海南石碌铁矿碧玉及其对矿床成因的制约

Jasper and its constraint on the genesis of the Shilu Fe ore deposit in Hainan Province

海南石碌铁矿是我国著名的富铁矿床。由于其复杂的地质特征,矿床的形成机制和富集机理一直存在争议。本文对石碌铁矿的碧玉和铁矿石进行了详细的矿相学和岩相学研究,特别是对肉眼无法识别的微小的碧玉进行了识别和观察。结果发现,碧玉除了在铁矿层的露头中有发育,在微观尺度上,微小的碧玉在铁矿石中也普遍发育,并和铁矿具有密切的共生关系,说明碧玉是石碌矿床重要的组成部分。由于碧玉是一种与火山-热液活动有关的化学沉积产物,因此可以明显地排除铁矿的矿浆喷溢型成因模式和矽卡岩型成因模式观点,表明原始的石碌铁矿是一套化学沉积的Si-Fe建造,从而为矿床的火山-热液沉积模式提供了直接有力的证据。由于Si-Fe质沉积过程有可能直接沉积形成富铁矿,所以石碌矿床的富铁矿是否像前人所提出的由构造去硅作用富集形成,值得进一步研究。

The Shilu Fe ore deposit in Hainan Province, China, is famous for its extreme enrichment of Fe. Its genesis, however, is still unclear due to its complicated geological characteristics. Models from magmatic-volcanic origin, through high-temperature hydrothermal origin （ skarn deposit） , to sedimentary origin have been proposed. Here the jasper, especially the fine-grained jasper that may not be detected by naked eye, and Fe ores from the deposit are carefully investigated for their geological characters. Spare jasper with lens-like shape being distributed in the outcrop, it is also found under the thin sections that fine-grained jasper is widely distrihuted in most low-grade and high-grade Fe ores, indicating a genetic relationship between the jasper and the Fe ores. The jasper is thus an important part of the ore deposit. As jasper is a kind of chemical sediment that is formed related to volcanic hydrothermal fluid activities, this finding provides solid evidence for the genesis of Shilu Fe ore deposit, which is actually a Si-Fe formation originally formed by volcanic exhalation.