宁芜盆地与梅山铁多金属矿床有关的火山—次火山岩的岩石地球化学和年代学研究

发布时间：2018-05-20 01:17

  本文选题：梅山铁多金属矿床 + 岩石地球化学　； 参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：梅山铁多金属矿床是宁芜盆地内代表性矿床之一,其Fe-Cu-Au-Mo矿化在时空和成因方面与大王山组橄榄安粗岩系火山岩和成矿母岩辉长闪长玢岩密切相关。对梅山矿区大王山组紫红色安山岩和含矿辉长闪长玢岩及矿体下部的新鲜辉长闪长玢岩进行LA-MC-ICP-MS锆石U-Pb定年,获得年龄分别为138~139Ma和138~141Ma;对大王山组黑云母安山岩进行黑云母Ar-Ar定年获得138Ma的坪年龄;因此梅山铁多金属矿床成矿主岩的形成时间应在138~141Ma左右,伴随的Fe-Cu-Au-Mo矿化稍晚,都属于早白垩世,略早于盆地内其它矿床,可视为岩浆热液成矿系统的下限年龄。根据年代学和地质事实证据,初步认为宁芜盆地早白垩世火山活动从北段开始,火山活动时限介于7~10 Ma。梅山矿区的主岩大王山组火山岩及次火山岩的造岩矿物化学特征暗示其母岩浆为氧逸度较高的幔源岩浆,且在岩浆演化过程中可能发生富硅熔体和富铁熔体的液态不混溶作用。岩石地球化学特征表明其属于橄榄安粗岩系,主要发生斜长石和单斜辉石的分离结晶作用,具有富集大离子亲石元素(LILE),亏损高场强元素(HFSE)的特征。显著的Nb、Ta和Ti亏损表明暗示岩浆起源于俯冲带环境,轻微的Eu负异常表明岩浆在相对高的氧逸度的条件下演化。成矿主岩的岩石地球化学和Sr-Nd-Hf同位素特征表明岩浆起源于类似于EMⅠ型的富集岩石圈地幔,其源区可能受到俯冲洋壳沉积物的交代作用,其母岩浆为含角闪石的尖晶石相二辉地幔橄榄岩部分熔融而成,岩浆在上升过程中受到地壳混染作用较小。矿物化学、岩石地球化学及锆石微量元素证据表明成矿主岩形成的构造环境为与古太平洋板块俯冲有关的活动大陆边缘陆缘弧环境。俯冲熔体交代机制暗示梅山铁矿床不混溶作用发生的关键因素磷元素的加入可能不是岩浆上升过程中含磷地层的混染,而可能是在地幔源区俯冲沉积物的贡献。而与俯冲交代有关的富含挥发分的偏基性的母岩浆、较高的氧逸度(由俯冲沉积物交代地幔楔所引起)、浅部岩浆房分离结晶作用、较浅的侵位深度可能是梅山Fe-Cu-Au多金属矿化的有利因素。
[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，

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