Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district （Cretaceous basin） of the middle-lower Yangtze River polymetall...Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district （Cretaceous basin） of the middle-lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed： one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic （-granitic） rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization （typically for zircons） ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131-127 Ma. In situ zircon Hf compositions of εHf（t） of the granodiorite are mainly from -3 to -8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.展开更多
Lithium separation technique for three reference materials has been established together with precise determination of lithium isotope using a Neptune multi collector-inductively coupled plasma mass spectrometry （MC-...Lithium separation technique for three reference materials has been established together with precise determination of lithium isotope using a Neptune multi collector-inductively coupled plasma mass spectrometry （MC-ICP-MS）. The solutions of lithium element standard reference materials, potassium, calcium, sodium, magnesium and iron single element, were used to evaluate analytical methods applied. Three separate stages of ion-exchange chromatography were carried out using organic cation-exchange resin （AG 50W-X8）. Lithium was enriched for the three stages using different eluants, which are 2.8 M HCl, 0.15 M HCl and 0.5 M HCl in 30% ethanol, respectively. The columns for the first and second stages are made of polypropylene, and those for the third stage are made of quartz. Total reagent volume for the entire chemical process was 35 mL for three reference materials. The recovery yielded for the three stages is 98.9-101.2% with an average of 100.0%, 97.6-101.9% with an average of 99.9%, and 99.8-103.3% with an average of 100.6%, respectively. The precision of this technique is conservatively estimated to be ±0.72-1.04‰ （2σ population）, which is similar to the precision obtained by different authors in different laboratories with MC-ICP-MS. The δ7 Li values （ 7 Li/ 6 Li relative to the IRMM-016 standard） determined for andesite （AGV-2） and basalt （BHVO-2） are 5.68‰ （n=18）, 4.33‰ （n=18）, respectively. The δ7 Li value （ 7Li/6Li relative to the L-SVEC standard） determined for IRMM-016 is -0.01‰ （n=15）. All these analytical results are in good agreement with those previously reported. In addition, the results for the same kinds of samples analyzed at the MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, are consistent with those obtained at the Plasma Laboratory, University of Maryland, within analytical uncertainty. According to these experiment results, it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples.展开更多
: The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclog...: The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclogites are obviously correlated with the types of their surrounding rocks. The helium isotope composition of the eclogites from the Bixiling complex possesses characters of mantle-derived rocks with the 3He/4He ratio being 5.6 Ra. The 4He concentration of the eclogites exhibits visible inverse correlation with the δ18O value of the quartz in the eclogites from the Sulu area. The δ18O values of the eclogites change synchronously with those of the country rocks. Those results suggest that protoliths of the eclogites were basic-ultrabasic rock bodies or veins intruding into the continental crust in the early stage; strong exchange and hybridization between the basic-ultrabasic rocks and continental rocks and the atmospheric water during the intrusion led to abrupt increase of the 3He/4He ratios, δ18O values and Nd(0) values of the intrusive bodies or veins, which show characters of continental rocks. This indicates that the eclogites are autochthonous.展开更多
The Maoniuping REE deposit, located about 22 km to the southwest of Mianning, Sichuan Province, is the second largest light REE deposit in China, subsequent to the Bayan Obo Fe-Nb-REE deposit in the Inner Mongolia Aut...The Maoniuping REE deposit, located about 22 km to the southwest of Mianning, Sichuan Province, is the second largest light REE deposit in China, subsequent to the Bayan Obo Fe-Nb-REE deposit in the Inner Mongolia Autonomous Region. Tectonically, it is located in the transitional zone between the Panxi rift and the Longmenshan-Jinpingshan orogenic zone. It is a carbonatite vein-type deposit hosted in alkaline complex rocks. The bastnaesite-barite, bastnaesite-calcite, and bastnaesite- microcline lodes are the main three types of REE ore lodes. Among these, the first lode is distributed most extensively and its REE mineralization is the strongest. The δ^34Sv.cDT values of the barites in the ore of the deposit vary in a narrow range of ＋5.0 to ＋5.1‰ in the bastnaesite-calcite lode and ＋3.3 to ＋5.9‰ in the bastnaesite-barite lode, showing the isotopic characteristics of magma-derived sulfur. The