【作者】 朱捌；

【导师】 田景春；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2010， 博士

【摘要】 南岭成矿带位于欧亚大陆东南缘,东南邻太平洋板块,北西接江南造山带。古生代以来,先后经历了加里东、海西—印支、燕山期等多期次的构造岩浆活动,形成了三条近东西向展布的岩浆岩带,自北向南分别为越城岭—诸广山、花山—大东山—贵东、怀集—莲花山,它们均受控于区域性深大断裂控制。南岭成矿带内还发现有大量的稀有和有色金属矿产,是我国稀有和有色金属矿产最集中的产地之一,也是花岗岩型铀矿的聚集区。诸广山南部矿田位于南岭东西向构造带和万洋山-诸广山南北向构造带的复合部位,矿田内的产铀岩体的形状可看作由两部分组成:西部岩体呈东西向展布,主要由燕山早期岩体组成;东部呈南北向展布,主要由印支期岩体组成,其间有少量燕山期岩体分布。诸广山岩体内部,各类脉岩十分发育,包括细晶岩、石英斑岩、花岗斑岩、伟晶岩、石英脉、辉绿岩、辉绿玢岩、闪长玢岩、拉辉煌斑岩和闪斜煌斑岩等,其中尤以白垩纪基性岩脉与岩体内广泛分布的铀矿化的关系十分密切。由此可知,诸广山南部矿田内是构造岩浆和热液活动中心,尤其是晚白垩到第三纪时期,区域伸展活动,深部地幔流体对岩体的改造作用进一步加强,为区内大规模铀成矿提供了有利条件。本文以诸广南部矿田为研究对象,在系统收集、归纳、整理现有地质、地球物理和地球化学资料基础上,采用地球化学、同位素地球化学、流体地球化学等方法,对区内产铀花岗岩及中基性脉岩的岩石学特征、地球化学特征、同位素地球化学特征,并在此基础上,研究区内构造、成矿流体活动性质及其演化特征、成矿物质来源、成矿定位机制以及基性岩脉的源区特征、成因机制及其与铀矿化的成因联系,查明地幔流体成矿作用的表现形式、地球化学标志及定位标志。通过研究,得出以下几点成果认识:(1)开展了精细的锆石SHRIMP U-Pb年代学研究。初步获得的结果表明,印支期岩体的年龄为239 ~ 231Ma,属于印支早期岩浆活动产物;燕山期岩体的年龄为160 ~ 154Ma,属于燕山早期岩浆活动产物;不同方向的基性岩脉是燕山晚期岩浆活动产物。(2)对印支期花岗岩进行岩石学、地球化学和同位素地球化学研究,表明印支期岩体是后碰撞作用产物。具有富硅、富铝、碱含量较高、钾大于钠和过铝质等主量元素特征;在微量元素蛛网图上,富集Rb、Th,亏损Ba、Sr、P、Ti、Nb、Ta,铀富集明显;在稀土元素方面,稀土总量较高,轻稀土富集明显和Eu亏损强烈;在同位素方面,εNd(t)值较低(平均为-11.5)、(87Sr/86Sr)i值较高(平均为0.72295)和Nd模式年龄古老(平均为1941Ma)。上述特征清楚显示,印支期花岗岩应属于壳源型或S型花岗岩范畴。印支期花岗岩的CaO/Na2O比值变化明显,为0.11 ~ 0.50,反映其源区由砂质岩和泥质岩混合组成。但由于它们具有高的Rb/Sr和Rb/Ba比值,因而在Rb/Sr-Rb/Ba图解上,大部分数据点都投影于泥质岩区域内,表明它们的源区主要由泥质岩或泥质岩与砂质岩按一定比例混合组成。在构造环境判别图解上,反映出在后碰撞作用的环境下,位于中-下地壳部位的古老变质沉积岩由于在地壳缩短之后的伸展、减薄环境下产生的减压、导水和地幔上涌等因素的综合影响下,分别由泥质岩或由泥质岩和砂质岩组成的混合源区发生部分熔融而形成本区的印支期花岗岩。(3)燕山期花岗岩的SiO2含量(69.47 ~ 77.50%)、碱总量(6.46% ~ 10.07%)、K2O/Na2O比值(0.91 ~ 1.23)和ACNK值(0.94 ~ 1.31)变化较为明显;在微量元素蛛网图上,富集Rb、Th,亏损Ba、Sr、P、Ti和Nb、Ta亏损轻微,铀富集明显;在稀土元素方面,稀土总量稍低且变化较为明显,Eu亏损明显,轻稀土轻微富集,配分模式呈特征的海鸥型;在同位素方面,εNd(t)值较低(-12.6 ~ -10.0)、(87Sr/86Sr)i值变化较大(0.70761 ~ 0.77651)和Nd模式年龄古老(1763 ~ 1964Ma)。上述特征清楚显示,燕山期花岗岩总体上可归属于壳源型或S型花岗岩范畴(。7)燕山期花岗岩的CaO/Na2O(0.10 ~ 0.84)、Rb/Sr(1.8 ~ 30.0)和Rb/Ba(0.53 ~ 232.0)比值变化明显。在Rb/Sr-Rb/Ba图解上,数据点基本上都投影于泥质岩区域内。在构造环境判别图解上,燕山期花岗岩都投影于后碰撞花岗岩区域内,表明它们应是在伸展的构造环境中形成的板内岩浆活动产物。(4)白垩纪中基性脉岩的主量元素组成如SiO2、TiO2、Al2O3和碱总量变化明显;在微量元素蛛网图上,分布形式明显呈现左侧“隆起”和右侧相对平缓的特征,Nb、Ta显示亏损;在稀土分布模式图解上,LREE/HREE比值和(La/Yb)N值较高,Eu基本没有亏损,配分模式呈右倾型。早白垩纪辉绿岩εNd(t)值(-8.2 ~ 4.3)和(87Sr/86Sr)i值(0.70828 ~ 0.72338)变化明显,它们的铅同位素组成又具有Dupal异常铅特征,反映它们源自相对富集的不均一地幔源区;晚白垩纪辉绿玢岩εNd(t)值(-2.2 ~ -0.9)、(87Sr/86Sr)i值(0.71276 ~ 0.71312)、206Pb/204Pb (18.500 ~ 18.574)和207Pb/204Pb( 15.718 ~ 15.790)比值变化小。在Nd-Sr、Nd-Pb和Pb-Pb相关图解上,早白垩世数据点基本上都位于MORB和EMⅡ端员之间和太平洋深海浊积岩区域内,反映辉绿岩的地幔源区因受到俯冲太平洋板块及其沉积物脱水所分泌的流体交代作用的影响而发生富集;晚白垩世辉绿玢岩数据点都位于MORB和EMⅡ端员之间,反映它们源自具有MORB和EMⅡ端员按一定比例混合特征的富集地幔源区。反映源区的富集作用主要归因于俯冲带流体对上覆地幔楔的交代改造。(5)通过对302矿床脉石矿物的氢、氧同位素组成的研究,确定的成矿期成矿流体的δDH2O=-65 ~ -82‰,δ18OH2O=6.8 ~ 0.6‰,矿后期成矿流体的δDH2O=-50 ~ -65‰,δ18OH2O=-0.8 ~ -7.1‰,在δDH2O-δ18OH2O图解上,成矿期数据点都位于地幔流体演化区域边缘,反映成矿期成矿流体主要由地幔流体和部分大气降水混合而成,而矿后期成矿流体则可能主要由大气降水演化形成。在包裹体均一温度-盐度图解上,数据点呈现明显的正相关分布,反映高温高盐度的地幔流体与低温低盐度的大气降水之间不同程度的混合,进一步证实成矿流体由地幔流体和大气降水混合组成。