邯邢地区矽卡岩富铁矿床形成机理及关键控制因素

发布时间：2018-06-28 10:04

  本文选题：邯邢地区 + 磁铁矿　； 参考：《中国地质大学》2017年博士论文

【摘要】：邯郸邢台地区大地构造位置属于华北克拉通之中部造山带中南段,是我国大型矽卡岩铁矿床的重要矿集区。该地区铁矿床规模大,矿石品位高,已发现的矿床/点100多个,已探明储量达8亿多吨,是我国重要的富铁矿矿石产出基地。前人对该地区的矿化特征、成矿岩体的侵位时代和岩石成因等开展了较多研究,但关于该地区矽卡岩铁成矿流体组成、性质及演化过程、磁铁矿沉淀机制等成矿过程的重要信息和关键问题的研究明显欠缺,很大程度制约了该地区成矿规律和成矿模式总结。邯郸邢台地区矽卡岩铁矿床与中奥陶统的膏岩层空间关系极为密切,不含膏岩层的早奥陶统灰岩未发现工业价值的磁铁矿矿化。膏岩层的的加入是否对形成富铁矿起到关键作用?论文选取邯邢地区最为典型的白涧和西石门大型富铁矿床为研究对象,在详细的野外地质观察基础上,开展详细的矿物学、地球化学及流体包裹体研究,深入探讨该地区铁矿床的成矿流体性质及演化、膏岩层作用机制以及高品位矿体形成机理,并建立该地区的矽卡岩铁矿成矿模式。在符山和白涧侵入体中发现四类磁铁矿。第一类为岩浆型磁铁矿,这类磁铁矿一般发育钛铁矿出溶结构,钛铁矿在晚阶段热液作用下蚀变形成榍石。在热液蚀变过程中,第一类岩浆磁铁矿常被第二类和第三类的热液磁铁矿交代。第四类磁铁矿为直接从热液中沉淀的产物,不发育出溶及孔洞结构。岩浆磁铁矿在被交代过程中微量元素如Ti、Al、Mg、Mn、Cr、Zn、Ga和Co等含量降低,而Fe含量升高。对磁铁矿微量元素用前人所设计的微量元素图解进行投点时,发现这些图解并不能有效区分不同成因磁铁矿(岩浆vs热液)。通过对磁铁矿详细的结构观察和成分分析,我们提出Fe vs V/Ti图解能有效区分岩浆磁铁矿与热液磁铁矿,并能检测岩浆磁铁矿的蚀变程度。白涧铁矿床矿化由早到晚,成矿温度由高往低可分为三个阶段:(I)干矽卡岩阶段;(II)湿矽卡岩阶段;(III)硫化物阶段。不同阶段形成的磁铁矿微量元素组成存在明显差异。磁铁矿中的Ti、V、Cr、Ni、Ga等元素含量从早阶段到晚阶段依次下降,说明温度对这些元素起到重要控制作用。微量元素Co和Ni在黄铁矿中高度富集,因此与黄铁矿共生的磁铁矿往往亏损这两种元素。Si和Ca等不相容元素在震荡环带结构磁铁矿中高度富集,反映了了在非平衡条件下,磁铁矿快速生长,这些元素通过表面吸附作用进入磁铁矿。磁铁矿溶解再沉淀现象十分多见,这个过程淋滤了磁铁矿中杂质元素如Si、Ca、Mg和Al等,提高了磁铁矿纯度。对比白涧层间矿体磁铁与白涧侵入体中的岩浆磁铁矿,发现两者在结构和微量元素组成上存在巨大差异。层间矿体明显富集Si和Ca等不相容元素,且发育震荡环带结构,而相容元素Ti、V和Cr等含量比岩浆磁铁矿低2个数量级,显示了明显的热液磁铁矿特征,并非矿浆贯入成矿。白涧铁矿矿区内矽卡岩辉石发育核-幔-边结构,从核部到幔部和边部,Na和Fe显著升高,Mg显著降低。外矽卡岩原生辉石几乎为纯透辉石,部分被晚阶段富铁辉石交代。过渡金属元素如Ni、Co、V、Cr和Zn等在辉石中的含量主要受辉石Fe含量控制;高场强元素如Nb、Ta、Zr和Hf则与辉石端元成分组成关系不大,主要受控于温度和流体成分。稀土元素总量与辉石中的P含量成明显正相关关系,磷灰石沉淀可能是导致辉石中P和REE总量下降的直接的原因。白涧磷灰石强烈富集轻稀土,磷灰石大量沉淀可能导致热液轻稀土的亏损,具体表现为La/Sm比值降低。综合辉石结构和成分特征,我们认为富镁的内矽卡岩核部辉石和外矽卡岩的原生辉石主要形成于静岩压力下的高温、低盐度、低水/岩比值的流体扩散交代阶段(Diffusive matasomastism);富铁内矽卡岩辉石以及外矽卡岩的次生辉石可能主要形成于静水压力下,流体发生沸腾作用,形成高盐度的富铁流体,流体受断裂/角砾岩构造控制明显,具有高的水/岩比值。白涧铁矿部分矿体发育在大理岩层间,受断裂构造控制明显,这套高盐度富铁的成矿流体可能是形成白涧高品位层间矿矿石的关键因素。西石门成矿岩体闪长岩中的造岩矿物和干矽卡岩矿物中的流体包裹体含大量不透明子矿物和盐类子矿物。分析结果表明,这些包裹体中的不透明子矿物绝大多数为磁黄铁矿,透明子矿物为氯化钠和氯化钾。透辉石中含透明子晶的包裹体均一温度为420℃-620℃,集中在500℃左右,盐度介于42.2-71.8 wt%NaCl,峰值60%wt%NaCl左右;含不透明子晶流体包裹体在加热过程中并不均一,盐度51.4-70.8 wt%NaCl,峰值62 wt%NaCl左右。利用体积法估算透辉石包裹体中铁的含量平均值为4 wt%,最高可达9 wt%。透辉石中出现大量含黄铁矿子晶和盐类子晶的包裹体说明西石门铁矿的成矿流体为高温、高盐度、还原性富铁流体。邯邢地区中奥陶统碳酸盐岩地层中发育大量蒸发岩,主要为硬石膏岩和石膏岩,最厚可达147 m,并形成石膏矿床(矿点)30多处;而包括西石门在内的邯邢地区矽卡岩铁矿床与中奥陶统中的膏岩层关系十分密切,铁矿床主要产在中生代岩浆岩与中奥陶统的接触带,其次为离接触带不远的碳酸盐层间构造带;相反,侵位于石炭系和二叠系地层(不含膏岩层)中的岩体未发现有工业价值铁矿,只伴有黄铁矿化或硫铁矿矿床。由于膏盐层中的SO42-在高温条件下具很强的氧化性,在矽卡岩铁矿成矿过程中可以起到很好的氧化剂作用。邯邢地区铁矿石中硫化物的δ34S‰为6.0-18.7‰,多集中在11.6-18.7‰之间,具有海相硫酸盐的硫同位素组成特征;而矿区侵入岩中δ34S‰主要集中在2.5-6.5之间,为深源岩浆硫的特点。这说明邯邢地区矽卡岩铁矿热液成矿过程中有大量奥陶系膏盐层的加入。还原性质的岩浆流体与高氧逸度的溶解膏岩层的外部流体混合将导致成矿流体氧逸度升高和磁铁矿的沉淀:12Fe~(2+)+SO_4~(2-)+12H_2O = 4Fe_3O_4 + H_2S+22H~+虽然上述反应产生大量的H~+,H~+可通过与围岩碳酸岩反应被消耗,从而促进反映持续向右进行、磁铁矿不断沉淀,形成较大规模的高品位磁铁矿矿体。上述反应对热液铁矿成矿过程中二价铁氧化成三价铁的机制提供了新的见解和证据,同时也很好地解释了许多与热液磁铁矿相关的矿床如矽卡岩型铁矿床、铁氧化物铜(金)矿床以及磁铁矿-磷灰石矿床中出现大量富集重硫的硫化物的原因。以上研究表明,邯邢地区矽卡岩富铁矿早阶段成矿流体在上升过程中可能发生沸腾作用,形成的流体具有高温、高盐度、氧逸度低的特点,这样的流体能溶解大量的Fe。高盐度流体与正在冷却的岩浆岩充分反应,导致区域大范围的强烈的钠钙质蚀变,在此过程中成矿流体萃取大量的铁质,为形成大型富铁矿床提供了成矿物质基础。沸腾包裹体测温数据计算表明邯邢地区成矿深度较浅(5km),岩浆流体向上迁移过程中容易快速冷却,这个过程不利于形成富铁的石榴子石和辉石等矿物,因而热液中的铁质没有被大量消耗。成矿流体在上升过程中与围岩中的膏岩层反应或者与溶解膏岩层的外部流体混合,导致成矿流体氧逸度突然升高,从而大量的Fe2+被氧化形成Fe3+,磁铁矿在这个过程中大量沉淀。另一方面膏岩层物质的溶解形成的大理岩中的构造薄弱带是重要的控矿构造,由于离岩体较远且处于相对开放的空间,成矿流体能有效聚集并快速冷却,在此过程中成矿流体与围岩反应,磁铁矿快速的大量的沉淀,形成致密块状的高品位磁铁矿体。晚阶段流体能与早阶段形成的富含杂质元素的磁铁矿反应,磁铁矿发生溶解再沉淀,杂质显著降低,磁铁矿纯度得到提高,从而对铁矿石得到进一步的富集。
