The project main objectives are to: 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, and 2) geophysically delineate and characterize the subsurface Precambrian geology using existing ground and new (proposed) airborne geophysical data. 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 elements, and lessen U.S. dependence on foreign sources for these metals.
Science Issue and Relevance

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.
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 elements,
- and lessen U.S. dependence on foreign sources for these metals.
Methodology to Address Issue
This project has two main objectives:
- 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.
- 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 that 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.
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.
Reference
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.
Geophysical, Spectral, and Petrophysical Characterization: Since the vast majority of the St. Francois Mountain terrane is concealed beneath Paleozoic rocks and Quaternary deposits, delineation of buried structures, rock types, and IOA and IOCG ore systems must rely on potential field (aeromagnetic and gravity) geophysical data. Characterization of the host rocks, ore minerals, and ore-formation mineral assemblages are key to understanding the chemistry of ore forming systems.
We plan to use modern geophysical data processing techniques, spectral imaging, and petrophysical characterization to refine our understanding of the St. Francois Mountain terrane. Our initial efforts were to compile and interpret existing magnetic and ground gravity data, and we determined the existing magnetic and gravity data available were insufficient to distinguish important features at deposit scale. We acquired new magnetic, gravity gradiometry, and radiometric data (2014: magnetic and gravity gradiometry; 2015: magnetic and gamma ray) and used modern geophysical data processing techniques, which provided new insights into our understanding of the geology of the Precambrian basement. We also are examining and spectrally imaging our archive of several hundered, hand, core, and rock samples with CoreScan's new technique. Results will provide a unique library of compositional parameters and mineral maps related to an iron-oxide mineralized terrane in the U.S. Any newly acquired data from exposed parts of the St. Francois Mountains will aid in mapping surface variations in surface element chemistry and surface and subsurface magnetic signatures related to iron-oxide related alteration types. Models using recently developed in-house 3-D software of shallow deposits will be calculated to define the deposits' geometry and depth extent.
Our results will be used in other project activities to help refine the regional geologic framework, to relate the regional geophysical characteristics to new geochronological data of subsurface plutons, volcanic unites, and mineralized rock, and related the detailed mineralogy to the petrophysics (susceptibility and density) and regional geochemistry across the study area.
Regional Geologic Framework Studies: The Missouri iron-oxide deposits are members of the iron-oxide-copper-cobalt-gold rare earth element (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. Understanding the framework and ore genesis of the Missouri deposits hinges on understanding the buried Precambrian basement geology. The study area is predominantly concealed beneath a thick sequence Paleozoic rocks, Quaternary deposits, and dense vegetation. Recent work by the USGS, in conjunction with the Missouri Department of Natural Resources Division of Geology and Land Survey, laid the groundwork for understanding the regional geologic framework and ore genesis of the deposits. Integration of recently acquired data and interpretations is required to define the regional geologic and tectonic setting.
Our objective is to develop an updated geologic framework for the iron-oxide-apatite (IOA) and (IOCG) ore deposits by producting a regional scale integrated geophysical/geologic regional map and a modern geologic map of the Ironton, MO area. The Ironton area includes most of the outcropping ore deposits in the St. Francois Mountains, is relatively well exposed, and contains the complex volcanic geology and caldera structures that controlled the emplacement of the IOAand IOCG mineralizing systems. The new regional digital compilation will incorporate recent geologic mapping, geochronology, drill core data, and results of the latest USGS geophysical surveys.
Another goal is to provide a continental-scale framework for metallogeny and genesis of A-type 1.4 Gagranites along the southern margin of Laurentia. IOCG deposits in southeast Missouri are temporally and spatially associated with ~1.4 Ga igneous rocks; similar rocks exposed throughout southern Laurentia could host similar deposits.
Geochronology of St. Francois Mountains Terrane and Associated Ore Deposits: Our objective is to determine the ages of formation of the deposits in the St. Francois Mountains terrane. Our initial work focused on the age and origin of Pea Ridge deposit rare earth element mineralization. New age data from this regional study of plutonic rocks will provide a temporal framework for derivation of improved tectonic and petrologic models for the Eastern Granite-Rhyolite province and the iron deposits. The results are critical for interpreting the results of potential field geophysics studies and isotope tracer studies. Important dating targets include:
- volcanic rocks to definitively define the relationship between plutonism and volcanism;
- granitic rocks beneath the Missouri Gravity Low, identified by geophysics but never dated;
- rare Proterozoic metasedimentary rocks;
- regional granitic rocks, and;
- apatite and monazite in magnetite-apatite ore deposits.
