Low Ga Content Research Articles

Investigation of Wetting Behavior and Brazing Reliability of Zn-15Al-xGa Filler Metals in Cu/Al Joints

Ga elements with different contents (0.1-1.5wt.%) were melted into the Zn-15Al filler metal to change the microstructure and thus improve the properties of the Cu/Al joints. The results showed that the addition of Ga element reduced the solidus and liquidus temperatures as well as the surface tension of the Zn-15Al filler alloy. Low concentrations of Ga (≤0.5wt%) can effectively increase the wettability of the filler metal. With increasing Ga addition amount, the size and proportion of the CuAl2 phase within the Cu/Zn-Al/Al brazed joint microstructure were increased, and also guided the transformation of the interfacial constituent phases on the Cu side interface from Al4.2Cu3.2Zn0.7/Al3Cu5Zn2 to Al4.2Cu3.2Zn0.7/CuAl2/Al3Cu5Zn2, which effectively adjusted the crack propagation path and increased the shear strength during the fracture process of the shear strength test on the brazed joint. The shear strength test results indicated the Cu/Zn-Al-0.5Ga/Al joint have the highest shear strength (85.8MPa, 15% improvement over the Cu/Zn-Al/Al joint). Consequently, appropriate Ga addition (0.5wt%) enhanced both the meltability and wettability of Zn-15Al filler metal, which was suitable for obtaining high-quality Cu/Al brazed joints.

Fluorescent sphalerite rich in tungsten, copper, gallium, silver, and other elements from the Cordilleran-style, polymetallic veins of Philipsburg, Montana

Sphalerite from the central, high-sulfidation zone (enargite-stable) of the Philipsburg polymetallic mining district, southwest Montana, displays unusually bright fluorescence (red, orange, yellow, blue, purple, green) under longwave UV light (365 nm). LA-ICP-MS analysis reveals the fluorescent sphalerite has very low Fe (average < 100 ppm) and variable content of other trace elements that correlate to luminescence color banding. Mean/maximum content (in ppm) in fluorescent sphalerite for selected elements are 5.7/7900 Ag, 107/11800 As, 1400/4730 Cd, 917/30400 Cu, 381/5000 Ga, 32/696 Ge, 119/2130 In, 230/8190 Mn, 43/3000 Pb, 16/1700 Sb, and 89/1980 W. This study is the first to document elevated tungsten content (>10 ppm) in sphalerite. Copper is closely correlated with Ga, consistent with the coupled substitution: Cu+ + Ga3+ = 2Zn2+. Similar coupled substitution reactions can be written for Ag+, In3+, As3+, Sb3+, Bi3+, and Ge4+. However, the brightest red fluorescent bands are most closely related to the unexpected presence of W. Sphalerite with high Cu and Ga but lacking W fluoresces yellow and shows a single Raman peak at 349 cm−1 corresponding to pure sphalerite. In contrast, red-fluorescent sphalerite shows the presence of a second peak at 427 cm−1 that increases in intensity with increased W content. We propose that tungsten enters the sphalerite lattice as W6+ via a substitution such as W6+ + 4Cu+ = 5Zn2+ and that this substitution creates lattice strain that results in the anomalous fluorescence and Raman signals. Sphalerite bands with low concentrations of Cu and Ga fluoresce blue or green. Vivid blue fluorescence is displayed by sphalerite with high Cd (>1000 ppm) but low concentrations of all other trace elements. Sphalerite from the low-sulfidation peripheral mines of the Philipsburg district contains high Fe (>10,000 ppm) and does not fluoresce. Nonetheless, this sphalerite is also highly enriched in trace metals, including Ag (mean 2480/max 8660 ppm), Cu (1610/3440), Mn (7020/8100), and Sb (1960/6390). The results of this study underscore the importance of including tungsten in the list of analytes in future studies of trace elements in sphalerite. In addition, a hand-held UV lamp may be a rapid and cost-effective method to screen sphalerite of variable composition in outcrop or drill core. It may be a useful exploration tool to vector towards a high-sulfidation zone of a zoned porphyry or epithermal deposit, when it is present.

