浙江衢州新路火山岩盆地西段热点作用及其对铀成矿的控制作用
摘要
新路火山岩盆地是浙江省重要的产铀基地。文章通过对该区热点作用的研究,解释了该区铀矿床(点)的形成机制,以期获得该区铀矿找矿的新突破。地球物理资料显示,该区深部40 km处存在相对低速体的塑性体(地幔柱冠状体之上的幔枝构造),在其上部地层存在相对高速体的岩浆侵入体;中生代以来发育4次岩浆旋回;地层结构表现出下部为变质基底,中部为滑脱层,上部为上叠火山岩和白垩纪沉积盆地的三层式结构。热点作用的地质、地球物理特征明显。流体包裹体研究表明,成矿热液的温度为317~420℃,盐度w(NaCleq)为39.76%~49.68%,其成分为CO2及含碱、H2O、卤素、氮和一些金属元素,地幔流体特征明显,与铀矿伴生的微量元素及成矿同期的硫同位素也指示出成矿流体来源于上地幔或下地壳。地球物理和地球化学特征均指示出该区存在热点成矿作用,据此建立了该区的热点活动模式。文章认为,热点对该区铀成矿的控制主要表现为:①当深部基性岩浆运移至上地壳时,使硅铝质岩石发生部分熔融,形成酸性岩浆,喷出地表形成了新路火山岩,侵入时则形成次火山岩体和各类酸性侵入岩体,为成矿准备了有利的赋矿层位或有利围岩;②地幔柱上隆作用,形成或复活了一系列断裂构造,完善或形成了成矿所需的导矿构造和储矿构造;③地幔柱上隆时,提供了成矿所需的大量热能,造成围岩蚀变,从而萃取了围岩中的部分铀源;④随着酸性岩浆的不断分异结晶,岩浆中有用组分浓度不断增高,提供了深部热液中的成矿物质。
Xinlu volcanic basin is not only a significant base for uranium production but also the only uranium ore district for exploration in Zhejiang Province at present.In order to make a breakthrough in uranium prognoses,the authors explained the formation mechanism of uranium deposits based on studying the hotspot action in the study area so as to gain confidence in finding concealed deep uranium resources.According to the geophysical deep profile,the relatively low velocity fluid occurs at the depth of-40 km,and the relatively high-velocity magma intrusion occurs in upper strata;there are four magmatic cycles from Mesozoic in the study area;there are also three tiers of stratigraphic configuration showing the obvious hotspot action with the lower tier being metamorphic basement,the middle tier being slippage strata,and the upper tier being lava and Cretaceous sediments.An analysis of fluid inclusions indicates that the metallogenic hydrothermal temperature is 317~420℃,salinity w(NaCleq) is 39.76%~49.68%,and the hydrothermal fluid is composed of CO2,OH-,H2O,halogen,N2,metal elements suggesting features of mantle fluid.Metallogentic hydrothermal fluid originated from the upper mantle or the lower crust,as evidenced by an analysis of trace elements and sulfur isotopes associated with uranium element.The hotspot metallogenesis occurred here.An integrated geophysical and geochemical investigation was made and,on such a basis,a model of hotspot action in the study area was established.There are four aspects reflecting uranium metallogenesis controlled by the hotspot: ① basic magma in deep melts partially with salic rock formed acid magma,which then erupted and resulted in the formation of Xinlu volcanic basin or intrudeed and resulted in the generation of secondary volcanic rock and acid intrusive rock.All of these products would provide favorable strata or wall rock for metallogenesis;② To some extent,a series of faults occurred as a result of mantle plume,which were U-bearing hydrothermal transferring structure or storing structure of mineralization in the process of uranium metallogenesis;③ Part of uranium was extracted from altered wall rock,resulting from heat energy due to the upheaval of the mantle plume;④ The concentration of useful components increased in magma because of differentiation,thus providing the metallogenic material.
