繁昌桃冲铁矿成因探讨

桃冲铁矿,开采历史悠久,由于其品位富,以平炉富矿为主要矿石类型,受到了重视。有关矿床的成因也一直被人们所注意。自三十年代提出火成接触变质——热液成因的观点以来(谢家荣、程裕淇1935),人们习惯于将矿床划归于矽卡岩型。作者通过野外调查和初步研究之后,对本区铁矿的成因产生了疑问。本文就现有资料的分析,对层状矽卡岩的形成条件和铁矿的成因,做如下讨论。     

长江中下游中生代沉积盆地的含矿建造

本文讨论了长江中下游地区中生代沉积盆地演化与成矿作用的关系。印支旋回本区在挤压构造环境下，形成坳褶盆地和海退序列的含矿建造；早中三叠世在局限台地－萨布喻环境下形成周冲村组富铁碳酸盐、铅锌、膏（盐）等含矿建造；中三叠世与三角洲前缘亚相有关的沉积环境下形成黄马青组含铜砂岩建造。     

安徽庐江龙桥铁矿层新资料及成矿作用多阶段演化模式

根据龙桥铁矿层位岩性，地球化学特征及其与南京地区中三叠世周冲村期含膏岩系的对比，结合含矿层位的展布与区域构造及火山岩盆地的构造分析。论证龙桥铁矿含矿层位是中三叠世东马鞍山期（周冲村期）萨布哈－泻湖沉积环境下，含铁沉积（菱铁矿，铁白云石，磁铁矿及赤铁）矿源层。经燕夺浆侵入的热变质和热液叠加构造，成矿作用经历多阶段演化。     

繁昌桃冲铁矿成因探讨

The problems of the formation conditions for stratiform skarns and the genesis of the Taochong iron deposits are dealt with in this paper. Following is a summary of this discussion: 1. Stratiform skarns in this area occur in carbonate rocks of the Upper and Middle Carboniferous Period and the lower part of the Permian Qixia Group. No outcropping or concealed igneous bodies have ever been found, let alone any indications of an igneous contact zone or a corresponding zonality from "dry" skarn to "wet" skarn. The mineral facies and zonation of the skarns depend predominantly on the properties of the initial host rocks, and the development of skarns seems to have had much to do with chemical potential of silicon in these host rocks. As a result of the reaction of iron-bearing carbonates with siliceous materials in the rocks, iron-bearing silicates were formed, which in turn were transformed by pneumato-hydrothermal processes of the later stage. The stratiform skarns of this area, therefore, probably fall into the category of stratabound skarns subjected to transformation of thermometamorphism. 2. The iron deposits bear undisputable stratabound characteristics. The positions of ore-bearing beds and the petrological features as well as the mineral associations all point to a sedimentary ore-forming process of iron-carbonate (siderite). The presumption of siderite ore source is supported by the following facts: (l) Remnants of sedimentary siderite which survived the metamorphism have recently been observed in magnetite ore from neighbouring Xinqiao mining area. Siderite can have as many as 12.07% Fe⁺⁺ and, after corrosion, shows oolitic texture. (2) The ore is mainly of calcite/ dolomite- magnetite type. Mineral associations are quite simple and sulfides are rarely seen. (3) A comparison of the analytical data suggests that the content of organic carbon in iron ore decreases due to oxidation caused by metamorphism but is still higher than that in magnetite of contact- metasomatic skarn. (4) The paleogeographic reconstruction shows that this area was once an ancient underwater uplift favorable for the precipitation of iron carbonates. After its formation, the siderate bed underwent thermodynamic metamorphism and was hence decomposed into magnetite, which was then subjected to the superimposed transformation by subsequent hydrothermal fluids, leading to the partial activation and migration of iron matter and thus the formation of such ore as hematite (specularite) at shallow depth of the Changlongshan mining area. In brief, this deposit has a complex genesis: it experienced sedimentation, thermal metamorphism and transformation by hydrothermal fluids.