Discussion on the interrelationship among Cu-Ni sulfide deposits, mafic volcanic rocks and intrusive rocks in the Sipu region, northern Guangxi, China

Abstract

The Sipu region of North Guangxi is located in the southwest of the “Jiangnan Ancient Land”, where there are developed the oldest stratum in southern China, the Proterozoic Sipu Group, and there are also largely exposed mafic intrusive rocks, mafic volcanic rocks and copper-nickel sulfide deposits. Both mafic intrusive rocks and volcanic rocks are rich in MgO (6.52%–26.39%), but poor in K2O (0.05%–1.00%) and TiO2 (0.33%–0.89%). They are also rich in trace elements such as Rb and Ba while poor in Ta, Nb and the like. Both of them have medium contents of rare-earth elements, 30.26×10−6–126.71×10−6, in which LREEs are slightly rich with ΣLREE/ΣHREE of 1.35–2.46, δEu 0.79–1.33, displaying weak or no δEu anomaly, with the same geochemical features. The right-inclined distribution patterns and the features show that magma would be formed at the comagmatic undiagenetic stage. All studies show that mafic intrusive rocks and volcanic rocks are the products of the same source region evolving in different stages and times. The copper-nickel sulfide deposits are characterized by liquation, crystallization and fractionation of mafic rocks, and have some interrelations with mafic intrusive rocks and volcanic rocks with respect to magmatic genesis.