scholarly journals Temporal and Petrogenetic Links Between Mesoproterozoic Alkaline and Carbonatite Magmas at Mountain Pass, California

2021 ◽  
Author(s):  
Kathryn E. Watts ◽  
Gordon B. Haxel ◽  
David M. Miller
Keyword(s):  
The United States ◽  
Mountain Pass ◽  
Pass System ◽  
Metasedimentary Rocks ◽  
Scientific Goal ◽  
Mineral Scale ◽  
Critical Minerals ◽  
Shallow Crust ◽  
Geochemical Constraints ◽  
Metasomatized Mantle

Abstract Mountain Pass is the site of the most economically important rare earth element (REE) deposits in the United States. Mesoproterozoic alkaline intrusions are spatiotemporally associated with a composite carbonatite stock that hosts REE ore. Understanding the genesis of the alkaline and carbonatite magmas is an essential scientific goal for a society in which critical minerals are in high demand and will continue to be so for the foreseeable future. We present an ion microprobe study of zircon crystals in shonkinite and syenite intrusions to establish geochronological and geochemical constraints on the igneous underpinnings of the Mountain Pass REE deposit. Silicate whole-rock compositions occupy a broad spectrum (50–72 wt % SiO2), are ultrapotassic (6–9 wt % K2O; K2O/Na2O = 2–9), and have highly elevated concentrations of REEs (La 500–1,100× chondritic). Zircon concordia 206Pb/238U-207Pb/235U ages determined for shonkinite and syenite units are 1409 ± 8, 1409 ± 12, 1410 ± 8, and 1415 ± 6 Ma (2σ). Most shonkinite dikes are dominated by inherited Paleoproterozoic xenocrysts, but there are sparse primary zircons with 207Pb/206Pb ages of 1390–1380 ± 15 Ma for the youngest grains. Our new zircon U-Pb ages for shonkinite and syenite units overlap published monazite Th-Pb ages for the carbonatite orebody and a smaller carbonatite dike. Inherited zircons in shonkinite and syenite units are ubiquitous and have a multimodal distribution of 207Pb/206Pb ages that cluster in the range of 1785–1600 ± 10–30 Ma. Primary zircons have generally lower Hf (<11,000 ppm) and higher Eu/Eu* (>0.6), Th (>300 ppm), Th/U (>1), and Ti-in-zircon temperatures (>800°C) than inherited zircons. Oxygen isotope data reveals a large range in δ18O values for primary zircons, from mantle (5–5.5‰) to crustal and supracrustal (7–9‰). A couple of low-δ18O outliers (2‰) point to a component of shallow crust altered by meteoric water. The δ18O range of inherited zircons (5–10‰) overlaps that of the primary zircons. Our study supports a model in which alkaline and carbonatite magmatism occurred over tens of millions of years, repeatedly tapping a metasomatized mantle source, which endowed magmas with elevated REEs and other diagnostic components (e.g., F, Ba). Though this metasomatized mantle region existed for the duration of Mountain Pass magmatism, it probably did not predate magmatism by substantial geologic time (>100 m.y.), based on the similarity of 1500 Ma zircons with the dominantly 1800–1600 Ma inherited zircons, as opposed to the 1450–1350 Ma primary zircons. Mountain Pass magmas had diverse crustal inputs from assimilation of Paleoproterozoic and Mesoproterozoic igneous, metaigneous, and metasedimentary rocks. Crustal assimilation is only apparent from high spatial resolution zircon analyses and underscores the need for mineral-scale approaches in understanding the genesis of the Mountain Pass system.

Uranium and Vanadium Resources of Utah: An Update in the Era of Critical Minerals and Carbon Neutrality

2021 ◽  
Author(s):  
Stephanie E. Mills ◽  
Bear Jordan
Keyword(s):  
United States ◽  
Native Americans ◽  
Colorado Plateau ◽  
The United States ◽  
Mining District ◽  
Paradox Basin ◽  
Carbon Neutrality ◽  
Uranium Exploration ◽  
San Juan County ◽  
Critical Minerals

Utah is the second largest vanadium producing state and the third largest uranium producing state in the United States. Carnotite, a primary ore mineral for both vanadium and uranium, was first discovered and used by Native Americans as a source of pigment in the Colorado Plateau hysiographic province of eastern Utah. Radioactive deposits have been ommercially mined in Utah since about 1900, starting with radium, followed by vanadium, and thenuranium. In 1952, the discovery of the Mi Vida mine in Utah’s Lisbon Valley mining district in San Juan County kicked off a uranium exploration rush across the Colorado Plateau. As a result, the United States dominated the global uranium market from the early 1950s to late 1970s. In the modern mining era, Utah is an important contributor to the domestic uranium and vanadium markets with the only operating conventional uranium-vanadium mill in the country, multiple uranium-vanadium mines on standby, and active uranium-vanadium exploration. Overall, Utah has produced an estimated 122 million lbs U3O8 and 136 million lbs V2O5 since 1904. Most of this production has been from the sandstone-hosted deposits of the Paradox Basin, with minor production from volcanogenic deposits and as byproducts from other operations across the state

scholarly journals Geochemical and Sr–Nd isotopic constraints on the petrogenesis and geodynamic significance of the Jebilet magmatism (Variscan Belt, Morocco)

