The early stages of ferromanganese ore genesis on the guyots of the Magellan Seamounts (The Pacific Ocean)

Abstract

Fe-Mn crusts play an important role in marine mineral deposit research because of their widespread occurrence and high concentrations of valuable and rare metals. Most Fe-Mn crust deposits occur on the tens of thousands of seamounts found in the ocean. Data on the structure, texture, composition, age, and deposit characteristics will help define which factors are key for the creation of mineral accumulation and which combination of factors leads to the formation of potentially economic concentrations of metals. In this paper, we address the structure and characteristics of the oldest Fe-Mn crust stratigraphic sections (Late Cretaceous and Paleocene) collected from the Magellan seamounts. A complete section of the crusts on the Magellan Seamounts includes four layers, each 2—4 cm thickness: the Late Paleocene (?) Early Eocene layer I 1, the Mid Late Eocene layer I—2, the Miocene layer II and the Quaternary layer III. In some cases, the main CMC section is underlain by relict layers. The chemical and mineral composition of the layers was determined both by X-ray diffraction and precision methods; concentrations of the main ore components and phosphorus were determined by the methods of classical chemistry. The age of 12 samples was determined, the mineral composition of four, the chemical composition of 22 samples. The results of the relict layers analysis allow to distinguish two groups of samples among them. Among the relict layers, two age ranges are established — the second half of Late Cretaceous (R1) and the first half of Paleocene (R2). High concentrations of barium, lithium, gallium, and zinc suggest that hydrothermal sources could be the source of the material. But not through direct delivery, but via the phase of transfer of sea bottom water. Thus, the analysis of lithological and geochemical parameters and fossil fauna of foraminifera in the relict layers of the Magellan Seamounts ore section indicates two stages of their formation: Late Campan Maastricht and Early Middle Paleocene. The discreteness of the formation of relict layers in time once again proves that the sharply changing environmental conditions controlled the growth of the CMC ore section.