赣南会昌地区花岗岩成因、蚀变带矿物地球化学及其与铀成矿的关系

发布时间：2018-03-15 08:34

本文选题：赣南　切入点：富城岩体　出处：《南京大学》2015年硕士论文　论文类型：学位论文

【摘要】：本文研究的珠兰埠花岗岩和富城花岗岩分别位于赣南会昌地区会昌盆地东西两侧。其中富城岩体西部与橄榄玄粗岩系列火山岩接触,河草坑铀矿田就产于该花岗岩体的内外接触带。作为矿床围岩的富城岩体西部花岗岩中发育大面积的蚀变带,在宏观上表现出“上红下绿”的特征。为了深入探讨本区蚀变与铀矿化的关系,本文运用电子探针技术对该蚀变带中的黑云母及其蚀变产物绿泥石进行了矿物化学对比研究。结果表明,富城岩体中黑云母属铁叶云母,黑云母铝铁镁组分的特征符合过铝质S型花岗岩的特点,可推断其源区物质主要来源于地壳沉积岩；根据黑云母成分估算的富城花岗岩岩浆的氧逸度较低(1g(fO2)值约为-15.0～-14.3),表明该花岗岩的源岩具有较强还原性,有利于铀在源区沉积岩中的富集；富城岩体U含量在13 ppm以上,远高于世界花岗岩的平均铀含量(3.5 ppm)；花岗岩中黑云母的氟含量达1.41～2.01wt%,表明该花岗质岩浆富F,而富F岩浆中U溶解度高,可能是富城岩体富铀的重要原因之一。黑云母常被绿泥石交代,呈黑云母假象。绿泥石矿物化学分析结果表明,绿泥石以鲕绿泥石和蠕绿泥石为主,属于富铁的绿泥石,主要形成于还原环境；绿泥石的形成温度介于246～307℃之间,平均276℃。此外,通过显微镜下特征等的对比分析,查明下部绿色蚀变层主要由绿泥石化产生,为还原环境蚀变产物；上部红化蚀变层则是较晚期赤铁矿化的结果,为氧化环境蚀变产物。全岩U、Th含量分析结果表明,上部红化蚀变层U含量(3.5～9.4 ppm,平均6.6 ppm)明显低于下部绿色蚀变层(7.7～23.1 ppm,平均13.9 ppm),而红化蚀变层与绿色蚀变层的Th含量基本相似,其平均值分别为35.7 ppm和36.5ppm。而富城复式岩体未蚀变的新鲜岩石平均U含量为22.5ppm(任海涛,2013),可见矿前期的带状大体积面型绿色蚀变活化了矿物晶格中的结构铀,铀发生部分转移；成矿期高氧逸度的流体萃取绿色蚀变层中已经活化了的铀而形成含铀成矿热液,同时形成了以赤铁矿化为主的红化蚀变层,含铀流体中的六价铀可能主要以氟合铀酰离子(UO2F42-和UO2Fs-)及铀酰氟化物(UO2F2)的形式迁移,在绿色层和红色层的氧化还原界面部位沉淀成矿。这可能是富城岩体西部蚀变带中的花岗岩型铀矿体多产于红化蚀变和绿色蚀变的接触部位的原因。Th的价态(正四价)很难随氧化还原条件而改变,因此未参与流体成矿过程。此外,岩石氧化还原电位测试结果显示绿色蚀变层岩石的还原性最强,随着红化蚀变的加强,岩石的还原能力减弱,这为上述成矿过程提供了佐证。富城花岗岩的活动铀浸出率平均为52%(任海涛,2013),绿色蚀变层的活动铀浸出率平均为30%,而红化蚀变层的活动铀浸出率平均仅为8.6%,这暗示富城花岗岩活动铀浸出率很高,存在很大的成矿潜力,绿色蚀变层的活动性铀已经部分迁出,而红化蚀变层的活动性铀几乎完全迁出。这些迁移的铀可能是河草坑铀矿田成矿所需铀的来源。为了深入研究富城西部产铀花岗岩体蚀变带的地球化学特征,本文选择会昌白垩纪断陷红盆北侧珠兰埠花岗岩体进行对比研究,从年代学、地球化学特征以及产铀潜力等方面揭示会昌断陷红盆两侧花岗岩体铀成矿作用的差异性。研究表明,珠兰埠花岗岩形成于225～228Ma左右,年龄与富城岩体相近,为印支期花岗岩。珠兰埠花岗岩具有S型花岗岩的岩石学和地球化学特征。样品具有高Si、Al特征,铝饱和-过饱和,K20/Na2O比值大于1.2,Ca、Mg含量低,具有较高的Rb、Th、U等大离子亲石元素,亏损Sr、Ba、Eu等元素,Ga/Al比值和Zr+Nb+Ce+Y含量较低。εHf(t)介于-7.7～-12.9之间,平均为-9.7；两阶段Hf模式年龄介于1.74～2.06Ga,平均1.87Ga；两阶段Nd模式模式年龄为1.65～1.80Ga,εNd(t)介于-7.9～-9.8,平均为-9.0；(87Sr/86Sr)i值介于0.7156～0.7264之间。综合岩相学和地球化学特征分析,认为珠兰埠花岗岩来源于古元古代地壳富泥质组分,在板块碰撞加厚期后的应力舒张阶段,发生部分熔融而形成的印支期S型花岗岩。珠兰埠岩体U含量(平均为10.9ppm)虽然高于中国东部上地壳平均值(1.5ppm,高山等,1999),但明显低于东部富城复式岩体平均U含量(22.5ppm,任海涛,2013)。且珠兰埠岩体活动铀元素浸出率(平均为25.7%)也远低于富城岩体(平均为52%,任海涛,2013),表明珠兰埠岩体的活动性铀含量低,且珠兰埠岩体蚀变和构造相对均不发育,不利于成岩后铀元素的迁移成矿。
[Abstract]:This paper studies the zhulanbu granite and Fucheng granite are located in the Huichang area of the Huichang basin. The East and west sides of Fucheng pluton Western contact with shoshonitic volcano rock, inner and outer contact zone of Hecaokeng uranium ore field is produced in the granite. As the development of a large area of the granite rock deposit Fucheng pluton in the alteration zone, characterized by "green" red in the macro. In order to discuss the relationship between the alteration and uranium mineralization, using biotite and etching electron probe technology of the alteration zone in the product of chlorite were studied. The results show that the mineral chemical contrast, Fucheng pluton in the clouds the mother is siderophyllite, biotite characteristics of aluminum iron and magnesium components in accordance with the characteristics