摘要
晶质菱镁矿矿床赋存于海相碳酸盐岩建造,为富镁碳酸盐经后期变质重结晶的产物,属沉积-变质型矿床。本次研究将中国境内的晶质菱镁矿矿床按变质重结晶程度分为三类(高、中和低),并进行了地质和地球化学研究,获得如下认识:(1)产于古生代海相碳酸盐岩中的菱镁矿矿床经历低程度变质重结晶作用(绿片岩相),矿石结晶度差,品位相对较低(44.98%~47.35%),且保留有海相碳酸盐岩建造的碳同位素地球化学特征(δ^(13)C_(V-PDB):-0.4‰~+0.3‰);(2)大型(>5000万t)优质(MgO>46%)晶质菱镁矿矿床集中分布在华北克拉通东部的古元古代胶-辽-吉活动带海相碳酸盐岩中,矿体后期经历中等程度变质重结晶作用(中—低角闪岩相),矿石发生中等程度的重结晶作用,继承了海相碳同位素地球化学特征(δ^(13)C_(V-PDB):-1.9‰~+1.7‰);(3)经历高角闪岩相(高级)变质作用的菱镁矿矿床矿石结晶程度最优,但强烈的变质作用引发外源含硅热液流体加入而发生蛇纹石化作用,矿石品位低(MgO=44.42%~45.55%),具有较高的TFeO、Mn和Ti含量,整体亦显示较低的碳同位素组成(δ^(13)C_(V-PDB):-4.1‰~-3.5‰)。因此,沉积-变质型菱镁矿矿体的镁质富集可能发生在海相沉积成岩期,后期变质作用引发富镁碳酸盐矿物重结晶作用,镁质碳酸盐和钙质碳酸盐矿物进一步发生近原地分离重结晶作用,形成晶质菱镁矿矿体和富镁白云石夹石,但过高(高角闪岩相及以上)或过低(绿片岩相)的变质作用可能均不利于形成大型优质晶质菱镁矿矿床。
The sedimentary-metamorphic sparry magnesite deposits are hosted in the Mg-rich marine carbonate Formations and suffered metamorphic recrystallization of late-stages.Geochemical and stable isotope(C and O)study has been carried out on three typical magnesite deposits suffered by high-,medium-and lowmetamorphic grades.Geological observation and geochemical data shows:①The magnesite ores that hosted in Paleozoic marine sedimentary rocks endured low grade metamorphic recrystallization,shows relatively low contents of magnisium(44.98%~47.35%),and inherited the marine carbon isotopic characteristics(δ^(13)C_(V-PDB):0.4‰~+0.3‰).②Most of the large-class(>50 Mt)magnesite deposits in China are located at the Paleoproterozoic Jiao-Liao-Ji belt,east margin of North China Craton.These magnesite ore endured medium grade metamorphic recrystallization,shows relatively high contents of magnisium(MgO>46%),and inherited the marine carbon isotopic characteristics(δ^(13)C_(V-PDB):1.9‰~+1.7‰).③The magnesite ores that endured high grade metamorphic recrystallization with large crystals particle size of more than 1cm,altered by silica-metamorphic fluids.These serpentinized magnesite ores show relatively low contents of magnisium(MgO=44.42%~45.55%),high contents of TFeO,Mn,Ti,and low carbon isotopic compositions(δ^(13)C_(V-PDB):4.1‰~3.5‰).Therefore,the magnesium enrichment process may be happened during the marine sedimentary and diagenetic epoch,with the sparry magnesite ores formed during the metamorphic recrystallization of late-stages.The Mg-and Ca-carbonate may occur fractional crystallization during the metamorphism,formed the dolomite interlayers in the magnesite orebodies,the high(high amphibolite to granulite facies)or low(greenschist facies)metamorphic recrystallization were not beneficial to the development of sedimentary-metamorphic sparry magnesite deposit.
作者
胡古月
王登红
郑军
余旭辉
武文博
宋立军
朱永新
HU Guyue;WANG Denghong;ZHENG Jun;YU Xuhui;WU Wenbo;SONG Lijun;ZHU Yongxin(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;Sichuan Geology and Mineral Bureau Regional Geological Survey Team,Chengdu,Sichuan 610213,China;College of Earth Science,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Hebei Institute of Geological Survey,Shijiazhuang,Hebei 050081,China;Gansu Institute of Geological Survey,Lanzhou,Gansu 730000,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2024年第1期138-162,共25页
Acta Geologica Sinica
基金
中国地质调查局项目(编号DD20221695)资助的成果。
关键词
富镁碳酸盐岩建造
沉积-变质型菱镁矿矿床
变质重结晶
晶质菱镁矿
Mg-rich marine carbonate formations
sedimentary-metamorphic magnesite deposit
metamorphic recrystallization
sparry magnesite
