Overview
Airborne Geophysics for Rare Earth Element Deposits (AGREED) Project

graphic showing helicopter doing survey, with data from multiple sensors. Helidopter system used by Precision GeoSurveys to fly Bokan Mountain. Maps generated by USGS with data provided by UCore.

The majority of larger domestic REE deposits are hosted in carbonatite or peralkaline intrusions and related pegmatites and veins. Intrusion-hosted rare earth element deposits make excellent geophysical targets because of their distinct gamma ray, density, and magnetic properties. As such, airborne geophysical surveying has figured prominently in the discovery of many REE deposits and is routinely used by the mining industry to map the extent of surface and subsurface mineralization once a deposit shows economic promise.

Thus far, no airborne geophysical data have been collected by the USGS at a resolution sufficient for studying the ore genesis, setting, or characterization of REE deposits. Only coarsely spaced airborne magnetic data and ground gravity data exist over these deposits. However, high resolution data over domestic REE deposits are available from the mining industry. Innovation in geophysical methods and model development, expansion of geophysical skills, and keeping current on technological advancements over deposits of strategic importance requires access to modern geophysical data.

Objectives

The overall project objective is to coordinate airborne geophysical efforts over domestic REE deposits and create a petrophysical library that will contribute to and complement geophysical model development and characterization of rare earth deposits. Specifically our project will:

  • Work with mining industry to obtain high resolution airborne geophysical data over rare earth deposits.
  • Create a petrophysical library from surface and core samples that describe the range of petrophysical properties of host rocks, structures, and mineralized systems, with an emphasis on REE concentrations and occurrences.
  • Interpret and model the data using modern techniques, many developed in-house.

USGS has acquired mining industry data over three advanced REE deposits with active exploration efforts. Project activities will focus on interpretation, modeling and publications. Publications on method development, geophysical analyses, and geophysical characterization of domestic REE deposits are planned. Initial focus areas are the Bokan Mountain deposit in southeastern Alaska (data acquired from UCore Rare Metals and Precision GeoSurveys, Inc.), Elk Creek deposit in Nebraska (data acquired from NioCorp, formerly Quantum Rare Earth), and the Bear Lodge deposit in Wyoming (data acquired from Rare Element Resources).

Planned for late 2013/early 2014 will be a high resolution magnetic and gravity gradiometry survey of the Pea Ridge iron oxide copper-gold rare earth element (IOCG-REE) deposit in southeast Missouri. This survey will be flown by the USGS.

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