塔北库鲁克赛铁矿成矿机制研究

发布时间：2018-02-25 07:29

本文关键词： 新元古代铁建造铁同位素冰川作用塔里木　出处：《南京大学》2017年硕士论文　论文类型：学位论文

【摘要】：新元古代铁建造是继大氧化事件(GEO),沉积间断10亿年(～1800 Ma至～750Ma)之后,再次大规模出现的铁建造类型。这类铁建造常与新元古代冰碛岩伴生,是新元古代雪球地球事件的重要标志。与形成于贫氧深海环境的太古代-古元古代铁建造不同,新元古代铁建造形成时大气中自由氧的含量已经相对较高。库鲁克赛铁矿产于新疆库鲁克塔格地区赛马山一带。矿区内由东往西大体圈定出3个矿化地段,15个铁矿矿体。矿体一般沿地层走向断续出露,形态以似层状、透镜状为主。本文研究对象为第一个矿化段内的1号铁矿体。该矿体呈透镜状产出,赋存于冰碛岩地层之中。赋矿地层与下部青白口系白云岩地层呈角度不整合接触。矿石本身即是铁质胶结的冰碛岩,赤铁矿含量普遍大于15%。来自铁矿体本身的碎屑锆石和侵入其内部的辉绿岩脉的岩浆锆石的U-Pb定年工作限定了库鲁克赛铁矿的形成时间介于1800Ma-630Ma,区域地层对比工作进一步限定库鲁克赛铁矿形成时代为新元古代南华纪早期,形成时间介于768土10 Ma-740±7Ma。矿石和矿体下部基岩的锆石年龄谱值对比和镜下岩相学研究表明,矿石中碎屑物质主要来自于青白口系下部独断山组地层。铁矿具有高Sc、Zr含量、低Zn/Co比值、正Y异常和无Eu异常的特征;同时,Nd同位素研究表明,铁矿具有低的Nd同位素比值,这都反应了库鲁克赛铁矿的成矿元素主要来自于风化的大陆地壳。成矿矿物以赤铁矿为主,具有正Ce异常,Fe同位素无明显分馏的特征,反映出库鲁克赛铁矿形成于相对富氧或者从贫氧向富氧变化的环境,氧化速度较快,氧化Fe~(2+)的氧化剂有较大可能是溶解于海水中的自由O_2。本文综合该矿的矿床地质和地球化学特征,提出了库鲁克赛铁矿床的冰川前缘沉积模型:库鲁克赛铁矿形成于成冰纪的冰水沉积环境,铁来自冰下水体,当冰下通道中流出的富铁(Fe~(2+))缺氧水体与表层富氧海水混合时,亚铁离子被快速氧化而发生化学沉积,并胶结冰水中的近源碎屑组分,形成富铁砾岩型铁矿体。
[Abstract]:The Neoproterozoic iron formation was a type of iron formation which appeared again in large scale after the great oxidation event (1 billion years between 1800Ma and 750Ma). This kind of iron formation is often associated with the Neoproterozoic moraine rocks. Is an important symbol of the Neoproterozoic snowball event. Unlike the Archaean-Paleoproterozoic iron formation formed in the oxygen-poor deep-sea environment, During the formation of Neoproterozoic iron formation, the content of free oxygen in the atmosphere was already relatively high. The Kulukesi iron ore deposit is located in the Sheshan area of Kuluktag area, Xinjiang. From east to west, there are 3 mineralized areas and 15 iron ores in the mining area. Ore bodies. The orebodies are generally exposed intermittently along the strike of the strata. The morphology of the ore body is laminar and lenticular. The object of this paper is the No. 1 iron ore body in the first mineralized section. The orebody is lenticular. The ore-bearing strata are in contact with the dolomite strata of the lower Qingbakou system. The ore itself is an iron-cemented moraine rock. The content of hematite is generally greater than 15. U-Pb dating of zircon from clastic zircon and magmatic zircon intruding into the diabase vein of the ore body limits the formation time of Kuluksai iron deposit between 1800 Ma-630 Ma.The regional stratigraphic correlation is carried out. In one step, Kuluksai iron ore was formed in the early Neoproterozoic South China. The zircon age spectrum of ore and the lower bedrock of the orebody and the lithologic study under the mirror show that the clastic material in the ore mainly comes from the formation of Dudufushan formation in the lower part of Qingbakou system, and the iron ore has a high content of SC Zr, and the formation time is between 768 and 10 卤7 Ma.The zircon age spectrum of the ore and the lower bedrock of the orebody are compared. The characteristics of low Zn/Co ratio, positive Y anomaly and no EU anomaly, and ND isotopic study show that iron ore has low ND isotope ratio. All these indicate that the ore-forming elements of Kulukesai iron deposit mainly come from weathered continental crust. The ore-forming minerals are mainly hematite and have the characteristics of no obvious fractionation of iron isotopes with positive ce anomalies. This reflects that the Kulukesi iron ore is formed in a relatively oxygen-rich or changing environment from poor oxygen to oxygen-rich, and the oxidation rate is relatively fast. Oxidizing Fe~(2) is more likely to be free OCS dissolved in seawater 2.The geological and geochemical characteristics of the deposit are summarized in this paper. The glacial front sedimentary model of the Kulukesai iron deposit is proposed: the Kulukesai iron deposit was formed in the glacial water sedimentary environment of the ice forming period, and the iron comes from the subglacial water body. When the iron rich iron from the subglacial passage flows out, the anoxic water is mixed with the surface oxygen-rich seawater. The iron ions were rapidly oxidized and deposited chemically, and the near-source clastic components in the glacial water were cemented to form iron-rich conglomerate iron ore bodies.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.31

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