Laboratory Testing & General Mineral Processing Engineering

Laboratory Testing & General Mineral Processing Engineering 2017-04-04T06:57:51+00:00
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QC Duplicate Samples – Duplicate Labs (19 replies)

Raje Singh
1 year ago
Raje Singh 1 year ago

Would you recommend sending samples from the same prospect to two different laboratories for the same analysis because of time constrain? Any QC implication!

Carl Jenkins
1 year ago
Carl Jenkins 1 year ago

It really depends on the sampling purpose; you should put your QC in your sample stream (blank, standard, duplicate, one each at least 10 samples) and get sufficient data for statistics. Counter-check with other lab is sometime advisable, but not really mandatory if your QC samples work well (at least for NI 43-101). Many variables must be considered however. I look forward for more comments as well.

David Kano
1 year ago
David Kano 1 year ago

It’s not recommended to work with two different labs but if you have to do it, you have to use good certified standards to ensure that there wouldn’t be a bias introduced by one lab compared with the other one. The same labs with the same analysis methods could give you two different set of results because of a systematic bias and it can be only controlled by standards.

1 year ago
Hauptsturm 1 year ago

If your lab does not have capacity to handle the required work load you can divide the samples between two laboratories. However, split carefully 20 to 30 two identical samples covering the concentration and matrix range of your sampling target. Divide these twins between the two laboratories. From the results you can check if the results are compatible. Best way to do is to plot the difference d = x1-x2, or relative difference dr = (x1-x2)/x2 against your result x2. Relative difference is usually better, if the concentration range is large. If both plots show a random distribution around the zero-line the results are compatible and you can use them for interpretation. If they show constant or regular concentration dependent differences and you can model the difference, you can correct the results of the other lab to be compatible with yours.

Raje Singh
1 year ago
Raje Singh 1 year ago

Thank you very much for your comment. The program is a resource upgrade drilling program.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

There are two questions you need to ask. The first question you need to ask is why the one lab is faster. The second question to ask is where the bottleneck is with your existing lab.

The analytical lab business is global and if one lab is promising faster delivery you really have to ask why. Most companies doing exploration are looking at longer wait times for results and are looking at different labs.

Be sure to do your due diligence in checking out the new lab. Ask who is using this lab. Is the lab ISO certified? Have they had an audit done by an independent geochemist? What were the results of the audit? And what has been done to address deficiencies in the audit? (There are ALWAYS deficiencies) A good lab will share this information with you. They will share the results used in the ISO certification. They should also give you the names of the geochemists that completed audits and if they can, share the reports. And of course, visit the lab and do your own inspection. If they do not have time, do not use them.

Before changing labs, talk to the geochemist you work with at the lab you’re using. Usually there are bottlenecks within the lab. These may include a shortage of certified assayers to sign of the work, or back log of samples in sample preparation. From personal experience I get far better service by working with a lab. You may be surprised to find that they may have a solution to the problem that you have not considered. 

1 year ago
Sturmbann 1 year ago

Comparative analysis of different lab results should be used to ascertain which labs are professional. Once this established use only the professional lab. i.e. far better to send to one reliable lab, than two unreliable labs.

Paul Morrow
1 year ago
Paul Morrow 1 year ago

I don’t know about correcting the results to be compatible with yours. Isn't the golden rule that "a bias is never consistent"? Correcting for a bias, especially if you only do basic relative difference assessment in a mineral resource situation I would not agree with. Best to assess the bias with QQ anyway and draw your conclusions from that.

Personally, I would tackle this from a different angle: if you have only a few samples and a small programme, surely these can be prioritised somewhere and a solution can be found using one prep lab and another assay lab, in which case they can fly pulps around the world pretty cheaply. If you have a large programme, sit down with the lab and work out some sort of priority scheme, after all you will be a preferred customer; if you can pick your mineralisation you can always prioritise those samples? Getting involved with two labs might cost you more time and hassle in the end.
What are your thoughts?

Raje Singh
1 year ago
Raje Singh 1 year ago

Thank you very much for your comments. All points well noted.I can now make a better decision.

Sachin Prakash
1 year ago
Sachin Prakash 1 year ago

In laboratory practice, we know that there is primary lab and secondary laboratory. Primary lab would be a handling mostly your sample to get assay and secondary for cross check / round robin. This practice it is to ensure that your precision it is come from the only one lab. So, you can advice that your data are reliable and also you get the high confident of laboratory as primary lab. Every lab could give you a different precision that you cannot average them.

