【摘要】：酒泉盆地青西凹陷下白堊統(tǒng)下溝組中所發(fā)育的湖相泥晶白云巖具有獨特的復雜礦物組分和特殊的斷陷湖盆沉積構造背景,完全不同于一般的熱液交代白云石化或封閉環(huán)境下熱液充填白云石(巖),是十分罕見的中生代湖泊環(huán)境中由熱液噴流直接沉淀形成的泥晶原生含鐵白云巖。凡此套熱水沉積巖發(fā)育處,除了含有中-高溫的礦物,還會含有黃鐵礦,多呈極細碎屑狀、多數無晶形,大部分以碎屑集合體的形式存在,這些碎屑狀的黃鐵礦或以條帶狀構造分布于泥質云巖條帶中,亦或以角礫狀構造和脈狀構造分布于噴爆角礫巖格架間。本論文通過對該處黃鐵礦及圍巖進行深入和系統(tǒng)的巖石學、礦物學和地球化學的綜合研究,包括對黃鐵礦的結構構造研究、常量元素分析、微量元素分析和硫同位素分析,對圍巖結構研究、碳-氧-鍶同位素分析、微量元素分析和稀土元素分析等,首次對湖相“白煙型”熱水沉積巖中的黃鐵礦進行系統(tǒng)的研究,并獲得以下結論和認識:1)酒泉盆地青西凹陷下溝組熱水沉積巖中的黃鐵礦主要為噴流沉積型和氣水熱液型兩種成因類型。其中,噴流沉積型黃鐵礦的標型構造為:團塊狀、角礫狀、斑點狀、洖狀、侵染狀、結核狀、層狀、層紋狀和透鏡狀,其標型結構為:碎屑結構、自形粒狀、鑲邊結構、格狀結構、半自形粒狀和它形結構;氣水熱液型黃鐵礦的標型構造為:條帶狀和脈狀,其標型結構為:侵蝕結構。2)黃鐵礦的成礦流體來源主要為噴口內熱液和湖底熱鹵水。湖底熱鹵水的特征為:富含Sb、Ba、Sr、Mn和V等熱水沉積標型元素,LREE相對富集,具典型的負Eu異常稀土配分模式,氧同位素值明顯負偏;鍶同位素組成以少量幔源物質混入,主要受殼源物質影響最深為特征,反映紋層狀泥晶含鐵白云巖的沉積環(huán)境為受基底斷裂控制的,和具備穩(wěn)定、封閉和缺氧等條件的深湖底低洼熱鹵水池。噴口內熱液的特征為:富硫、貧Ni,幔源鍶較多混入(低87Sr/86Sr比值),溫度高于黃鐵礦的形成溫度。3)微米級莓球狀黃鐵礦小而均一、由極細小晶粒組成的層狀構造的黃鐵礦反應成礦環(huán)境為靜滯-缺氧的湖泊環(huán)境。4)黃鐵礦因其成因類型的不同,有其特有賦存位置:與噴口熱液有關的噴流沉積I型黃鐵礦主要存在于熱液噴口內和煙囪上;噴流沉積II型黃鐵礦存在于受沉積作用更強的位置;氣水-熱液型黃鐵礦主要存在于構造裂縫和沉積間隙中。5)建立湖相“白煙型”熱水沉積巖中黃鐵礦成因模式。
[Abstract]:The lacustrine mudstone developed in Xiagou formation of Lower Cretaceous in Qingxi Sag of Jiuquan Basin has unique complex mineral components and special sedimentary tectonic setting of faulted lacustrine basin. Completely different from the general hydrothermal metasomatism dolomitization or closed environment hydrothermal filling dolomite (rock) is a very rare Mesozoic lacustrine environment formed by hydrothermal jet direct precipitation of primary iron dolomite. Where the hot water sedimentary rocks are developed, in addition to the intermediate-high temperature minerals, they will also contain pyrite, most of which are very fine clastic, most of which are amorphous, and most of them are in the form of clastic aggregates. The clastic pyrite is distributed in the muddy dolomite belt or in the breccia framework by breccia structure and vein structure. In this paper, a comprehensive study of the petrology, mineralogy and geochemistry of pyrite and its surrounding rock is carried out, including the structural study of pyrite, the analysis of major elements, the analysis of trace elements and the analysis of sulfur isotopes. For the first time, the pyrite in the lacustrine "Baiyan" hot water sedimentary rock is systematically studied, including the study of surrounding rock structure, carbon-oxygen-strontium isotope analysis, trace element analysis and rare earth element analysis. The main conclusions are as follows: 1) Pyrite in the hydrothermal sedimentary rocks of Xiagou formation in Qingxi Sag Jiuquan Basin is mainly composed of two genetic types: jet sedimentary type and gas-water hydrothermal type. Among them, the typomorphic structure of jet sedimentary pyrite is: lump, breccia, speckled, filiform, infective, nodule, laminar and lenticular, its typomorphic structure is: clastic structure, self-shaped granular structure, edge structure. Lattice structure, hemiautomorphism granular structure and other shape structure; The typical structure of gas-hydrothermal-type pyrite is zonal and vein-like, and its typomorphic structure is erosion structure. 2) the ore-forming fluid of pyrite is mainly derived from hydrothermal solution in the nozzle and hot brine at the bottom of the lake. The characteristics of the hot brine at the bottom of the lake are as follows: rich in Sb,Ba,Sr,Mn and V, relatively enriched in LREE, typical negative Eu anomalous rare earth partitioning model, and obvious negative deviation of oxygen isotopic value; Sr isotopic composition is characterized by a small amount of mantle-derived materials, which is mainly influenced by crust-derived materials. It shows that the sedimentary environment of laminated mud-grained iron-bearing dolomite is controlled by basement faults and is stable. Deep lake bottom low-lying hot brine pool with closed and anoxic conditions. The characteristics of hydrothermal solution in the nozzle are: sulfur rich, rich in sulfur, rich in Ni, mantle source strontium (low 87Sr/86Sr ratio), and temperature higher than pyrite formation temperature. 3) micron raspberry globular pyrite is small and uniform. The ore-forming environment of pyrite reaction in stratified structure consisting of very fine grains is a lake environment of static hysteresis and anoxia. 4) pyrite is formed in different genetic types. It has its own location: I type pyrite which is related to nozzle hydrothermal deposition mainly exists in hydrothermal vent and chimney; The II type pyrite exists in the position where the sedimentary action is stronger, the gas-water hydrothermal type pyrite mainly exists in the structural fracture and the sedimentary gap. 5) the genetic model of pyrite in the lacustrine "Baiyan" hot water sedimentary rock is established.
【學位授予單位】：成都理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P618.31

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