scholarly journals Relative Abundance and Compositional Variation of Silicates, Oxides and Phosphates in the W-Sn-Rich Lodes of the Panasqueira Mine (Portugal): Implications for the Ore-Forming Process

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 551 ◽  
Author(s):  
António Mateus ◽  
Jorge Figueiras ◽  
Ivo Martins ◽  
Pedro Rodrigues ◽  
Filipe Pinto
Keyword(s):  
Relative Abundance ◽  
Chemical Nature ◽  
Fault Zones ◽  
Compositional Variation ◽  
Early Cambrian ◽  
Forming Process ◽  
Mineral Deposition ◽  
World Class ◽  
Panasqueira Mine ◽  
Opening And Closing

Panasqueira is a world-class W-Sn-Cu lode-type deposit located in Portugal. It consists of a dense swarm of subhorizontal quartz lodes criss-crossed by several ENE–WSW and N–S fault zones, bordering Late Variscan granite and hosted in Late Ediacaran—Early Cambrian metasediments. The relative abundance and compositional variation (assessed with EPMA) of the main silicates, oxides and phosphates forming the quartz lodes and their margins were examined, aiming to explore: (i) mineral and geochemical zonation at the mine scale; and (ii) some conclusions on the chemical nature of prevalent fluid inflows and T-conditions of mineral deposition. Quartz lodes nearby or far from the known greisen-granite cupola display significant differences, reflecting multiple fluid influxes of somewhat distinct composition related to various opening and closing events extending for several My, ranging from an early “oxide–silicate stage” (OSS) to a “main sulfide stage” (MSS), and further on to a post-ore carbonate stage (POCS); however, a rejuvenation event occurred after MSS. The onset of OSS was placed at ca. 299 ± 5 Ma and the rejuvenation event at ca. 292 Ma. The OSS was confined to ≈500 ≤ T ≤ 320 °C, following rutile and tourmaline growth under ≈640 ≤ T ≤ 540 °C (depending on aSiO2). The rejuvenation event (≈440–450 °C) preceded a late chlorite growth (≈250–270 °C) and the progression towards POCS.

scholarly journals Compositional Variation of Eudialyte-Group Minerals from the Lovozero and Ilímaussaq Complexes and on the Origin of Peralkaline Systems

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 548
Author(s):  
Lia N. Kogarko ◽  
Troels F. D. Nielsen
Keyword(s):  
Linear Trend ◽  
Major And Trace Elements ◽  
High Tech ◽  
Compositional Variation ◽  
Elemental Distribution ◽  
Magma Chambers ◽  
Eudialyte Group ◽  
System A ◽  
Distribution Of Elements ◽  
World Class

The Lovozero complex, Kola peninsula, Russia and the Ilímaussaq complex in Southwest Greenland are the largest known layered peralkaline intrusive complexes. Both host world-class deposits rich in REE and other high-tech elements. Both complexes expose spectacular layering with horizons rich in eudialyte group minerals (EGM). We present a detailed study of the composition and cryptic variations in cumulus EGM from Lovozero and a comparison with EGM from Ilímaussaq to further our understanding of peralkaline magma chambers processes. The geochemical signatures of Lovozero and Ilímaussaq EGM are distinct. In Lovozero EGMs are clearly enriched in Na + K, Mn, Ti, Sr and poorer Fe compared to EGM from Ilímaussaq, whereas the contents of ΣREE + Y and Cl are comparable. Ilímaussaq EGMs are depleted in Sr and Eu, which points to plagioclase fractionation and an olivine basaltic parent. The absence of negative Sr and Eu anomalies suggest a melanephelinitic parent for Lovozero. In Lovozero the cumulus EGMs shows decrease in Fe/Mn, Ti, Nb, Sr, Ba and all HREE up the magmatic layering, while REE + Y and Cl contents increase. In Lovozero EGM spectra show only a weak enrichment in LREE relative to HREE. The data demonstrates a systematic stratigraphic variation in major and trace elements compositions of liquidus EGM in the Eudialyte Complex, the latest and uppermost part of Lovozero. The distribution of elements follows a broadly linear trend. Despite intersample variations, the absence of abrupt changes in the trends suggests continuous crystallization and accumulation in the magma chamber. The crystallization was controlled by elemental distribution between EGM and coexisting melt during gravitational accumulation of crystals and/or mushes in a closed system. A different pattern is noted in the Ilimaussaq Complex. The elemental trends have variable steepness up the magmatic succession especially in the uppermost zones of the Complex. The differences between the two complexes are suggested to be related dynamics of the crystallization and accumulation processes in the magma chambers, such as arrival of new liquidus phases and redistributions by mush melts.

