FAQs

Certified reference materials (CRMs) are used to calibrate and verify the accuracy of chemical analyses in the mining industry. They play a vital role in Quality Assurance/Quality Control (QA/QC) programs for mineral exploration, mine development, and mineral processing.

CRMs are essentially control samples with known chemical compositions.  They are inserted into batches of samples undergoing analysis to monitor the consistency and accuracy of the analytical results.  This helps to ensure that the data obtained from the analysis of real samples is reliable and can be used for informed decision-making.

CRMs play a pivotal role in ensuring the accuracy and reliability of analytical data generated during mining and exploration programs.  

Geochemical data underpins all major technical and financial decisions, including resource definition, grade control, mine planning, metallurgical evaluation and environmental monitoring, so poor analytical data can lead to costly mistakes. 

By methodically inserting CRMs into sample batches, companies can monitor laboratory performance and verify their analytical methods are producing accurate results.  

CRMs help identify analytical bias, calibration problems, contamination, or instrument drift before these issues affect large datasets. 

CRMs also support compliance with reporting standards and industry best-practice QA/QC procedures. They provide confidence that laboratory results are consistent over time and across laboratories. 

In exploration and mining, reliable analytical data is essential, and CRMs provide an independent benchmark against which laboratories can assess their performance, helping ensure that decisions are based on precise and reliable information. 

Simply put, laboratories use CRMs to verify the accuracy and consistency of their analytical results.  

CRMs are routinely included at regular intervals in sample batches as part of a laboratory’s QA/QC program. When a CRM is analysed alongside unknown samples, the laboratory compares the CRM reported result to the certified value. If the result falls within acceptable limits, it confirms that the analytical method and instrument calibration are performing correctly. If results fall outside expected ranges, it may indicate issues such as calibration drift, contamination, preparation errors, or analytical bias. 

CRMs are also used during method development, instrument calibration verification, staff training, and inter-laboratory comparison programs. In mining and exploration, they help maintain confidence in assay data used for operational decision-making. 

Different CRMs are designed for different applications, including crushed rock, pulverised ore, synthetic materials and trace-level standards. Selecting the correct CRM for the sample matrix and analytical method is imperative for obtaining meaningful QA/QC results. 

A reference material becomes “certified” when its values have been determined through a rigorous technical and statistical process and are supported by documented evidence. 

CRMs are produced under strict quality systems, typically in accordance with the requirements of ISO 17034. ISO is an international organisation body that ensures for products, services, and systems are safe, reliable, and high-quality.  

The material must first be carefully prepared and tested to ensure it is sufficiently homogeneous and stable for its intended use. 

Certified values are then determined using validated analytical methods, often involving multiple laboratories and repeated measurements. The resulting data is statistically evaluated to determine the final certified values and associated uncertainties. 

A CRM certificate provides important supporting information, including the certified values, uncertainty estimates, traceability information, intended use, and storage instructions. 

The certification process ensures users can truly rely on the material as an independent standard for verifying analytical accuracy. Certification is what distinguishes a CRM from a general reference material or an internal laboratory standard. 

A Reference Material (RM) is any material that is sufficiently homogeneous and stable for use in analytical measurement or quality control. It may have indicative or informational values assigned to it, but these values may not have undergone full certification. 

A Certified Reference Material (CRM) is a higher-level reference material that has been fully characterised using validated analytical methods and statistical evaluation. Certified values are reinforced by documented uncertainties and traceability information. 

CRMs are produced under strict quality systems, typically in accordance with the requirements of ISO 17034. The certification process includes homogeneity testing, stability studies, analytical characterisation, and uncertainty calculations. 

While both RMs and CRMs can be useful for laboratory quality control, CRMs provide a greater level of confidence because the assigned values have been independently validated and documented. 

In mining and exploration, CRMs are the preferred standard for QA/QC programs because they provide a reliable benchmark for assessing laboratory accuracy and performance. 

