A Mineralization Mechanism As Well As Minerogenetic Prospect Of Carlin-type Gold Deposit In Southwestern Of Guizhou

In recent years, the region of Southwest China where the Emeishan basalts are widespread is an igneous rock province commonly accepted by the international geological circles at present time. Its formation is concerned with the product of a unique mantle dynamic process, i.e. the Emei mantle plume activity. Emei mantle plume activity and mineralization is a advanced question for study or discussion, and it is one of the hot question that geological researchers study in recent years.The Carlin-type gold deposits in southwestern of Guizhou province considered to a body of gold triangle in Yunnan,Guizhou and Guangxi is a representative Carlin-type gold deposit in China at present time. Many units and researchers progress in deep-going investigations to it using many studying means and technology, achiever great studying result; however, now none organic combine to study between Emei mantle plume activity and a origin of Carlin-type gold deposits in southwestern of Guizhou province, about some deep levels questions, i.e. Emei mantle plume activity is how to affect regional mineralization background of Carlin-type gold deposits, how to cause hydrothermal solution, how to produce ore-forming matter, sedimentary process that hydrothermal solution is how to lead to form gold deposits etc. few someone knows to above all question at present. And, the sedimentary process of hydrothermal solution is whether or not universality, what is a dynamic pressure in whole hydrothermal solution mineralization, ore-forming fluid is how to produce and move; all the questions don't be convinced to explain in ore deposit science in recent years. In the academic thesis, the Carlin-type gold deposits in southwestern of Guizhou province is a researching sample, studies how gold deposit is formed in concentrate district of the Carlin-type gold deposits through Emei mantle plume activity in southwestern of Guizhou province. Through the research on a mechanism forming Carlin-type gold deposits in Emei mantle plume activity, may explain and answer to a great extent above questions.The Emei mantle plume is one of the most typical mantle plume in China. According to the tridimentional velocity-texture diagram of mantle plume charted in terms of the seismological-tomographic imagery, the Emei mantle plume is a composite low-velocity plume at the 50-450-km depth, which is composed of a number of "plum flower-shaped" sub-plumes. The initial mushroom-shaped head of the mantle plume is measured at 1000-1500 km in diameter, and its tailing part is located around the area of Panzhihua, about 250 km in diameter. The occurrence of this composite low-velocity plume reflects the heterogeneity of the Emei mantle plume in both vertical and lateral directions and the characteristics of its multi-stage evolution. The activity period of the Emei mantle plume is from Late Paleozoic to Early Cenozoic, the overall evolutionary trend of magmas from old to young is: from mafic to acidic to alkaline; from eruption to intrusion; from marine facies to marine-continental alternative facies; and from mantle source to mantle source-predominating mantle/crust mixed source. The gap process is from the Devonian to the Mesozoic, its cracking evolutionary is from southeast to northwest.The mafic-acidic magmatic activities in response to the Emei mantle plume tectonism started at the Devonian of the Late Paleozoic, extensively developed from the Permian of Late Paleozoic to the whole Mesozoic, even till the Early Mesozoic. During the early period (Late Paleozoic) large-scale mafic magmatic activity is dominant; during the late period (Mesozoic to Early Cenozoic) large-scale acidic and alkaline magmatic activities are dominant, associated with minor mafic-ultramafic magma intrusion.Evolutionary of magmas from mafic to acidic and alkaline includes about seven activity stages. According to a peculiarity of Emei mantle plume activity, uniting a period of Emei mantle plume activity as well as a feature of Emei mantle plume activity in region, through much study and contrast, the regional mineralization of Emei mantle plume activity is divided into four mineralization series and six mineralization the second series in southwestern of china. The carlin type gold deposit is one of the important unit in southwestern, Guizhou.In southwestern of Guizhou province, development of sedimentary stratium is well, its distribution is widespread. However, main stratium hosting gold is upper Permian series and lower Triassic series in Yangzi stratium district, middle Triassic series in Youjiang stratium district, they are separately named to Long Toushan stratotype as well as Lai Zishan stratotype. The carlin-type gold deposits may be divided into three types further in southwestern of Guizhou province, firstly micro-particle disseminated type gold deposits occurring in continental source siliceous clastic rock, secondly micro-particle disseminated type gold deposits occurring in carbonate rock , thirdly micro-particle disseminated type gold deposits occurring in volcanic clastic rock (tuff).A sedimentary process of hydrothermal solution is very important role in a mineralization of long time to the Carlin type gold deposits. In whole period of Emei mantle plume activity, magma process is intense as well as frequent, which forms a excellent environment occurring hydrothermal