Structure And Sedimentary Characteristics Of Ore-Bearing Layer In Limei Ore Field In Western Hunan Qingxudong Formation

Western Hunan-Western Hubei metallogenic belt is one of the 16 important metal logenic belts in China, which is located in the transition zone between the Yangtze pl atform and Nanhua active belt. It has been known that ore formation is an important prospecting target, while the ore-hosting horizon of the Pb-Zn deposit in northwestern Hunan is Lower Cambrian Qingxudong Formation(?1q). So it has high mineral prospe cting values to take “structure and sedimentary characteristics of ore-bearing layer in Limei ore field in western Hunan Qingxudong Formation” as a dissertation topic.This study is based on the geological survey project “Geological research and pro specting of ore field in Huayuan exploration area Zhangjiajie west of Hunan”. A lot o f factual informationshad been gained by field observation, such as profile survey, obs ervation of tectonic line, drillhole information and sampling analysis. Furthermore, com bined with previous data, a comprehensive analysis was carried out and this paper wa s finished on time. With a thoughtful examination, this research has yielded positive fi ndings. Those mainly are tectonic lithofacies paleogeography, ore-forming structures an d metallogenic regularity. The main understandings are listed as follows:1. The lithofacies paleogeographic map, which aimed to deepen understanding of sedimentary facies and tectonic evolution, had been determined in detail on ?1q in Li mei ore-field of Western Hunan. Single factor and multifactor analysis were used to d raw comprehensively through measured profiles. The sedimentary facies of ?1q from NW to SE were: restricted platform facies, algal limestone facies and neritic shelf faci es. The distribution of the ?1q was controlled by tectonic with the direction NE-NEE.The characteristic of sedimentary facies showed it was beach-reef-beach, as well as t hat belonged to carbonate hinge zone system. Pb-Zn deposits were all distributed in th e algal limestone facies with thickness over 100 m in the rich orebody concentrated ar ea.2. Two stages of diagenetic metallotectonic had been proposed in study area. 1) The direction of the early compressive stress field was NW-SE, which formed NE-NE E fold structure as Limei and Taiyang mountain, and along with Malichang thrust-faul ted. The ore fluid passageway structure, ore-hosting structure and ore-bearing structure were formed in this stage. 2) The direction of the later shearing-compresive stress fie ld was NE-SW, which controlled Huayuan-Zhangjiajie major fault that involved some destruction on the ore-bearing stratum through a left-lateral compression and thrust of early stage and a right-lateral extension and slip of later stage3. Deposit was mainly controlled by all kinds of fracture fissure and algal limest one strata. The sedimentary facies of beach-reef-beach belt was under control of the e arly structure of ?1q. Under the constraint of the early structure,the strates bended and folded in diagenetic stage,and then lots of pores and cracks formed by the fold activi ties offered ore-hosting space in Algal reef limestone and Shallow facies rocks. While the interlayer breccia and carbonatization were continued developing in the later stage,that made the ore forming fluids gathered and mineralized in pores and cracks.4. A metallogenic prediction had been carried out based on lithofacies distribution of ?1q and Huayuan-Chadong syngenetic fault. It was verified that ore algal limeston e facies of ?1q was distributed in NE-NEE and crossed the Huayuan-Chadong fault b y drilling-revealed of concealed deposits in Yangjiazhai and Danaopo. In addition, ore deposits had been discovered in 600 meters deep in the north and 100 meters deep i n the south of the Huayuan-Chadong majoy fault. So we could conclude that the nort hern rock of hanging wall of Huayuan-zhangjiajie fault Slipped 500 meters. It can be indicated that the Huahuan-chadong fault is not the north border of ore field. Therefor e, the north fault zone, with a larger prospecting prospect, is the target selection for t he next step.