The geology, geochemistry and mineralization of the South Windarra, nickel ore deposit, W.A.

Abstract

A geochemical and mineralogical study has been carried out on the South Windarra Archaean nickel deposit, W.A. Within the ultramafic pile a series of flows has been identified. Two mineralized ultramafics form the base of this sequence, while thinner barren flows, with typical spinifex textures, overlie. The two types of ultramafics are compared, with the intention of providing useful parameters for discriminating between barren and mineralized units. The comparison is made using data from field relationships, thin sections, polished sections together with geochemical analyses of whole rocks and trace elements (Ni, Cr, Zn, V, S). It is concluded that sulphides were concentrated at depth, as an immiscible liquid in an ultramafic magma, prior to extrusion. This ultramafic magma consisted of abundant olivine crystals forming a crystal mush viscous enough to hold an immiscible sulphide fraction. Barren units have higher Ca and lower Mg and are considered to have been less viscous due to a lower crystal content and differing composition. These were unable to sustain an immiscible sulphide fraction.