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Barite removal from heavy mineral separates

Barite is an occasional voluminous component of the non-magnetic heavy mineral fraction of altered volcanic tuffs and sandstones, and can swamp out the target zircon population.  Unfortunately barite is remarkably immune to dissolution in strong mineral acids. To quantitatively remove this barite, we have modified the method described by Breit et al. (Chemical Geology, 52:333-336, 1985) for barite dissolution via anion replacement in the presence of high concentrations of aqueous sodium carbonate, followed by dissolution of the product barium carbonate in dilute HCl. Our modifications include: a) treatment of the heavy mineral separate AFTER annealing in a 900°C muffle furnace for 48 hours; b) treatment of the heavy mineral separate without any grinding; c) scaling up of the volumes of reagent, maintaining a ~10:1 ratio of sodium carbonate:barite in an aqueous solution of approximately 25 ml within a 30 ml Savillex PFA vial; d) increasing the temperature of reaction to 180°C in a 125 ml Parr dissolution vessel; and d) applying sequential treatments to remove large amounts of coarse barite. We have found that each treatment cycle can dissolve approximately 2 grams of coarse bladed barite, with no ill-effects on the zircon crystals, and your patience is rewarded with a barite-free zircon separate!