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.
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.
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 (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,
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.
Dempsey, W. J., and Meuschke, J. L., 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.
Kisvarsanyi, E.B., 1981, Geology of the Precambrian St. Francois terrane, southeastern Missouri:Missouri Department of Natural Resources Report of Investigations 64, 58 p.
Day, W.C., Kisvarsanyi, E.B., Nuelle, L.M., Marikos, M.A., and Seeger, C.M., 1989, New data on the origin of the Pea Ridge iron-apatite deposit, southeast Missouri---Implications for Olympic Dam-type deposits: Geological Society of America Abstracts with Programs, v. 21, no. 6, p. A132.
Skirrow, R.G., Bastrakov, E., Raymond, O.L., Davidson, G., and Heithersay, P., 2002, The geological framework, distribution and controls of Fe-Oxide Copper-Gold mineralisation in the Gawler Craton, South Australia -Part II: Alteration and mineralisation, in Porter, T.M., ed., Hydrothermal iron oxide copper-gold & related deposits: A global perspective: Adelaide, PGC Publishing, v. 2, p 33-47.
There are three geophysical efforts of the project:
Project News Story: Aerial survey to look for valuable minerals in southeastern Missouri, Véronique LaCapra, St. Louis Public Radio, posted January 8, 2016.
The Missouri iron-oxide deposits are members of the iron-oxide gold-copper (IOCG-REE) deposit type, which have proven to be an important type for associated rare earth element (REE) mineral resources critical for modern industrial applications. Recent work by the USGS, in conjunction with the Missouri Department of Natural Resources Division of Geology and Land Survey, has laid the groundwork for understanding the regional geologic framework and ore genesis of the deposits. USGS research conducted from 1989 to1994 has shown that the deposits are both hosted in and genetically related to the Mesoproterozoic rhyolitic and granitic rocks of the St. Francois Mountains of southeastern Missouri.
...is critical in the development of a process-oriented ore deposit model transferable to other similar terranes worldwide to support future mineral resource assessments for undiscovered IOCG and REE deposits worldwide.
A preliminary model for the ore deposits has been proposed, linking their genesis to late-stage magmatic processes related to igneous rocks present in the host terrane.
Our preliminary fluid inclusion, stable isotope, and geochemical data point to the source ore fluids were the result of immiscibility of an iron-oxide-gold-copper-rare earth element-rich phase sourced from high-iron trachytes common in the late stages of the regional volcanism.
The focus of this task is to build upon past efforts by the USGS and other partners --
This research will be fully integrated into the other project activities and will form the foundation for associated geophysical, isotopic, mineralogical, and geochemical studies.
The major goals of this task are to
This task will provide critical information on the nature of the ores and wall rocks of the mineral deposits, and provide the foundation for other laboratory studies of the project.
Methods used include standard observations using
We will research the age and origin of Pea Ridge Rare Earth Element mineralization. Currently, the age of the Pea Ridge Rare Earth Element deposits is thought to be about 1.4 Ga, based on TIMS analysis of one xenotime grain. However, previous geochemical analyses of xenotime indicates multiple compositions, suggesting several episodes of xenotime formation. The previous TIMS age data probably represent a mixture of these age components. We will use SHRIMP spot analysis of xenotime in situ (to preserve textural context(s) of ore deposition) to decipher the complex history of the Pea Ridge deposit.
Our objective here is to determine the ages of formation of uraniferous rare-earth-element-bearing phosphate minerals (xenotime and monazite) that occur at Pea Ridge. We will obtain ore samples from existing cores for uranium-lead geochronology. In addition, we intend to collect outcrop samples of Mesoproterozoic plutonic rocks of the St. Francois Mountains that host the rare earth element deposits or that are related to the Mesoproterozoic magmatic activity of the region. We will date ore samples from core, in situ (in polished thin section). We will extract zircon from the plutonic rock samples. To better understand the genesis of the rare earth element minerals, we will also analyze dated zones for trace elements.
We will address the origin and evolution of igneous plutons and volcanic rocks in the St. Francois Mountains terrane. Our principal objectives are to fully characterize the whole-rock geochemistry (major, trace, and rare earth element) and radiogenic isotope (Sr, Nd, and Pb) signature of intrusive and volcanic rocks in the study area.
We will collect samples for analysis from outcrops and drill cores, and from previous collections of other workers (e.g., underground workings of mines). Analyses we will perform include:
We will provide stable isotope data that can help constrain the origin of metals and fluids in the mineral deposits being studied.
Our principal objectives are to document the carbon, oxygen, hydrogen, and sulfur isotope composition of ore and gangue minerals in the deposits, and those in adjacent altered wall rocks.
