非傳統(tǒng)穩(wěn)定同位素-6a-應(yīng)用實(shí)例

1、白云鄂博礦床成因白云鄂博礦床成因朱祥坤朱祥坤中國(guó)地質(zhì)科學(xué)院地質(zhì)研究所中國(guó)地質(zhì)科學(xué)院地質(zhì)研究所白云鄂博白云鄂博: :富饒的神山富饒的神山 丁道衡先生丁道衡先生1927年發(fā)現(xiàn)年發(fā)現(xiàn)鐵礦石鐵礦石 何作霖先生何作霖先生1936年發(fā)現(xiàn)年發(fā)現(xiàn)含含REE礦物礦物(獨(dú)居石獨(dú)居石) 新中國(guó)成立后建立的第新中國(guó)成立后建立的第一座鐵礦山一座鐵礦山白云鄂博礦區(qū)丁道衡塑像白云鄂博礦區(qū)丁道衡塑像 Bayan Obo REE-Nb-Fe deposit The largest LREE ore deposit in the world A large Nb deposit A Large Fe deposit Timing

2、 of Mineralisation Origin of the Deposit Geological map of Bayan Obo ore deposit (after Bai et al., 1996)1Overthrust; 2Inferred fault; 3Geological boundaries; 4Inferred geological boundaries; 5Iron bodies; 6Carbonatite dykes; 7Ore-hosted dolomite; 8Fluorite type iron ores; 9 Massive type iron ores;

3、10Aegirine type iron ores; 11Riebeckite type iron ores; 12Dolomite type iron ores; 13Biotite type iron ores; 14Sample location; 15Location of drill hole. H1H15Unit of Bayan Obo Group, see table 1; CCarboniferous; QQuaternary; HRelicts of slate and quartzite; DTDolomite marble; STMineralized slate; M

4、eta-ultrabasic rocks; Migmatitic gneisses; Granites; Migmatitic Granites; Basic-intermediate rocks The ore-hosting dolomite marbleThe ore-hosting dolomite marbleMt：magnetiteHm：hematiteRE：REE mineralsAe：aegirineFl：fluoriteFlHmAeMtREREREMtAeHmFlFlIron oresLate-stage veinsDol: dolomite； Fl：fluorite； Mo

5、n：monaziteMonDolDolDolFlThe normal carbonate sediments on the north of KuangouMt 0.5 mmMtREAeMt：magnetiteRE：REE mineralsAe：aegirineMtDolFl 0.5 mmMtDolMt：magnetiteDol：dolomiteFl：fluorite0.5 mmMtHmMt：magnetiteHm: hematiteFl：fluoriteFlCarbonatite dykesDolBarREDol：dolomite；RE：REE minerals；Bar：barite 1 m

6、m Timing of Mineralisation Origin of the Deposit Sm-Nd同位素體系同位素體系: REE 鐵同位素：鐵同位素：Fe礦礦 鎂同位素：白云質(zhì)大理巖（寄主巖石）鎂同位素：白云質(zhì)大理巖（寄主巖石）(143Nd/144Nd)p=(143Nd/144Nd)i+147Sm/144Nd(et-1)Single source at t0(143Nd/144Nd)p=(143Nd/144Nd)i+147Sm/144Nd(et-1)Single source at t0Two sources at t0 and t1 respectively (143Nd/144N

7、d)p=(143Nd/144Nd)i+147Sm/144Nd(et-1)Single source at t0Two sources at t0 and t1 respectively Single source at t0, recrystalised at t1 (143Nd/144Nd)p=(143Nd/144Nd)i+147Sm/144Nd(et-1)All publised whole-rock data,ca. 1.3Ga; Nd(t) = -0.2 Timing of REE Mineralizatiom Initial/main mineralization: ca. 1.3G

8、a, mantle source ; Late stage mineralization: ca. 0.44 Ga, internal recycling Other ages: disturbance Timing of Mineralisation Origin of the Deposit The origin: hot debate Sedimentary origin? Hydrothermal origin? Magmatic origin (carbonatite)? Multiple origin?Mg Isotopes: 24Mg , 25Mg, 26MgFe Isotope

9、s: 54Fe, 56Fe, 57Fe Carbonate sedimentsIgneous rocksMg isotopes Different genetic types of rocks* Reference dataMg isotopes Bayan Obo ore deposit * Reference data*Fe isotopes Different genetic types of iron ores & rocks* Reference data*Fe isotopes various types of rocks from Bayan Obo ore bodies

10、 The normal distribution of 56 Fe values for iron ores (bulk sample and Fe oxides) *Fe isotope compositions of Bayan Obo ore deposit * Reference dataSummary Nd: mantle source Mg: magmatic origin Fe: magmatic origin Sr: mantle source mainly (mantle+?) C-O: double sources (mantle+?)小小 結(jié)結(jié) Sm-Nd同位素體系同位素體系: REE 鐵同位素：鐵同位素：Fe礦礦 鎂同位素：白云質(zhì)大理巖（寄主巖石）鎂同位素：白云質(zhì)大理巖（寄主巖石）小小 結(jié)結(jié) 全巖的全巖的Sm-Nd同位素演化線于同位素演化線于1.3Ga左右相交，左右相交，Nd(t) 在零在零附近，說(shuō)明附近，說(shuō)明REE礦化時(shí)間在礦化時(shí)間在1.3Ga左右，成礦物質(zhì)來(lái)自地左右，成礦物質(zhì)來(lái)自地幔。幔。 鐵同位素：鐵同位素：Fe同位素組成比較均一，同位素組