Geochemistry and Zircon U–Pb Dating of the Mingyang Mafic–Ultramafic Rock Complex in Beishan Area of Gansu and Its Prospecting Significance

The Mingyang rock body is a newly discovered copper-nickel mineralized Mafic-Ultramafic rock body, which is located on the north side of the gubaoquan-hongliuyuan Fault in the southern belt of Beishan, Gansu. The rock intruding in the Dunhuang rock group,which mainly composed of gabbro, diabase peridotite, olivine gabbro, gabbro, etc. The rock composition is characterized by low alkali and low titanium, slightly enriched in light rare earths, with obvious positive Eu anomalies; enriched in large ion-lithophile elements (LILE) Rb, Ba, Sr and K, and relatively deficient in high field strength elements (HFSE) Th, U, Nb, Ta, Zr and Hf. During the magmatic evolution, the separation and crystallization of olivine, plagioclase and pyroxene occurred, it has experienced a certain degree of assimilation and contamination. The geological, geophysical and geochemical information show that it has the better potential of copper and nickel ore. The first crystallization ages of (452.9±2.4) Ma and (457.7±2.1) Ma for olivine gabbro and gabbro in the Mingyang rock mass were obtained by LA-ICP-MS zircon U-Pb dating. The rocks may be the products of the Early Paleozoic continental margin rifting environment. The discovery of early Paleozoic Cu-Ni-bearing rocks in the Beishan area is of great significance to the understanding of regional tectonic evolution.