Stable isotope geochemistry and palynology of the late Precambrian to Early Cambrian sequence in Newfoundland

1992 ◽  
Vol 29 (8) ◽  
pp. 1662-1673 ◽  
Author(s):  
Harald Strauss ◽  
Stefan Bengtson ◽  
Paul M. Myrow ◽  
Gonzalo Vidal
Keyword(s):  
Stable Isotope ◽  
Organic Carbon ◽  
Isotope Geochemistry ◽  
Depositional Environments ◽  
Early Cambrian ◽  
Bacterial Sulfate Reduction ◽  
Stable Isotope Geochemistry ◽  
Forming Process ◽  
Late Precambrian ◽  
Clastic Sediments

A sequence of clastic sediments in southeastern Newfoundland straddling the Precambrian–Cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid-resistant organic-walled microfossils. A detailed study of the Chapel Island Formation, which includes the boundary interval, has revealed fluctuations in the isotopic composition of organic carbon. These are largely interpreted as caused by differences in the depositional environments. Highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite-forming process, sometimes under sulfate-limited conditions. Palynological results are quite limited with respect to diagnostic microfossils.

scholarly journals Recognition of a Middle–Late Jurassic arc-related porphyry copper belt along the southeast China coast: Geological characteristics and metallogenic implications

Geology ◽  
2021 ◽  
Author(s):  
Jingwen Mao ◽  
Wei Zheng ◽  
Guiqing Xie ◽  
Bernd Lehmann ◽  
Richard Goldfarb
Keyword(s):  
Late Jurassic ◽  
Porphyry Copper ◽  
Fault Zones ◽  
Southeast China ◽  
Geological Characteristics ◽  
Metallogenic Model ◽  
World Class ◽  
Definition Of ◽  
Back Arc ◽  
China Coast

Recent exploration has led to definition of a Middle–Late Jurassic copper belt with an extent of ~2000 km along the southeast China coast. The 171–153 Ma magmatic-hydrothermal copper systems consist of porphyry, skarn, and vein-style deposits. These systems developed along several northeast-trending transpressive fault zones formed at the margins of Jurassic volcanic basins, although the world-class 171 Ma Dexing porphyry copper system was controlled by a major reactivated Neoproterozoic suture zone in the South China block. The southeast China coastal porphyry belt is parallel to the northeast-trending, temporally overlapping, 165–150 Ma tin-tungsten province, which developed in the Nanling region in a back-arc transtensional setting several hundred kilometers inboard. A new geodynamic-metallogenic model linking the two parallel belts is proposed, which is similar to that characterizing the Cenozoic metallogenic evolution of the Central Andes.

scholarly journals Compositional variation of the human fecal microbiome in relation to azo-reducing activity: a pilot study

Gut Pathogens ◽  
2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Sara A. Zahran ◽  
Marwa Ali-Tammam ◽  
Amal E. Ali ◽  
Ramy K. Aziz
Keyword(s):  
Pilot Study ◽  
Gut Microbiota ◽  
Relative Abundance ◽  
Microbial Community Composition ◽  
Illumina Miseq ◽  
Compositional Variation ◽  
Fecal Microbiome ◽  
Azo Reduction ◽  
Stool Samples ◽  
Reducing Activity

