摘要
四川西北部地区,一些产于中—上三叠统浊积岩系中的层控金矿 床。近年在其人工重砂样中发现了为数可观的微细球粒。研究结果表 明,这种微细球粒为宇宙尘埃。在热液型金矿床中发现地外来源的宇宙 尘,在我国尚属首次。 微球粒呈钢灰色,金属光泽,粒径多在100μm以下。按其成分属富 铬的铁质宇宙尘系列。球粒的微结构构造复杂多样,即维氏台登构造显 示的十分清晰。 宇宙尘在金矿床中的含量变化,与矿化强度和热液蚀变强度呈正相 关关系。这种关系表明,在内生条件下,热水溶液对矿质的搬运,除化学形式外,机械形式搬运是不可忽视的。
Cosmic dust has been found in sea-floor sediments and strata of various ages,. even in migmatitic granite. However, in a hydrothermal gold deposit, its occurrence has, at least in China, never been reported.In recent years, the authors have unexpectedly discovered numerous steel-grey microspherolites in man-made heavy concentrate samples from several stratabound disseminated gold deposits located in Middle-Upper Triassic turbidite series in north western Sichuan. Microprobe analysis, X-ray energy spectroscopy, X-ray powder patterns, scanning electron microscopy and microstructural features of the surfaces show that the particles are cosmic dust. It is the first discovery in China.As far as the essential composition is concerned, the cosmic dust of gold deposits in northwestern Sichuan belongs to chromium-rich ferruginous series. The grain; size ranges between 25 and 185μm, being dominantly less than 100 μm. The mi-crotextures and microstructures are complex and diverse, being usually myrmekitic (lamellar), incrustified. scaly-air imprint, vesicular, welded, impact, crater and rhy-oring-corrugated in shape.The content of the particles (cosmic dust) in these gold deposits is generally in positive correlation with both the iridium content in the strata and the intensities of mineralization and hydrothermal alteration. The high abnormal content of Ir is important evidence for the extraterrestrial source of the particles. The fact that a geologic body with strong alteration and mineralization is rich in cosmic dust may raise a new concept: under the endogenic conditions, it is not only possible but also realistic for mineralized material to be transported in the mechanical form in addition to the generally accepted chemical one in hydrothermal solutions.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1995年第2期146-155,T001,共11页
Acta Geologica Sinica
基金
国家自然科学基金(编号 4880099)
关键词
金矿床
宇宙尘
川西北
三叠世
gold deposit, cosmic dust, northwestern Sichuan, Middle-Upper Triassic
