Lattice location of gold in natural pyrite crystals

The lattice location of gold atoms in naturally occurring Au-doped pyrite c rystals has been investigated with a nuclear microprobe using ion channelin g. The specimens consisted of 300-mu m diameter pyrite crystals in veins em bedded in a quartz matrix from the Emperor mine in Fiji. The specimens were prepared by standard geological specimen preparation techniques and the py rite crystals were analysed in situ in the quartz matrix. Significant trace elements in the crystals, determined by Proton Induced X-ray Emission with a 3 MeV H+ microprobe, were Cu, As, Mo, Zn, Te, Au and Pb. The Au concentr ation was about 0.2 wt%. By the use of 2 MeV He+ ion channeling, the Miller indices of the lowest order crystal axes nearest to the normal were determ ined from backscattering yield maps from two-dimensional angular scanning a nd comparison of the resulting patterns with published gnomonic projections . Channeling angular yield curves were obtained from Fe, S, As and Au signa ls. The results indicate that at least 35% of the Au is substituted onto la ttice sites. (C) 1999 Elsevier Science B.V. All rights reserved.