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The laser microprobe has been applied to the excitation of trace elements homogeneously distributed in powdered materials. Precision of intensity ratios is about ±11% (coefficient of variation), and detection levels are comparable to those of the dc arc. Matrix effects were studied for four different materials and found to be significantly less than in the dc arc. Use of the probe as the source in a “universal” method is suggested.

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Two new rapid and accurate methods are presented for determining mercury in low-grade ores and tailings: (1) A combustion–atomic absorption technique is described wherein a small sample of finely pulverized ore is heated to about 700°C, and the vaporized Hg is detected by atomic absorption. This method is suitable for determining Hg in the 0.1–5.0 lb/ton range, and the precision is about 5% coefficient of variation; (2) an x-ray fluorescence method is described wherein the unweighed, finely ground sample is merely packed into a holder, and the Hg line-to-background ratio is obtained. The problem of matrix effects is avoided by preparing standards to simulate the type of ore being analyzed. The method is suitable for determining Hg over a wide concentration range, with a lower limit of about 0.1 lb/ton. The precision, based on the analysis of a 2.0 lb/ton Hg ore, is about 5% coefficient of variation. These two techniques are compared to the commonly used Whitton and Bureau of Mines methods.