摘要
通过锆石U-Pb定年、全岩主微量元素、Sr-Nd-Pb和锆石Hf同位素测试,对滇西姚安Au-Pb-Ag矿床含矿正长斑岩和粗面岩的地球化学特征进行了分析,系统探讨了其岩浆起源和演化过程.正长斑岩和粗面岩的锆石U-Pb年龄分别为33.8±0.42 Ma和33.9±0.60 Ma,它们与同时代滇西镁铁质火山岩和煌斑岩具有相似的稀土和微量元素配分模式和Sr-Nd-Pb同位素组成,而与区内同时代加厚地壳来源的富碱埃达克质岩石存在Sr-Nd-Pb-Hf同位素组成的明显差异.全岩SiO_2与主微量元素关系指示正长斑岩和粗面岩总体上可由矿区内同时代的基性岩浆岩分异演化而来,表明它们与这些基性岩浆岩起源相似,较高的Rb/Sr(≥0.1)和较低的Ba/Rb(﹤20)比值,指示其源区为富金云母富集地幔,较低的εHf和古老的模式年龄暗示源区的交代富集发生在中元古代.姚安富碱岩浆活动与矿化关系密切.正长斑岩和粗面岩较滇西镁铁质火山岩和煌斑岩具有稍高的初始Pb同位素组成,暗示岩浆可能遭受了地壳混染,从而提高了母岩浆中的金属含量,增强了岩浆成矿潜力;适中的氧逸度利于Au富集;角闪石分离结晶和较多黑云母发育指示母岩浆含水量较高,利于成矿流体的形成.这些特征综合起来为矿化发育提供了有利条件.
Newly-determined zircon U-Pb ages, whole rock major and trace elements, Sr-Nd-Pb and zircon Hf isotope data, are used to firstly examine the geochemical characteristics of the ore-related syenite porphyry and trachyte in the Yao'an Au-Pb-Ag deposit,western Yunnan,and then to systematically discuss the origin and evolution processes of the parental magmas in this paper.The zircon U-Pb ages of the syenite porphyry and trachyte in the Yao'an Au-Pb-Ag deposit respectively are 33.8±0.42 Ma and33.9±0.60 Ma. And their patterns of trace elements and REE, and the Sr-Nd-Pb isotopes, are very similar to the contemporary mafic volcanic rocks and lamprophyre from the western Yunnan, but obviously different from the contemporary alkali-rich adakitic rocks in the western Yangtze craton. The relationships of SiO_2 contents with major and trace element contents of the whole-rocks indicate that magmas for the syenite porphyry and trachyte could be formed by differentiation of the contemporary mafic magmas in the diggings. This implies that syenite porphyry and trachyte may have similar source to the mafic magmas. High Rb/Sr(≥0.1) and low Ba/Rb(﹤20) ratios of the syenite porphyry and trachyte indicate that they were derived from a metasomatized enriched mantle source with abundant phlogopite. And the low εHfand the old model age of the rocks indicate that the metasomatism of the source region might happen in Mesoproterozoic. The alkali-rich magmation in Yao'an is closely related with the mineralization. The syenite porphyry and trachyte of Yao'an have a higher initial Pb isotopic composition than the mafic volcanic rocks and lamprophyre from the western Yunnan, which implies that some degrees of the crustal contamination might occur during evolution process of the magmas which could increase the metal contents of the magma and enhance the mineralization potential of the magmas. The moderate oxygen fugacity of the magmas in favour of the Au enrichment. And the obvious fractional crystallization of hornblende and the formation of abundant biotite indicate that the primary magmas were very hydrous, which facilitated the formation of oreforming fluids. All of these features could provide advantageous conditions for the mineralization in the Yao'an deposit.
