African Mineral Standards
African Mineral Standards is a leading manufacturer of "matrix matched, multi-element Certified Reference Materials" and has a long history of manufacturing the highest quality products for the testing industry; an industry for which quality is of the utmost importance.
African Mineral Standard makes the AMIS range of Matrix (multi-element) Certified Reference Materials (CRM'S). We make them for geologists, chemists, metallurgists, exploration companies, mining companies and commercial laboratories.
AMIS products look for trouble. They have to be good. Every single bit of AMIS product gets tested and stringent procedures are in place to ensure product quality and to establish a chain of custody all the way to the customer.
AMIS Quality Management is independently audited during annual ISO 9001:2008 audits.
Analytical (assay) bias results from differences in methods, techniques, equipment and calibrations and is an issue in all branches of analytical science (chemical, biological etc).
In exploration and mining, where major decisions are based on assay results, low or high bias analytical results may cause inaccurate and materially unacceptable numbers.
It is a property that can only be measured by inter-laboratory testing and can be detected with a well designed assay quality assurance program using control samples, data quality objectives and control rules. These programs measure assay results for accuracy and precision and assure the required analytical quality at a minimum cost.
What is an acceptable bias? This depends on the absolute affect of the error on the operation, and we can use the financial definition of materiality as a guide. Anything over 5% (+-2.5%) needs to be reported.
Therefore process control and ROM sample bias of <2.5% is probably not material. This should be tighter for concentrate and bullion samples; and could be wider for low grade or tailings samples.
Assay quality assurance (clients duty)
A well set up quality assurance program for assay data should more than pay for itself through significant savings from process improvement, or additional value from auditable mineral resource categorization.
If your economic element control samples show a <0.1% bias, a CV 90% detection of critical systematic error and a false rejection rate of <5%; then the company might be advised to save money by increasing the ratio of samples to controls. Alternatively if you have no control results, or control samples are showing that analytical results are poor; then you need to place a higher priority on error prevention. You will probably discover, by looking at real numbers, you can stop chasing some ghosts You might even be able to start some method improvement.
Anybody sending samples to an assay lab has to set up a quality assurance (QA) program over and above any QA program run by the lab. Both the customer and the lab QA program have one goal (to check the lab) and both programs must be auditable.
The customer QA program should comprise at least:
1. Prior testing the primary and secondary labs for accuracy and bias.
2. Submission of routine QC samples, including reference materials and blanks, either as field samples or inserted in the lab as pulps.
3. Use of random secondary reference materials to check the labs treatment of the primary reference material.
4. Monthly QC meetings with the lab.
5. Actioning of QC failures.
6. Reporting of QC actions.
Certified Reference Materials (CRM's)
A CRM is a reference material, characterised by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertianty, and a statement of metrological traceability.
The difference between a CRM and an AMIS reference material is solely in the last two requirements (uncertainty and traceability). From May 2009 AMIS certificates have fulfilled the CRM requirements by including the Combined Standard Uncertainty and a statement on the Metrological Traceability.
Combined standard uncertainty: The samples used in this certification process have been selected in such a way as to represent the entire batch of material and were taken from the final packaged units; therefore all possible sources of uncertainty (sample uncertainty and measurement uncertainty) are included in the final combined standard uncertainty determination. The uncertainty measurement takes into consideration the between lab and the within lab variances and is calculated from the square roots of the variances of these components using the formula:
Combined standard uncertainty=sqrt((between lab.var/no of labs) + ( mean square within lab.var /no of assays))
Metrological Traceability: The values quoted in our certificates are based on the consensus values derived from statistical analysis of the data from an inter laboratory measurement program. Traceability to SI units is via the standards used by the individual laboratories the majority of which are accredited and who have maintained measurement traceability during the analytical process.
Code of conduct
AMIS will continue to provide outstanding products and problem-solving solutions by building partnerships with our customers and maintaining a culture of excellence in customer service. We will also continue to create an environment for shared success, generating consistent growth and opportunities for our customers, shareholders and staff.
We strive to uphold our corporate values of exemplary corporate citizenship, employment of exceptional people, world-class quality procedures and standards, superior customer service, financial performance and accountability.
"Commutability" is a term used to describe the issues raised using assay standards that might not effectively test the matrix or grade of the samples being tested; or which might have been characterised using different analytical methods to the laboratory doing the analysis. In other words, you may be using the wrong assay standard or CRM to test your labs performance (for your mines ore).