We will utilize both U-Pb zircon sensitive high-resolution ion microprobe (SHRIMP) dating and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb analysis of magnetite deposits.
Radiogenic Isotopes and Geochemistry: Our task is focused on obtaining modern radiogenic isotope data (Nd-Sr-Pb) and trace element geochemistry to provide definitive information on source, age, and tectonic setting of magmas associated with rare earth element mineralization in southeast Missouri. The new geochemical information will help to evaluate the regional distribution and origin of rare earth element mineralized occurrences and their host rocks in order to distinguish between sources and settings associated with fertile or barren igneous rocks. The radiogenic isotope data will constrain the types of geochemical processes controlling the evolution of rare earth element mineralizing systems during magma transfer through the crust and the origin of hydrothermal fluids. New results will help to identify economically important targets that resemble the large Fe-rare earth element Pea Ridge deposit. These radiogenic isotope data are critical to understanding the relationship between basement terranes and the complexly mineralized units.
Our initial efforts were focused on the Pea Ridge iron-oxide-apatite (IOA) deposit. Our current phase of research using radiogenic isotopes will be to broaden the effort from the Pea Ridge IOA deposit to include major igneous units from across the St. Francois Mountains terrane with the goal of fully understanding the tectonic setting as well as why the terrane hosts IOA and IOCG deposits and other 1.4 Ga igneous terranes across Laurentia appear to be barren. Is the IOA/IOCG ore formation in Missouri a singular event and if so, what is unique about the crustal architecture that led to mineral deposit formation?
Stable Isotope Applications: We address basic ore genesis questions at the regional scale using stable isotope methods, using both published and new data on regional patterns in oxygen, hydrogen, and sulfur isotopes. We will tie in stable isotope data to the iron oxide-copper-cobalt-gold rare earth element deposits of the region to help constrain the origin of metals and fluids.
- What were the sources of the ore-forming fluids?
- To what extent were fluid-rock reactions important in establishing the isotope and chemical properties of the fluids?
- Did the fluids access both magmatic and surficial solute reservoirs through space and time?
Ore, Mineral, and Fluid Geochemistry: In order to advance genetic and exploration models of iron oxide-apatite (IOA) and iron oxide-copper-cobalt-gold (IOCG) deposits that may host rare earth elements, additional knowledge is needed of the physical conditions (pressure-temperature), source(s) of ore fluid components, and processes that produce the minerals and mass transfer observed in these deposits. Our work initially focused on the Pea Ridge IOA rare earth element deposit in southeast Missouri. To facilitate comparisons, the next step is to collect similar data sets on other deposits in southeast Missouri. Resulting data, interpretations, and chemical models will be used to identify the key factors that produced each deposit type and help characterize the nature of the hydrothermal fluids and processes responsible for ore formation in the Missouri metallogenic province. This information will be used in the development of a USGS IOA-IOCG deposit model.
Data Management: Several data streams will be developed as an outgrowth of this project's research. This task will develop a project database containing archived and new geophysical, petrophysical, and geochemical data sets derived from all phases of the project. The compilation of project-generated data on a single user-friendly platform will facilitate the sharing of data, modeling, interpretation, and publication. The main datasets developed from this project will be released to the public.
USGS Global IOGC Model Development: Our objectives are to bring together all of the research done on the southeast Missouri IOA and IOCGdeposits into one concise occurrence model relevant to Missouri and southern Laurentia. We will also update the USGS grade and tonnage models for IOA deposits and develop a robust data set and grade tonnage model for IOCG deposits worldwide. An integrated global USGS IOA/IOCG ore deposit model will be developed that pulls together the research done in Missouri with research from ore deposits around the world into a concise description of the deposit type and grade and tonnage information to help in future mineral resource assessments.

Completed Activities - Setting and Origin of Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri: In our previous phase of this project, we focused on the Pea Ridge iron oxide-apatite deposit and its rare earth element resources. While many activities continue on with an emphasis of expanding efforts to a regional scale, some activities were intended to provide the needed data to determine current project efforts.
Geochemistry of Ores and Altered Wall Rocks: The task's major goals were to characterize the inorganic geochemical composition of ores and altered wall rocks in the mineral deposits, and document the basic mineral textures and paragenesis. Methods used included standard observations including hand lens, binocular microscope, and polarizing microscope (both transmitted and reflected light). Findings provided critical information on the nature of the ores and wall rocks of the mineral deposits, and provided the foundation for future laboratory studies of the project.
