Spectrographic Determination of Selenium in Stibnite

Stibnite, Sb2S3, is present in low-temperature ore deposits of many genetic types. It occurs as the principal ore mineral in most antimony deposits, which contain only small amounts of other metals. The mineral is associated with arsenic, mercury, and thallium sulfides in Carlin-type gold deposits in which stibnite contains as much as 15 mol percent As2S3. Preliminary studies by routine spectrographic analysis indicate that stibnite contains several hundred micrograms per gram of such other elements as copper, lead, zinc, bismuth, cadmium, mercury, thallium, silver, tellurium, and selenium. These elements, especially selenium, volatilize from the arc so rapidly that it becomes extremely difficult for the optical system to detect and record their emission spectra. Therefore, we have developed a new set of analytical conditions that optimize the determination of these volatile elements. We report here on a quantitative spectrographic method suitable for the determination of selenium in a few milligrams of stibnite and applicable in evaluating the compositional variations of selenium in stibnite over a wide range of sample sizes and concentrations.