δ^13Cv-PDB values and the δ^Ov.SMOW values in the bastnaesite-calcite lode range from -3.9 to -6.9‰ and from ＋7.3 to ＋9.7 ‰, respectively, which fall into the range of ＂primary carbonatltes＂, showing that carbon and oxygen in the ores of the Maoniuping deposit were derived mainly from a deep source. The δ^13Cv.PDB values of fluid inclusions vary from -3.0 to -5.6‰, with -3.0 to -4.0‰ in the bastnaesitecalcite lode and -3.0 to -5.6‰ in the bastnaesite-barite lode, which show characteristics of mantle- derived carbon. The δDv-SMOW values of fluid inclusions range from -57 to -88‰, with -63 to -86‰ in the bastnaesite-calcite lode and -57 to -88‰ in the bastnaesite-barite lode, which show characteristics of mantle-derived hydrogen. The δ^18OH2OV.SMOW values vary from ＋7.4 to ＋8.6‰ in the bastnaesitecalcite lode, and ＋6.7 to ＋7.8‰ in the bastnaesite-barite lode, almost overlapping the range of ＋5.5 to ＋9.5‰ for magmatic water. The 4He content, R/Ra ratios are （13.95 to 119.58）×10^-6 （cm^3/g）STP and 0.02 to 0.11, respectively, and ^40Ar/^36Ar is 313± 1 to 437 ± 2. Considering the 4He increase caused by high contents of radioactive elements, a mantle-derived fluid probably exists in the inclusions in the fluorite, calcite and bastnaesite samples. The Maoniuping deposit and its associated carbonatite-alkaline complex were formed in 40.3 to 12.2 Ma according to K-Ar and U-Pb data. All these data suggest that large quantities of mantle fluids were involved in the metallogenic process of the Maoniuping REE deposit through a fault system.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 40930419)the National Special Research Programs for Non-Profit Trades (Sponsored by MLR, Grant Nos. 200911007 and 200811114)Open Foundation of State Key laboratory of Geological Processes and Mineral Resources, School of the Earth Sciences and Resources, China University of Geosciences, Beijing (Grant No. GPMR201029)
文摘Late Mesozoic volcanic-subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district （Cretaceous basin） of the middle-lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed： one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic （-granitic） rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore-forming event, detailed zircon U-Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun-Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization （typically for zircons） ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA-MC-ICP-MS zircon U-Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131-127 Ma. In situ zircon Hf compositions of εHf（t） of the granodiorite are mainly from -3 to -8 and their corresponding 176Hf/177Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore-forming event in the study area.
基金supported by grants from the Natural Science Foundation of China (no. 40973013,41173003)the Ministry of Land and Resources (no.201011027)+2 种基金China Geological Survey (no.1212011120298, 1212010816027)the Ministry of Science and Technology (no. K0802)the Open Foundation of Chinese Academy of Geological Sciences (no. 2009-SYS-06)
文摘Lithium separation technique for three reference materials has been established together with precise determination of lithium isotope using a Neptune multi collector-inductively coupled plasma mass spectrometry （MC-ICP-MS）. The solutions of lithium element standard reference materials, potassium, calcium, sodium, magnesium and iron single element, were used to evaluate analytical methods applied. Three separate stages of ion-exchange chromatography were carried out using organic cation-exchange resin （AG 50W-X8）. Lithium was enriched for the three stages using different eluants, which are 2.8 M HCl, 0.15 M HCl and 0.5 M HCl in 30% ethanol, respectively. The columns for the first and second stages are made of polypropylene, and those for the third stage are made of quartz. Total reagent volume for the entire chemical process was 35 mL for three reference materials. The recovery yielded for the three stages is 98.9-101.2% with an average of 100.0%, 97.6-101.9% with an average of 99.9%, and 99.8-103.3% with an average of 100.6%, respectively. The precision of this technique is conservatively estimated to be ±0.72-1.04‰ （2σ population）, which is similar to the precision obtained by different authors in different laboratories with MC-ICP-MS. The δ7 Li values （ 7 Li/ 6 Li relative to the IRMM-016 standard） determined for andesite （AGV-2） and basalt （BHVO-2） are 5.68‰ （n=18）, 4.33‰ （n=18）, respectively. The δ7 Li value （ 7Li/6Li relative to the L-SVEC standard） determined for IRMM-016 is -0.01‰ （n=15）. All these analytical results are in good agreement with those previously reported. In addition, the results for the same kinds of samples analyzed at the MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, are consistent with those obtained at the Plasma Laboratory, University of Maryland, within analytical uncertainty. According to these experiment results, it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples.
