铜陵地区晚泥盆世五通组叶腊石的发现及其资源意义

Pyrophyllite Formation and Its Resource Implication in the Late Devonian Wutong Formation of Tongling Mineralization Cluster

叶山铁矿是铜陵新桥矿田一小型沉积—热液叠加改造型铁矿床。文章采用粉晶X射线衍射(XRD)、扫描电子显微镜(SEM)等研究手段,对叶山铁矿区内晚泥盆世五通组沉积岩进行系统矿物学研究。结果发现,五通组碎屑岩中除了常见的碎屑矿物石英、长石、伊利石和高岭石,还含有大量叶腊石,伴生一定量赤铁矿和针铁矿。XRD定量显示叶腊石含量介于7.54%~70%,且沉积层中部为叶腊石富集层位,其含量皆高于50%。微结构观察发现叶腊石多呈自形—半自形的块状、板条状形态,多环绕石英颗粒生长,甚至有的颗粒已经完全由片状叶腊石组成,但是仍具有石英棱柱状形态的假象结构。化学成分分析显示,岩石样品SiO_(2)含量较高,介于44.47%~80.23%,Al_(2)O_(3)含量介于10.49%~28.75%。根据矿物组成和化学成分特征,铜陵叶山矿区五通组沉积岩已经具有叶腊石矿石品质,矿石类型属于硅铝质叶腊石,这种叶腊石矿石是陶瓷原料、耐火材料、无碱玻璃等重要原料。矿石微结构观察和矿区地质背景综合研究显示,五通组叶腊石可能为区域中生代岩浆热作用下高岭石和石英再活化产物。该研究成果为铜陵乃至长江中下游成矿带内具备类似地质条件、寻找非金属叶腊石粘土矿物资源提供基础矿物学理论支撑。

Yeshan iron deposit is a small-scale Carboniferous syn-sedimentary hydrothermally overprinted deposit in the Xinqiao ore field,Tongling mineralization cluster.In this paper,systematic mineralogical research has been carried out on sedimentary rocks of the Late Devonian Wutong Formation in Yeshan iron deposit using powder X-ray diffraction(XRD),scanning electron microscopy(SEM).Our results indicate that the dominant minerals in the Wutong Formation are detrital quartz and feldspar,and clay minerals including pyrophyllite,illite,and kaolinite,with some hematite and goethite.Higher average concentration of pyrophyllite in the studied Wutong sedimentary profile with from 7.54%to 70%occurs in the middle of the profile.Pyrophyllite in the samples shows micrometer scale euhedral to semi-euhedral block forms and grew around quartz particles.Pseudomorphic hexagonal prisms quartz particles consisting of lamellar pyrophyllite are also identified in the sedimentary rocks.The pyrophllite bearing ore compositions based on the XRF data show that the SiO_(2)content ranges from 44.47%to 80.23%,and Al_(2)O_(3)from 10.49%to 28.75%.According to mineral assemblages and chemical compositions of the Wutong Formation sedimentary rocks from the Yeshan deposit,pyrophyllite bearing sedimentary rocks are proposed to be pyrophyllite ore and the ore belongs to silicaalumina pyrophyllite ores,which is an important raw clay mineral resource applied in the fields of ceramic raw material,refractory material,and alkali-free glass.The microstr uctures of the ore and the geological background of the mining area indicate that the pyrophyllite in the Wutong Formation may be the products of the reactivation of detrial kaolinite and quartz under Mesozoism.The finding of this study is an important for pyrophyllite ore prospecting in the Tongling region and the Middle-Lower Yangtze River Mineralization Belt which has similar ore-forming geological settings including the Wutong formation and Mesozoic magma.