地学前缘 ›› 2016, Vol. 23 ›› Issue (3): 221-229.DOI: 10.13745/j.esf.2016.03.026

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铜陵焦冲金矿岩浆作用过程：来自闪长玢岩的证据

杜静国，杜杨松，陈林杰，庞振山   

  1. 1. 中国地质大学(北京) 地球科学与资源学院， 北京100083
    2. 安徽省地质矿产勘查局 321地质队, 安徽 合肥 240031
    3. 中国地质调查局 发展研究中心， 北京 100037
  • 收稿日期:2014-11-23 修回日期:2015-09-10 出版日期:2016-05-15 发布日期:2016-05-15
  • 通讯作者: 杜杨松（1957—），男，教授，博士生导师，从事矿物学、岩石学、矿床学方面研究。
  • 作者简介:杜静国(1989—)，男，博士研究生，从事矿物学、岩石学和矿床成因研究。E-mail：m15210963604@163.com
  • 基金资助:

    中国地质调查局项目（12120115034401，12120113069900）; 国家自然科学青年基金项目（41302062）; 中央高校基本科研业务费专项资金资助项目（2011YYL125）

Magmatic processes in Jiaochong gold deposit, Tongling, China: Evidence from dioritic porphyrite

DU Jingguo, DU Yangsong, CHEN Linjie   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. No.321 Geological Team, Anhui Bureau of Geology and Mineral Resource Exploration,Tongling 240031, China
    3. Development and Research Center, China Geological Survey, Beijing 100037, China
  • Received:2014-11-23 Revised:2015-09-10 Online:2016-05-15 Published:2016-05-15

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摘要：

本文主要针对安徽铜陵焦冲金矿区的闪长玢岩进行了详细的岩相学观察和矿物电子探针分析。岩相学观察表明，岩石内发育独特的石英斑晶、斜长石斑晶及其中的角闪石包裹体和角闪石斑晶。石英斑晶呈港湾状或次圆形，由溶蚀的次圆形内核和生长边构成，在内核与边部之间有熔融包裹体产出；斜长石斑晶具明显的“核幔边”环带结构，幔部发育明显的溶蚀界面，溶蚀界面处大量熔融包裹体呈环带分布；角闪石包裹体分别包裹于斜长石斑晶的核部和幔部，后者的边部被溶蚀呈次圆形；角闪石斑晶呈长条形，包裹有细针状的磷灰石。电子探针分析结果表明，斜长石中An含量自核部至边缘呈降低趋势，幔部出现多个An峰值；而来自斜长石斑晶核部、幔部和基质中的角闪石Al2O3含量从核部至基质也逐渐下降。采用角闪石斜长石温压计和角闪石全铝压力计，分别对斜长石斑晶核部及包裹的角闪石、斜长石斑晶幔部及包裹的角闪石和基质中共生的角闪石斜长石微晶的结晶温度和压力进行估计，结果表明，温度为806.84~808.75、791.00~797.86和660.3~683.9  ℃,压力为675~706、463~487和206~212 MPa，对应的形成深度为25.52~26.70、17.50~18.40和7.79~8.02 km。角闪石斑晶的结晶压力和深度为448~483 MPa和16.93~18.25 km，与包裹于斜长石幔部的角闪石包裹体一致。根据以上岩相学和角闪石斜长石矿物化学分析结果，本文提出一个多重岩浆房模型：来自深部幔源的流体（透岩浆流体）将不同层位的岩浆房串联活化，活化后的中基性岩浆和花岗闪长质岩浆混合形成中性岩浆，最后中性富流体的岩浆快速上侵冷却就位于地表，同时释放大量的挥发分（含矿物质），后期的减压排气作用可能是主要的成矿机制。

关键词: 溶蚀, 多重岩浆房, 闪长玢岩, 焦冲金矿, 铜陵

Abstract:

This paper presents new petrographic observations and microprobe analyses for the dioritic porphyrite from the Jiaochong gold deposit. Petrographic observations indicate the existence of unique quartz, plagioclase and hornblend phenocrysts in the rock. The quartz phenocryst is composed of resorbed core and growth rim, with melt inclusions along the border between core and rim. The plagioclase phenocrysts consist of resorbed core, resorbed growth mantle, and growth rim, with melt inclusions along resorption surfaces in the mantle. Hornblende poikilotopes are observed within core and mantle of the plagioclase phenocrysts. Hornblend phenocrysts are elongated in shape and contain acicular apatite poikilotopes. Microprobe analyses show that the An content of plagioclase from core to rim presents a reduced tendency and appears some An peaks at mantle, the aluminum content of hornblende from core of plagioclase to the matrix is decreasing. Using AmpPl geothermobarometry and wholeAl content of hornblende geobarometry the crystallization temperature and pressure of plagioclase phenocryst core and hornblende inclusions within it, the mantle of plagioclase and its hornblende inclusions, and coexisting HblPl micolites in the matrix are calculated respectively. The results show that the temperatures are 806.84808.75, 791.00797.86 and 660.3683.9  ℃, respectively. The pressures are 6.757.06 kb, 4.634.87 kb, and 2.062.12 kb respectively. The corresponding formation depths are 25.5226.70, 17.5018.40, and 7.798.02 km, respectively. Besides, the crystallization conditions of hornblende phenocryst are similar to those of embedded hornblende in the mantle of plagioclase phenocryst, the pressure of crystallization and corresponding depths are 4.484.83 kb and 16.9318.25 km, respectively. On the basis of the petrographic and geochemical analytical results, the present paper proposes the model of multiple magma chambers: the deep mantlederived transmagmatic fluids activate differentlevel magma chambers, as a result, forming intermediatebasic and granodioritic magmas,and the magma mixing between them has occurred. Finally, the mixing intermediate meltfluid flow driven by fluid pressure emplace rapidly near the surface, meanwhile, large amounts of volatile (orebearing fluid) are released. The exhalation process caused by decompression is probably the main mineralization mechanism.

Key words: resorption, multiple magma chamber, dioritic porphyrite, Jiaochong gold deposit, Tongling

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