Mineralogy and Mineral Chemistry: 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 worked 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 were used to characterize, identify, and determine the composition of the constituent phases.
Evolution of Mineralization and Alteration: 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 studied modeling of fluid-rock reactions in ore zones and altered wall rocks which is hoped to provide a mineralizing system aspect to the deposit studies.
References
- 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.
Below are other science projects associated with this project.
Geophysical Mapping of Geologic Systems Host to Critical Mineral Deposits, Southern Midcontinent, US
Mineville, Eastern Adirondacks – Geophysical and Geologic Studies
Magmas to Metals: Melt Inclusion Insights into the Formation of Critical Element-Bearing Ore Deposits
Continental Scale Geophysics — Integrated Approaches to Delineate Prospective Environments for Critical Metals
Below are data or web applications associated with this project.
In situ U-Pb dating of apatite and rutile from St. Francois Mountains IOA and IOCG deposits, southeast Missouri
Helicopter magnetic and gravity gradiometry survey over the Pea Ridge iron mine and surrounding area, southeast Missouri, 2014
Geochemical and Modal Data for Mesoproterozoic Igneous Rocks of the St. Francois Mountains, Southeast Missouri
Geochemical Database for Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri, 2016-2017
Operation Basement: Missouri Precambrian Sample Database
Airborne magnetic and radiometric survey, Ironton, Missouri area
Geochemical Database for Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri
Below are publications associated with this project.
Petrology and geochronology of 1.48 to 1.45 Ga igneous rocks in the St. Francois Mountains terrane, southeast Missouri
Absence of magnetite microlites, geochemistry of magnetite veins and replacements in IOA deposits, SE Missouri, USA: Relations to intermediate intrusions
Geochemistry of hematite veins in IOA-IOCG deposits of SE Missouri, USA: Relation to felsic magmatism and caldera lakes
Crustal architecture beneath the southern Midcontinent (USA) and controls on Mesoproterozoic iron-oxide mineralization from 3D geophysical models
Compilation of new and previously published geochemical and modal data for Mesoproterozoic igneous rocks of the St. Francois Mountains, southeast Missouri
Review of the geochemistry and metallogeny of approximately 1.4 Ga granitoid intrusions of the conterminous United States
A special issue devoted to proterozoic iron oxide-apatite (±REE) and iron oxide copper-gold and affiliated deposits of Southeast Missouri, USA, and the Great Bear Magmatic Zone, Northwest Territories, Canada: Preface
Regional geologic and petrologic framework for iron oxide ± apatite ± rare earth element and iron oxide copper-gold deposits of the Mesoproterozoic St. Francois Mountains terrane, southeast Missouri, USA
Mineralogy, chemistry, and fluid-aided evolution of the Pea Ridge Fe oxide-(Y + REE) deposit, southeast Missouri, USA
Mineral thermometry and fluid inclusion studies of the Pea Ridge iron oxide-apatite–rare earth element deposit, Mesoproterozoic St. Francois Mountains Terrane, southeast Missouri, USA
Oxygen, hydrogen, sulfur, and carbon isotopes in the Pea Ridge magnetite-apatite deposit, southeast Missouri, and sulfur isotope comparisons to other iron deposits in the region
Iron and oxygen isotope signatures of the Pea Ridge and Pilot Knob magnetite-apatite deposits, southeast Missouri, USA
Below are news stories associated with this project.
Below are partners associated with this project.
- Overview
The project main objectives are to: 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, and 2) geophysically delineate and characterize the subsurface Precambrian geology using existing ground and new (proposed) airborne geophysical data. 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 elements, and lessen U.S. dependence on foreign sources for these metals.
Science Issue and Relevance
Sources/Usage: Public Domain. Visit Media to see details.Schematic figure showing principal characteristics and inferred setting of iron oxide ± apatite (IOA)- and iron oxide-copper-gold (IOCG)-type mineral deposits in Missouri iron metallogenic province (based on available drill core and surface information). From Day and others, 2016, doi:10.2113/econgeo.111.8.1825.(Public domain.) 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.
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 elements,
- and lessen U.S. dependence on foreign sources for these metals.
Methodology to Address Issue
This project has two main objectives:
- 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.
- 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 that 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.
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.
Reference
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.