The stable isotope data will be acquired by analysis of whole rocks and mineral separates using gas-source mass spectrometry.
How did the IOCG and related deposits in the St. Francois Mountains form? Specifically, what were the pressure-temperature conditions and depth of ore formation, chemical composition of ore fluids, and sources of ore fluid components that produced IOCG (e.g. Boss-Bixby) and related iron oxide and rare earth element (e.g. Pea Ridge) deposits? The initial focus will be on the Pea Ridge deposit.
The objectives of this task are to use fluid inclusion data collected from ore and gangue minerals to ascertain the presence or absence of basinal or crustal vs. magmatic or mantle fluids and their relative importance to ore formation as well as advance understanding of the P-T-X conditions and processes of mineral precipitation. Melt inclusions in coeval intrusive and extrusive igneous rocks may also be characterized. Ultimately, such data may elucidate the controls on iron oxide versus copper-gold versus rare earth element mineralization in the district and their relation to the geotectonic framework of the region.
Knowledge of the mineralogy and mineral chemistry of various mineral phases in the iron-oxide-copper-cobalt-gold-rare earths deposits of southeast Missouri is incomplete. Without a detailed characterization, certain paragenetic and petrogenetic aspects of this deposit will remain uncertain.
We will work to characterize the mineralogy and mineral chemistry of samples from the iron-copper-cobalt-gold-rare earths deposits of southeast Missouri.
Electron microprobe wavelength-dispersive spectroscopy and scanning electron microscope (SEM) petrography and energy-dispersive spectroscopy will be used to characterize, identify, and determine the composition of the constituent phases.
The consensus among many workers is that the iron-copper-cobalt-gold-rare earths deposits of southeast Missouri belong to the iron oxide-copper-gold (IOCG) family of mineral deposits (e.g., Kisvarsanyi and Kisvarsanyi, 1989; Seeger, 2000). However, the ages of these deposits, relative contributions of magmatic and meteoric fluids during mineralization, and sources of the contained metals, remain uncertain.
We will study modeling of fluid-rock reactions in ore zones and altered wall rocks, which will provide a mineralizing system aspect to the deposit studies.
Kisvarsanyi, G., and Kisvarsanyi, E.B., 1989, Precambrian geology and ore deposits of the southeast Missouri iron metallogenic province: Society of Economic Geologists, Field Trip Guidebook Series, v. 4, p. 1-40.
Seeger, C.M., 2000, Southeast Missouri iron metallogenic province: Characteristics and chemistry, in Porter, T.M., ed., Hydrothermal iron oxide copper-gold and related deposits: A global perspective: Adelaide, PGC Publishing, v. 1, p. 237-248.
Day, W.C., and Granitto, Matthew, 2014, Geologic field notes and geochemical analyses of outcrop and drill core from Mesoproterozoic rocks and iron-oxide deposits and prospects of southeast Missouri: U.S. Geological Survey Open-File Report 2014–1053, 7 p. http://pubs.usgs.gov/of/2014/1053/
Aleinikoff, J., Neymark, L., Selby, D., Day, W., Slack, J., Holm-Denoma, C., Pillers, R., Seeger, C., and Samson, I., 2015, U-Pb and Re-Os geochronology of REE-rich breccia pipes and magnetite ore from the Mesoproterozoic Pea Ridge Fe-REE-Au deposit, St. Francois Mountains, Missouri, USA: Society for Economic Geologists 2015 Conference, Hobart, Australia, 27-30 September 2015. View Aleinikoff SEG abstract. [PDF file, 36 KB]
Aleinikoff, J.N., Selby, D., Day, W.C., Slack, J.F., Pillers, R.M., Seeger, C., and Samson, I.M., 2013, U-Pb and Re-Os geochronology of REE-rich breccia pipes from the Mesoproterozoic Pea Ridge Fe-REE-Au deposit, St. Francois Mountains, Missouri: Geological Society of America Abstracts with Programs, v. 45, p. 499. View Aleinikoff abstract.
Day, W.C., Aleinikoff, J., Seeger, C.M., and Slack, J.F., 2015, Regional geologic setting of the Mesoproterozoic iron oxide ore systems of southeast Missouri, USA: Society for Economic Geologists 2015 Conference, Hobart, Australia, 27-30 September 2015. View Day SEG abstract. [PDF file, 19 KB]
Hofstra, A.H., Meighan, C.J., and Emsbo, P., 2013, Microthermometric and ion ratio analyses of fluid inclusions from the Pea Ridge iron oxide-apatite (IOA) and Boss-Bixby iron oxide copper-gold (IOCG) deposits support a magmatic-hydrothermal origin: Geological Society of America Abstracts with Programs, v. 45, p. 499. View Hofstra 2013 GSA abstract.
