Mathematics – Logic
Scientific paper
Mar 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.1181g&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 6, pp.1181-1202
Mathematics
Logic
1
Scientific paper
The history of major, trace, and actinide element mobility and fluid infiltration has been studied in two deep fractures (>1 km) in the Lac du Bonnet batholith as part of the Canadian Nuclear Fuel Waste Management Program. Core samples collected from two fracture zones, FR1 and FR2 (~1175 m deep), containing saline groundwater (TDS = 50 g/L) were investigated mineralogically, chemically, and isotopically ( 238 U-series, O and H). Several sequentially overprinting alteration stages were identified, from early high-temperature to later low-temperature hydrothermal alteration. K-feldspar, illite, chlorite, and later kaolinite formed during these stages. Subsequent infiltration of oxidizing fluids produced alteration of the chlorite to hydrous iron oxides. Fracture zone FR1 contains predominantly hematite coating; fracture zone FR2 is characterized by the formation of a breccia and by an intense alteration of the granite in contact with this breccia to illitic clay. Alteration occurred during infiltration either of formation brines or of isotopically evolved meteoric water where 18 O = 8 to 12 and D = -65 to -20 , at calculated temperatures between ~250 and 25°C. Loss of Ca, Na, and Sr and, to some extent, Ba was observed in all the altered samples relative to fresh granite. A sharp increase in K, Mg, U, Th, and REE was observed in the illitic clay rich zone. Pronounced disequilibria of 234 U / 238 U (<0.5), 230 Th / 234 U (~0.7), and 226 Ra / 230 Th (~0.9) exist in the illitic clay, indicating loss of 234 U, 230 Th, and 226 Ra to the groundwater within the last 1.5 Ma. In contrast, an excess of 234 U, 230 Th, and 226 Ra was measured in the brecciated samples. The disequilibria are consistent with a model involving loss of 234 U, 230 Th, and 226 Ra to groundwater by -recoil from U deposited on the illitic clay surfaces. These radionuclides were deposited subsequently in the nearby brecciated zone.
Gascoyne Mel
Griffault Lise Y.
Kamineni Choudari
Kerrich Robert
Vandergraaf Tjalle T.
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