Volcanological Controls on the Localization of the Komatiite-Hosted Ni-Cu-(PGE) Coronet Deposit, Kambalda, Western Australia

Abstract

Coronet is a small komatiite-hosted Ni-Cu-(PGE) ore deposit within the northwestern part of the Kambalda dome. Coronet is unusual in that it is concealed beneath a faulted wedge of Lunnon Basalt, which also forms the footwall of the deposit. The orebody consists of four major ore surfaces, Coronet South, Coronet North, and two hanging-wall ore surfaces, SO1H and SO2H. The orientation of the two hanging-wall ore surfaces is oblique to the trend of Coronet North. The SO1H is the main mineralized ore shoot and is spatially associated with the base of the second flow unit. The mineralization is predominantly interspinifex in nature. The SO2H surface follows a similar trend to the SO1H and is inferred to represent the continuation of the SO1H. The SO2H ore is unusual in that the footwall is sedimentary. The orebody is locally hosted by shallow intrusive units, which are inferred to represent dense flows that burrowed into the wet, unconsolidated, sedimentary substrate. Adjacent to the Coronet ore shoot is the smaller McCloy ore shoot, which has a sedimentary footwall. The sedimentary units thin toward the ore shoot suggesting incomplete erosion by the ore-hosting flows. The contrast in distribution of sedimentary units at Coronet and McCloy illustrates the role of synemplacement erosion as a primary control on the distribution of the sedimentary units. The distribution of sedimentary units, the nature of the contacts with the komatiite flows, the abundance and distribution of vesicles in the flows, and the trend of primary volcanic facies at Coronet are consistent with the emplacement of komatiite lavas by early open channel flow followed by a transition to laminar emplacement.