文摘: The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclogites are obviously correlated with the types of their surrounding rocks. The helium isotope composition of the eclogites from the Bixiling complex possesses characters of mantle-derived rocks with the 3He/4He ratio being 5.6 Ra. The 4He concentration of the eclogites exhibits visible inverse correlation with the δ18O value of the quartz in the eclogites from the Sulu area. The δ18O values of the eclogites change synchronously with those of the country rocks. Those results suggest that protoliths of the eclogites were basic-ultrabasic rock bodies or veins intruding into the continental crust in the early stage; strong exchange and hybridization between the basic-ultrabasic rocks and continental rocks and the atmospheric water during the intrusion led to abrupt increase of the 3He/4He ratios, δ18O values and Nd(0) values of the intrusive bodies or veins, which show characters of continental rocks. This indicates that the eclogites are autochthonous.
文摘The Maoniuping REE deposit, located about 22 km to the southwest of Mianning, Sichuan Province, is the second largest light REE deposit in China, subsequent to the Bayan Obo Fe-Nb-REE deposit in the Inner Mongolia Autonomous Region. Tectonically, it is located in the transitional zone between the Panxi rift and the Longmenshan-Jinpingshan orogenic zone. It is a carbonatite vein-type deposit hosted in alkaline complex rocks. The bastnaesite-barite, bastnaesite-calcite, and bastnaesite- microcline lodes are the main three types of REE ore lodes. Among these, the first lode is distributed most extensively and its REE mineralization is the strongest. The δ^34Sv.cDT values of the barites in the ore of the deposit vary in a narrow range of ＋5.0 to ＋5.1‰ in the bastnaesite-calcite lode and ＋3.3 to ＋5.9‰ in the bastnaesite-barite lode, showing the isotopic characteristics of magma-derived sulfur. The δ^13Cv-PDB values and the δ^Ov.SMOW values in the bastnaesite-calcite lode range from -3.9 to -6.9‰ and from ＋7.3 to ＋9.7 ‰, respectively, which fall into the range of ＂primary carbonatltes＂, showing that carbon and oxygen in the ores of the Maoniuping deposit were derived mainly from a deep source. The δ^13Cv.PDB values of fluid inclusions vary from -3.0 to -5.6‰, with -3.0 to -4.0‰ in the bastnaesitecalcite lode and -3.0 to -5.6‰ in the bastnaesite-barite lode, which show characteristics of mantle- derived carbon. The δDv-SMOW values of fluid inclusions range from -57 to -88‰, with -63 to -86‰ in the bastnaesite-calcite lode and -57 to -88‰ in the bastnaesite-barite lode, which show characteristics of mantle-derived hydrogen. The δ^18OH2OV.SMOW values vary from ＋7.4 to ＋8.6‰ in the bastnaesitecalcite lode, and ＋6.7 to ＋7.8‰ in the bastnaesite-barite lode, almost overlapping the range of ＋5.5 to ＋9.5‰ for magmatic water. The 4He content, R/Ra ratios are （13.95 to 119.58）×10^-6 （cm^3/g）STP and 0.02 to 0.11, respectively, and ^40Ar/^36Ar is 313± 1 to 437 ± 2. Considering the 4He increase caused by high contents of radioactive elements, a mantle-derived fluid probably exists in the inclusions in the fluorite, calcite and bastnaesite samples. The Maoniuping deposit and its associated carbonatite-alkaline complex were formed in 40.3 to 12.2 Ma according to K-Ar and U-Pb data. All these data suggest that large quantities of mantle fluids were involved in the metallogenic process of the Maoniuping REE deposit through a fault system.
