SEPARATION OF HEAVY MINERALS FROM MUDROCKS

The non-clay-mineral fraction of mudrocks is receiving increased atten tion. The heavy-mineral fraction in fine-grained rocks, however, has l argely been neglected, partially because of the difficulty in separati ng heavy minerals from the host mudrock. We propose a technique that w ill separate some heavy minerals from a clay matrix. This method was d eveloped initially by soil scientists for separating quartz and feldsp ar from clays, and later modified for mudrocks. The technique involves fusing the rocks with sodium bisulfate, making clay minerals soluble in basic solutions. We have tested this procedure on nine common heavy minerals: andradite, almandine, grossular, zircon, magnetite, schorl, apatite, rutile, and a gem variety of tourmaline. Each mineral was fu sed and the mass reduction and resultant chemical changes observed. Ph ysical grain alterations were examined by SEM and chemical changes ana lyzed by electron microprobe, almandine, grossular, and zircon survive d the fusion process in high percentages and showed little chemical ch ange, Andradite, although it showed small mass loss, was highly etched by the process. Schorl, gem tourmaline, magnetite, and rutile showed a high mass loss with some chemical change to the residue, Apatite was totally dissolved. The chemical resistance of several heavy-mineral s pecies makes this technique useful for provenance studies of mudrocks, especially when combined with chemical studies of heavy minerals.