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April 2017 - Volume 13, Number 2
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Sulfides
Ekaterina S. Kiseeva and Marie Edmonds - Guest Editors
Overview Advertisers Next Issue 2017 Topics
Despite the bulk silicate Earth only containing 250 parts per million of sulfur, sulfide minerals and liquids have a powerful impact on the behavior and fractionation of a wide range of elements in the Earth's crust and underlying mantle. This issue focuses on the broad topics of magmatic and volcanogenic sulfide deposits, the behavior of sulfides during mantle melting and volcanism, and the mineralogy of sulfides and sedimentary sulfides and their role in the early development of the biosphere.
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Gemological Institute of America
International Mineralogical Association
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Volume 13, Number 3 (June) • Rock Coatings
GUEST EDITORS: Michael Schindler and Ronald Dorn
Chemical and/or biological processes can produce coatings on the surfaces of rocks and minerals. These coatings form at the interface between the lithosphere, biosphere, and atmosphere in a diverse range of environments, such as common soils, deserts, volcanic weathering environments, smelter-impacted areas, Antarctica and glaciated environments, and have even been found on Mars. Coatings on rocks and minerals can range from the nano- to the centimeter scale and are information packed on different scales. They provide fascinating records of the biological, geochemical, and environmental conditions present during coating development. Through the study of these coatings, scientists are uncovering important details about climate and environmental changes, temperature variations in the world's oceans, and so much more. This issue will introduce the reader to how these coatings form, how they react with their environment, and a few of the fascinating records that can be deciphered from them.
How Volcanoes Work (February 2017)
Sulfides (April 2017)
Coatings on Rocks and Minerals: Records of Climate Change, Atmospheric Pollution, and Organic Life (June 2017)
Mineral Resources and Sustainable Development (August 2017)
Boron: Light and Lively (October 2017)
Layered Intrusions: Natural Laboratories for Magma Chamber Processes (December 2017)
Mineralogy of Sulfides
By David J. Vaughan and Claire L. Corkhill
Metal sulfides are the most important group of ore minerals. Here, we review what is known about their compositions, crystal structures, phase relations and parageneses. Much less is known about their surface chemistry, their biogeochemistry, or the formation and behaviour of 'nanoparticle' sulfides, whether formed abiotically or biogenically.
Magmatic Sulfide Ore Deposits
By Stephen J. Barnes, David A. Holwell and Margaux Le Vaillant
Magmatic sulfide ore deposits are products of natural smelting: concentration of immiscible sulfide liquid ('matte'), enriched in chalcophile elements, derived from silicate magmas ('slags'). Sulfide ore deposits occupy a spectrum from accumulated pools of matte within small igneous intrusions or lava flows, mined primarily for Ni and Cu, to stratiform layers of weakly disseminated sulfides within large mafic–ultramafic intrusions, mined for platinum-group elements. One of the world's most valuable deposits, the Platreef in the Bushveld Complex (South Africa) has aspects of both of these end members. Natural matte compositions vary widely between and within deposits, and these compositions are controlled largely by the relative volumes of matte and slag that interact with one another.
Sulfide Minerals in Hydrothermal Deposits
By Lluís Fontboté, Kalin Kouzmanov, Massimo Chiaradia and Gleb S. Pokrovski
Hydrothermal ore deposits are large geochemical anomalies of sulfur and metals in the Earth's crust that have formed at <1 to ~8 km depth. Sulfide minerals in hydrothermal deposits are the primary economic source of metals used by society, which occur as major, minor and trace elements. Sulfides also play a key role during magmatic crystallization in concentrating metals that subsequently may (or may not) be supplied to hydrothermal fluids. Precipitation of sulfides that themselves may have little economic value, like pyrite, may trigger the deposition of more valuable metals (e.g. Au) by destabilizing the metal-bearing sulfur complexes. We review why, where and how sulfide minerals in hydrothermal systems precipitate.
Volcanic Sulfides and Outgassing
By Marie Edmonds and Tamsin A. Mather
Sulfides are a major potential repository for magmatic metals and sulfur. In relatively reduced magmas, there may be a dynamic interplay between sulfide liquids and magma degassing as magmas ascend/erupt. Sulfide-bubble aggregates may segregate to shallow levels. Exsolved fluids may oxidize sulfides to produce SO2 gas and metals, which can vent to the atmosphere with chalcophile metal ratios reflecting those in their parent sulfide liquids. Sulfide breakdown and/or sequestration timing and balance define the role of sulfides in both ore formation and the environmental impacts of volcanic eruptions, including during the evolution of large igneous provinces, which are key periods of heightened volcanism during Earth history.
Chalcophile Elements and Sulfides in the Upper Mantle
By Ekaterina (Kate) S. Kiseeva, Raul O.C. Fonseca and Duane J. Smythe
Sulfides are among the most important petrogenetic agents in magmatic systems. They are ubiquitous in most upper-mantle rock types, common as inclusions in diamonds and they host significant amounts of geochemically and economically important chalcophile ('sulfur-loving') elements, such as Cu, Ni, Pb, In, Au and the platinum-group elements. Despite their low abundance (<< 1% of the bulk rock), residual sulfides have a disproportionate control over the chalcophile element budget in upper mantle lithologies, as well as that of melts derived from the Earth's mantle.
Sedimentary Sulfides
By David Rickard, Marc Mussman and Jeffrey A. Steadman
Sedimentary sulfides constitute over 95% of the sulfide on the surface of the planet, and their formation, preservation and destruction largely determines the surface environment. The sulfide in sediments is mainly derived from the products of sulfate-reducing bacteria, which are currently responsible for oxidizing over half the organic matter flux reaching sediments. Pyrite is the mineral overwhelmingly produced. The geochemistry of pyrite, both in terms of its isotopic composition and its trace-element loading, has varied dramatically over geologic time. As such, it is a major source of our current understanding about the nature of the early Earth and of the Earth's subsequent geochemical and biological evolution.
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