Ives, B.T., Metzger, A., Mickus, K.L., and McCafferty, A.E., 2013, Regional gravity survey to aid in determining the REE potential of the Pea Ridge mine and the surrounding area, southeast Missouri: Geological Society of America Abstracts with Programs, v. 45, p. 276. View Ives 2013 GSA abstract.
Ives, B.T., Mickus, K.L., and McCafferty, A.E., 2014, Regional gravity survey investigating poorly studied areas of the northwest St. Francois terrane, southeast Missouri: Geological Society of America Abstracts with Programs, v. 46, no. 1, p. 6. View Ives 2014 GSA abstract.
Ives, B.T., Mickus, K.L., McCafferty, A.E., Seeger, C., and Starkey, M., 2014, Analyzing the Paleozoic basement structure and lithologies of the northwest St. Francois terrane, Missouri using gravity data to investigate possible mineral deposits of economic interest: Geological Society of America Abstracts with Programs, Vol. 46, No. 6, p. 308. View Ives 2014 GSA poster abstract.
Johnson, C.A., Day, W.C., and Rye, R.O., 2013, Stable isotope geochemistry of the Pea Ridge iron oxide-rare earth element deposit, St. Francois Mountains, southeastern Missouri: Temperature of ore formation, source of hydrothermal fluid, and source of sulfur: Geological Society of America Abstracts with Programs, v. 45, p. 499. View Johnson abstract.
McCafferty, A.E., 2014, Insights into concealed iron oxide-rare earth element deposits from new airborne geophysical data, southeast Missouri: Geological Society of America Abstracts with Programs, v. 46, No. 4, p. 15. View McCafferty 2014 abstract.
McCafferty, A.E., Day, W.C., Slack, J.F., McDougal, R.R., and Driscoll, R.L., 2013, Geophysical setting of iron oxide-copper-cobalt-gold-rare earth element deposits of southeast Missouri: Geological Society of America Abstracts with Programs, Vol. 45, No. 7, p. 537. View McCafferty 2013 abstract.
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]
Meighan, C.J., Hofstra, A.H., Marsh, E.e., Lowers, H.A., Koenig, A.E., and Hitzman, M.W., 2015, Zr-in-rutile and Ti-in-quartz thermometry support a metasomatic origin for the Pea Ridge iron oxide-apatite-REE deposit, southeast Missouri, USA: Society for Economic Geologists 2015 Conference, Hobart, Australia, 27-30 September 2015. View Meighan SEG abstract. [PDF file, 32 KB]
Mercer, C.N., Watts, K.E., Meighan, C.J., and Bennett, M.M., 2015, Mineral and melt inclusion constraints on the petrogenesis of regional magmas and magnetite ore from the Pea Ridge (IOA-REE) and Boss Bixby (IOCG) deposits, USA: Society for Economic Geologists 2015 Conference, Hobart, Australia, 27-30 September 2015. View Mercer SEG abstract. [PDF file, 20 KB]
Neymark, L., Aleinikoff, J., Holm-Denoma, C., Pietruszka, A., Pillers, R., and Moscati, R., 2015, High spatial resolution SHRIMP and LA-ICPMS U-Pb geochronology of Pea Ridge Fe-REE-Au deposit, USA: Goldschmidt Conference, Prague, Czech Republic, 16-21 August 2015. View Neymark Goldschmidt abstract.
Slack, J.F., Day, W.C., McCafferty, A.E., Seeger, C., and Nold, J.L., 2013, A new look at iron oxide-apatite and iron oxide-copper-gold-rare earth element deposits in the Mesoproterozoic St. Francois Mountains terrane of southeast Missouri: Geological Society of America Abstracts with Programs, v. 45, p. 498. View Slack abstract.
Slack, J.F., McCafferty, A.E., Aleinikoff, J.N., Ayuso, R.A., Belkin, H.E., Cosca, M.A., Day, W.C., Hofstra, A.H., Johnson, C.A., Meighan, C.A., Neymark, L.A., Nold, J.L., Seeger, C.M., and Selby, D., 2014, Mesoproterozoic iron oxide-apatite and iron oxide-copper-gold-rare earth element deposits of southeast Missouri, USA: Geology, geophysics, and exploration potential: Society of Economic Geologists, Conference Proceedings, 27-30 September 2014, Keystone, Colorado, USA. [PDF file, 143 KB]
Central Mineral and Environmental Resource Science Center
Crustal Geophysics and Geochemistry Science Center
Eastern Mineral and Environmental Resources Science Center