Inhomogeneous Distribution of REE and Initial Nd Isotopic Compositions in Scheelite Crystals from an Archaean Gold Deposit (Mt Charlotte, Western Australia)

Abstract

Scheelite (CaWO4) is a widespread accessory mineral in mesothermal Au deposits of various ages. Scheelite can host relatively large amounts of Sr and R E E (up to > 1 wt.% REE), and has been used to date mineralisation, and to constrain the nature and origin of the ore-forming fluids (Anglin et al., 1996; Eichhorn et al., 1997; Kent et al., 1996; Mfiller et al., 1991). The Archaean Yilgarn Craton (Western Australia) consists of large volumes of felsic basement supporting relatively thin (< 8 km) greenstone belts. Many large Au deposits were formed in the greenstone belts of the Eastern Goldfields Province during a major crustal scale mineralising event at around 2.63 Ga. The Mt Charlotte deposit is a large quartz stockwork embedded in a differentiated gabbroic sill (locally known as 'Golden Mile Dolerite') within the Norseman-Wiluna greenstone belt, and is spatially associated with the giant shearhosted Golden Mile deposit (Clout et al., 1990). Previous Sm-Nd isotopic studies on scheelite from Mt Charlotte (Kent et al., 1996) have revealed large variations in R E E concentrations and in 1478m/144Nd ratios (~ 0.2 to 0.4). The Sm-Nd data define an errorchron at 2772 +_ 86 Ma, older than the mineralising event (2.63 Ga). We present in situ trace element data obtained by UV laser ablation high-resolution inductivelycoupled plasma mass-spectrometry (LA-HR-ICPMS, using a Merchantek LUV266 laser microprobe and a Finnigan MAT E L E M E N T ) on scheelite from Mt Charlotte, with the aim to decipher the nature of the inhomogeneous distribution of R E E in scheelite. The morphology of the R E E zoning in scheelite was VIEPS, Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia