山东张家洼矽卡岩型铁矿矿物学特征及其对成矿环境的指示意义

张家洼矽卡岩型铁矿位于华北克拉通东南部,赋存在石炭系本溪组与奥陶系马家沟组之间的假整合面处及闪长岩体与奥陶系马家沟组大理岩的接触带附近,富铁矿石资源量已达大型规模。研究发现矽卡岩矿物种类在内外接触带分布有一定区别,内带为石榴石等钙质矽卡岩矿物,而外带为阳起石、金云母等镁质矽卡岩矿物,整体构成钙镁质矽卡岩。对矽卡岩矿物系统的研究表明,透辉石及石榴石发育有环带,其氧化物含量随矿物环带的形成比例不断变化,暗示酸碱度及氧逸度随着成矿流体的演化而发生相应的变化,即由早期矽卡岩阶段的相对还原的酸性环境演化为退化蚀变阶段相对氧化的碱性环境从而导致铁质逐渐萃取多次富集、沉淀,后期随着磁铁矿的沉淀又逐渐在硫化物阶段转化为还原环境生成金属硫化物。

Mineralogy of the Zhangjiawa skarn iron deposit in Shandong Province and its implications for metallogenic environment

Abstract: The Zhangjiawa skarn iron deposit with high-grade iron is located in Laiwu of Shandong Province within southeastern North China Craton. The Laiwu hydrothermal metasomatic iron deposit is located at the unconformity between Carboniferous Benxi Formation and Ordovician Majiagou Formation and near the contact zone between Majiagou Formation and Late Yanshanian diorite, with the mineral reserves reaching a large-size deposit. Recent researches show that mineral compositions are somewhat different with the distance from the contact zone. The inner zone consists of calcium skarn minerals such as garnet, pyroxene, amphibole and episode, while the outer zone is composed of magnesium skarn minerals such as phlogopite and serpentine. The zoning structures of garnets and pyroxene in the Zhangjiawa iron deposit indicate that the ore-forming environment of the deposit changed gradually with the evolution of mineralization. The environment was somewhat reducing and acid at the beginning and, with the growth of silicate minerals and magnetite, became oxidative and alkaline. Finally, polymetallic sulfides crystallized and the environment became acid and reducing.