| 福建永定大坪铌钽矿化花岗斑岩体的流体演化对铌钽富集的制约 |
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| 引用本文： | 刘永超,李建康,邹天人,江善元,丁欣,王娴.福建永定大坪铌钽矿化花岗斑岩体的流体演化对铌钽富集的制约[J].地质学报,2017,91(5):1052-1065. |
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| 作者姓名： | 刘永超 李建康 邹天人 江善元 丁欣 王娴 |
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| 作者单位： | 中国地质科学院矿产资源研究所,中国地质科学院矿产资源研究所 |
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| 摘 要： | 福建永定大坪铌钽矿化花岗斑岩体位于永定县城南部的大石凹-蓝地火山喷发盆地,对斑岩型铌钽矿床的产出具有重要的指示意义。本文通过岩相学、显微测温和激光拉曼等实验对大坪岩体ZK10001和ZK10401钻孔不同深度岩石样品中的流体和熔体包裹体进行了研究,试图揭示岩体的熔体-流体演化过程,分析铌钽等成矿元素的富集机制。观测结果表明,大坪岩体主要发育气液两相盐水溶液包裹体和硅酸盐熔体包裹体。流体包裹体均一温度集中在175～225℃,盐度集中在3%～7%NaCleq,密度集中在0.75～0.95g/cm~3,成矿流体主要为中低温、低盐度和低密度的流体,总体属于H_2O-NaCl体系。熔体包裹体主要分布于石英斑晶雪球结构的环带中,含有钠长石、石英和钽铁矿等子矿物。熔体包裹体完全均一温度较高,能够代表早期原始岩浆的组成。研究表明,大坪岩体的原始岩浆富铌钽等成矿元素和碱性组分,大坪岩体的铌钽矿化是岩浆高度分异的产物,铌钽的富集过程经历了斑晶阶段和基质阶段等两阶段结晶分异过程:在早期斑晶结晶阶段,少量铌钽矿物与斑晶一起结晶,并被斑晶包裹;岩浆演化晚期发生流体出溶现象,但未分异出大量流体,F等挥发分促进了铌钽在结晶残余熔体中富集,并在基质间隙中沉淀。大坪矿化岩体的存在指示出斑岩型铌钽矿床存在的可能性。
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| 关 键 词： | 流体包裹体 熔体包裹体 铌钽 大坪斑岩体 福建永定 |
| 收稿时间： | 2016/7/11 0:00:00 |
| 修稿时间： | 2016/12/30 0:00:00 |
Constraints of Fluid Evolution on Nb and Ta Enrichment of the Daping Granite Porphyry in Yongding, Fujian |
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| LIU Yongchao,LI Jiankang,ZOU Tianren,Jiang Shanyuan,DING Xin and WANG Xian.Constraints of Fluid Evolution on Nb and Ta Enrichment of the Daping Granite Porphyry in Yongding, Fujian[J].Acta Geologica Sinica,2017,91(5):1052-1065. |
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| Authors: | LIU Yongchao LI Jiankang ZOU Tianren Jiang Shanyuan DING Xin and WANG Xian |
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| Institution: | Institute of Mineral Resources, Chinese Academy of Geological Sciences,Institute of Mineral Resources, Chinese Academy of Geological Sciences |
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| Abstract: | The Daping granite porphyry intrusion with Nb-Ta mineralization locates in Dashiao-Landi volcanic basin in the south of Yongding, Fujian, which is of certain indicating significance for the existence of porphyry Nb-Ta deposit. In order to reveal melt-fluid evolution and enrichment mechanism of Nb and Ta, fluid and melt inclusions in the rock samples from different depths of drilling ZK10001 and ZK10401 were analyzed by means of petrography, microthermometric experiments and laser Raman spectroscopy. Aqueous two-phase inclusions and silicate melt inclusions are dominated in Daping intrusion. The homogenization temperatures, salinities and densities of fluid inclusions mainly vary from 175 °C to 225 °C, from 3% to 7% NaCl equivalent and from 0.75 g/cm3 to 0.95 g/cm3, respectively. The ore-forming fluid of Daping intrusion is characterized by medium-low temperature, low salinity and low density, roughly belonging to the H2O-NaCl system. Melt inclusions which contain albite, quartz and tantalite mainly distribute in snowball texture in quartz phenocrysts. Homogenization temperatures of melt inclusions are relatively high, which implies that they can represent primitive magma. This study shows that primitive magma of the Daping intrusion was rich in Nb, Ta and alkaline components. The Daping intrusion with Nb-Ta mineralization is the product of highly fractionated magma which enrichment process of Nb and Ta can be divided into two stages: phenocrysts formation in deep process and matrix formation in shadow process. At the early stage of magma evolution, a small fraction of niobium-tantalum minerals crystallized and was wrapped in phenocrysts to coincide with the crystallization of phenocrysts. During the late magmatic stage, small volumes of fluids exsolved, while Nb and Ta preferred to go into residual melt and concentrated in voids of matrix under the effect of volatiles (for example, F). Nb and Ta enrichment characteristics of the Daping intrusion imply the possible occurrences of porphyry Nb-Ta deposit. |
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| Keywords: | fluid inclusion melt inclusion Nb-Ta Daping granite porphyry Yongding County in Fujian Province |
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