Trace and minor elements in sphalerite from metamorphosed sulphide deposits

Abstract

Sphalerite is a common sulphide and is the domi- nant ore mineral in Zn-Pb sulphide deposits. Precise determi- nation of minor and trace element concentrations in sulphides, including sphalerite, by Laser-Ablation Inductively-Coupled- Plasma Mass-Spectrometry (LA-ICP-MS) is a potentially valuable petrogenetic tool. In this study, LA-ICP-MS is used to analyse 19 sphalerite samples from metamorphosed, sphalerite-bearing volcanic-associated and sedimentary exhalative massive sulphide deposits in Norway and Austra- lia. The distributions of Mn, Fe, Co, Cu, Ga, Se, Ag, Cd, In, Sn,Sb,Hg, Tl, Pb and Bi are addressed withemphasisonhow concentrations of these elements vary with metamorphic grade of the deposit and the extent of sulphide recrystalliza- tion. Results show that the concentrations of a group of trace elements which are believed to be present in sphalerite as micro- to nano-scale inclusions (Pb, Bi, and to some degree Cu and Ag) diminish with increasing metamorphic grade. This is interpreted as due to release of these elements during sphalerite recrystallization and subsequent remobilization to form discrete minerals elsewhere. The concentrations of lattice-bound elements (Mn, Fe, Cd, In and Hg) show no correlation with metamorphic grade. Primary metal sources, physico-chemical conditions during initial deposition, and element partitioning between sphalerite and co-existing sul- phides are dominant in defining the concentrations of these elements and they appear to be readily re-incorporated into recrystallized sphalerite, offering potential insights into ore genesis. Giventhat sphalerite accommodates a variety of trace elements that can be precisely determined by contemporary microanalytical techniques, the mineral has considerable po- tential as a geothermometer, providing that element partitioning between sphalerite and coexisting minerals (gale- na, chalcopyrite etc.) can be quantified in samples for which the crystallization temperature can be independently