【作者】 汤庆艳；

【导师】 张铭杰； 李楚思；

【作者基本信息】 兰州大学 ， 矿物学、岩石学、矿床学， 2013， 博士

【摘要】 镍、铜和铂族元素(PGE)是十分重要的战略资源,地幔柱岩浆成矿作用是Cu-Ni-PGE硫化物矿床的重要成矿机制。峨眉山二叠纪地幔柱与西伯利亚地幔柱形成时间相近,形成了Fe-Ti-V氧化物矿床和Ni-Cu-PGE硫化物矿床两种类型完全不同的矿床,但发现的Ni-Cu-PGE硫化物矿床资源量远比不上西伯利亚大火成岩省。本论文选择峨眉山大理地区的苦橄岩、玄武岩和凝灰岩及镍铜铂族硫化物矿床(朱布、力马河和青矿山矿床等),通过系统的矿物学、岩石学、锆石U-Pb年代学、主-微量元素、铂族元素、Sr-Nd-Hf同位素和流体化学组成及C-He-Ar同位素组成系统研究,对比西伯利亚地幔柱成因Noril’sk-Talnakh铜镍铂族硫化物矿床和我国金川超大型Cu-Ni-PGE硫化物矿床的成矿因素和构造环境,揭示了峨眉山地幔柱铜镍铂族硫化物矿床成矿的控制因素和深部动力学,探讨了流体化学组成、稀有气体同位素及碳同位素示踪体系与岩石地球化学相结合来研究大陆苦橄质及高镁玄武岩浆的来源及演化的方法的适用性。取得了如下主要研究成果：1.通过锆石U-Pb年龄及Hf同位素确定宾川北部新鲜的苦橄岩为峨眉山地幔柱的产物,确证这些归属存在争议的苦橄岩是研究峨眉山地幔柱起源及演化理想的样品。峨眉山大火成岩省宾川北部新鲜的苦橄岩形成时代被质疑为三叠纪或新生代,选择与苦橄岩-玄武岩密切共生的安山质凝灰岩进行锆石U-PbSHRIMP定年和Hf同位素研究,确认最年轻的锆石206Pb/238U平均谐和年龄为256.2±.4Ma, εHf (-0.5～6.6)与峨眉山大火成岩省锆石的εHf值一致,与峨眉山苦橄岩具有相似的橄榄石Fo-Ni-Mn组成和全岩Th/Nb和Ti/Dy比值,与新生代富橄榄石钾质岩墙相比具有明显不同的Fo-Ni-Mn相关性及较低的Th/Nb和较高的Ti/Dy比值,表明这些归属存存争议的苦橄岩是峨眉山大火成岩省组成的一部分。2.确认峨眉山大火成岩省铜镍硫化物矿床成矿母岩浆是苦橄质岩浆分异演化的产物,并在深部发生过硫化物熔离。岩浆矿床橄榄石Ni亏损,成矿母岩浆与峨眉山苦橄岩搬运岩浆(基质)具有相似的MgO/FeO比值。橄榄石Fo值与Ni含量正相关表明其成分变化受分离结晶作用控制,负相关表明橄榄石与硫化物熔浆发生了Fe-Ni交换。朱布和力马河岩体的橄榄石Fo值与Ni含量均存在正、负两种相关性,青矿山岩体橄榄石现有数据Fo值与Ni含量具正相关性。在Fo值相同时,成矿岩体橄榄石Ni含量都低于苦橄岩中橄榄石的Ni含量,表明成矿岩体在橄榄石结晶之前岩浆发生过硫化物熔离。3.峨眉山铜镍硫化物矿床镁铁-超镁铁质岩的主量元素组成受控于岩浆矿物组成,微量元素和Sr-Nd同位素组成揭示成矿岩浆起源于地幔柱系统,上升和就位过程中受到不同程度的地壳物质混染。超镁铁质岩主量元素成分主要受控于橄榄石和辉石,辉长岩受控于辉石和斜长石,辉长闪长岩受控于斜长石、单斜辉石、角闪石、黑云母及铁钛氧化物。成矿岩体富集大离子亲石元素和轻稀土元素,明显亏损Nb；随岩石基性程度降低,微量元素富集程度增大。单斜辉石(87Sr/86Sr)i和CNd(t)具有亏损地幔的特征。Sr-Nd端元混合模拟计算表明朱布和力马河铜镍硫化物矿床地幔柱起源的岩浆中有15-20%的上地壳物质的加入,Nb/Th-Th/Yb比值计算表明青矿山矿床母岩浆经历了10%的地壳混染。4.峨眉山铜镍硫化物矿床镁铁-超镁铁质岩母岩浆PGE含量不同程度地低于苦橄岩,表明不同矿床的母岩浆在深部经历过不同程度硫化物熔离作用。成矿岩体全岩Pd/Ir比值较苦橄岩略高,揭示存在橄榄石和铬尖晶石的分离结晶。朱布铜镍铂族硫化物矿床的母岩浆PGE含量相对其它矿床更高。模拟计算表明朱布母岩浆含有7ppb Pd.9.3ppb Pt和0.8ppb Ir,略低于峨眉山苦橄岩。硫化物熔离时R因子(岩浆与硫化物质量比)变化于100-6000之间。5.地幔柱岩浆铜镍硫化物矿床流体挥发份组成指示成矿岩浆具有相对还原的流体介质环境,S饱和的途径可能不同。峨眉山大火成岩省朱布和西伯利亚Noril’sk铜镍铂族硫化物矿床成矿岩体中橄榄石和单斜辉石的流体挥发份对比研究表明,流体组分均以H20为主；母岩浆中H20含量估算表明,朱布矿床约0.39wt.%(96%), Noril’sk矿床约0.6wt.%。朱布母岩浆中流体组分H2和CO2含量较高;Noril’sk矿床CO2含量较高(65%),H2含量高,可检测到He。成矿岩浆早期流体挥发份平均含量为2589mm3.STP/g,朱布以N2(27%)和CO2(26%)为主,Noril’sk矿床以H20为主,硫的含量明显增加。成矿岩浆晚期流体总量明显增加,平均含量为10171.34mm3.STP/g,朱布以H2(53%)和CO2(23%)为主,Noril’sk矿床H2和H2S含量明显增加。CO/CO2比值表明岩浆起源于相对还原的环境,成矿阶段的流体更加还原,晚期流体相对较为氧化。岩浆上升过程中捕获了大量的含硫还原性流体组分。朱布矿床C02和CH4的碳同位素组成(分别为-44.85--22.83‰和-22.9‰～-7.01‰)具地壳和地幔混合特征,而Noril’sk矿床C02和CH4碳同位素较低,为地壳特征。表明Noril’sk与朱布矿床相比地壳混染程度更高。6.确定地幔柱岩浆铜镍硫化物矿床成矿岩浆演化过程中硫饱和的主要控制因素明显不同。含矿岩体的微量元素和同位素特征表明,与Noril’sk矿床以围岩硫加入不同,峨眉山大火成岩省铜镍硫化物矿床地壳物质混染是硫化物熔离成矿的关键因素。朱布含矿侵入体的形成经历了早期的岩浆通道阶段(边部带)和晚期的就位分离结晶阶段(中心层状杂岩体)。硫化物的熔离与成矿主要发生在通道阶段,在分离结晶阶段形成次要的硫化物矿化,不混熔的硫化物珠滴与流过通道的新岩浆不同程度发生反应。金川超大型铜镍硫化物矿床He和Ar同位素组成及模式计算表明成矿岩浆是地幔柱与大陆岩石圈地幔共同作用的结果,其中加入了20%的地壳流体和63%的大气饱和水,深循环地壳流体是硫饱和的重要因素。7.地幔柱大规模岩浆作用为超大型铜镍硫化物矿床成矿准备了充分的成矿金属,峨眉山地幔柱铜镍硫化物矿床成矿深部动力学特征与NOril’sk和金川超大型矿床相似,具有较好的找矿潜力。朱布铜镍硫化物矿床辉长岩中锆石U-Pb年龄263.2±5.6Ma,εHf《t)值(-3.05-+3.61)表明其岩浆源区与Noril’sk相似,主要以地幔柱为主,存在少量地壳物质的混染。锆石U-Pb定年和Hf同位素研究表明金川铜镍硫化物矿床是华北克拉通边缘的裂谷环境高镁岩浆作用的产物,二辉橄榄岩中锆石U-Pb年龄为821±11Ma,εHf(t)值(-11～-5)表明岩浆起源于地幔柱,存在大陆岩石圈地幔的混染。在峨眉山大火成岩省寻找铜镍硫化物矿床首先应该寻找类似朱布的基性超基性岩体,然后查明这些岩体的岩浆通道。更多还原

【Abstract】 Nickel, copper and platinum group elements (PGE) are important metals. These metals mainly come from magmatic sulfide deposits. Some of these deposits are related to mantle plume activity in a continental setting. The Emeishan and Siberian large igneous provinces (LIP) are both formed by mantle plume in the Permian. However, these two LIPs host different types of magmatic deposits. The former mainly hosts many world-class Fe-Ti-V oxide deposits whereas the latter hosts several world-class Ni-Cu-PGE sulfide