河北迁安杏山铁矿床地球化学特征及其对成矿物质来源的指示

丁文君; 陈正乐; 陈柏林; 董法先; 崔玲玲

河北迁安杏山铁矿床地球化学特征及其对成矿物质来源的指示

1.
中国地质大学（北京）地球科学与资源学院，北京 100083
2.
中国地质科学院地质力学研宄所，北京 100081

基金项目:

全国危机矿山接替资源找矿项目 200799094

全国危机矿山接替资源找矿项目 20089950

详细信息

作者简介:
丁文君（1984-)，女，在读硕士，主要从事矿床地球化学研究。E-mail: dingdngwj@yeah.net

中图分类号: P618.31
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- 被引次数: 15
出版历程
- 收稿日期: 2009-09-23
- 刊出日期: 2009-12-01

GEOCHEMICAL CHARACTERS OF BAND IRON FORMATIONS FROM XINGSHAN IRON DEPOSIT IN QIAN'AN AREA, HEBEI PROVINCE: IMPLICATION FOR THEIR ORIGIN

1.
School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China
2.
Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China

摘要

摘要: 不同学者曾对迁安地区铁矿床的前寒武地质、岩石学和地球化学等方面进行了深入的研究，但是其成矿物质来源至今没有进行深入探讨。危机矿山勘察在迁安杏山矿床中发现了富大铁矿体，但其成因不明。本文通过对迁安富矿和普通矿石的主量、微量元素和稀土元素研究，结果表明它们的化学成分主要由Fe₂O₃(T)、SiO₂组成，并且Al₂O₃和TiO₂具有较低的含量，指示其形成时几乎没有碎屑物质的加入。而经PAAS标准化后，稀土元素的配分模式表现轻稀土亏损、重稀土富集的特征，无论是富矿还是普通矿石，都具有Eu正异常、其Co/Zn和Ni/Zn比值与热液类似的特征，表明形成时有高温热液加入；其Y/Ho > 44、Y的正异常表明其有海水的成因；La/La^*表明其没有陆源碎屑加入；La_N/YV_N < 1，表明既有海水特征，又有热液特征，所有这些数据都显示了迁安铁矿矿石的物质来源为海水和热液，与其他地方BIF铁矿物质来源一致。由于富矿和普通矿石的物质来源一致、主微量及稀土元素含量和分布类似、铁矿物主要为磁铁矿、原始沉积条带明显，推断富矿可能是火山一沉积建造原始沉积时由于局部富铁环境而形成的。
- 条带状铁建造 /
- 迁安 /
- 地球化学
Abstract: The origin of Qian'an BIFs remains unclear, although plenty of efforts have been done in this area (especially on the Precambrian geology, petrology and geochemistry). In the early stage of "Exploring Mines Facing A Resourse Crisis" project, large and high-grade iron ores were discovered. The ma\or and trace element analyses reported in this paper provide new insights on the origin and formation environment of Qian'an BIFs. The average bulk compositions of the BIFs are rich in total Fe and Sio₂, and very low in Al₂o₃ and Tio₂ contents, indicating that a minor terrigenous component input. Their PASS-normalized REE patterns show strongly enriched HREE and positive anomalies of La, Eu and Y. All of the geochemistry fingerprints, in combination with Co/Zn, Ni/Zn, Y/Ho (> 44), La/La^* and La_N/Yb_N (< 1) ratios, strongly suggest a combined origin of hydrothermal water and marine for Qian'an BIFs > consistent with BIFs otherwhere. There are no distinct differences between High-Grade and normal ores, which have apparently similar original sedimentary belts, in ma\or and trace element content, PASS-normalized REE pattern and Fe-bearing mineral assemblage (mainly magnetite), demonstrating that they might have the same origin. It is suggested that the high-grade ores were probably formed at locally Fe-rich environment during volcanic-sedimentary activity.
- band iron formations (BIFs) /
- Qian'an /
- geochemistry

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海南岛位于华南和印支陆块之间，东邻菲律宾板块，其形成和演化受特提斯和太平洋两大动力学系统的控制。因此，有关海南岛的构造单元划分、各单元的构造属性以及构造演化过程长期存在争议。海南岛东北部潮滩鼻榴辉岩的发现为岛屿晚古生代以来大地构造演化的研究打开了一个新的窗口。然而，潮滩鼻榴辉岩孤立的露头、不寻常的洋壳型高温变质类型以及特殊的石炭纪变质时代（Liu et al.，2021；刘晓春等，2021）使研究者难以探究其真实的构造含义。所以，在海南岛和邻近区域寻找与榴辉岩有关的高压变质岩石是一项非常迫切的任务。最近，笔者在海南岛东部黄竹岭地区开展地质调查时又识别出了新的榴辉岩体（图1），其在海南省区域地质志中曾被称为公庙斜长角闪岩（海南省地质调查院，2017），在新填制的海南黄竹岭地区1∶5万地质图中被称为变质玄武岩（周岱等，2021），笔者称其为公庙榴辉岩。

