迪庆春都斑岩铜矿床地球化学及成岩成矿模式研究

【作者】 邹国富；

【导师】 李峰；

【作者基本信息】 昆明理工大学 ， 矿产普查与勘探， 2011， 博士

【摘要】 中甸岛弧隶属于世界三大斑岩铜矿带之一的古特提斯—喜马拉雅斑岩成矿域,地处该成矿域东缘印支期义敦岛弧南端。烂泥塘、雪鸡坪、刺来及春都等复式斑岩体呈北西西向展布于该岛弧西斑岩带,已有矿化信息、找矿勘查及研究工作表明,该区具备优越的成矿地质条件,找矿前景巨大。本文以中甸岛弧西斑岩带印支期中酸性浅成—超浅成相斑(玢)岩侵入体和赋存于其中的典型矿床—春都斑岩铜矿床为研究对象,以板块构造理论、岩石学、矿床学、区域成矿学、矿床地球化学和斑岩成矿理论等为指导,在大量收集和系统分析前人研究成果的基础上,通过详细的野外地质工作和大量室内岩矿分析测试工作,深入开展成矿地质背景,矿床地质特征、斑岩体岩石地球化学、矿床地球化学及成岩成矿模式的研究,探讨构造—岩浆耦合控岩控矿机制,总结其成矿规律,建立成矿模式,从而完善和丰富中甸岛弧斑岩铜矿床成矿理论,为地质找矿和成矿预测提供科学依据。主要取得了以下研究成果和认识：在宏观地质研究和分析基础上,通过室内镜下鉴定、主量元素、微量元素、稀土元素及同位素的综合分析研究,揭示了春都矿区及中甸岛弧西斑岩带复式斑岩体具有岛弧火成岩的基本特征和埃达克质岩的地球化学亲和性,具Ⅰ型花岗岩的特征,形成于印支期甘孜—理塘洋壳向格咱微陆块俯冲的消减带(俯冲带)构造环境,是活动大陆边缘的产物,岩浆起源于下地壳或上地幔部分熔融。复式岩体由主岩体—早期侵入的闪长玢岩及晚期以岩枝、岩脉侵入其中的花岗闪长斑岩组成,花岗闪长斑岩为成矿母岩。闪长玢岩的形成明显受结晶分异作用控制,受部分熔融作用控制微弱,而花岗闪长斑岩同时受部分熔融和分离结晶作用所控制；二者具同源岩浆结晶分异演化关系。Cu、Pb、Zn等成矿金属物质主要来自下部地壳或上地幔；硫具幔源硫的特征,主要来自深部岩浆,同时有部分地层还原硫的混入；成矿流体以原始岩浆水为主,同时有大气降水的加入。通过深入细致的野外地质工作及室内岩矿鉴定,确定了矿区内主要蚀变类型有钾长石化、硅化、黑云母化、绢云母化、青磐岩化以及粘土化,建立的蚀变分带模型显示,矿区存在以呈雁列式产出的花岗闪长斑岩岩枝或岩脉为中心,向外依次出现钾硅化带(钾长石、黑云母及硅化带)→绢英岩化带(石英绢云母化带)→(泥化带)→青磐岩化带→角岩化带,具有与“二长岩蚀变”模式类似的蚀变特征。但与典型的斑岩铜矿床相比,本区蚀变分带的规律性较差,存在重复—偏对称现象,表现为呈带状、枝状及脉状分布的空间特征,显示蚀变类型及其分带受斑岩体控制明显。一般情况下,铜矿化强度与蚀变类型有显著关系,在硅钾化带、绢英岩化带及其过渡带矿化强度较好。采用激光剥蚀—等离子体质谱仪(LA-ICP-MS)锆石U-Pb测年法,对矿区岩体年龄进行精确测定。结果表明,春都硅化钾化闪长玢岩锆石U-Pb年龄为246.1±3.0—260.8±2.5Ma,与雪鸡坪石英闪长玢岩体角闪石40Ar—39Ar年龄(249.92±4.99Ma)和刺来闪长玢岩锆石U-Pb年龄(252.3±3.4Ma)基本一致,结合闪长玢岩与围岩的宏观地质关系及区域岩浆演化特征,推测闪长玢岩成岩年龄应在240Ma左右。春都含矿母岩花岗闪长斑岩体锆石U-Pb年龄为217.5±1.9-217.3±1.8Ma,与中甸岛弧岩浆活动的高峰成矿期215Ma基本一致。由无矿闪长玢岩到花岗闪长斑岩,矿区复式斑岩体的岩浆活动持续时间约25Ma,如此之久的岩浆—热液系统是形成具有一定规模的斑岩铜矿床必要条件之一。根据测年结果,结合中甸岛弧区域地质背景分析,认为,中甸岛弧西斑岩带在板片俯冲环境下,至少存在两期较大规模的中—酸性岩浆浅成—超浅成侵位活动,一是甘孜—理塘洋盆在中三叠世—晚三叠世早期向西侧的中咱地块发生俯冲消减作用,沿NNW向的格咱河深大断裂发生浅成—超浅成岩浆侵入,形成早期呈岩株或岩枝产出的无矿闪长玢岩；二是晚三叠世中晚期,英安质岩浆沿着闪长玢岩底部的构造薄弱带(NNW向断裂构造系统)上侵至玢岩体内,形成春都花岗闪长斑岩。由于西斑岩带先期侵位的闪长玢岩的阻隔或压制作用,晚阶段(主成矿期)岩浆侵入活动主体区域向东迁移至中—东斑岩带,并导致西斑岩带岩浆侵入活动相对较弱或侵位较深,斑岩体主要呈岩枝或岩脉产出,岩体规模相对较小。主成矿期中甸岛弧侵入体主要岩石类型有较高的相似性,主要有石英二长斑岩、花岗闪长斑岩等,为斑岩型铜(钼)矿床的成矿母岩。通过总结矿区斑岩成因模式及成矿规律,系统分析研究了春都矿区及中甸岛弧西斑岩带成岩成矿机理,建立了春都“雁列式斑岩脉”控矿模式。中三叠世—晚三叠世早期,甘孜-理塘洋壳开始向西俯冲,随着俯冲深度的增加,导致板片脱水和部分熔融,引发地幔物质部分熔融,形成上侵的钙碱性系列的岩浆,岩浆在上升过程中不断分异演化,沿格咱河深大断裂侵入,形成岩株或岩枝状闪长玢岩。至晚三叠世中晚期,在持续的由东向西挤压俯冲作用下,中甸岛弧区西斑岩带的NNW向断裂构造产生左行走滑,由此派生一定的NE—SW向局部引张,形成雁列式断裂构造系统；同时底部的安山质岩浆已演化为英安质岩浆,不断演化的岩浆沿NNW向雁列式走滑断裂构造系统侵入早期玢岩体内或围岩,形成晚期呈岩枝或岩脉产出的含矿花岗闪长斑岩—“雁列式花岗闪长斑岩脉”。从花岗闪长斑岩岩浆中分离出来的含矿热液,进入闪长玢岩或花岗闪长斑岩顶部的裂隙带后,与下渗的大气降水及溶解其中的部分成矿物质混合,形成混合流体。这种富含Cu、Pb、Zn、Fe等成矿物质和H2O、CO2、S2-、Cl-等挥发性组分的成矿流体进入围岩裂隙中,与围岩发生硅钾化、绢英岩化等蚀变,热液中的Cu等金属元素与硫结合,形成浸染状产出的黄铁矿、黄铜矿等金属硫化物；或随着温度的降低,成矿流体中的金属硫化物直接析出,形成脉状的金属硫化物。受NNW向雁列式花岗闪长斑岩脉的控制,春都铜矿床各矿体也呈现出“雁列式”分布的特征,形成与典型斑岩铜矿床不同的“雁列式斑岩脉”矿化格局。此控矿模式在中甸岛弧西斑岩带具有重要的代表性。系统分析了春都铜矿及中甸岛弧西斑岩带成矿地质条件,总结了找矿标志,依据春都“雁列式斑岩脉”控矿模式,优选了6个找矿靶区。同时指出,在今后的找矿工作中,应把握好“雁列式斑岩脉”控矿模式对含矿斑岩和矿体的控制规律,在平行NNW走滑雁列式断裂构造系统和沿其走向延伸方向做重点的控制和总体部署,并加强深部找矿工作。更多还原

【Abstract】 Zhongdian island arc is part of The Tethys-Himalayan Porphyry Metallogenic Realms, which is one of the three biggest Porphyry Copper Mining Area in the world. It is located in the eastern edge of the metallogenic realms of the south of the Indosinian Yidun arc. Lannitang, Xuejiping, Cilai and Chundu etc. complex porphyry bodies line NNW trending in the west of Zhongdian arc porphyry belt, The obtained mineralization information, ore prospecting exploration, and the result of research, all