Geochemistry of Ore‐bearing Lamprophyre from the Cu‐Ni Deposit in Dhi Samir, Yemen

Abstract

Abstract:Magmatic Cu‐Ni sulfide deposits are generally associated with mafic‐ultramafic rocks and it has not been reported that lamprophyre is one of the surrounding rocks of Cu‐Ni sulfide deposits. The Dhi Samir deposit in Yemen, however, is a rare example of Cu‐Ni deposits which are hosted in lamprophyre dikes. In this paper, comprehensive research is made on petrology, petrochemistry and isotope geochemistry for Cu‐Ni‐bearing rocks in the Dhi Samir area and the results show that dark rocks related to Cu‐Ni orebodies are sodium‐weak potassium and belong to calc‐alkaline series lamprophyre, especially camptonite, characterized by enriched alkali, iron and titanium. In these rocks large‐ion‐lithophile elements are obviously concentrated, while high field strength elements slightly depleted, showing clear negative anomalies of Ta and Nb, and weak deficiency of Ti. The ΣREE is very high (225.67–290.05 ppm) and the REE partition curves are flat and right‐inclined, featuring a LREE‐enriched pattern with low negative Eu anomalies. Study of magmatic source areas indicates that the rocks have low (87Sr/86Sr) and high εNd(t), and the magmas were probably derived from the enriched mantle I (EM‐I) end‐member. Based on the LA‐ICPMS on zircon U‐Pb isotope dating, the lamprophyre in the Dhi Samir mining area has an age of 602±2.6 Ma, indicating that the rock was formed in the late Proterozoic and in an intraplate setting due to magmatism of an extensional environment in the post‐Pan‐Africa orogeny.