Abstract

Members of the Widgiemooltha dike suite in the Cowarna Rocks area of Western Australia include the 150 km long Celebration dike and a number of smaller dikes of magnesian tholeiitic basalt. The Celebration dike is zoned from olivine gabbro to quartz dolerite and has a contaminated cap of orthopyroxene dolerite and felsite. The magnesian basalts, some of which intrude the Celebration dike, are saturated to oversaturated in sulfur, and some of them contain from 20 to 80 percent sulfides as droplets and as massive segregations.The basalt dikes are undeformed and unmetamorphosed and crystallized rapidly from a sulfur-saturated silicate magma, or from a silicate-sulfide liquid mixture. Textures in these rocks, including inhomogeneities in the sulfide segregations, are attributed entirely to magmatic processes, or to postmagmetic cooling in a static environment. Similar textural features in other nickel deposits have been considered to be evidence for the action of nonmagmatic processes (e.g., metamorphism). The observations made in this paper indicate that such processes are not necessary for the formation of the textures described.

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