DETERMINATION OF TRACE ELEMENTAL SIGNATURES IN PLACER GOLD BY LASER-ABLATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY AS A POTENTIAL AID FOR GOLD EXPLORATION

It is possible that placer gold retains the trace element composition ('signature') of the pal ent lode. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) offers sensitive detection limits of 59 elements with sub-millimetre sample spot sizes, ideal for signa ture analysis of placer. Here, the optimum laser parameters, analytica l precision and reproducibility of elemental signatures are determined in placer nuggets by infrared LA-ICP-MS. The highest precision was of fered by Q-switched ablation at a relatively low energy level; using A u as an internal standard; these parameters gave median precision valu es of 33-82% RSD for trace elements in nuggets. In addition to major c onstituents such as Ag, Cu and Hg, placer from several rivers world-wi de commonly contained a wide range of trace elements including, in som e cases, unusual REE patterns. At least two distinct signatures could be distinguished in placer fi om most of the rivers examined, while mu ltiple examples of certain signatures were also seen. Tracking these s ignatures back to their original tributaries may offer a means of iden tifying the number and approximate location of deposits within a river watershed, thereby significantly aiding exploration. (C) 1998 Elsevie r Science B.V.