楚雄盆地构造变形及其成矿作用研究

【作者】 邹海俊；

【导师】 韩润生； 方维萱；

【作者基本信息】 昆明理工大学 ， 矿产普查与勘探， 2008， 博士

【摘要】 博士论文，《楚雄盆地构造变形及其成矿作用研究——以大姚六苴铜矿区为例》，结合国家危机矿山接替资源勘查试点项目《云南省大姚县六苴铜矿小河—石门坎矿段接替资源勘查》（编号：200453001）选题。构造变形分析及其成矿作用研究，对于研究楚雄盆地的构造演化和寻找新的铜矿资源有着重要的指导意义。以楚雄盆地形成和构造演化为背景，以大姚六苴铜矿区为例，在矿床地质特征研究基础上，恢复了该区的构造变形史，进行了构造应力场数值模拟。利用流体包裹体及同位素资料研究了成矿流体性质及来源，应用构造—流体耦合成矿作用的理论与方法提出了六苴铜矿床的成矿模式，最终对六苴铜矿区及整个楚雄盆地进行了成矿预测。1．确定了楚雄盆地动力学类型，总结了构造演化历史。楚雄盆地属于会聚型的后陆盆地，经历了元古代基底及古生代中间层形成期（Pt～P2）、中生代后陆盆地形成与充填期（T3～K2）、新生代盆山耦合期（E～Q）。2．首次在楚雄盆地使用构造岩ESR定年，确定了大姚六苴铜矿区构造演化的时间序列。在总结提出构造活动分期原则和依据的基础上，研究了六苴铜矿区构造变形特征。制作了构造演化剖面（平衡剖面），恢复构造变形史。喜山早期以来，六苴铜矿区表层地壳缩短率约为20．5％。通过断裂和褶皱构造以及显微构造变形分析，厘定该区经历了燕山中期（137Ma）、燕山晚期（96～65Ma）、喜山早期（46．8±4．5～56．0±5．6 Ma）、喜山中期（32．4±3．0～42．3±4．1 Ma）、喜山晚期（23．5±2．4～29．3±3．0 Ma）五期构造活动，恢复了三维主压应力方向，各期最大主压应力方向分别为为177°、44°、129°、185°和91°。大雪山背斜形成于喜玛拉雅运动早期（第Ⅰ幕），与滇中大规模成矿作用关系密切。3．使用先进的ANSYS软件，首次模拟了六苴铜矿区不同期构造应力场，研究了构造应力场控矿特征。通过主压应力轨迹图、主压应力场、剪切应力场、平均应力（流体势）场、能量场研究，结合地质特征，认为各变形期构造变形强弱为：喜山早期>喜山中期>喜山晚期>燕山晚期>燕山中期；高值应力集中常出现在强度较高的砂岩层分布区，岩石易产生破裂，并成为流体聚集的有利场所；低值应力集中区出现在断裂带及强度较低的泥岩和砂质泥岩分布区；最大主压应力为流体运移的主要驱动力，平均应力最大梯度方向指示流体运移方向及有利聚集场所；总能量场指示了变形的强弱。燕山晚期铜矿源层（K₂m）形成后，喜山早期近EW向主压应力作用使古河道（K₂ml）位于强烈的剪切破裂带，应力驱动成矿流体运移，在砂岩层中聚集沉淀；喜山中期（改造成矿期）NW-SE向主压应力的作用形成“裙边”褶皱，产生NE向断裂，沟通了早期断裂构造，形成脉状矿体；喜山晚期时，SN向应力作用形成NW向、NNW的扭性断裂，错断矿体和地层。4．研究了流体包裹体地球化学特征，确定了成矿流体性质及成矿物质来源。大姚六苴铜矿床流体包裹体原生流体包裹体以气液两相为主，偶见气液三相和气液固三相流体包裹体，大小4～20μm，气液比10～30％；包裹体世代特征明显，两组相互穿插为菱形格状。存在四期主要流体活动，分别代表了沉积—成岩期、层状矿体形成期、脉状矿体形成期及破坏期。成矿温度以中低温为主，成矿流体压力为4×10⁵～30×10⁵Pa，深度为1～1．5km。激光拉曼光谱成分测试表明存在H₂O-SO₂-CO₂-CH₄（C₃H₈-C₂H₆）—HSO₄^-—HCO₃^-型和H₂O-SO₂-CO₂-N₂-CO-CH₄-HSO₄^-型两种性质的成矿流体。铜来源于含矿地层（矿源层）；成矿流体为大气水—含有机质地层建造水的混合流体；碳质来自下部有机质分解。有机质来源于下部煤层（T₃）及有机质分解。SO₂（HSO_<sup>-）来源于滨湖相及浅湖相沉积物（石膏等蒸发盐类）及生物细菌还原硫。5．首次建立了斜歪褶皱（大雪山—桃树坪褶皱）数学模型，估算了其特征参数。大雪山背斜由纵弯作用形成。大雪山背斜-桃树坪向斜为轴面西倾的斜歪倾伏相似褶皱，完整褶皱波长λ约14．55km，二倍振幅2A约718．35m，计算出大雪山背斜的中和面深度H_中和面约为932m，推测中和面深度大约在1～1．5 km。大雪山背斜数学模型为：f（x）=α·sin（2πTx）+b·arctg（c·x-（?））6．首次提出六苴铜矿床构造—流体—耦合成矿作用模式，探讨了成矿流体运移和聚集模式及其成矿作用：燕山期的构造活动与演化形成了含铜矿源层；喜山早期构造一热演化促使大气降水深循环、深部含有机质流体向上运移发生水／岩相互作用，导致矿源层中成矿元素活化、迁移及非含矿流体向成矿流体转化；应力梯度和热梯度为成矿流体的运移提供了驱动力，驱使成矿流体向上、向砂（页）岩储层以及向断裂两侧等高孔渗异常区运移，成矿流体在砂岩储层中聚集，沉淀出矿质，形成层状、似层状铜矿体。7．确定了楚雄盆地和大姚六苴铜矿区成矿预测标志，共提出八个找矿远景区（靶区）。在六苴铜矿床Ⅰ靶区，经钻孔工程验证，发现了深部隐伏矿体，取得了良好的找矿效果。更多还原

