A large number of heavy metal deposits associated with granitic plutons, such as Cu-Au- and Mo porphyry deposits and W-Sn vein-type deposits, were formed by hydrothermal fluids of magmatic, meteoric, or seawater origin. Important tasks for hydrothermal geochemists have been to unravel the details of important processes (e.g., chemical reactions between solid-melt, melt-melt, melt-fluid, solid-fluid, and fluid-gas) and environments (geological, geophysical and geochemical) responsible for the formation of various types of mineral deposits. A success in these tasks may result in the development of new and effective methods for the exploration and exploitation of natural resources. Dave’s Ph.D. thesis (1984) at Penn State was a study of W skarn deposits in King Island, Tasmania (one of the largest tungsten deposits in the world). It was the first modern-styled geochemical study, utilizing stable isotope geochemistry and thermodynamics among others, to unravel the geochemical processes and environments for the formation of W and Mo deposits. After moving to the ORNL, David carried out experimental studies to determine the oxygen isotope fractionations and solubilities of scheelite (CaWO4) and powerlite (CaMoO4) in hydrothermal solutions (Wesolowski et al., 1984, 1986). These works played key roles in the development of an important theory postulating that the redox state of granitic magmas, which is largely influenced by the source rock types of magmas (e.g., oxidized subducted oceanic crust; carbon-rich sedimentary rocks), is the key parameter that determines the associated metal deposits types. David, with Tsubasa Otake and me, conducted an experimental study aimed at understanding the mechanisms of transformation of iron oxides in nature. Until our work (Otake et al., 2007, 2008), essentially all geochemists had thought that the transformation of magnetite (Fe3O4) to hematite (Fe2O3), or hematite to magnetite, was a redox reaction, requiring an oxidant (e.g., O2) or a reductant (e.g., H2, C). However, we have shown that the transformations of the Fe oxides occur easily through leaching/addition of Fe2+ from/to Fe oxides by hydrothermal fluids (i.e., simple cation exchange between H+ and Fe2+) without involving a redox reaction. This recognition has far-reaching implications beyond ore deposit research, such as to understand the evolution of the atmospheric/oceanic chemistry through geologic time.

David Wesolowski's contributions to hydrothermal geochemistry

255th National Meeting (2018)

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