(A). Map showing location of concealed and exposed Mesoproterozoic rocks in the St. Francois Mountains terrane (after Pratt et al., 1979), iron oxide and other metal deposits and prospects, and locations of new airborne magnetic and gravity gradiometry surveys. (B) Interpreted geology within airborne geophysical survey areas (after Kisvarsanyi, 1981)(Public domain.) Geophysical, Spectral, and Petrophysical Characterization: Since the vast majority of the St. Francois Mountain terrane is concealed beneath Paleozoic rocks and Quaternary deposits, delineation of buried structures, rock types, and IOA and IOCG ore systems must rely on potential field (aeromagnetic and gravity) geophysical data. Characterization of the host rocks, ore minerals, and ore-formation mineral assemblages are key to understanding the chemistry of ore forming systems.
We plan to use modern geophysical data processing techniques, spectral imaging, and petrophysical characterization to refine our understanding of the St. Francois Mountain terrane. Our initial efforts were to compile and interpret existing magnetic and ground gravity data, and we determined the existing magnetic and gravity data available were insufficient to distinguish important features at deposit scale. We acquired new magnetic, gravity gradiometry, and radiometric data (2014: magnetic and gravity gradiometry; 2015: magnetic and gamma ray) and used modern geophysical data processing techniques, which provided new insights into our understanding of the geology of the Precambrian basement. We also are examining and spectrally imaging our archive of several hundered, hand, core, and rock samples with CoreScan's new technique. Results will provide a unique library of compositional parameters and mineral maps related to an iron-oxide mineralized terrane in the U.S. Any newly acquired data from exposed parts of the St. Francois Mountains will aid in mapping surface variations in surface element chemistry and surface and subsurface magnetic signatures related to iron-oxide related alteration types. Models using recently developed in-house 3-D software of shallow deposits will be calculated to define the deposits' geometry and depth extent.
Our results will be used in other project activities to help refine the regional geologic framework, to relate the regional geophysical characteristics to new geochronological data of subsurface plutons, volcanic unites, and mineralized rock, and related the detailed mineralogy to the petrophysics (susceptibility and density) and regional geochemistry across the study area.
Map showing Precambrian basement provinces of the United States and location of St. Francois Mountains terrane in southeast Missouri. Neodymium (Nd) line separates basement rocks with Nd model ages greater than (northwest side) and less than (southeast side) 1.6 Ga. Modified from Bickford et al. (2015).(Public domain.) Regional Geologic Framework Studies: The Missouri iron-oxide deposits are members of the iron-oxide-copper-cobalt-gold rare earth element (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. Understanding the framework and ore genesis of the Missouri deposits hinges on understanding the buried Precambrian basement geology. The study area is predominantly concealed beneath a thick sequence Paleozoic rocks, Quaternary deposits, and dense vegetation. Recent work by the USGS, in conjunction with the Missouri Department of Natural Resources Division of Geology and Land Survey, laid the groundwork for understanding the regional geologic framework and ore genesis of the deposits. Integration of recently acquired data and interpretations is required to define the regional geologic and tectonic setting.
Our objective is to develop an updated geologic framework for the iron-oxide-apatite (IOA) and (IOCG) ore deposits by producting a regional scale integrated geophysical/geologic regional map and a modern geologic map of the Ironton, MO area. The Ironton area includes most of the outcropping ore deposits in the St. Francois Mountains, is relatively well exposed, and contains the complex volcanic geology and caldera structures that controlled the emplacement of the IOAand IOCG mineralizing systems. The new regional digital compilation will incorporate recent geologic mapping, geochronology, drill core data, and results of the latest USGS geophysical surveys.
Another goal is to provide a continental-scale framework for metallogeny and genesis of A-type 1.4 Gagranites along the southern margin of Laurentia. IOCG deposits in southeast Missouri are temporally and spatially associated with ~1.4 Ga igneous rocks; similar rocks exposed throughout southern Laurentia could host similar deposits.
Geochronology of St. Francois Mountains Terrane and Associated Ore Deposits: Our objective is to determine the ages of formation of the deposits in the St. Francois Mountains terrane. Our initial work focused on the age and origin of Pea Ridge deposit rare earth element mineralization. New age data from this regional study of plutonic rocks will provide a temporal framework for derivation of improved tectonic and petrologic models for the Eastern Granite-Rhyolite province and the iron deposits. The results are critical for interpreting the results of potential field geophysics studies and isotope tracer studies. Important dating targets include:
- volcanic rocks to definitively define the relationship between plutonism and volcanism;
- granitic rocks beneath the Missouri Gravity Low, identified by geophysics but never dated;
- rare Proterozoic metasedimentary rocks;
- regional granitic rocks, and;
- apatite and monazite in magnetite-apatite ore deposits.
