Rachel Collins, PhD candidate

Thank you for the support provided through the Bev Vogt Graduate Research Grant. The award made it possible for me to complete an intensive 2025 field season in the southern Pueblo Mountains, where I am studying the newly identified Ladycomb Layered Mafic Intrusion (LLMI). The LLMI is a previously unmapped layered mafic intrusion on the Oregon–Nevada border that I discovered during my Master's research, and my dissertation aims to map its full extent, document its internal layering, understand how it formed, and it's relationship to nearby silicic calderas and hydrothermal Au/Ag/Cu mineralization. I use a combination of field mapping, petrography, and geochemistry to examine how mafic magmas moved through the crust and produced both layered rocks and copper- and Fe-Ti-V bearing mineralized zones. This work contributes to a broader understanding of magma plumbing beneath the Columbia River Basalt Group and magmatism in the northern Basin and Range.

I completed detailed 1:24,000-scale mapping of the Ladycomb Peak and Van Horn Basin quadrangles. This work significantly clarified the intrusion’s boundaries, refined the internal stratigraphy of the Border Series, Lower and Upper zones, and feeder dikes, and led to the identification of several new felsic units. I also mapped the geometry of copper-bearing mineralized zones and collected approximately 75 samples for petrographic and geochemical analysis. Field access was extremely difficult—there are no roads in the majority of the Van Horn Basin quadrangle, and the terrain is rugged, exposed, and consistently above 100°F during the summer—but the grant’s travel support made it possible to complete this work safely and thoroughly. The next steps include returning to complete several focused structural and stratigraphic transects, filling in remaining data gaps, beginning detailed petrographic and geochemical analysis, and expanding reconnaissance farther south to evaluate the potential for similar layered intrusions in Oregon and Nevada.

I anticipate completing my dissertation in June 2028.