LOOKING FOR GRAINS IN ALL THE WRONG PLACES: IMPROVING ZIRCON SEPARATION TECHNIQUES IN BASALTS AND THEIR METAMORPHIC EQUIVALENTS

The value of zircon in geochronology and trace element studies has proven invaluable across a variety of geologic settings. While heavy mineral separation techniques are commonly successful in recovering zircon from silicic igneous rocks and detrital sedimentary rocks, recovering zircon from rocks with generally low zircon concentrations (e.g., basalt and amphibolite) can prove frustrating. As such, many laboratories expend little effort in attempting to extract zircon from these “low yield” rocks. Over the past several years, attempts to improve mineral separation techniques at Columbus State University have significantly improved our ability to recover zircon in appreciable amounts from mafic and meta-mafic rocks that have yielded no zircon from previous attempts. Success in recovering significant populations of zircon from the Marble Hill Hornblende Schist, Mitchell Dam Amphibolite, and a variety of basalts from the southwestern U.S. have proven promising for the determination of the primary crystallization ages in rocks that have previously yielded little or no meaningful geochronological data. The slow feed rate provided by a custom, 3D printed granular feeder allows for large sample sizes to be processed easily on our Gemini style shake table. In this project, we outline effective strategies for zircon recovery from mafic and meta-mafic rocks. In addition, we compare the geochemical properties of mafic and meta-mafic samples with zircon recovery rates in an attempt to identify geochemical proxies for zircon potential. We also attempt to compare the effectiveness of our in-house techniques with similar processes on a standard Wilfley table. It is our hope that this comparison will reveal differences in zircon recovery rates between table designs and provide valuable insight into the best methods for "low loss” zircon recovery.