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本文通过方解石和白云石的碳和氧同位素分析,对比研究了白云鄂博赋矿白云岩、黑脑包微晶丘、北京西山微晶丘、宽沟北正常沉积灰岩和白云鄂博碳酸岩墙,从而探讨了赋矿白云岩的成因及其与超大型Fe-Nb-REE矿床的成因关系。结果为:①黑脑包腮林忽洞群顶部微晶丘和北京西山寒武系顶部微晶丘碳酸盐的δ~(13)C值都在0±2‰左右,δ~(18)O值为18.3‰～25.1‰,均具有典型海相沉积碳酸盐岩的特点;②白云鄂博东矿采场δ~(13)C值为-7.9‰～-1.1‰,δ~(18)O值为9.1‰～20.9‰;矿区东西两端δ~(13)C值-7.9‰～-0.6‰,δ~(18)O值8.6‰～25.7‰;均介于地幔流体与典型沉积碳酸盐岩之间。部分赋矿白云岩样品中白云石与方解石之间的碳氧同位素分馏△~(13)C和△~(18)O值均小于0‰,表明其受到过次生蚀变作用,低δ~(18)O值白云石样品所对应的负△~(18)O值反映了地幔镁质流体对沉积碳酸盐岩的强烈交代作用;③矿区—富稀土碳酸岩墙的δ~(13)C值为-7.2‰～-4.7‰,δ~(18)O价值为11.9‰～16.4‰,表明其碳酸岩岩浆并非原始地幔来源,而可能与俯冲板块携带的沉积碳酸盐岩与地幔流体在深部的高温混合熔融有关。碳酸岩墙中白云石与方解石之间的碳和氧同位素分馏均小于0‰,说明该碳酸岩墙中的白云石与方解石并非同成因矿物,至少其中之一为
Based on the carbon and oxygen isotopic analysis of calcite and dolomite, the dolomite, black brain microcrystalline mound, Beijing Xishan microcrystalline mound, Kuangoubei normal sedimentary limestone and Bayan Obo carbonate rock wall were comparatively studied. The authors discussed the genesis of the ore-dressing dolomite and its genetic relationship with the super-large Fe-Nb-REE deposit. The results were as follows: ① δ 13 C values of microcrystalline cumulus microclimate at the top of the Kailin group and the top of the Xishan Cambrian in Beijing were both 0 ± 2 ‰, The O values ranged from 18.3 ‰ to 25.1 ‰, all of which were typical of marine sedimentary carbonate rocks. ② The δ ~ (13) C values of stopes in the Bayan Obo Dong Mine ranged from -7.9 ‰ to -1.1 ‰, and δ ~ (18) O values ranged from 9.1 ‰ to 20.9 ‰. Δ 13 C values at the east and west ends ranged from -7.9 ‰ to -0.6 ‰ and δ 18 O values ranged from 8.6 ‰ to 25.7 ‰, both of which ranged from that of mantle fluid and typical sedimentary carbon Between the rock salt. The δ13C and △ ~ (18) O values of dolomite and calcite in some dolomite ore samples were all less than 0 ‰, indicating that they were underwent secondary alteration and the δ ~ (18) The negative △ ~ (18) O values corresponding to the O-value dolomite samples reflect the intense metasomatism of mantle magma fluids on the sedimentary carbonate rocks. ③ The δ ~ (13) C values ranged from -7.2 ‰ to -4.7 ‰ and δ ~ (18) O values ranged from 11.9 ‰ to 16.4 ‰, indicating that carbonate rocks are not the source of the original mantle and may be related to sedimentary carbonate and mantle fluid carried by the subducted plate In the deep high temperature mixing melting related. The carbon and oxygen isotopic fractions between dolomite and calcite in carbonate rock walls are both less than 0 ‰, indicating that the dolomite and calcite in the carbonatite wall are not the same genetic mineral, at least one of them is