The Metallogenic System Of Co-rich Manganese Crusts In Western Pacific

Abstract: Based on the theory of Metallogenic System, the study on the major elements, transition metal elements and rare earth elements was carried out on the Co-rich Mn crusts from western Pacific, including Magellan seamount cluster and Marcus-Wake seamount cluster, and the ore-forming background and ore-controlling factors were analyzed synthetically. Thus the structure and conception model for the Metallogenic System of Co-rich Mn crusts in western Pacific were subsequently constructed, which is deep consideration about formation processes and distribution pattern of Co-rich Mn crusts, and would provide a theoretical support for the exploration and exploitation of those crusts. Base on above studies, some conclusions were obtained as follows: (1) ore-forming background of Co-rich Mn crusts were mainly controlled by drifting of seamounts and variations of Oxygen Minimum Zone (OMZ), and it is confirmed that the seamounts in western pacific drifted mainly westward, and the water depth of summits of those seamounts are nearly constant since Neogene; (2) it is confirmed that the ore-forming epoch of Co-rich Mn crusts from western Pacific is Neogene ~ Quaternary, that those crusts are hydrogenetic, that phosphatization events occurred universally in specific geological times, that the substrate rocks, the types of crusts configuration do not influence the major elements composition of the crusts from the western Pacific ore-forming province, and that the composition of Co-rich Mn crusts in the Magellan seamount cluster do not exhibit any geographical zonation, which show the homogeneity in the Metallogenic System of Co-rich Mn Crusts in western Pacific; (3) three types of ore-controlling factors are identified through compilation of ore-controlling factors, which are geological, orbital, and oceanic factors; (4) on the basis of study on ore-forming processes, it is discovered that short-term fluctuations of the major elements composition of Co-rich Mn crusts with time were controlled by Milankovitch cycles, that is the highest-order periods of eccentricity of earth orbit; and that the long-term variation trends of major elements composition of Co-rich Mn crusts from western Pacific ore-forming province are rather consistent. Considering the background of ore-forming process and ore-controlling factors as well as the long-term variation trends of major elements, it is proposed that the ore-forming processes of Co-rich Mn crusts in the western Pacific ore-forming province can be divided into five stages; (5) it is identified that there were three types of anomalies, which have close relationship with Co-rich Mn crusts formation and are geological, oceanographic and climatic anomalies respectively.