New Zealand Journal of Geology and Geophysics abstracts
U-Pb geochronology and geochemistry of molybdenum-bearing granodiorite
porphyry at Copperstain Creek, west Nelson, New Zealand
Robert L. Brathwaite
Institute of Geological & Nuclear Sciences
P.O. Box 31 312
Lower Hutt, New Zealand
email: b.brathwaite@gns.cri.nz
Sandra L. Kamo
Jack Satterly Geochronology Laboratory
University of Toronto
22 Russell Street
Toronto, ON, M5S 3B1, Canada
email: skamo@geology.utoronto.ca
Kevin Faure
Institute of Geological & Nuclear Sciences
P.O. Box 31 312
Lower Hutt, New Zealand
k.faure@gns.cri.nz
Abstract A molybdenite-mineralised granodiorite porphyry
at Copperstain Creek has a U-Pb zircon age of 133.5 ± 0.2 Ma. This
is older than the Early Cretaceous (126–105 Ma) Separation Point Suite,
with
which other molybdenum-bearing granodiorite porphyries in west Nelson have
been correlated on the basis of similar compositions and K-Ar ages. The Copperstain
Creek granodiorite differs compositionally from the high Na and Sr/Y rocks
of the Separation Point Suite in having medium Na and low Sr/Y. Oxygen isotope
δ18Omagma values of ≤10‰ for the Copperstain
Creek granodiorite and granites from the Separation Point Suite indicate that
both
are I-type granites. However, the Copperstain Creek granodiorite porphyry
has a minimum δ18Omagma value of 9.4‰, which
indicates a magma with a crustal component, whereas the Separation Point Suite
granites
have values (5.4–7.9‰) which are very primitive (“mantle-like”).
These new U-Pb age and oxygen isotope data indicate that the Copperstain Creek
granodiorite
is not related to the Separation Point Suite granitoids.
Keywords granodiorite; U-Pb zircon age; molybdenite;
oxygen isotopes
G03011; Received 27 May 2003; accepted 16 January 2004; Online publication
date 20 May 2004
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 219–225
0028–8306/04/4702–0219 © The Royal Society of New Zealand 2004
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