Continental Scale Geophysics — Integrated Approaches to Delineate Prospective Environments for Critical Metals

Scientific Issue and Relevance

Iron-oxide-copper-gold (IOCG), igneous rare earth element (REE), and platinum group element (PGE) ore bodies are some of our most important strategic deposits in providing valuable metals that underpin domestic high technology and military industries. Stakeholders such as mining industry and academia have increasingly shown an interest in large scale data sets and their utility in mineral exploration. Regional geophysical data that is available over continental scales such as magnetic, gravity, and magnetotelluric data can provide a foundation towards identifying and understanding the footprints and deep plumbing systems underlying these important ore systems.

We expect that maps and other products from our project will (1) guide mining industry exploration strategy; (2) contribute to a better understanding of the tectonic evolution of the U.S.; and (3) improve our understanding of how heat, magma, and fluids interact at crustal and even lithospheric scales to form large mineralized systems.

Methodology to Address the Issue

Over the last several decades, the Mineral Resource Program has developed large-scale geophysical databases including magnetic and gravity data at continental scales. Now, with new EarthScopeUSArray magnetotelluric (MT) data online, we have the opportunity to combine magnetic, gravity, and electrical data over large areas within the conterminous U.S. The availability of these data provides a powerful tool to define individual and multi-parameter physical properties (magnetization, density, and electrical conductivity) and map major crustal boundaries, conduits, and prospective domains that underlie mineral deposits of strategic importance. We will use continental-scale geophysical data to map the locations of deep crustal and mantle structures that may act as controls on the emplacement of strategic mineral deposits and ultimately better define prospective domains for these deposits in the U.S.

• Regional and High-Resolution Gravity and Magnetics
  Focus will be on mapping lithospheric architecture beneath the iron-oxide-apatite ± rare earth element and iron-oxide-copper-gold deposits in southeast Missouri. The deposits are hosted in the Mesoproterozoic granite and rhyolite rocks within the St. Francois Mountain terrane. We are combining neodymium (Nd) isotope data with magnetic and gravity data to evaluate major crustal boundaries in the area of iron-oxide mineralization.

• Magnetotellurics
  EarthScope magnetotelluric data doesn't cover the entire U.S., so we will collect new magnetotelluric stations in southern Missouri and northern Arkansas. Collection of this data, in combination with EarthScope magnetotelluric data, will allow for comparison and integration with regional potential-field data over a large portion of the central and eastern continental U.S. The new data will fill in missing areas within the important Mesoproterozoic province in the midcontinent, which is host to iron-oxide-copper-gold deposits. We will use the new data to characterize the electrical properties associated with the major density and magnetization domains underlying iron mineralization in the deep crust.

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