 months ago
Paul Morrow 8 months ago

This been always a difficult question. Typically you want a CRM for QA of alltest parameters as you say but there often isn't such a CRM available. One option is to introduce more than one CRM but that can be costly. Alternatively prepare a new CRM from a material of similar matrix and ensure it is certified for all your required test parameters - also costly. Another alternative is to prepare a homogeneous secondary/internal standard that has been well characterized through a proficiency testing program with the minimum of six results per test parameter required. This option doesn't provide you with as much 'peace of mind' but doesn't cost as much. The choice of which way to go will depend on data quality requirements and budgetary constraints.

8 months ago
Standartenfurer 8 months ago

I guess it's a cost-benefit analysis: if it's a short drilling program then making your own may be too expensive and just using two or three different standards may be the way to go.

By the way, CRM's are to monitor the system and is part of QC, as opposed to QA which is there to prevent errors by SOP's etc. Just one of those nomenclature things that bugs me.

Marshal Dienes
8 months ago
Marshal Dienes 8 months ago

A few question here. Firstly, I think it is important that more than one CRM is used in any QC program, as one CRM will only tell you about the accuracy of the assay data around the CRM have certified value, and not around other important parts of your assay grade distribution. I tend to use CRMs with a certified value around the likely economic marginal cut-off for the metal/s of interest, one high grade, and one around the “average” grade of the deposit. I know of several commercial suppliers that can supply some CRMs that have been certified for a large multi-elemental suite if you wish to control several (or more) elements.

The other thing to consider is that the certified values of the CRM have been determined by a similar analytical method as being used at the project. It is no good using a copper CRM (for example) with the certified value being obtained by a two acid digest when your samples are going through a four acid digest process – in this example the CRM value will most likely report high.

Another thing to consider is the CRM’s composition in terms of the gangue and mineralization. Again, one could obtain erroneous results if you are evaluating an oxide gold deposit, while using a CRM with a sulphide/refractory gold composition. Good commercial suppliers will tell you the composition of the CRM to aid the selection of the most suitable for your project.

In any drill-out/resource development evaluation stage I think it is best practice to use a selection of matrix matched CRMs – “MMCRMs” (i.e. CRMs made from material from your deposit). This allows you to have the elements important to the project certified, and, more importantly, will allow the nuances of the deposit’s mineralization to be reflected in the CRM.

I was once involved in a project where we were using off-the-shelf CRMs to monitor accuracy during a major resource evaluation drill out. The CRMs were returning good results, so we thought we were obtaining accurate results. Towards the end of the evaluation a budget (finally!) was made available to develop several MMCRMs. Low and behold, during the certification process of our MMCRMs we discovered an unusual mineralization style/matrix structure that retarded the chemical digestion. So, while our (off-the-shelf) CRMs were indicating that we were obtaining accurate results, our drill samples were actually reading low due to the unusual mineralogy of the deposit. If we were running MMCRMs from the start, we would have quickly detected a problem with the digestion method being used. (Luckily for this project all of our results were biased low, so there was a degree of conservatism built into the results, however the project evaluation could have been a disaster if this had been a marginal deposit).

So, for me, the sooner one can develop MMCRMs the better, and, in particular, are critical in any major resource drill out phase.

Finally, I would highly recommend that one actually talks to the geochemist at the commercial CRM businesses. They are a wealth of information, and are usually very happy to help you select the best suite of CRMs for your project.

“Best cost-effective strategy”? (Sounds like a Mining Engineer question) – do not compromise your QC program!

Tony Verdeschi
8 months ago
Tony Verdeschi 8 months ago

I see you’ve received some valuable feedback already but I’m happy to help if you want to discuss custom and off the shelf CRMs. We have 59 (soon to be 63) OREAS Super CRMs® available, many with ore grade base/precious metal concentrations. Super CRMs® contain multiple method-specific certification of full elemental suite ICP-OES and ICP-MS and can provide up to 150 certified analytes in a single CRM quite handy for QC monitoring of ICP packages.

8 months ago
Unterstarm 8 months ago

Can anybody help me in identifying good, but cost effective limestone CRM's where the limestone will be used for cement manufacture?

Sugar Watkins
8 months ago
Sugar Watkins 8 months ago

You could try BAS-CRM 393 BAS-CRM 513, though I know limestone CRMS are trickier to obtain than other metallic CRM's.

Bit of an outside shot but why not try GPO-16, it’s a phosphate CRM but I know is cheaper and its CaO content is 45% ash and more accessible (geostats), could use to test other variables as mentioned above in the previous discussions.

Alan Carter
8 months ago
Alan Carter 8 months ago

I agree with you here, that is: it depends on life/economics. Making your own CRMs from drill core samples and getting a certification round robin exercise done can take several months - how many of us are involved in projects that are certain to be around that long these days?? Or what manager wants to pay for 5 years of reference materials upfront in order to make the per unit price reasonable?

But for operations I would certainly get my own matrix matched reference materials made up, bearing in mind the range of concentrations and elements required. Costs can be shared among different departments as met and concentrate departments also need to send samples to labs.

For off the shelf CRMs there is often an issue with the certification methodology vis a vis the actual assay methodology used in the project. As noted above, the matrix is often ignored and it really is quite important. Overall I find that experience, communication and pragmatism are required more than a hard-line approach to control limits. 

8 months ago
Standartenfurer 8 months ago

Just coming back to this, you may have seen the paper by Nigel Brand on gold homogeneity in CRMs. Interesting data and not what I thought in terms of individual performance.