The certified values listed on a CRM certificate are determined through a detailed analytical and statistical process designed to ensure accuracy, reliability, and traceability. 

The process typically begins with careful preparation of the candidate material, followed by homogeneity and stability testing to confirm the material is suitable for certification. 

Analytical characterisation is then performed using validated analytical methods. This commonly involves multiple laboratories and several analytical techniques to minimise bias and improve confidence in the final values. Alternatively, a single, highly reliable method can be used with established and fully evaluated uncertainties 

The resulting data is statistically evaluated to determine the certified value for each analyte along with its associated uncertainty. This includes evaluating method comparisons, identifying and removing outliers, and weighting datasets based on their precision and methodology. 

The final certified values and uncertainties are documented on the CRM certificate, together with traceability information and instructions for use. 

This rigorous process ensures the CRM provides laboratories with a reliable and independent benchmark for assessing analytical accuracy. 

Homogeneity refers to how consistent a material is from sample to sample throughout a CRM batch. In a homogeneous CRM, every jar, sachet, or portion contains effectively the same concentration of the certified analytes, within acceptable limits. 

Homogeneity is critical because laboratories typically analyse only a small sub-sample of the CRM. If the material is not sufficiently homogeneous, different portions may produce different analytical results, reducing the reliability of the CRM. 

To measure homogeneity, samples are taken from across the production batch and analysed statistically. Testing may evaluate both between-unit homogeneity and within-unit homogeneity, depending on the intended sample size and application. 

Good homogeneity ensures the CRM performs consistently across laboratories, instruments, and analytical runs. It is a key requirement of ISO 17034 and an essential part of the CRM certification process. 

Without sufficient homogeneity, a CRM cannot reliably be used to assess laboratory accuracy or analytical performance. 

Stability testing evaluates whether a CRM maintains its certified values over time and under expected storage or transport conditions. 

A CRM must remain stable throughout its intended shelf life so that users can rely on the certified values during routine laboratory use. Changes in moisture content, oxidation, segregation, chemical reactions, or contamination can all potentially affect stability. 

Stability studies may include short-term testing to simulate transport conditions and long-term testing to assess storage over months or years. Samples are periodically analysed and compared to the original certified values to identify any significant changes. 

The results of stability testing help determine expiry dates, recommended storage conditions, and handling instructions. 

Stability is an important requirement of ISO 17034 because even a well-characterised CRM is only useful if its values remain reliable over time. Proper storage and handling by the user also play an important role in maintaining stability. 

Uncertainty is a statistical measure of the confidence associated with a certified value. It indicates the range within which the true value is expected to lie, based on the available analytical data and statistical evaluation. 

Every measurement contains some degree of uncertainty and CRM certificates provide uncertainty estimates so users can properly interpret analytical results. 

Uncertainty is a quantified parameter that characterises the dispersion of values attributed to a measured quantity. It expresses how much you doubt the accuracy of your result due to factors like instrument limitations or human error. 

Uncertainty may include contributions from factors such as analytical measurement variability, between-laboratory differences, homogeneity, stability, and sample preparation. 

For example, a CRM may report an iron value of 62.50% Fe ± 0.15% Fe. This means the true value is expected to fall within that uncertainty range at a stated level of confidence. 

Understanding uncertainty is important because it helps laboratories determine whether analytical results are acceptable and whether differences between results are statistically meaningful. 

Well-characterised uncertainties are a key feature of Certified Reference Materials and an important requirement of ISO 17034. 

Traceability refers to the ability to link a measurement result back to a recognised reference through a documented and unbroken chain of comparisons, each with known uncertainties. 

In Certified Reference Materials, traceability helps ensure that certified values are accurate, reliable, and internationally comparable. This is achieved through validated analytical methods, calibrated instruments, recognised standards, and carefully controlled quality systems. 

Traceability is important because it gives laboratories confidence that their analytical results are based on recognised measurement systems rather than arbitrary values. It also supports consistency across laboratories, instruments, and analytical methods. 

