Cd. Anglin et al., SM-ND DATING OF SCHEELITE AND TOURMALINE - IMPLICATIONS FOR THE GENESIS OF ARCHEAN GOLD DEPOSITS, VAL DOR, CANADA, Economic geology and the bulletin of the Society of Economic Geologists, 91(8), 1996, pp. 1372-1382
Sm-Nd analyses of 19 scheelite samples from auriferous quartz-carbonat
e-tourmaline-scheelite-gold veins from three mines in the Val d'Or gol
d camp in the Abitibi greenstone belt in western Quebec (the Sigma, Pa
scalis-North, and Siscoe Extension mines) yield a linear array on an i
sochron diagram with a mean square weighted deviation (MSWD) of 3.6 co
rresponding to an age of 2596 +/- 33 Ma and epsilon(Ndi) = 2.5. Eight
scheelite samples from the Pascalis-North mine alone define an excelle
nt linear array with an MSWD = 0.31, an age of 2593 +/- 18 Ma, and eps
ilon(Ndi) = 2.7. These ages are interpreted to represent the age of qu
artz-carbonate-tourmaline-scheelite vein-hosted gold mineralization in
the three mines sampled. Sm-Nd analyses of tourmaline suggest that th
is mineral may also be useful for Sm-Nd dating of hydrothermal mineral
ization. The Sm Nd scheelite age of ca. 2600 Ma is in good agreement w
ith U-Pb ages obtained from mineralization-related rutile and titanite
in the Val d'Or area. These results indicate that the quartz-carbonat
e-tourmaline-scheelite vein-hosted gold mineralization was emplaced ap
proximately 70 m.y. later than the youngest observed premineralization
magmatic activity and approximately 60 m.v. later than peak regional
metamorphism in the Val d'Or area. These ages do not support hypothese
s for deposit formation which involve fluids derived from spatially re
lated intrusive rocks or metamorphism, although they do not preclude a
n earlier stage of introduction of gold into tile Val d'Or area. The s
cheelite Sm-Nd age and depleted mantlelike epsilon(Ndi), and the miner
alogy and alteration of the quartz-carbonate-tourmaline veins, are con
sistent with the derivation of the mineralizing fluids from a relative
ly homogeneous external source, and introduction into the upper crust
as part of a single, large hydrothermal system. The formation of the V
al d'Or gold deposits also appears to be broadly synchronous with the
growth of zircon in high-grade metamorphic rocks of the lower crust un
derlying the greenstone belt material, suggesting that these may be re
lated processes.