George, You problem is similar to fluoration metal-reach samples. We use another path for fluorating refractory minerals. According to Ustiov (1991, patent from 1980) we adding to sample of mineral pure and dried KCl. The refractory minerals with KCL at the presence CLF3 (KBr for BrF5) gives an eutectically liquid and extraction of oxygen are 100 %. My comments to this method: we take about 10-15 % KCl (KBr) from a sample mass and grinding to powder under CCl4 (no alcohol). The ammount of ClF3 (BrF5) must be taken accordingly the KCl (KBr) presence and we take the amount of ClF3 multiplied to 2-3 times, as for reaction needs. The Ni-vessels we heat up to 700 C. After that all must be OK. And at the end. We found about 7 years ago that the Ni-vessel size are important. We use a long cylindrical fingers with small inner diameter. We heat only end of fingers, but the upper part of fingers are upon "cold" zone, created by cold water flow. The gas convection and mixind gives us a fast and complete reaction. 100-% yield we obtain after 30 minits of heating maximum. Best regards, Elena