2014 GSA Annual Meeting in Vancouver, British Columbia (1922 October 2014)
Paper No. 127-6
Presentation Time: 9:00 AM-6:30 PM


EDWARDS, Ashley1, MATTINSON, Chris G.2, and FAGIN, Brittany1, (1) Department of Geological Sciences, Central Washington University, 400 E. University Way, Ellensburg, WA 98926, ashleyedwardsgeo@gmail.com, (2) Geological Sciences, Central Washington University, 400 E University Way, Ellensburg, WA 98926-7418

Mineral separations concentrate the minerals zircon and apatite necessary for geochronology; three processing methods before magnetic and density (LST, MEI) separation were tested: a control hand-washed sample, samples processed with a spiral panning table, and a sample processed with a Gemini Table. Laser diffractometry determined the grain size distribution of processed samples. The test sample was a hbl-bt tonalite from Mount Stuart, WA; expected yields per kg, from a CIPW-norm: 300 mg zircon; 3200 mg apatite. After sieving to <500 μm, the raw crushed sample contained 2% of grains <20 μm, 13% <125 μm, and 30% <250 μm. The hand-washed control sample recovered the most zircon and apatite (72 mg zircon and 333 mg apatite, considered the maximum yield); LST lights contained 0.02% of grains <20 μm, 12% <125 μm. Panner #1 (58 g/min feed-rate, 9 rpm rotation) recovered 3.7 mg zircon and 1.0 mg apatite from 5.2 g of panner-heavies; panner lights contained 0.5% of grains <20 μm, 15% <125 μm. Panner #5 (36 g/min, 25 rpm) recovered 13.2 mg zircon and 13.0 mg apatite from 34 g of panner heavies; panner lights contained 0.2% of grains <20 μm, 12% <125 μm grains. LST lights from a set of panner heavies contained 0% of grains <20 μm, 0.2% <125 μm. Faster panner rotation increased yield by concentrating more heavies. The Gemini table recovered 330 mg of zircon + apatite (zircon not yet separated from apatite) from 45 g of heavies; Gemini lights contained 0% of grains <20 μm, 4% <125 μm. Yield differences of the techniques are mainly explained by grain size. In thin section, most zircon and apatite are <125 μm, and ~30% of zircons are <20 μm; the control process most efficiently recovered small grains explaining its higher yield. Using magnetic minerals as a proxy for heavies (mostly hornblende) shows that the Gemini heavies (61% <250 μm, of which 72% were magnetic) more efficiently concentrated small grains than the panner (#5 heavies had 16% <250 μm, of which 59% were magnetic). However, the panner concentrated zircon relative to apatite 4-5X more than the control. Even the best yield (control) recovered only 12% of the zircon + apatite expected from the CIPW norm, probably due to loss of zircon + apatite as inclusions in other minerals. In thin section, ~25% of zircons were inclusions in magnetic minerals, and therefore would be lost during magnetic separation.

2014 GSA Annual Meeting in Vancouver, British Columbia (1922 October 2014)
General Information for this Meeting
Session No. 127--Booth# 167
Mineralogy/Crystallography (Posters)
Vancouver Convention Centre-West: Exhibition Hall C
9:00 AM-6:30 PM, Monday, 20 October 2014

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