Petrogenesis of Pyroxenites and Melt Infiltrations in the Ultramafic Complex of Beni Bousera, Northern Morocco

The origin of pyroxenites and their relation to melt migration in the mantle have been investigated in two pyroxenite-rich zones in the Beni Bousera massif. Based on combined field, microtextural, mineralogical and geochemical observations, the pyroxenites were separated into four types. Type-I Cr-diopside websterites contain bright green diopside and have primitive bulk Ni, Cr and Mg-number. Their trace element systematics are characterized by slight light rare earth element (LREE) enrichment compared with the middle (MREE) and heavy (H)REE, and negative high field strength element (HFSE) anomalies in bulk-rock and mineral compositions suggesting that they result from melting of metasomatized mantle. Trace element concentrations of melts calculated to be in equilibrium with Type-I cpx have a subduction-like signature and show a close similarity to certain lavas erupted in the Alboran Basin. Calculated mineral equilibration temperatures of ∼1200 to 1350°C are close to the basalt liquidus and higher than for other pyroxenite types in Beni Bousera, which generally yield 45 to 20-30 kbar. Type-III pyroxenites display strong variations of LREE and HFSE depletion and strong bulk Nb/Ta fractionation. Calculated melts in equilibrium with augitic cpx are variably enriched in incompatible trace elements similar to intraplate basalts. Type-IV pyroxenites are composed of green diopside, opx, garnet and plagioclase and/or spinel. Whole-rocks have high Na2O, CaO and Al2O3 concentrations and high Mg-number, are HREE depleted, and have positive Eu and Sr anomalies. Garnets are characterized by low HREE/MREE and positive Eu anomalies. The absence of bulk-rock HREE enrichment indicates a metamorphic origin for this garnet, which is corroborated by the presence of Al-rich metamorphic spinels. Relict magmatic plagioclase indicates a shallower (<10 kbar) crustal origin for these pyroxenites. Their metamorphic assemblage yields temperatures and pressures of 800-980°C and 14 kbar, indicating a pressure increase during the metamorphic overprint. The whole-rock geochemistry of Type-IV pyroxenites is comparable with that of rocks from the lower crustal section of the Kohistan (northern Pakistan) paleo-arc, indicating a possible origin of these rocks as cumulates in the deeper arc crust and subsequent delamination into the underlying mantl

Rare Earth Elements in Mineral Deposits: Speciation in Hydrothermal Fluids and Partitioning in Calcite

Studying the speciation and mineral-fluid partitioning of the rare earth elements (REE) allows us to delineate the key processes responsible for the formation of economic REE mineral deposits in natural systems. Hydrothermal REE-bearing calcite is typically hosted in carbonatites and alkaline rocks, such as the giant Bayan Obo REE deposit in China and potential REE deposits such as Bear Lodge, WY. The compositions of these hydrothermal veins yield valuable information regarding pressure (P), temperature (T), salinity, and other physicochemical conditions under which the REE can be fractionated and concentrated in crustal fluids. This study presents numerical simulation results of the speciation of REE in aqueous NaCl-H2O-CO2-bearing hydrothermal fluids and a new partitioning model between calcite and fluids at different P-T-x conditions. Results show that, in a high CO2 and low salinity system, bicarbonate/carbonate are the main transporting ligands for the REE, but predominance shifts to chloride complexes in systems with high CO2 and high salinity. Hydroxyl REE complexes may be important for the solubility and transport of the REE in alkaline fluids. These numerical predictions allow us to make quantitative interpretations of hydrothermal processes in REE mineral deposits, particularly in carbonatites, and show where future experimental work will be essential in improving our modeling capabilities for these ore-forming processes

Fluid Chemistry of Mid-Ocean Ridge Hydrothermal Vents: A Comparison between Numerical Modeling and Vent Geochemical Data

Seawater-basalt interaction taking place at mid-ocean ridges was studied using numerical modeling to determine the compositional evolution of hydrothermal fluids and associated alteration mineralogy forming within newly emplaced crustal material. Geochemical modeling was carried out in a closed seawater-basalt system at discrete temperature intervals between 2 and 400°C at 500 bars, varying fluid/rock ratios, and secondary mineral assemblages representative of basalt alteration in natural systems. In addition to temperature, the fluid/rock ratio has a fundamental control on the resulting system chemistry. At rock-buffered conditions (low fluid/rock ratios), the mineral-solution equilibrium was characterized by high cation to proton activity ratios for aCa2+/(aH+)2 and aNa+/aH+ and very low dissolved Mg concentrations due to the precipitation of smectites and chlorite. A complex secondary mineral alteration assemblage dominated by Ca- and Na-bearing minerals including zeolites, calcite, epidote, prehnite, clinozoisite, and albite was predicted to form. The resulting fluid composition was alkaline and reduced relative to ambient seawater, with Eh values ranging between −0.2 and −0.6 V. In contrast, seawater-buffered conditions (high fluid/rock ratios) resulted in lower cation to proton activity ratios for aCa2+/(aH+)2 and aNa+/aH+ and higher dissolved Mg concentrations comparable to the value of this element in ambient seawater. A more simple mineral assemblage was predicted to form at these conditions with the predominance of Al-Si- and Mg-bearing minerals including kaolinite, quartz, and talc in addition to large amounts of anhydrite. The resulting fluid composition was mildly acidic and oxidized relative to seawater with Eh values ranging between −0.2 and 0 V. These modeling results were compared to a compilation of submarine hydrothermal vent fluid compositions from mid-ocean ridge settings and analogous basalt-dominated environments. The agreement obtained between the simulations and the compiled fluid data indicates that mid-ocean ridge hydrothermal processes can be closely reproduced by mineral-solution equilibria for a broad range of temperatures and fluid/rock ratios

