The evolution of bauxite accumulation in the Phanerozoic

Abstract

Introduction: Bauxites are the main raw material for aluminium production. They are associated with weathering crust formations (WCF) and are represented by laterites, colluvial, deluvial-proluvial, karst, alluvial, and lacustrine-marshy formations. Hundreds of publications by many authors have been dedicated to various aspects of bauxite geology, including those on the evolution of bauxite accumulation. These works distinguishing different periods of bauxite accumulation followed the actualistic approach (―the present is the key to the past‖). However, the recognition of evolution requires considering the features of each of the periods in the context of changing tectonic regimes and climates, as well as the influence of organic matter on the weathering. These aspects are discussed in the article. Methodology and scope of work: The main research methods included the comparative-lithological and historical-geological methods. A lot of attention was paid to interruptions in sedimentation during which lateritic WCs could be formed. These periods correspond to the periods of bauxite formation. It was necessary to identify the features of each of the periods in order to establish the evolution of bauxite accumulation in the Phanerozoic. This article is based on the data presented in a three-volume collection ―Historical Minerageny‖ [1] and the monograph [2]. Meanwhile, the factual base of the world minerageny is being rapidly updated. Therefore, whenever possible, we used materials from various sources as of 2021, including data on numerous deposits of bauxite-bearing WCF in the world. Results and discussion: The first Phanerozoic bauxites appeared in the Early Cambrian in isolated areas of fold belts during their peneplanation. In the Eifelian, payable deposits of high quality were formed in the Northern Urals. During the Frasnian, bauxite accumulation expanded into the territory of the Middle Timan. The number of known Devonian deposits does not exceed two dozen and their total reserves are about a billion tonnes. In the Early Carboniferous, bauxite accumulation shifted to the Precambrian platforms of the Northern hemisphere and within them to the peripheral parts of coal-bearing basins. It continued in the Middle Carboniferous on the Chinese and North American platforms, whereas on the territory of Korea it lasted till the Early Permian. Bauxites formed in the lateritic, diagenetic, and epigenetic stages. During the latter, it happened when bauxites were overlapped by coal-bearing deposits. Organics took an active part in weathering which resulted in the formation of bacterial biomorphoses. The number of deposits sharply increased (hundreds) and their total reserves increased to 4 billion tonnes. Deposits of Mesozoic bauxites tend to be found in fold belts, and within them in the Epihercynian and Epicimmerian young platforms of the Northern hemisphere. The karst type of bauxites predominates. They have a gibbsite-boehmite composition in platform varieties and a diaspore-boehmite composition in areas subjected to folding. The Precambrian platforms were dominated by low wet landscapes with a warm humid climate and kaolin WCs. There are more than 1,000 deposits of Mesozoic bauxites, however, most of them are small, although the quality of the raw material is high. The total alumina reserves of the Mesozoic bauxites (3.3 billion tonnes) are somewhat less than those of the Paleozoic bauxites but their deposits are more numerous. Bauxite accumulation in the Cenozoic was on a grandiose scale. This was due to the expansion of the areas of levelled land with a tropical climate, a relatively high stand of the continents, their fragmentation, and the increase in coastal areas with a large amount of precipitation, and an abundance of organic matter. All this led to the formation of powerful lateritic weathering crusts with many large and super-large bauxite deposits. A significant share in the total reserves falls on the deposits of island arcs, however, the main deposits are concentrated on the continents of the former Gondwana, especially in West Africa and in the north-east of South America. In these areas lateritic, lateritic-sedimentary, and karst types of WCs of gibbsitic and boehmite-gibbsitic composition were formed. Conclusion: In general, during the Phanerozoic, the evolution of bauxite accumulation was of pulsating directional character expressed in an uneven increase in the area and reserves of this type of raw material with time.