[Abstract]:The geotectonic position of the Xingtai area in Handan is in the middle and south section of the Central Orogenic Belt of the North China Craton. It is an important ore collection area of the large skarn iron deposit in China. This area has large scale, high ore grade, more than 100 found ore deposits / points and more than 800 million tons of proven reserves. It is an important ore producing base in China. The mineralizing characteristics of the area, the emplacement age of the ore-forming rock mass and the petrogenesis have been studied more, but the important information and key problems about the composition, nature and evolution process of the skarn iron ore-forming fluid, the deposit mechanism of magnetite and so on are obviously deficient, and the metallogenic regularity and formation of this area have been restricted to a great extent. The ore pattern is summed up. The skarn deposit in Xingtai area of Handan is closely related to the gypsum rock in the Middle Ordovician, and the early Ordovician limestone without gypsum rock has not found the magnetite mineralization of industrial value. Is the gypsum rock formation playing a key role in the formation of rich iron ore? The paper selects the most typical Bai Jian and Xi Shi in Hanxing area. On the basis of detailed field geological observation, the detailed mineralogy, geochemical and fluid inclusions are carried out on the basis of detailed field geological observation. The characteristics and evolution of the ore-forming fluid in the iron deposit in this area, the mechanism of the gypsum rock stratum and the mechanism of the high grade ore form, and the formation of the skarn ore-forming in this area are established. Four types of magnetite are found in the rune and Bai Jian intrusions. The first class is magmatic magnetite. This kind of magnetite usually develops ilmenite dissolving structure, and ilmenite is altered to form titanite in the late stage of hydrothermal solution. In the process of hydrothermal alteration, the first class magmagnetite is often replaced by second types of magnetite and third types of hydrothermal magnetite. The four type magnetite is a product that precipitates directly from the hydrothermal solution and does not develop dissolution and pore structure. In the process of metasomatism, the trace elements such as Ti, Al, Mg, Mn, Cr, Zn, Ga and Co are reduced and the content of Fe is increased. Different genetic magnetite (magma vs hydrothermal fluids) are distinguished effectively. Through detailed structural observation and composition analysis of magnetite, we suggest that Fe vs V/Ti diagrams can effectively distinguish magmagnetite from hydrothermal magnetite and detect the alteration degree of