本文選題：梅山鐵多金屬礦床 + 巖石地球化學(xué)　； 參考：《中國地質(zhì)大學(xué)(北京)》2015年碩士論文

【摘要】：梅山鐵多金屬礦床是寧蕪盆地內(nèi)代表性礦床之一,其Fe-Cu-Au-Mo礦化在時(shí)空和成因方面與大王山組橄欖安粗巖系火山巖和成礦母巖輝長閃長玢巖密切相關(guān)。對梅山礦區(qū)大王山組紫紅色安山巖和含礦輝長閃長玢巖及礦體下部的新鮮輝長閃長玢巖進(jìn)行LA-MC-ICP-MS鋯石U-Pb定年,獲得年齡分別為138~139Ma和138~141Ma;對大王山組黑云母安山巖進(jìn)行黑云母Ar-Ar定年獲得138Ma的坪年齡;因此梅山鐵多金屬礦床成礦主巖的形成時(shí)間應(yīng)在138~141Ma左右,伴隨的Fe-Cu-Au-Mo礦化稍晚,都屬于早白堊世,略早于盆地內(nèi)其它礦床,可視為巖漿熱液成礦系統(tǒng)的下限年齡。根據(jù)年代學(xué)和地質(zhì)事實(shí)證據(jù),初步認(rèn)為寧蕪盆地早白堊世火山活動從北段開始,火山活動時(shí)限介于7~10 Ma。梅山礦區(qū)的主巖大王山組火山巖及次火山巖的造巖礦物化學(xué)特征暗示其母巖漿為氧逸度較高的幔源巖漿,且在巖漿演化過程中可能發(fā)生富硅熔體和富鐵熔體的液態(tài)不混溶作用。巖石地球化學(xué)特征表明其屬于橄欖安粗巖系,主要發(fā)生斜長石和單斜輝石的分離結(jié)晶作用,具有富集大離子親石元素(LILE),虧損高場強(qiáng)元素(HFSE)的特征。顯著的Nb、Ta和Ti虧損表明暗示巖漿起源于俯沖帶環(huán)境,輕微的Eu負(fù)異常表明巖漿在相對高的氧逸度的條件下演化。成礦主巖的巖石地球化學(xué)和Sr-Nd-Hf同位素特征表明巖漿起源于類似于EMⅠ型的富集巖石圈地幔,其源區(qū)可能受到俯沖洋殼沉積物的交代作用,其母巖漿為含角閃石的尖晶石相二輝地幔橄欖巖部分熔融而成,巖漿在上升過程中受到地殼混染作用較小。礦物化學(xué)、巖石地球化學(xué)及鋯石微量元素證據(jù)表明成礦主巖形成的構(gòu)造環(huán)境為與古太平洋板塊俯沖有關(guān)的活動大陸邊緣陸緣弧環(huán)境。俯沖熔體交代機(jī)制暗示梅山鐵礦床不混溶作用發(fā)生的關(guān)鍵因素磷元素的加入可能不是巖漿上升過程中含磷地層的混染,而可能是在地幔源區(qū)俯沖沉積物的貢獻(xiàn)。而與俯沖交代有關(guān)的富含揮發(fā)分的偏基性的母巖漿、較高的氧逸度(由俯沖沉積物交代地幔楔所引起)、淺部巖漿房分離結(jié)晶作用、較淺的侵位深度可能是梅山Fe-Cu-Au多金屬礦化的有利因素。
[Abstract]:Meishan iron polymetallic deposit is one of the representative deposits in Ningwu Basin, and its Fe-Cu-Au-Mo mineralization is closely related to the volcanic rocks of the olive-an trachyte series and the parent rocks of the ore-forming parent rocks in terms of their space-time and genetic origin. LA-MC-ICP-MS zircon U-Pb dating has been carried out on the fuchsia andesite of the Dawangshan formation and the ore-bearing gabbrodiorite porphyrite and the fresh pyrodiorite porphyrite in the lower part of the orebody in Meishan mining area. The obtained ages are 138~139Ma and 138N141Ma.The plateau age of biotite andesite from the Dawangshan formation is determined by biotite Ar-Ar dating. Therefore, the forming time of the main ore-forming rocks of the Meishan iron polymetallic deposit should be about 138~141Ma, followed by the later Fe-Cu-Au-Mo mineralization. Both belong to the early Cretaceous, slightly earlier than other deposits in the basin, and can be regarded as the lower limit age of magmatic hydrothermal metallogenic system. Based on the geochronological and geological evidences, it is preliminarily considered that the early Cretaceous volcanic activity began in the northern part of Ningwu Basin, and the time limit of volcanic activity is 710 Ma. The petrogenic mineralogical characteristics of Dawangshan formation volcanic rocks and subvolcanic rocks in Meishan mine indicate that the parent magma is mantle magma with high oxygen fugacity, and the liquid immiscibility of silicon-rich melt and iron-rich melt may occur during the evolution of magma. The petrogeochemical characteristics indicate that it belongs to the olioan trachyte series, mainly occurs the separation and crystallization of plagioclase and clinopyroxene, and is characterized by the enrichment of large ion lithophile element Lilei, and the depletion of high field strength element (HFSE). The significant depletion of NB, Ta and Ti suggests that the magma originated from the subduction zone environment, and the slight negative EU anomaly indicates that the magma evolved under relatively high oxygen fugacity. The petrogeochemistry and Sr-Nd-Hf isotopic characteristics of the main ore-forming rocks indicate that the magma originated from the enriched lithospheric mantle similar to EM 鈪，

本文編號：1912537