Petrogenesis of Pyroxenites and Melt Infiltrations in the Ultramafic Complex of Beni Bousera, Northern Morocco

ISSN:0022-3530ISSN:1460-241

Tellurium Transport and Enrichment in Volcanogenic Massive Sulfide Deposits: Numerical Simulations of Vent Fluids and Comparison to Modern Sea-Floor Sulfides

Volcanogenic massive sulfide deposits may represent a significant future source of Te, which is a critical element important for the green energy transition. Tellurium is enriched in these settings by up to 10,000 times over its crustal abundance, indicating that fluids in sea-floor hydrothermal systems may transport and precipitate Te. The major element composition of these hydrothermal fluids is controlled by fluid-rock interaction and is well documented based on experimental, modeling, and natural studies; however, controls on Te mobility are still unknown. To better understand Te enrichment in this deposit type, numerical simulations of the mafic-hosted Vienna Woods and the felsic-hosted Fenway sea-floor vents in the Manus basin were performed to predict Te mobility in modern sea-floor hydrothermal vent fluids and Te deposition during sulfide formation. These simulations demonstrate that the mobility of Te in sea-floor hydrothermal systems is primarily controlled by fluid redox and temperature. Tellurium mobility is low in reduced hydrothermal fluids, whereas mobility of this metal is high at oxidized conditions at temperatures above 250°C. Numerical simulations of the reduced vent fluids of the mafic-hosted Vienna Woods site at the back-arc spreading center in the Manus basin yielded Te concentrations as low as 0.2 ppt. In contrast, the more oxidized model fluids of the felsic-hosted Fenway site located on Pual Ridge in the eastern Manus basin contain 50 ppt Te. The models suggest that Te enrichment in these systems reflects rock-buffer control on oxygen fugacity, rather than an enriched source of Te. In fact, the mafic volcanic rocks probably contain more Te than felsic volcanic rocks. The association of elevated Te contents in the felsic-hosted Fenway system likely reflects magmatic volatile input resulting in lower pH and higher Eh of the fluids. More generally, analysis of sulfide samples collected from modern sea-floor vent sites confirms that redox buffering by the host rocks is a first-order control on Te mobility in hydrothermal fluids. The Te content of sulfides from sea-floor hydrothermal vents hosted by basalt-dominated host rocks is generally lower than those of sulfides from vents located in felsic volcanic successions. Literature review suggests that this relationship also holds true for volcanogenic massive sulfides hosted in ancient volcanic successions. Results from reactive transport simulations further suggest that Te deposition during sulfide formation is primarily temperature controlled. Modeling shows that tellurium minerals are coprecipitated with other sulfides at high temperatures (275°–350°C), whereas Te deposition is distinctly lower at intermediate (150°–275°C) and low temperatures (100°–150°C). These predictions agree with geochemical analyses of sea-floor sulfides as Te broadly correlates positively with Cu and Au enrichment in felsic-hosted systems. The findings of this study provide an important baseline for future studies on the behavior of Te in hydrothermal systems and the processes controlling enrichment of this critical mineral in polymetallic sulfide ores

Impact of sex and gender on post-COVID-19 syndrome, Switzerland, 2020.

Background Women are overrepresented among individuals with post-acute sequelae of SARS-CoV-2 infection (PASC). Biological (sex) as well as sociocultural (gender) differences between women and men might account for this imbalance, yet their impact on PASC is unknown. Aim We assessed the impact of sex and gender on PASC in a Swiss population. Method Our multicentre prospective cohort study included 2,856 (46% women, mean age 44.2 ± 16.8 years) outpatients and hospitalised patients with PCR-confirmed SARS-CoV-2 infection.ResultsAmong those who remained outpatients during their first infection, women reported persisting symptoms more often than men (40.5% vs 25.5% of men; p < 0.001). This sex difference was absent in hospitalised patients. In a crude analysis, both female biological sex (RR = 1.59; 95% CI: 1.41-1.79; p < 0.001) and a score summarising gendered sociocultural variables (RR = 1.05; 95% CI: 1.03-1.07; p < 0.001) were significantly associated with PASC. Following multivariable adjustment, biological female sex (RR = 0.96; 95% CI: 0.74-1.25; p = 0.763) was outperformed by feminine gender-related factors such as a higher stress level (RR = 1.04; 95% CI: 1.01-1.06; p = 0.003), lower education (RR = 1.16; 95% CI: 1.03-1.30; p = 0.011), being female and living alone (RR = 1.91; 95% CI: 1.29-2.83; p = 0.001) or being male and earning the highest income in the household (RR = 0.76; 95% CI: 0.60-0.97; p = 0.030). Conclusion Specific sociocultural parameters that differ in prevalence between women and men, or imply a unique risk for women, are predictors of PASC and may explain, at least in part, the higher incidence of PASC in women. Once patients are hospitalised during acute infection, sex differences in PASC are no longer evident