deposits. Several magmatic Ni-Cu-PGE sulfide deposits have been also found in the Emeishan LIP but they are much smaller than those in the Siberian LIP. Nonetheless, the Ni-Cu-PGE sulfide deposits in the Emeishan LIP are useful for a study of genetic relationships between mantle plume activity and Ni-Cu-PGE sulfide mineralization. Furthermore, a better understanding on the origin of these deposits is helpful to the on-going mineral exploration in the region. Hence, a comparative study of the Ni-Cu-PGE deposits in the Emeishan LIP, the Noril’sk deposits in Siberian LIP and the Jinchuan Ni-Cu deposit in North China Craton have been carried out using integrated approaches including geochronology, mineralogy, petrology and geochemistry of major, trace elements, PGE and C-He-Ar and Sr-Nd-Hf isotopes. The data of volatiles, noble-gas isotopes and carbon isotopes from this study provide new insight into magma-crust interaction during continental basaltic magmatism, which forms another part of this thesis. The most important conclusions from this study are summarized below.1. The Binchuan picrites associated with Emeishan flood basalts in NW Yunnan have been confirmed as a part of Emeishan LIP by zircon U-Pb SHRIMP age of256.2±1.4Ma for the andesitic tuff interlayer. Hence, these picrites can be used to investigate the nature of the Emeishan mantle plume. Some researchers believe that the Binchuan picrites associated with flood basalts in NW Yunnan are the integral parts of the Permian Emeishan LIP whereas others believe that they are Triassic picritic porphyrites or Cenozoic olivine-rich dikes. The zircon U-Pb SHRIMP age of256.2±1.4Ma for the andesitic tuff within the Binchuan volcanic succession which contains the age-disputed picrites is within the range of ages for the Emeishan LIP. The εHf values (-0.5to6.6) of comagmatic zircons (-256Ma) from the andesitic tuff of the Binchuan volcanic succession are within the range (-5to10) of zircons from the Emeishan LIP. The age-disputed picrites and the undisputed Emeishan picrites have similar olivine Fo-Ni-Mn compositions and whole-rock trace element ratios such as Th/Nb and Ti/Dy. The Cenozoic olivine-rich dikes in SW Sichuan and NW Yunnan can be distinguished from the picrites associated with the Emeishan flood basalts by different olivine Fo-Ni-Mn correlations and whole-rock trace element ratios. The results from this study confirm that the age-disputed picrites in NW Yunnan and SW Sichuan belong to the Permian Emeishan LIP.2. Depletion of Ni is olivine from the Ni-Cu-PGE sulfide deposits such as Zhubu, Limahe and Qingkuangshan in the Emeishan LIP indicates a previous sulfide segregation event which took place at depth. Olivine compositions show that the most primitive parental magmas of these deposits have MgO/FeO ratios similar to the transporting magma (i.e., groundmass) of the Emeishan picrites. Both positive and negative Fo-Ni correlations of olivines are observed in the Zhubu and Limahe deposits. Only positive Fo-Ni correlation has been found in the Qingkuangshan deposit. At a given Fo content, the Ni contents of olivines from these deposits are significantly lower than that of olivines from the Emeishan picrites with the same Fo contents, indicating the olivines in these deposits crystallized from a Ni-depleted magma due to previous sulfide segregation at depth.3. The whole-rock major element compositions of the Emeishan Cu-Ni-PGE sulfide deposits are