龙门山地区北川石沟里泥盆系养马坝组铁质鲕粒沉积及其环境分析

龙门山地区中泥盆统养马坝组铁质鲕粒是我国"宁乡式"鲕粒赤铁矿矿床重要铁质赋存形式。为查明龙门山地区泥盆系铁质鲕粒的沉积环境和成因机制,以甘溪石沟里剖面精细实测为基础,通过薄片鉴定和扫描电镜分析,对铁质鲕粒的沉积特征进行了详细研究。研究结果表明:龙门山地区甘溪石沟里泥盆系养马坝组铁质富集于生屑灰岩、鲕粒生屑灰岩和生屑鲕粒灰岩,呈层状或透镜状夹于粉砂质泥岩和泥岩中。铁质鲕粒是重要的铁质赋存载体,类型多样,根据鲕粒成分可将其划分为灰泥鲕粒、绿泥石鲕粒、铁化鲕粒和铁质鲕粒4种类型。龙门山地区石沟里剖面养马坝组铁质鲕粒沉积于有障壁海岸的潟湖环境中,根据鲕粒的纵横向分布特征,建立了有障壁海岸铁质鲕粒的成因分布模式,从障积滩外侧、障积滩内侧到潟湖,依次发育灰泥鲕粒、铁化鲕粒、绿泥石真鲕、绿泥石薄皮鲕和铁质鲕粒。

The Oolitic Iron Deposits and Environmental Analysis of the Devonian Yangmaba Formation in the Shigouli Profile,Beichuan County,Longmenshan Area

Iron oolites of the Middle Devonian Yangmaba Formation in the Longmenshan area are an important form of iron deposit in China's Ningxiang-type oolitic hematite deposit. To recover their sedimentary environment and ge-netic mechanism,the sedimentary characteristics of iron oolites were studied in detail by thin section identification and scanning electron microscope analysis and detailed measurement of the Ganxi Shigouli section. The study shows that the eutrophic iron is concentrated in layers and lenses of bioclastic limestone,oolitic bioclastic limestone and bioclastic oolitic limestone. The surrounding rock is silty mudstone and mudstone. Iron oolites are important stores and carriers of iron and occur in four types,depending on the difference in mineral composition:microlites,chlorite oolites,ferritic oolites and iron oolites. Iron oolites are deposited in a lagoon at the edge of the reef. The distribution of oolites enabled the genetic distribution pattern of oolitic iron at the reef edge to be established. In turn,from the outer reef shoal to the inner shoal,to the lagoon,normal or ferritic oolites,chlorite oolites,chlorite thin-skin oolites and iron were developed.