Structural controls on nickel sulphide ore shoots in Archaean komatiite, Kambalda, WA: the volcanic trough controversy revisited

Abstract

Structural evaluation of the extensive exploration database for the Kambalda–Tramways area (Archaean Yilgarn Craton, Western Australia) is addressing the long outstanding issue of whether the trough structure embayments that partly confine the nickel sulphide (NiS) ore shoots are volcanic or tectonic in origin. The trough structures are complex linear domains associated with talc–carbonate alteration overprinting thickened komatiite overlying footwall basalt. Two end-member trough structure types are recognised: (1) re-entrant trough structures, and (2) open trough structures. The re-entrant trough structures are narrower at the top than at the base, strongly asymmetric in cross-section, restricted in distribution to Kambalda Dome, and transgress and truncate ore. The open trough structures are wider at the top than at the base, weakly asymmetric in cross-section, prevalent outside Kambalda Dome, and are mineralised along their lateral margins. In addition to trough-associated ore, other NiS ore shoots overlie near-planar komatiite-basalt contacts and are overlain by serpentinite with relict igneous textures. All these features indicate the possibility that the trough structures reflect structural folding, thickening and alteration at rock contacts marking different competency during regional fold–thrusting. Consequently, NiS exploration strategies should consider structural and metamorphic features, as well as volcanologic and stratigraphic features. Recognition of folding and thrusting patterns related to major competency contrasts in favourable komatiite–basalt stratigraphy near the crest of regional anticlines and domes would aid exploration success.