MECHANICAL AND CHEMICAL DISSOLUTION METHODS VERSUS SELECTIVE FRAGMENTATION FOR MINERAL AND FOSSIL SEPARATION AND CONCENTRATES FROM SELECT GEOLOGIC MATERIALS

Historically, the first steps in mineral and fossil comminution/separation in rocks have involved mechanical force (crushing and grinding) or chemical dissolution. Selective fragmentation is a technology that uses high voltage pulse power fragmentation in an insulating medium (water) to progressively break materials along grain boundaries. Some advantages of selective fragmentation include low dust production, fewer fractured grains, coarser mineral separates, and no hazardous chemical exposure or waste. This study attempts to determine qualitative differences between selective fragmentation and traditional comminution practices in a variety of samples that represent commonly processed rocks at the USGS.

Selective fragmentation of geologic materials was performed on samples including granodiorite, quartz pebble conglomerate, amphibolite, ash flow tuff, and fossiliferous carbonate. Minerals and fossils of interest include zircon (igneous and detrital grains), apatite, amphibole, monazite, titanite, sanidine, and conodont tests. Each sample has corresponding splits reduced by traditional methods (jaw crusher and vertical grinder or acid-buffer dissolution for carbonates). Both the selective fragmentation splits and traditional splits were further processed for mineral and fossil concentrations of interest by using magnetic separation and heavy liquids. Splits of selective fragmentation and traditionally reduced methods were examined visually by binocular scope and in more detail by electron microscopy. Some initial observations for selective fragmentation include rapid comminution (<10 minutes/sample), more composite grains, more fully intact grains, and less fine-grained material (e.g. dust). Traditional sample reduction methods observations include, heavy dust generation, many fractured grains of interest, but few composite grains. Buffered acetic acid digestion of carbonate rocks yields almost complete recovery of conodonts and other residue that can typically be concentrated in magnetic and heavy liquid separation splits relatively easily. The separation of condont by selective fragmentation requires large efforts in post-processing methods including large sample throughput in magnetic separation and heavy liquid separation.