Under ISO 17034, CRM producers must demonstrate appropriate traceability for certified values. This gives users confidence that the CRM can reliably support QA/QC programs, method validation, and laboratory performance monitoring. 

In industries such as mining, environmental testing, manufacturing and pharmaceuticals, traceability is essential for producing defensible and trustworthy analytical data. 

While CRMs are widely used in mining and mineral exploration, they are also essential across many other industries that depend on accurate analytical testing. 

Environmental laboratories use CRMs for testing soils, water, sediments, and air quality. The food and agriculture industries use them to verify nutrient content, contaminants, and food safety compliance. Pharmaceutical companies rely on CRMs for quality control, method validation, and regulatory testing. 

CRMs are also commonly used in petrochemical analysis, metallurgy, manufacturing, recycling, forensic science, clinical laboratories, and academic research. 

In all of these industries, CRMs help laboratories verify analytical accuracy, monitor instrument performance, and maintain confidence in reported results. They are a fundamental part of all QA/QC systems and help ensure analytical data is consistent, reliable, and traceable. 

Matrix matching refers to selecting a CRM that closely resembles the composition and physical characteristics of the samples being analysed. 

A matrix-matched CRM behaves similarly to routine samples during sample preparation, digestion, and instrumental analysis. This is important because different sample types can respond differently during analytical testing, potentially affecting recovery and accuracy. 

For example, iron ore samples are best monitored using iron ore CRMs rather than unrelated geological materials. Similarly, sulphide ores, bauxites, laterites, and concentrates may each require CRMs with similar mineralogy, particle size and chemistry. 

Matrix-matched CRMs are particularly important for complex analytical methods, trace-level analysis, and difficult sample matrices where matrix effects may influence results. 

Using an appropriate matrix-matched CRM helps laboratories better assess analytical bias, digestion efficiency, and overall method performance under real operating conditions. 

In mining and exploration, selecting the correct matrix-matched CRM helps improve the reliability and relevance of QA/QC monitoring programs. 

Synthetic CRMs are manufactured materials designed to contain specific analyte concentrations or chemical compositions. Unlike natural geological CRMs, they are created by blending high-purity compounds or carefully controlled ingredients. 

Synthetic CRMs are valuable because they allow producers to target specific element levels, analyte combinations, or concentration ranges that may be difficult to source from natural materials. They are commonly used for trace-level analysis, method validation, calibration verification, and specialised laboratory applications. 

And as their composition can be tightly controlled, synthetic CRMs exhibit excellent homogeneity and consistency. This makes them particularly useful for monitoring instrument performance and analytical precision. 

While natural matrix-matched CRMs are often preferred for routine geological QA/QC, synthetic CRMs can provide improved analytical checks and support for specialised analytical techniques and quality control requirements. 

The best choice depends on the analytical method, sample type, and the objectives of the laboratory QA/QC program. 

The key difference between crushed and pulverised CRMs is simply the particle size. 

Crushed CRMs contain coarser material, usually less than 5mm,  and are designed to more closely resemble samples encountered earlier in the preparation process. They are often used to monitor crushing, splitting, and pulverising stages within laboratories or preparation facilities and also for PhotonAssay or PAL (Pulverise and Leach) gold analysis which utilises coarse crushed samples.   

For PhotonAssay and PAL, crushed CRMs give better much representation as exactly the same physical matrix and particle size are being tested as the field samples. 

Pulverised CRMs are ground to a very fine particle size, less than 54 microns, similar to the final pulp submitted for chemical analysis. These materials are primarily used to monitor analytical accuracy of techniques such as fire assay, XRF and ICP-MS. 

Crushed CRMs can help identify contamination, segregation, preparation bias, and coarse gold effects that may not be detected using fine pulverised materials alone.  

Pulverised CRMs are generally more homogeneous and are widely used for routine analytical QA/QC. 

Crushed CRMs are typically used to monitor the sample preparation stage of laboratory or plant workflows. 

