Elements Covers

Thematic Articles

Formation and Occurrence of Ferromanganese Crusts: Earth’s Storehouse for Critical Metals

Marine ferromanganese oxide crusts (Fe–Mn crusts) are potentially important metal resources formed on the seafloor by precipitation of dissolved and colloidal components from ambient seawater onto rocky surfaces. The unique properties and slow growth rates of the crusts promote adsorption of numerous elements from seawater: some, such as Te and Co, reach concentrations rarely encountered elsewhere in nature. Consequently, Fe–Mn crusts are potential sources of metals used in technologies considered essential for the transition to a low-carbon economy. However, the precise distributions and metal concentrations of Fe–Mn crusts at regional and local scales are poorly constrained because of the diversity of geological, oceanographic and chemical processes involved in their formation.

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Modern Seafloor Hydrothermal Systems: New Perspectives on Ancient Ore-Forming Processes

Seafloor massive sulfides are deposits of metal-bearing minerals that form on and below the seabed as a result of heated seawater interacting with oceanic crust. These occurrences are more variable than previously thought, and this variability is not necessarily reflected in the analogous volcanogenic massive sulfide deposits that are preserved in the ancient rock record. The geological differences affect both the geochemistry and the size of seafloor massive sulfide deposits. Current knowledge of the distribution, tonnage, and grade of seafloor massive sulfides is inadequate to rigorously assess their global resource potential due to the limitations in exploration and assessment technologies and to our current understanding of their 3-D characteristics.

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Deep-Ocean Mineral Deposits: Metal Resources and Windows into Earth Processes

Deep-ocean mineral deposits could make a significant contribution to future raw material supply. Growing metal demand and geopolitics are focussing increasing attention on their resource potential and economic importance. However, accurate assessment of the total amounts of metal and its recoverability are very difficult. Deep-ocean mineral deposits also provide valuable windows through which to study the Earth, including the evolution of seawater and insights into the exchange of heat and chemicals between the crust and the oceans. Exploration for, and potential extraction of, deep-ocean mineral deposits poses many geological, technical, environmental and economic challenges, as well as regulatory and philosophical questions. Great uncertainty exists, and the development and stewardship of these deposits requires an incremental approach, encouraging transparency and scientific and civil societal input to balance the interests of all.

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Ore Deposits of the Central Andes

The Central Andes has one of the richest base metal endowments on Earth. In 2017, the Central Andes accounted for the mine production of around 39% of the world’s copper, 23% of its silver, 20% of its molybdenum, 14% of its zinc, and 12% of its tin as well as significant shares of other metals including gold and lead (USGS 2018). These metals are found in a variety of ore deposits of which by far the most important are those that occur as part of the “porphyry system” in the sense of Sillitoe (2010). However, important ore deposits of other mineralization styles also occur in the Central Andes. This info box presents characteristics of main and/or representative Mesozoic ore deposits that occur between latitudes 11°S and 30°S.

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Nitrate Deposits of the Atacama Desert: A Marker of Long-Term Hyperaridity

The nitrate deposits of the Atacama Desert are unique when one considers that in most surface environments nitrate is produced or consumed by biological processes and is easily washed away by rain. Nitrate deposits have puzzled geologists since Charles Darwin’s visit to the Atacama in 1835 and several hypotheses have been proposed to explain their origin. Here, we review our current understanding of the nitrate deposits in the Atacama Desert and show that nitrate’s primary origin is predominantly atmospheric. However, its massive accumulation and preservation specifically in Atacama is due to the serendipitous convergence of climatic, tectonic and hydrologic conditions that are unique to the Central Andes.

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Turning up the Heat: High-Flux Magmatism in the Central Andes

The Neogene history of the Central Andes records one of Earth’s most productive periods of high-flux silicic magmatism. Subduction of an aseismic ridge, the Juan Fernández Ridge (JFR), led to changes in mantle melt productivity that initiated a transcrustal magmatic system culminating in massive caldera- and ignimbrite-forming eruptions. This volcanism is time transgressive, tracking the southward passage of the JFR beneath the Central Andes. The volcanic field is underlain by a composite, arc-long mid- and upper-crustal granodiorite batholith that represents extensive processing of the continental crust by mantle-derived magmas. This batholith stabilized the upper crust and contributed to the extreme elevations despite a net crustal loss beneath the Puna region.

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Magmatism in the Central Andes

Active continental margins are shaped by subduction-related magmatism, and the Central Andes of South America are a prime example. The Central Andean orogen has evolved over the past 25 My via magmas ascending from the mantle and interacting with increasingly thickened continental crust. This process is reflected in the volumes and compositional variations of the magmas that erupt at the surface. These compositional variations can be traced in time and space, and, herein, we provide explanations for their cause and explore the nature of the Central Andes transcrustal magma systems that feed the iconic stratovolcanoes today.

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The Topographic Evolution of the Central Andes

Changes in topography on Earth, particularly the growth of major mountain belts like the Central Andes, have a fundamental impact on regional and global atmospheric circulation patterns. These patterns, in turn, affect processes such as precipitation, erosion, and sedimentation. Over the last two decades, various geochemical, geomorphologic, and geologic approaches have helped identify when, where, and how quickly topography has risen in the past. The current spatio-temporal picture of Central Andean growth is now providing insight into which deep-Earth processes have left their imprint on the shape of the Earth’s surface.

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The Central Andes: Elements of an Extreme Land

The Central Andes and the Atacama Desert represent a unique geological, climatic, and magmatic setting on our planet. It is the only place on Earth where subduction of an oceanic plate below an active continental margin has led to an extensive mountain chain and an orogenic plateau that is second in size only to the Tibetan Plateau, which resulted from continental collision. In this article, we introduce the history of the Central Andes and the evolution of its landscape. We also discuss links between tectonic forces, magmatism, and the extreme hyperarid climate of this land that, in turn, has led to rich deposits of precious ores and minerals.

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The Science of Terroir

Terroir involves the complex interplay of climate, soil, geology, and viticulture, all of which influence the character and quality of a wine from a given grape variety, rootstock, and viticultural practice. Contrary to the assertions of some wine writers, the minerals and character of the soil cannot be tasted in the wine. Rather, it is their effect on the grape ripening process that gives certain wines a “sense of place”. Most important is water availability, which is a function of climate (rainfall and humidity) and soil water-holding capacity. The soil structure reflects the geologic history of a region and may have evolved over millions of years as influenced by faulting, weathering, and bedrock mineralogy. Far-field effects such as glaciation and resultant sea-level change can affect landscapes that are thousands of kilometers apart.

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