Determination of trace elemental signatures in placer gold by laser ablation–inductively coupled plasma–mass spectrometry as a potential aid for gold exploration

Abstract

It is possible that placer gold retains the trace element composition (`signature') of the parent 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 signature analysis of placer. Here, the optimum laser parameters, analytical precision and reproducibility of elemental signatures are determined in placer nuggets by infrared LA–ICP–MS. The highest precision was offered by Q-switched ablation at a relatively low energy level, using Au as an internal standard; these parameters gave median precision values of 33–82% RSD for trace elements in nuggets. In addition to major constituents such as Ag, Cu and Hg, placer from several rivers world-wide commonly contained a wide range of trace elements including, in some cases, unusual REE patterns. At least two distinct signatures could be distinguished in placer from most of the rivers examined, while multiple examples of certain signatures were also seen. Tracking these signatures back to their original tributaries may offer a means of identifying the number and approximate location of deposits within a river watershed, thereby significantly aiding exploration.