辽宁弓长岭铁矿床斜长角闪岩类地球化学特征研究及原岩恢复

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

弓长岭二矿区既是大型条带状铁矿床,同时又是大型磁铁富矿床,自1949年建矿以来,一直是鞍钢的主体矿山和高品位富矿的主要供应地。笔者在总结矿床地质特征的基础上,对矿区的主要变质岩-斜长角闪岩类的主量元素、微量元素和稀土元素进行了分析。结果显示:主量元素的平均化学成分与基性火山岩中玄武岩成分相似,MgO和CaO含量比较高,而且Na2O>K2O;微量元素:相容元素Sc、V、Cr、Co、Ni、Cu的含量比较高,属于右倾型;(Rb/Yb)N值为5.95～132.93,平均值为49.34,远远大于1,为强不相容元素富集型;大离子亲石元素Rb、Ba、K、Sr明显富集,但Th、U强亏损;高场强元素中Zr、Hf明显富集,而Nb、P为中等亏损,Ti为弱亏损,与亏损型洋中脊拉斑玄武岩很相近;稀土元素具有∑REE低(21.09×10-6～69.13×10-6,平均40.44×10-6)、LREE略有富集(LREE/HREE=1.70～2.58,平均2.27;(La/Yb)N:0.93～4.27,平均值1.60)的稍右倾型或平坦型特征。轻稀土分馏不明显((La/Sm)N:0.87～3.28,平均值1.42)。根据主量、微量和稀土元素的特征,并结合环境构造判别图解,笔者认为,研究区斜长角闪岩的原岩为大洋中脊拉斑玄武岩。

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 SiO_2 49.89%, TiO_2 0.86%,Al_2O_3 14.85%, Fe_2O_3 3.47%, FeO 7.88% ,MnO 0.24%, MgO 7.94%, CaO 8.65%, Na_2O 2.79%, K_2O 1.17%,and P_2O_5 0.07%, similar to things of basalt： MgO and CaO are high, Na_2O〉K_2O; 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.