海南石碌铁矿基性岩脉地球化学特征及其地质意义

Geochemical Characteristics and its Significance of Mafic Dikes of Shilu Fe-ore Deposit in Hainan Province

海南石碌铁矿是我国最大的富铁矿床.对产出于该矿床的基性岩脉进行了系统的岩石学和地球化学研究,探讨了其成岩环境和成岩方式及其与铁多金属矿的关系.结果表明,该基性岩脉主要由绿泥石（70％～83％）、石英（5％）、方解石（2％～3％）以及少量的磁铁矿、绢云母组成,岩石发生过强烈的蚀变作用,保留有辉石、斜长石的残留矿物假象;岩石相对富集大离子亲石元素和轻稀土元素、亏损高场强元素（Nb,Ta,Ti）;在Zr/Y-Zr、Ti-Zr-Y图解上落于由岛弧向板内构造环境过渡区域.结合海南岛其它地方及中国东南部地区同时代基性岩脉的地球化学特征以及前人对该基性岩脉的定年研究（97 Ma）,认为白垩世晚期海南岛已成为华南板块的一部分,与整个中国东南部一样经历了强烈的区域拉张作用,使得发生过流体交代作用的地幔岩石发生减压熔融,沿构造薄弱带灌入,同时携带了大量气水热液,对石碌铁多金属矿床进行了一定的改造富化.

The Shilu Fe-ore deposit is the largest rich iron deposit in china. The petrology and geochemistry of marie dikes from mining area are studied. The results show that the mafic dikes are mainly composed of eholorite （ 70% - 83 % ）, quartz （5 % ）, calcite （ 2% - 3 % ） and a small amount of magnetite and sericite, and it was suf- fered from strong metamorphism or alteration, so that most of minerals were partially or completely replaced, but the shape of original minerals, especially plagioclase and pyroxene are still visible. In chemical composition, the mafic dikes are enrichment of large-ion lithophile elements and deficit of light rare earth elements and high field- strength elements （Nb, Ta, Ti）, and it formed in tectonic setting of transition from island arc to within-plate in dia- gram of Zr/Y-Zr and Ti-Zr-Y. Finally, we think that the mafic dikes are product of partially melting of mantle wedge in subduction zone, which take places fluid-metasomatism, and subsequently experiences obviously crystal- lization differentiation of pyroxene and plagioclase based on the above analysis, moreover, the geological charac- teristics suggests that the Hainan island maybe suffered from strong extension during the Late Cretaceous by combi- ning with other contemporary marie dikes in Hainan Island, as a result, it caused the fractures of mining area to reactivate and the magma to emplaced which resulted in transformation and enrichment of the deposit.