引文
Andersen,T.,2002.Correction of Common Lead in U-Pb Analyses that do not Report204Pb.Chemical Geology,192(1-2):59-79.https://doi.org/10.1016/s0009-2541(02)00195-x
Baker,M.B.,Hirschmann,M.M.,Ghiorso,M.S.,et al.,1995.Compositions of Near-Solidus Peridotite Melts from Experiments and Thermodynamic Calculations.Nature,375:308-311.https://doi.org/10.1038/375308a0
Bi,X.W.,Hu,R.Z.,Cornell,D.H.,2000.The Evolution of OreForming Fluid and REE Geochemistry of Yao’an Au Deposit.Bulletin of Mineralogy,Petrology and Geochemisty,19(4):263-265(in Chinese).
Bi,X.W.,Hu,R.Z.,Hanley,J.J.,et al.,2009.Crystallisation Conditions(T,P,fO2)from Mineral Chemistry of Cuand Au-Mineralised Alkaline Intrusions in the Red RiverJinshajiang Alkaline Igneous Belt,Western Yunnan Province,China.Mineralogy and Petrology,96(1-2):43-58.https://doi.org/10.1007/s00710-009-0047-4
Bi,X.W.,Hu,R.Z.,Peng,J.T.,et al.,2005.Geochemical Characteristics of the Yao'an and Machangqing AlkalineRich Intrusions.Acta Petrologica Sinica,21(1):113-124(in Chinese with English abstract).
Botcharnikov,R.E.,Linnen,R.L.,Wilke,M.,et al.,2011.High Gold Concentrations in Sulphide-Bearing Magma under Oxidizing Conditions.Nature Geoscience,4(2):112-115.https://doi.org/10.1038/ngeo1042
Chen,F.K.,Li,X.H.,Wang,X.L.,et al.,2007.Zircon Age and Nd-Hf Isotopic Composition of the Yunnan Tethyan Belt,Southwestern China.International Journal of Earth Sciences,96(6):1179-1194.https://doi.org/10.1007/s00531-006-0146-y
Cheng,J.,Xia,B.,Zhang,Y.Q.,2007.Petrological and Geochemical Characteristics of Yao’an Alkailine Complex in Yunnan Province.Geotectonica et Metallogenia,31(1):118-125(in Chinese with English abstract).
Chung,S.L.,Chu,M.F.,Zhang,Y.Q.,et al.,2005.Tibetan Tectonic Evolution Inferred from Spatial and Temporal Variations in Post-Collisional Magmatism.Earth-Science Reviews,68(3-4):173-196.https://doi.org/10.1016/j.earscirev.2004.05.001
Chung,S.L.,Jahn,B.M.,1995.Plume-Lithosphere Interaction in Generation of the Emeishan Flood Basalts at the Permian-Triassic Boundary.Geology,23(10):889.
Foley,S.F.,Jackson,S.E.,Fryer,B.J.,et al.,1996.Trace Element Partition Coefficients for Clinopyroxene and Phlogopite in an Alkaline Lamprophyre from Newfoundland by LAM-ICP-MS.Geochimica et Cosmochimica Acta,60(4):629-638.https://doi.org/10.1016/0016-7037(95)00422-x
Gao,S.,Ling,W.L.,Qiu,Y.M.,et al.,1999.Contrasting Geochemical and Sm-Nd Isotopic Compositions of Archean Metasediments from the Kongling High-Grade Terrain of the Yangtze Craton:Evidence for Cratonic Evolution and Redistribution of REE during Crustal Anatexis.Geochimica et Cosmochimica Acta,63(13-14):2071-2088.https://doi.org/10.1016/s0016-7037(99)00153-2
Griffin,W.L.,Pearson,N.J.,Belousova,E.,et al.,2000.The Hf Isotope Composition of Cratonic Mantle:LAM-MC-ICPMS Analysis of Zircon Megacrysts in Kimberlites.Geochimica et Cosmochimica Acta,64(1):133-147.https://doi.org/10.1016/s0016-7037(99)00343-9
Guo,Z.F.,Hertogen,J.,Liu,J.Q.,et al.,2005.Potassic Magmatism in Western Sichuan and Yunnan Provinces,SETibet,China:Petrological and Geochemical Constraints on Petrogenesis.Journal of Petrology,46(1):33-78.https://doi.org/10.1093/petrology/egh061
He,J.,Wang,Q.Y.,Yan,G.C.,2018.Genesis and Geodynamic Settings of the Eocene Lamprophyres from JinshajiangRed River Tectonic Belt,Ludian,Western Yunnan Province.Earth Science,43(8):2586-2599(in Chinese with English abstract).
