贵州瓮福磷矿矿床地质特征与黔中古陆的时空展布关系及成矿模式

Geological characteristics of the Wengfu phosphate deposit in Guizhou Province and its temporal and spatial distribution relationship to the Central Guizhou Ancient Land and its metallogenic model

黔中地区瓮福磷矿处于扬子地块东南缘,是全球早震旦世陡山沱期成磷事件的典型代表。本文运用地层学、岩石学、矿物学、沉积学、古地理学等方法,综合研究瓮福磷矿矿床成因、找矿预测及成矿模式。研究表明,瓮福磷矿为浅水陆棚地区沉积的一套岩石组合,属于浅海台地相型,受控于陡山沱早期与晚期2次海侵旋回及规模,形成a、b等2层工业磷矿体。矿石质量特征指示沉积水体环境由浅至深,水动力条件由强到弱。中元古代末—新元古代期间扬子地块先后发生了晋宁、武陵、雪峰等多期次构造旋回运动。雪峰运动(结束时限约720 Ma)结束地台基底冒地槽沉积,促使黔中隆起或黔中山系不断发生地质演化形成黔中古陆,长期遭受剥蚀和夷平作用为磷块岩矿床的形成提供陆源碎屑。冰川事件(结束时限约635 Ma)之后,在扬子地块东南缘的黔中古陆东部地带形成瓮福磷矿(成矿时代介于600~550 Ma)。瓮福聚磷海湾浅滩磷块岩相带是今后地质找矿的优势靶区,白岩高坪含磷潮坪硅云岩相带次之,前雍无磷潮上坪硅云岩相带一定程度上不利于地质找矿。通过以上研究综合分析,建立了瓮福磷矿陡山沱期成矿模式。

The Wengfu phosphate deposit in the central Guizhou is tectonically located in the southeastern margin of the Yangtze block. It is a typical representative of the global Early Sinian Doushantuo phosphate ore-forming event. In this paper, by using stratigraphic, petrological, mineralogical, sedimentological, paleogeographic and other methods, we have comprehensively studied the genesis of the Wengfu phosphate deposit, proposed its metallogenic model and prospecting prediction suggestion of the area. The research shows that the phosphate-rich stratum of the Wengfu deposit is a set of rock series which were deposited in the shallow water shelf area, and belongs to the shallow sea platform type sedimentary rock. Due to the controlling influences of the two times of transgressive cycles and their scales in the early and late Doushantuo stages of the Ediacaran period, two layers of industrial phosphate ore bodies(Bed a and Bed b) were formed.The characteristics of ore quality of two phosphate beds indicate that their sedimentary water environments were changed from shallow to deep water levels, and their hydrodynamic conditions are changed from strong to weak ones. During the late Mesoproterozoic-Neoproterozoic period, multiple tectonic cycle movements including the Jinning, Wuling, and Xuefeng movements occurred successively in the Yangtze block. The Xuefeng Movement(ended at about 720 Ma) had ended the geosynclinal deposition on the platform basement. This had led to the continuous geological evolution of the Central Guizhou Uplift or the Central Guizhou Mountains to have formed the Central Guizhou Ancient Land, which was long-termly denudated and flattened to provide terrigenous debris for the formation of phosphorite deposits. After the glacial event(ended at about 635 Ma), the Wengfu phosphate deposit(with the metallogenic time of about 600~550 Ma)was formed in the eastern part of the Central Guizhou Ancient Land on the southeastern margin of the Yangtze block. The phosphorite-bearing lithofacies belt in the Wengfu Phosphorus Accumulation Bay Shoal is the favorable target area for the future geological prospecting of phosphorus resource. The Baiyan Gaoping Phosphorus-bearing tidal flat silicic dolomite facies belt is the secondly favorable target area for the phosphorus prospecting. However, the Qianyong phosphorus-free tidal flat silicic dolomite facies belt is not conducive to geological prospecting of phosphorus resource. Through the comprehensive analysis of the above studies, the metallogenic model of the Wengfu phosphate deposit in the Doushantuo period has been established.