| 孙睿,冯志强,白洋,白阳,张尚清,李春江.碾子沟金红石矿床超镁铁岩特征及其对矿床成因的揭示[J].矿产勘查,2026,17(5):812-825 |
| 碾子沟金红石矿床超镁铁岩特征及其对矿床成因的揭示 |
| Petrology and geochemistry of ultramafic rocks in the Nianzigou rutile deposit, North China Craton: Constraints on ore-forming evolution |
| 投稿时间：2026-05-26 |
| DOI：10.20008/j.kckc.202605006 |
| 中文关键词: 碾子沟金红石矿床 直闪岩 石榴子石直闪岩 超镁铁质岩 原岩恢复 |
| 英文关键词: Nianzigou rutile deposit anthophyllite rock garnet-anthophyllite rock ultramafic rocks protolith reconstruction |
| 基金项目:本文受山西省基础研究计划(202303021212041、202303021212042)和山西省地质勘查建设与发展专项资金项目(1499002024CGK02736)联合资助。 |
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| 中文摘要: |
| 碾子沟金红石矿床位于华北克拉通中部造山带恒山—五台地区，是中国乃至全球罕见的大型变质岩型金红石矿床之一。尽管前人围绕其赋矿直闪岩和石榴子石直闪岩的原岩属性、变质演化及成矿机制开展了较多研究，但对与之空间密切伴生的超镁铁质岩石组分认识仍较薄弱。本文选取矿区代表性直闪岩、石榴子石直闪岩及超镁铁质岩石样品，综合开展岩相学观察、X射线粉晶衍射分析(XRD)、背散射电子成像及能谱分析(BSE-EDS)和全岩主量元素分析。结果表明:直闪岩主要由直闪石组成，次为绿泥石、滑石及少量黑云母、普通角闪石和石英，红色和黄色金红石沿片理定向富集；石榴子石直闪岩主要由石榴子石、直闪石、蓝晶石、石英和金红石组成，局部可见十字石及石英+堇青石后成组合，黑色金红石浸染状特征明显；超镁铁质岩石序列包括橄榄岩、辉石岩和蛇纹岩，局部较好保存橄榄石(Fo≈85)、单斜辉石、斜方辉石及磁铁矿-钛铁矿等原生矿物组合和堆晶结构。主量元素协变关系显示，超镁铁质岩石具有高 MgO、低 Al2O3、低 CaO和低碱特征，石榴子石直闪岩具有显著高 Al2O3特征，直闪岩成分介于两者之间，整体记录了原始岩浆分异、蛇纹石化、直闪石化及变质分异的复合效应。结合前人矿物学、年代学及 P-T研究结果，认为碾子沟赋矿岩石应来源于幔源基性-超镁铁质岩浆体系，其中超镁铁质岩石代表较原始的堆晶端元，而直闪岩和石榴子石直闪岩则为富 Ti组分经早期流体改造并在高压角闪岩相变质-折返过程中形成和保存的产物。金红石成矿受原始富 Ti物质基础、高压变质固定及折返阶段流体条件共同制约，其中相对“干”的折返环境更有利于金红石的保存与富集。 |
| 英文摘要: |
| The Nianzigou rutile deposit is located in the Hengshan-Wutai region of the central orogenic beltwithin the North China Craton, and represents one of the rare large-scale metamorphic-type rutile deposits inChina and globally. Although previous studies have extensively investigated the protolith characteristics, metamor-phic evolution, and ore-forming mechanisms of the host amphibolite and garnet amphibolite, understanding of thecomposition of the closely associated ultramafic rocks remains limited. This study selects representative samples ofamphibolite, garnet amphibolite, and ultramafic rocks from the deposit area, and integrates petrographic observa-tions, X-ray powder diffraction (XRD), backscattered electron imaging with energy-dispersive spectroscopy (BSE-EDS), and whole-rock major element analyses. Results indicate that the amphibolite is primarily composed of tremo-lite, with minor chlorite, talc, and small amounts of biotite, hornblende, and quartz; red and yellow rutiles arealigned along foliation planes. The garnet amphibolite consists mainly of garnet, tremolite, kyanite, quartz, and ru-tile, with local occurrences of staurolite and late-stage quartz + sillimanite assemblages, and exhibits a distinct dis-seminated texture of black rutile. The ultramafic rock suite includes peridotite, pyroxenite, and serpentinite, preserv-ing locally well-developed primary mineral assemblages such as olivine (Fo≈85), clinopyroxene, orthopyroxene,magnetite-ilmenite, and cumulate textures. Major element covariation patterns reveal that the ultramafic rocks arecharacterized by high MgO, low Al2O3, low CaO, and low alkali contents, whereas the garnet amphibolite shows nota-bly high Al2O3 content, and the amphibolite lies chemically between them—collectively reflecting a complex historyof primitive magma differentiation, serpentinization, tremolitization, and metamorphic fractionation. Integrating priormineralogical, geochronological, and P-T data, we propose that the ore-hosting rocks at Nianzigou originated from amantle-derived mafic-ultramafic magmatic system, where the ultramafic rocks represent relatively primitive cumu-late end-members, while the amphibolite and garnet amphibolite formed and were preserved during high-pressureamphibolite-facies metamorphism and exhumation through fluid modification of Ti-rich components. Rutile miner-alization was controlled jointly by the availability of originally Ti-enriched material, high-pressure metamorphicfixation, and fluid conditions during exhumation, with relatively "dry" exhumation environments being more favor-able for rutile preservation and enrichment. |
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