Because they contain coarser particles, crushed CRMs behave more like real field or plant samples during crushing, splitting, drying, and pulverising. This helps laboratories and mining operations assess whether preparation procedures are introducing contamination, segregation, or preparation bias. 

Crushed CRMs are especially useful in gold applications where coarse gold effects may occur, as fine pulverised CRMs may not fully represent the behaviour of coarse mineralisation. 

They are also well suited to analytical methods that analyse larger crushed aliquots directly, such as PhotonAssay and PAL (Pulverise and Leach) systems, where matching the physical matrix and particle size of field samples is important. 

In reverse circulation (RC) drilling programs, crushed CRMs can better mimic the particle size and physical behaviour of real RC samples, improving the relevance of QA/QC monitoring. 

Another advantage is that crushed CRMs can often be submitted anonymously to laboratories, reducing the likelihood that technicians immediately recognise them as highly homogenised QA/QC materials. 

While pulverised CRMs are generally preferred for routine analytical QC, crushed CRMs provide additional confidence that the sample preparation stage itself is operating correctly. 

Many QA/QC programs use both crushed and pulverised CRMs to achieve more complete process monitoring.

Whether a CRM should be dried before use depends on the material type, analytical method, and the instructions provided on the CRM certificate. 

Users should always follow the instructions supplied with the CRM certificate and maintain consistent handling procedures throughout the analytical process. 

Some CRMs are certified on an “as-received” basis and should be used exactly as supplied. Drying these materials may alter moisture content or chemical composition and could affect the certified values. 

Other CRMs may require drying to align with specific laboratory methods or reporting bases. In these cases, recommended drying temperatures and handling procedures are usually provided by the CRM producer. 

Improper drying can potentially cause oxidation, moisture loss, volatilisation of certain elements, or physical changes to the material. 

Avoiding contamination is absolutely essential for maintaining the integrity and reliability of a CRM. 

CRMs should always be handled using clean tools and equipment. Spatulas, scoops, and sampling surfaces should be cleaned thoroughly between uses to prevent cross-contamination. 

Unused material should never be returned to the original jar, as this can introduce contaminants or moisture. CRM containers should only be opened when required and resealed immediately after use. 

Exposure to excessive humidity, dust, chemicals, or laboratory fumes should also be minimised. Gloves may be appropriate when handling sensitive materials. 

For pulverised materials, excessive shaking or rough handling should be avoided, as segregation of fine particles may occur. 

CRMs should always be stored according to the conditions specified on the certificate or product documentation. Following good laboratory practices helps ensure the CRM remains representative and reliable throughout its usable life. 

Quality control programs in mining and laboratory analysis commonly use multiple CRM levels to monitor analytical performance across different concentration ranges. 

For example, laboratories may use low-grade, medium-grade, and high-grade CRMs to ensure that analytical methods remain accurate throughout the expected sample range. This helps identify issues that may only become apparent at certain concentration levels. 

Different CRMs may also be selected for different commodities, matrices, or analytical methods. Some QA/QC programs rely on matrix-matched geological CRMs, while others incorporate synthetic standards or trace-level materials for specialised applications. 

CRMs are commonly used alongside blanks, duplicates, and check samples to provide a comprehensive assessment of laboratory performance. 

An effective QA/QC program is designed to detect analytical bias, contamination, preparation errors, and instrument drift before they affect important datasets. 

Selecting appropriate CRM levels and insertion rates is an important part of building a reliable and meaningful quality control system. 

Custom: We manufacture custom CRMs to the exact specifications of our clients. Catalogue: CRMs we hold pre-existing stock for and you can buy immediately based on specification.

We are the only company in the world with the ability to manufacture custom Crushed or Pulverised materials across different commodity classes.

Selecting the right CRM requires matching three key parameters to your project: analytical method, target grade range, and matrix composition.

Start by identifying the primary analytical method your laboratory will use, e.g. fire assay, ICP-MS, ICP-OES, XRF etc., as this determines what type of CRM is technically appropriate.