We will utilize both U-Pb zircon sensitive high-resolution ion microprobe (SHRIMP) dating and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb analysis of magnetite deposits.
Δ-δ plot for quartz-magnetite pairs in rocks from Pea Ridge deposit (Δ18Oquartz-magnetite = δ18Oquartz − δ18Omagnetite). Data for individual minerals form linear trends that are nominally consistent with isotopic equilibration under closed-system conditions of originally hydrothermal or igneous mineral pairs. Abbreviations: Amp = amphibole, Mag = magnetite, Qz = quartz. From Johnson and others, 2016, doi:10.2113/econgeo.111.8.2017.(Public domain.) Radiogenic Isotopes and Geochemistry: Our task is focused on obtaining modern radiogenic isotope data (Nd-Sr-Pb) and trace element geochemistry to provide definitive information on source, age, and tectonic setting of magmas associated with rare earth element mineralization in southeast Missouri. The new geochemical information will help to evaluate the regional distribution and origin of rare earth element mineralized occurrences and their host rocks in order to distinguish between sources and settings associated with fertile or barren igneous rocks. The radiogenic isotope data will constrain the types of geochemical processes controlling the evolution of rare earth element mineralizing systems during magma transfer through the crust and the origin of hydrothermal fluids. New results will help to identify economically important targets that resemble the large Fe-rare earth element Pea Ridge deposit. These radiogenic isotope data are critical to understanding the relationship between basement terranes and the complexly mineralized units.
Our initial efforts were focused on the Pea Ridge iron-oxide-apatite (IOA) deposit. Our current phase of research using radiogenic isotopes will be to broaden the effort from the Pea Ridge IOA deposit to include major igneous units from across the St. Francois Mountains terrane with the goal of fully understanding the tectonic setting as well as why the terrane hosts IOA and IOCG deposits and other 1.4 Ga igneous terranes across Laurentia appear to be barren. Is the IOA/IOCG ore formation in Missouri a singular event and if so, what is unique about the crustal architecture that led to mineral deposit formation?
Stable Isotope Applications: We address basic ore genesis questions at the regional scale using stable isotope methods, using both published and new data on regional patterns in oxygen, hydrogen, and sulfur isotopes. We will tie in stable isotope data to the iron oxide-copper-cobalt-gold rare earth element deposits of the region to help constrain the origin of metals and fluids.
- What were the sources of the ore-forming fluids?
- To what extent were fluid-rock reactions important in establishing the isotope and chemical properties of the fluids?
- Did the fluids access both magmatic and surficial solute reservoirs through space and time?
Photomicrographs of secondary fluid inclusions in apatite (A) and milky quartz (B–H) from Pea Ridge. A.–C. Saline liquid-rich inclusions. D. Hypersaline inclusion with halite, calcite, and hematite. E. Vapor-rich inclusion. F. Hypersaline inclusion with CO2. G. Vapor-rich inclusion with CO2. H. Inclusion assemblage with variable phase ratios. Similar inclusions are present in each alteration zone and within fragments in the REE-rich breccia pipes. From Hofstra and others, 2016, doi:10.2113/econgeo.111.8.1985.(Public domain.) Ore, Mineral, and Fluid Geochemistry: In order to advance genetic and exploration models of iron oxide-apatite (IOA) and iron oxide-copper-cobalt-gold (IOCG) deposits that may host rare earth elements, additional knowledge is needed of the physical conditions (pressure-temperature), source(s) of ore fluid components, and processes that produce the minerals and mass transfer observed in these deposits. Our work initially focused on the Pea Ridge IOA rare earth element deposit in southeast Missouri. To facilitate comparisons, the next step is to collect similar data sets on other deposits in southeast Missouri. Resulting data, interpretations, and chemical models will be used to identify the key factors that produced each deposit type and help characterize the nature of the hydrothermal fluids and processes responsible for ore formation in the Missouri metallogenic province. This information will be used in the development of a USGS IOA-IOCG deposit model.
Data Management: Several data streams will be developed as an outgrowth of this project's research. This task will develop a project database containing archived and new geophysical, petrophysical, and geochemical data sets derived from all phases of the project. The compilation of project-generated data on a single user-friendly platform will facilitate the sharing of data, modeling, interpretation, and publication. The main datasets developed from this project will be released to the public.