Tracking the global anthropogenic gallium cycle during 2000–2020: A trade-linked multiregional material flow analysis

Byproduct metals are essential to global low carbon transition since they are irreplaceable in modern renewable energy technologies. Gallium (Ga) is classified as one critical byproduct metal due to its extensive use in electronic applications and low carbon technologies, as well as its limited resource endowment. It is urgent to uncover the global and regional Ga stocks and flows so that the potential supply risks can be mitigated. This study maps the global and regional Ga cycles for the period of 2000–2020 by employing a trade-linked multiregional material flow analysis (MFA) method. Our results show that 79% of the global Ga co-mined from bauxite ended up in red mud or entered the aluminum cycle as an impurity, indicating a significant recycling potential. Different involved regions have different but complementary roles in the global Ga supply chain. China dominates the global primary Ga production, accounting for 97% of the global total in 2020. Japan and the United States are key players in high-purity Ga refining and rely on Ga to support their electronic devices manufacturing. Unfortunately, Ga recycling practices are still not occurring due to the low Ga concentrations in major applications. Since the global demand for Ga will continue to grow in the near future, it is urgent to initiate collaborative efforts so that Ga recycling can be enhanced. These efforts are critical to ensure the sustainable Ga supply and facilitate the global transition toward low carbon development.

The Enhanced Performance of Oxide Thin-Film Transistors Fabricated by a Two-Step Deposition Pressure Process.

It is usually difficult to realize high mobility together with a low threshold voltage and good stability for amorphous oxide thin-film transistors (TFTs). In addition, a low fabrication temperature is preferred in terms of enhancing compatibility with the back end of line of the device. In this study, α-IGZO TFTs were prepared by high-power impulse magnetron sputtering (HiPIMS) at room temperature. The channel was prepared under a two-step deposition pressure process to modulate its electrical properties. X-ray photoelectron spectra revealed that the front-channel has a lower Ga content and a higher oxygen vacancy concentration than the back-channel. This process has the advantage of balancing high mobility and a low threshold voltage of the TFT when compared with a conventional homogeneous channel. It also has a simpler fabrication process than that of a dual active layer comprising heterogeneous materials. The HiPIMS process has the advantage of being a low temperature process for oxide TFTs.

Gallium distribution in the Dulong Sn polymetallic deposit, SW China

The Dulong Sn polymetallic deposit is located in the SE Yunnan-West Guangxi ore province, and represents one of the three largest cassiterite-sulfide deposits in China. The deposit is a potential gallium (Ga) deposit in China with abundant tin and zinc resources. However, the occurrence of Ga in the deposit and the control on its mineralogy are still poorly understood. Here, we provide a detailed account of the gallium distribution in silicate, oxide, and sulfide minerals at Dulong, based on field geological and petrographic observations and geochemical analysis. Gallium is mainly hosted in Al-rich minerals, such as muscovite (avg. 139 ppm), biotite (avg. 86.8 ppm), and feldspar (avg. 21.3 ppm), in the ore-related granite. This distribution behavior of gallium is consistent with its predicted partitioning between the phenocrysts and melt. In the Sn ore, chlorite has high Ga content (avg. 104 ppm), probably caused by the gallium tends to form hydroxyl complexes. In contrast, pyroxene and sphalerite have low Ga content (avg. 1.24 and 1.50 ppm, respectively). Meanwhile, two types of magnetite (Mag-I and Mag-II) have been identified based on mineral paragenesis: Mag-I is mainly associated with sphalerite. It is porous, with the pores filled with Ga-rich aluminosilicates (e.g., chlorite), and has high Ga content (avg. of 18.3 ppm). Mag-II is mainly associated with sphalerite, pyrrhotite, and chalcopyrite, and has low Ga (avg. 1.34 ppm). The dissolution of Ga-rich aluminosilicates in magnetite likely provided gallium to magnetite, resulting in higher Ga content in Mag-I. The magnetite Ga content decrease with increasing distance from the mineralization center, and the magnetite mineralization temperature also shows a similar trend. This study confirms that the dominant substitution for Ga in muscovite is Ga3+ ↔ Al3+, and in magnetite it is Ga3+ ↔ Mn2+ + Me+ and Ga3+ ↔ Cu+ + Zn2+. Most of the Ga is hosted in chlorite and magnetite in the highly chloritized sulfide ore at Dulong, which is a critical factor that can significantly affect the estimation of economically recoverable by-product elements in the sulfide ore.