magmagmagnetite. The mineralization temperature of the Bai Jian iron deposit from high to late can be divided into three from high to low. Phase: (I) dry skarn stage; (II) wet skarn phase; (III) sulfide phase. The composition of trace elements of magnetite in different stages is distinct. The content of Ti, V, Cr, Ni, Ga in magnetite decreased from the early stage to the late stage, indicating that temperature plays an important control role in these elements. Trace elements Co and Ni are in yellow. The iron ore is highly enriched, so the magnetite, which is symbiotic with pyrite, often loses the loss of the two elements,.Si and Ca, which are highly enriched in the concussion belt structure magnetite, reflecting the rapid growth of magnetite under unbalanced conditions. These elements are absorbed into magnetite by surface adsorption. Magnetite dissolves and re precipitates ten. The impurity elements in magnetite, such as Si, Ca, Mg and Al, have been leached to improve the purity of magnetite. The comparison of the magmagmagnetite in the white Jian interlayer magnets and the Bai Jian intrusive body shows that there are great differences in the structure and the composition of the trace elements. The interlayer ore bodies obviously enrich the incompatible elements such as Si and Ca, and develop concussion. The content of Ti, V and Cr of the compatible elements is 2 orders of magnitude lower than that of magmagnetite. It shows obvious characteristics of the hydrothermal magnetite, not the ore slurry penetrated into the mineralization. The skarn pyroxene development nuclear mantle edge structure in the Bai Jian iron mine area, from the nucleus to the mantle and the edge, Na and Fe significantly increased, and the Mg was significantly reduced. The outer silicon card Iwahara Yukiishi was almost the same. The content of transition metal elements such as Ni, Co, V, Cr and Zn in pyroxene is mainly controlled by the Fe content of pyroxene, and the high field elements such as Nb, Ta, Zr and Hf are not closely related to the composition of the pyroxene end element, mainly controlled by the temperature and fluid components. The total amount of rare earth elements and the P content of pyroxene. Obviously positive correlation, apatite precipitation may be the direct cause of the decrease in the total amount of P and REE in the pyroxene. The white ravine apatite is strongly enriched with light rare earth, and a large amount of apatite precipitates may lead to the loss of the light rare earth of the hydrothermal solution. The specific expression is the reduction of the La/Sm ratio. The primary pyroxene of the pyroxene and outer skarn is mainly formed at high temperature, low salinity, and low water / rock ratio of the fluid diffusion metasomatism (Diffusive matasomastism), and the secondary pyroxene in the iron rich skarn pyroxene and the outer skarn may be mainly formed under the hydrostatic pressure, the fluid is boiling, and the high salinity