USGS Global IOGC Model Development: Our objectives are to bring together all of the research done on the southeast Missouri IOA and IOCGdeposits into one concise occurrence model relevant to Missouri and southern Laurentia. We will also update the USGS grade and tonnage models for IOA deposits and develop a robust data set and grade tonnage model for IOCG deposits worldwide. An integrated global USGS IOA/IOCG ore deposit model will be developed that pulls together the research done in Missouri with research from ore deposits around the world into a concise description of the deposit type and grade and tonnage information to help in future mineral resource assessments.
Sources/Usage: Public Domain. Visit Media to see details.Simplified geologic map of the Great Bear magmatic zone and locations of main deposits, prospects, and showings, and prospective iron oxide and alkali-altered systems. Modified from Corriveau et al. (2016). From Slack and others, 2016, doi:10.2113/econgeo.111.8.1803.(Public domain.) Completed Activities - Setting and Origin of Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri: In our previous phase of this project, we focused on the Pea Ridge iron oxide-apatite deposit and its rare earth element resources. While many activities continue on with an emphasis of expanding efforts to a regional scale, some activities were intended to provide the needed data to determine current project efforts.
Geochemistry of Ores and Altered Wall Rocks: The task's major goals were to characterize the inorganic geochemical composition of ores and altered wall rocks in the mineral deposits, and document the basic mineral textures and paragenesis. Methods used included standard observations including hand lens, binocular microscope, and polarizing microscope (both transmitted and reflected light). Findings provided critical information on the nature of the ores and wall rocks of the mineral deposits, and provided the foundation for future laboratory studies of the project.
Mineralogy and Mineral Chemistry: 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 worked 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 were used to characterize, identify, and determine the composition of the constituent phases.
Evolution of Mineralization and Alteration: 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 studied modeling of fluid-rock reactions in ore zones and altered wall rocks which is hoped to provide a mineralizing system aspect to the deposit studies.
References
- 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.
- Science
Below are other science projects associated with this project.
Geophysical Mapping of Geologic Systems Host to Critical Mineral Deposits, Southern Midcontinent, US
The objective of this project is to use high-resolution state-of-the-art airborne and regional ground geophysical methods to map an underexplored region of the southern Midcontinent that is important to economic and critical mineral deposits.Mineville, Eastern Adirondacks – Geophysical and Geologic Studies
The USGS is using a set of advanced imaging and analysis tools to study the rocks within the eastern Adirondacks of upstate New York. The goal of these studies is to gain a better understanding of the geology and mineral resources in the area.Magmas to Metals: Melt Inclusion Insights into the Formation of Critical Element-Bearing Ore Deposits
This project applies innovative melt inclusion and mineralogical techniques to characterize several distinctive magma types occurring together with prodigious, critical rare earth elements (REE) and gold-(antimony-tellurium) ore deposits within the U.S. We will characterize the pre-eruptive/pre-emplacement magmatic conditions in several districts. The goal is to determine the role of magmatism in...Continental Scale Geophysics — Integrated Approaches to Delineate Prospective Environments for Critical Metals
Regional geophysical data that are 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. Our project will use continental-scale geophysical data to map the locations of deep crustal and mantle structures that may act as... - Data
Below are data or web applications associated with this project.
In situ U-Pb dating of apatite and rutile from St. Francois Mountains IOA and IOCG deposits, southeast Missouri
Apatite (Ca5(PO4)3(Cl/F/OH)) and rutile (TiO2) samples were collected by the U.S. Geological Survey (USGS) from the iron oxide-apatite-rare earth element (IOA-REE) and iron oxide-copper-gold (IOCG) deposits hosted by the Mesoproterozoic, St. Francois Mountains terrane, southeast Missouri. Samples were prepared and analyzed for direct age dating on a laser ablation inductively coupled plasma mass sHelicopter magnetic and gravity gradiometry survey over the Pea Ridge iron mine and surrounding area, southeast Missouri, 2014