of them have showed that this area has great mine prospect with excellent mineralization geological conditions.This paper mainly talks about the Indosinian intermediate-acid shallow period-with ultra-shallow spot (porphyry) rock intrusive which is located the west porphyry belt of the Zhongdian island arc and the representative Chundu Porphyry Copper Deposit. With the guidance of theory of plate tectonics, Petrology, Mineral deposits, Regional metallogeny, Deposit Geochemistry, and Porphyry mineralization theory, on the basic of extensive collect and systems analysis the results of previous studies, Through the detailed geological work in field and the analysis of large number of the samples, the deep research of the basis of geological deposits, porphyry rock geochemistry, deposit geochemistry, and diagenetic mineralization model in the deposit, we’d like to investigate The Construction -Coupled magma Ore and rock-controlling mechanism, summarize the metallogenic regularity, and establish metallogenic model, for further, it helps to perfect and enrich the metallogenic theory of Zhongdian arc porphyry belt, and provide a scientific basis for the geological prospecting work and metallogenic prognosis. The main research results are as follows:On the basis of macroscopic geological research and analysis,by means of identification of rock and minerals,major element,trace element,Rare Earth Element and isotope. it reveals that the ChunDu mine and the composite porphyry bodies of Zhongdian island arc west porphyry belt have the basic characteristics of island arc igneous, and the geochemical affinity with adakitic rock. It indicate that the composite porphyry bodies bear the characteristics of the I-type granitoids, It was producing in the structure environment of the Indosinian Ganzi-Litang ocean crust western subduction on Gezan tiny island, It is the product of an active continental margin, Magma is mainly from the lower crust or upper mantle.The composite rock bodies are made up of two phases, diorite porphyrite is the main rock mass which is initial intrusive, and the post-intrusive granodiorite porphyry which is the apophysis or dyke, granodiorite porphyry is host rock of mining rock. The formation of diorite porphyry in the mine was significantly affected by crystal fractionation and by some weak control of partial melting.Granodiorite porphyry was controlled by partial melting as well as fractional crystallization. These two porphyry are comagmatic evolution of crystallization and differentiation. They are homologous magma chamber, and homologous heterogeneous product. Cu,Pb,Zn were mainly from the lower crust or upper mantle. Sulfur was mainly from the deep magma with the characteristics of mantle-derived sulfur,at the same time, there was a certain amount of crustal sediments(Reduced sulfur). Ore-forming fluids mainly were the original magmatic water, and a little surface water.Through deep detailed geological field work and indoor identification of rock and minerals, we identified the types of major alterations are potash feldspathization, silicification, biotitezation, sericitization, propylitization and argillified; and establish alteration zoning