Coordination of growth and drought responses by GA-ABA signaling in rice.

The drought caused by global warming seriously affects the crop growth and agricultural production. Plants have evolved distinct strategies to cope with the drought environment. Under drought stress, energy and resources should be diverted from growth toward stress management. However, the molecular mechanism underlying coordination of growth and drought response remains largely elusive. Here, we discovered that most of the gibberellin (GA) metabolic genes were regulated by water scarcity in rice, leading to the lower GA contents and hence inhibited plant growth. Low GA contents resulted in the accumulation of more GA signaling negative regulator SLENDER RICE 1, which inhibited the degradation of abscisic acid (ABA) receptor PYL10 by competitively binding to the co-activator of anaphase-promoting complex TAD1, resulting in the enhanced ABA response and drought tolerance. These results elucidate the synergistic regulation of crop growth inhibition and promotion of drought tolerance and survival, and provide useful genetic resource in breeding improvement of crop drought resistance.

Significant coercivity enhancement of Ga-doped sintered Nd-Fe-B magnet by grain boundary diffusion perpendicular to the c-axis

Grain boundary diffusion (GBD) process is the most effective approach for enhancing coercivity of Nd-Fe-B magnets with minimal consumption of heavy rare earth (HRE). However, understanding of GBD mechanism is still limited, especially on the anisotropic diffusion behavior within sintered magnets. Grain boundary (GB) phase is the key factor in determining the diffusion process, which acts as diffusion channel for HRE atoms. The effects of doping Ga on the grain boundary microstructure and diffusion behavior of Tb in the sintered Nd-Fe-B magnet were investigated. Sintered magnets with different Ga content (0.15 wt%, 0.45 wt%) were prepared. It should be noted that Tb was diffused perpendicular to the easy axis (c-axis) of the magnets. The coercivity increased more significantly to 2.802 T (1.006 T higher than that of the post-sinter annealed state) in magnets with high Ga content than the low Ga content magnets (2.291 T, 0.669 T higher than the post-sintered annealed state). Such a huge coercivity increment almost reached the same value by diffusing Tb along the easy axis reported by other researchers. Chemical compositions and microstructure of the GB phase were found to be key factors in influencing the HRE diffusion process. A considerable amount of Nd6Fe13Ga phase was observed near triple junctions after post-sinter annealing in the high Ga content magnets, which markedly decreased Fe concentration in the intergranular phase. In addition, amorphous intergranular metallic Cu-rich phases provided smooth diffusion channels for HRE atoms. (Nd1-x, Tbx)2Fe14B shell was much more obvious in the high Ga content magnets. Ga dopping induced novel modifications in diffusion behavior of HRE atoms and strongly influenced the magnetic properties of permanent magnets. The present approach provide new path for the manufacture of high performance magnets, which is interesting both for technical applications and fundamental studies.

A first look at the gallium-aluminium systematics of Early Earth’s seawater: Evidence from Neoarchean banded iron formation

Geochemical proxies archived in banded iron formations (BIFs) can provide information on the physico-chemical conditions in the Precambrian atmosphere-hydrosphere system and the element sources to ambient Early Earth’s seawater. We here report results of the first investigation of the Ga-Al systematics of BIFs and use adjacent magnetite and metachert bands of the well-studied and very pure 2.7 Ga-old Temagami BIF in Ontario, Canada, in an attempt to test the suitability of the Ga/Al ratio as a geochemical proxy. Due to very low Ga concentrations in BIFs and multiple mass interferences on the stable isotopes 69Ga and 71Ga, we conducted comparative analyses of dissolved samples with sector-field (SF-)ICP-MS and tandem ICP-MS/MS as well as laser-ablation (LA-)SF-ICP-MS on nano-particulate pressed powder tablets (NP tablets). The unexpected results indicate uniform Ga/Al weight ratios between 2.0×10−4 and 7×10−4 for the Temagami BIF, i.e. Ga/Al ratios that are slightly above those of potential clastic detritus but well below those of modern seawater or marine hydrothermal fluids. Consistent results from solution SF- and ICP-MS/MS and a two-component mixing experiment with BIF reference material IF-G and synthetic pure quartz sand corroborate the high analytical quality of these Ga and Al data. The Ga/Al ratios of the metachert bands show the same range of Ga/Al ratios as the magnetite bands and appear to be dominated by small amounts of finely dispersed Fe oxide particles that were deposited together with the chert. The Ga/Al ratios of the magnetite bands either suggest that (in contrast to other trace elements such as the rare earth elements and Y) Ga and Al were fractionated from each other during scavenging from Archean seawater by Fe (oxyhydr)oxides or that ambient Temagami seawater had significantly lower Ga/Al ratios than modern seawater, possibly due to different weathering, riverine, and estuarine processes in the Archean. While these first results demonstrate the potential of Ga-Al systematics as an additional geochemical tool for studies of Early Earth, they also reveal the knowledge gaps that still need to be addressed in future investigations.

