A 1g aliquot is encapsulated in a polyethylene vial and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when sample material is available.
Reference: Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.
Total Digestion – ICP
A 0.25 g sample aliquot is digested with a mixture of HClO4, HNO3, HCl, and HF at 200 °C to fuming and is then diluted with aqua regia. This leach is partial for magnetite, chromite, barite and other spinels and potentially massive sulphides.
Major Elements by Fusion ICP-OES
Samples are prepared and analyzed in a batch system. Each batch contains a method reagent blank, certified reference material, and 17% replicates. Samples are mixed with a flux of lithium metaborate and lithium tetraborate and fused in an induction furnace. The molten melt is immediately poured into a solution of 5% nitric acid containing an internal standard, and mixed continuously until completely dissolved (~30 minutes). The samples are then run for major oxides and selected trace elements (Code 4B) on an ICP.
For the ICP analysis, reagent blanks with and without the lithium borate flux are analyzed, as well as the method reagent blank. Interference correction verification standards are analyzed. Calibration is performed using multiple USGS and CANMET certified reference materials. Two of the standards are used during the analysis for every group of ten samples. This standard brackets the group of samples. The sample solution is also spiked with internal standards and is further diluted and introduced into an ICP-MS using a proprietary sample introduction methodology. Calibration is performed using USGS and CANMET certified reference materials.
Trace Elements and Detection Limits (ppm)
Typical ICP Analysis of some USGS and Canmet Standards (%)