model of the research district. With granodiorite-porphry as the center, which is echelon, potassium silicon belt appears outward in proper order (potash feldspar, black mica)→quartz-sericitization belt→(argillization belt)→propylitization belt→hornstone belt. The alteration character is similar to "monzonite alteration", but alteration regularity is relatively worse, there is repetition→slants symmetrical phenomenon. The alteration zone and its space characte-r of zoning are controlled by intrusive rocks. Generally speaking, the copper mineralization has obvious relation with the type of alteration, the strength of mineralization is better in potassium silicon belt, quartz-sericitization belt and its transition belt.Using LA-ICP-MS zircon U-Pb method, we accurated the determine age of rock body. The age of the Chundu’s diorite porphyrite is 246.1±3.0Ma-260.8±2.5Ma, and it is the same with the age of both Xuejiping’s quartz diorite porphyrite amphibole by 40Ar-39Ar (249.92±4.99Ma) and Cilai’s diorite porphyrite zircon by U-Pb (252.3±3.4Ma), with the macroscopical geological relationship and characteristic of the regional magmatic evolution between diorite and wall rocks, suggesting the age of diorite porphyrite should be about 240Ma. The age of Chundu’s Ore-bearing granodiorite porphyry is 217.5±1.9-217.3±1.8Ma, and it is consistent with the peak of the ore-forming stage(215Ma) of magmatic activity of Zhongdian arc. From barren diorite porphyrite to granodiorite porphyry the magmation of the complex porphyry bodies had lasting for 25Ma in this area. So long magmatic-hydrothermal system is one of the necessary conditions to form the sizable porphyry copper. According to dating results, combining with the analysis of the Zhongdian arc porphyry belt regional geology, this paper said:There are at least two large acid Shallow magma-ultra-shallow intrusive activity in the west porphyry belt of Zhongdian arc under the diving environment of ocean basin plate. First, Ganzi-Litang ocean occurred the subduction in Middle Triassic-Earlier of Late Triassic to the Zhongza masiff which was in the west, and also occurred the shallow area-ultra-shallow intrusive along the discordogenic fault—Gezahe fault which is NNW,and the main rock types is barren diorite porphyrite which is in the form of rock strains or rock vein. Second, In the Middle-Late period of Late Triassic, dacite magma invaded into the body of the diorite along weak belt of the bottom of the diorite, To form the Chundu granodiorite porphyry; As the western porphyry intrusion with a large number of early diorite barrier or deterrent effects, this phase of magmatism migrated eastward to middle-east porphyry belt, so the west porphyry belt magmatism is relatively weak or emplaced deeper. Rock body in the east porphyry rock is mainly rock strains or rock vein, but in the west porphyry rock the output mainly is rocks sticks or rock dykes and rock body is relatively small. they all have affinity for adakites, current intrusion major rock types are beschtauite, granodiorite porphyry etc., and constitute a host rock of mineralization for porphyry-type copper and molybdenum deposits.After summary the metallogenic