Distribution of Co and Ni in mafic-ultramafic rocks and minerals and mineralization implications
This paper summarizes the distribution characteristics of Co and Ni elements in whole rocks and major rock-forming minerals of various mafic-ultramafic rocks,and discusses controlling effects of different types of mantle source and their mineral element contents on Co-Ni mineralization.Our results indicate that the whole rock Co(15 × 10-6～250 × 10-6)and Ni(28 × 10-6～5045 × 10-6)contents in komatiites are generally higher than those in picrites(Co=11 × 10-6～177 × 10-6,Ni=29.9 × 10-6～2069 × 10-6)and basalts(Co=1.1 × 10-6～300 ×10-6,Ni=0.5 × 10-6～2837 ×10-6),suggesting melts formed by partial melting of the mantle at high degrees are more enriched in Co and Ni.The Co(21 × 10-6～220 × 10-6)and Ni(2.1 × 10-6～4060 × 10-6)contents in mantle peridotite xenoliths are significantly higher than those in pyroxenite xenoliths(Co=7 × 10-6～131 × 10-6,Ni=4.58 × 10-6～2311 × 10-6),indicating that peridotite sources are more likely to generate Co-and Ni-rich magmas than pyroxenite sources during partial melting.Mineralogical characteristics reveal that olivine in mantle xenoliths has Co and Ni contents of 41 × 10-6～437 × 10-6 and 148 × 10-6～8970 × 10-6,respectively,while spinel has Co contents ranging from 141 × 10-6 to 745 × 10-6 and Ni from 282 × 10-6 to 9587 × 10-6,both of which are higher than those in orthopyroxene(Co=10 × 10-6～364 × 10-6,Ni=5.02 × 10-6～4439 × 10-6),clinopyroxene(Co=4.09 × 10-6～385 × 10-6,Ni=11.1 × 10-6～5931 ×10-6),and garnet(Co=0.47 × 10-6～205 × 10-6,Ni=0.09 × 10-6～644 × 10-6).Meanwhile,olivine and spinel show negative correlations between their Co contents and Ni/Co ratios,whereas such correlation is not evident in orthopyroxene or clinopyroxene.These features indicate that spinel-facies peridotites could supply more Co and Ni to partial melts during partial melting than garnet-facies peridotites.Major rock-forming minerals in intrusive rocks exhibit similar Co and Ni variations compared to the counterparts in mantle xenoliths,indicating that olivine and spinel are main phases controlling Co and Ni contents in magmas during partial melting and magmatic differentiation,leading to Co-Ni decoupling,whereas orthopyroxene and clinopyroxene tend to make Co and Ni co-variations.Moreover,as parent rocks of laterite Ni deposits,peridotites and chromitites in ophiolites show higher Co and Ni contents.Ophiolitic olivine shows higher Ni contents(1280 × 10-6～5789 × 10-6)than spinel(229 × 10-6～2616 × 10-6),whereas its Co contents(41.2 × 10-6～193 × 10-6)are significantly lower than that of spinel(176 × 10-6～781 × 10-6),indicating that olivine-rich rocks during weathering are more likely to form Ni-rich laterite deposits,while those spinel-rich ones are more likely to contribute to Co mineralization in lateritic Ni deposits.
Mafic-ultramafic rockCo-Ni depositRock-forming mineralsCo-Ni elements
万方数据
维普