Next, define the grade range you expect to encounter across your sample suite. A CRM outside your expected grade window will not provide meaningful performance data for the intervals that matter most.

Finally, consider how closely the CRM matrix resembles your actual ore. A CRM prepared from material geochemically similar to your deposit will expose problems that a generic standard will not.

In practice, most programs require at least two or three CRMs spanning low, mid, and high-grade ranges. A single CRM inserted at one grade point tells you very little about laboratory performance across the full analytical range.

CRM grade selection should reflect the geological and operational context of the program.

As a general guide:

• Exploration programs: Select CRMs bracketing the expected range of assay results one below the anticipated average grade, one near the expected average, and one above. This ensures quality control across the full data distribution.
• Resource definition and mine geology: Grade control becomes more critical at this stage. CRMs should bracket the economic cut-off grade closely, with at least one CRM positioned at or near the cut-off itself, where classification and reporting decisions are most sensitive.
• Metallurgical and concentrate samples: These require CRMs appropriate to the much higher grades involved. Standard exploration-grade CRMs are not suitable and will not provide meaningful QC data at elevated concentrations.

A common mistake is using a single mid-grade CRM and assuming it covers the program. However, bias or drift may only manifest at certain grade levels so using multiple CRMs is the only way to detect grade-dependent analytical problems.

As closely as practical. The matrix of a CRM, i.e., its overall chemical and mineralogical composition, directly affects how well it will digest in acid, its spectral interferences, and the instrument response.

A CRM that does not resemble your ore may behave quite differently during preparation and analysis, meaning that even good QC results offer limited assurance that your samples are being analysed correctly.

For most base and precious metal programs, a CRM sourced from a geologically similar deposit type (orogenic gold, BIF, IOGC, pegmatite, ultramafic-hosted Ni etc) provides adequate matrix matching.

For technically complex ores such as refractory gold, complex polymetallic sulphide systems, rare earths, or deposits with unusual gangue mineralogy, matrix matching becomes substantially more important. In these cases, it is worth investing in CRMs specifically certified for your ore type, or engaging a CRM supplier to have custom made CRMs produced.

It is worth noting that perfect matrix matching is rarely achievable, and CRM certification itself requires sufficient material homogeneity across a large, prepared batch. The practical goal therefore is to use the closest available match and to be aware of any divergence between the CRM and your ore matrix.

Gold exploration programs analysed by fire assay should use fire assay-compatible CRMs which are typically fine-grained pulverised materials certified for 30g or 50g fire assay charge weights. The CRM particle size and mass submitted should be appropriate for the fire assay method in use.

For free-milling gold deposits, standard commercially available gold CRMs are generally suitable. For refractory ores (gold locked in sulphides, arsenopyrite, or carbonaceous material), it is important to use a CRM prepared from genuinely refractory material. A free-milling CRM will not expose incomplete liberation or poor fusion efficiency that may be affecting your actual sample suite.

Coarse gold deposits present a particular challenge — see the separate FAQs below.

Coarse gold deposits present a fundamental QC challenge rooted in the nugget effect.

When gold occurs as random, discrete coarse particles rather than fine disseminated grains evenly distributed through the sample, the probability of a sub-sample containing a gold particle is highly variable, and no amount of careful sample preparation fully eliminates this variability at typical fire assay charge weights.

Conventional fire assay typically analyses use 30g or 50g charges and so the result becomes highly variable depending on whether a gold particle happens to be included in that aliquot.

So, for coarse gold systems, that can simply be too small to obtain a representative sample. The practical implication of this is that a meaningful fire assay CRM for a nuggety gold deposit essentially cannot be produced.

For coarse gold programs, one approach is to focus quality control effort on:

• Coarse duplicate sampling (field duplicates, crusher duplicates) to quantify the magnitude of the nugget effect in your specific ore.
• Use of blanks to monitor contamination during preparation of high-grade material.
• Fine-grained gold CRMs to check laboratory performance on the dissolved fraction, accepting that the primary source of variability is sampling rather than analytical.