controlled by the types and abundances of major minerals. Whole-rock trace elements and Sr-Nd isotopes indicate that their parental magmas originated from mantle plume and were subsequently contaminated by variable proportions of crustal materials during magma ascent and emplacement. The compositions of ultramafic rocks in the host intrusions are mainly controlled by the abundances of olivine and pyroxenes; the compositions of coexisting gabbros are mainly controlled by the abundances of pyroxenes and labradorite; the compositions of coexisting gabbrodiorites are mainly controlled by the abundances of andesine, clinopyroxene, hornblende, biotite and Fe-Ti oxides. The intrusive rocks are all characterized by enrichments of large ion lithophile elements (LILE) plus light rare earth elements (LREE) and by significant Nb depletion. The Sr-Nd isotopes of clinopyroxene separates show the parental magmas have mantle-plume signatures. The Pd/Ir ratios in the sulfide-bearing intrusive rocks are variably lower than that in the Emeishan picrites, consistent with fractional crystallization of olivine and Cr-spinel from the parental magmas prior to the sulfide segregation which formed the deposits. Mixing calculation using Sr-Nd isotope data indicate15to20wt.%crustal contamination for the parental magmas of the Zhubu and Limahe intrusions. The ratios of Nb/Th and Th/Yb in whole rocks show that the Qingkuangshan parental magma was contaminated by～10wt.%crustal materials.4. The PGE contents in parental magmas of the Ni-Cu-PGE sulfide deposits in the Emeishan LIP are variably lower than that in the coeval Emeishan picrites. which indicate the parental magmas of the different deposits experienced various degrees of previous sulfide segregation at depth. The ratios of whole-rock Pd/Ir in these deposits are slightly higher tlian that of the Emeishan picrites, indicating that fractional crystallization of olivine and Cr-spinel played a role in PGE fractionation in the parental magmas. The estimated PGE contents in the parental magma of the Zhubu Ni-Cu-PGE deposit are slightly higher than that in the other deposits. The contents of PGE in the parental magma of the Zhubu deposit are estimated to be7ppb Pd,9.3ppb Pt and0.8ppb Ir. The compositional variations of bulk sulfides in the Zhubu deposit can be modeled by sulfide segregation from such magma with R factor (magma/sulfide mass ratio) varying from100to6000. The PGE tenors (i.e.,recalculated to100%sulfide) of the sulfide ores in the Qingkuangshan and Limahe deposits are much lower than those of the sulfide ores in the Zhubu deposit. This indicates that the parental magmas of the Qingkuangshan and Limahe deposits are more depleted in PGE than that of the Zhubu deposit.5. The volatiles released from olivine and clinopyroxene separates from the Zhubu and Nori’sk Ni-Cu-PGE sulfide deposits indicate that the parental magmas of these two deposits are similarly originated from reduced sources, and the mechanism for sulfur saturation may have been different for the different deposits. H2O is a dominant component in the volatiles released from the mineral separates from both deposits. The estimated H2O contents in the parental magmas of the Zhubu and Noril’sk deposits are0.39wt.%and0.6wt.