bentonite mineral separations. overview rare crystals of sanidine and/or zircon are separated from a...
TRANSCRIPT
Overview
Rare crystals of sanidine and/or zircon are separated from a clay-rich matrix based on their density and magnetic properties
Aqueous separations
Crushing and sieving (as needed)
Magnetic separation
Heavy Liquids Separation
Hand picking
SEM verification
Crushing and sieving
• As needed, dry the sample in the oven, prior to crushing.• Most bentonites require milling, and some crushing
prior to milling. • Following crushing, sieve to 125 – 355 um and
begin work on this size fraction, unless larger crystals are observed• Do not discard any material.
Aqueous separations
• Clay minerals often adhere to the minerals of interest and must be removed. • Washing at the sink is sufficient for some samples
while the additional agitation of the gold table is required for others. • For very clay-rich samples, washing in sodium
hexametaphosphate is needed to disaggregate and remove the clay minerals.
Magnetic separations• Sanidine and zircon possess a low magnetic
susceptibility. • Highly magnetic material is first separated with a
hand magnet• The Frantz separator concentrates the low
susceptibility fraction
Heavy liquids separations
• Density:• Sanidine: 2.55 – 2.62 g/cm3
• Zircon: 4.6 – 4.7 g/cm3
• Zircon is separated using undiluted Methylene Iodide (MI; density 3.32)• Sanidine is separated by two passes in diluted MI at
densities 2.55 and 2.62 g/cm3
Picking
• Picking under reflected light is typically sufficient• For especially small zircon,
picking under cross-polarized transmitted light can be helpful.