High resolution magnetic and gravity gradient data were collected using the HeliFalcon airborne gravity gradiometry system together with a stinger-mounted magnetometer. The survey took place out of the Sullivan, Missouri airport during March of 2014. The survey covers a 35 x 37 square-kilometer area centered on the Pea Ridge iron oxide-apatite rare-earth element deposit, which is located about halGeochemical and Modal Data for Mesoproterozoic Igneous Rocks of the St. Francois Mountains, Southeast Missouri
This data release accompanies the Data Series report 'Compilation of new and previously published geochemical and modal data for Mesoproterozoic igneous rocks of the St. Francois Mountains, southeast Missouri (https://doi.org/10.3133/ds1080). The compilation includes recently acquired as well as previously published geochemical and modal petrographic data for igneous rocks in the St. Francois MounGeochemical Database for Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri, 2016-2017
The Geochemical and geologic database for Mesoproterozoic igneous rocks and iron oxide-apatite-rare earth element (IOA-REE) and iron oxide-copper-cobalt-gold (IOCG) deposits of Southeast Missouri, 2016-2017 'Geochemical Database for Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri, 2016-2017' (MO_ROCK_IOCG_REE_GX2017) contains new geochemical data compilations for saOperation Basement: Missouri Precambrian Sample Database
In 1968, the Missouri Geological Survey (MGS) established the Operation Basement program to address three objectives: a) to obtain drill hole and underground mining data relative to the structure and composition of the buried Precambrian basement; b) to expand mapping in the Precambrian outcrop area and conduct research related to Precambrian geology and mineral resources; and c) to publish the reAirborne magnetic and radiometric survey, Ironton, Missouri area
This publication provides digital flight line data for a high resolution horizontal magnetic gradient and radiometric survey over the Ironton, Missouri area of southeast Missouri. Data were collected using a fixed wing aircraft with magnetometers mounted in the tail stinger and each wing tip pod and a fully calibrated gamma ray spectrometer. The survey took place out of the Farmington, Missouri aGeochemical Database for Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri
The Geochemical Database for Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri (IOCG-REE_GX) contains new geochemical data compilations for samples from IOCG-REE type deposits in which each rock sample has one "best value" determination for each analyzed species, greatly improving speed and efficiency of use. IOCG-REE_GX was created and designed to compile whole-rock - Publications
Below are publications associated with this project.
Filter Total Items: 17Petrology and geochronology of 1.48 to 1.45 Ga igneous rocks in the St. Francois Mountains terrane, southeast Missouri
The igneous geology of the St. Francois Mountains terrane in southeast Missouri is dominated by the products of 1.48 to 1.45 billion year old volcanic and plutonic magmatism but also includes volumetrically minor, compositionally bimodal contributions added during plutonism between 1.34 and 1.27 billion years ago. The 1.48 to 1.45 billion year old igneous rocks in the St. Francois Mountains terranAuthorsEdward A. du Bray, John N. Aleinikoff, Warren C. Day, Leonid A. Neymark, Seth D. BurgessAbsence of magnetite microlites, geochemistry of magnetite veins and replacements in IOA deposits, SE Missouri, USA: Relations to intermediate intrusions
The paragenesis, textures, and chemical compositions of magnetite in two mafic to intermediate intrusions and four IOA deposits in SE Missouri were studied to discriminate between igneous and hydrothermal sources. In this study, we found that replacement magnetite with mineral inclusion-rich cores yields erroneously high Ti, Al, Si, Mg, and Mn contents as determined by EMP and LA-ICP-MS due to ruAuthorsCorey J. Meighan, Albert H. Hofstra, David Adams, Erin E. Marsh, Heather A. Lowers, Alan KoenigGeochemistry of hematite veins in IOA-IOCG deposits of SE Missouri, USA: Relation to felsic magmatism and caldera lakes
The paragenesis, textures, and chemical compositions of secondary hematite in regional potassic altered rhyolites, four IOA deposits, the sedimentary iron deposit at Pilot Knob and the Boss IOCG deposit in SE Missouri were determined and compared to primary magnetite from the IOA and IOCG deposits. Magnetite is composed of elements characteristics of mafic to intermediate intrusions whereas hematiAuthorsCorey J. Meighan, Albert H. Hofstra, Erin E. Marsh, Heather A. Lowers, Alan KoenigCrustal architecture beneath the southern Midcontinent (USA) and controls on Mesoproterozoic iron-oxide mineralization from 3D geophysical models
