摘要
钼在硅酸盐地球中的丰度很低,作为中度不相容元素,简单的岩浆形成、演化过程很难使之从地壳丰度直接富集到工业品位。我们研究结果显示钼的成矿主要通过两阶段富集过程来实现:一是与风化、沉积有关的表生过程;二是与板块俯冲或深埋熔融有关的岩浆过程。钼是变价元素,在寒武纪大气氧再次升高以后,钼在地表化学风化过程中容易被氧化为水溶性的Mo O42-,进入地表径流和海洋湖泊中,并且在还原条件下进入富含有机质的黑色页岩等沉积物(岩)中。富钼沉积物(岩)在随板块俯冲到地幔或深埋等条件下可以因升温变质,进而发生部分熔融,形成富钼的原始岩浆,在俯冲条件下往往形成斑岩铜(金)钼矿床,氧逸度低于斑岩铜矿,而斑岩钼矿的氧逸度更低。具有高化学风化速率、大的流域面积的封闭、半封闭型水域和河口地区是表生过程中钼富集的最佳区域,是大型钼矿形成的基础。
Molybdenum is a rare element with very low abundance in the silicate Earth. It is a moderately incompatible element. Therefore, Mo cannot be enriched to minable grade through simple magmatism processes. Our studies show that one of the most important ways that enriches Mo is oxidation and reduction during chemical weathering. Molybdenum can be easily oxidized to form water solvable MoO4- in surface environment, especially after the second major elevation of atmospheric oxygen at ~ 550Myr ago, transported to oceans and lakes, and then retained by anoxic sediments, in the form of thio molybdates. Subsequent partial melting of metamorphosed Mo enriched sediments further enriches Mo, which may form Mo-rich magmas. Porphyry-Cu-Mo deposits in the American continents in the East Pacific is accompanied by slab melting. Direct partial melting of high grade metamorphosed Mo-rich sediments may form pure Mo porphyry with slightly lower oxygen fugacities. High chemical weathering rates, large catchment areas and closed or semi-closed water bodies are favorable places for Mo enrichment, which may form large Mo ore fields through later events.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第7期1807-1817,共11页
Acta Petrologica Sinica
基金
科技部973项目(2012CB416703)
国家自然科学基金项目(41090374
41121002)联合资助
关键词
钼
钼矿
化学风化
富钼沉积物
氧逸度
Molybdenum
Mo ore
Chemical weathering
Mo-rich sediments
Oxygen fugaeity