图 1 海南岛地质简图及榴辉岩的出露位置（据海南省地质调查院, 2017; Shen et al., 2018修改）

Figure 1. Simplified geological map of Hainan Island and exposed locations of eclogites (modified after Hainan Institute of Geological Survey, 2017; Shen et al., 2018)

下载: 全尺寸图片幻灯片

公庙榴辉岩主要呈较大的构造透镜体产出在泥盆纪强变形花岗岩中，西部与志留纪浅变质地层呈构造接触，并被三叠纪花岗岩所侵入。榴辉岩绝大部分退变严重，并遭受到强烈变形作用的改造，所以野外常以细粒斜长角闪岩的面貌出现，但局部可观察到相对粗粒的弱退变榴辉岩，肉眼可见石榴子石和翠绿色的绿辉石残留斑晶（图2a）。显微镜下观察和电子探针分析结果表明，榴辉岩相矿物主要包括石榴子石（含15%~44%镁铝榴石分子）、绿辉石（含33%~44%硬玉分子）、普通角闪石、黝帘石、石英和金红石−钛铁矿连晶（图2b），个别样品中含有蓝晶石或多硅白云母。使用传统的地质温压计对榴辉岩的峰期变质条件进行了初步估算，大致范围为780 ± 50 ℃、~2.0 GPa，属于高压中高温型榴辉岩。除角闪岩相至绿片岩相退变质作用之外，岩石在晚期还普遍叠加了一期葡萄石−绿纤石相变质作用。榴辉岩的原岩形成于~360 Ma，变质时代为310~290 Ma，但其原岩可能是在岛弧环境下形成的辉长岩，而非玄武岩。

图 2 公庙榴辉岩野外与显微特征

Hbl—普通角闪石；Grt—石榴子石；Omp—绿辉石a—野外特征；b—显微镜下特征

Figure 2. Field and microscopic characteristics of the Gongmiao eclogites

(a) Field photograph; (b) Photomicrograph Hbl−hornblende; Grt−garnet; Omp−omphacite

下载: 全尺寸图片幻灯片

榴辉岩的围岩只遭受到低级变质作用的影响，在浅变质地层和强变形花岗岩中均有白云母产出，后者中有时出现黑云母，但尚未发现其经历高压变质作用的岩相学证据。这2种岩石中的部分锆石发育很窄的变质增生边，使用离子探针小束斑获得的U-Pb年龄接近于榴辉岩最年轻的变质年龄（~285 Ma）。由此可见，榴辉岩的围岩与榴辉岩的变质时代接近，但变质级别明显不同，结合二者之间的构造接触关系，笔者推测这些岩石可能是在俯冲—增生—折返过程中混杂在一起的，代表一套增生型构造混杂岩。

公庙榴辉岩向北东距潮滩鼻洋壳型高温榴辉岩约100 km，两地榴辉岩具有相似的峰期矿物组合、相近的变质条件和p-T（压力−温度）演化轨迹以及近于相同的原岩和变质时代，似可在海南岛东部构成一条北东向长达100 km的晚古生代榴辉岩带。该榴辉岩带可能代表一条与古特提斯洋演化有关的古板块俯冲带，这对重构海南岛乃至古特提斯构造域东端晚古生代以来的大地构造演化将具有重要的启示。

图 1 迁安地区地质简图及其大地构造位置图

1.第四系；2.古近系新集组；3.上侏罗统；4.中元古界；5.中太古界三屯营组；6.磁铁石英岩；7.断层

Figure 1. Simplified geological map of Qian'an area and its geological setting

下载: 全尺寸图片幻灯片

图 2 杏山矿床BIF型铁矿石REE + Y分布图^[16]，图A为富矿，图B为普通矿石

Figure 2. PASS-noimalized REE + Y diagram of BIF from Qian'an area

下载: 全尺寸图片幻灯片

表 1 杏山矿床富矿及普通矿石主量元素分析数据(wt.%)

Table 1. Major element contents of BIF bulk samples from Xingshan deposit, Qian'an area(wt.%)

表 2 杏山矿床BIF型富矿全岩样品微量元素及稀土元素的分析结果

Table 2. Trace and rare earth element contents of Fe-iich BIFs from Xingshan deposit, Qian'an area

表 3 迁安矿床BIF型普通矿石全岩样品微量元素和稀土元素的分析结果

Table 3. Trace and rare earth element contents of BIFs from Qian'an deposit, Qian'an area

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