The Torrie, Sputnik, and Eddie kimberlite rocks, located near Yamba Lake, c
entral Slave province, N.W.T., are volcaniclastic, macrocrystic, heterolith
ic, olivine-rich tuff, and olivine-rich tuff breccia. Torrie and Sputnik ki
mberlite rocks contain pyroxene and garnet xenocrysts and megacrysts with m
ajor-element compositions consistent with derivation mostly from disaggrega
ted garnet lherzolite, with subordinate contributions from eclogite, spinel
lherzolite, garnet harzburgite, and websterite. The presence of primary gr
oundmass phlogopite and compositionally evolved spinel, and the absence of
mantle xenocrysts, xenoliths, and megacrystic ilmenite distinguish the Eddi
e kimberlite pipe from the other two kimberlite pipes. Large variations in
delta(18)O of garnet and clinopyroxene in xenocrysts and xenoliths (+3.98 t
o +6.36 parts per thousand), nonequilibrium intermineral isotopic fractiona
tion, and major-element heterogeneity are interpreted as resulting from inf
iltration of fluids or melts produced by dehydration or melting of subducte
d oceanic crust into overlying peridotite. Although the timing is unconstra
ined for the xenocysts, the xenolith must have experienced this metasomatic
interaction shortly before entrainment in the kimberlite. Variable delta(1
8)O values for magnesian ilmenite are also interpreted to result indirectly
from such metasomatic activity in the mantle as well. The Torrie and Sputn
ik kimberlite rocks have low concentrations of diamond indicator minerals c
onsistent with their low-diamond grades. These kimberlite rocks did not sam
ple a significant amount of garnet harzburgite, the rock type commonly asso
ciated with high-diamond grades in other kimberlite rocks. Furthermore, met
asomatism just prior to kimberlite eruption may have caused the resorption
of any diamond present.