Abstract Background Through an arsenal of microbial enzymes, the gut microbiota considerably contributes to human metabolic processes, affecting nutrients, drugs, and environmental poisons. Azoreductases are a predominant group of microbiota-derived enzymes involved in xenobiotic metabolism and drug activation, but little is known about how compositional changes in the gut microbiota correlate with its azo-reducing activity. Results To this end, we used high-throughput 16S rRNA amplicon sequencing, with Illumina MiSeq, to determine the microbial community composition of stool samples from 16 adults with different azo-reducing activity. High azo-reducing activity positively correlated with the relative abundance of phylum Firmicutes (especially genera Streptococcus and Coprococcus) but negatively with phylum Bacteroidetes (especially genus Bacteroides). Typical variations in the Firmicutes-to-Bacteroidetes and Prevotella-to-Bacteroides ratios were observed among samples. Multivariate analysis of the relative abundance of key microbial taxa and other diversity parameters confirmed the Firmicutes proportion as a major variable differentiating high and non-azo-reducers, while Bacteroidetes relative abundance was correlated with azo-reduction, sex, and BMI. Conclusions This pilot study showed that stool samples with higher azo-reducing activity were enriched in Firmicutes but with relatively fewer Bacteroidetes. More samples and studies from different geographical areas are needed to bolster this conclusion. Better characterization of different azoreductase-producing gut microbes will increase our knowledge about the fate and differential human responses to azodye-containing drugs or orally consumed chemicals, thus contributing to efforts towards implementing microbiome testing in precision medicine and toxicology.

Compositional Variation in Wolframites from the Barroca Grande Mine, Portugal: Evidence for Fault-Controlled Ore Formation

1988 ◽  
Vol 52 (367) ◽  
pp. 497-503 ◽  
Author(s):  
D. A. Polya
Keyword(s):  
Electron Probe ◽  
Trace Element Composition ◽  
Fault Zones ◽  
Element Composition ◽  
Compositional Variation ◽  
Main Stage ◽  
Fluid Migration ◽  
Major Pathway ◽  
Ore Formation ◽  
Vertical Fault

AbstractThe major and trace element composition of over 40 wolframites from the Barroca Grande mine of the Panasqueira W-Sn-Cu quartz-vein hosted orebody have been determined by electron probe microanalysis.The hübnerite content of wolframite is largely uniform (12 to 20 mol. %) throughout most of the mine, suggesting relative uniformity in composition of the main stage ore-forming fluids. However, wolframites show a striking pattern of enrichment in niobium adjacent to major sub-vertical fault zones. Typical wolframite Nb2O5 contents are below 1000 ppm, whilst values greater than 1000, 2000 and 4000 ppm are generally only found in wolframites less than 50, 30, and 10 metres respectively from major sub-vertical faults. This strongly suggests that some of these fault zones acted as major pathways for hydrothermal fluid migration during ore formation. The idea that the greisened cupola at Panasqueira was the sole major pathway for fluid movement is discounted.

scholarly journals Geochronology and Geochemistry of Uraninite and Coffinite: Insights into Ore-Forming Process in the Pegmatite-Hosted Uraniferous Province, North Qinling, Central China

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 552 ◽  
Author(s):  
Feng Yuan ◽  
Shao-Yong Jiang ◽  
Jiajun Liu ◽  
Shuai Zhang ◽  
Zhibin Xiao ◽  
...  
Keyword(s):  
Central China ◽  
Compositional Variation ◽  
Ionization Mass ◽  
Low Grade ◽  
Forming Process ◽  
Early Devonian ◽  
The North ◽  
North Qinling ◽  
Uranium Minerals

The biotite pegmatites in the Shangdan domain of the North Qinling orogenic belt contain economic concentrations of U, constituting a low-grade, large-tonnage pegmatite-hosted uraniferous province. Uraninite is predominant and ubiquitous ore mineral and coffinite is common alteration mineral after initial deposit formation. A comprehensive survey of the uraninite and coffinite assemblage of the Chenjiazhuang, Xiaohuacha, and Guangshigou biotite pegmatites in this uraniferous province reveal the primary magmatic U mineralization and its response during subsequent hydrothermal events. Integrating the ID-TIMS (Isotope Dilution Thermal Ionization Mass Spectrometry) 206Pb/238U ages and U-Th-Pb chemical ages for the uraninites with those reported from previous studies suggests that the timing of U mineralization in the uraniferous province was constrained at 407–415 Ma, confirming an Early Devonian magmatic ore-forming event. Based on microtextural relationships and compositional variation, three generations of uranium minerals can be identified: uaninite-A (high Th-low U-variable Y group), uranite-B (low Th-high U, Y group), and coffinite (high Si, Ca-low U, Pb group). Petrographic and microanalytical observations support a three-stage evolution model of uranium minerals from primary to subsequent generations as follows: (1) during the Early Devonian (stage 1), U derived from the hydrous silicate melt was mainly concentrated in primary magmatic uaninite-A by high-T (450–607 °C) precipitation; (2) during the Late Devonian (stage 2), U was mobilized and dissolved from pre-existing uraninite-A by U-bearing fluids and in situ reprecipitated as uraninite-B under reduced conditions. The in situ transformation of primary uraninite-A to second uraninite-B represent a local medium-T (250–450 °C) hydrothermal U-event; and (3) during the later low-T (100–140 °C) hydrothermal alteration (stage 3), U was remobilized and derived from the dissolution of pre-existing uraninite by CO2- and SiO2-rich fluids and interacted with reducing agent (e.g., pyrite) leading to reprecipitation of coffinite. This process represents a regional and extensive low-T hydrothermal U-event. In view of this, U minerals evolved from magmatic uraninite-A though fluid-induced recrystallized uraninite-B to coffinite, revealing three episodes of U circulation in the magmatic-hydrothermal system.

