应用电感耦合等离子体质谱/光谱法研究上扬子区新华磷块岩稀土元素特征及沉积学意义

Study on Geochemical Characteristics of Rare Earth Elements of Xinhua Phosphate Rocks in the Upper Yangtze,South China by ICP-MS/AES and Its Sedimentology Implications

新华磷矿床是我国重要的富集稀土元素的沉积型含稀土磷块岩矿床,本文利用电感耦合等离子体质谱/光谱法（ICP-MS/AES）,辅以岩矿鉴定等分析技术,结合沉积学理论研究了新华磷块岩稀土元素地球化学特征及相关问题。结果表明,新华磷块岩稀土总量（∑REEs）较高,集中值介于800×10-6~1200×10-6,其组成属轻稀土＋钇型,稀土元素主要以类质同象形式存在于胶磷矿中;新华磷块岩和昆阳磷块岩具相似的REEs配分曲线和明显铈负异常,δCe介于0.28~0.36,表明上扬子区南缘成磷环境为氧化条件,且为稳定的滨浅海被动大陆边缘沉积环境;但新华磷块岩与其上覆黑色岩系REEs配分曲线迥异,后者表现出不明显的铈、铕异常,说明黑色岩系主要形成于深海-半深海静水还原环境,从梅树村期早期至晚期经历了海平面升高的过程,地层层序整体显示向上变深的沉积相变,磷块岩和黑色岩系之间的接触面可能为三级层序甚至更小层序级别的界面。这些沉积学的认识揭示了上扬子区下寒武统层序地层学意义和海相沉积环境特征,对华南早寒武世生命大爆发和层序地层学深入研究提供了证据。

Xinhua phosphorus is a sedimentary phosphate deposit in China with strong REEs enrichment. In this study,Inductively Coupled Plasma-Mass Spectrometry（ ICP-MS） and Inductively Coupled Plasma-Atomic Emission Spectrometer（ ICP-AES） as well as rock-mineral identification,major and trace elements analysis together with sedimentology theory have been used to study geochemical characteristics of REEs in Xinhua phosphate rocks. ∑REEs of Xinhua phosphate rocks range from 800 × 10-6to 1200 × 10-6and are dominated by LREEs and Yttrium. REEs occur in collophanite by isomorphism dominantly. REEs pattern curves show remarkably negative Ce anomaies with values ranging from 0. 28 to 0. 36 in Xinhua phosphate rocks,which are similar to those of Kunyang phosphate rocks,indicating phosphorus in the south of the upper Yangtze was formed in an oxidative environment and precipitated at the stable epicontinental sea of the passive continental margin. However,REEs pattern curves of the upper black shales and weak Ce and Eu anomalies are different from those of Xinhua phosphate rocks,which reflect black shales were formed in a deep and bathyal sea of a reductive environment. The Meishucunian period had a transgression process and the Meishucunian stage had an upward deep regressive sequence,the boundary between phosphate rocks and black shales possibly being a third-order even less scale sequence boundary. All of this sedimentology information is helpful to reveal the sequence of stratigraphy and marine sedimentary environment,which provides evidence for biological outbreak and stratigraphy sequence of early Cambrian in the Yangtze area,South China.