Recognising and documenting the nugget effect is more useful than attempting to use a CRM that cannot be properly certified for this style of mineralisation.

A better approach is to use a different analytical technique such as PhotonAssay or PAL (Pulverise and Leach).

Crushed Gold CRMs are ~3mm rock chips specifically produced using our patent-pending, in-house manufacturing process.

Engineered specifically for large mass analytical methods like PhotonAssay™ and PAL, they are the only CRMs designed for these laboratory techniques. They are certified and matrix-matched to routine samples.

Quality control programs for laboratory analysis rely on treating certified reference materials (CRMs) identically to routine samples. Matching the physical and chemical characteristics, method of use, and handling in all laboratory processes for both CRMs and routine samples develop superior confidence in the results.

Pulverised CRMs have been used for PhotonAssay™ and PAL, but they behave adversely compared to crushed samples. To solve this issue, CrushedCRMs™ have been developed as the essential quality control material for these laboratory. methods.

Produced under our 17034 accreditation, we guarantee the inter-comparability of measurement results worldwide and the highest level of quality assurance that an accredited impartial manufacturer can obtain.

The Chrysos PhotonAssay technique uses a large sample mass (typically 500g or more) with a coarse grain size (2-3mm) using gamma-ray fluorescence. High-energy gamma rays are fired at the sample to “excite” gold atoms, causing those atoms to emit their own characteristic energy signal, which can then be measured and quantified.

This sample format creates a fundamental incompatibility with standard pulverised CRMs, which are produced in small particle sizes and are not appropriate for a 500g bulk measurement of a crushed sample. Specially designed CRMs for PhotonAssay available from IMS should be used in this instance.

As discussed above, this is not ideal and is generally not recommended. Pulverised CRMs submitted as a 500 g mass of fine powder do not represent the physical form of the ore being measured, and the homogeneity characteristics and certified uncertainty of a pulverised CRM are established for small sub-sample masses, not for 500 g bulk measurements.

Therefore, the QC data generated using pulverised CRMs in a PhotonAssay program will have limited diagnostic value and may give a misleading picture of analytical performance.

For fit-for-purpose QC in PhotonAssay programs, crushed CRMs prepared and certified for the relevant submission mass are strongly preferred.

Copper-gold deposits require CRMs certified for both gold and copper, ideally from a sulphide-bearing matrix comparable to your ore. The interaction between gold and copper during fire assay, particularly where high copper concentrations may affect the assay, means that a CRM carrying both analytes at representative grades provides better diagnostic value than separate gold-only and copper-only standards.

For the gold component, ensure the CRM is compatible with your fire assay method and charge weight. For the copper component, check that the CRM grade range covers your expected Cu distribution. High-grade copper intervals may require a separate CRM at elevated copper levels if the standard range CRM does not capture the upper tail of your data.

ICP analysis of a copper-gold digest should also be validated with matrix-matched CRMs where possible, as copper matrices can introduce interferences on gold and other elements of interest.

Iron ore QC programs typically involve XRF analysis for major elements (Fe, SiO₂, Al₂O₃, P, S, MnO, TiO₂) and loss on ignition (LOI). So the CRM selection should reflect this.

• Use multi-element iron ore CRMs certified for the full suite of elements measured, not just total iron.
• LOI is a critical parameter in iron ore QC. It is best to ensure your CRM has a certified LOI value and that the CRM behaves consistently in your laboratory’s LOI procedure.
• Iron ore is hygroscopic — adsorbed moisture can affect LOI measurements and introduce variability. For programs where hygroscopic moisture is analytically significant, CRM handling and storage conditions should be controlled accordingly.
• Calibration standards for XRF should ideally span the full range of expected values as a multi-point calibration. A single-point CRM at one grade level is insufficient for a full XRF suite.