model and rules of the porphyry in this mine,system analysis the metallogenic mechanism of Chundu mine and western porphyry of Zhongdian arc porphyry belt,we established Chundu "Echelon porphyry dyke" ore-control mode. Middle Triassic-Earlier of Late Triassic, Ganzi-Litang oceanic crust started to westward subduction, with the deep increasing, it leaded to dehydration and slab partial melting, and then caused partial melting of mantle material and formed intrusion and calcalkaline magma. in the rising process Magma constantly occured differentiation and evolutioned along the Gezanhe deep fault, mainly was in the form of rock strains or rock vein. Untill the mid-late Triassic, the continuous extrusion subduction from east to west, The NNW-trending faults of the Zhongdian arc west porphyry delt generated sinistral strike-slip, which derived some NE-SW fault expanded somwhere, en echelon fault structure system had formed. At the same time,the andesitic magma at the bottom had been changed into dacite magma, When the continually evolving magma invaded into the earlier porphyry rock body or wall-rock along the NNW-trending strike-slip fault structure echelon system, and formed mineral-bearing granodiorite porphyry which was mainly rock strains or rock vein—"En echelon granodiorite porphyry vein". The mineral-bearing hydrotherm which separated from the granodiorite porphyry magma entered into the fissures of the top part of the diorite or granodiorite porphyry. In this process, the atmospheric water dissolving formation minerals in infiltration process mixed with the original magma, and formed the mixed-mineralization fluids. The mixed Ore-forming fluid was rich in mineral, such as Cu,Pb,Zn,Fe etc. and rich in volatile elements, like H2O, CO2, S-2, Cl- and others. With ore-forming fluid flowing into fissures of the diorite or wall-rock, the occurrence of alterationas as silica,potassium-based and phyllic with wall-rocks can be seen,then hydrothermal copper and other metal elements and sulfur formed pyrite, chalcopyrite and other metal sulfides, which precipitated from the ore-bearing hydrothermal, and with decreasing temperature, the metal sulfide ore-forming fluids direct precipitated in the formation of metal sulfide vein. Under the control of NNW-trending strike-slip echelon fault structure system, Chundu copper’s ore body is also showing the distribution of en echelon features, it is different from the typical porphyry copper deposit-"echelon porphyry" ore-controlling mode, this control mode ore has an important representation in Zhongdian arc west porphyry belt.This paper analysises systematic the geological conditions of Chundu copper deposit and porphyry delts in western of Zhongdian arc and summaries the prospecting criteria. According to the ore-controlling model of the "En echelon porphyry vein". We chose six exploration targets, and also point out in the prospecting work, we should deeply hold on the control rules of the "Echelon-porphyry vein" ore-bearing model on porphyry and ore mining, and we should focus on the parallel NNW echelon faults slip systems and make a good work plane. The deep exploration work should be given more attention.更多还原