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Overview

Why are we doing this research?

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.

What are we doing?

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 EarthScope 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.

Potential Impact

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.

References

Phillips, J.D., Duval, J.S., and Ambroziak, R.A., 1993, National geophysical data grids; gamma-ray, gravity, magnetic, and topographic data for the conterminous United States: U.S. Geological Survey Data Series 9, 1 disc.

Project Data Maps
Maps of data to be used for this project: A) Map of EarthScope stations showing their collection and processing status; B) Bouguer gravity anomaly map (Phillips and others, 1993); and C) Residual magnetic anomaly map of the conterminous United States (Philips and others, 1993).

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Project Activities

Regional and High-Resolution Gravity and Magnetics

Contact: Anne McCafferty, anne@usgs.gov

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.

Gravity and Magnetics Maps of St. Francois Mountain terrane.
Gravity and Magnetic Maps of St. Francois Mountain terrane. White dots represent location of iron oxide deposits.
Integrated interpretation map of St. Francois Mountain terrane.
Integrated Interpretation Map of St. Francois Mountain terrane.

Magnetotellurics

Contact: Paul Bedrosian, pbedrosian@usgs.gov

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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Products

Abstracts of Posters and Presentations

Ayuso, R.A., Slack, J.F., Day, W.C., and McCafferty, A.E., 2016, Nd-Pb isotope geochemistry and Pb-Pb age estimates of the Mesoproterozoic Pea Ridge iron oxide-apatite-rare earth element deposit, southeast Missouri, USA: Geological Society of America Abstracts with Programs, Vol. 48, No. 5, doi:10.1130/abs/2016NC-274936.

Bedrosian, P., 2015, From Archean to Present – Structure and Evolution of the North American Mid-Continent through the Lens of EarthScope Magnetotelluric Data: American Geophysical Union Annual Meeting, https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/84721.

McCafferty, A.E., and Phillips, J.D., 2015, Shallow to Deep Crustal Controls on Localization of Mesoproterozoic Iron Oxide Copper-Gold-Rare Earth Element Deposits in Southeast Missouri (USA): Evidence from Gravity and Magnetic Data: Society for Economic Geologists 2015 Conference, Hobart, Australia, 27-30 September 2015. View McCafferty SEG 2015 abstract. [PDF file, 119 KB]

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