Compilation and recalculation of Cretaceous-Miocene intrusive igneous crystallization geochronology from the northern Rocky Mountains, Montana and Idaho, USA

This dataset presents a recalculated compilation of geochronology ages of Cretaceous-Miocene intrusive rocks and volcanic plugs in the northern Rocky Mountains USA, with a focus on Montana and Idaho. Mineral assessments and prospectivity mapping requires detailed spatiotemporal understanding of magma systems in the upper crust to predict when and where ore deposits may have formed. However, legacy geochronology data from various stakeholders may be stored in disparate databases and in formats and calculations that are not comparable. These igneous bodies are commonly regionally associated with significant mineral deposits, including porphyry copper, replacement tungsten-silver deposits and polymetallic mineralization of precious metals including gold and silver.

Samples selected were dated with U-Pb zircon TIMS, LA-ICPMS, SIMS (or SHRIMP), K-Ar and Ar-Ar geochronology. We excluded Rb-Sr, and fission track zircon and apatite geochronology from the data set because (1) the low closure temperature of these system can be affected by thermal perturbations associated with regional tectonics and (2) these systematics are readily reset during hydrothermal alteration. In both cases, it is highly likely that those systematics may yield dates inaccurate to initial crystallization. An attempt was made to preserve as much data as possible, but some samples were excluded because no uncertainties were reported. In order to ensure that this database was internally comparable, we recalculated the data so that all samples of individual isotope systems used the same decay constants, parental isotope compositions, the same monitor mineral values (when applicable), and finally included propagation of uncertainty associated with decay constant uncertainties. This compilation should be a robust data layer for the study of the distribution in time and space of a variety of different mineral systems within the region.