The relative criticality of mineral commodities is evaluated using a wide range of parameters and in different contexts (e.g., from the standpoint of their importance to national security, or to a specific industrial application), which explains the multiplicity of classification schemes and variations in terminology applied to these commodities in the literature, media and government reports. The core group of critical metals, listed alphabetically, includes: antimony, beryllium, chromium, cobalt, gallium, germanium, indium, lithium, niobium, platinoids, rare-earth elements (REE, including yttrium), tantalum and tungsten. The present retrospect briefly describes the emergence of critical metals as a distinct resource type and the evolution of society's perception of these commodities over the past 100 years.
Abstract Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ 26 Mg values (−1.89 to −1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.
Marked thickness changes in early Dinantian (Courceyan-Chadian) sediments occur across the Cardiff-Cowbridge Anticline, a major east-west Variscan fold in the Vale of Glamorgan. They resulted from differential subsidence over an active concealed basement fault zone, the Vale of Glamorgan Axis, which is coincident with the hinge of the Anticline; the latter formed in response to inversion on this basement fault. A Caledonian ancestry for the Vale of Glamorgan Axis is indicated by pronounced Upper Old Red Sandstone overstep across it. Across the Severn Estuary, between South Wales and the Bristol-Mendips region, there is a significant offset of isopachs and facies belts in both the Courceyan-Chadian and Arundian sequences. It is suggested that these result from intra-Carboniferous dextral strike-slip along a major fault zone underlying the Severn Estuary (the Severn Estuary Fault Zone), and that the Vale of Glamorgan Axis was a synthetic structure, developed in conjunction with this strike-slip movement. By inference, the Severn Estuary Fault Zone shares a common history with the Vale of Glamorgan Axis, extending back to the Devonian and possibly earlier. Late Dinantian (Holkerian) facies distribution reflects uplift and emergence on the north-south Usk Anticline and Malvern Lineament. Continued uplift is recorded in Silesian sequences in south-east Wales and the Bristol-Mendips area. The orientation of structures bordering the Severn Estuary is consistent with their development in a right-lateral strike-slip zone.
Two techniques for automated sea-ice tracking, image pyramid area correlation (hierarchical correlation) and feature tracking, are described. Each technique is applied to a pair of Seasat SAR sea-ice images. The results compare well with each other and with manually tracked estimates of the ice velocity. The advantages and disadvantages of these automated methods are pointed out. Using these ice velocity field estimates it is possible to construct one sea-ice image from the other member of the pair. Comparing the reconstructed image with the observed image, errors in the estimated velocity field can be recognized and a useful probable error display created automatically to accompany ice velocity estimates. It is suggested that this error display may be useful in segmenting the sea ice observed into regions that move as rigid plates of significant ice velocity shear and distortion.< >
The presence of Neogene fault systems can have a significant impact on hydraulic connectivity of aquifers, juxtaposing otherwise disconnected aquifers, enhancing recharge and/or discharge or acting as barriers to flow and consequently compartmentalising groundwater resources. Previously, regional airborne electromagnetics (AEM) transects allied with groundwater investigations have pointed to the potential for localised compartmentalisation of the Daly River Basin groundwater systems. However, existing data is sparse, and equivocal.In this context, the main aim of the Daly River Basin Project is to determine if compartmentalisation of the aquifers is a significant factor and thus should be explicitly considered in groundwater modelling and water allocation planning. The objectives of the project main goals of the project are to: (1) map Neogene faults through the use of airborne electromagnetic (AEM) and morphotectonic mapping, and (2) assess the permeability and transmissivity of mapped fault zones and their role in potential groundwater system compartmentalisation. Data acquisition includes 3325 line-kilometres of new AEM and airborne magnetics, ground (ground magnetic resonance (GMR)), and borehole geophysics, drilling, groundwater sampling and hydrochemical analysis, geomorphic and morphotectonics mapping. Hydrogeophysical, geomorphic and hydrogeological data will also be used to better understand groundwater-surface water connectivity and the potential for managed aquifer recharge schemes to replenish extracted groundwater resources. The outcomes of this project will inform decisions on water allocations and underpin effective and efficient groundwater use. This paper specifically reports on the ability of AEM and morphotectonics mapping to identify Neogene fault systems in the Daly River Basin.
The Bayan Obo Fe-REE-Nb deposit, Inner Mongolia, China,
is the world’s largest REE resource and is also exploited as a major Fe
oxide deposit. The deposit consists of replacement bodies hosted in dolomite
marble and of magnetite, hematite, and REE minerals associated with apatite,
aegirine, amphibole, fluorite, calcite, and barite. Fluid inclusions from
monazite-(Ce), bastnasite-(Ce), apatite, aegirine, fluorite, and barite
were studied from eight samples to provide new constraints on ore genesis. During early disseminated monazite mineralization the
fluids are best represented by the system H 2 O-CO 2 -NaCl,
with salinities ranging from 1 to 5 wt percent NaCl equiv and X (CO 2 ) values from 0.3 to 0.45, at temperatures of >280° to 330°C and
pressures of >0.7 kbar. Fluids in apatite and bastnasite from the
main-stage banded ores were initially aqueous, with salinities ranging from
6 to 10 wt percent NaCl equiv. They developed significant CO 2 contents (X (CO 2 ) = 0.1–0.3) due to carbonate dissolution at
temperatures of >400° to ~300°C and pressures of >0.9 to 1.4 kbars.
Evidence for phase separation from coexisting brine and CO 2 -rich
fluid inclusions in vein fluorite indicates pressures of 0.8 to 1.0 kbar
during vein formation. These pressures can be used to infer temperatures of
430° to 460°C for aegirine alteration and of 340° to 240°C for apatite,
bastnasite, and fluorite vein fill. Fluids responsible for aegirine
alteration were dominantly aqueous, with salinities from 5 to 15 wt percent
NaCl equiv, whereas those responsible for apatite and bastnasite
mineralization had salinities of 1 to 6 wt percent NaCl equiv and X (CO 2 ) values from 0.25 to 0.75. Inclusions in late-stage fluorite and barite have
homogenization temperatures from 240° to 150° and 200° to 130°C,
respectively. The general salinity trend in these inclusions suggests
dilution from around 15 to 5 wt percent NaCl equiv down to very low
salinities (<1 wt % NaCl equiv) during barite precipitation.
Halite-bearing inclusions may indicate episodes of boiling or
aqueous-carbonic fluid immiscibility. These fluids are similar to those in some carbonatitic,
alkaline igneous, and other igneous-related REE- and Fe-rich magmatic
hydrothermal systems. However, they are different from fluids in
igneous-related Fe oxide-Cu-Au-U-REE deposits, which have previously been
compared to those at Bayan Obo.
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