Chuxiong Basin Tectonic Deformation And Mineralization Study

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Study on the Structural Deformation and its Metallogenic Process in the Chuxiong Basin, is based on thePilot Project of Superseded Resourse Exploration for the State Crisis Mine——The Projectof Superseded Resourse Exploration to the Xiaohe-Shimenkan Ore-body in Liuju Copper Deposit, Dayao, Yunnan Province (Number: 200453001).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:â‘ the Proterozoic and Paleozoic stage (Pt～P₂) when the basement and middle layer formed;â‘¡the Mesozoic stage (T₃～K₂) when the backland formed and been filled;â‘¢the 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:â‘ from 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;â‘¡high 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(2Ï€Tx) + 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 theâ… target 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.