Jean Rasczak
1 year ago
Jean Rasczak 1 year ago

You can, but is strongly recommended (or mandatory) to control both labs with blind samples (i.e. pulps duplicates and most importantly with standard materials). You have to be sure that they are using the same protocol and working in similar conditions (how they take the sample, which is the amount of mass, type and concentrations of the solutions they use, how they are doing the readings of the instruments, experience of the people involved, etc). This kind of things affects the precision and more importantly the presence of a bias in the results.

There are a lot of things that can leads to a bias in a lab and if this occur you will be in a worse position due to time constrain regarding your initial situation. In my experience it is more difficult to control two labs than one. If you have a good laboratory with reliable results maybe better to wait a little bit (if you can).

1 year ago
Obersturmbann 1 year ago

I would have to agree with you. There are way too many examples of projects that used two laboratories running amok because of different preparation, sub-sampling, and analytical procedures being used. There will be much conspiring against you, as each laboratory is reticent about telling others exactly what they do (the details that might have an impact on the results), so it is very difficult to get them to do EXACTLY the same thing because you don't really know that is! And even if you can achieve that, it’s amazing how easy it is to get different results for the quality control samples designed to demonstrate that the labs are producing the same results.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

If you are forced to use two labs (and really it isn't a great idea for the reasons mentioned above) at least get a percentage of the samples from both umpired at a common third laboratory (utilizing the same digest, finish etc). That may provide some confidence that the numbers are reasonably consistent (fit for purpose).

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

Are you able to talk to your preferred lab about increasing their throughput?

1 year ago
Standartenfurer 1 year ago

For the past six months I was doing the same, using two labs. I`ve put the prill split on a graph and then request from both labs an explanation of the value differences. It is in my opinion good to hear from their side as why there are differences. My next step will be to get the policy and procedures of both labs and then from there on I will take it further. A third lab! also crossed my mind but I first want to ensure that both labs policies and procedures are more or less the same , then I will go to a third lab. With the P&P and take it from there.

Alan Carter
1 year ago
Alan Carter 1 year ago

The main issue with two laboratories is the differences that occur in sample preparation and hence the need for standards. However, do some testing before sending anything to either lab to ensure that the standards are in fact performing as standards and the labs fall within the expected range of certification for the standards (you should see this in the certificates).

I would also recommend that you manage your despatches so you get a spread of data from you sampling region into both labs. It can be very complicated trying to assess whether an apparent bias is related to the laboratory or to the area in which you are sampling.

Also beware that you can often have two (or more laboratories) within the same laboratory especially with large programs. I suggest talk to your lab about differences between day and night-shift work and whether your data is read on one machine or multiple machines.

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

Out of my experience, I have observed that, different laboratory have different precision in testing’s. This happens because of the equipments being used are of different make, solution being used are of different quality, difference in experience of the test conducting persons etc. As a result, you may have a different set of results. Therefore, it is strongly recommended to carry out tests in a single laboratory, for the same project. My suggestion is to try for a laboratory of higher capacity which can give you tests results within a short period of time.

1 year ago
Oberfuhrer 1 year ago

Adding a new lab part way through a drill project is not wise unless you know the new lab well, they know you well, and ideally you have used them before (i.e. a number of batches which have all passed QAQC checks on CRMs and blanks). Definitely you do not want to do this without a lot of consideration part way through a resource drill-out.

I've found several times that sending samples to a new lab often throws a spanner in the works and you end up bouncing discussions around for a month before getting acceptable certified results. After having this happen a couple of times I would now always send in a test batch of samples to any new lab I was thinking of signing up; include extra CRM/blank material for the check samples (e.g. 200g of gold CRMs for a single check sample) as they may need to run repeat analysis 3 or 4 times to nail the QAQC.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

Not wise, I agree the best way to control a lab is by inserting QC samples (standards, blanks, duplicates) and also by sending 10% of samples (rejects) to a second lab, also inserting QC samples. Reject samples are better than asking the prime lab to send the prepared pulps; if the pulps were prepared under poor QC conditions, such as poor dust control systems or bad samples prep procedures, the error goes away with the samples, and the second lab for sure will get the same results, but preparing a new pulp out of the rejects could unmask any error.

1 year ago
Sudhirkumar 1 year ago

Before sending samples to two separate labs, you will want to have done QA/QC checks on them. Both will have slightly different results due to their own errors. In the past, we have done round robin checks of various labs using known standards to determine which we can use for validation of our own internal lab.

In this process we have identified several labs which get essentially the same results for the sample. We have also identified labs which we don't use for QA/QC checks on our own lab due to the amount of variation and drift from mean of the standard which we have seen.

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