安徽庐枞盆地小包庄铁矿的矿床地质特征和成矿机制以及与罗河铁矿的关系

Geological Characteristics and Metallogenic Mechanism of the Xiaobaozhuang Iron Deposit and Their Genetic Relationship with the Luohe Iron Deposit in the Lujian-Zongyang Basin,Anhui Province

小包庄铁矿位于长江中下游成矿带庐枞火山岩盆地中,是近年发现的又一大型玢岩型铁矿床。本文基于详细的岩相学、矿相学观察,对小包庄铁矿的围岩及典型矿物的主微量元素、硫同位素、流体包裹体进行了分析测试,结果显示,小包庄铁矿磁铁矿矿石中不同成矿阶段形成的黄铁矿、硬石膏的δ34S值异常高,黄铁矿集中在6‰~15‰之间,硬石膏集中在16‰~24‰之间,并且随着成矿期次由早到晚、深度由深到浅,黄铁矿、硬石膏的δ34S值逐渐降低,同时测得小包庄铁矿下部三叠系东马鞍山组膏盐层的δ34S值为30.1‰,反映了小包庄铁矿有膏盐层硫的加入。包裹体测温结果表明,小包庄铁矿透辉石-磁铁矿-硬石膏化蚀变阶段、绿帘石化蚀变阶段、碳酸盐-硬石膏-黄铁矿化蚀变阶段和硬石膏-石英-黄铁矿化蚀变阶段的成矿流体温度分布区间分别为326~496℃、259~317℃、178~280℃和107~189℃,盐度分布区间为14%~21%NaCleqv、11%~20%NaCleqv、6%~16%NaCleqv、2%~13%NaCleqv,成矿流体经历了从高温高盐度向低温低盐度演化的过程。从成矿岩体、矿体矿石特征、蚀变分带以及成矿温度等方面与罗河铁矿进行对比表明,小包庄铁矿与罗河铁矿为同一类型的两个独立矿床,其在空间上上下叠覆的模式可能是由闪长质岩浆在不同深度侵位造成的。

The Xiaobaozhuang iron deposit,located in the Lujian-Zongyang volcanic basin,Middle-Lower Yangtze River metallogenie belt,is one of important porphyry-like type iron deposits found in recent years.Based on detailed field geological investigation and petrographical study,this paper analyzed the wall rocks and main ore minerals using EPMA,ICP-MS,sulfate isotope and fluid inclusion.The resultsvalues of pyrites and gypsums decrease gradually with the depth from deep to shallow and alteration-evaporates salt layers,reflecting that there was addition of sulphur from gypsum-salt layers in the Xiaobaozhuang iron deposit.Microthermometry results show that the homogenization temperatures of fluid inclusions in diopside-magnetite-anhydrite stage,epidote stage,carbonate-anhydrite-pyrite stage and anhydrite-quartz-pyrite stage are 326-496℃,259-317℃,178-280℃and 107-189℃,respectively,and salinities are 14%-21%NaCleqv,11%-20%NaCleqv,6%-16%NaCleqv and 2%-13%NaCleqv,respectively.These features suggest that ore-forming fluids experienced a process from high temperature and high salinity to low temperature and low salinity.Compared with the Luohe iron deposit from the characteristic of metallogenic rock,ore body,ore,alteration zoning and metallogenic temperature,the Xiaobaozhuang iron deposit and Luohe iron deposit are two independent deposits.The spatially superimposed structure of Xiaobaozhuang iron deposit and Luohe iron deposit may result from the emplacement of dioritic magma at different depths.