Comparative Study Of Cobalt-rich Crusts And Polymetallic Nodules In Seamounts Of Magellan Sea

Cobalt-rich crusts and polymetallic nodules are rich in metallic elements such as Co,Ni,Cu,Pb,Zn,rare earth elements(REE)and platinum group elements(PGE),which are of great economic value and development prospects,and are widely concerned at home and abroad.In this paper,using mineral phase microscopy,laser ablation,X-ray diffraction,X-ray fluorescence spectroscopy,plasma mass spectrometry and other technical means,the two plate-shaped crusts collected from the Magellan Sea Mountain and the 3 nodules in the nearby deep sea basin were collected.Testing and analysis of mineralogy,geochemistry,etc.were carried out,which accumulated necessary analysis data for discussing the origin of crusts and nodules in the study area and the ore-forming model,laying a foundation for follow-up work.Microscopically,it can be observed that there are three microstructure combinations in crusts and nodules:(1)relatively loose mottled and dendritic microstructure combinations;(2)Dense combination of dendritic and columnar microstructures.(3)Relatively dense combination of laminated,columnar and lamellar microstructures.Loose type ? denser type ? dense type structure.With the structural sequence of the loose type?the denser type?the dense type,the Mn phase element content tends to decrease while the Fe phase element content tends to increase.The phosphatization of the crust has a certain interference effect on the above characteristics.Seamount crusts are dominated by vernadite(?-Mn O),and also contain a small amount of sodium manganite and goethite and very few non-ferro-manganese minerals such as quartz sand.Due to the occurrence of phosphate events,there is carbon Fluorapatite(CFA)in the crust.Although the growth environment of sea basin nodules is very different from that of crusts,in terms of mineral composition,unless the iron-manganese phase mineral content is slightly higher,they are very close to the water-formed crusts in the same study area,mainly vernadite,with only a small amount of todorokite,this feature is very different from other deep-sea nodules in the Pacific Ocean.The main element composition of crusts and nodules is mainly Mn and Fe,and most other elements show a certain correlation with them.The source and enrichment mechanism of trace elements in crusts and nodules are roughly the same.The standardized distribution curve of rare earth elements in North American shale shows the same REY distribution pattern.Ce is positive and abnormal.LREE is more enriched than HREE.The crusts and nodules are in oxidized and suboxidized environments.The crusts in the Magellan Sea are typical water formations,while the nodules in the deep ocean basins are more complicated.The inner layer of the nodules has a high Mn/Fe value and is relatively enriched in Ni.Its characteristics are similar to the mixed type nodules between diagenetic and hydroformed in the eastern part of the Central Pacific CC zone;while the outer layer of the nodules has a lower Mn/Fe value.It is richer in Co,and its characteristics are more similar to the cobalt-rich crusts formed by water in the study area.It shows that there may be significant differences in the extraction and enrichment methods of nodules at different stages of their growth process.This understanding helps us to have a more comprehensive understanding of the formation mechanism and material sources of deep ocean basin nodules in addition to traditional diagenetic models.The mineralization of sea crusts can be divided into three mineralization stages:(1)the early stage with low growth rate;(2)the middle stage with high growth rate;(3)the late stage with moderate growth rate.The nodules are divided into two mineralization periods,(1)rapid mineralization and a forming period that is greatly affected by diagenesis;(2)a growth period with moderate mineralization rate and mainly hydrogenesis.