Geology topics

Ian Ridley

Publications and source records attributed to Ian Ridley.

3 recordsLinked to original sources

USGS2017

Feasibility study for the quantitative assessment of mineral resources in asteroids

This study was undertaken to determine if the U.S. Geological Survey’s process for conducting mineral resource assessments on Earth can be applied to asteroids. Successful completion of the assessment, using water and iron resources to test the workflow, has resulted in identification of the minimal adjustments required to conduct full resource assessments beyond Earth. We also identify the types of future studies that would greatly reduce uncertainties in an actual future assessment. Whereas this is a feasibility study and does not include a complete and robust analysis of uncertainty, it is clear that the water and metal resources in near-Earth asteroids are sufficient to support humanity should it become a fully space-faring species.

Open-File Report↗

USGS2011

Trace and minor element variations and sulfur isotopes in crystalline and colloform ZnS: Incorporation mechanisms and implications for their genesis

Various models have been proposed to explain the formation mechanism of colloform sphalerite, but the origin is still under debate. In order to decipher influences on trace element incorporation and sulfur isotope composition, crystalline and colloform sphalerite from the carbonate-hosted Mississippi-Valley Type (MVT) deposit near Wiesloch, SW Germany, were investigated and compared to sphalerite samples from 52 hydrothermal vein-type deposits in the Schwarzwald ore district, SW Germany to study the influence of different host rocks, formation mechanisms and fluid origin on trace element incorporation. Trace and minor element incorporation in sphalerite shows some correlation to their host rock and/or origin of fluid, gangue, paragenetic minerals and precipitation mechanisms (e.g., diagenetic processes, fluid cooling or fluid mixing). Furthermore, crystalline sphalerite is generally enriched in elements like Cd, Cu, Sb and Ag compared to colloform sphalerite that mainly incorporates elements like As, Pb and Tl. In addition, sulfur isotopes are characterized by positive values for crystalline and strongly negative values for colloform sphalerite. The combination of trace element contents, typical minerals associated with colloform sphalerite from Wiesloch, sulfur isotopes and thermodynamic considerations helped to evaluate the involvement of sulfate-reducing bacteria in water-filled karst cavities. Sulfate-reducing bacteria cause a sulfide-rich environment that leads in case of a metal-rich fluid supply to a sudden oversaturation of the fluid with respect to galena, sphalerite and pyrite. This, however, exactly coincides with the observed crystallization sequence of samples involving colloform sphalerite from the Wiesloch MVT deposit.

Wiesloch↗

USGS2009

A New Occurrence Model for National Assessment of Undiscovered Volcanogenic Massive Sulfide Deposits

Volcanogenic massive sulfide (VMS) deposits are very significant current and historical resources of Cu-Pb-Zn-Au-Ag, are active exploration targets in several areas of the United States and potentially have significant environmental effects. This new USGS VMS deposit model provides a comprehensive review of deposit occurrence and ore genesis, and fully integrates recent advances in the understanding of active seafloor VMS-forming environments, and integrates consideration of geoenvironmental consequences of mining VMS deposits. Because VMS deposits exhibit a broad range of geological and geochemical characteristics, a suitable classification system is required to incorporate these variations into the mineral deposit model. We classify VMS deposits based on compositional variations in volcanic and sedimentary host rocks. The advantage of the classification method is that it provides a closer linkage between tectonic setting and lithostratigraphic assemblages, and an increased predictive capability during field-based studies.

Open-File Report↗