辽东海城－大石桥超大型菱镁矿矿床的地质特点及成因

中国海城－大石桥菱镁矿矿床举世闻名，矿床分布于辽东元古宙裂谷海槽北缘的次一级盒地中。含镁建造属元古宙上辽河群大石桥岩组的上部．按含矿建造组成岩石的各种成因标志，确定建造的沉积岩相为闭塞台地相，因此．推测它形成于裂谷边缘的泻湖环境。由于长期潮汐作用，泻湖内有充分的富镁海水周期性地供给，在当时炎热干旱的气候条件下，泻湖中的卤水不断浓缩，并通过化学与生物化学成矿作用，在泻湖盆地内形成了大型－超大型的菱镁矿矿床。元古宙末期矿床遭受了绿片岩－角闪岩相区域动力热流变质作用的改造。

GEOLOGICAL CHARACTERISTICS AND CENESIS OF HAICHENG-DASHIQIAO SUPERLARGE MAGNESITE DEPOSITS,EASTERN LIAONING PROVINCE

Haicheng-Dashiqiao magnesite deposlts in Liaoning province are wellknown in the world for their sizes and quality,which are distributed in the secondarybasins of Liaodong proterozoic paleorift.Magnesium-bearing formation belongs to theupper Dashiqiao rock series of the Proterozoic Liaohe group.According to the variousgenetic features of the rocks in the formation,its sedimentary lithofacies has beenrecognized as enclosed tableland environment.Therefore,it is suggested that thisformation was formed in lagoons near the north range of the rift.Due to long period oftidings,magnesium-rich sea water was provided for the lagoons periodically. Under hotand dry climate,brines in the lagoon were concentrated continuously and the large-superlarge magnesite deposits were formed by chemical and biochemical processes. At theend of Proterozoic,the magnesite deposits were undergone greenschist-amphibolite.faciesregional dynamo-hydrothermal metamorphism.