粤北302铀矿床围岩蚀变分带、成矿流体与成矿物质来源研究

发布时间：2018-03-13 20:03

本文选题：岩石地球化学　切入点：蚀变分带　出处：《南京大学》2015年硕士论文　论文类型：学位论文

【摘要】：302铀矿床位于粤北地区诸广南部岩体东南部的花岗岩内,在大地构造位置上处于闽赣粤后加里东隆起与湘桂粤北海西—印支坳陷结合部位。本文在野外地质工作的基础上,通过岩相学、岩石地球化学、LA-ICP-MS锆石U-Pb定年、电子探针定性及定量分析、H-O同位素和Sr-Nd同位素分析等方法,对与矿化相关的新鲜的花岗岩、蚀变围岩、蚀变矿物和副矿物等进行分析研究,以探讨矿床的成因。岩石地球化学研究表明,长江岩体新鲜的中粒黑云母花岗岩具有高Si02含量(72.27～75.08 wt.%),和较高的碱含量(Na2O+K20=7.68～8.10 wt.%),属于高钾钙碱系列。岩体A/CNK值为1.03～1.05,属弱过铝质花岗岩,富集轻稀土元素((La/Yb)N=7.24～11.04),Eu负异常明显(δEu=0.14～0.30),明显富集Rb、Th和U,而强烈亏损Ba、Sr、P和Ti,并轻微亏损Nb。 LA-ICP-MS锆石U-Pb定年结果表明,长江岩体的年龄为164±2 Ma(MSWD=6.3,N=13).围岩蚀变研究表明,在水平方向上,由矿脉向外蚀变围岩可依次分为4个带,且距离矿脉由近到远,蚀变程度逐渐减弱,总体表现为：硅化+红化→绢云母化→绿泥石化+碱性长石化→弱蚀变或正常花岗岩。U矿化与硅化和赤铁矿化密切相关。蚀变分带是在复杂的构造背景条件下,由多期多阶段的流体与岩石发生相互作用形成。蚀变围岩中绿泥石绝大多数属于鲕绿泥石和蠕绿泥石,以贫Si富Fe为特征,属于矿前期中高温热液蚀变范围。副矿物研究表明,蚀变围岩中主要副矿物为铀钍石、锆石、磷钇矿、磷灰石、褐帘石和黄铁矿等。铀钍石是最重要的富铀矿物。锆石最常见,磷钇矿和磷灰石数量较少,褐帘石只出现在弱蚀变花岗岩或正常花岗岩中。距离矿脉由近到远,副矿物的组合可简单概括为：铀钍石+锆石+磷钇矿→锆石+褐帘石+磷灰石。石英的H-O同位素研究表明,成矿流体的δ18OH2O值为-7.09‰～3.24‰,δDH2O值为-105‰～63‰,是在强烈的构造-岩浆活动的地质背景下,由大气降水在深循环过程中通过水-岩相互作用演化形成,δDH2O值的偏低可能由成矿流体经历了热液沸腾作用和/或少量有机水的混入引起。萤石的微量元素和Sr-Nd同位素研究表明,成矿期萤石的εNd(t)值(平均值为-11.6)几乎一致,与长江岩体的值(平均为-10.9)十分相似,与油洞岩体的值(平均为-13.2)也较接近,而与基性岩脉的值(平均为1.4)区别明显；萤石的稀土元素配分模式也与长江岩体更为相似,与油洞岩体区别相对较明显,反映成矿流体中的稀土元素主要来源于长江岩体。萤石的(87Sr/86Sr)i值介于赋矿围岩长江岩体和基性岩脉的(87Sr/86Sr)i值之间,反映成矿流体中的Rb-Sr组分来源于两者之间不同程度的混合。上述研究可能指示：成矿流体中的多数组分是在流体与围岩(尤其是长江岩体)之间相互作用过程中获得的。白垩纪以来,研究区内构造-岩浆活动十分强烈,粤北地区的陆壳处于伸展拉张期,大气降水来源的氧化性流体沿断裂构造下渗循环,在地温升高、强烈构造及岩浆活动的条件下温度升高形成热液,这种氧化性热液在与花岗岩的水-岩反应过程中溶解浸取花岗岩中的铀等元素,随着流体的运移,在有利的物理化学条件及构造部位,铀卸载富集成矿。
[Abstract]:302 uranium deposit is located in the north area of the Guangnan Department of southeast in the granite rock, the tectonic position in Fujian Guangdong Jiangxi and Guangdong Hunan Jialidonglong after the Hercynian Indosinian depression binding site. In this paper, on the basis of field geological work, through petrography, geochemistry, LA-ICP-MS zircon U-Pb dating and analysis the probe of qualitative and quantitative, H-O isotope and Sr-Nd isotope analysis method, and on the mineralization related to fresh granite, altered rocks, analysis of altered minerals and accessory minerals, the genesis of the deposit. The rock geochemical studies show that the Yangtze River Rock fresh medium grained biotite granite with high Si02 content (72.27 ~ 75.08 wt.%), the content of alkali and high (Na2O+K20=7.68 ~ 8.10 wt.%), which belongs to high potassium calc alkaline series. Rock mass A/CNK value from 1.03 to 1.05, is weakly peraluminous granite, enriched in light rare earth elements ( (La/Yb) N=7.24 ~ 11.04), obvious Eu negative anomaly (Eu=0.14 ~ 0.30), Th and U are significantly enriched in Rb, Sr, and strong depletion of Ba, P and Ti, Nb. LA-ICP-MS, and slight depletion of U-Pb zircon dating results show that the rock mass at the age of 164 + 2 Ma (MSWD=6.3, N=13) the wall rock alteration. Research shows that in the horizontal direction, from outward vein altered rocks can be divided into 4 zones, and the distance between the veins from near to far, the alteration degree gradually weakened, the overall performance is: + red, silicification sericitization, chloritization + alkali feldspar, weak alteration.U or normal granite