庙垭铌-稀土矿床的热液蚀变作用:来自碳酸岩碳-氧同位素的制约
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摘要
对湖北省庙垭铌-稀土矿床火成碳酸岩全岩进行了碳-氧同位素分析结果显示,庙垭碳酸岩δ13C值为-5.84‰~-3.46‰,与正常地幔和初始火成碳酸岩值基本一致,δ18O值为11.3‰~13.4‰,明显高于正常地幔和初始碳酸岩值,与富CO2-H2O流体交代后的碳酸盐岩的C-O同位素结果相似。结合矿物学、岩石学和流体包裹体观察和研究结果,初步判断庙垭碳酸岩可能经历了后期热液蚀变作用改造过程。应用水-岩交换模型计算进一步获得热液蚀变温度为约400~600°C,水/岩比为10~200。通过与区域上杀熊洞碱性-碳酸岩杂岩体和内蒙古白云鄂博Nb-Fe-REE矿床中碳酸岩的C-O同位素组成进行对比,初步认为后期热液流体交代蚀变作用过程对与火成碳酸岩相关的超大型Nb-REE矿床形成可能具有重要意义。
Whole-rock carbon and oxygen isotope compositions for the carbonatite of the Miaoya Nb-REE deposit in the Hubei Province were measured. The results show that δ13 C values of the carbonatite range from-5.84‰ to-3.46‰, consistent with the normal mantle δ13 C values, whereas their δ18 O values vary from 11.3‰ to 13.4‰, evidently higher than the normal mantle and the primary carbonatite values. Combined with the mineralogy, petrology and fluid inclusion observations, it is suggested that the Miaoya carbonatite might have experienced alteration by post-carbonatite hydrothermal fluid. Water-rock exchange modeling further indicates that the alteration temperatures are about 400~600° C and water/rock ratios are 10~200. Compared with the regional Shaxiongdong syenite-carbonatite complexes and the Inner Mongolia Bayan Obo Nb-Fe-REE deposit by C-O isotope compositions, we hypothesis that the post-carbonatite hydrothermal alteration could be of great significance to the carbonatite-related super-large Nb-REE deposits.
Whole-rock carbon and oxygen isotope compositions for the carbonatite of the Miaoya Nb-REE deposit in the Hubei Province were measured. The results show that δ13 C values of the carbonatite range from-5.84‰ to-3.46‰, consistent with the normal mantle δ13 C values, whereas their δ18 O values vary from 11.3‰ to 13.4‰, evidently higher than the normal mantle and the primary carbonatite values. Combined with the mineralogy, petrology and fluid inclusion observations, it is suggested that the Miaoya carbonatite might have experienced alteration by post-carbonatite hydrothermal fluid. Water-rock exchange modeling further indicates that the alteration temperatures are about 400~600° C and water/rock ratios are 10~200. Compared with the regional Shaxiongdong syenite-carbonatite complexes and the Inner Mongolia Bayan Obo Nb-Fe-REE deposit by C-O isotope compositions, we hypothesis that the post-carbonatite hydrothermal alteration could be of great significance to the carbonatite-related super-large Nb-REE deposits.
引文
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[18]杨学明,杨晓勇,郑永飞,郭范,张兆峰,张培善,Le Bas M J.白云鄂博富稀土元素碳酸岩墙的碳和氧同位素特征[J].高校地质学报,2000,6(2):205-209.
[19]Matsuhisa Y.Oxygen isotope composition of volcanic rocks from the East Japan Island Arcs and their bearing on petrogenesis[J].Journal of Volcanology and Geothermal Research,1979,5:271-296.
[20]van Groos K A F,Wyllie P J.Liquid immiscibility in the system Na2O-Al2O3-Si O2-CO2at pressures up to 1 kilobar[J].American Journal of Science,1966,264:234-255.
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[22]O’Neil J R,Clayton R N,Mayeda T K.Oxygen-isotope fractionations in systems containing dolomite[J].Journal of Geology,1966,74:174-196.
[23]Taylor H P.Water/rock interactions and the origin of H2O in granitic batholiths[J].Journal of Geological Society of London,1977,133:509-558.
[24]舒勇,郑永飞,魏春生,周建波,杨学明,杨晓勇.白云鄂博碳酸岩墙碳氧同位素地球化学[J].地球化学,2001,30(2):169-176.
[25]Fan H R,Hu F F,Yang K F,Pirajno F,Liu X,Wang K Y.Integrated U-Pb and Sm-Nd geochronology for a REE-rick carbonatite dyke at the giant Bayan Obo REE deposit,Northern China[J].Ore Geology Reviews,2014,63:510-519.
[26]Harlov D E,Andersson U B,Foerster H,Nystrom J O,Dulski P,Broman C.Apatite-monazite relations in the Kiirunavaara magnetite-apatite ore,northern Sweden[J].Chemical Geology,2002,191:47-72.
[27]Woodard J,Hetherington C J.Carbonatite in a post-collisional tectonic setting:geochronology and emplacement conditions at Naantali,SW Finland[J].Precambrian Research,240:94-107.
[2]Xu C,Chakhmouradian A R,Taylor R N,Kynicky J,Li W B,Song W L,Fletcher I R.Origin of carbonatites in the South Qinling orogen:implications for crustal recycling and timing of collision between the South and North China blocks[J].Geochmica et Cosmochimica Acta,2014,143,189-206.
[3]李石.湖北庙垭碳酸岩地球化学特征及岩石成因探讨[J].地球化学,1980,4:345-355.
[4]Xu C,Campbell I H,Allen C M,Chen Y J,Huang Zhi L,Qi L,Zhang G S,Yan Z F.U-Pb zircon age,geochemical and isotopic characteristics of carbonatite and syenite complexes from the Shaxiongdong,China[J].Lithos,2008,105(1-2):118-128.
