Reference Materials are Control Samples with known grade characteristics that are inserted into a sample batch to test the assay results for samples with unknown grade characteristics. Their use is not just best practice in Assay Laboratory QA/QC, it is law.
Compliance
Reference Material use in Sample and Laboratory QA/QC is mandated for Mining Company financial reporting by stock exchanges. Technical Reports backing up the financials must, under a section on the analysis of samples, include a discussion of laboratory accreditation, precision and accuracy, including the use of quality control programs (blanks, duplicates, certified or standard reference materials), and submission of samples to other laboratories for verification. This is pretty much the global standard now. Companies wishing to raise money for exploration and mining have to play by the investors rules.
This was not always so. Regulators felt the need to tighten Reporting Rules for Exploration and Mining companies after a couple of epic mining scandals in the late 20th century. The biggest (financially) being the infamous Bre-X in 1997 where sampling and assay protocols were put under the spotlight; but this had been preceded by the Australian Nickel Boom (aka the Poseidon Bubble) in 1970, which had been caused by the usual combination of investor greed and optimistic claims made by exploration companies.
After the Nickel Boom in 1974 the Rae Committee, set up to investigate it, recommended changes to the regulation of Australasian stock markets. The financial regulators in turn asked professional societies to get their houses in order, with respect to how mining companies should feed technical information to the investment community. This resulted in the publication of the JORC Code in 1989. JORC is a professional code of practice setting minimum standards for Public Reporting of mineral Exploration Results, Mineral Resources and Ore Reserves. It established overriding principles of transparency, competency and materiality that determined the minimum amount of information that should be publicly reported. It was given immense weight by being incorporated into the Listing Rules of the Australian and New Zealand Stock Exchanges, compliance being made mandatory for listed public companies in Australia and New Zealand.
In fact the JORC Code proved such a good piece of work that it was adapted and adopted by Canada as the basis for it's CIM Code which was incorporated into the Canadian Security Administrators (CSA) rules as Ni 43-101; and by South Africa as the SAMREC Code which was incorporated into the Johannesburg Stock Exchange Listing Rules as Section 12. Internationally the Council of Mining and Metallurgical Institutes (CMMI) have been promoting these codes as the CRIRSCO initiative. CRIRSCO is recognised by global organisations such as the International Accounting Standards Board (IASB), the United Nations Economic Commission for Europe (UNECE) and the International Council on Mining and Metals (ICMM), as the key international organisation representing the mining industry on issues relating to the classification and reporting of mineral assets.The CRIRSCO International Reporting Template, first published in 2006, is a document that represents the best of the CRIRSCO-style codes; reporting standards that are rapidly becoming recognised and adopted world-wide for market-related reporting and financial investment.
Other National Reporting Standards that are now in accordance with the principles of the CRIRSCO Template are Brazil, Chile, Europe, Kazakhstan, Mongolia, Russia and Indonesia. The SEC is currently preparing a code compliant with the CRIRSCO Code to replace their ancient Industry Guide 7 in the United States of America. Other countries progressing towards CRIRSCO Codes include India, China, Turkey and Argentina.
Getting back to how the use of reference materials has been mandated in law and as an example; in the JSE Listing Rules Section 12 for Mineral Companies, Clause 12.11.iv.3.hh, Exploration Companies – annual disclosure requirements, sample and assay laboratory quality assurance and quality control procedures [refer to (SAMREC Code) T3.4(i),3.5(iv) and 3.6(i)]. In the SAMREC Code Table 1, Section 3 Exploration & Drilling, Sampling Techniques and Data; applying to Exploration Results, Mineral Resources and Mineral Reserves; Clause 3.6.(i) requires: "demonstrate that adequate field sampling process verification techniques (QA/QC) have been applied, e.g. the level of duplicates, blanks, reference material standards, process audits, analysis, etc".
Compliance aside, laboratory QA/QC "Best Practice" is a whole another thing (refer to links).