Isotope Geochemistry ebook is available to be downloaded here.
- Title: Isotope Geochemistry- The Origin and Formation of Manganese Rocks and Ores
- Author: Vladimir Kuleshov
- Publisher: Elsevier
- Pages: 437
Manganese is the 10th most abundant element in the Earth’s crust. Most of its industrial use is in steel making with a much lesser amount going into the production of batteries. It is very similar to iron in its chemical properties. Both are commonly found in +2 and +3 valences with high spin states for the 3d electrons and with similar ionic radii. Mn and Fe2+ ions have radii 0.83 and 0.78 Å, while the 3+ ions have 0.70 and 0.65 Å (Li, 2000, Table I-4). Accordingly, manganese is commonly found substituted in small amounts in iron minerals. Manganese, however, also has access to a higher valence state, +4, which gives rise to a plethora of complex manganese oxide minerals that do not have Fe counterparts.
By contrast, Mn sulfides are quite rare compared to their Fe cousins. The net result is a tendency, in sedimentary systems with a large redox gradient, to partition iron into the more reducing parts of the system as the sulfide, whereas manganese will move toward areas of higher oxidation potential and tends to precipitate when it encounters mildly oxidizing conditions.
It follows from the above that manganese has geochemical significance in its own right, both as an abundant constituent of the Earth’s crust and as a critical industrial metal. It has additional significance in two ways: first, its oxides are highly effective adsorbents for other metals (especially Cu, Pb, Zn plus Ba) so these minerals carry a record of the composition of fluids they have been exposed to. Second, its various redox states provide a useful window into the history of oxidation levels at the Earth’s surface.
Among the most effective ways to probe the mechanisms of action of manganese in Earth surface environments is to study the behavior of the stable isotopes of manganese minerals. Therefore, the appearance of a new book with many new details on this ebook of the manganese deposits in the former Soviet Union and elsewhere was very welcome when the Russian edition of this book came out in Dec. 2013 (Kuleshov, 2013). To bring this information to a wider audience, we present the translation of the original Russian text with some updates.
By way of introducing the subject, I present a few preliminary observations. An examination of the distribution of manganese among the various reservoirs that make up the Earth reveals much about how the element behaves in geochemical cycles. Table P1 compares manganese and iron in some common rock reservoirs and in some key rock types and types of natural waters. The geochemistry of manganese closely resembles that of iron, but iron has such a greater crustal abundance that it normally swamps out any manganese present. Therefore an understanding of manganese behavior, especially when it comes to the formation of ore deposits, entails an understanding of how manganese and iron differ.
Note the similarity of Mn/Fe ratios in all solid reservoirs. Therefore, ordinary sedimentary processes will not separate manganese from iron. Seawater has higher Mn/Fe ratios, and in the open ocean surface waters are somewhat enriched in Mn compared with deep waters. Note, however, the very strong enrichment of Black Sea deep water in Mn, which suggests an important role for anoxic basins in the genesis of Mn deposits. Manganese ores are far from uniformly distributed in time and space. The Early Proterozoic of South Africa saw the formation of the world’s largest endowment of manganese. It is followed in size by a much younger array of deposits ringing the present-day Black Sea that formed in the Oligocene.
Questions about the geochemistry of manganese, the regularities of the distribution of manganese deposits, and the composition of manganese ores and conditions of their formation have been treated in an extensive scientific literature, consisting of over 5000 titles. Among them are commonly known works by V.I. Vernadskii, A.E. Fersman, A.G. Betekhtin, N.S. Shatskii, N.M. Strakhov, and S. Roy. Substantial contributions to the explanation of the nature of manganese-ore deposits have been provided by the research of I.M. Varentsov, J.B. Maynard, K.F. Park, J. Ostwald, B. Bolton, F. Veber, N. Beukes, J. Gutzmer, G.S. Dzotsenidze, D.G. Sapozhnikov, E.A. Sokolova, L.E. Schterenberg, and
many other Russian and international researchers.
Despite the accumulation of a vast array of data on the geology of manganese deposits and particularly pertaining to the chemical composition of manganese rocks and ores, many questions of manganese ore-genesis remain only partially answered. This is the case, first and foremost, with genetic models of the formation of the principal industrial types of manganese ores that are contained in such giant deposits
and manganese-ore basins as the Kalahari (Republic of South Africa), groups of Oligocene deposits of the Paratethys (Ukraine, Georgia, Kazakhstan, and Bulgaria), the northern Urals (Russia), the Gulf of Carpentaria (Groote Eylandt, Arnhem Land, and elsewhere in Australia), and others.
The structure of any model of ore genesis, including manganese ores, is predicated upon the presence of a logically complete and factually justified conceptual basis. That is, the model should account for such important questions as the sources of ore and non-ore components, the conditions of formation (exogenous conditions: climate, paleogeography, type of paleo-water body, physico chemical conditions; endogenous conditions: temperature, pH, Eh, pressure), as well as the ore formation process’s evolution over time (in part for concrete deposits, in whole for the history of the establishment of the Earth’s lithosphere). Naturally, the conditions will vary for different industrial ore types.
To date the question also remains open as to the principal regularities of the evolution of the processes of accumulation of manganese in rocks of the lithosphere over the entire course of the Earth’s formation. The formation of manganese rocks and ores has occurred unevenly over the course of geological history; this has been recorded in epochs and periods of manganese accumulation and is contingent upon the predominance of a given mechanism (model) of manganese ore-genesis.
In the present work, by means of generalizing the data available from the literature and particularly factual material, an attempt has been made to briefly clarify certain particularities in the genetic aspect of the formation of the manganese deposits themselves as much as the principal regularities of manganese ore-genesis in the history of the geological development of rocks of the lithosphere.
The principal types of manganese ores of deposits under development are oxides and carbonates. The oxides present the greater practical interest; however, the principal reserves of manganese—with the exception of the braunite-lutite of the deposits of the Kalahari manganese-ore field (Republic of South Africa)—are contained mainly within carbonate rocks. Therefore, the study of carbonates is undoubtedly of great practical significance.