【Abstract】 This doctoral dissertation, A case study of Liuju Copper Deposit,Dayao : Study on the Structural Deformation and its Metallogenic Process in the Chuxiong Basin, is based on thePilot Project of Superseded Resourse Exploration for the State Crisis Mine——The Projectof Superseded Resourse Exploration to the Xiaohe-Shimenkan Ore-body in Liuju Copper Deposit, Dayao, Yunnan Province （Number: 200453001）. Study on the structural deformation and its MetaUogenic Process has important steering significance for the evolution of Chuxiong Basin and to explore more copper resources.On the background basis of the forming and structural evolution of Chuxiong basin, it takes Liuju Copper District,Dayao, as a case to study the deposit characteristics and to restore the structural deformation history, and the modelling of structural stress fields has been done. With the research of fluid inclusions and some isotopes, it studies the properties and origins of the ore-forming fluids. It Uses the theory and methods of fluid-structure coupling metallogenic process to present the ore-forming model for the Liuju Copper Deposit Finally, ore-exploration prognosis has been done to the Liuju Copper district and Chuxiong Basin.1. It determines the dynamic type of Chuxiong Basin and summarizes the structural evolution history. The basin is a Convergent backland basin, with three evolution stages:①the Proterozoic and Paleozoic stage （Pt～P₂） when the basement and middle layer formed;②the Mesozoic stage （T₃～K₂） when the backland formed and been filled;③the Cenozoic stage （E^Q） when the basin reformed.2. It is the first time to use ESR dating of tectonites to attain the time of structural evolution in the Chuxiong basin. Based on the principles and basises for partitioning the period of stuctural activities, it studies the deforming features of Liuju Copper District. Some balanced sections are made to restore the deformation history. Scince the early Himalayan Movement,the crust constiction ratio of Liuju distict is as to 20.5%. Through the analysis of faults, folds and microstructures, it determines 5 stages of tectonic movement: middle Yanshan stage （137Ma） , late Yanshan stage （96～65Ma） , （46.8±4.5～56.0±5.6 Ma）, （32.4±3.0～42.3±4.1 Ma） and the late Himalayan stage （23.5±2.4～29.3±3.0 Ma）. The main compress stress direction in each stage seperately are 177°、44°、129°、185°and 91°. The Daxueshan anticline was formed in the early Himalayan stage, wich has close relationship with large scale metallogenic process in Chuxiong basin.3. For the first time, it has used the advanced software of ANSYS to model the tectonic stress fields of the district.On the study of the main compress stress fields and its track plot, shear stress fields, mean stress fields and enegy fields, with the geological features, it deems that:①from strong to weak intensity of structural deformation is as: the early Himalayan stage > the middle Himalayan stage > the late Himalayan stage > middle Yanshan stage > late Yanshan stage;②high stress centralizing areas often appear at the sandstone areas, the sandstone rocks is easy to be broken thus to become the favorable assembing sites for the ore-forming fluids. Low stress areas are at fault zones and mudstone area. The biggest main compress stress is the major driving force to fluid movement The largest grads direction of mean stess is to show the fluid moving direction and gathering sites. Total enegy field indicates the deformation intensity. After the Cu-source bed （K₂m） formed, the EW-trending compress stress located