Mineralogy and Geochemistry of Manganese Nodules From the Southern Ocean

摘要

X-ray diffraction studies on 228 nodules from 91 bottom trawls and 58 piston cores from the Southern Ocean collected during USNS ELTANIN cruises show that todorokite is the principal manganese oxide phase present. A correlation exists between manganese content of the gross sample and the relative amount of todorokite as expressed by the ratio of peak areas 3.34 Angstrom A (quartz) plus 3.2 Angstrom A (plagioclase- phillipsite) vs. 9.7 Angstrom A (todorokite). The areal distribution of values for this ratio roughly corresponds to the rate of delivery of detrital quartz and feldspar to a particular area, the relative proportion of todorokite being lowest near the Antarctic continent, especially in the Drake Passage and Scotia Sea. Throughout the Southern Ocean, ferromanganese accumulations display a complex mineralogy. Birnessite and MnO2 are manganese phases of secondary importance. Minor amounts of crystalline gaothite and/or maghemite were detected in many of the samples, but much of the iron present is evidently contained in an amorphous hydroxide. Authigenic and detrital silicates are contained in the ferromanganese accumulations. Quartz, plagioclase, montmorillonite, and phillipsite are almost invariably present, while clinoptilolite and amphibole occur less frequently. Amphibole is more abundant in nodules from the Drake Passage and Scotia Sea. Examinatjon of nodules contained within sediment cores shows that the mineralogy and chemical composition of the concretions have remained relatively constant at any one location throughout much of the Brunhes paleomagnetic epoch. The distribution of the concretions in general has also remained unchanged.