The Parameters of the Hyperfine Structure of 57Fe Nuclei in FeBO3 and Fe0.91Ga0.09BO3 Single Crystals

The parameters of the hyperfine interaction of 57Fe nuclei in single crystals of iron borate FeBO3 and its isostructural solid solution Fe0.91Ga0.09BO3 have been determined by Mössbauer spectroscopy. A theoretical model has been developed to describe resonant transitions of iron nuclei in the approximation of a combined magnetic dipole and electric quadrupole hyperfine interaction, taking into account the statistical distribution of Ga and Fe over octahedral positions in the Fe0.91Ga0.09BO3 crystal. It has been established that even a low Ga concentration leads to a significant change in the hyperfine structure of the 57Fe nuclei inFeBO3, which manifests itself in the appearance of additional components in the Mössbauer spectra of the Fe0.91Ga0.09BO3 single crystal.

Effects of Calcium Ions on the Antimicrobial Activity of Gramicidin A.

Gramicidin A (gA) is a linear antimicrobial peptide that can form a channel and specifically conduct monovalent cations such as H+ across the lipid membrane. The antimicrobial activity of gA is associated with the formation of hydroxyl free radicals and the imbalance of NADH metabolism, possibly a consequence caused by the conductance of cations. The ion conductivity of gramicidin A can be blocked by Ca2+ ions. However, the effect of Ca2+ ions on the antimicrobial activity of gA is unclear. To unveil the role of Ca2+ ions, we examined the effect of Ca2+ ions on the antimicrobial activity of gramicidin A against Staphylococcus aureus (S. aureus). Results showed that the antimicrobial mechanism of gA and antimicrobial activity by Ca2+ ions are concentration-dependent. At the low gA concentration (≤1 μM), the antimicrobial mechanism of gA is mainly associated with the hydroxyl free radical formation and NADH metabolic imbalance. Under this mode, Ca2+ ions can significantly inhibit the hydroxyl free radical formation and NADH metabolic imbalance. On the other hand, at high gA concentration (≥5 μM), gramicidin A acts more likely as a detergent. Gramicidin A not only causes an increase in hydroxyl free radical levels and NAD+/NADH ratios but also induces the destruction of the lipid membrane composition. At this condition, Ca2+ ions can no longer reduce the gA antimicrobial activity but rather enhance the bacterial killing ability of gramicidin A.

Volatile evolution of magmas associated with the Bairong deposit, Tibet, and implications for porphyry Cu-Mo mineralization

