论变质重结晶作用对晶质菱镁矿矿床成矿的贡献OA北大核心CSTPCD

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 low-metamorphic grades.Geological observation and geochemical data shows:① The 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(δ13CV-PDB:-0.4‰～+0.3‰).② Most 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(δ13CV-PDB:-1.9‰～+1.7‰).③ The 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(δ13CV-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.