Several types of critical mineral-bearing ore deposits in the southern Midcontinent region of the U.S. are hosted in Mesoproterozoic igneous rocks largely concealed beneath Paleozoic cover. Discerning the architecture of igneous intrusions and volcanic centers in the crust is fundamental to understanding the geologic evolution of this vast region and its mineral resources. To advance the understanAuthorsAnne E. McCafferty, Jeffrey D. Phillips, Albert H. Hofstra, Warren C. DayCompilation of new and previously published geochemical and modal data for Mesoproterozoic igneous rocks of the St. Francois Mountains, southeast Missouri
The purpose of this report is to present recently acquired as well as previously published geochemical and modal petrographic data for igneous rocks in the St. Francois Mountains, southeast Missouri, as part of an ongoing effort to understand the regional geology and ore deposits of the Mesoproterozoic basement rocks of southeast Missouri, USA. The report includes geochemical data that is (1) newlAuthorsEdward A. du Bray, Warren C. Day, Corey J. MeighanReview of the geochemistry and metallogeny of approximately 1.4 Ga granitoid intrusions of the conterminous United States
The conterminous United States hosts numerous volumetrically significant and geographically dispersed granitoid intrusions that range in age from 1.50 to 1.32 billion years before present (Ga). Although previously referred to as A-type granites, most are better described as ferroan granites. These granitoid intrusions are distributed in the northern and central Rocky Mountains, the Southwest, theAuthorsEdward A. du Bray, Christopher S. Holm-Denoma, Karen Lund, Wayne R. PremoA special issue devoted to proterozoic iron oxide-apatite (±REE) and iron oxide copper-gold and affiliated deposits of Southeast Missouri, USA, and the Great Bear Magmatic Zone, Northwest Territories, Canada: Preface
No abstract available.AuthorsJohn F. Slack, L. Corriveau, M.W. HitzmanRegional geologic and petrologic framework for iron oxide ± apatite ± rare earth element and iron oxide copper-gold deposits of the Mesoproterozoic St. Francois Mountains terrane, southeast Missouri, USA
This paper provides an overview on the genesis of Mesoproterozoic igneous rocks and associated iron oxide ± apatite (IOA) ± rare earth element, iron oxide-copper-gold (IOCG), and iron-rich sedimentary deposits in the St. Francois Mountains terrane of southeast Missouri, USA. The St. Francois Mountains terrane lies along the southeastern margin of Laurentia as part of the eastern granite-rhyolite pAuthorsWarren C. Day, John F. Slack, Robert A. Ayuso, Cheryl M. SeegerMineralogy, chemistry, and fluid-aided evolution of the Pea Ridge Fe oxide-(Y + REE) deposit, southeast Missouri, USA
The Kiruna-type Pea Ridge iron oxide-apatite (IOA) deposit is hosted by a sequence of 1.47 Ga rhyolite tuffs of the St. Francois Mountains, southeast Missouri, USA. It consists of a series of altered zones composed mainly of amphibole, magnetite, hematite, and quartz, together with the presence of several rare earth element (Y + REE)-rich breccia pipes. In many cases, the fluorapatite within theseAuthorsDaniel E. Harlov, Corey J. Meighan, Ian D. Kerr, Iain M. SamsonMineral thermometry and fluid inclusion studies of the Pea Ridge iron oxide-apatite–rare earth element deposit, Mesoproterozoic St. Francois Mountains Terrane, southeast Missouri, USA
Mineral thermometry and fluid inclusion studies were conducted on variably altered and mineralized samples from the Mesoproterozoic Pea Ridge iron oxide-apatite (IOA)-rare earth element (REE) deposit in order to constrain P-T conditions, fluid chemistry, and the source of salt and volatiles during early magnetite and later REE mineralization.Scanning electron microscopy (SEM)-cathodoluminescence aAuthorsAlbert H. Hofstra, Corey J. Meighan, Xinyu Song, Iain Samson, Erin E. Marsh, Heather A. Lowers, Poul Emsbo, Andrew G. HuntOxygen, hydrogen, sulfur, and carbon isotopes in the Pea Ridge magnetite-apatite deposit, southeast Missouri, and sulfur isotope comparisons to other iron deposits in the region
Oxygen, hydrogen, sulfur, and carbon isotopes have been analyzed in the Pea Ridge magnetite-apatite deposit, the largest historic producer among the known iron deposits in the southeast Missouri portion of the 1.5 to 1.3 Ga eastern granite-rhyolite province. The data were collected to investigate the sources of ore fluids, conditions of ore formation, and provenance of sulfur, and to improve the gAuthorsCraig A. Johnson, Warren C. Day, Robert O. RyeIron and oxygen isotope signatures of the Pea Ridge and Pilot Knob magnetite-apatite deposits, southeast Missouri, USA
New O and Fe stable isotope ratios are reported for magnetite samples from high-grade massive magnetite of the Mesoproterozoic Pea Ridge and Pilot Knob magnetite-apatite ore deposits and these results are compared with data for other iron oxide-apatite deposits to shed light on the origin of the southeast Missouri deposits. The δ18O values of magnetite from Pea Ridge (n = 12) and Pilot Knob (n = 3AuthorsTristan Childress, Adam C. Simon, Warren C. Day, Craig C. Lundstrom, Ilya N. Bindeman - News
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