Acta Petrologica et Mineralogica

In this study, the whole-rock geochemistry and zircon U-Pb ages are reported for the meta-basic rocks of the Li’eryu Formation of the South Liaohe Group from the cobalt exploration area in Kuandian. These data provide a significant insight into the tectonic background, as well as the source of cobalt. Geochemical features of the meta-basic rocks in boreholes show that they are orthorhombic amphibolite, and have similar rare-earth elements (REEs) patterns, with slightly negative Eu anomalies. REEs and trace elements compositions have affinity to those of E-MORB. Based on the mineral compositional analyses and p-t estimates using conventional geothermobarometers, the clinopyroxene-bearing amphibolite (ZK2-1) records p-t conditions of p=0.82~1.00 GPa and t= 712~751℃, which probably constrained the peak high amphibolites-facies stage. The metamorphic p-t conditions of (clinopyroxene-bearing) amphibolite (ZK1-1 and ZK3-1) are p= 0.42~0.81 GPa, t= 688~759℃ and p=0.59~0.85 GPa, t=703~739℃, respectively, which represent the conditions of the retrograde stage. The metamorphic zircon from the meta-basic rocks yield the SHRIMP U-Pb ages of 1 857~1 850 Ma. The integrated study of geochemistry and zircon U-Pb dating reveals that their protoliths of the meta-basic rocks are mid-Paleoproterozoic tholeiitic basalt and formed in an extended tectonic environment. Their protoliths underwent significant crustal assimilation imply that the scale of the mid-Paleoproterozoic oceanic basin may be limited. By comparing the geochemical characteristics of meta-basic rocks in the North and South Liaohe groups, it is believed that meta-basic rocks in the Kuandian area are not the main source of cobalt mineralization. The material sources of cobalt mineralization still needs further research.

meta-basic rocks; Kuandian area; Li'eryu Group; Paleoproterozoic; metamorphic events; cobalt mineralization