of aluminous S type granite, it can be concluded that the source materials are mainly derived from the crust sedimentary rocks; according to the estimation of biotite composition Fucheng The granite magma of the low oxygen fugacity (1g (fO2) is about -15.0 ~ -14.3), indicates that the source rocks of the granite has strong reducibility, is conducive to the enrichment of uranium in the source region of sedimentary rocks; Fucheng pluton U content is over 13 ppm, far higher than the world average uranium content of granite (3.5 ppm); fluorine content in biotite granite in 1.41 ~ 2.01wt%, shows that the granitic magma rich in F and F rich magma U high solubility, may be one of important reasons for Fucheng uranium rich rock. Biotite chlorite is often explained, is biotite chlorite illusion. Chemical analysis results show that the chlorite chamosite and aphrosiderite mainly belong to the Fe rich chlorite, mainly formed in the reducing environment; formed between the temperature between 246~307 DEG C chlorite, average 276 degrees. In addition, by comparing the microscopic characteristics of the analysis, find out the lower layer is mainly composed of green green alteration Chloritized, for reducing environment alteration products; the upper red alteration layer is relatively late hematitization results for oxidizing environment alteration products. The whole rock U, Th analysis results show that the content of the upper layer of red altered U content (3.5 ~ 9.4 ppm, average 6.6 ppm) was significantly lower than that under green alteration layer (7.7 ~ 23.1 ppm, average 13.9 ppm), and the content of Th alteration layer and green alteration layer are similar, the average values were 35.7 ppm and 36.5ppm. and the average U content of urban complex rock mass without alteration of the fresh rock is 22.5ppm (Ren Haitao, 2013), visible the large volume type ore belt green alteration was activated in the lattice structure of uranium minerals, uranium partial transfer; extraction of high oxygen fugacity mineralization green alteration layer have been activated uranium and uranium metallogenic hydrothermal formation, while the formation of red hematite mineralization alteration to the layer containing. Six the price of uranium in the fluid may be the main fluoride uranyl ions (UO2F42- and UO2Fs-) and uranyl fluoride (UO2F2) in the form of migration, reduction in oxidation layer and the interface part of the green red layer deposits. This is probably the valence of.Th causes contact parts of granite type uranium deposits in Fucheng pluton in the alteration zone the red body prolific in the alteration and the alteration of the green (positive tetravalent) is very difficult with the redox conditions changed, so did not participate in the ore-forming process. In addition, the rock redox potential test results show that the reduction of the strongest green