TH-PB AND U-PB DATING OF ORE-STAGE CALCITE AND PALEOZOIC FLUID-FLOW

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.