2013 ◽  
Vol 151 (4) ◽  
pp. 666-691 ◽  
Author(s):  
ABDERRAHIM ESSAIFI ◽  
SCOTT SAMSON ◽  
KATHRYN GOODENOUGH
Keyword(s):  
Partial Melting ◽  
Wall Rock ◽  
Ultramafic Rocks ◽  
Isotopic Ratios ◽  
Isotopic Signatures ◽  
Plate Convergence ◽  
Metasedimentary Rocks ◽  
Microgranular Enclaves ◽  
Crustal Origin ◽  
Shallow Crust

AbstractIn the Variscan fold belt of Morocco, the Jebilet massif is characterized by Palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic–granitoid bimodal association and peraluminous granodiorites emplacedc. 330 Ma, intruded by younger leucogranitesc. 300 Ma. The mafic–ultramafic rocks belong to a tholeiitic series, and display chemical and isotopic signatures consistent with mixing between mantle-derived and crust-derived magmas or assimilation and fractional crystallization. The granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of A2-type granites. The peraluminous, calc-alkaline series consists mainly of cordierite-bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths. Detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust (<30 km) by partial melting of tonalitic sources at high temperatures (up to 900°C) and by partial melting of metasedimentary protoliths at relatively low temperatures (c. 750°C), respectively. Mixing between the coeval mantle-derived and crust-derived magmas contributed to the large variation of initial εNdvalues and initial Sr isotopic ratios observed in the granitoids. Further contamination occurred by wall-rock assimilation during ascent of the granodioritic plutons to the upper crust. The ultramafic–granitoid association has been intruded by leucogranites that have high initial Sr isotopic ratios and low initial εNdvalues, indicating a purely crustal origin. The heating events that caused emplacement of the Jebilet magmatism are related to cessation of continental subduction and convective erosion/thinning of the lithospheric mantle during plate convergence.

Magma Mushes of the Fogo Island Batholith: a Study of Magmatic Processes at Multiple Scales

2020 ◽  
Author(s):  
B Graham ◽  
G Dunning ◽  
A M Leitch
Keyword(s):  
Newfoundland And Labrador ◽  
Multiple Scales ◽  
Accessory Mineral ◽  
Crystal Mush ◽  
Liquid Environment ◽  
Similar Composition ◽  
Geochemical Study ◽  
Magmatic Enclaves ◽  
Mineral Scale ◽  
Shallow Crust

Abstract This field, petrographic, and geochemical study examines mingling of compositionally similar rocks at multiple scales. Evidence of complex magma interaction in a multi-component crystal mush reservoir is preserved within the Wild Unit, located along the northeast shoreline of Fogo Island, Newfoundland and Labrador, Canada. The irregular contacts and lack of chilled margins between units, the back-intrusion of younger units by older units, the similar composition of units, and an overlap in U-Pb zircon ages suggest all units interacted as viscous crystal mushes at similar temperatures in the shallow crust. Abundant rounded to ellipsoidal magmatic enclaves, of which there are at least three populations based on composition and crystallinity, appear to represent separate magmas that were entrained either as earlier mush material or crystal-poor intrusions that experienced break-up. Evidence of changes in liquid environment at deeper levels is preserved both in the field and at the mineral-scale, where it is highlighted by abrupt compositional spikes in traverses across early forming plagioclase and pyroxene crystals. Heterogeneity in textures and composition of both major minerals (plagioclase and pyroxene) and an accessory mineral (zircon) point to processes such as crystal exchange and capture affecting tonalite crystal mushes, magmatic enclaves, and other intrusions in the study area earlier in their histories at deeper levels.

Fool’s Gold: Psychologists Using Disingenuous Reasoning to Mislead Legislatures into Granting Psychologists Prescriptive Authority

2003 ◽  
Vol 29 (4) ◽  
pp. 489-524
Author(s):  
Brent Pollitt
Keyword(s):  
Primary Care ◽  
Mental Illness ◽  
Nurse Practitioners ◽  
Primary Care Physicians ◽  
American Psychological Association ◽  
The United States ◽  
Psychotropic Medications ◽  
American Psychological ◽  
Training Requirements ◽  
Prescriptive Authority

Mental illness is a serious problem in the United States. Based on “current epidemiological estimates, at least one in five people has a diagnosable mental disorder during the course of a year.” Fortunately, many of these disorders respond positively to psychotropic medications. While psychiatrists write some of the prescriptions for psychotropic medications, primary care physicians write more of them. State legislatures, seeking to expand patient access to pharmacological treatment, granted physician assistants and nurse practitioners prescriptive authority for psychotropic medications. Over the past decade other groups have gained some form of prescriptive authority. Currently, psychologists comprise the primary group seeking prescriptive authority for psychotropic medications.The American Society for the Advancement of Pharmacotherapy (“ASAP”), a division of the American Psychological Association (“APA”), spearheads the drive for psychologists to gain prescriptive authority. The American Psychological Association offers five main reasons why legislatures should grant psychologists this privilege: 1) psychologists’ education and clinical training better qualify them to diagnose and treat mental illness in comparison with primary care physicians; 2) the Department of Defense Psychopharmacology Demonstration Project (“PDP”) demonstrated non-physician psychologists can prescribe psychotropic medications safely; 3) the recommended post-doctoral training requirements adequately prepare psychologists to prescribe safely psychotropic medications; 4) this privilege will increase availability of mental healthcare services, especially in rural areas; and 5) this privilege will result in an overall reduction in medical expenses, because patients will visit only one healthcare provider instead of two–one for psychotherapy and one for medication.

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