Thorium-232-lead-208 and uranium-238-lead-206 radiometric ages for ore
-stage calcite show that Mississippi Valley-type (MVT) ore deposits ca
n form in distinct tectonic settings. An age of 251 +/- 11 million yea
rs for the Jumbo Mine in Kansas, United States, is in agreement with o
ther ages for MVT deposits in the midcontinent of North America. The s
imilarity of ages of these deposits supports the concept that they for
med in response to fluid flow during the late Paleozoic Alleghenian-Ou
achita orogeny. An age of 351 +/- 15 million years for Twelve Mile Bor
e and Bloodwood-Kapok deposits in Australia indicates that these MVT o
res were deposited in a rifting environment.