Sulfide evolution in komatiite-hosted nickel deposits

01.06.2018 bis 31.05.2020

There are two main questions to be answered in this project: 1) What processes are involved in the formation of komatiite-hosted sulfide deposits and 2) what are the sources of S for ore formation in the Kambalda deposits?
1. Processes that will be investigated include early stages of a komatiite lava flow, represented by emplacement mechanisms of the komatiite melt into the vent, and late stages, represented by mechanisms to form matrix ore.
Komatiite-magma emplacement into shallow levels in proximity to the eruption site are poorly understood. The komatiitic dykes recently intersected in Kambalda can help to identify and describe these processes. This study could also link the vent to one of the known lava flows higher in the stratigraphy.
To form matrix sulfides, the currently favoured adjusted "billiard-ball-model" of Usselmann et al. (1979) is unable to explain observed multiple layers of matrix ore. It is also in disagreement with the theory that the pinchout, where sulfides are bound by older rocks from beneath and above, forms due to an increased sulfide height from the matrix sulfide formation, and hence shows that the basal sulfide layer is not solidified at the same time. The hypothesis to be tested here is, that both matrix sulfide layers, observed in Moran, formed from two distinct mechanisms. The basal homogeneous matrix sulfide layer formed by olivine sinking into a sulfide melt pool as originally proposed, but by including variations of the sulfide melt pressure into the calculation. In contrast, the inhomogeneously layered matrix sulfide pile above could have formed by precipitation of olivine with a co-accumulation of sulfides in a dynamic lava flow system, forming sulfide-rich and sulfide-poor layers depending on the sulfide supply.
2. The source of sulfur for the Kamblada Ni deposits is probably the sediments which were eroded by the komatiite, but previous multiple S isotope studies could (due to poor sample coverage) neither prove nor disprove this hypothesis although it worked for other deposits. The second matrix ore layer formed when the lava channel was already established without sulfide-bearing sediments available, pointing to another source (like mantle or sedimentary components in older basalt). The available sample suite of pre-, early-, main-, and post-ore stages will allow to investigate samples with variable ‘R’ factors, which should be reflected in multiple S isotopes.
Both objectives investigate a komatiitic deposit type, but the research outcomes will be discussed in regards to their application to magmatic sulfide deposits in general.