沉积体系域控矿机制讨论——以华南泥盆纪某些沉积层控矿床为例

THE CONTROLS OF THE DEPOSITIONAL SYSTEMS TRACTS ON ORE DEPOSITS: EXAMPLES FROM SOME OF THE DEVONIAN SEDIMENTARY AND STRATABOUND DEPOSITS IN SOUTHERN CHINA

摘要:

七十年代末期,由于地震地层学的扩展,层序地层学应运而生并已成为沉积地质学研究领域的前沿学科,也是全球沉积地质计划(GSGP)的重要内容之一和第十三届国际沉积学大会的中心议题之一,由此可见地质工作者对进行层序地层研究的热衷程度。七·五期间,在刘宝珺教授领导的《中国南方岩相古地理及沉积、层控矿产远景预测》项目中,运用层序地层学的理论和方法对中国南方震旦纪至二叠纪的沉积层序进行了研究,并建立了离散型被动大陆边缘、汇聚型挤压盆地和板内盆地中的沉积层序模式和海平面升降曲线。

Abstract:

The study is designed to examine the relationship between the depositional systems tracts and ore deposits with the aid of the concepts and methods of sequence stratigraphy. The Devonian strata in southern China may be divided into four depositional sequences, of which Sequences 1, 2 and 4 are controlled by relative sea-level changes, while Sequence 3 by a combination of relative sea-level changes and tectonic activity. In fact, the effective basin spaces are often controlled by the sea-level changes and tectonic activity which, in turn, control the characteristics and geometry of the sediments. depositional styles, sedimentary environments and geochemical field of the sea area. Therefore, some of the depositional systems tracts may be in itself the ore-bearing beds. For example, the Ningxiang-type iron deposits consist of the sand bodies of the transgressive systems tract, the coastal onlap sand bodies formed synchronously in response to the sea-level rises, whereas the low-velocity sedimentary manganese deposits are often associated with condensed sections. Since the condensed sections are in the oxygen-deficient conditions.they may serve as the infilled spaces of the ferruginous sulfides, as exemplified by the Chengbu pyrite deposit. The ore bodies of the Baiyunpu lead-zinc deposit and Xikuangshan antimony deposit are all hosted in the palaeokarst cavities of carbonate rocks. which belong to the highstand systems tract where subacrial corrosion by fresh water took place during the sea-level fall. The palaeokarst surface was then onlapped by micritic limestones formed during the sea-level rise.
It follows that some of the depositional systems tracts not only consist of the ore-bearing beds, but also provide the infilled spaces, favourable sedimentary environments and ore-forming material for mineralization.