Geochemistry of post-1540 Ma granites in the Cloncurry district, northwestQueensland

Proterozoic Fe oxide Cu-Au-Co mineralization in the Cloncurry district is s patially and temporally related to intrusion of voluminous postpeak metamor phic granites that form most of the Williams and Naraku batholiths. Detaile d mapping and geochemical study of these granites in the southern part of t he district have identified two groups of intrusions that are referred to h ere as the Cloncurry Supersuite and Eureka Supersuite. The Cloncurry Supersuite is composed mainly of monzogranite and syenogranit e which consist of quartz, plagioclase, alkali feldspar, hornblende, biotit e with accessory magnetite, titanite, apatite, and zircon. The timing of in trusion of the Wiley Igneous Complex is interpreted to be pre- or syn-D-3, based on overprinting relationships, while hornblende geobarometry suggests an emplacement depth of approximately 14 km. The granites are subalkaline, high-g, metaluminous rocks and range from 59 to 74 wt percent SiO2. Increa sing SiO2 is accompanied by increasing K2O, Rb, and Th, and decreasing MgO, Fe2O3, FeO, TiO2, CaO, P2O5, Sr, Eu, Zr, Cu, Zn, Ni, V, and Sc. This is co nsistent with fractionation of observed phases including plagioclase, amphi bole, biotite, magnetite, titanite, and apatite. The Eureka Supersuite ranges from diorite to syenogranite in composition. M ore mafic varieties contain pyroxene and hornblende, while more felsic vari eties contain biotite as the only ferromagnesian silicate. Sodiccalcic alte ration events are closely linked in space and time to intrusion of Eureka S upersuite magmas. The timing of intrusion is interpreted to be pre- and pos t-D-3, based on overprinting relationships between different plutons and my lonitic fabrics. Hornblende geobarometry suggests an emplacement depth of a pproximately 10 lan for the Mount Angelay Igneous Complex. Eureka Supersuit e granites in the Mount Angelay Igneous Complex range from 51 to 76 wt perc ent SiO2. The granites are alkaline and K2O-rich, leading to their classifi cation as a shoshonite series. With increasing SiO2 content, TiO2, Al2O3, F e2O3(T), MnO, MgO, CaO, P2O5, Sr, Eu, Cu, Zn, Ni, V, and Sc decrease, indic ating fractionation of observed minerals including apatite, magnetite, pyro xene, hornblende, plagioclase, and biotite. Some samples are characterized by very high abundances of K2O, P2O5, Sr, Pa, and light rare earth elements (LREE) compared to other Eureka Supersuite samples. This may reflect their derivation from a source that was variably enriched in incompatible elemen ts. Compared with many other shoshonitic rocks, high-K Eureka Supersuite sa mples are strongly depleted in Sr and to a lesser extent Eu, and enriched i n Y and heavy rare earth elements (HREE). This suggests that garnet was not a stable phase in the source region, that the source contained plagioclase as a stable phase, and/or the granites evolved by extensive plagioclase fr actionation. Partial melting in the lower crust to generate post-1540 Ma granites was mo st likely caused by intrusion of basic magma into the crust. Eureka Supersu ite magmas were probably derived from partial melting of variably incompati ble element-enriched gabbroic rocks, while Cloncurry Supersuite magmas were most likely derived from partial melting of more felsic material of diorit ic to tonalitic composition.