| 邯邢式铁矿形成机制:来自河北武安斑状二长岩中“含铁熔体-流体”的证据 |
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| 引用本文： | 杨誉博,苏尚国,霍延安,宁亚格,顾大鹏.邯邢式铁矿形成机制:来自河北武安斑状二长岩中“含铁熔体-流体”的证据[J].地学前缘,2022,29(3):304-318. |
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| 作者姓名： | 杨誉博 苏尚国 霍延安 宁亚格 顾大鹏 |
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| 作者单位： | 1.中国地质大学(北京) 地球科学与资源学院, 北京 1000832.北京市地质调查研究院, 北京 100195 |
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| 基金项目： | 中国地质调查局项目(12120115069701);国家自然科学基金项目(92162213) |
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| 摘 要： | 人们对邯邢式铁矿形成机制一直存在争议。为解决这一科学问题,本文对在河北武安赵庄地区斑状二长岩中发现的“含铁熔体-流体”脉及团斑进行了详细的矿物学及岩石学研究。结果显示:“含铁熔体-流体”矿物组合分带明显,其中核部矿物组合为Di+Amp+Mt+Ap+Pl,边部矿物组合为Prh+Cal。“含铁熔体-流体”中磁铁矿具有明显的环带结构,中心部分TiO2含量为2.23%,边部磁铁矿TiO2含量为0.36%0.57%。核部∑REE高过边部两个数量级,在球粒陨石标准化稀土元素分配图中呈右倾型曲线,与武安地区侵入岩同源,在未经流体加入时的高温岩浆环境中结晶。边部磁铁矿在球粒陨石标准化稀土元素分配图中显示REE轻微亏损,且有明显的Ce负异常,指示了磁铁矿结晶环境有大量富含挥发分的流体加入。在磁铁矿(Ti+V)-(Al+Mn)图解中,“含铁熔体-流体”中的磁铁矿落于斑岩型磁铁矿和Fe-Ti、V型磁铁矿区域,也处于热液型磁铁矿与岩浆型磁铁矿之间。这表明“含铁熔体-流体”并非侵入岩与围岩发生接触交代反应后形成的远端夕卡岩脉,而是源于深部的“含铁熔体-流体”在浅部结晶的产物。以高钛、富集REE为特征的磁铁矿是深部岩浆房铁矿浆结晶的磁铁矿微晶。由于富含挥发分的流体注入岩浆房形成流体超压,磁铁矿微晶与气泡结合沿岩浆通道快速上升。最后在1.552.19 km的深度形成以低Ti、亏损REE为特征的磁铁矿,并结晶形成角闪石等流体晶矿物。
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| 关 键 词： | 含铁熔体-流体 磁铁矿 邯邢式铁矿 成矿机制 |
| 收稿时间： | 2021-03-08 |
Formation mechanism of Hanxing type iron deposit: Evidence from the iron-bearing melt-fluid assemblage in porphyritic monzonite from Wu’an,Hebei Province |
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| YANG Yubo,SU Shangguo,HUO Yan&#x,an,NING Yage,GU Dapeng.Formation mechanism of Hanxing type iron deposit: Evidence from the iron-bearing melt-fluid assemblage in porphyritic monzonite from Wu’an,Hebei Province[J].Earth Science Frontiers,2022,29(3):304-318. |
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| Authors: | YANG Yubo SU Shangguo HUO Yan&#x an NING Yage GU Dapeng |
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| Institution: | 1. School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China2. Beijing Geological Survey Institute, Beijing 100195, China |
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| Abstract: | The formation mechanism of the Hanxing type iron deposit has been controversial. In order to resolve this issue, we conducted a detailed mineralogical and petrological study of the iron-bearing melt-fluid veins and plaques found in the porphyritic monzonite from Zhaozhuang area, Wu’an, Hebei Province, located in the metallogenic belt of Hanxing. The iron-bearing melt-fluid mineral assemblage showed obvious zonal pattern, with the mineral assemblages Di + Amp + Mt + Ap + Pl at the core and Prh + Cal at the edge. The magnetite in the assemblage had a well-defined zonal structure. At the core the TiO2 content was 2.23% and at the edge 0.36%-0.57%, while ∑REE was two orders of magnitude higher at the core than at the edge. The chondrite-normalized REE plot for the magnetite is a right dipping curve, suggesting its homology to the Wu’an intrusive rocks crystallized in a high temperature magmatic environment without fluid addition. The magnetite at the edge showed slight REE depletion and obvious negative Ce anomaly, indicating an addition of large amounts of volatile fluids in the crystallization environment. In the (Ti+V)-(Al+Mn) diagram, the magnetite from the assemblage fell under the same areas as porphyry-type and Fe-Ti- and V-type magnetites, and also between the areas of hydrothermal and magmatic magnetites. These results suggested that the iron-bearing melt-fluid is not distal skarn vein formed by metasomatic interaction between intrusive rock and wall rock, but rather a product of shallow crystallization of deep magma by the following proposed mechanism: First, high-Ti, REE-rich magnetite microcrystals are formed from deep magmatic fangtie pulp; then, as fluid overpressure is reached due to injection of fluid rich in volatile matter, the magnetite microcrystals are combined with bubbles and rise rapidly along the magmatic channel: eventually, low-Ti, REE-depleted magnetite is formed at depths of 1.55-2.19 km, then crystallized to form fluid crystal minerals such as amphibole. |
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| Keywords: | melt-fluid bearing iron magnetite Hanxing type iron deposit metallogenic mechanism |
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