Volatiles are considered to play an important role in porphyry Cu mineralization, and high apatite S and Cl contents are often used to distinguish fertile magma systems from barren ones in the subduction zone. However, magmatic volatile evolution and its implications in post-collisional porphyry deposits remain enigmatic. To address this issue, we conducted zircon U-Pb dating and Hf isotope, and zircon and apatite chemical compositions of multi-stage magmatic rocks from the Bairong post-collisional porphyry Cu-Mo deposit in the Gangdese belt, Tibet. The magmatic rocks included pre-mineralized porphyritic monzogranite and biotite monzogranite, syn-mineralized monzogranite porphyry, and post-mineralized dacite porphyry that formed in 14.1–12.7 Ma, ca. 12.1 Ma, and 11.8–11.6 Ma, respectively. All these intrusions have depleted zircon Hf isotope (εHf(t) = 1.7–8.0, 3.7–9.0, 3.3–9.7 for pre-, syn-, and post-mineralized intrusions, respectively) together with the research results of contemporaneous magmatic rocks in the adjacent area, suggesting that the multi-stage intrusions at Bairong are derived from a cogenetic magma chamber in post-collisional extension setting. All the intrusions have similar zircon CeN/CeN*, EuN/EuN* ratios with average ΔFMQ values of 2.1 – 2.6, together with the high apatite EuN/EuN* ratios and low Ga concentrations, implying that their magmas are all oxidized. These intrusions have zircons (10,000 × EuN/EuN*) /Y all > 1 and Ce/Nd/Y mostly > 0.01, and obtain low average titanium-in-zircon temperatures of 659 to 714 °C, which indicate their magmas are hydrous. Apatite Cl contents decrease, combined with the drop of apatite XCl/XOH and the surge of XF/XCl ratios from pre- to syn-mineralized intrusions, possibly indicating that fluid exsolved from magma at the syn-mineralization stage. The apatite SO3 contents in these different-stage intrusions, however, are almost unchanged. Combined with previous studies, the buffering effect of magmatic anhydrite maintains the stability of magma S content, which together with fluid exsolution leads to the S-Cl decoupling. Consequently, we conclude that the oxidized and hydrous magma with effective fluid exsolution is a critical control on the formation of Bairong porphyry Cu-Mo mineralization. Considering the wide variations of apatite Cl contents and the occurrences of S-Cl decoupling, simple application of high apatite SO3 and Cl contents to distinguish the ore-forming and barren systems in the post-collisional porphyry system should be cautious.

Spectroscopic Characterizations of Porous Mixed Metal Oxides Derived from Metal–Organic Framework MIL-53(Ga, Al) for Propane Dehydrogenation

The structure and properties of porous mixed metal oxide catalysts (GaxAl2–xO3 and Pt/GaxAl2–xO3) derived from calcination treatment of bimetallic MIL-53(Ga, Al) precursors were comprehensively characterized using XRD, N2 adsorption–desorption isotherms, TEM, and solid-state NMR. Both Ga and Pt species are highly dispersed in Pt/Ga0.1Al1.9O3 and Pt/Ga0.5Al1.5O3 catalysts with low Ga content, whereas Ga2O3 particles are present in Ga1.0Al1.0O3 and Ga1.5Al0.5O3 catalysts with high Ga content. Well-mixed Al and Ga species in the calcined Ga0.1Al1.9O3 and Ga0.5Al1.5O3 samples are identified from 1H–71Ga S-RESPDOR and 1H–27Al TRAPDOR NMR experiments. The coordination states and relative amounts of Al and Ga species in the MIL-53(Ga, Al) derivatives are determined by 27Al and 71Ga MAS NMR measurements. It is found that Pt species are readily anchored with pentacoordinate Al, favoring the formation of tetrahedral GaIV species, and the synergy between highly dispersed Pt and tetrahedral GaIV active species in Pt/Ga0.1Al1.9O3 and Pt/Ga0.5Al1.5O3 catalysts renders their superior catalytic performance with high conversion and good recyclability toward the propane dehydrogenation reaction.

Trace elements in sulfide minerals from the Huangshaping copper-polymetallic deposit, Hunan, China: Ore genesis and element occurrence

