Sedimentary basin reservoir-forming/mineralization system

Abstract：The sedimentary basin incorporates organic and inorganic， metallic and non-metallic mineral deposits， forming a relatively independent mineral resource-hosting unit and an reservoir-forming （mineralization） macro-environment， which may be called the sedimentary basin reservoir-forming （mineralization） system. The system is generally located in a low-temperature， low-pressure environment and an open system， in which mineralizing fluids， organisms/organic matter （fluids） play a vital role and are significantly affected by temperature changes. Mineralization generally has no direct genetic relationship with magmatic activities.The initial occurrences of mineralizing materials that form sedimentary deposits are mostly scattered； from their initial accumulation through mineralization to mineral deposit formation， marked changes take place in their environment. They generally experience a process from primitive mineralizing material accumulation→mineralization→enrichment， mineral deposit formation， reworking and reposition. The driving force of migration of mineralizing materials mainly comes from compaction and abnormal pressure， tectonism， seepage flow， molecular diffusion， volatilization and buoyancy force. The main passageways of migration are pores， faults formed by tectonic processes and microfractures and unconformity produced by non-tectonic processes. The relationships between mineral source rocks and reservoirs are highly varied， including such associations as self-generating and self-accumulation， late generation and early accumulation， early generation and late accumulation. The sites where sedimentary minerals are deposited are generally traps （e.g. anticlinal， fault and lithologic traps） sealed by mudstones and evaporites with poor permeability or abrupt boundary transformation zones of geochemical environment， tectonic features and lithology-lithofacies. Generally， the time interval between primitive mineralizing material accumulation and mineral deposit formation-redeposition may be long， even up to several hundred million years. The formation of sedimentary mineral deposits usually progresses through a mineralization process， generally characterized by multiple mineralization phases and marked reworking in the late phase， which results not only in repeated superimposition and further enrichment of a mineral deposit but also in its reworking and modification or formation of a secondary mineral deposit. The above-mentioned characteristics determine that the sedimentary mineral deposit forms and especially is sited relatively late. The useful sedimentary minerals in a basin are rich， with diverse features. Their mineralization and distribution pattern have complex relations and show the diversity of coexistence， synthetic affinity and exclusivity. The above-mentioned characteristics vary somewhat in different types of sedimentary mineral deposit and each type of deposit has its own characteristics. According to different tectonic dynamic environments， the basin mineralization system may be divided into various types， such as the rift extension， convergence， transformation and cratonic types， and the mineral deposits in various environments differ in mineralization characteristics， types， distributions and combinations. Affected obviously by the evolution of the hydrosphere， atmosphere and biosphere on the earth's surface in the geological history and its reversibility， the formation of exogenous sedimentary mineral deposits of the basin is generally characterized by significant stages， development with time and more complex mineral types. The enrichment and deposit formation of sedimentary minerals in the basin system also show characteristics of obvious spatial regionalization and partial enrichment. Owing to its own mineralization characteristics and reservoir-forming/mineralization environments， the sedimentary basin reservoir-forming/mineralization system should be proposed as an independent mineralization system that stand side by side with and is distinguished from other mineralization systems such as orogenic and shield mineralization systems. The special study of it will certainly reveal the intrinsic relation between various types of sedimentary mineral deposit and their coexisting basin as well as their reservoir-forming patterns and distribution characteristics and enrich and develop the system of mineralization theories. Moreover， it lays a theoretical foundation for overall consideration of multiple mineral deposits in the basin， scientific and high-efficiency mineral exploration and comprehensive prediction.