%, respectively. H2and CO2contents are relatively high in the Zhubu and Noril’sk volatiles. Sulfur is low in the volatiles from both deposits. He is detectable in Noril’sk volatiles. The total contents of volatiles released at temperature>400℃are2589mm3.STP/g on average. N2(27%) and CO2(26%) are main components of volatiles released from the Zhubu samples. H2O is the main component of volatiles released from the Noril’sk samples. Sulfur contents in the volatiles increase with releasing temperatures. The total volatile contents at each releasing stage are up to10171.34mm3.STP/g. H2(53%) and CO2(23%) are main components of the volatiles from the Zhubu samples. The H2and H2S contents are higher in the volatiles released from the Noril’sk sample. The variation of CO/CO2with releasing temperature indicates that the parental magmas of both deposits changed from relatively reduced to more oxidized on cooling. The results also show that sulfur-bearing volatiles were transported by ascending magma. The carbon isotopes of CO2and CH4of volatiles from the Zhubu samples are from-44.85%o to-22.83‰and from-22.9‰to-7.01‰, respectively. These data indicate mixing between mantle and crust. The isotopic values of the Noril’sk samples are much lower, indicating a dominant crustal origin.6. The different Cu-Ni-PGE sulfide deposits associated with mantle plume magmatism could have formed by sulfide saturation in magma induced by fractional crystallization, sulfur addition, or/and crustal contamination. Based on trace elements and isotopes, it is proposed that sulfide saturation in the parental magma of the Emeishan Cu-Ni-PGE sulfide deposits was mainly triggered by crustal contamination, although the sulfur saturation in Noril’sk parental magma may have been caused by assimilating anhydrite. The formation of the Zhubu intrusion can be explained by two stages:a conduit stage for the sulfide ore-bearing marginal zone and an in situ differentiation stage for the layered sequence. Important sulfide segregation mainly occurred at the conduit stage. Highly variable metal tenors of bulk sulfides in the marginal zone indicate a dynamic magma-passing system for this zone. Comparatively,sulfur saturation was triggered by significant amounts of crustal fluids in Jinchuan Cu-Ni-PGE sulfide deposit. This is indicated by the results of He and Ar isotopic mixing calculations, which show that about20%crustal fluid and63%air saturated fluid were added into mantle-derived magma for the Jinchuan intrusion.7. Mantle plume magmatism in continental settings is ideal for the formation of giant magmatic Cu-Ni-PGE sulfide deposits. The Cu-Ni-PGE sulfide deposits in the Emeishan and Siberian LIPs and the Jinchuan Ni-Cu sulfide deposit share some similarities in sulfide concentration mechanisms. In these deposits, flow differentiation played a critical role in sulfide-liquid accumulation. The zircon U-Pb SHRIMP age for the Zhubu deposit is263.2±5.6Ma. The εHf values (-3.05to3.61) of comagmatic zircons (～263Ma) from this deposit indicate a mantle plume-derived magma with minor crustal contamination. The lower part of the marginal zone of the Zhubu intrusion could have been brought up by faulting and hence future exploration in Zhubu area should look for such a target. At the regional scale, it is important to look for mafic-ultramafic intrusions with ages and petrological characteristics that are similar to that of the Zhubu deposit. The εHf values (-11to-5) of comagmatic zircons with U-Pb age of821±11Ma from the Jinchuan ore-bearing mafic-ultramafic intrusion indicate interaction of mantle plume with sub-continental lithospheric mantle during magmatism.更多还原