Disseminated and Massive Nickel Sulphide deposits, Honeymoon Well Complex, Western Australia

Martin Gole, and Michael Woodhouse

Both disseminated and massive Ni sulphide mineralisation is hosted in a variety of komatiitic rocks within the Honeymoon Well ultramafic complex, located in the northern part of the 2700 Myr old Agnew-Wiluna greenstone belt, Western Australia. The ultramafic complex, extending over a 10 x 2 km area, is a structurally thickened part of the Mt Keith Ultramafic Sequence. This sequence hosts the nickel deposits at Perseverance, Yakabindie and MT Keith. The Honeymoon Well sulphide resource is 155.5 MT at 0.71% Ni (includes 2.5 MT at 3.36% Ni) in one massive and three disseminated sulphide deposits. Despite greenschist facies metamorphism and several episodes of deformation igneous textures are widely preserved in the ultramafic rocks.

The host rocks of the disseminated deposits are totally serpentinised olivine accumulate, mesocumulate and minor orthocumulate. Sulphide assemblages are dominated by pentlandite and heazlewoodite and occur in modified magmatic-textured lobate to blebby aggregates interstitial to former olivine grains. The massive sulphide deposit consists of massive sulphide, massive sulphide breccia and matrix sulphide hosted in a sequence of spinifex-textured thin komatiite flows. These sulphides have significantly lower Ni/S ratio than the disseminated sulphides reflecting an Fe-rich sulphide assemblage of pyrrhotite - pentlandite - pyrite - chalcopyrite. All the Ni sulphide deposits are thought to have been originally part of a single mineralised horizon with lateral variations in physical volcanology leading to the formation of komatiite sequences ranging from those dominated by olivine mesocumulate - adcumulate to those dominated by spinifex-textured thin flows. Subsequent stratigraphic stacking within a D1 thrust duplex and D2 folding and strike slip shearing has significantly displaced two of the deposits from their original stratigraphic position. Late As-bearing carbonate fluids have affected parts of the sulphide deposits.