The Huangshaping copper-polymetallic deposit, which is located in southern Hunan Province, China, is an important resource base for Pb–Zn minerals. This study used the major sulfides (sphalerite, pyrite, pyrrhotite), which formed during the Pb–Zn mineralization stage of the Huangshaping deposit, to determine the genesis of the Pb–Zn ore minerals and element occurrence. In-situ LA-ICP-MS analysis of minerals was conducted to determine their trace element concentrations and reveal the distribution and occurrence of trace elements in different sulfides. The formation temperature and genesis of the Pb–Zn ore minerals were also constrained based on the deposit geology and trace element data. Trace elements were significantly different among different sulfides in the Pb–Zn mineralization stage of the deposit. Sphalerite primarily enriches Mn, Cu, Ag, Sn, and Pb and is the main carrier mineral of Ga, In, and Cd. Pyrite relatively enriches Tl, Sb, W, and Se, and pyrrhotite primarily enriches Ge. In sphalerite, Fe, Mn, Cd, Ga, In, Cu, Sn, Ag, and Ge exist by substituting for other elements (such as Zn). The replacement method of Ge is Ge4++2Cu+↔3Zn2+, whereas that of In (Ga) is In3+(Ga3+) + Cu+↔2Zn2+. In pyrrhotite, Ge is incorporated through coupling substitution, and the abnormal concentrations of Pb, Ag, and Se are caused by galena that has replaced pyrrhotite. In pyrite, W occurs as a solid solution. When galena replaces pyrite, it causes abnormal concentrations of Pb, Tl, Sb, and Ag. The sphalerite is characterized by high concentrations of high-temperature ore-forming elements (e.g., Fe, Mn, In, and Sn) and relatively low concentrations of Cd, Ge, Ga, and other elements. Thus, the sphalerite was formed at a medium–high temperature (288–341 °C). The trace element characteristics of sphalerite are consistent with those of high-temperature hydrothermal deposits. The deposit geology, pyrite Co/Ni ratio (averaging 0.13, n = 29), S/Se ratio (averaging 173,905, n = 19), pyrrhotite Co/Ni ratio (averaging 0.10, n = 26), and binary diagram of trace elements in sphalerite indicate that Pb–Zn mineralization is related to the late-stage hydrothermal activity of skarn mineralization. The Pb–Zn mineralization and W–Mo(Fe) mineralization together constitute a skarn-type mineralization system.

Epicotyl morphophysiological dormancy in seeds of Paeonia ostii (Paeoniaceae): Seasonal temperature regulation of germination phenology

Paeonia is one of the most popular ornamental plants in temperate regions, and its seeds have epicotyl dormancy. Our primary aim was to determine the sequence of temperatures required for radicle and shoot emergence in seeds of P. ostii and how these two distinct stages of dormancy-break are correlated with natural seasonal temperature changes. We tested the effects of various temperature regimes and sequences of regimes on growth of the underdeveloped embryo inside the seed, radicle emergence and shoot growth in the laboratory and germination responses to temperature under natural temperatures in an experimental garden and analyzed ABA and GA concentrations during the dormancy-breaking process. Prior to radical emergence, embryo length increased c. 330%. Embryo elongation and radicle emergence occurred in early October following seed dispersal in summer. The epicotyl-plumule did not differentiate until after embryo growth was completed and the radicle had emerged. Cold stratification was required to break epicotyl dormancy; consequently, shoot emergence did not occur until February when the temperature began to increase. Thus, seed dormancy break in P. ostii is phenologically well adapted to the seasonal cycle of the temperate zone. ABA and GA analyses suggest that root dormancy might be due to high ABA content and shoot dormancy to low GA content. • Seeds of Paeonia ostii have deep simple epicotyl morphophysiological dormancy. • The plumule does not differentiate until embryo growth is competed. • Radicle emergence occurs only at warm temperatures in autumn. • Shoots emerge only in spring in root-emerged seeds that have been cold stratified. • The timing of dormancy-break is regulated by changes in seasonal temperatures.

Linking uplift and mineralisation at the Mount Novit Zn-Pb-Ag Deposit, Northern Australia: Evidence from geology, U–Pb geochronology and sphalerite geochemistry