Xinlu volcanic basin is not only a significant base for uranium production but also the only uranium ore district for exploration in Zhejiang Province at present.In order to make a breakthrough in uranium prognoses,the authors explained the formation mechanism of uranium deposits based on studying the hotspot action in the study area so as to gain confidence in finding concealed deep uranium resources.According to the geophysical deep profile,the relatively low velocity fluid occurs at the depth of-40 km,and the relatively high-velocity magma intrusion occurs in upper strata;there are four magmatic cycles from Mesozoic in the study area;there are also three tiers of stratigraphic configuration showing the obvious hotspot action with the lower tier being metamorphic basement,the middle tier being slippage strata,and the upper tier being lava and Cretaceous sediments.An analysis of fluid inclusions indicates that the metallogenic hydrothermal temperature is 317~420℃,salinity w(NaCleq) is 39.76%~49.68%,and the hydrothermal fluid is composed of CO2,OH-,H2O,halogen,N2,metal elements suggesting features of mantle fluid.Metallogentic hydrothermal fluid originated from the upper mantle or the lower crust,as evidenced by an analysis of trace elements and sulfur isotopes associated with uranium element.The hotspot metallogenesis occurred here.An integrated geophysical and geochemical investigation was made and,on such a basis,a model of hotspot action in the study area was established.There are four aspects reflecting uranium metallogenesis controlled by the hotspot: ① basic magma in deep melts partially with salic rock formed acid magma,which then erupted and resulted in the formation of Xinlu volcanic basin or intrudeed and resulted in the generation of secondary volcanic rock and acid intrusive rock.All of these products would provide favorable strata or wall rock for metallogenesis;② To some extent,a series of faults occurred as a result of mantle plume,which were U-bearing hydrothermal transferring structure or storing structure of mineralization in the process of uranium metallogenesis;③ Part of uranium was extracted from altered wall rock,resulting from heat energy due to the upheaval of the mantle plume;④ The concentration of useful components increased in magma because of differentiation,thus providing the metallogenic material.
引文
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陈肇博.1982.华东南中生代火山岩中的铀矿床[J].地质学报,(3):235-242.
邓家瑞,张志平.1999.赣杭构造带区域大地构造背景的探讨[J].铀矿地质,15(2):71-85.
杜乐天.1982.花岗岩型铀矿的主要地质规律及成矿模式[A].花岗岩型铀矿文集[C].北京:原子能出版社.
杜乐天.1988.幔汁H-A-C-O-N-S流体[J].大地构造与成矿学,12(1):87-94.
杜乐天.1997.我国地幔流体研究现状与展望[J].地球物理学报,40(增刊):60-69.
韩效忠,刘蓉蓉,刘权,王明太,腰善丛,惠小朝.2010.浙江省衢州地区新路火山岩盆地西段铀成矿模式[J].矿床地质,29(2):332-342.
胡绍康.1982.华南花岗岩型铀矿化与钨(锡)、铌、钽、稀土矿化的关系[A].花岗岩型铀矿文集[C].北京:原子能出版社.
李子颖.2006.华南热点铀成矿作用[J].铀矿地质,22(2):65-69.
刘从强,黄智龙,许成.2004.地幔流体及其成矿作用——以四川冕宁稀土矿床为例[M].北京:地质出版社.
刘正义,韩效忠,高阳,杜乐天,李晓光.2011.热液铀矿床铀富集的物理化学条件[J].东华理工大学学报,34(1):1-10.
毛景文,李晓峰,赫英,张荣华,等.2005.深部流体成矿系统[M].北京:地质出版社.
毛孟才.2002.赣杭铀成矿带大洲矿田定位条件分析及富大铀矿寻找[J].地质找矿论丛,17(3):164-168.
牛树银,侯增谦,孙爱群.2001.核幔成矿物质(流体)的反重力迁移--地幔热柱多级演化成矿作用[J].地学前缘,8(3):95-101.
牛树银.2008.幔枝构造与资源环境[M].北京:地质出版社.161-203.
邱林飞,欧光习,张建锋,张敏.2009.浙江大桥坞铀矿床深部流体作用的地质地球化学证据[J].铀矿地质,25(6):330-337.
