宣龙铁矿铁质鲕粒的显微结构及成因

MICROSTRUCTURES OF FERRUGINOUS OOLITE AND THEIR GENETIC CHARACTERISTICS IN THE XUANLONG IRON DEPOSIT,HEBEI PROVINCE

宣龙铁矿的铁质鲕粒由各种不同的核心和微层状外壳组成．核心的组分主要是石英砂粒、赤铁矿内碎屑和凝块以及粒状菱铁矿等．外壳的纹层分别由显微结构不同的板状、片状、均匀和不均匀粒状泥晶赤铁矿以及少量菱铁矿组成．其中板伏、片状、均匀粒状赤铁矿和菱铁矿主要是以化学或生物化学方式在核心表层逐层沉积结果；不等粒状赤铁矿微层则是鲕粒滚动中对铁质颗粒粘附而成．菌藻类生长繁殖改变沉积环境的物化性质，对铁质沉积起着重要作用．

The ferruginous colttes in the Xuanlong iron deposit consist of various nucleiand concentric lamellar shells.The mineralogical components of the oolite nuclei aremainly terrigenous quartz sand,hematitic intraclast or clot,small amount of siderite,etc.The oolite shell is composed of micritic hematites and small amount of sideritesdifferent in their microstructure and lamellarity.The sheet,flaky and equigranularhematitic micrites forming lamellae were directly precipitated from marine water onoolite surface,and inequigranular hematitic micrite was formed by the adherence inthe process of rolling of oolite.The ferruginous oolite was mainly deposited in highenergy environment of shallow or deep water zone.