(6)成矿组分具有多来源特征:方解石的δ13C值(-8.4 ~ -5.3‰)反映碳主要来自地幔;萤石的(87Sr/86Sr)i值(0.71474～0.71697)介于矿区内辉绿岩(0.70861～0.72473)和赋矿花岗岩(0.73519 ~ 0.77152)之间,反映锶主要来源于基性岩脉(富集地幔),或基性岩脉(幔源)与赋矿岩体(壳源)之间不同程度的混合。沥青铀矿的εNd(t)值(平均为-11.5)和Nd模式年龄(平均为1787Ma)相似于赋矿花岗岩(油洞岩体分别为-13.2和1945Ma,长江岩体分别为-11.0和1770 Ma)而与辉绿岩(分别为-1.4和809 Ma)区别明显。(7)主成矿组分铀来自地壳而不是地幔,这是因为南岭地区的基底变质岩具有高的铀含量(一般为4 ~ 6×10-6)、赋矿花岗岩不仅铀含量高(长江岩体平均为19.5×10-6,油洞岩体平均为11.1×10-6),而且碱交代作用明显。当富含CO2的地幔流体与其相互作用时,很容易与其中活化的铀形成稳定的铀酰碳酸络离子UO2(CO3)22-和UO2(CO3)34-而被转移进入成矿流体。根据地幔流体成矿作用判别标志,诸广山岩体内的302矿床与贵东岩体内的石土岭、仙石和希望矿床一样,可能都属于地幔流体成矿作用范畴,从而进一步证实,与其它大型、超大型金属矿床一样,地幔流体在大型、超大型花岗岩型铀矿床形成中同样具有十分重要的意义。更多还原

【Abstract】 Nanling metallogenic belt locates Southeast of Eurasia, whose Southeast is Pacific Plate and Northwest is Jiangnan Orogen. It formes three Magmatic belt ,which are yuechengling-wanyangshan,qitianlling-zhuguangshan,huashan-dadongshan-east of guizhou province and who are controlled by regional discordogenic fault,and comes through many tectonic- magmatic activities since Paleozoic.Nanling metallogenic belt also discovers a lot of rare and non-ferrous metal belt which is one of the rare and non-ferrous metal assemble area and granital uranium ore assemble area.The uranium ore field of south zhuguang mountain lies in the mulriple part of Naling west-east tectogene and wanyangshan-zhuguangshan south-north tectogene,the mother body of uranium rock is composed of two parts:the west rock is formed by early Yanshanian rocks which are distributed as west-east and the east is composed of Indosinian rocks and a few of Yanshanian rocks,which are distributed as south-north.Many kides of dike rocks shch as aplite、quartz porphyry and granite porphyry ect.are discovered in the zhuguangshan rock..The relationship between basic dyke and uranium mineralization distributed in the rock is close.So,. The uranium ore field of south zhuguang mountain is the center of tectonic- magmatic activitie and thermal fluid,alteration of mantle fluild to rock,specially during lateCretaceous to tertiary,provides advantaged congdition to uranium ore field.in the study erea. The paper ,taking uranium ore field of south zhuguang mountain as study object and based on collection and coordination of geology、physical geography and geochemistry deta.,analyses the character of lithology geochemistry and isotope geochemistry of granite and basic dykite and studies the property of tectonic and mine liquid and its evolvement,the source and mechanism of mine liquid ,as well as the source and mechanism of basic dykite and its relationship to uranium mineralization,at the same time ,the paper also discusses manifestation geochemistry sign and position mark of mantle liquid metallogenesis. The paper gains these conclusion. (1) The subtle chronology study of zircon SHRIMP U-Pb.The results show that the age of Indosinian rock is 239 ~ 231Ma,which belongs to early Indosinian and the age of Yanshanian is 160 ~ 154Ma,which belongs to early Yanshanian, different basic dykite is the result of late Yanshanian.