Reference materials have always been used for assay lab quality control (QC) and quality assurance (QA) but their use has increased and been more prominent following tightening of various codes, legislation and regulations worldwide for the recording and reporting of mineral resources and reserves. This followed several prominent poor corporate governance and fraud cases. South African and Canadian stock exchange rules actually specify QA/QC from exploration through to the mineral resouce statement. It will also be required for an independent sign-off of exploration data or a mineral resource. They have become necessary since SOX for mining company internal audit procedures. Although corporate compliance requirements still fall short of what has become best practice or what is necessary.
There is little doubt, that in the competition for investment money, especially in a high risk industry like exploration and mining, the company with the best set of books will attract the best premium. While audit trails and quality assurance are a very small part of the business, they are an important cornerstone.
Control Sample Failure Checklist
Good laboratories will report results within the manufacturers two standard deviation levels with a failure rate of <10 %. If your laboratory is not achieving that or if your control sample results are failing the quality criteria that you have set:
1. Check that you are using the correct Reference Material (with a grade and matrix matching your samples).
2. Read the manufacturers certificate and make sure your Control Chart limits match or are within the Certificate limits.
3. Note: if your laboratory has developed a bias you will automatically see more failures.
-Check the product labeling to make sure you are using the correct Reference Material
1. Check that the Product Code on the packaging matches the Code in your QC program.
2. The Laboratory Pack (tub) containers have two labels. A small label with a batch and a tub number is put on the tub during batch production and will be correct. A large label is put on the tub during dispatch and also shows the product (batch) code. The batch code on the small label must correspond with the batch code on the large label (IF IT DOESN'T, IMMEDIATELY CONTACT AMIS).
3. Explorer Packs have been repackaged from the original tubs. The Product Code is on the label. Sample values and limits must be taken from the certificate.
-Check you are using appropriate limits
1. Check that you have set appropriate limits for that Reference Material for your laboratory (from your own results).
2. Check that you are applying the appropriate rules to accept or to fail a run (ref to Westgard).
-You still have a problem:
4. If you can, run a multi-element scan to check that the reference material major and trace element chemistry matches that published in the certificate (IF IT DOESN'T, IMMEDIATELY CONTACT AMIS).
5. Check that the matrix of the Reference Material matches or is close to the matrix of your samples and that the appropriate analytical techniques, fluxes etc. have been used for your matrix.
-Feel free to check the mathematics on the certificate.
1. AMIS round robin data and statistics are published in the certificate and are available in a digital format on request.
2. AMIS round robin data and statistics are also available in the round robin proficiency report. These reports are made available to Laboratories that participate in the AMIS round robins and customers may ask Laboratory Managers to see this report.
1. Find out, how much has been sold to other customers?
2. Have there been any complaints about the product?
Control samples are normally samples of a matrix-matched RM or CRM, made and priced so that they can be used to check the accuracy and precision of runs of analytical results for samples being analysed by a specific analytical method. They are inserted into each batch of samples. The control samples assay results are checked on control charts or by using statistical techniques.
The manufacturer will have tested and documented the values expected for different tests and different methods. These "Recommended Concentrations and Limits" are summarised on a "Certificate of Analysis", which is useful for selecting a specific control material.
To behave the same during analysis control sample characteristics should be the same or similar to the sampled material. However, there is a catch. Because the Control Sample property values are based on a measurement campaign using a number of independent laboratories (round robin), the recommended concentrations and limits will reflect the average results and cumulative precision produced by the participating laboratories. These "consensus values and limits" should not generally be used for setting the control limits in a single lab because they include a between-laboratory component of variation that can make the manufacturers control limits too wide for single lab use; depending on the commutability of the CRM with respect to the samples being tested (see Limits).
Control samples that have not been tested by an interlaboratory process may be used to test lab precision, but thats only half the job. Properly characterised (by a sufficiently large round robin) RM's or CRM's are still needed to test laboratory bias (accuracy).
Critical systematic error
The critical systematic error is measured from blank and duplicate sample failures and should be very high, probably up to 90%. That is, 90% of the blank samples submitted come back with nothing in them.
Data quality objectives
These data quality objectives need to be reported:
1. Analytical bias (say <2.5%)
2. Coefficient of variation (say<5%)
3. Detection of critical systematic error (say >90%)
4. False rejection rate (say <5%)
Data quality objectives are realistic operating specifications giving allowable levels of inaccuracy (and imprecision) for different grades of material, and for each process related analytical or operating quality requirement. Objectives have to be set and must take into account cost implications if limits are set too tight or too loose. These will result in too many QC failures (true and false). There must be realistically high probabilities for error detection and realistically low probabilities for false alerts. Primary and secondary laboratories have to be checked for compatible equipment, methods and detection limits and obviously, the success of the program relies on having appropriate grade and matrix control materials.
