Origin of iron-rich minerals,ooids and pisoids in the Jurassic ooidal ironstones of the Labino-Malkin region(Caucasus)

This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus),represented by ooidal ironstones,biogenic limestones,and nodular phosphorites.All rocks contain ooids/pisoids.Based on the mineral composition,nine types of ooids and three possible scenarios for their formation have been identified.The mineral composition of ooids indicates the variable conditions of their deposition and repeated changes in physical and chemical conditions of the environment,including fluctuations in theredox regime.The access of oxygen in the bottom environment as a factor of increasing oxic conditions was associated with the regression of the sea and/or the inflow of meteoric waters.The main sources of ooids are the drift of material from the continent and convecting metal-bearing meteoric and/or deep solutions.

Ooidal ironstones in the Meso-Cenozoic sequences in western Siberia: assessment of formation processes and relationship with regional and global earth processes

This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia.The formation of such carbonate-based ironstones is a continuing problem in sedimentary geology,and in this study,we use a variety of data and proxies assembled from core samples to develop a model to explain how the ooidal ironstones formed.Research on pyrite framboids and geochemical redox proxies reveals three intervals of oceanic hypoxia during the deposition of marine ooidal ironstones in the Late Cretaceous to the Early Paleogene Bakchar ironstone deposit in western Siberia;the absence of pyrite indicates oxic conditions for the remaining sequence.While goethite formed in oxic depositional condition,chamosite,pyrite and siderite represented hypoxic seawater.Euhedral pyrite crystals form through a series of transition originating from massive aggregate followed by normal and polygonal framboid.Sediments associated with goethite-chamosite ironstones,encompassing hypoxic intervals exhibit positive cerium,negative europium,and negative yttrium anomalies.Mercury anomalies,associated with the initial stages of hypoxia,correlate with global volcanic events.Redox sensitive proxies and ore mineral assemblages of deposits reflect hydrothermal activation.Rifting and global volcanism possibly induced hydrothermal convection in the sedimentary cover of western Siberia,and released iron-rich fluid and methane in coastal and shallow marine environments.This investigation,therefore,reveals a potential geological connection between Large Igneous Provinces(LIPs),marine hypoxia,rifting and the formation of ooidal ironstones in ancient West Siberian Sea.

高磷鲕状赤铁矿石工艺矿物学研究

通过光学显微镜、电子探针、x射线衍射、化学分析、MLA等分析手段，对高磷鲕状赤铁矿石的化学组成、矿物组成、矿物嵌布及鲕粒特征进行了详细研究．结果表明：矿石中的铁主要赋存于赤铁矿和褐铁矿中，主要脉石矿物为石英、鲕绿泥石和胶磷矿．矿石矿物组成复杂，赤铁矿通常与石英、鲕绿泥石、胶磷矿和黏土矿物层层环状包裹形成鲕粒．鲕粒可分为富铁鲕粒和贫铁鲕粒，其粒度主要为0．1—0．5mm．此研究结果为该铁矿资源的合理开发利用提供了依据．

湖北长阳半峡背斜岩层应变分析

利用核部Ｍ型小褶皱、层间小褶皱、方解石脉及劈理等地质标志体，对半峡背斜进行了系统的线应变测量；在此基础上，运用长短轴法，Ｆｒｇ法及Ｒｆ／Φ法对南津关组、分乡组鲕粒灰岩的鲕粒应变进行测量、统计与分析。应变分析结果表明：半峡背斜岩层发生过两次明显的变形。第一次在半峡背斜形成之前，岩层在成岩作用或构造作用下形成的变形。第二次是在半峡背斜形成过程中发生的变形，半峡背斜不同构造部位、不同岩性的应变值与褶皱弯滑作用形成的应变协调一致。

鲕状铁建造的特征与形成机制——以鄂西泥盆系火烧坪铁矿床为例

鲕状铁建造(Ooidal Ironstones,OIS)是一种独特的含砂质、泥质、硅质或硅质碳酸盐,且铁质鲕粒含量超过50%,铁含量超过15%的沉积铁矿床。上扬子地区中—上泥盆统OIS广泛发育,被称之为"宁乡式铁矿",是我国南方重要的铁矿资源。本文选取鄂西地区的火烧坪铁矿床作为研究对象,通过对沉积相的识别与划分、矿石组构的鉴定与统计、鲕粒的显微形貌和成分分析,试图精确厘定铁质鲕粒的形成环境以及形成过程,建立和完善火烧坪乃至"宁乡式铁矿"的成矿模式。研究表明,火烧坪铁质鲕粒主要产于以含泥砂质碳酸盐为主的滨-浅海带,特别是滨-浅海转换带远端和浅海带近端,而具有工业意义的矿层均产于海侵旋回中海进—海退—海进的快速转换带。结合火烧坪铁矿沉积环境,本文为鲕粒的胶体化学成因模型提供了新证据,并完善了OIS成矿模型:(1)海进过程中,风化作用加剧所导致的海水富营养化促使海水深部呈缺氧的还原环境,Fe^(2+)得以局部富集;(2)短时期的海退给鲕粒的形成提供了核心物质的来源的同时,还使得水体动力环境和氧化还原环境发生改变,促进了鲕粒的沉积和生长;(3)又一次的海进使OIS得以沉积埋藏和保存。

鄂西晚泥盆世含磷鲕状铁矿石中磷的赋存状态与形成

广泛分布于我国南方泥盆纪地层的＂宁乡式＂铁矿储量巨大,然而含磷高严重制约了该类型铁矿的开发利用.铁矿石中磷的赋存状态是设计该类型铁矿＂提铁降磷＂方案的理论基础,是开发该铁矿首先要了解的问题.充分利用湿化学全岩分析、电感耦合等离子体质谱分析等全岩元素分析,扫描电子显微镜、X射线衍射等物相分析,电子探针微分析、激光剥蚀电感耦合等离子体质谱分析等微区分析技术,对鄂西晚泥盆世含磷鲕状铁矿石中磷的赋存状态、物质来源与磷矿物形成过程进行了初步探讨.铁矿石中的含磷矿物主要为碳氟磷灰石,分别以短柱状磷灰石晶体颗粒（65%以上粒径小于20μm）、磷灰石内碎屑（粗砂至极粗砂级,集中形成透镜状或带状层理）以及鲕粒中与赤铁矿相互包裹的凝胶状磷灰石（层厚度1050μm）3种形式存在.磷灰石晶体是在孔隙水中重结晶而生成,磷质可能来源于晚震旦世地层的磷块岩;磷灰石内碎屑是古海水体中原位化学沉积的产物,磷质可能来源于古海周边的大陆;鲕粒中凝胶状磷灰石也是原位化学沉积的产物,但与铁质沉积位置相同,并与富铁的鲕绿泥石混合或相互包裹形成鲕粒.