The sup 87 Sr/ sup 86 Sr values of Canadian Shield brines and fracture minerals with applications to groundwater mixing, fracture history, and geochronology

Journal Article · Mon Jan 01 00:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90208-3· OSTI ID:7061192

McNutt, R H ^[1]; Frape, S K; Fritz, P; Jones, M G; MacDonald, I M ^[2]

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1. McMaster Univ., Hamilton, Ontario (Canada)
2. Univ. of Waterloo, Ontario (Canada)

Analyses of saline waters, fracture minerals, and host rocks from seven localities on the Canadian Shield demonstrate the utility of the {sup 87}Sr/{sup 86}Sr ratio in the study of groundwater systems in crystalline rocks. The ratios range from 0.704 to 0.753 and have obtained their signatures by mineral/rock interactions, primarily involving the feldspars. The authors have identified brines from isolated pockets in the same mines where extensive flow regimes exist. There is a mixing of different brines as well as mixing with meteoric waters. The isotopic results on calcites from fractures and shear zones show more than one generation of mineral growth in a given fracture. The {sup 87}Sr/{sup 86}Sr ratios of the calcites vary from values identical to the present-day brine in the fracture zone to ratios with Archean signatures. This implies that activity may occur in fault zones over a very long time. The brines are very rich in Sr (up to 2400 mg/l), very low in Rb, and have relatively radiogenic {sup 87}Sr/{sup 86}Sr ratios. They are ubiquitous in Shield rocks and, if they were present throughout geological time, they may be one reason why Rb/Sr ages of felsic plutons are commonly younger than associated U/Pb ages.

• OSTI ID: 7061192
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 54:1; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GROUND WATER
IONIC COMPOSITION
ISOTOPE DATING
ROCK-FLUID INTERACTIONS
WATER CHEMISTRY
BASEMENT ROCK
BRINES
FELDSPARS
GEOCHEMISTRY
GEOLOGIC FRACTURES
MINERALIZATION
ONTARIO
STRONTIUM 86
STRONTIUM 87
AGE ESTIMATION
ALKALINE EARTH ISOTOPES
BETA DECAY RADIOISOTOPES
CANADA
CHEMISTRY
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC STRUCTURES
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MINERALS
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
RADIOISOTOPES
STABLE ISOTOPES
STRONTIUM ISOTOPES
WATER
580000* - Geosciences