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Browsing by Author "David, Mady K"

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    High technology metal signatures of the Vermilion - Big Fork greenstone belt, Minnesota
    (2017) David, Mady K
    Renewable energy resources increasingly rely on high technology metals (HTM) which include, but are not limited to, Ga, Ge, In, Nb/Ta, Se, or Te. These metals generally do not form their own minerals but tend to concentrate in sulfide ore in general, and sphalerite ([Zn,Fe]S), chalcopyrite (CuFeS2), galena (PbS), and stannite (Cu2FeSnS4) in particular. As the need for these metals will rise with the more widespread use of green technologies, the demand of HTM will begin to outpace the supply situation within the near future (e.g., Dennehy, 2015). In addition, there is insufficient information available about the processes that control how these metals accumulate in ore deposits. Previous research indicates that HTM tend to occur in elevated concentrations in only two deposit types: massive sulfide deposits and hydrothermal veins and skarns associated with granites (e.g., Damman and Kieft, 1990; Ishihara, 2006); the reasons for this are not well understood. Due to a general lack of data about the behavior of these metals under ore-forming conditions, our knowledge about how these metals become enriched, get transported, or accumulate is insufficient. Within northern Minnesota lies the Vermillion district, a granite-greenstone rock unit which holds volcanic massive sulfide (VMS) deposits. These deposits can contain significant concentrations of HTM and even though no sulfide deposit has been identified in the Vermillion district yet, a significant zinc anomaly has been discovered. As little HTM data are available for Northern Minnesota, the HTM potential of the district or the distribution of these metals in individual rock units and lakes is unclear. This research project is designed to gather available data on HTM (crustal/mantle abundances, ore deposit whole-rock and ore minerals concentrations), analyze samples from the Vermilion Zn anomaly and associated rocks, and establish our current knowledge about HTM in Minnesota and other prominent ore deposits with significant HTM concentrations. This initial assessment will form the basis of further research, which will incorporate additional data as well as data analysis.
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    MASTODONS (Mammut americanum) AND THE LATE-GLACIAL VEGETATION OF THE EASTERN USA
    (Geological Society of America, 2018-11) Drazan, Jacqueline L; Mooers, Howard D; Moen, Ron; Pastor, John; Larson, Phillip C; Swartz, Jennifer A; David, Mady K; Bopray, Croix K; Jaksa, Michael P; Messer, Blake S
    Numerous studies of tooth plaques and remains of gut contents of have confirmed that mastodon diet was composed of woody browse species, forbs, nuts, and fruits. However, fossil gut contents also suggest that mastodon diet included significant amounts of spruce, even though spruce is a low-quality, chemically-defended food. Most extant large mammals only browse on spruce when all other food sources are exhausted, and mastodon tusk growth increments indicate that mastodons were not food limited as they moved toward extinction (Fisher, 2009). Here we review the vegetation associated with mastodon habitat from the Great Lakes to the Gulf Coast, USA, over the period 18-10 ka cal BP using pollen assemblage data from 29 sites located near proboscidean fossil remains. Pollen data were acquired from the Neotoma Database and pollen abundance was converted into species biomass abundance using the Landscape Reconstruction Algorithm (LRA) of Sugita (2004a, 2004b). Although spruce was the dominant conifer throughout the Great Lakes Region until ca. 10 ka cal BP, deciduous species such as ash, oak, and elm comprised 50% or more of the vegetation assemblages even at the earliest and northernmost sites, and remained at similar levels until mastodon extinction. Many of these species have been found in mastodon gut contents. These vegetation assemblage reconstructions support the suggestion that mastodons were not food limited as they neared extinction. Moreover, these analyses of landscapes surrounding mastodon sites strongly suggest that the contemporaneous forest, composed of large amounts of spruce intermixed with ash, elm, and oak, was unlike the forests found in much of eastern North America today.