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Setting and Origin of Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri

Introduction:

The geological framework and origin of the iron-copper-cobalt-gold-rare earth element (IOCG-REE) deposits in southeast Missouri are not well defined. In most areas, the geology surrounding the deposits is uncertain, owing to limited outcrops of the host Precambrian igneous rocks (St. Francois Mountains terrane) and a widespread cover, as much as about 450 meters thick, of Cambrian sedimentary rocks. As a result, the geometry, age, and petrology of buried plutons and subvolcanic intrusions in the St. Francois terrane--and potentially undiscovered metal deposits--are unknown, except where data are available from drill cores.

At right is a map showing Precambrian basement geology of southeastern Missouri. From: Kisvarsanyi, E.B., 1981, Geology of the Precambrian St. Francois terrane, southesastern Missouri: Missouri Department of Natural Resources, Division of Geology and Land Survey Report of Investigations, No. 64, 58 p.

This project has two main objectives:

1. Geologically, characterize the setting and origin of the iron-copper-cobalt-gold-rare earth element deposits, and advance the knowledge of rare earth element and Co potential within iron oxide-copper-gold (IOCG) deposits of southeast Missouri. An improved understanding of the distribution, age, and origin of these deposits, and their genetically related pluton(s), will provide a valuable database for new industry exploration in the region and future mineral resource assessments.

   and

2. Geophysically delineate and characterize the subsurface Precambrian geology using existing ground and new (proposed) airborne geophysical data. Develop a petrophysical database that contributes to mapping controls on rocks and structures host high contents of IOCG-rare earth mineralization.

The geologic and geophysical components will address a regional area that includes known concealed deposits at Pea Ridge, Bourbon, Camel's Hump, Boss Bixby, and Kratz Spring. Depths to these deposits vary from 325 to 415 meters below the topographic surface.

Terrain and Magnetic Anomaly Map of southeastern Missouri.
From:
Dempsey, W. J., and Meuschke, J. L., 1951a, Total intensity aeromagnetic
map of Berryman quadrangle, Missouri: U.S. Geological Survey
Geophysical Investigations Map GP-77, scale 1:31,680.
and
----1951b, Total intensity aeromagnetic map of Sullivan quadrangle
and part of Union quadrangle, Missouri: U.S. Geological Survey
Geophysical Investigations Map GP-78, scale 1:31,680

Relevance and Impact:

Characterization of the distribution and origin of mineral deposits containing critical metals is an important component of the Mineral Resources Program of the USGS. Rare earth elements and cobalt are among such critical metals, chiefly due to their increasing use in high-technology and defense industries and the scarcity of economic deposits within the United States.

The St. Francois Mountains terrane likely has the highest potential for undiscovered large rare earth element deposits in the conterminous United States. This terrane is geologically analogous to iron-copper-gold-rare earth element-uranium deposit and similar (but smaller) deposits that have been discovered there in recent years. All of these deposits in the Gawler Craton (south Australia) occur within granite and rhyolite, beneath hundreds of meters of flat-lying sedimentary rock, and each was  discovered by airborne geophysics (see Skirrow et al., 2002). Geological and geophysical techniques used successfully in the Gawler Craton, by the Australian Geological Survey Organisation and the Geological Survey of South Australia, will be evaluated by this project, and where relevant, applied to the St. Francois Mountains terrane.

The impact of this project will be significant in greatly improved understanding of iron-copper-cobalt-gold-rare earth element deposits in southeast Missouri. Data generated by the project will significantly advance the potential for new discoveries in the study area, including likely applications to other buried Mesoproterozoic terranes in the Midcontinent region. Identifying new targets for exploration could result in the discovery of new deposits, which if delineated by drilling and determined to be commercially economic to mine, would increase the domestic resource for critical metals such as rare earth element, and lessen U.S. dependence on foreign sources for these metals.

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