Iron ore deposits vary considerably in mineralogy, and this affects analytical behaviour. The three primary ore types requiring different CRM considerations are:

• Hematite ores: the most common direct shipping ore type. Standard iron ore CRMs are widely available for haematite-dominated systems.
• Goethite-rich ores: goethitic iron ores typically carry higher LOI values due to structurally bound water. CRMs for goethite-bearing systems should have certified LOI values reflecting this, and LOI behaviour during ignition should be verified against expected ranges.
• Magnetite ores and concentrates: magnetite programmes frequently produce high-grade concentrates requiring CRMs at significantly elevated iron grades. Additionally, if magnetite concentrates are produced, negative LOI values (oxidation of Fe2+ to Fe3+ during ignition) may be relevant, and CRM certification should cover this range.

Matching mineralogy is particularly important where LOI is a key product specification parameter. Using a haematite CRM on a magnetite-concentrate program, for example, will not provide meaningful QC data for LOI behaviour.

Particle size selection should be fit for purpose and matched to the analytical method. Most standard exploration CRMs are pulverised to a nominal 75 micron (200 mesh) or finer specification, which is appropriate for fire assay, ICP dissolution, and most XRF applications.

However, there are practical considerations at both ends of the particle size spectrum:

• Very fine CRMs (high proportion passing 75 microns or finer) can exhibit handling effects such as electrostatic behaviour, poor flow properties, and difficulty achieving consistent sub-sampling. These issues can introduce variability that is not a reflection of laboratory performance.
• Coarser CRMs may have implications for homogeneity as the ability to sub-sample a consistent aliquot from a batch becomes more difficult as particle size increases. CRM certification tests homogeneity explicitly, but coarser materials carry inherently greater sub-sampling uncertainty.

Always check the certified particle size specification and confirm it is compatible with your analytical method and the mass being submitted.

Most commercially available pulverised CRMs are prepared to a nominal 75-micron (P80 or P90 passing) specification, though this varies by supplier and material.

Some CRMs are prepared to finer specifications (e.g. 53 microns or sub-45 microns) for applications requiring more complete dissolution or finer feed material.

Always refer to the CRM certificate of analysis or product data sheet for the specific particle size specification, as this is a certified parameter.

The mass submitted should be sufficient for the primary analytical method, with enough remaining for at least one repeat analysis if required.

Understanding how your laboratory batches their samples important here as different analytical methods have different minimum charge weights, and submitting less than the method requires will invalidate the QC result.

Below are some indicative mass requirements by method:

• Multi-acid digest / ICP (MAD): Typically, a 0.25g to 0.5g analytical aliquot is used so submit 1-2g to allow for sample handling and potential repeats.
• Fire assay (FA): Standard 30g or 50g charge. The CRM mass submitted should match the standard charge weight as submitting a partial charge invalidates the fire assay result.
• PhotonAssay (PA): Normally requires 500g or more of material. Standard pulverised CRMs are not suitable for PhotonAssay — see the specific PhotonAssay FAQ.
• PAL cyanidation assay: Method-specific charge weights apply. Consult your laboratory for the required mass and confirm CRM compatibility with the leach procedure.

Always check the certified minimum sub-sample mass specified on the certificate. Submitting below this mass risks non-representative sampling and introduces uncertainty that is not accounted for in the certified uncertainty budget.

Yes, without exception.

A single CRM at one grade level monitors laboratory performance only at that specific concentration. Analytical bias, calibration errors, and method-specific problems frequently manifest differently across the grade range — a laboratory may perform acceptably at mid-grade while showing systematic bias at low or high grades.

As a minimum, most programs should include:

• A low-grade CRM: positioned below the expected average grade or near the lower limit of economic interest. This monitors performance in the region where detection limit proximity and low-level accuracy are most critical.
• A mid-grade CRM: positioned near the expected average grade of the sample population. This is the most representative QC check for the bulk of your data.
• A high-grade CRM: positioned at or above the expected upper grade range or economic cut-off. This monitors performance where high-grade intercepts have the most influence on resource estimates and mine planning decisions.