False rejection rate
The false rejection rate is measured on the reanalysis of QC failures and shoud be very low, say <5%. That is, <5% of the failures, when reanalysed, came back with the same results. Or 95% of the failures you picked up were genuine QC failures.
ISO - The International Organisation for Standardisation
The International Organization for Standardization (ISO) is a network of the national standards institutes of 164 countries. ISO sets rigorous standards for business, government and industry.
ISO 9001:2015 is a validated quality standard and is globally the most widely utilized quality standard for quality management systems. ISO 9001:2015 is applicable to any manufacturing and service organization providing a framework for system development focusing on the customer, quality system performance and ongoing improvement. Created by the International Organization for Standardization it is based on the eight quality management principles: customer focus, leadership, involvement of people, process approach, system approach to management, continual improvement, fact based decision-making and mutually beneficial supplier relationships. When fully adopted, these principles have been proven to enhance organizational performance in providing quality products and services to customers.
The AMIS Quality Management System is ISO 9001:2015 Certified. Our Certificate states: “The AMIS Quality Management System ISO 9001:2015 certificate is issued by TÜV Rheinland South Africa, under the scope: A producer and global supplier of matrix-matched Certified Reference Materials; for the mining, exploration and geochemical laboratory industries.”
The AMIS ISO 9001:2015 certificate is available on this website for download. Questions about it can be directed to the AMIS Quality Specialist
The manufacturers limits are meant to give an idea of the range within which you should expect your labs mean to fall. They are probably set too wide to be used as routine control limits for an individual laboratory.
Certification of the CRM is based on a measurement campaign, so allocation of property values takes place on the basis of agreement among the independent measurement results and, not necessarily with direct traceability to Standard International units. Two of the ISO assumptions that allow this are; that there will be enough capable labs and that the results from each lab will be statistically compatible (ISO Guide 35 Clause 9.2.3 and Clause 10). To overcome the effects of this "inter-laboratory issue", and to achieve "a property value having satisfying uncertainty" (ISO Guide 35 Clause 10.2.2) CRM producers must raise the minimum number of laboratories involved (in practice to 15 laboratories per analyte, 8 samples to each) and scrutinize the data with the aid of outlier treatment techniques. This should lead to a very accurate measure for a given method; notwithstanding the underlying assumption that what the good inter-laboratory labs reported was accurate. However, an amount of bad data may have an effect, resulting in limits which may too broad for effective monitoring of a single laboratory or production process. This is a major concern to the CRM producer and it should be an issue (by simple extension) to the CRM consumer.
CRM consumers are advised to set their own limits, (normally within the CRM producers limits) based on their own data quality objectives and control measurements. For example, limits probably don't need to be as tight, for plant residues or for geochem grade levels; but they need to be tighter for high ore and concentrate grade levels (purely for financial considerations).
The CRM consumer may for various reasons choose to use the manufacturers limits to monitor the performance of a single laboratory. However, if the lab is reporting accurately (no bias) then these limits are unlikely to adequately monitor precision 2SD failure's lower than 5% could be an issue (see Control Rules). If the lab has a bias, 2SD failures higher than 5% will become a problem.
The precision or bias issue thus identified might be due to either lab problems or CRM commutability and must be discussed with the laboratory manager. Commutability issues can be investigated using the matrix chemistry published in the CRM's certificate. If commutability is not the cause of the greater or less than 5% 2SD failure rate, then the CRM's have done their job and the lab problem can be fixed. That's what CRM's are for.
Manufacture begins with canvassing potential customers about desired characteristics for new standards. Ore with these characteristics is sourced from a mine or exploration project. The ore is crushed, then dry-milled and air classified to 100% <54µ. This fine powder is mixed in a blender for 14 hours and then split down into numbered 1 kg tubs. These lots are sampled for quality control and for round robin analysis. Quality control for a normal sized batch comprises sampling 30 tubs selected from the whole stream. Round robin samples are selected the same way, so that one laboratory will receive samples from the beginning, end, and from throughout the batch.
Matrix Reference Materials
A matrix reference material is defined as a reference material that contains major, minor, and trace components. Matrix materials are intended to be used in conjunction with the analysis of real samples of the same or a similar matrix. They are normally materials that are sampled from nature (ISO D GUIDE 30:2013(E) 2.4.).
The Matrix matched CRM should have similar chemical, mineral and grade characteristics; to the samples being tested in the laboratory. This will give the lab a fair test (see Commutability above). With reference to the major and trace element data published in the CRM certificates, particular attention should be taken to the elements most likely to cause problems in the lab.
