Trace elements (Whole rock) : ICP-Q-MS

The sample powders were dissolved using an HF/HNO3 (1:1) mixture in screwtop Teflon beakers for ~2 hours at ~100 8C, followed by evaporation to dryness, then refluxing in 7N HNO3 for N12h at ~ 100 ℃ and, finally, diluting the sample solution by 2% HNO3. An internal standard solution of 5 ppb Rh and Bi was added and the spiked solution was diluted with 2% HNO3 to a sample/solution weight ratio of 1:2000. An internal standard was used for monitoring the signal shift during inductively coupled plasma-mass spectrometry (ICP-MS) measurements using Agilent 7500s spectrometer; which shows a good stability range with ~10% variation. The precision was generally better than F5% (2σ) for most trace elements, as shown by the statistics of duplicate analyses on five rock standards AGV-1, AGV-2, GSP-1, JB-1 and JG-1 (Table A).