Where a program has a clearly defined cut-off grade, positioning one CRM at or near that cut-off is strongly recommended, as this is the grade range where classification decisions are most sensitive to analytical error.

Understanding how your laboratory processes samples is important before designing your insertion protocol.

Most laboratories work in fixed batch sizes — fire assay is commonly batched in 50-pot or 40-pot configurations. Blanks, standards, and duplicates submitted by the laboratory itself all consume some positions in each batch, which affects how many positions are available for client QC material.

A practical guide for insertion frequency is listed below:

• A minimum insertion rate of 1 CRM per 20 samples is widely used as a baseline in exploration programs — this equates to approximately 5% QC.
• For resource definition drilling or grade control, higher insertion rates of 1 in 10 (10%) are common.
• Where multiple CRM grades are being used, rotate them through the batch so that each grade level is represented regularly rather than clustering all CRMs of one type together.

Coordinate with your laboratory to understand their batch structure. Inserting CRMs at positions that fall at the beginning, middle, and end of a fire assay batch, for example, provides better coverage of potential within-batch drift than random placement.

CRMs and blanks serve different but complementary QC functions and should be used together.

CRMs monitor analytical accuracy and bias — they tell you whether the laboratory is returning the correct value. Blanks monitor contamination during sample preparation — they tell you whether material from a previous sample is carrying over into subsequent samples.

The placement of blanks is important. Blanks should be submitted as low-grade or near-zero grade material inserted immediately after high-grade samples or known mineralised intervals. The purpose of a blank is to detect contamination during sample preparation and analysis. Ideally, a blank should contain:

• negligible concentrations of the target analytes
• minimal contamination risk
• physical properties reasonably compatible with the preparation process.

A blank that returns an elevated value indicates preparation contamination, most commonly from incomplete cleaning of crushing or pulverising equipment between samples.

Blanks can themselves be a source of contamination if not handled correctly. A blank submitted after a high-grade sample will pick up contamination which is the intended function. However, the elevated blank result represents material that may also have been carried forward into the next sample in sequence.

Therefore, when reviewing blank data, consider not just whether the blank has failed, but what the contamination implications are for the sample immediately following the blank in the preparation sequence. A blank only tells you contamination has occurred — it does not tell you exactly where contamination entered the workflow. Interpretation still requires understanding the preparation sequence and laboratory process.

The combination of CRMs (accuracy) and blanks (contamination) provides a more complete picture of laboratory performance than either tool alone.

Yes. CRMs and blanks address different failure modes and neither substitutes for the other. A QC program relying solely on CRMs will not detect preparation contamination. A program relying solely on blanks will not detect analytical bias or calibration drift. A robust QC program incorporates both, along with field duplicates or preparation duplicates to monitor sampling precision.

As a working framework:

• CRMs: inserted at regular intervals throughout the batch to monitor analytical accuracy across the grade range.
• Blanks: inserted after high-grade samples or mineralised intervals to monitor preparation contamination.
• Duplicates (field or preparation): inserted to monitor sampling precision and preparation reproducibility, distinct from the accuracy and contamination checks provided by CRMs and blanks.

Together, these three QC tools provide a defensible, comprehensive quality assurance framework appropriate for programs operating under JORC, NI 43-101, SAMREC, or equivalent reporting codes.

Custom: We manufacture custom CRMs to the exact specifications of our clients. Catalogue: CRMs we hold pre-existing stock for and you can buy immediately based on specification.

We are the only company in the world with the ability to manufacture custom Crushed or Pulverised materials across different commodity classes.

Our flexible system allows us to produce custom batches from small to 20 tonnes.

Pilbara Standards was the original name of IM Standards. Set up in 2012 it became the world’s leading supplier of iron ore certified reference materials. 

In 2021 we rebranded to Independent Mineral Standards, to better reflect the growing breadth of our product range and our focus on certified reference materials across multiple commodities.