the paleo-revierbed at the intense shearing zones, stress drived the ore-forming fluids to move, and fluids gathered in the sandstone and deposited minerals, and layer-like ore-bodies are formed. In middle Himalayan stage （reforming-metallogenic stage）, under the effect of NW-SE-trending stress, the southern "Skirt-edge" folds were form, with the generation of NE-trending faults wich connected earlier faults to form the vein ore-bodies. In late Himalayan stage, with the SN-trending stress, NW-trending and NNW-trending shearing faults were formed to cut ore-bodies and strata.4. Study on the geochemical features of fluid inclusions to clarify the ore-forming fluid property and origin of metallogenic materials. The original inclusions mainly are vapor-liquid double-state ones, with occasional vapor-liquid triple-state and vapor-liquid-solid triple-state ones. Size of inclusions are about 4～20μm, with vapor-liquid ratio of 10～30%. Inclusions have clear features of generations, two inclusion teams interlude with each other to appear rhombus shapes. Inclusion research indicates that there existed 4 stage fluid activities, wich respectively represents sedimentary-diagenesis stage, layer-like ore-body forming stage, vein ore-body forming stage and reforming-breakage stage. The metallogenic temperatures primarily were middle-low temperatures, with 4×10⁵～30×10⁵Pa hydrostatic pressure of ore-forming fulid and 1～1.5km ore-forming depth. Raman microspectrometry of fluid inclusions shows there existed two types of ore-forming fluids: H₂O-SO₂-CO₂-CH₄（C₃Hg-C₂H₆） -HSO₄^--HCO₃^- type and H₂O-SO₂-CO₂-N₂-CO-CH₄^- HSO₄^- type. Cu came from Cu-bearing strata. Ore-forming fluid were the mixture of rainwater and organ-bearing stratum water. Carbon （C） were from the decomposing of organic matter whose origins were lower coal layer（T₃） and decomposed organ matter. SO₂ （HSO₄^-） came from the sediments （gypsum etc.） and the bacteria deoxidizing.5. For the first time, it constructs a methimatical model for the Daxueshan-Taoshuping fold, and rekons its featured parameters. The Daxueshan anticline was formed by lengthways-banding process. It is a oblique similar fold with W-trend axis plane. The whole fold wavelengthλis 14.55km with duple swing of 718.35m. The neutralisation plane depth is about 932m, and maybe is up to 1～1.5 km. The methimatic fold model is discribed as:f（x） =a·sin（2πTx） + b·arctg（c·x-φ）6. It puts forward a medol or the structure-fluid coupling metallogenic process first, and studies the fluid movement and assembling ways and metallogenic process. In Yanshanian stage, Cu-bearing strata formed; The early Himalayan tectono-thermal evolution drived the rainwater to cycle deep and drive organ-bearing fluid to move upward, fluid-rock interraction ocured, wich led to metallogenic elements to be activated and transferred along with ore-forming fluid. The stress grads and thermal grads oferred motivity for the ore-forming fluid movement, wich drived fluid to transfer upward to the sandstone layer and around the fault zones. Ore-forming fluid gathered within the sandstone layer and precipate the metal sulphides, thus to form layer-like ore-bodies.7. It presents some signs for ore prognosis in Liuju Copper district and Chuxiong Basin. 8 total ore-exploration perspective areas （target areas） are determined. In theⅠtarget area of Liuju Deposit, drills have revealed the deep concealed ore-body, good ore-exploration effects are obtained, wich indicates the method of structure-fluid coupling metallogenic process is effictive.更多还原