The subeconomic Mount Novit Zn-Pb-Ag deposit is located approximately 20 km south of Mount Isa, Queensland. In contrast to the nearby Mount Isa, Hilton and George Fisher Zn-Pb-Ag deposits, mineralisation at Mount Novit is situated to the west of the regional-scale Mount Isa Fault and is hosted in the Moondarra Siltstone as opposed to the Urquhart Shale. Lower-grade (<4 wt.% Zn + Pb) Zn-Pb-Ag mineralisation primarily replaces pre-existing carbonate alteration and veining and consists of pyrrhotite, pyrite and sphalerite with lesser galena. Higher-grade (>10 wt.% Zn + Pb) mineralisation occurs as a matrix supported breccia dominated by sphalerite and pyrrhotite with galena, pyrite, and magnetite. In-situ U–Pb geochronology was completed on apatite and two textural varieties of monazite. Fine-grained (<50 µm) subhedral to anhedral monazite is located within highly foliated biotite alteration directly adjacent Zn-Pb-Ag mineralisation and yields a mean weighted 207Pb/206Pb age of 1527 ± 18 Ma (MSWD = 1.06). This age is consistent with the formation of highly foliated biotite alteration during D3 deformation of the Isan Orogeny. Apatite from the same fabric yields a lower intercept age of 1443 ± 29 Ma (MSWD = 1.30). Consistent with previous studies, this age is interpreted to represent the age of a major thrusting event along the Mount Isa Fault that resulted in the cooling of the Mount Novit area below ∼375 °C. Coarse-grained monazite is coeval with Zn-Pb-Ag mineralisation and yields a mean weighted 207Pb/206Pb age of 1457 ± 11 Ma (MSWD = 0.28). Sphalerite from Mount Novit has low concentrations (<1 ppm) of Ge and Ga and a relatively high concentration of In (5 to >10 ppm), possibly reflecting the leaching of the metals from an underlying basement unit. The GGIMFis geothermometer (Frenzel et al., 2016) produced a mean formation temperature of 345 ± 52 °C. The timing and temperature of Zn-Pb-Ag mineralisation is consistent with the age and cooling temperature of apatite presented in this study. Based on these correlations, we suggest that Zn-Pb-Ag mineralisation at Mount Novit was emplaced during an episode of major thrusting along the Mount Isa Fault, with the precipitation of Zn-Pb-Ag mineralisation driven by the cooling of the Mount Novit area below ∼375 °C. A key implication of this study is a new model for synorogenic Zn-Pb-Ag mineralisation to the south of Mount Isa, which contrasts with the widely accepted regional-scale syngenetic metallogenic model.

Phase stability and phase transformations in Al-Pd-Mn quasicrystalline alloys with low-Ga content

Gallium having low surface energy (∼ 600 mJ/m2) and low melting temperature (29.76 °C), was utilized to substitute Al in Al-Pd-Mn quasicrystalline alloys, which may be considered for future development of a quaternary QC alloy with low surface energy. The influence of Ga up to 5 at% in decagonal Al70-XGaXPd10Mn20 (x = 0, 2.5, 5.0) alloys on the stability of decagonal phase was investigated systematically. The surface morphology and phase stability were studied in as-cast (slow cooling from liquid) and also in annealed condition (i.e., annealing at temperature 800 °C for 24 h). It is observed that Ga influences the stability of decagonal phase and the evolution of microstructure. The phase transformation from the mixed icosahedral and decagonal quasicrystal phases coexisting in as-cast Al70-XGaXPd10Mn20 (x = 0, 2.5, 5.0) alloys to a single decagonal quasicrystalline phase was observed on annealing, implying relative phase stability of quaternary decagonal phase around these compositions.

Metallographic Cooling Rate and Petrogenesis of the Recently Found Huoyanshan Iron Meteorite Shower

AbstractThe Huoyanshan iron meteorite shower, recently found in the Gobi Desert of Hami, Xinjiang, China, has very high Ni (21.1 wt%) content and low Au (2.0 ppm), Ir (0.02 ppm), Ge (1.7 ppm), and Ga (1.1 ppm) contents, and was classified into IAB‐sLH subgroup. The iron has a finest octahedrite structure of Widmanstätten pattern (the intergrowth of kamacite [α] and taenite [γ]) with plessite matrix, and euhedral schreibersite (Sch) crystals exclusively enclosed in kamacite bands. The textural features suggest the following formation process: γ→γ + Sch→γ + Sch + α, and then γ→α2 + γ. The metallographic cooling rate of Huoyanshan iron was determined to be 3–50°C/Myr using both the taenite Ni profile‐matching and taenite central Ni content methods, with the bandwidths corrected for crystallographic orientation by electron backscatter diffraction (EBSD). The cooling rate of Huoyanshan is consistent with other sLH irons and confirms the slow cooling history of the IAB low‐Au subgroups. These slow cooling rates require immediate re‐accretion with a thick brecciated fragments layer in the parent body after the impact melting event. The depleted but unfractionated Re, Os, Ir, Ru, and Pt and the enriched Pd and Au abundances of Huoyanshan iron and other sLH subgroup irons show complementary feature to that of refractory metal nuggets in Ca‐, Al‐rich inclusions (CAIs), which could be explained by extracting the metallic Fe‐Ni with HSE predominantly remained in CAIs from a CAI‐bearing asteroid. The very high Ni content of sLH subgroup and its Mo isotope evidence (Worsham et al., 2017, https://doi.org/10.1016/j.epsl.2017.02.044) suggest it has an oxidized parent body with non‐carbonaceous chondrite‐like precursor composition. We propose that the sLH subgroup was produced by impact melting of a LL like and CAI‐bearing asteroid, followed by fast burying of thick and porous silicate breccia.

