Sources of Fe in eolian and soil detritus at Yucca Mountain, Nevada, USA
Eolian deposits and adjacent soil horizons at Exile Hill near Yucca Mountain, Nevada, provide a desert environment where the origins of exotic eolian materials can be discerned. Petrographic, chemical, X-ray diffraction, and electron microprobe data allow an assessment of Fe mineral sources. Fe-rich minerals in local rhyolitic tuff bedrock consist of distinctive biotite and amphibole phenocrysts and groundmass Mn-hematites. Although the local tuffs contain only 1% FeO, detrital components of eolian and soil deposits have {approximately}3% FeO. Exotic minerals from distant sources provide most of the excess Fe in the surficial deposits. The exotic Fe sources are principally smectite, low-Mn hematite, low-F biotite, and high-Fe amphibole not found in local tuffs. Iron contents and the exotic Fe fraction increase with decreasing grain size, such that the clay fractions have {approximately}5--6% FeO, almost all of which is in exotic smectites. The distant origin of these smectites is evident in their high Fe content and distinct Sc/FeO enrichment trends, which differ from the strong local Sc/FeO control defined by coarser soil detritus. Approximate crustal average lanthanide composition in soil and eolian smectites rule out any significant contribution of local smectite derived from tuff alteration. The eolian and soil smectites instead inherit their high Fe content from eolian biotite.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- Sponsoring Organization:
- USDOE Office of Civilian Radioactive Waste Management, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 314108
- Report Number(s):
- LA-UR--98-2843; CONF-9706169--; ON: DE99001781
- Country of Publication:
- United States
- Language:
- English
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