The preparation and characterisation of four chromium ore reference materials are described in this paper. The sample material for GCr‐1, GCr‐3 and GCr‐4 was collected from chromite deposits in Tibet, Qinghai province and Inner Mongolia. GCr‐2 is a composite sample from GCr‐1 and GCr‐4. Sample homogeneity was tested by WD‐XRF and the relative standard deviations were < 1.0%. An F‐test showed that all four materials were homogeneous. Thirteen laboratories involved in the inter‐laboratory programme provided 672 determinations (eighteen oxides and elements). Sixteen components were characterised as certified values, of which Cr2O3 ranged from 17.59 to 57.80% m/m. The contents of FeO and CO2 were taken as reference values.

The preparation and characterisation of three nickel ores and two nickel concentrate certified reference materials are described in this paper. The samples of nickel ore and nickel concentrate were collected from the Hongqiling nickel deposit in Jilin province. The raw materials were crushed and passed through a 2.0-mm sieve. The rough samples were then ground for 48 hr in a high-alumina ball mill to a final size of < 0.074 mm. Homogeneity of the samples was tested by X-ray fluorescence spectrometry (WD-XRF) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The relative standard deviations (RSD) of results on mass fraction measurements by WD-XRF were < 1.0% m/m for eighteen components. F-tests showed that all five samples were homogeneous.Nineteen laboratories contributed with measurement results (2127 in total) for the certification of mass fractions for twenty-three elements and compounds. Twenty-three components in the nickel ores and twenty components in the nickel concentrates were characterised as certified values, while the Ni mass fractions ranges from 0.1 to 9.02% m/m in these certified reference materials. These five samples were approved as national certified reference materials by the National Organisation of Reference Materials of China in 2012.Certified ore reference materials are very important in the chemical analysis and quality control of raw and final products in mineral exploration, mining and metallurgy. They are used for the calibration of different types of instruments, as well as for method validation in the determination of major and trace elements. Readily available nickel ore certified reference materials are limited in number. A nickel-copper-cobalt ore (SU-1b) with a Ni mass fraction of 1.953% m/m was prepared by CANMET (Mining and Mineral Sciences laboratory, Canada). A nickel sulfide ore reference material (OREAS 72

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This study describes the preparation and characterisation of certified reference materials of three molybdenum ores (GBW07141 to GBW07143, abbreviated to GMo‐1 to GMo‐3) and one molybdenum concentrate (GBW07144, abbreviated to GMo‐4). The source of these materials was molybdenum deposits in Luanchuan in Henan Province, China. Sample homogeneity was tested by WD‐XRF. All the relative standard deviations were < 3.0%, and F‐tests showed that all four materials were homogeneous. Thirteen laboratories participated in this interlaboratory programme, and to set the values, various reliable analytical methods based on different principles were adopted. Up to twenty‐six elements and compounds in the three molybdenum ores and eighteen components in the molybdenum concentrate were characterised as certified values. Owing to the wide spread of the data, only indicative values could be obtained for Ag and Re in GMo‐1 and for nine components in GMo‐4. The certified values and uncertainties for Mo of the three molybdenum ores and the molybdenum concentrate were, respectively, 0.066 ± 0.003, 0.15 ± 0.01, 0.54 ± 0.02 and 50.08 ± 0.14% m/m.