mineralization and silicification and hematitization are closely related. The alteration zoning is in complicated tectonic background conditions, fluid and rock formed by multi-stage interaction. Chlorite in altered rocks belong to the vast majority of chamosite and ripidolite, with poor Si Fe rich features, belong to high temperature hot mineral liquid in the early Alteration of accessory minerals range. Research shows that the alteration of accessory mineral rock for uranium and thorium ore, zircon, xenotime, apatite, allanite and pyrite. Uranium thorium is the most important. The most common uranium rich mineral xenotime and zircon, apatite, allanite number only in the weakly altered granite or granite veins. Normal distance from near to far, combination of accessory minerals can be summarized as the following: uranothorite + + xenotime zircon, zircon and allanite + apatite. H-O isotope study of quartz indicate that the ore-forming fluid of delta 18OH2O value is -7.09% ~ 3.24. DH2O values for -105% ~ 63 per thousand, is the geological background in the intense tectonic magmatic activity, from atmospheric precipitation in the deep circulation process by water rock interaction and evolution, the low DH2O values may consist of the ore-forming fluid experienced mixed hydrothermal boiling and / or a small amount of organic water caused by fluorite. Trace elements and Sr-Nd isotopes indicate that the mineralization of fluorite Nd epsilon (T) values (mean -11.6) is almost the same, and the Yangtze River Rock value (average -10.9) are very similar, and the oil hole rock value (average -13.2) is relatively close, and the average value of mafic dikes (1.4) the difference is obvious; the distribution patterns of rare earth elements of fluorite and rock is more similar to the Yangtze River, and the difference between oil hole rock is relatively obvious, reflect the rare earth elements in ore-forming fluid mainly derived from the Yangtze river rock. Fluorite (87Sr/86Sr) I value between ore body and surrounding rock of the Yangtze River dikes (87Sr/86Sr) I between the values, reflect the Rb-Sr group in the ore forming fluid source between the two different degrees of mixing. The study may indicate: most groups in the ore forming fluid is in fluid and the surrounding rock (especially the Yangtze River Rock) interactions in the process of the research. Since the Cretaceous. The tectonic magmatic activity in the area is very strong, the continental crust in the north of Guangdong Province in the extension period, oxidizing fluid source of atmospheric precipitation infiltration along the tectonic cycle, in the temperature rise, strong tectonic and magmatic activities under the conditions of temperature rise of hydrothermal oxidation, the hydrothermal water and dissolved in granite rock reaction process of leaching uranium in granite and other elements, with the migration of fluid flow in the physical and chemical conditions, favorable tectonic position and uranium enrichment, unloading.

【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P619.14

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