(2) The study of lithology geochemistry and isotope geochemistry of Indosinian rock shows that they are Indosinian collision,which are rich Si Al and high alkali K>Al.. The spider map of trace element shows positive Rb、Th and negative Ba、Sr、P、Ti、Nb、Ta,rich in U;∑REE is high, positive LREE and negative Eu, lowεNd(t),high (87Sr/86Sr)I and old Nd pattern age.Ale of these show Indosinian granite belong to lithosphere type or S type.The ratio of CaO/Na2O changes between 0.11 to 0.50,which shows the source is composed of arenite and argillaceous rock.which are admixture in definite ratio because of high Rb/Sr and Rb/Ba. The tectonic discrimination diagrams reflecte that the admixture source fusion,which is composed of argillaceous rock and arenite, forms the Indosinian granite.(3) The range of SiO2 content(69.47 ~77.50%)、alkaline gross (6.46% ~ 10.07%)、K2O/Na2O ratio (0.91 ~1.23) and ACNK (0.94~1.31)value from the Yanshanian granites is obviously wider. In the standard and modular diagram of trace element, the Yanshanian granites show moderate Rb and Th enrichment,Ba、Sr、P、Ti loss、moderate Nb and Ta depletion, obvious uranium enrichment;The granites display mew’s wing REE patterns:lower and obvious change of REE content,negative Eu anomaly, light REE enrichment;However, The granites have a small rage of moderately negativeεNd(t) values(-12.6~-10.0), a great change of 87Sr / 86Sr ratio(0.70761 ~ 0.77651) and an old age of Nd mode (1763~1964Ma).Then It can be concluded that the Yanshanian granite belongs to crustal type or S-type granites category. (7) The CaO/Na2O (0.10~0.84), Rb/Sr (1.8~30.0) and Rb/Ba (53~232.0) ratio in these Yanshanian granite are change significantly. As shown in the plot Rb/Sr vs. Rb/Ba , datas are almost in the shale area, while these granite dates fall into collide granite area in the tectonic environment graph, which indicate they are the product of within-plate magmatic activity formed in stretched tectonic environment(4) The Cretaceous medium-basic dykes are significantly varied in their major elements concentration(SiO2、TiO2、Al2O3 and alkali gross);The standard and modular diagram of trace element,uplift at left and relatively flat at right,shows negative Nb、Ta trend;The REE pattern is a right distribution with higer LREE/HREE and (La/ Yb) N ratio、basic Eu value without loss. TheεNd(t) (8.2-4.3) and (87Sr / 86Sr) i value of Early Cretaceous diabase (0.70828 ~ 0.72338) change obviously, while their lead isotope composition has anomaly Dupal characteristic which reflects these diabases are derived from concerntratly inhomogeneous mantle source; Late Cretaceous diabase-porphyrites have a slight variation inεNd(t) value (-2.2~-0.9 )、(87Sr /86Sr) i value ( 0.71276 ~0.71312)、206Pb / 204Pb (18.500 ~ 18.574) and 207Pb / 204Pb (15.718 ~ 15.790) ratios. In the Nd - Sr, Nd - Pb and Pb - Pb related