Mechanism and modes of microbial minerogenesis of polymetallic nodules on the ocean floor

This paper presents a quantitative analysis of the relations of the occurre nce of polymetallic nodules with the geochemical actions of microbes in the seawater, pore water and sediments at the bottom of the eastern Pacific Oc ean basin. Emphasis is laid on the relations of the activity intensity and biochemical transformation rate of aerobic bacteria (iron bacteria, Thiobac illus thioparus, halobacteria and manganese-oxidizing bacteria) and anaerob ic bacteria (sulphate-reducing bacteria, denitrifying bacteria, Thiobacillu s denitrificans) with mineralization. The experimental research on the migr ation and accumulation of ore-forming elements caused by microbial and chem ical actions shows that the microbes have changed the conditions of oxidati on and reduction in the system, and their effect on the element precipitati on is much stronger than the chemical actions and accelerates the enrichmen t of Fe and Mn. It demonstrates that the microbes can change the environmen t to promote the accumulation of ore-forming elements, thus leading to indi rect mineralization. It is first found under the scanning electron microscope (SEM) and transmis sion electron microscope (TEM) that there are fossil microbes of various si zes and forms in the shells of polymetallic nodules, and even ultra microfo ssil bacteria at the cores. On the walls of some mineralized microbes there are sheaths of Fe and Mn oxides. After the death of the microbes, their bo dies are accumulated on the interface of seawater-sediments and form polyme tallic nodules. Microstructures of polymetallic nodules formed by microbes are also discussed, and two modes of microbial minerogenesis of polymetalli c nodules, both direct and indirect, are suggested in the paper.