A cryogenic density separation technique for conodont and heavy mineral separations

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Procedures for the use of the nontoxic sodium polytungstate for heavy mineral separations in the study of conodonts or heavy minerals have been described by Callahan (1987), Krukowski (1988), and Savage (1988). These procedures are rapidly being adapted in industrial and university laboratories because they are easy to apply, provide excellent results, and avoid the potential toxicity of most heavy mineral separation mediums. However, the settling time required for most described techniques using sodium polytungstate solution (sp. gr. 1.0-3.1 gcm-³) is considerable and most of the fluid is not immediately reusable. Thus, large quantities of this expensive fluid are required to process multiple samples. Merrill (1987) described the cryogenic density separation of conodonts, noting the rapidity of the technique. The purpose of this paper is to describe modifications of the cryogenic technique. These modifications allow immediate reuse of unwashed portions (80-95 percent per sample) of the heavy medium (thus requiring smaller amounts of the heavy fluid) and increase the rapidity of the technique, especially when separating larger samples (7-25 g).