摘要
西藏南部江孜盆地的下白垩统地层为一套浊积海底扇沉积序列。在沙拉岗一带, 这套地层中发育一段明显的硅化层。矿物学和岩石地球化学分析表明: 硅化层主要由硅化程度不等的硅化泥岩和硅化灰岩组成, 其矿物组成单调,主要包括石英、低温钠长石和被交代残余的方解石; 硅化泥岩的地球化学特征以继承原岩为主, 而硅化灰岩则受硅化流体改造的程度较大; 硅化灰岩中的微量元素随着硅化程度的递进表现出4种类型的迁移规律, 硅化灰岩的w(∑REE)和w(LREE) /w(HREE)等指标均与硅化程度成正相关关系。综合这些特征表明, 参与硅化层发育的流体可能是一种富SiO2 的偏碱性中低温热流体, 它的活动导致了硅化层的发育并可能和该区内锑矿的产生具有直接的成因联系。
The Lower Cretaceous in southern Tibet mainly consists of the submarine fan system, which is widely developed in Jiangzi Basin Near the Shalagang antimony deposit, which is the biggest in southern Tibet, a segment of the submarine fan was silicified According to the mineralogy and geochemistry features, the silicified mudstones and limestones were identified Besides the quartz, the albite was found in the silicified mudstones, but the silicified limestones contain only calcite without albite The geochemical data show that the silicified mudstones contain relatively high content in Al 2 O 3 and Na 2 O,and reveal high value of ΣREE and distinctly δ (Eu) anomaly These features indicate that the elements of the silicified mudstones are mainly derived from the source rocks For the silicified limestones, the contents of the trace elements are related to the silicification, and four groups are identified to reveal the mobility of the trace elements The values of ΣREE and LREE/ HREE are increasing with the growing of the silicification intensity With these geological and geochemical features, it can be inferred that the fluids, which led to the silicification processes, are characterized by mid low temperature, rich in SiO 2 and alkali material and metal elements It is suggested that these SiO 2 rich fluids have close associations with the genesis of the antimony mineralization in this area
出处
《现代地质》
CAS
CSCD
北大核心
2005年第2期267-273,共7页
Geoscience
基金
国家"973"计划项目 (2002CB412606)
高等学校博士点基金 (20040558050)
中山大学青年教师启动基金项目。
关键词
西藏
硅化
钠长石
微量元素迁移
稀土元素
锑矿
Tibet
silicification
albite
trace element mobility
REE
antimony mineralization