He,W.Y.,Mo,X.X.,He,Z.H.,et al.,2015.The Geology and Mineralogy of the Beiya Skarn Gold Deposit in Yunnan,Southwest China.Economic Geology,110(6):1625-1641.https://doi.org/10.2113/econgeo.110.6.1625
Hou,Z.Q.,Duan,L.F.,Lu,Y.J.,et al.,2015.Lithospheric Architecture of the Lhasa Terrane and Its Control on Ore Deposits in the Himalayan-Tibetan Orogen.Economic Geology,110(6):1541-1575.https://doi.org/10.2113/econgeo.110.6.1541
Hou,Z.Q.,Pan,G.T.,Wang,A.J.,et al.,2006b.Metallogenesis in Tibetan Collisional Orogenic Belt:Ⅱ.Mineralization in Late-Collisional Transformation Setting.Mineral Deposits,25(5):521-543(in Chinese with English abstract).
Hou,Z.Q.,Qu,X.M.,Yang,Z.S.,et al.,2006c.Metallogenesis in Tibetan Collisional Orogenic Belt:Ⅲ.Mineralization in Post-Collisional Extension Setting.Mineral Deposits,25(6):629-651(in Chinese with English abstract).
Hou,Z.Q.,Yang,Z.S.,Xu,W.Y.,et al.,2006a.Metallogenesis in Tibetan Collisional Orogenic Belt:Ⅰ.Mineralization in Main Collisional Orogenic Setting.Mineral Deposits,25(4):337-358(in Chinese with English abstract).
Hou,Z.Q.,Zeng,P.S.,Gao,Y.F.,et al.,2006.Himalayan CuMo-Au Mineralization in the Eastern Indo-Asian Collision Zone:Constraints from Re-Os Dating of Molybdenite.Mineralium Deposita,41(1):33-45.https://doi.org/10.1007/s00126-005-0038-2
Hou,Z.Q.,Zhou,Y.,Wang,R.,et al.,2017.Recycling of Metal-Fertilized Lower Continental Crust:Origin of NonArc Au-Rich Porphyry Deposits at Cratonic Edges.Geology,45(6):563-566.https://doi.org/10.1130/g38619.1
Hu,Z.C.,Liu,Y.S.,Gao,S.,et al.,2012.Improved In Situ Hf Isotope Ratio Analysis of Zircon Using Newly Designed X Skimmer Cone and Jet Sample Cone in Combination with the Addition of Nitrogen by Laser Ablation Multiple Collector ICP-MS.Journal of Analytical Atomic Spectrometry,27(9):1391-1399.
Jiang,Y.H.,Jiang,S.Y.,Ling,H.F.,et al.,2006.Low-Degree Melting of a Metasomatized Lithospheric Mantle for the Origin of Cenozoic Yulong Monzogranite-Porphyry,East Tibet:Geochemical and Sr-Nd-Pb-Hf Isotopic Constraints.Earth and Planetary Science Letters,241(3-4):617-633.https://doi.org/10.1016/j.epsl.2005.11.023
Li,Y.,Audétat,A.,2012.Partitioning of V,Mn,Co,Ni,Cu,Zn,As,Mo,Ag,Sn,Sb,W,Au,Pb,and Bi between Sulfide Phases and Hydrous Basanite Melt at Upper Mantle Conditions.Earth and Planetary Science Letters,355-356:327-340.https://doi.org/10.1016/j.epsl.2012.08.008
Li,Y.,Mo,X.X.,Yu,X.H.,et al.,2011.Zircon U-Pb Dating of Several Selected Alkali-Rich Porphyries from the Jinshajiang-Ailaoshan Fault Zone and Geological Significance.Geoscience,25(2):189-200(in Chinese with English abstract).
