MICROPROBE CHANNELING ANALYSIS OF PYRITE CRYSTALS

Nuclear microprobe analysis has provided much useful information about the composition of microscopic inclusions in minerals, mainly through the use of particle induced X-ray emission (PIXE). However, this technique, while powerful, does not provide any direct information about the chemical state, in particular the lattice location, of the elements in the mineral. This information is often of crucial importance in understanding the ore genesis. The technique of ion channeling may be used to identify lattice location, but many minerals occur as microscopic crystals. Therefore it is necessary to utilise a nuclear microprobe with the technique of channeling contrast microscopy (CCM). As many minerals contain interesting trace elements, it is necessary to measure both the yield of backscattered particles and the induced X-rays to get a clear picture of the lattice location of the elements in the crystal. CCM with PIXE was used to analyse natural pyrite crystals containing a variety of substitutional and nonsubstitutional elements and natural pyrite crystals from a gold bearing ore. In the latter case, evidence was obtained,for two habits for Au in the 400 mum crystals: one as inclusions of Au rich minerals, the other substituted on the pyrite lattice sites.