摘要
辽东半岛古元古界辽河群大石桥组三段地层中赋存有全球最大工业储量的菱镁矿矿床。在总结和整理已发表的辽东半岛晶质菱镁矿床地质和地球化学数据的基础上,本次研究进行了Mg和B同位素测试及研究工作,获得以下认识:①菱镁矿矿体呈北东东走向,产于大石桥组三段,但不同矿床的矿体厚度差异较大(30~300 m),菱镁矿矿体与顶、底板高镁白云岩之间以断层接触为主,常可见到绿泥石化板岩和碳质千枚岩产于大型菱镁矿矿体的内部韧性剪切面上,说明地层经历了强烈构造形变作用;②围岩白云岩与晶质菱镁矿矿石的地球化学特征基本一致,均表现为大离子亲石性元素(K、Rb、Ba、Sr等)亏损和氧同位素负漂移(δ^(18)O:-24.9‰~-11.0‰);③在经历构造形变和角闪岩相变质作用后,菱镁矿矿石仍继承有海相蒸发沉积岩的稳定同位素地球化学特征(δ^(13)C:-2.7‰~+1.6‰;δ^(34)S:+15.6‰~+23.7‰;δ^(26)Mg:-1.53‰~-0.49‰;δ^(11)B:+9.8‰~+13.4‰);④后期裂控型滑石具有相对较高的δ^(26)Mg值(-0.32‰~-0.15‰),发生滑石矿化的菱镁矿(δ^(11)B:+7.7‰~+8.4‰)和围岩变粒岩(δ^(11)B:+4.3‰)显示较低的δ^(11)B值,这反映了变质热液作用所引发的Mg和B同位素分馏现象。因此,辽东半岛海城-大石桥地区菱镁矿矿床镁质富集的根本原因可能为湖相沉积碳酸盐岩经准同生阶段的富镁卤水交代所致,非后期变质热液交代作用的结果。
The world’s largest sparry magnesite deposit belt is located at the third Member of Dashiqiao Formation of Liaohe Group in Liaodong Peninsula.It is still controversy that these deposits were formed by Mg-rich parasyngenetic brines(2.1±0.1 Ga)altered the carbonate precursor to magnesite in an evaporative shallow-marine setting or,epigenetic metamorphic hydrothermal metasomatism(1.85±0.05 Ga).Based on summarizing the geological features and published data,stable isotopes of B and Mg were carried out on the critical geological samples of Haicheng-Dashiqiao magnesite deposit belt.Geological observation and geochemical data shows:(1)Though the magnesite deposits are strictly hosted in the third Member of Dashiqiao Formation,the ore thickness shows significant variation among different deposits(30~300 m);The contact relationship between the magnesite ores and its wall rocks of dolomites are mainly performed by faults,with metasomatic magnesite veins constrainted at the margins(5~10 m)of orebodies;the chloritization slates and carbonaceous phyllites are commonly occurred in the ductile share zone of magnesite orebodies,which indicate that the third member of Dashiqiao Formation endured intense tectonic deformation during the late stages;(2)Both of the sparry magnesite and dolomite exhibited depleted characteristics of large ion lithophile elements(e.g.K,Rb,Ba,Sr)and"negative shift"of oxygen isotope(δ^(18)O:24.9‰~-11.0‰);As controlled by hydrothermalism,the∑REE values of carbonates show positive relationship to the content of SiO2;(3)Though endured amphibolite facies metamorphism,the magnesite ores inherited the stable isotopic characteristics(δ^(13)C:-2.7‰~+1.6‰;δ^(34)S:+15.6‰~+23.7‰;δ^(26)Mg:-1.53‰~-0.49‰;δ^(11)B:+9.8‰~+15.3‰)of evaporative shallow-marine sediment;(4)The fracture-controlling talc ores show relatively heavy magnisium isotopic composition(-0.32‰~-0.15‰),with the light boron isotopic compositions of talc-magnesite(δ^(11)B:+7.7‰~+8.4‰)and leptynite(δ^(11)B:+4.3‰),
作者
胡古月
孙新胜
郑军
余旭辉
王东波
李延河
赵悦
陈翰
徐莺
ALISON Ord
HU Guyue;SUN Xinsheng;ZHENG Jun;YU Xuhui;WANG Dongbo;LI Yanhe;ZHAO Yue;CHEN Han;XU Ying;ALISON Ord(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;Liaoning No.5 Geological Team Co.LTD,Yingkou,Liaoning 115100,China;College of Earth Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Sichuan Geology and Mineral Bureau Regional Geological Survey Team,Chengdu,Sichuan 610213,China;Institute of Multi pur pose Utilization of Mineral Resources,Chinese Academy of Geological Sciences,Chengdu,Sichuan 610041,China;Centre for Ex ploration Targeting,School of Earth Sciences,Unirversity of Western Australia,Perth 6009,Australia)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2022年第4期1340-1355,共16页
Acta Geologica Sinica
基金
中国地质科学院矿产资源研究所基本业务费项目(编号kk2002)
中国地质调查局工作项目(编号DD20190379)
国家留学基金委项目(编号201808110080)联合资助的成果。
关键词
辽东半岛
古元古代辽河群
菱镁矿矿床
潟湖相富镁卤水交代
变质重结晶
Liaodong Peninsula
Paleoproterozoic Liaohe Group
magnesite deposit
Mg-rich parasyngenetic brines in shallow-marine setting
metamorphic recrystallization
