The Diamond-Bearing Ultrapotassic (Lamproitic) Rocks of the West Kimberley Region, Western Australia

Two age populations of zircons from the Timber Creek kimberlites, Northern Territory, as determined by laser-ablation ICP-MS analysis

“…The Argyle lamproite pipe, a significant diamond producer that occurs off-craton in the Halls Creek Mobile Belt, has been dated at ca 1200 Ma(Jaques et al 1986). The youngest known bodies are Miocene lamproites in the west Kimberley region(Atkinson et al 1990;Jaques et al 1984). These bodies, some diamondbearing, are predominantly pipes that have undergone little erosion.…”

Re–Os isotopic composition of peridotitic sulphide inclusions in diamonds from Ellendale, Australia: Age constraints on Kimberley cratonic lithosphere

“…Graham et al (1999) indicate that the Os isotopic composition of the Argyle lherzolites and lamproite is influenced by a $1500 Ma enriched-mantle component (represented by a picroilmenite megacryst from the Maude Creek kimberlite on the eastern Kimberley craton, with initial c Os = +27). Additionally, the West Kimberley lamproites have Ti-rich phlogopite, diopside and richterite compositions, with LREE-and LILE-enriched trace element compositions (Jaques et al, 1984). Along with high 87 Sr/ 86 Sr (0.711-0.720) and unradiogenic Nd isotopic ratios (e Nd = À7 to À15) (McCulloch et al, 1983;Jaques et al, 1984), these indicate derivation of the West Kimberley lamproites from a peridotitic source that had experienced long-term enrichment by metasomatism, with addition of incompatible element-enriched fluid phases to depleted mantle.…”

“…Additionally, the West Kimberley lamproites have Ti-rich phlogopite, diopside and richterite compositions, with LREE-and LILE-enriched trace element compositions (Jaques et al, 1984). Along with high 87 Sr/ 86 Sr (0.711-0.720) and unradiogenic Nd isotopic ratios (e Nd = À7 to À15) (McCulloch et al, 1983;Jaques et al, 1984), these indicate derivation of the West Kimberley lamproites from a peridotitic source that had experienced long-term enrichment by metasomatism, with addition of incompatible element-enriched fluid phases to depleted mantle. Jaques et al (1989) reported unusually Fe-rich olivine and Ti-garnet diamond inclusions at Ellendale, which likely represent a metasomatised rather than depleted lithospheric mantle source.…”

Reconsideration of ‘soda-minettes’

“…These rocks are among the most potassic of basic igneous rocks as defined by whole-rock atomic K/Na (or molecular K20/Na20): this ratio ranges up to 45 (see, e.g. Jaques et al, 1984;Bergman, 1985), although it averages 6.5 and can be lower than 1.5. No one has proposed--and surely no one would propose, except in jest--labelling as 'sodalamproites' such potassic to ultrapotassic rocks, which are dominated by K-rich minerals, merely because their groundmass includes a sodic amphibole.…”