The role of dense brines in the formation of vent-distal sedimentary-exhalative (SEDEX) lead–zinc deposits: field and laboratory evidence
The role of dense brines in the formation of vent-distal sedimentary-exhalative (SEDEX) lead–zinc deposits: field and laboratory evidence
复制标题
DOI：
10.1007/s00126-001-0216-9
复制
发表时间：
2002-03
影响因子：
4.8
通讯作者：
D. Sangster
中科院分区：
文献类型：
--
作者：
D. Sangster
世界上大多数沉积物喷出（SEDEX）铅锌矿床位于喷口远端。它们的下方没有不协调的蚀变带或网状喷口复合体，这些蚀变带或网状喷口复合体可以指示矿石流体到达海底的路径。由于缺乏喷口复合体，加上硫化物矿物取代了主岩矿物组合，一些研究人员认为，尽管这些矿床具有良好的层状性质，但矿化是由矿石流体沿着渗透性地层在海底横向迁移形成的。然而，在简单的实验室实验的支持下，现场观察提出了一种表征喷口远端 SEDEX 沉积物成因的替代过程。冷盐水（例如，约 120 °C 和 > 15 wt% 氯化钠当量）比海水密度大，在排入大海后，会以抱底流体的形式从排放口流出，类似于浊流的行为。它们的高密度和高速度阻止它们与上覆海水混合，从而阻止矿液的显着冷却和稀释。当在海底凹陷处静止时，添加 H2S 和/或稀释矿液以降低盐度，最终导致出口远端 SEDEX 沉积物沉淀。此外，致密的成矿流体可以通过置换密度较低的孔隙水而沉入盐水池下方的可渗透沉积物中。因此，矿石流体能够有效地覆盖和/或替换固结沉积物堆中预先存在的矿物。
A majority of the world's sediment-hosted exhalative (SEDEX) lead–zinc deposits are vent-distal. They are not underlain by a discordant alteration zone or stockwork vent complex that would indicate the path by which ore fluids reached the seafloor. The absence of a vent complex, together with sulfide mineral replacement of host rock mineral assemblages has led several investigators to suggest that, in spite of the well-layered nature of these deposits, mineralization was formed by sub-seafloor lateral migration of ore fluids along permeable strata. Field observations, supported by simple laboratory experiments, however, suggest an alternative process for characterizing the genesis of vent-distal SEDEX deposits. Cool, saline brines (e.g., ~120 °C and >15 wt% NaCl equiv.) are denser than seawater and, upon discharging into the sea, would flow away from the discharge vent as bottom-hugging fluids, similar to the behavior of turbidity currents. Their high densities and velocities prevent them from mixing with overlying seawater, thereby precluding significant cooling and dilution of the ore fluid. Upon coming to rest in a seafloor depression, the addition of H2S and/or dilution of the ore fluids to lower salinities result in the eventual precipitation of a vent-distal SEDEX deposit. Furthermore, the dense ore-forming fluid can sink into permeable sediments beneath the brine pool by displacing less dense pore water. The ore fluids are thus capable of effectively overprinting and/or replacing pre-existing minerals in the consolidating sediment pile.