Field Trips

Go beyond the conversation of Rocky Mountain Earth Science at the RMS-AAPG 2026 Convention and actively participate in one of the great field trips.

Field Trip 1: “Critical Minerals from Sea Bug Corpses”

Special Publication 124, Montana Mining and Mineral Symposium 2024

Field Trip Highlights: This field trip shows correlations between trace element concentrations and depositional environments.  The Permian age Phosphoria Formation, found in Montana, Idaho, Utah and Wyoming, was deposited during marine transgressive-recessive cycles in a foreland basin during the assembly of the Pangean continent.  The Retort and Meade Park members contain high phosphate and hydrocarbon content of the formation.  At the depositional margins of the Retort depocenter, very well-sorted ore grade peloidal phosphorite is present.  Elevated levels of cadmium, chromium, copper, fluorine, molybdenum, nickel, rare earth elements (REE), selenium, uranium, vanadium, and zinc were also found in peloidal phosphorite.  The exceptionally high concentrations of metals have been interpreted to reflect fundamental transitions from anoxic to oxic marine conditions.   

Phosphoria Formation was historically mined in Montana for phosphorous until the 1990s.  In the 1950s and 60s, the formation was also evaluated for vanadium and uranium. With recent economic and political pressures for domestic rare earth elements (REE), the Phosphoria has received another look as a potential resource. REE mineralization in the Phosphoria has been noted historically, but with recent economic and political pressures for domestic REE production, a deeper understanding of how the depositional environment impacts the location and quantities of REE mineralization has become a priority.  

This field trip consists of a trip to the former Edgar Mine, a source of peloidal phosphorite, located south of Drummond.  At the mine site, samples from the Retort member obtained from other abandoned or reclaimed mines from southwestern Montana will be provided for viewing, along with their assay results and description of their lithologies.  This information is to demonstrate that lithologies and assay results can be used as a method in determining whether economic REE production is realistic.  The samples used in this trip are discussed in the Montana Bureau of Mines and Geology Special Publication 124.

Field Trip 2: “Fault, Fold, and Cleavage Duplexes of Sandy Hollow”

Field Trip Highlights: The incredible exposures of folded and faulted rocks within Sandy Hollow, located about 50 miles south of Butte, have long been used by structural geologists as analogs for the structures that characterize thin-skinned fold-thrust belts around the world. Understanding the geometry and deformation mechanisms associated with folds and faults is crucial when assessing hydrocarbon potential in these tectonic settings. The series of fault-propagation folds and associated thrust faults observed around Sandy Hollow are structural analogs to what occurs at depth within many oil and gas fields in foreland settings. On this field trip we will focus on the outcrop to meso-scale duplexes that commonly occur within these larger fault-propagation folds and thrust faults, in an attempt to gain a better geometric understanding of smaller-scale, more distributed deformation zones that may not be directly visible on seismic surveys. The field trip will highlight the wide array of deformation mechanisms that operate within duplexes, which may include faulting, folding, or pressure solution (cleavage). Field examples of fault, fold, and cleavage duplexes will be used to demonstrate how porosity and permeability may be either created or destroyed during progressive deformation. Understanding how strain evolved within these common but small-scale structures allows for detailed inferences to be made regarding porosity and permeability within larger potential hydrocarbon targets, specifically in anticlines above fault-propagation folds like those on display in Sandy Hollow.