alteration rock, with the strengthening of red alteration, reduced the ability of rock, which provides evidence for the ore-forming process. Activities of Fucheng granite uranium leaching rate averaged 52% (Ren Haitao, 2013), activity of uranium leaching green alteration layer for the average rate of 30%, while the activity of uranium leaching alteration of red layer average rate 8.6%, suggesting that the activity of Fucheng granite uranium leaching rate is very high, there is great potential for metallogenic activity of uranium, green alteration layer has been partially moved, and the activity of the uranium red alteration layer almost completely out of uranium migration. These may be a source of Hecaokeng uranium mineralization of uranium. In order to required study of uranium granites in western urban alteration geochemical characteristics, this paper chooses Huichang Cretaceous faulted red basin of North zhulanbu granite were investigated from the chronology, reveals Huichang down faulted basin on both sides of granite uranium mineralization differences in geochemical characteristics and uranium metallogenic potential. Research shows that zhulanbu granite formed in 225 ~ 228Ma, and the age of Fucheng pluton is similar to Indosinian granite. Petrology and earth zhulanbu granite with S type granite. The chemical characteristics of samples with high Si, Al The characteristics of aluminum, saturated and supersaturated, K20/Na2O ratio is greater than 1.2, Ca, low Mg content, high Rb, Th, U and other large ion lithophile elements, Ba, loss of Sr, Eu and other elements, the ratio of Ga/Al and Zr+Nb+Ce+Y were low. Epsilon Hf (T) between -7.7 ~ -12.9, average -9.7; two stage Hf model between the ages of 1.74 ~ 2.06Ga, average 1.87Ga; two stage Nd model age of 1.65 ~ 1.80Ga ~ Nd (T) from -7.9 to -9.8, the average is -9.0; (87Sr/86Sr) I value between 0.7156 and 0.7264. Comprehensive analysis of petrographic and geochemical characteristics, think Zhu LAN Bu granite from the Paleoproterozoic crustal mud rich component in stress relaxation phase plate collision thickening stage after the partial melting and the formation of the Indosinian S type granite. Zhulanbu rock U content (average 10.9ppm) is higher than that of average China in the upper crust (1.5ppm, alpine, 1999). But obviously lower than that of the East The average U content of urban complex (22.5ppm, Ren Haitao, 2013). And zhulanbu rock activity of uranium leaching rate (average 25.7%) is far lower than that of Fucheng pluton (the average is 52%, Ren Haitao, 2013), the activity of the uranium content of the Pearl LAN Bu rock, and zhulanbu rock alteration and relatively are not developed, is not conducive to the migration of uranium mineralization into rock.

【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】：P588.121;P619.14

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