solution in southwestern of Guizhou, the hydrothermal solution exist widespread in the area, and through a model of long-term cycle, it forms hydrothermal solution bearing a lot ore-forming matter. In southwestern of Guizhou, the gold of the hydrothermal solution is main migrated in form of AuH₃SiO₄^°, secondly in form of [AuCl₂]^-as well as[Au(HS)₂]^-. In the system made up ore-forming structure and cycle of hydrothermal solution, ore-bearing hydrothermal solution migrates up along with ore-controlling fault structure belt in a process of structure movement, it arrives in second ore-hosting or ore-bearing fault structural belt of shallow place or near surface of earth.. Moreover, the system of ore-forming hydrothermal solution change from closed state to part-opened or opened state, special, as a happening process concealed burst function of hydrothermal solution, due to release pressure rapidly as well as a mount of scatter and disappear of volatilizing matter, moreover, ore-forming hydrothermal solution appear out boiling, in order that much condition and parameter happens to change in ore-bearing hydrothermal solution, which leads that the system of hydrothermal solution depart from balance state rapidly, and lead to increase a density of ore-forming matter in hydrothermal solution, lead that complex compound loses stable, and SiO₂ density achieves super-saturation state, as a lots deposits of much cryptocrystalline-microcrystalline siliceous rock and basanite as well as pyrite and other sulphide bearing As, Sb, Hg etc. in hydrothermal solution stage , gold removes to form gold deposits main in the form of AuH₃SiO₄^°, secondly in form of [AuCl₂]^-as well as[Au(HS)₂]^-. Under normal conditions, resolving reaction formula of gold complex compound is:AuH₃SiO₄⁰+ H₂O→Au (natural gold) + H₄SiO₄+O₂ [AuCl₂]^-→Au (natural gold) + Cl₂↑[Au(HS)₂]^-→Au (natural gold) + HS^-or [Au(HS)₂]^- + CH₄ + H⁺→Au (natural gold) +H₂S + C_organAs is shown from the ore-forming process of gold deposits in southwestern of Guizhou, The Emei mantle plume activity is firstly condition that gold deposit forms in ore concentrating district. It provides matter source forming gold deposit etc. and ore-forming power source; moreover, it transforms sedimentary environment in the area. According to Emeishan basalt eruption of intermission as well many times, vibration of crust is frequent in the area, which makes tidal flat facies, edge platform facies, isolated platform and basin facies change frequently, which lead to form complex ore-bearing rock , that is, a sedimentary formation containing basalt clay rock , siltstone clay rock as well as thin bed bioclastic limestone. Lead to form hosting gold formation of Long Toushan stratotype in Yang Zi platform region and Lai Zishan stratotype in You Jiang orogenic belt.In southwestern of Guizhou, a mineralization process of Carlin-type gold deposits is a result from many times movement of Emei mantle plume activity. Its matter source and ore-forming process may be summarized by following model:Main source of gold matter: core of the earth→mantle of the earth→crust of the earth→near the earth's surfaceExisting state: gas→adding gas-liquid facies→ore-bearing fluid→solidMain channel: mantle plume→sub-mantle plume→mantle branch→ore-hosting belt Show form: deformation of structures→magam's activity→metamorphism→mineralizationOre-forming process: mantle plume activity→hydrothermal solution's cycle→source beds forming by deposit process of hydrothermal solution→forming gold ore bodies adding reformation process of hydrothermal solutionMoreover, mineralization of gold deposits still is obviously controlled by mineralizer and mineralizing environment. In the thesis, gives three stages process model of Carlin-type gold deposits in southwestern of Guizhou: matter source model of gold deposits, forming model of gold-bearing formation, metallogenic model of Carlin-type gold deposit in the mineralizing concentrating district.According to the deep study to mineralization in southwestern of Guizhou, is considered in following to ore-forming process of the gold deposit: As the region of Southwest Guizhou is located in an unique geotectonic setting at the juncture between the Tethys-Himalaya tectonic domain and the Pacific tectonic domain, the Emei mantle plume activity would last for a long period of time. During the Hercynian Dongwu Movement Guizhou experienced most intense tectonic activity. A larger-scale Emei mantle plume activity occurred around the areas of Xingyi, Anlong, Xingren and Zhenfeng of southwestern Guizhou since there had prevailed a relatively close environment, i.e., the sedimentary environment in a transitional zone from platform facies to platform marginal slope facies. In addition, eruption of the early Late Permian Emeishan basaltic magma caused by the Emei mantle plume activity marked the peak stage of basic magmatism. Accompanied by seafloor volcano-hydrothermal activities, on the one hand direct sediment gushing ore-forming matter with some gas and liquid of volcanic activity, on the other hand, move as well as deposit a lot of ore-forming matter carried out by ocean water dissolving process with volcanic rock, large amounts of Au, As, Hg, Sb and other trace elements found their way by deposit process of hydrothermal solution, in the form of extreme dispersion, into this sedimentary basin environment. With the variation of paleo-sea level, the Longtan Formation coal system seams that