Red Light and the Dormancy-Germination Decision in Arabidopsis Seeds.

The Arabidopsis dormancy-germination transition is known to be environmentally cued and controlled by the competing hormones abscisic acid (ABA) and gibberellin (GA) produced by the seed. Recently, new molecular details have emerged concerning the propagation of red light through a complex gene regulatory network involving PhyB, PIF1, and RVE1. This network influences the formation of the PIF1-RVE1 complex [1,2]. The PIF1-RVE1 complex is a transcription factor that regulates the production of ABA and GA and helps shift the balance to high concentration of ABA and low concentration of GA, which corresponds to a dormant seed state. This newly discovered gene regulatory network has not been analyzed mathematically. Our analysis shows that this gene regulatory network exhibits switch-like bistability as a function of the red light input and makes a suite of biologically testable predictions concerning seed dormancy and germination in response to the amplitude and periodicity of an oscillatory red light input.

Fe13Ga9 intermetallic in bcc-base Fe–Ga alloy

Fe−Ga alloys (Galfenols) are of interest due to their pronounced magnetostriction, whereby the mechanistic understanding is limited. By means of powder X-ray and neutron diffraction it is shown that as-cast Fe-38.4 at%Ga alloy consists of Fe13Ga9 intermetallic with a monoclinic Ni2In/NiAs-related structure, which coexists with bcc solid solution. By means of electron backscatter diffraction it is shown that the Fe13Ga9 intermetallic develops with two different but closely related orientation relationships with respect to the matrix, which can be derived by the relation between the atomic structures of Fe13Ga9 and the matrix. First principles calculations reveal that Fe13Ga9 should be stable at 0 K and that this phase may also expected to develop in alloys for lower Ga contents and may have to be considered upon interpreting macroscopically observed magnetostriction.

Agates from Paleoproterozoic Volcanic Rocks of the Onega Structure, Central Karelia

Agate mineralization in Central Karelia, Northwest Russia is related to the Paleoproterozoic volcanic rocks of the Ludicovian Superhorizon (2.05–1.95 Ga) within the Onega structure. Agates and parental volcanic rocks were studied with optical and electron microscopy, electron microprobe, X-ray diffraction, Raman spectroscopy, and ICP-MS. It is shown that fine-grained quartz, and fibrous and fine-flake chalcedony are the major minerals in the agate structure. Inclusions of coarse-crystalline calcite, and microinclusions of chlorite, iron oxides and hydroxides, hydroxylapatite, epidote, mica (phengite), apatite, pyrite, chalcopyrite, titanite, and leucoxene are present in agates. The presence of contrast rhythms within agate amygdules is marked by compositional variation in impurity mineral phases and different microtextures of silica layers represented by different-grained aggregates of quartz, fine-flake and fibrous chalcedony, and quartzine. This indicates stage-by-stage mineral crystallization at variable temperatures and pressures during agate formation, which may also reflect the heterogeneity of the initial hydrothermal fluid. High concentrations of Ti, Cr, Mn, Ni, and Cu (10–120 ppm) and the low concentrations of Li, Co, Ga, Zn, Sr, Zr, Mo, and Sn (0.5–10 ppm) are characteristic of quartz–chalcedony agates. Calcite in agates is characterized by high concentrations of Mn (1253–6675 ppm), Sс, Ti, Ni, Sr, Y, La, Ce, and Nd (5–56 ppm). The chondrite-normalized REE distribution pattern in agates shows a decay profile from La to Lu and a negative Eu anomaly in some samples. Low contents of rare metals and REE in agates compared to parental volcanic rocks indicate a gradual chemical depletion of circulating fluids during agate formation.