ISOLATING ZIRCON FROM MAFIC ROCKS: DEVELOPMENT OF A PROGRAMMABLE, OPEN-SOURCE GRANULAR FEEDER FOR ISOLATING HEAVY MINERALS IN SILICA POOR ROCKS

The isolation of zircon, baddeleyite or monazite for geochronological studies (e.g. U-Pb dating), generally necessitates a series of steps that include hydraulic sorting, magnetic separation, and heavy liquid separation prior to hand picking and mounting grains. Silicic rocks (e.g. granitoids) are among the most common rocks used in geochronological studies due to a higher likelihood that they contain a substantial amount of zircon. However, in many geologic settings low silica (e.g. mafic) rocks dominate the igneous record, and therefore have the potential to provide a greater range of information than their silicic counterparts. Due to the zircon poor nature of mafic rocks, a more efficient method is essential to reduce loss of uncommon zircon grains in samples of this type, especially during hydraulic separation (e.g. water shake table). We find that a slow granular feed method (e.g. ~40 ml/hr) can significantly improve zircon recovery during hydraulic sorting. Initially this was accomplished by feeding the sample at the desired rate by hand, which required constant monitoring of the process. With the larger sample volumes (e.g.>1000cm3) often required for silica poor rocks, hand feeding of the sample can be tedious and time consuming. As such, a small volume, automated granular feeding system is ideal for the hydraulic sorting process, but can be cost prohibitive ($5-$15k). However, the widespread adoption of additive manufacturing has placed the means of producing a simple, low-cost alternative within reach of even small labs with limited budgets. Here, we provide an open source design for a 3D printed, variable rate, vibratory feeder that automatically supplies powdered samples onto a hydraulic separation apparatus. We find this variable rate, low cost feeder (<$150), when coupled with a UV light for zircon identification, especially useful for processing low silica rocks that require a slower feed rate and large sample volumes. Using this feeder in combination with common mineral isolation techniques, we have been able to significantly improve zircon recovery in the metamafic Marble Hill Hornblende Schist as proof of concept of its effectiveness.