diagram, the Early Cretaceous date fall into MORB、EMⅡand the Pacific Ocean deep-sea turbidite group, which reflects the mantle source of diabase enriched by the influence of fluids metasomatism caused by Pacific-Oceanic Plate subduction and sediment dehydration, Whereas the Late Cretaceous data locate between the MORB and EMⅡ,which indicates they derived from mantle source with mixing MORB and EMⅡmember according to a certain proportion. The enrichment reflect source, owing to fluid metasomasis between subduction zones and overlying mantle wedge.(5) Based on the study of hydrogen and oxygen isotopic composition in 302 metallic miner, we get some fluid date(δDH2O=-65 ~ -82‰,δ18OH2O=6.8 ~ 0.6‰for metallogenic epoch;δDH2O=-50 ~ -65‰,δ18OH2O=-0.8 ~ -7.1‰for late stage of metallogenic epoch). In theδDH2O-δ18OH2O diagram ,dates in metallogenic epoch mainly fall into the edge of evolution area of. These indicate fluid of metallogenic epoch is composed by mixing mantle fluid and atmospheric fall, while fluid in late stage of metallogenic epoch is mainly evolved from atmospheric fall. The homogenization temperature obviously shows positive correlation with salinity distribution of inclusions, indicating mantle fluid with high temperature and salinity mixed with low salinity atmospheric fall according to different degree, which also verify metallogenic epoch mixed by mantle fluid and atmospheric fall .(6) Ore-forming components with multiple source characteristics: calciteδ13C value (-0.84%~-0.53 %)mainly reflects the carbon from the mantle; (87Sr / 86Sr) i value of Fluorite (0.71474 ~ 0.71697) is between the diabase (0.70861 ~ 0.72473) and ore-rich granite (0.77152~0.73519) , reflecting strontium mainly from the mafic dikes or a mixture of mafic dikes and ore-rich rock. TheεNd (t) value (- 11.5 on average) and Nd age pattern (1787Ma on average) of detrital uraninite share similar with ore-rich granite(-13.2, 1945Ma forεNd (t), Nd in oil hole rock; -11.0,1787Ma forεNd (t), Nd in Yangtze rock), but obviously differ in diabase(-1.4 forεNd (t) ; 1770Ma for Nd) .(7) Because of basement metamorphic in the Nanling region with high content of uranium( 4 ~ 6×10-6) and ore-rich granite with high content of uranium (19.5 x 10-6 for Yangtze rock , 11.1 x 10-6 for oil hole rock) and obvious alkali metasomasis , the major uranium is from the crust, but not the mantle. When the fluid rich in CO2 reacts with uranium, especially activate uranium to produce stable UO2(CO3)22- or UO2(CO3)34-, which are transferred into the ore-forming fluid.According to the mineralization of mantle fluid, the 302 metallic belongs to the ore-forming processes of mantle fluid like Shi-tuling、Xianshi and Xiwang metallic, It is thereby confirmed that as other large and super-large metallics, mantle fluid has very vital significance in formation of large and super-large metallic deposit.更多还原