沉积盆地成藏(矿)系统
Sedimentary basin reservoir-forming/mineralization system
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摘要: 提要:沉积盆地集有机和无机、金属与非金属矿产于一盆,构成了相对独立的矿产赋存单元和成藏(矿)大环境;称之为沉积盆地成藏(矿)系统。盆地成矿系统一般处于低温、低压环境和开放体系中;成矿流体、生物-有机质(流体)在其中起着极为重要的作用,且常受温度变化的明显影响;成矿作用一般与岩浆活动无直接成因联系。形成沉积矿产的成矿物质,初始赋存大多呈分散状;从其初始聚集到成矿作用发生和矿藏形成,所处环境发生了显著的变化;一般都经历了原始成矿物质聚集→转化成矿→富集成藏及改造定位3个阶段。成矿物质运移的动力主要来自压实作用和异常压力、构造作用、渗流携带作用、分子扩散、挥发作用和浮力等;运移的途径主要为孔隙、构造作用形成的断裂和非构造产生的微裂隙及不整合面等。矿源岩与储集层的关系多样,可有自生自储、新生古储、古生新储等组合。沉积矿产的聚集成矿场所,一般为由渗透性差的泥岩、膏盐层等封盖的圈闭构造(背斜、断层、岩性等),或处于地球化学环境、构造特征、岩性-岩相等突变的边界-转化带。原始成矿物质聚集与矿藏形成—定位之间间隔的时间一般可较长,时差可达几亿年。沉积矿藏形成通常具动态成矿过程,一般成矿期次多和后期改造明显:既可使已形成的矿藏多期叠加进一步富集,也可使其遭受改造而发生改变或形成次生矿藏。以上特点决定了沉积矿藏的形成,特别是其定位时代相对较晚。同盆共存的各类沉积矿产资源丰富、特征多样;其成矿作用和分布组合关系复杂,具有共存多样性、共荣亲和性和排他性等特征。以上特征在不同类型沉积矿产似不尽相同,各自还有其个性特点。 根据地球构造动力学环境的不同,可将盆地成矿系统分为裂陷伸展、聚敛、转换、克拉通等类型;各类环境中矿产的成矿特点、类型和分布组合等有别。受地史上地球表层水圈、大气圈和生物圈演化及其不可逆性的明显影响,盆地外生沉积矿藏的形成及特征一般具有明显的阶段性和随时间发展,矿种更为复杂多样等特征。盆地系统沉积矿产的富集成矿同时也具有明显的空间分区性及偏富极的特点。沉积盆地成藏(矿)系统有其自身的成矿特点和成藏(矿)环境,应将其作为一种独立的成矿系统提出,以与造山带和地盾等成矿系统相并列和区别。对其专门研究,必将揭示各种沉积矿藏同盆共存的内在联系、成藏模式和分布规律,丰富和发展已有成矿理论体系,为盆地内多种矿产兼顾,科学高效勘探和综合预测奠定理论基础。Abstract: 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.