四川盆地西南部乐山地区砂岩型铼钼矿地质特征及超常富集成矿

Geological Characteristics of Sandstone-Type Rhenium-Molybdenum Deposits and Super-Enrichment Mineralization in the Leshan Area,Southwestern Sichuan Basin

铼(Re)是一种在地壳中的丰度极低的分散元素,却是国防和航空航天领域不可或缺的关键原材料。由于其丰度很低,其超常富集成矿作用机理及过程是备受关注的重要科学问题。四川盆地西南部乐山地区的犍为-沐川-马边一带,在侏罗系地层中分布有砂岩型铼钼矿床(点)。本文以该区犍为县古匡岩矿床(点)为研究对象,对中侏罗统沙溪庙组中的含矿地层、矿化特征等进行了详细的研究,并对与铼钼富集密切相关的沥青进行了扫描电子显微镜、能谱和有机碳同位素分析。结果表明,含矿砂岩为三角洲前缘分流河道沉积环境下的产物,而非相对低能、还原的分流间湾沉积环境,并不是表生条件下氧化-还原作用富集成矿。矿床中的沥青是由来自下伏三叠系须家河组古油藏发生热裂解形成的,铼钼元素超常富集成矿与古油藏有机质具有密切的空间和成因关系。该类型矿床为铼等稀散元素超常富集成矿机理研究提供了新的研究思路和对象。

Rhenium(Re)is a dispersed element with extremely low abundance in the crust,but it is a critical raw material in national defense and aerospace.Because of its scarcity,the mechanism and process of its super-enrichment are an important scientific issue.In the Jurassic strata of the Qianwei-Muchuan-Mabian region in southern Sichuan Basin,there are sandstone-type rhenium-molybdenum deposits(spots).Taking the Gukuangyan deposit(spot)in Qianwei County as an example,this work discussed the ore-bearing strata and mineralization features of the Middle Jurassic Shaximiao Formation,and conducted scanning electron microscope,energy spectrum and organic carbon isotope analysis of bitumen related to rhenium and molybdenum enrichment.The results show that the ore-bearing sandstone is not enriched and mineralized by redox process under supergene condition,but rather is a product of the delta front distributary channel sedimentary environment as opposed to the relatively low-energy and reduced interdistributary bay sedimentary environment.The bitumen in the deposit was formed by thermal cracking from the ancient oil reservoir of the underlying Triassic Xujiahe Formation.There is a close spatial and genetic relationship between the super-enrichment mineralization of rhenium and molybdenum and the organic matter of the ancient oil reservoir.For the study of the mechanism of super-enrichment mineralization,including the mineralization of rhenium and other rare elements,this type of deposit offers a new research idea and object.