[5]Ling M X,Liu Y L,Williams I S,Teng F Z,Yang X Y,Ding X,Wei G J,Xie L H,Deng W F,Sun W D.Formation of the world’s largest REE deposit through protracted fluxing of carbonatite by subduction-derived fluids[J].Scientific Reports,2013,3:1776-1783.
[6]Smith M P,Campbell L S,Kynicky J.A review of the genesis of the world class Bayan Obo Fe-REE-Nb deposits,Inner Mongolia,China:multistage processes and outstanding questions[J].Ore Geology Reviews,2015,64:459-476.
[7]Poletti J E,Cottle J M,Hagenpeter G A,Lackey J S.Petrochronological constraints on the origin of the Mountain Pass ultrapotassic and carbonatite intrusive suite,California[J].Journal of Petrology,2016,57:1555-1598.
[8]Zhu J,Wang L X,Peng S G,Peng L H,Wu C X,Qiu X F.U-Pb zircon age,geochemical and isotopic characteristics of the Miaoya syenite and carbonatite complex,central China[J].Geological Journal,2016,Doi:10.1002/gj.2859.
[9]Santos V S,Clayton N C.Variations of oxygen and carbon isotopes in carbonatite:a study of Brazilian alkaline complexes[J].Geochimica et Cosmochimica Acta,1995,59:1339-1352.
[10]Meng Q R,Zhang G W.Geologic framework and tectonic evolution of the Qinling orogen,central China[J].Tectonophysics,2000,323:183-196.
[11]Wu Y B,Zhou G Y,Gao S,Liu X C,Qin Z W,Wang H,Yang J Z,Yang S H.Petrogenesis of Neoarchean TTG rocks in the Yangtze Craton and its implication for the formation of Archean TTGs[J].Precambrian Research,2014,254:73-86.
[12]Dong Y P,Zhang G W,Neubauer F,Liu X M,Genser J,Hauzenberger C.Tectonic evolution of the Qinling orogen,China:review and synthesis[J].Journal of Asian Earth Sciences,2011,41:213-237.
[13]Ling W L,Ren B F,Duan R C,Liu X M,Mao X W,Peng L H,Liu Z X,Cheng J P,Yang H M.Timing of the Wudangshan,Yaolinghe volcanic sequences and mafic sills in South Qinling:U-Pb zircon geochronology and tectonic implication[J].Chinese Science Bulletin,2008,53:2192-2199.
[14]Xu C,Kynicky J,Chakhmouradian A R,Li X H,Song W L.A case example of the importance of multi-analytical approach in deciphering carbonatite petrogenesis in South Qinling orogen:Miaoya rare metal deposit,central China[J].Lithos,2015,227:107-121.
[15]Ying Y C,Chen W,Lu J,Jiang S Y,Yang Y H.In situ U-Th-Pb ages of the Miaoya carbonatite complex in the South Qinling orogenic belt,central China[J].Lithos,in press.
[16]Taylor H P J,Frechen J,Degens E T.Oxygen and carbon isotope studies of carbonatites from the Laacher See district,West Germany,and the Alno district,Sweden[J].Geochimica et Cosmochimica Acta,1967,31:407-430.
[17]Keller J,Hoefs J.Stable isotope characteristics of recent natrocarbonatites from Oldoinyo Lengai[A].Bell K,Keller J.Carbonatites Volcanism:Oldoinyo Lengai and Petrogenesis of Natrocarbonatites[M].Berlin:LAVCEI Proceeding in Volcanology.Springer-Verlag,1995:113-123.
[18]杨学明,杨晓勇,郑永飞,郭范,张兆峰,张培善,Le Bas M J.白云鄂博富稀土元素碳酸岩墙的碳和氧同位素特征[J].高校地质学报,2000,6(2):205-209.
[19]Matsuhisa Y.Oxygen isotope composition of volcanic rocks from the East Japan Island Arcs and their bearing on petrogenesis[J].Journal of Volcanology and Geothermal Research,1979,5:271-296.
[20]van Groos K A F,Wyllie P J.Liquid immiscibility in the system Na2O-Al2O3-Si O2-CO2at pressures up to 1 kilobar[J].American Journal of Science,1966,264:234-255.
[21]Demény A,Ahijado A,Casillas R,Vennemann T W.Crustal contamination and fluid/rock interaction in the carbonatites of Fuerteventura(Canary Islands,Spain):a C,O,H isotope study[J].Lithos,1998,44:101-115.
[22]O’Neil J R,Clayton R N,Mayeda T K.Oxygen-isotope fractionations in systems containing dolomite[J].Journal of Geology,1966,74:174-196.
[23]Taylor H P.Water/rock interactions and the origin of H2O in granitic batholiths[J].Journal of Geological Society of London,1977,133:509-558.
[24]舒勇,郑永飞,魏春生,周建波,杨学明,杨晓勇.白云鄂博碳酸岩墙碳氧同位素地球化学[J].地球化学,2001,30(2):169-176.
[25]Fan H R,Hu F F,Yang K F,Pirajno F,Liu X,Wang K Y.Integrated U-Pb and Sm-Nd geochronology for a REE-rick carbonatite dyke at the giant Bayan Obo REE deposit,Northern China[J].Ore Geology Reviews,2014,63:510-519.
[26]Harlov D E,Andersson U B,Foerster H,Nystrom J O,Dulski P,Broman C.Apatite-monazite relations in the Kiirunavaara magnetite-apatite ore,northern Sweden[J].Chemical Geology,2002,191:47-72.
[27]Woodard J,Hetherington C J.Carbonatite in a post-collisional tectonic setting:geochronology and emplacement conditions at Naantali,SW Finland[J].Precambrian Research,240:94-107.