is formed. The fluid is controlled obviously by the fracture / breccia structure and has a high water / rock ratio. The part of the Bai Jian iron ore body is developed between the marble layers and is controlled obviously by the fracture structure. The high salinity and iron rich metallogenic fluid may be the key factor for the formation of high grade interlayer ore in the Bai Jian. The rock ore in the diorite of the West Shimen ore-forming rock mass The fluid inclusions in the mineral and dry skarn minerals contain a large number of opaque subminerals and salt subminerals. The analysis results show that most of the opaque subminerals in these inclusions are pyrrhotite, hyaluronic minerals are sodium chloride and potassium chloride. The homogeneous temperature of the transparent subcrystal in Diopside is 420 C -620 C, concentrated in 500. The salinity is around 42.2-71.8 wt%NaCl and the peak value is about 60%wt%NaCl, and the fluid inclusions containing opaque subcrystal are not homogeneous during the heating process, and the salinity 51.4-70.8 wt%NaCl is about 62 wt%NaCl. The average value of the iron content in the diopside inclusions is estimated to be 4 wt% by using the volume method, and the maximum of the 9 wt%. diopside can be found to contain a large number of yellow iron. The inclusions of ore subcrystal and salt subcrystal indicate that the ore-forming fluid of West Shimen iron ore is high temperature, high salinity and reductive iron rich fluid. The Middle Ordovician carbonate strata in the Middle Ordovician of Hanxing area are mainly composed of anhydrite and gypsum rock, with the thickness of up to 147 m and more than 30 places in the stone gypsum deposit (ore point), including West Shimen. The skarn iron deposit in Hanxing area is closely related to the ointment strata in the Middle Ordovician. The iron ore deposit is mainly produced in the contact zone of Mesozoic Magmatic Rock and Middle Ordovician, followed by the carbonate interlayer structural belt, which is not far from the contact zone. On the contrary, the rock mass in the Carboniferous and Permian strata (without the gypsum rock) has not been found to have industrial value. Iron ore is only accompanied by pyrite or pyrite ore. Because the SO42- in the gypsum salt layer has strong oxidation under high temperature, it can play a very good oxidizing agent in the metallogenic process of skarn iron ore. The sulphide in the iron ore of Hanxing area is 6.0-18.7% 34S per 1000, in the multiple collection of 11.6-18.7 per thousand, with marine sulphate. The characteristics of sulfur isotopes are characterized, and the delta 34S per 1000 in the mining area is mainly concentrated in the 2.5-6.5, which is the characteristic of the deep source magma sulfur. This indicates that a large number of Ordovician gypsum salts are added to the hydrothermal mineralization process of the skarn iron mine in Hanxing area. The increase of oxygen fugacity of ore fluid