Lu,Y.J.,Campbell,M.T.,Li,Z.X.,et al.,2015.Paleogene Post-Collisional Lamprophyres in Western Yunnan,Western Yangtze Craton:Mantle Source and Tectonic Implications.Lithos,233:139-161.https://doi.org/10.1016/j.lithos.2015.02.003
Lu,Y.J.,Kerrich,R.,Cawood,P.A.,et al.,2012.Zircon SHRIMP U-Pb Geochronology of Potassic Felsic Intrusions in Western Yunnan,SW China:Constraints on the Relationship of Magmatism to the Jinsha Suture.Gondwana Research,22(2):737-747.https://doi.org/10.1016/j.gr.2011.11.016
Lu,Y.J.,Kerrich,R.,Kemp,A.I.S.,et al.,2013b.Intracontinental Eocene-Oligocene Porphyry Cu Mineral Systems of Yunnan,Western Yangtze Craton,China:Compositional Characteristics,Sources,and Implications for Continental Collision Metallogeny.Economic Geology,108(7):1541-1576.https://doi.org/10.2113/econgeo.108.7.1541
Lu,Y.J.,Kerrich,R.,McCuaig,T.C.,et al.,2013a.Geochemical,Sr-Nd-Pb,and Zircon Hf-O Isotopic Compositions of Eocene-Oligocene Shoshonitic and Potassic AdakiteLike Felsic Intrusions in Western Yunnan,SW China:Petrogenesis and Tectonic Implications.Journal of Petrology,54(7):1309-1348.https://doi.org/10.1093/petrology/egt013
Mo,X.X.,Zhao,Z.D.,Deng,J.F.,et al.,2003.Response of Volcanism to the India-Asia Collision.Earth Science Frontiers,10(3):135-148(in Chinese with English abstract).
Mole,D.R.,Fiorentini,M.L.,Thebaud,N.,et al.,2014.Archean Komatiite Volcanism Controlled by the Evolution of Early Continents.Proceedings of the National Academy of Sciences,111(28):10083-10088.https://doi.org/10.1073/pnas.1400273111
Qian,X.G.,Li,Z.W.,2000.Geologicial and Geochmical Characteristics of the Yaoan Gold Ore Deposit in Central Yunnan.Geotectonica et Metallogenia,24(Suppl.1):30-36(in Chinese with English abstract).
Tapponnier,P.,Lacassin,R.,Leloup,P.H.,et al.,1990.The Ailao Shan/Red River Metamorphic Belt:Tertiary LeftLateral Shear between Indochina and South China.Nature,343:431-437.
Wang,Q.,Xu,J.F.,Jian,P.,et al.,2006.Petrogenesis of Adakitic Porphyries in an Extensional Tectonic Setting,Dexing,South China:Implications for the Genesis of Porphyry Copper Mineralization.Journal of Petrology,47(1):119-144.https://doi.org/10.1093/petrology/egi070
Wang,X.C.,Li,X.H.,Li,W.X.,et al.,2009.Variable Involvements of Mantle Plumes in the Genesis of Mid-Neoproterozoic Basaltic Rocks in South China:A Review.Gondwana Research,15(3-4):381-395.https://doi.org/10.1016/j.gr.2008.08.003
Williams,I.S.,1992.Some Observations on the Use of Zircon U-Pb Geochronology in the Study of Granitic Rocks.Earth and Environmental Science Transactions of the Royal Society of Edinburgh,83(1-2):447-458.
Xia,P.,Xu,Y.G.,2005.Domains and Enrichment Mechanism of the Lithospheric Mantle in Western Yunnan:A Comparative Study on Two Types of Cenozoic Ultrapotassic Rocks.Science in China(Series D),48(3):326-337.
Yang,J.H.,Du,Y.S.,Yu,X.,et al.,2017.Early Permian Volcanic Fragment-Bearing Sandstones in Babu of Southeast Yunnan:Indicative of Paleo-Tethyan Ocean Subduction.Earth Science,42(1):24-34(in Chinese with English abstract).
