福建马坑铁矿区辉绿岩与成矿

发布时间：2018-04-29 06:41

本文选题：福建马坑铁矿 + 成矿地质体　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：马坑铁矿位于福建省龙岩市,是闽西南晚古生代永梅拗陷成矿带中的大型磁铁矿床,其成因的破解对于成矿带上其他具“马坑式”矽卡岩特征的矿床勘探具有巨大意义。尽管研究工作已相对成熟,但其成因学者们始终未能得出统一结论。本文在收集、总结前人资料的基础上,通过野外调查、数据分析,认为马坑铁矿赋矿层位主要为P1j-q(下二叠统经畲-栖霞组)灰岩与C1l(下石炭统林地组)砂岩的硅钙界面之间。矿体形态受构造控制明显,呈层状、似层状,赋存于马坑背斜虚脱空间中。矿区中存在由辉绿岩至大理岩所形成的内-外矽卡岩岩性剖面,自辉绿岩开始向两侧依次出现蚀变辉绿岩→矽卡岩化辉绿岩→榴石透辉石矽卡岩→榴石透辉石磁铁矿→大理岩。局部能见到更复杂矽卡岩矿物如透闪石、阳起石、符山石、钙蔷薇辉石等,但分带性较弱。磁铁矿与石榴子石与透辉石等矽卡岩共生,与大理岩接触界线截然并靠大理岩一侧存在流体逃逸构造。辉钼矿以浸染状或者裂隙充填的形式存在于林地组砂岩或辉绿岩中,形成晚于磁铁矿。最新榴石Sm-Nd等时线年龄显示成矿在160Ma左右,而被认为与成矿相关的大洋、莒舟花岗岩的锆石U-Pb年龄范围在120-155Ma,尽管没有对应160Ma的辉绿岩,由成矿专属性看来,富铁流体与基性岩浆来自深源地幔,钼矿由壳源岩石渗滤富集。因此辉绿岩作为马坑铁矿的致矿母岩,形成典型的矽卡岩蚀变分带,而大洋、莒舟花岗岩带来后期铅锌钼矿化,其岩浆热液在一定程度上对矿区进行叠加改造,如第二期的矽卡岩矿物细脉,林地组石英砂岩硅化等。由观察研究可知,矿体与辉绿岩直接接触,而与花岗岩基相隔林地组地层。本文认为由于古太平洋板块的俯冲作用,福建龙岩处于活动大陆边缘环境,俯冲的洋壳随深度加大便发生脱水作用,挥发分进入上覆地幔楔发生注水熔融,形成马坑辉绿岩的原生岩浆,岩浆上升至上地壳形成岩浆房,经历一定程度AFC作用,随着推覆作用进行,地层皱褶破裂,由于压力骤降,岩浆侵位在矿区以岩脉形式产出,同时幔源的富铁高温高盐度流体与辉绿岩共享岩浆通道,上升至硅钙界面,由于与灰岩发生化学反应沉淀出矽卡岩矿物与磁铁矿。基性岩浆上升至壳幔边界加热下地壳熔融得花岗质岩浆,在140Ma左右,下地壳花岗质岩浆沿不同岩浆通道侵位,形成大洋、莒舟花岗岩,空间上不与铁矿接触,而呈托举形式。
[Abstract]:Ma Keng iron mine, located in Longyan, Fujian Province, is a large magnet deposit in the metallogenic belt of the late Paleozoic Yong Mei depression in the south of Fujian Province. Its causes are of great significance to the exploration of other ore deposits with the characteristics of "pits" skarn in the metallogenic belt. Although the research has been relatively mature, its genetic scholars have not been able to draw a unified conclusion. On the basis of collecting and summarizing the previous data, through field investigation and data analysis, it is believed that the ore bearing strata of Ma Keng iron ore are mainly between P1j-q (the lower two series of the she Qixia formation) limestone and the silico calcium interface of the sandstone of C1l (Lower Carboniferous woodland group). The form of ore body is controlled obviously, and is layered and layered, and exists in the deficiency of Ma Keng anticline. There is a lithologic section of the inner and outer skarn formed by diabase to marble. From the beginning of the diabase to both sides, the altered diabase, skarite diabase, eclogite diopside skarn, eclogite diopside magnetite and marble were appeared on both sides of the diabase. The more complex skarn minerals such as dioptite, Yang Qishi, were found in the region. It is found that the magnetite and pomegranite are symbiotic with diopside rocks such as diopside, and the boundary between the marble and the marble is obvious and there is a fluid escape structure on the marble side. The molybdenite is found in the form of the sandstone or diabase in the form of the marbles or the form of the diopter or fissures, which is later than the magnetite. The age of the stone Sm-Nd isochronous line shows that the mineralization is around 160Ma, and the zircon U-Pb age of the Junzhou granite is considered to be in 120-155Ma, although there is no 160Ma corresponding to the diabase, the rich iron fluid and basic magma are derived from the deep source mantle, and the molybdenum ore is enriched by the shell source rock. A typical skarn alteration zone is formed for the ore-forming parent rock of Ma Keng iron ore, while in the ocean, Junzhou granite brings late lead, zinc and molybdenum mineralization, and its magmatic hydrothermal solution is superimposed on the mining area to a certain extent, such as the second phase skarn mineral vein and the silicified quartz sandstone in the woodland group. In this paper, the subduction of the paleopacific plate in Fujian Longyan is situated on the active continental margin, and the subducted oceanic crust is dehydrated with depth and stool, and the volatile matter enters the overlying mantle wedge with water injection melting, forming the primary magma of the horse pit and the magma up to the upper ground. The crust formed a magma chamber and experienced a certain degree of AFC action. With the push of nappe, the formation folds ruptured, because of the sudden pressure drop, the magma emplacement produced in the form of rock veins in the mining area. At the same time, the mantle derived iron rich high temperature high salinity fluid shared the magma channel with the diabase, rising to the calcium silicate interface, and precipitated the skarn with the chemical reaction with the limestone. Minerals and magnetite. The crust of basic magma rises to the crust and mantle boundary to melt the granitic magma. At about 140Ma, the granitic magma of the lower crust emplacement along different magma channels, forming the ocean and Junzhou granite, which is not in contact with the iron ore in space, but in the form of lifting.

【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.31

【参考文献】