GSA Connects 2021 in Portland, Oregon

Paper No. 118-3
Presentation Time: 2:30 PM-6:30 PM


ACOB, Erliana1, NARANJO, Alexis1, MARSHALL, Collin E.2 and MATTINSON, Chris G.3, (1)Geology, Central Washington University, 400 E University Way, Ellensburg, WA 98926, (2)Geological Sciences, Central Washington University, 400 E University Way, MS 7418, Ellensburg, WA 98926, (3)Geological Sciences, Central Washington University, 400 E University Way, Ellensburg, WA 98926

Mineral separation techniques are designed to concentrate the heavy minerals within a sample so age determination is possible. The Jasper Canyon Research (JCR) concentrating table is a benchtop-sized device that utilizes various tilts, vibration settings and water flow rates to better separate dense minerals, such as zircon, from a bulk sample. Dense minerals are trapped in the grooved, vibrating table, and water carries away lower-density minerals. 6 trials were performed using 1 kg samples of a tonalite from Mt. Stuart, WA, and included testing variables such as the table tilt angle, water flow rate, vibration rate, reconcentration, and volume reduction. Initial tests used a feed rate of ~0.5-0.6 kg/hr, a starting table tilt of 7°, and a medium vibration rate. After the sample finishes feeding onto the table, the tilt angle is gradually increased to 12° to reduce the volume, leaving 300-1000 mg of heavy minerals trapped in each of the 11 table grooves. Zircon is primarily concentrated in the first 4 grooves, and can be further concentrated in the first groove by emptying the grooves after the sample finishes feeding, and then re-running the groove contents. Our tests show that starting with a shallower table tilt angle of 6° results in a visibly larger yield of zircon grains. The test that had an especially large zircon yield within the first few table grooves involved a higher initial vibration setting along with the shallow tilt table angle. The higher vibration rate caused heavy minerals to spread out across the grooves. During the volume reduction process of this test, the vibration setting was lowered, causing the heavy minerals to concentrate more towards the center of the grooves, further reducing the volume. Zircon is concentrated well enough that magnetic separation and hand-picking are sufficient to prepare samples for geochronology, without the use of heavy liquids. A shortwave UV light proves to be conducive to monitoring zircon concentration effectiveness while samples are being processed on the concentrating table. Whole-rock geochemistry will be used to determine the theoretical zircon yield in terms of weight %, and XRD analysis on the concentrates from all trials will aid in determining actual yield (resulting in concentration and yield efficiency measurements).