Zajacz,Z.,Seo,J.H.,Candela,P.A.,et al.,2010.Alkali Metals Control the Release of Gold from Volatile-Rich Magmas.Earth and Planetary Science Letters,297(1-2):50-56.https://doi.org/10.1016/j.epsl.2010.06.002
Zeng,P.S.,Mo,X.X.,Yu,X.H.,2002.Nd,Sr and Pb Isotopic Characteristics of the Alkaline-Rich Porphyries in Western Yunnan and Its Compression Strike-Slip Setting.Acta Petrologica et Mineralogica,21(3):231-241(in Chinese with English abstract).
Zhang,H.,Ma,D.F.,Zhang,H.,et al.,2017.Zircon LA-ICP-MS U-Pb Dating and Geological Significance of Quartz Monzonite-Porphyry from Xifanping Copper Deposit in Yanyuan County,Sichuan Province,China.Acta Mineralogica Sinica,37(4):475-485.
Zhang,Y.Q.,Xie,Y.W.,Tu,G.C.,1987.Preliminary Studies of the Alkali-Rich Intrusive Rocks in the Alaoshan-Jinshajiang Belt and Their Bearing on Rift Tectonics.Acta Petrologica Sinica,3(1):19-28(in Chinese with English abstract).
Zhao,X.,Yu,X.H.,Mo,X.X.,et al.,2004..Petrological and Geochemical Characteristics of Cenozoic Alkali-Rich Porphyries and Xenoliths Hosted in Western Yunnan Province.Geoscience,18(2):217-228(in Chinese with English abstract).
Zhu,X.P.,Mo,X.X.,White,N.C.,et al.,2013.Petrogenesis and Metallogenic Setting of the Habo Porphyry Cu-(MoAu)Deposit,Yunnan,China.Journal of Asian Earth Sciences,66:188-203.
毕献武,胡瑞忠,Cornell,D.H.,2000.姚安金矿床成矿流体形成演化的稀土元素地球化学.矿物岩石地球化学通报,19(4):263-265.
毕献武,胡瑞忠,彭建堂,等,2005.姚安和马厂箐富碱侵入岩体的地球化学特征.岩石学报,21(1):113-124.
程锦,夏斌,张玉泉,2007.云南姚安碱性杂岩体的岩石学和地球化学特征.大地构造与成矿学,31(1):118-125.
贺娟,王启宇,闫国川,2018.滇西金沙江-红河构造带鲁甸始新世煌斑岩成因及动力学背景.地球科学,43(8):2586-2599.
侯增谦,潘桂棠,王安建,等,2006b.青藏高原碰撞造山带:Ⅱ.晚碰撞转换成矿作用.矿床地质,25(5):521-543.
侯增谦,曲晓明,杨竹森,等,2006c.青藏高原碰撞造山带:Ⅲ.后碰撞伸展成矿作用.矿床地质,25(6):629-651.
侯增谦,杨竹森,徐文艺,等,2006a.青藏高原碰撞造山带:Ⅰ.主碰撞造山成矿作用.矿床地质,25(4):337-358.
李勇,莫宣学,喻学惠,等,2011.金沙江-哀牢山断裂带几个富碱斑岩体的锆石U-Pb定年及地质意义.现代地质,25(2):189-200.
莫宣学,赵志丹,邓晋福,等,2003.印度-亚洲大陆主碰撞过程的火山作用响应.地学前缘,10(3):135-148.
钱祥贵,李志伟,2000.滇中姚安金矿床地质地球化学特征.大地构造与成矿学,24(增刊1):30-36.
杨江海,杜远生,于鑫,等,2017.滇东南八布早二叠世含火山岩屑砂岩指示古特提斯洋俯冲.地球科学,42(1):24-34.
曾普胜,莫宣学,喻学惠,2002.滇西富碱斑岩带的Nd、Sr、Pb同位素特征及其挤压走滑背景.岩石矿物学杂志,21(3):231-241.
张玉泉,谢应雯,涂光炽,1987.哀牢山-金沙江富碱侵入岩及其与裂谷构造关系初步研究.岩石学报,3(1):19-28.
赵欣,喻学惠,莫宣学,等,2004.滇西新生代富碱斑岩及其深源包体的岩石学和地球化学特征.现代地质,18(2):217-228.