甘肃北山地区红山铁矿硅质岩的地球化学特征及沉积环境

通过野外地质调查和系统的岩石主量元素、微量元素、稀土元素等的研究,探讨红山铁矿床硅质岩的地球化学特征及其沉积环境。红山铁矿床中广泛发育一套与铁矿体呈共生关系的硅质岩。研究表明,与铁矿密切共生的呈层状和透镜状产出的灰色、紫红色硅质岩总体属于低硅类型的硅质岩。在SiO2-Al2O3判别图解中,SiO2与Al2O3负相关,样品数据点均落入热水沉积区域;稀土元素配分模式经北美页岩标准化后呈平缓型,与东太平洋热泉水、红海热卤水具有相似的正Eu异常和配分模式,δEu值均大于1,显示热水沉积的特征;硅质岩中的V、Ni、Cu、Ba等微量元素的含量具有陆缘海盆热水沉积的特征。

Geochemical characteristics and depositional environment of siliceous rocks in the Hongshan iron deposit,Beishan area,Gansu Province

Geochemical characteristics and depositional environment of siliceous rocks in the Hongshan iron deposit were studied based on the field investigation and analysis of major elements,trace elements and rare earth elements.A suite of siliceous rocks closely related to Fe mineralization is widespread in the Hongshan iron deposit.The massive chert is gray and purple in color and has low SiO2 content,whereas SiO2 is negatively correlated with Al2O3.In SiO2-Al2O3 discrimination diagrams,chert samples fall into the hydrothermal region.The North American shale normalized REE patterns of siliceous rocks are flat with obvious positive Eu anomaly.These characteristics are similar to those of East Pacific hot springs and Red Sea hot brine,indicating their hydrothermal origin.Trace elements such as V,Ni,Ba and Cu have hydrothermal characteristics of continental-margin cherts.