Variations d'épaisseur du Cambrien moyen en Meseta marocaine occidentale: signification géodynamique des données de surface et de subsurface

1988 ◽  
Vol 25 (12) ◽  
pp. 2104-2117 ◽  
Author(s):  
Christine Bernardin ◽  
Jean-Jacques Cornée ◽  
Michel Corsini ◽  
Stéphane Mayol ◽  
Jacques Muller ◽  
...  
Keyword(s):  
Field Data ◽  
Fault Zones ◽  
Northwestern Part ◽  
Early Cambrian ◽  
Middle Cambrian ◽  
Late Precambrian ◽  
Intracontinental Rift ◽  
Late Evolution ◽  
Geophysical Investigations

The western part of the Moroccan Meseta contains thick Middle Cambrian terrigenous deposits, in places 7000 m thick. Field data and geophysical investigations indicate subsident grabens controlled by major N30°E and N60°E fault zones on the northwestern part of the African shield. These grabens correspond to the late evolution of an intracontinental rift that originated during Late Precambrian and Early Cambrian time and can be considered evidence of the opening of the Iapetus paleo-ocean in Morocco.

Release of Neurosecretion in the Crayfish Sinus Gland

1968 ◽  
Vol 26 ◽  
pp. 150-151
Author(s):  
Richard R. Shivers
Keyword(s):  
Chemical Nature ◽  
Storage Site ◽  
Neurosecretory Granules ◽  
Sinus Gland ◽  
Diameter Class ◽  
Dense Membrane ◽  
Neurohemal Organ ◽  
Dense Vesicles

The sinus gland is a neurohemal organ located in the crayfish eyestalk and represents a storage site for neurohormones prior to their release into the circulation. The sinus gland contains 3 classes of dense, membrane-limited granules: 1) granules measuring less than 1000 Å in diameter, 2) granules measuring 1100-1400 Å in diameter, and 3) granules measuring 1500-2000 Å in diameter. Class 3 granules are the most electron-dense of the granules found in the sinus gland, while class 2 granules are the most abundant. Generally, all granules appear to undergo similar changes during release.Release of neurosecretory granules may be initiated by a preliminary fragmentation of the “parent granule” into smaller, less dense vesicles which measure about 350 Å in diameter (V, Figs. 1-3). A decrease in density of the granules prior to their fragmentation has been observed and may reflect a change in the chemical nature of the granule contents.

The Potentials of Scanning Microscopy

1968 ◽  
Vol 26 ◽  
pp. 352-353
Author(s):  
A. V. Crewe
Keyword(s):  
Salient Feature ◽  
Secondary Emission ◽  
Resolving Power ◽  
X Rays ◽  
Scanning Microscope ◽  
Forming Process ◽  
Additional Tool ◽  
Detection Systems ◽  
Conventional Microscope ◽  
Present Information

If the resolving power of a scanning electron microscope can be improved until it is comparable to that of a conventional microscope, it would serve as a valuable additional tool in many investigations.The salient feature of scanning microscopes is that the image-forming process takes place before the electrons strike the specimen. This means that several different detection systems can be employed in order to present information about the specimen. In our own particular work we have concentrated on the use of energy loss information in the beam which is transmitted through the specimen, but there are also numerous other possibilities (such as secondary emission, generation of X-rays, and cathode luminescence).Another difference between the pictures one would obtain from the scanning microscope and those obtained from a conventional microscope is that the diffraction phenomena are totally different. The only diffraction phenomena which would be seen in the scanning microscope are those which exist in the beam itself, and not those produced by the specimen.

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