The petrogenesis of the Xiaonvzhai metamorphic gabbro-diorite in the Liaoji Paleoproterozoic orogenic belt and its constraints on Co-Ni enrichment
The Liaoji orogenic belt is a major Paleoproterozoic orogenic zone in the North China Craton.During the extension of the Paleoproterozoic basin,the Liaoji orogenic belt accumulated substantial continental sediments.These sediments,combined with multi-stage magmatic and metamorphic events,provided favorable conditions for mineral enrichment and formation of the deposits.Cu-Co deposits have been found in association with metamorphic sedimentary rocks,particularly in phyllite-schist.In addition,magmatic Co-Ni deposits associated with mafic rocks have been reported in the region.However,the enrichment mechanisms and metallogenic models for the magmatic Co-Ni deposits remain unclear.In this study,we investigated the petrography,mineral chemistry,zircon U-Pb geochronology,whole-rock geochemistry,and sulfide-sulfur isotopes of the Xiaonvzhai metamorphic gabbro-diorite from the Liaohe Group to further understand the Co-Ni metallogenic mechanisms and the source of the Co-Ni in the Liaohe Group.The studied samples of the metamorphic gabbro-diorite have variable compositions,i.e.,SiO2(26.1％to 57.3％),MgO(2.90％to 25.0％),CaO(3.17％to 10.7％)and FeOT(6.43％to 38.94％),indicating that they belong to the calc-alkaline series.They are characterized by slightly enriched light rare earth elements and flat heavy rare earth patterns,with relatively negative anomalies in high field strength elements(such as Ta,Nb,and Ti).Zircon U-Pb isotopic dating defined the age of the metamorphic gabbro-diorite to be approximately 2.17Ga,with zircon εHf(t)values of-1.3～+5.0,suggesting that the mafic magma source of the pluton was derived from partial melting of the enriched lithospheric mantle that would likely be related to the lithospheric extension.The Co-Ni contents in the metamorphic gabbro-diorite are mainly from cobaltite(Co:14.8％to 31.3％;Ni:2.92％to 14.2％)and pentlandite(Co:5.70％to 8.53％;Ni:27.3％to 34.0％).These Co-Ni-rich minerals coexist with quartz,epidote and other minerals,suggesting that the mineralization may be associated with late-stage hydrothermal fluids.The δ34 S values of cobaltite,pentlandite and pyrite range from+4.5‰ to+5.5‰,suggesting a relatively uniform sulfur source.These δ34S values are heavier than those of the mantle,suggesting that the S in the sulfide may be of continental crustal origin.Drilling samples from two holes in the Xiaonvzhai area revealed high concentrations of Ni(0.09％to 0.94％),Co(0.01％to 0.13％)and Cu(0.02％to 0.79％).These results indicate that the Paleoproterozoic metamorphic mafic rocks in the Liaoji orogenic belt have significant potential for Cu-Co-Ni mineralization.
万方数据
维普