丘志力,章邦桐.1991.670矿床多期成矿作用特征及控矿因素研究[J].中山大学学报(自然科学版),30(2):140-149.
涂光炽,李朝阳.2006.浅谈比较矿床学[J].地球化学,35(1):1-5.
王正其,李子颖.2007.幔源铀成矿作用探讨[J].地质论评,33(5):608-615.
张铭杰,王先彬,刘刚.1998.中国东部新生代碱性玄武岩的流体组成及碳、氧同位素地球化学特征[J].地球化学,27(5):452-457.
周家志.1996.对670地区铀成矿的认识[J].铀矿地质,12(1):17-25.
周肖华,严兆彬,胡玉江.2004.浙赣中生代火山岩岩相与铀矿床类型研究[J].东华理工学院学报,27(4):327-332.
Bailey D K.1983.The chemical and thermal evolution of rifts[J].Tectonophysics,94(1-4):585-597.
Candela P Aand Holland HD.1968.A mass ti-ansfer model for copperand molybdenumin magmatic hydrothermal systems:The origin ofcopper porphyry-type ore deposits[J].Econ.Geo1.,81(1):1-19.
Hofmann C,Courtillot V,Feroud G,Rochette P,Yirgu G,Ketefo Eand Pik R.1997.Ti ming of the Ethipoianflood basalt event andi m-plication for plume birth and global change[J].Nature,389:838-841.
Mungall J E.2002.Roastingthe mantle:Slab melting andthe genesis ofmajor Au and Au-rich Cu deposit[J].Geology,30(10):915-918.
Neugebauer H J.1987.Models of lithospheric thinning[J].Annu.Rev.Earth Planet.Sci.,15:421-443.
Olson Pand Singer H.1986.Creeping plumes[J].Journal of Geophysi-cal Research,91:6367-6374.
Robb L.2005.Introduction to ore-forming process[M].Oxford:Blackwell.166p.
Schilling J.1991.Fluxes and excess temperatures of mantle plumes in-ferred fromtheir interaction with migrating mid-ocean ridge[J].Na-ture,352:397-403.
Sillitoe R H.1997.Characteristics and controls of the largest porphyrycopper-gold and epithermal gold deposits in the circum-Pacific region[J].Australian Journal of Earth Sciences,44(3):373-388.
Solomon M.1990.Subductlomarc reversal and the origin of porphyrycopper-gold deposits inisland arcs[J].Geology,18(7):630-633.
Taylor S R.1987.The composition and petrogenesis of thelower crust:Axenolith study[J].Journal of Geophysical Research,92(B13):13981-14005.
White Rand Mckenzie D.1989.Magmatismat rift zones:The genera-tion of volcanic continental margins and flood basalts[J].Journal ofGeophysical Research,94(6):7685-7729.
陈跃辉,陈肇博,陈祖伊,蔡煜琦.1998.华东南中新生代伸展构造与铀成矿作用[M].北京:原子能出版社.153-156.
陈肇博.1982.华东南中生代火山岩中的铀矿床[J].地质学报,(3):235-242.
邓家瑞,张志平.1999.赣杭构造带区域大地构造背景的探讨[J].铀矿地质,15(2):71-85.
杜乐天.1982.花岗岩型铀矿的主要地质规律及成矿模式[A].花岗岩型铀矿文集[C].北京:原子能出版社.
杜乐天.1988.幔汁H-A-C-O-N-S流体[J].大地构造与成矿学,12(1):87-94.
杜乐天.1997.我国地幔流体研究现状与展望[J].地球物理学报,40(增刊):60-69.
韩效忠,刘蓉蓉,刘权,王明太,腰善丛,惠小朝.2010.浙江省衢州地区新路火山岩盆地西段铀成矿模式[J].矿床地质,29(2):332-342.
胡绍康.1982.华南花岗岩型铀矿化与钨(锡)、铌、钽、稀土矿化的关系[A].花岗岩型铀矿文集[C].北京:原子能出版社.
