Petrography, mineralogy, and chemistry of calcite-silica deposits at Exile Hill, Nevada, compared with local spring deposits

Technical Report · Fri Dec 01 04:00:00 EST 1995

DOI:https://doi.org/10.2172/249259· OSTI ID:249259

Vaniman, D T; Chipera, S J; Bish, D L

Chemical, mineralogic, and petrographic analyses of siliceous calcretes from Exile Hill east of Yucca Mountain, Nevada, indicate that pedogenic processes alone account for the formation of the calcretes. These calcretes have been interpreted by some observers as evidence of seismically triggered eruptions of deep water. Such an origin could have important consequences if Yucca Mountain is developed as an unsaturated site for the disposal of high-level nuclear waste. At odds with this hypothesis are the absence of features that should be present at fault-fed springs (e.g., fissure-ridge mounds with microterraces) and the preservation within root casts of delicate pedogenic microfossils, such as calcified filaments and needle-fiber calcites. Mineral-chemical evidence of pedogenic origin is found in heavy-mineral concentrations, reflected in Fe and Sc enrichments. These concentrations, which occur in the most massive of the vein calcretes, require derivation of detritus from a mixture of weathered and eolian materials that occur in the overlying B soil horizons, as opposed to direct incorporation of adjacent unweathered bedrock. Carbonate and silica abundances and accumulation rates are well within the scope of pedogenic processes. Calcium is derived from rainwater or eolian sources, whereas silica is derived in part by dissolution of local volcanic glasses or from dissolution of unstable silica minerals that are abundant in the local tuffs. In contrast with local deposits that are of spring or seep origin, the siliceous calcretes at Yucca Mountain are pedogenic in origin as well as evolution and provide no evidence in support of conjectured spring activity.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 249259
• Report Number(s): LA--13096-MS; ON: DE96012103
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
CALCRETES
GEOLOGY
HIGH-LEVEL RADIOACTIVE WASTES
ORIGIN
SITE CHARACTERIZATION
SPENT FUELS
UNDERGROUND FACILITIES
UNDERGROUND STORAGE
YUCCA MOUNTAIN