海南岛石碌韧性剪切带的主要特征与“北一”式铁矿的成因

在详细介绍了海南石碌韧性剪切带宏观和显微构造特征的基础上,本文运用“构造控制成岩成矿”新理论,对石碌铁矿成因进行了全面剖析。通过多年的调查及研究,提出石碌矿床控矿构造是韧性剪切带及其“构造透镜体(箭鞘褶皱)”。石碌富铁矿床主要成因是:原始沉积的贫铁矿在构造透镜体形成过程中经过塑性流动富集、压溶去硅等构造—成岩成矿作用,使贫铁变富铁,形成厚大的“北一”式矿体。总结了“北一”式铁矿的主要特征,根据厘定的石碌韧性剪切带及其构造透镜体的构造控矿及成岩成矿机制圈定了“北一”式矿体的找矿靶区,并进一步探讨了在基底变质岩系中和深部的找矿问题。

MAIN FEATURES OF THE SHILU DUCTILE SHEAR ZONE IN HAINAN ISLAND AND METALLOGENY OF THE "BEIYI-TYPE" IRON ORE DEPOSIT

The tectonic evolution of Hainan Island experienced four main stages:the pre-geosynclinal stage in Archean and Paleoproterozoic,the geosynclinal stage since Mesoproterozoic,the plateform one during Late Paleozoic and the diwa(geodepression) stage during Meso-Cenozoic.The Shilu Group in age of Neoproterozoic was a geosynclinal record,with the original and lower-grade iron ore formed.The Shilu ductile shear zone occurred in the earliest Cambrian,and in the deformational process the Beiyi-type iron-rich ore deposit created.The paper introduced megascopic and microscopic structural features of the Shilu ductile shear zone and the pressure solution,plastic flow and synkinematic geochemical characteristics in the process of mylonitization in details.In the light of the theory of structure controlling diagenesis and ore-forming,the metallogeny of the Shilu iron ore deposit was analyzed.The Beiyi-Jixinhe and the Fengshuxia-Zhengmei mylonitic belts played a key role in formation and distribution of the ore deposit.Based on the recent study,a concept of “Beiyi-type” ore deposit was represented,its main metallogenetic laws were summarized,and the prospecting target regions discussed.Furthermore,the ore-search in the Precambrian basement rocks and in the deeper crust of Hainan Island were explored.