巫山县桃花赤铁矿地质特征及成因探讨

STUDY ON THE GEOLOGICAL CHARACTERISTICS AND GENESIS OF TAOHUA HEMATITE DEPOSIT IN THE WUSHAN COUNTY

巫山县桃花赤铁矿含矿层为上泥盆统黄家蹬组，矿体呈层状一似层状分布于贺家坪背斜轴部及两翼。矿石颜色为紫红色和深紫红色，以豆状结构、鲕状结构和砂状结构为主，发育块状及务带状构造。矿石矿物以赤铁矿为主，次为菱铁矿，平均含量为90％；脉石矿物有石英、水云母、胶鳞矿、鲕绿泥石、方解石等。矿石单样品TFe为25％～56．80％，平均TFe为43．58％。矿石有害成分S质量分数低（0．05％～1．3％），P质量分数较高（0．5％～1．1％）。综合赤铁矿地质特征及区域古地理分析，桃花赤铁矿为渝东-鄂西地区晚泥盆世海相沉积赤铁矿，矿床类型属”宁乡式”铁矿床。赤铁矿形成于半封闭的、氧气充足的湿热古内陆海盆近岸处，古海盆附近的古陆风化壳为成矿物源区。风化剥蚀作用形成的陆源碎屑物质经流水带入海盆。海水中的铁质胶体在充足的沙粒和适合的水动力奈件下以胶体化学的方式形成赤铁矿鲕粒，赤铁矿鲕粒在强烈搅动环境中搬运和富集，最后在晚泥盆世黄家瞪期就位于近滨相至远滨相上部。

Taohua hematite deposit in the Wushan County occurred in the Huangjiadeng Formation of upper Devonian with stratified or stratoid ore bodies lying in the axis and limbs of the Hejiaping anticline. The iron ores were claret and deep-claret colored, with partly massive and partly banded structures. Hematite was the main mineral composition and the siderite was the minor mineral composition. Gangue minerals consisted of quarts, hydromica, collophane, chamosite, calcite,etc. The average content of the ore minerasl was 90%, total iron content （TFe） of one-sample is 25%-56.80% ,and the average content of total iron content （TFe） is 43.58%. The amount of sulfur in ore was very low （0.05%- 1.3%） with higher amount of phosphorus （0. 5% -1.1%）. Based on the characters of the hematite and the paleogeography of the area,it was indicated that the Taohua hematite deposit was the marine hematite deposit widespread in the east of Chongqing and west of Hubei, and they belonged to Ningxiang-type iron deposit. The hematite was generated in littoral zone of paleo sea basin which had a semi-enclosed,adequate oxygenation and humid tropical environment. Weathering crust of old land near the paleo sea basin was the source area and the weathered elastics were brought into the sea basin by river. Iron colloid formed iron oolite by the pattern of colloid chemistry in a suitable hydrodynamic condition of sufficient sand. After being transported and enriched in intensive agitate of wave and tide process,all of oolite deposited at nearshore and upper offshore at the Huangjiadeng stage of late Devonian.