ABSTRACT: Ocean Lithogenetic Barriers and Metallogenesis
Alexander A. Ainemer
Ocean lithospheric barriers are boundaries on either side of which there are different environments of lithogenesis. The variety of barriers makes an integral system forming a carbonate oceanic infrastructure (carbonate boundaries). The important functions of barriers for ore-forming processes are mobilization and concentration of elements. According to this, all lithogenetic barriers are subdivided into mobilizing and concentrating barriers. The former, which enhance the extraction of elements from seawater, include the photosynthesis layer, the river/ocean barrier, the jump layer, the oxygen minimum layer, the critical depth of carbonate accumulation, and the hydrosulfuric water interface, etc. Boundaries that promote the concentration of elements may include the sedime t/bottom water barrier, upwelling, water/basalt barrier, sediment/interstitial water barrier, brine seawater barrier, etc.
This classification of barriers is tentative but valid, for it focuses on critical points of chemical transformations. On entering the oceans from different sources, mobile transitional metals that form most ore-producing elements in nodules, metalliferous sediments, and sulfides are dispersed by passage through mobilization barriers. The matrix of these metals is hydrated and is transformed to ore matter at concentration barriers. One of the main indications of concentration barriers, including interstitial water/sediments and bottom water/basalt, is an effective ratio of contacting solid and liquid phases that control initial and final conditions of both nodule and hydrothermal ore formation. Because of the changes in the redox potential and pH of environments, the sorption on the s lid phases of hydrogenous forms from solutions or leaching of elements from rocks and transformation to solution will take place only at certain rock/water or sediment/water ratios.
That means that sediments with a specific surface area providing an optimal phase ratio are required for nodule formation. It might be for this reason that nodule formation is most effective in siliceous sediments of the radiolarian belt.
At the water/basalt barrier, the optimal phase ratio for hydrothermal ore formation is achieved at a certain flow speed of ocean water circulation through rocks and intimately related to anomalous permeability of the ocean floor and to its higher heat exchange within local structures.
The important properties at the contact of different phases at concentration barriers are sedimentary porosity and permeability of basalt layer rocks.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990