New Mexico Geological Society Annual Spring Meeting — Abstracts

The use of heavy liquids for mineral separations into light and heavy fractions is important if mineralogic studies are to be undertaken, especially with respect to volumetrically minor phases. Applications for this technique include: heavy minerals radiometric dating (i.e. zircon, amphiboles, biotite), geochemical analyses of a particular heavy mineral (i.e. rare earth element studies; apatite, sphene, garnet, etc.), and in the cases discussed here, polished sections of heavy separates for ore microscopy.

The procedure begins with a crushed (100% < 10 mesh), labeled sample from a surface, drill hole, underground mine or soil material. Well-blended samples are split into aliquots of 40 to 60 grams: samples are placed into a centrifuge bottle with sodium metatungstate liquid, having a density of approximately 2.85, and shaken. Centrifugation at 1000 rpm for ten minutes yields a well-developed separation of "heavies" with a density of greater than 2.85, and "lights". Liquid nitrogen is used to freeze the heavy fraction in the bottom of the bottle, allowing the lights to be poured off with the tungstate liquid. The heavies are then allowed to thaw, rinsed with a warm dilute tungstate liquid, and poured off into a separate filter. The lights and heavies are rinsed with distilled water to free the sample of the very soluble, non-toxic sodium metatungstate liquid. This procedure permits the reuse of expensive tungstate liquid. The light fraction is stored or studied as needed: the heavy fraction is dried and cast in cold-setting epoxy. Samples are polished using tungsten carbide and diamond abrasives. Polished samples are studied using ore petrographic techniques, reflected light microscopy, XRD, SEM, and microprobe methods to determine supergene to hypogene mineral ratios, quantitative mineralogy, and ore-gangue mineralogy.