Mechanisms Of Platinum Group Element Fractionation In Ultramafic Melts And Implications For The Exploration For Magmatic Nickel Sulphide Deposits

Platinum-group elements (PGE) are important as petrogenetic tracers, but owing to their low abundances and complex behaviour they are among the least understood elements in geochemistry. This study investigates the mechanisms of PGE fractionation in ultramafic systems (komatiites, komatiitic basalts, ferro-picrites) and focuses on the role of chromite. Samples from a range of occurrences have been analysed to assess potential controls on PGE behaviour, such as geochemical affinities (Munro-type and Karasjok-type), age (2.0 and 2.7 Ga), emplacement styles, metamorphic grade and nickel-sulphide mineralisation endowment and style. -- Data obtained by in-situ laser ablation ICP-MS analysis provide the first direct evidence that Ru can exist in solid solution in chromite with concentrations up to several hundred ppb. The data show that the behaviour of Ru is dominantly controlled by the sulphide-saturation state. In systems that did not equilibrate with a sulphide liquid, chromites have distinctly higher Ru concentrations than chromites from systems that interacted with a sulphur-source during crystallisation. Carius tube digestion isotope dilution ICP-MS analyses of chromite separates confirm the accuracy of the in-situ study and also show that Ir is weakly compatible in chromite. Anomalously high Pt and Pd concentrations in chromite separates reflect the presence of platinum-group minerals (PGM) and suggest that PGM are common accessory phases in komatiites. A study of the PGE-mineralogy shows that PGM in komatiites can be of magmatic and post-magmatic origin and that they often remain undetected due to grain sizes less than 5 urn. As a consequence, the presence of PGE minerals has to be taken into account when whole-rock PGE signatures are interpreted. -- The association of Ru-poor chromites with Ni mineralisation and Ru-rich chromites with barren systems provides a new tool for the exploration for nickel-sulphide deposits. This model applies to all magma types and is independent of the age, the geochemical affinity, and other sample characteristics.

This book is written by a leading authority on the subject of magmatic sulfide deposits. An overview of deposit types, accompanied by a summary of the resources of nickel, copper and platinum-group elements in the world’s principal known deposits, is followed by a summary of the relevant physical chemistry. The core of the book comprises a discussion about the geology and geochemistry of each of the deposit types in turn, accompanied by the implications of this data to the origin of the deposits in the light of our understanding of the chemical processes involved. A final chapter focuses on the use of the genetic concepts in exploration.

The book (Special Issue) presents impressive new results related to a wide spectrum of occurrences of platinum-group minerals (PGM) and natural compounds enriched in platinum-group elements (PGE), which are associated with various complexes and deposits, such as Uralian-Alaskan-type complexes, layered intrusions and placers. The geographical locations of the involved deposits and complexes include, on a truly international scale, different areas of the Urals, Western and Eastern Sayans and Gornaya Shoria in Siberia, Southern Central Asian Orogenic Belt in China, Northern Michigan, USA, South Africa and Zimbabwe, etc. Of particular interest is the first description of a new species of PGM, thalhammerite (approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association), which is a new species of palladium-silver sulfobismuthide discovered in the Noril’sk region of Russia. Additionally, comprehensive reviews, on compositional variations in Pt–Fe alloy minerals and processes of transformations of PGM in exogenic environments, are presented which will also attract attention from international readers.

Highly Siderophile and Strongly Chalcophile Elements in High Temperature Geochemistry and Cosmochemistry, Volume 81 This RiMG (Reviews in Mineralogy & Geochemistry) volume investigates the application of highly siderophile (HSE) and strongly chalcophile elements. This volume has its origin in a short course sponsored by the Mineralogical Society of America and the Geochemical Society held in San Diego, California on the 11th and 12th December 2015, ahead of the American Geophysical Union’s Fall Meeting, which featured a session with the same title. Topics in this volume include: analytical methods and data quality experimental constraints applied to understanding HSE partitioning nucleosynthetic variations of siderophile and chalcophile elements HSE in the Earth, Moon, Mars and asteroidal bodies HSE and chalcophile elements in both cratonic and non-cratonic mantle, encompassing both sub-continental and sub-oceanic lithosphere the importance of the HSE for studying volcanic and magmatic processes, and an appraisal of the importance of magmatic HSE ore formation in Earth’s crust. Highly siderophile and strongly chalcophile elements comprise Re, Os, Ir, Ru, Pt, Rh, Pd, Au, Te, Se and S and are defined by their strong partitioning into the metallic phase, but will also strongly partition into sulfide phases, in the absence of metal. The chemical properties of the HSE mean that they are excellent tracers of key processes in high temperature geochemistry and cosmochemistry, having applications in virtually all areas of earth science. A key aspect of the HSE is that three long-lived, geologically useful decay systems exist with the HSE as parent (107Pd-107Ag), or parent-daughter isotopes (187Re-187Os and 190Pt-186Os). The material in this book is accessible for graduate students, researchers, and professionals with interests in the geochemistry and cosmochemistry of these elements, geochronology, magmatic ore bodies and the petrogenesis of platinum-group minerals.

Platinum-Nickel-Chromium Deposits: Geology, Exploration, and Reserve Base is the first reference book to combine information on the discovery of numerous minerals within existing deposits. This book recognizes the close affinity and great natural coexistence of platinum, palladium, chromium, nickel, copper, gold, and silver hosted by unique stratigraphy (mafic-ultramafic intrusive of layered ingenious complex) in a diverse structural set up. The chapters are organized in a logical sequence of introductory physical and chemical properties, demand-supply scenario, price trend, substitution-recycling and uses of these metals, stratigraphy and host rocks, geochemistry, global distribution of existing deposits in six mega continents, genetic system, reserves-resources overview, common characteristic features aiding as exploration guides for new targets, hazards, and sustainable development. This reference book is a must for students, research scholars, teachers, and professional explorers in economic geology, geography, and allied subjects. Presents over 150 full color illustrations including maps, diagrams, and charts Illustrates the key concepts in a clear and informative manner Authored by one of the world’s leading geoscientists Provides unique coverage of high value mineral deposits through an approach accessible to industry professionals, academic researchers, and students alike

As the importance and dependence of specific mineral commodities increase, so does concern about their supply. The United States is currently 100 percent reliant on foreign sources for 20 mineral commodities and imports the majority of its supply of more than 50 mineral commodities. Mineral commodities that have important uses and face potential supply disruption are critical to American economic and national security. However, a mineral commodity's importance and the nature of its supply chain can change with time; a mineral commodity that may not have been considered critical 25 years ago may be critical today, and one considered critical today may not be so in the future. The U.S. Geological Survey has produced this volume to describe a select group of mineral commodities currently critical to our economy and security. For each mineral commodity covered, the authors provide a comprehensive look at (1) the commodity's use; (2) the geology and global distribution of the mineral deposit types that account for the present and possible future supply of the commodity; (3) the current status of production, reserves, and resources in the United States and globally; and (4) environmental considerations related to the commodity's production from different types of mineral deposits. The volume describes U.S. critical mineral resources in a global context, for no country can be self-sufficient for all its mineral commodity needs, and the United States will always rely on global mineral commodity supply chains. This volume provides the scientific understanding of critical mineral resources required for informed decisionmaking by those responsible for ensuring that the United States has a secure and sustainable supply of mineral commodities.