The values quoted in our certificates are based on the consensus values derived from statistical analysis of the data from an inter laboratory measurement program. Traceability to SI units is via the standards used by the individual laboratories the majority of which are accredited and who have maintained measurement traceability during the analytical process.
National Nuclear Regulator
African Mineral Standards is licensed by the South African National Nuclear Regulator to produce, distribute and export reference materials containing uranium according to Nuclear Authorisation COR-206.
African Mineral Standards packaging is designed to protect the contents from moisture, oxidation, ordinary segregation, electrostatic segregation and tampering.
Laboratory Packs contain 1 kg of material sealed into 2.5 litre capacity bottles (space to shake). These are delivered sealed in barrier foil pouches with an oxygen reducer.
Explorer Packs contain between 50 to 250 gm of material (whatever you want). The Explorer Pack is reference material in a standard, unmarked, paper geochem envelope , vacuum sealed into a protective barrier foil pouch. Explorer Pack's are designed by a geologist, especially for the busy field geo and will withstand abusive treatment.
Reference Materials (RM's)
Reference materials, commonly referred to as "standards", are an important element in exploration and mining best practice. They are samples, with a known grade, made from a specific ore, used as control samples to check results for specific methods from chemical analysis.They have been tested and found fit for their purpose, which can include the calibration of a measurement system, assessment of a measurement procedure, assigning values to other materials and quality control.
They are used to check on:
- accuracy from individual analyses
- method bias
- sample custody procedures
- sample traceability
- assay laboratory quality assurance
- the integrity of the mineral resource database
- the integrity of the mineral resource estimate
Mining professionals have to plan very carefully, for future resource and reserve audits, right from the commencement of exploration. Resource audits are similar to financial audits. They follow a sequence of paperwork set out in a logical path, to validate that best practice has been followed from geological sample to the database and into the mineral resource model. A sample audit trail, as an example, will establish that a specific set of assay results used for a mineral resource or a production efficiency calculation can be traced back to a specific sampler, a specific sample and a specific analysis.
Typically, an uncertainty statement is presented as follows: Au =0.77±0.04 g/t, where the number following the symbol ± is the numerical value of an expanded uncertainty, U = kuc, with U determined from a combined standard uncertainty multiplied by a coverage factor k = 2 or, a t-critical value for N-1 accepted laboratories. Since it can be assumed that the possible estimated values of the standard are approximately normally distributed with standard uncertainty, uc, the certified value of the CRM is believed to lie in the interval defined by U with a level of confidence of approximately 95 %, e.g. a mean value of 0.77±0.04g/t will have intervals of: 0.73<0.77<0.81 g/t.
The expanded uncertainty (U) at a confidence level of 95% is determined by multiplication of the combined uncertainty (uc) by a coverage factor (k) found from N-1 degrees of freedom (df), where N is the number of laboratory means accepted in the establishment of the certified value. The t-critical value for 5% significance can be found in a t-critical table.
Uranium standards, shipping-export-import regulations
Shipping of AMIS uranium bearing reference materials to countries such as Canada and Australia should not be a problem for two reasons. Firstly AMIS uranium standards contain such small quantities of uranium and thorium they generally do not classify as radioactive. Secondly African Mineral Standards is licensed by the South African National Nuclear Regulator to produce, distribute and export reference materials containing uranium according to Nuclear Authorisation COR-198.
The regulations (IAEA Safety Standards Series No. TS-R-1) are written in officialese, which makes them a bit inaccessible. Our guide summarizes the relevant bits. Notwithstanding, the ultimate responsibility to let the goods through will in any event rest on local customs officials. We will give them the paperwork filled out according to the international conventions; but customers are still advised to pass our paperwork by their customs officials first.
Use of reference materials
A simple example of how reference materials are used is as follows. They are placed in the middle of a stream of similar samples being submitted for assay. The reference materials should report results within set confidence limits. Their results are used as a check of the overall accuracy and precision of results in the final database or resource calculation. They will also verify that other individual assays match the correct samples in a batch.
This is one of the ways assay laboratory quality control and quality assurance is managed. It is also a standard auditing procedure to check on the efficiency of mine sampling procedures and metallurgical processes and, it is one of the things an exploration manager has to do to generate a bankable mineral resource.
The bankability of mineral resources is especially important. Audit trails are needed when due diligences or reviews are undertaken on a mine or exploration project. These happen when money is being raised or if the project is being sold or, simply if production and metallurgical process efficiencies are being audited as a management check. Audit trails provide a high degree of assurance (to share holders, financial institutions, exploration project management and mine management) that mine or exploration sampling meets the standards required by best practice and by the compliance codes for stock exchanges around the world (NI 43-101, SAMREC, JORC etc).