Editorial for Special Issue “Geochemistry and Mineralogy of Hydrothermal Metallic Mineral Deposits”

Abstract

Deposits presents the results of diverse geochemical and mineralogical research from across the globe. It is aimed to demonstrate that geochemical and mineralogical variation, both within and among hydrothermal ore deposits can be applied to genetic models, to exploration and drilling programs, and more. The eight contributions reflect a wide range of deposits, as well as different types of geochemical and mineralogical research applied to them. While most of these studies are focused on gaining a better understanding of deposit genesis, the results have a far greater application, as highlighted below.Isotopic analyses of ore and gangue minerals have been applied to research on hydrothermal metallic mineral deposits for a little more than a century. Advances in analytical methods over the past few decades have lowered detection limits and allowed determination of ages and isotopic compositions that were previously not possible. Molnar et al. [1] use isotopic analyses of uraninite and molybdenite to assist in unraveling hydrothermal events related to Rompas gold-uranium mineralization in northern Finland. The mineralization is hosted by Paleoproterozoic rocks with a complex magmatic, metamorphic, and structural history, and the detailed isotopic analyses provide insight into the relation between mineralization and orogenic events [1]. This study also illustrates the importance of detailed field and mineralogical studies as the basis for isotopic analyses.The study of platinum-group elements (PGE) mineralization in the Great Dyke of Zimbabwe at the Unki mine, by Chalumba [2] shows how detailed mineralogical relations can separate distinct processes. The concentration of PGE, nickel, and base metals in ultramafic to mafic rocks has often been attributed to magmatic processes. Yet, in this study, mineralogical relations indicate that the magmatic ore has been overprinted by a secondary phase of hydrothermal alteration. These results demonstrate the importance of basic descriptive mineralogical data in distinguishing hydrothermal and magmatic processes.For a little more than half a century, the study of fluid inclusions in minerals have been a routine part of many studies of hydrothermal metallic mineral deposits. Kowalski and Kissin [3] have used this well-tested method to investigate the Archean Brookbank-Cherbourg gold deposit in northwestern Ontario, Canada. Hydrothermal gold deposits form over a wide range of deep Earth conditions, with mesothermal deposits hosted in more ductile shear zones and formed at higher temperature and pressure conditions, compared to epithermal deposits that are hosted by fissures and breccias (relatively brittle) and formed at generally lower temperature and pressure conditions. The fluid inclusion data at Brookbank-Cherbourg are consistent with field observations indicating a transitional character for the deposit with gold, hosted both in a shear zone and a fissure vein. This study provides further confirmation of the important role that fluid inclusion studies play in determining th...