摘要
下侏罗统日当组是扎西康Sb-Pb-Zn-Ag多金属矿集区重要的赋矿地层和矿源层。为探讨日当组成矿元素的初始富集机理,本文开展了系统的元素地球化学研究。结果表明,日当组各类岩石的SiO2、MgO、K2O、Rb、Zr等指示的陆源背景与世界平均页岩相近,推测陆源输入很可能不是成矿相关元素富集的主因;岩石的Fe3+/TFeO<0.5,U、V、Cr、Co和Ni的富集系数小于5,Ce无明显负异常,指示沉积过程中氧化-次氧化的底层水条件,成矿元素并非缺氧-硫化底层水条件下的矿物自生富集;P和Ba的富集系数大多小于1,反映了一种正常偏低的古生产力条件,指示成矿元素也非高生产力条件下生物富集。据地层中As、Sb、Ag的富集和部分岩石出现Eu正异常,以及区域上该地层中发育蚀变安山岩和热水沉积硅质岩夹层的地质事实,推测海底热液活动很可能是扎西康矿集区日当组赋矿地层中成矿元素富集的主要原因。
The Lower Jurassic Ridang Formation is an important ore hosting layer and ore source bed in the Zhaxikang Sb-Pb-Zn-Ag polymetallic ore-concentrated district in South Tibet.The initial enrichment mechanism for ore-forming elements of the Ridang Formation has been discussed in this study.Geochemical study shows that the contents of SiO2,MgO,Rb and Zr in various rocks from the Ridang Formation are similar to the world＇s average shale on terrigenous background,and thus,the continental input could not serve as a major factor for the enrichment of ore forming elements.For these rocks,the Fe3＋/TFe ratios are less than 0.5,the enrichment factor （EF） values of U,V,Cr,Co and Ni are less than 5,and Ce has no obvious negative anomaly,reflecting that they formed in the condition of oxidized to sub oxidized bottom water during sedimentation and the ore-forming elements could not be concentrated by authigenous minerals under the condition of anoxic-sulfurized bottom water.The EF values of P and Ba that serve as indicators of productivity are less than 1,suggesting a low to normal ancient productivity condition and reflecting that the ore-forming elements are not the products of biological enrichment under high productivity condition.The enrichment of As,Sb and Ag,locally positive Eu anomalies,as well as the existence of altered andesite and hydrothermal sediments in the reginal Ridang Formation suggest that seafloor hydrothermal activity is likely responsible for the enrichment of ore-forming elements in the Ridang Formation of the Zhaxikang ore-concentrated district.
出处
《矿物岩石地球化学通报》
CAS
CSCD
北大核心
2014年第5期598-608,共11页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
西藏矿产资源潜力评价项目(1212010813025
1212010881631
1212011121023)
关键词
海底热液活动
元素富集
日当组
扎西康Sb-Pb-Zn-Ag多金属矿集区
藏南
seafloor hydrothermal activity
element enrichment
Ridang Formation
Zhaxikang Sb-Pb-Zn-Ag polymetallic ore-concentrated district
South Tibet
