A PRELIMINARY U-Pb DATE ON CAVE SPAR, BIG CANYON, GUADALUPE MOUNTAINS, NEW MEXICO, USA

U-Pb dating of a football-sized, dogtooth spar, calcite crystal collected from a cave in Big Canyon, Guadalupe Mountains, New Mexico, USA, gave an age estimate of 87- 98 Ma for calcite deposition. This Upper Cretaceous (Laramide) date is important because: (1) it implies that there may have been a major karsting episode in the Guadalupe Mountains in the Laramide; (2) it implies that the Laramide was a time of heating and deeply circulating hydrothermal water; (3) it relates to the possible time of regional uplift above sea level of the Guadalupe Mountains along with the rest of the western United States; and (4) it relates to a time of possible hydrocarbon maturation and migration in the Delaware Basin. Spar (or “geode”) caves are lined with dogtooth and/or nailhead spar calcite crystals. In the Guadalupe Mountains, these can be small, individual caves or small to large rooms intercepted by later, larger, sulfuric acid cave passages. They can range from a few meters up to tens of meters or more in size, but most are (on the average) about 5 m. From fluid-inclu-sion temperature data (~30-85ºC), spar crystals in the Guadalupe Mountains are known to have precipitated fro