include terrigenous clastic matter, carbonated rock matter, chalcedony, organic matter and a lots ore-forming matter were formed. Which forms main gold-bearing formation or source bed like Zi mudang gold deposit, Shi Yindong gold deposit, Ge Tang gold deposit, Ni Pu gold deposit, He Taoshu gold deposit etc. Triassic Period, the region follows mainly a outline of geological structure earlier stage, the reef facies belt distributing along the Ba Suo-Ce Heng deep fault and Po Ping contemporaneous fault become a line of demarcation dividing two facies among south facies with north facies. In northern, basement is uprised, which sediments carbonate rock ,fine-clastic rock and clay rock of platform facies in continental sea; southern is subsided intensely ,leads to form Yin Zhi downwarping region, which deposits flysch formation of great thickness. In addition, according to a formation and development of rift, Guang Xi scale in south of Nan Panjiang forms a center of downwarping region of rift; which makes up a slope zone among Ba Suo-Ce Heng deep fault, which main involves a area of the southern of Xing Yi, the most part of Ce Heng, the southern of Zhen Feng, and Wang Mo etc., the area deposits turbidite rock and tuffaceous turbidite rock of deep water basin facies in continental sea type. Some slope belts often are changing belt to geochemistry peculiarity, some hollow winding place in the reef facies may form partial close condotion, which leads to collect and deposit for ore-forming matter. In Triassic Period of northwestern of Guang Xi, the Emei mantle plume activity leads to form many times volcanic activity, on the one hand direct sediment gushing ore-forming matter with some gas and liquid of volcanic activity, on the other hand, move as well as deposit a lot of ore-forming matter carried out by ocean water dissolving process with volcanic rock, which offers a mount of ore-forming matter for source bed by deposit process of hydrothermal solution. Therefore, form some rock of high goechemical background value bearing Au, As, Sb, Hg etc. at partial area as well as partial seam in the southern of southwestern of Guizhou, e.g. Xi Yuan formation, Xu Man formation, Bian Yang formation and so on, the seams make up gold-bearing formations or source beds of continental source siliceous clastic rock-type gold deposits like Lan Nigou gold deposit, Ya Ta gold deposit, Bai Di gold deposit, Luo Fan gold deposit, Ban Qi gold deposit, Dou Yajing gold deposit and so on. In the gold-bearing formations or source beds of Da Chang bed, coal seams and strata of Permian System and turbidite strata of middle Triassic series at the diagenetic stage, Au, As, Hg and Sb and other trace elements were extremely homogeneously dispersed but in response to the Emei mantle plume activity, As, Au, Hg, Sb and other ore-forming materials were continuously extracted by earth surface water, ocean water, deeply circulating water (confined water, phreatic water, water of aeratedzone etc.) as well as magma water from the gold-bearing formations or source beds, thereafter forms ore-forming hydrothermal solutions that removes in a lots Au-Si complex compound as well as Au-S complex compound. During the Yanshanian period ,due to intensely tectonic movement, mix the hydrothermal solutions closed in plume of sedimentary in the sedimentary basin with the earth surface water, which leads to a intensive change in geochemistry condition, makes relative closed balance system of the hydrothermal solutions disrupt, under a prompt of tectonic power and adding reformation process of mixing hydrothermal solution, those ore-forming elements were transported upwards by metasomatism and cavity filling along tectonically weak loci such as folds and faults or advantage geochemical protective screen, which collects a large mount of ore-forming matter of Au and so on and forms sedimentary process of hydrothermal solutions, and ore-forming matter of gold etc. deposits with pyrite, gold is absorbed or bundled by pyrite etc. therefore, which forms gold bodies.Result from three types Carlin-type gold deposit or mineral occurrence: volcanic clastic rock or tuff-type gold deposit in Da Chang bed, carbonate rock-type gold deposit in coal seam of Long Tan formation and continental source siliceous clastic rock-type gold deposit in turbidite strata of middle Triassic series as well as abnormalities and mineralization of other trace elements were formed.In the thesis, finally according to theoretical research in home and spot test in open, uniting prognostic foundation as well as gold abnormalities feature in the region, dividing multiplying volume to mean content of Au,As in abnormalities of dispersion trains, extracting and analysing synthetical information, may primary divide two grades to minerogenetic prospect province orâ… ,â…¡grades, there are seven minerogenetic prospect provinces. That is: five minerogenetic prospect provinces toâ… grade, they include: Gui Shun minerogenetic prospect province in Pan Xian county, Xia Shan minerogenetic prospect province in Xing Ren county, Bai Ceng-Luo Dong minerogenetic prospect province in Wang Mo county, Bao Shu-Da Guan minerogenetic prospect province in Wang Mo county and Xiong Wo minerogenetic prospect province in Xing Yi city; two minerogenetic prospect provinces toâ…¡grade, they include: Ding Yun-Yong Ningzheng minerogenetic prospect province in Guan Ling county and Hua Jiang minerogenetic prospect province in Guan Ling county.