李子颖.2006.华南热点铀成矿作用[J].铀矿地质,22(2):65-69.
刘从强,黄智龙,许成.2004.地幔流体及其成矿作用——以四川冕宁稀土矿床为例[M].北京:地质出版社.
刘正义,韩效忠,高阳,杜乐天,李晓光.2011.热液铀矿床铀富集的物理化学条件[J].东华理工大学学报,34(1):1-10.
毛景文,李晓峰,赫英,张荣华,等.2005.深部流体成矿系统[M].北京:地质出版社.
毛孟才.2002.赣杭铀成矿带大洲矿田定位条件分析及富大铀矿寻找[J].地质找矿论丛,17(3):164-168.
牛树银,侯增谦,孙爱群.2001.核幔成矿物质(流体)的反重力迁移--地幔热柱多级演化成矿作用[J].地学前缘,8(3):95-101.
牛树银.2008.幔枝构造与资源环境[M].北京:地质出版社.161-203.
邱林飞,欧光习,张建锋,张敏.2009.浙江大桥坞铀矿床深部流体作用的地质地球化学证据[J].铀矿地质,25(6):330-337.
丘志力,章邦桐.1991.670矿床多期成矿作用特征及控矿因素研究[J].中山大学学报(自然科学版),30(2):140-149.
涂光炽,李朝阳.2006.浅谈比较矿床学[J].地球化学,35(1):1-5.
王正其,李子颖.2007.幔源铀成矿作用探讨[J].地质论评,33(5):608-615.
张铭杰,王先彬,刘刚.1998.中国东部新生代碱性玄武岩的流体组成及碳、氧同位素地球化学特征[J].地球化学,27(5):452-457.
周家志.1996.对670地区铀成矿的认识[J].铀矿地质,12(1):17-25.
周肖华,严兆彬,胡玉江.2004.浙赣中生代火山岩岩相与铀矿床类型研究[J].东华理工学院学报,27(4):327-332.
Bailey D K.1983.The chemical and thermal evolution of rifts[J].Tectonophysics,94(1-4):585-597.
Candela P Aand Holland HD.1968.A mass ti-ansfer model for copperand molybdenumin magmatic hydrothermal systems:The origin ofcopper porphyry-type ore deposits[J].Econ.Geo1.,81(1):1-19.
Hofmann C,Courtillot V,Feroud G,Rochette P,Yirgu G,Ketefo Eand Pik R.1997.Ti ming of the Ethipoianflood basalt event andi m-plication for plume birth and global change[J].Nature,389:838-841.
Mungall J E.2002.Roastingthe mantle:Slab melting andthe genesis ofmajor Au and Au-rich Cu deposit[J].Geology,30(10):915-918.
Neugebauer H J.1987.Models of lithospheric thinning[J].Annu.Rev.Earth Planet.Sci.,15:421-443.
Olson Pand Singer H.1986.Creeping plumes[J].Journal of Geophysi-cal Research,91:6367-6374.
Robb L.2005.Introduction to ore-forming process[M].Oxford:Blackwell.166p.
Schilling J.1991.Fluxes and excess temperatures of mantle plumes in-ferred fromtheir interaction with migrating mid-ocean ridge[J].Na-ture,352:397-403.
Sillitoe R H.1997.Characteristics and controls of the largest porphyrycopper-gold and epithermal gold deposits in the circum-Pacific region[J].Australian Journal of Earth Sciences,44(3):373-388.
Solomon M.1990.Subductlomarc reversal and the origin of porphyrycopper-gold deposits inisland arcs[J].Geology,18(7):630-633.
Taylor S R.1987.The composition and petrogenesis of thelower crust:Axenolith study[J].Journal of Geophysical Research,92(B13):13981-14005.
White Rand Mckenzie D.1989.Magmatismat rift zones:The genera-tion of volcanic continental margins and flood basalts[J].Journal ofGeophysical Research,94(6):7685-7729.
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