A Special Issue (Part-II): Mafic-ultramafic rocks andalkaline-carbonatitic magmatism and associated hydrothermalmineralization - dedication to Lia Nikolaevna Kogarko

This is the second part of a two-volumespecial issueof Open Geoscience (formerly Central European Journalof Geosciences) that aims to be instrumental in providingan update of Mafic-Ultramafic Rocks and Alkaline-Carbonatitic Magmatism and Associated HydrothermalMineralization. Together, these two volumes provide a detailedand comprehensive coverage of the subjects thatare relevant to the research work of P.Comin-Chiaramonti(Italy) and LiaN. Kogarko (Russia) towhomPart-I and Part-II have been respectively dedicated.To a significant extent, the development of advanced samplingtechnologies related to alkaline and carbonatiticmagmatism by Lia N. Kogarko, has allowed geoscientiststo measure and sample the deep crust of the planet notonly for the exploration for the mineral deposits, but alsoto answer basic scientific questions about the origin andevolution of alkaline rocks (kimberlites, lamproites and relatedrocks associated with carbonatites). The papers presentedin this Part-II of the special issue cover the petrologyand geochemistry of the rocks collected from the surfaceand penetrated by drilling. Lia Kogarko proposed anew theory for the evolution of alkaline magmatism in thegeological history of the Earth – that the appearance of alkalinemagmatism at the Archaean-Proterozoic boundary(~2.5 – 2.7 Ga), and its growing intensity, was related tochanges in the geodynamic regime of the Earth and oxidationof the mantle due to mantle-crust interaction

Stable H–C–O isotope and trace element geochemistry of the Cummins Range Carbonatite Complex, Kimberley region, Western Australia: implications for hydrothermal REE mineralization, carbonatite evolution and mantle source regions

The Neoproterozoic Cummins Range Carbonatite Complex (CRCC) is situated in the southern Halls Creek Orogen adjacent to the Kimberley Craton in northern Western Australia. The CRCC is a composite, subvertical to vertical stock ∼2 km across with a rim of phlogopite–diopside clinopyroxenite surrounding a plug of calcite carbonatite and dolomite carbonatite dykes and veins that contain variable proportions of apatite–phlogopite–magnetite ± pyrochlore ± metasomatic Na–Ca amphiboles ± zircon. Early high-Sr calcite carbonatites (4,800–6,060 ppm Sr; La/YbCN = 31.6–41.5; δ13C = −4.2 to −4.0 ‰) possibly were derived from a carbonated silicate parental magma by fractional crystallization. Associated high-Sr dolomite carbonatites (4,090–6,310 ppm Sr; La/YbCN = 96.5–352) and a late-stage, narrow, high rare earth element (REE) dolomite carbonatite dyke (La/YbCN = 2756) define a shift in the C–O stable isotope data (δ18O = 7.5 to 12.6 ‰; δ13C = −4.2 to −2.2 ‰) from the primary carbonatite field that may have been produced by Rayleigh fractionation with magma crystallization and cooling or through crustal contamination via fluid infiltration. Past exploration has focussed primarily on the secondary monazite-(Ce)-rich REE and U mineralization in the oxidized zone overlying the carbonatite. However, high-grade primary hydrothermal REE mineralization also occurs in narrow (<1 m wide) shear-zone hosted lenses of apatite–monazite-(Ce) and foliated monazite-(Ce)–talc rocks (≤∼25.8 wt% total rare earth oxide (TREO); La/YbCN = 30,085), as well as in high-REE dolomite carbonatite dykes (3.43 wt% TREO), where calcite, parisite-(Ce) and synchysite-(Ce) replace monazite-(Ce) after apatite. Primary magmatic carbonatites were widely hydrothermally dolomitized to produce low-Sr dolomite carbonatite (38.5–282 ppm Sr; La/YbCN = 38.4–158.4; δ18O = 20.8 to 21.9 ‰; δ13C = −4.3 to −3.6 ‰) that contains weak REE mineralization in replacement textures, veins and coating vugs. The relatively high δD values (−54 to −34 ‰) of H2O derived from carbonatites from the CRCC indicate that the fluids associated with carbonate formation contained a significant amount of crustal component in accordance with the elevated δ13C values (∼−4 ‰). The high δD and δ13C signature of the carbonatites may have been produced by CO2–H2O metasomatism of the mantle source during Paleoproterozoic subduction beneath the eastern margin of the Kimberley Craton