and the precipitation of magnetite: 12Fe~ (2+) +SO_4~ (2-) +12H_2O = 4Fe_3O_4 + H_2S+22H~+, although the above reaction produces a large amount of H~+, H~+ can be consumed by the reaction with the rock carbonatite, thus promoting the continuous reflection to the right, magnetite precipitation and the formation of a large scale high grade magnetite ore. The mechanism of the oxidation of two valent iron into trivalent iron during the metallogenic process of hydrothermal iron ore provides new insights and evidence. At the same time, it is well explained that many of the ore deposits associated with hydrothermal magnetite, such as skarn type iron deposits, iron oxide copper (gold) deposits and magnetite apatite deposits, are caused by a large amount of sulphur enriched in the magnetite ore deposit. The study shows that the early stage of ore-forming fluid in the skarn iron ore rich iron ore in Hanxing area may be boiling in the process of rising, and the fluid is characterized by high temperature, high salinity and low oxygen fugacity. This fluid can dissolve a large number of Fe. high salinity fluids and fully react with the cooling magma rock, resulting in a large area of strong sodium calcium. In this process, the ore-forming fluid extracts a large amount of iron, which provides a material basis for forming large iron rich deposits. The calculation of the temperature measurement data of the boiling inclusions indicates that the metallogenic depth of the Hanxing area is shallow (5km), and the magma fluid is easy to cool rapidly during the upward migration process. This process is not conducive to the formation of iron rich pomegranite and pyroxene. The iron in the hydrothermal solution is not consumed much. The ore-forming fluid reacts with the gypsum rock layer in the surrounding rock or mixed with the external fluid of the dissolved gypsum rock, resulting in a sudden increase in oxygen fugacity of the ore-forming fluid, so that a large number of Fe2+ are oxidized to Fe3+, and the magnetite is precipitated in a large amount in this process. On the other hand, the gypsum rock is on the other hand. The structural weak zone in marble formed by the dissolution of the layer material is an important ore controlling structure. The ore-forming fluid can be effectively aggregated and cooled rapidly because of the distant and relatively open space from the rock mass. In this process, the ore-forming fluid is reacting with the surrounding rock, and the magnetite is rapidly precipitated, forming a dense and massive high grade magnet ore body. The late phase fluid can react with the magnetite rich in the early stage, which is rich in impurity elements. The magnetite is dissolved and reprecipitated, the impurity is reduced significantly, the purity of magnetite is improved and the iron ore is enriched further.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P618.31
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本文编号：2077620