Continental flood basalts (CFB) in the Karoo large igneous province have been divided into the North and South Karoo groups. Picrites from the Luenha river, Mozambique, have been shown to represent the primitive mantle-like end-member required to explain the geochemical characteristics of the North Karoo CFBs, which have elevated ΔNb compared to the South Karoo CFBs. These picrites exhibit a narrow range of bulk-rock Nd isotope compositions (εNd180Ma -2.0 to +1.4) but a wide range of bulk-rock, plagioclase and groundmass Sr isotope compositions (full range 87Sr/86Sr180Ma 0.704096-0.71061), extending to high values suggestive of crustal contamination in the origin of these rocks. Despite this, preliminary O isotope data for olivine from one sample with elevated 87Sr/86Sr show uniform, mantle-like δ18O values (4.68±0.38‰ to 5.53±0.37‰). New O isotope data to be acquired in November 2019 on the NordSIM Cameca IMS 1280 ion microprobe will determine the O isotope composition of a sample inferred to most closely represent the parental magma as well as test the intra- and inter-sample O-isotopic variability of these picrites. Combined with the available bulk-rock and plagioclase phenocryst compositions, these data allow us to constrain the progress of crustal contamination and evaluate the homogeneity of the parental magmas. Most importantly, we aim to distinguish between the effects upon the samples of crustal contamination versus mantle source heterogeneity.