ABSTRACT

Sm-Nd isotopic study for the ore-bearing Jinchuan ultramafic rocks in Gansu province, China, reveals the age of 1508 ± 31 Ma, which is obtained by Sm-Nd internal isochron method. The Rb-Sr isotopic system of the Jinchuan rocks have been contaminated by crustal materials, but little influence of crustal materials disturbed their Sm-Nd isotopic system. The determined results for acid-washed pyroxenes show that the source region of the Jinchuan ultramafic rocks may possess the following features: relatively homogeneous negative ε_Nd(T) values, relatively dispersed ε_Sr(T) values (generally larger than +60), and exhibiting a horizontal distribution in Nd-Sr correlation diagram.