Geochemical characteristics and original rock restoration of plagioclase amphibolites in the Gongchangling iron deposit , Liaoning Province

Abstract：Iron resources in the second ore district of Gongchangling is not only a large-sized banded low grade iron ore deposit but also a large-sized high grade iron ore deposit. Since 1949, it has become the main mine providing high grade iron for the Anshan Steel Iron Group Cooperation. The authors studied the second ore district of Gongchangling, and analyzed major elements, trace elements, rare earth elements of the amphibolites. Some conclusions have been reached: ① the average compositions of major elements are SiO2 49.89%, TiO2 0.86%，Al2O3 14.85%, Fe2O3 3.47%, FeO 7.88%,MnO 0.24%, MgO 7.94%, CaO 8.65%, Na2O 2.79%, K2O 1.17%，and P2O5 0.07%, similar to things of basalt: MgO and CaO are high, Na2O＞K2O;②as for trace elements, the content of compatible elements (Sc, V, Cr, Co, Ni, Cu) is high, (Rb/Yb）N=5.95～132.93, with an average of 49.34; Rb, Ba, K, Sr, Zr, Hf are enriched, whereas Th, U, P, Nb, Ti are depleted, similar to things of deficiency type mid-ocean ridge tholeiite;③REE:∑REE ratios are relatively low (21.09×10-6～69.13×10-6, averagely 40.44×10-6), LREE/HREE=1.70～2.58, (2.27 on average)；(La/Yb)N=0.93～4.27 (1.60 on average), and (La/Sm)N=0.87～3.28 (1.42 on average)；④the original rock of amphibolites is basalt and, according to the discrimination diagram of environment structure, the original rock of amphibolites should be mid-ocean ridge tholeiite.