Widespread CO2-rich cordierite in the UHT Bakhuis granulite belt, Surinam

The Bakhuis Granulite Belt, approx. 30 x 100 km, transects the large Paleoproterozoic greenstone belt along the north-eastern coast of South America. Part of the Granulite belt witnessed typical Ultrahigh-Temperature Metamorphism (UHTM). A metapelite area in the NE of the belt shows assemblages characteristic of UHTM: aluminous (up to 10 wt.%) orthopyroxene + sillimanite +/- sapphirine. Leucosomes commonly show mesoperthite or K-rich antiperthite. Ternary feldspar thermometry indicates a peak temperature of 1000-1050°C and pressure is estimated to have been around 9 kbar. Metapelites elsewhere in the belt lack mineral assemblages characteristic of UHTM. However, feldspar thermometry for these metapelites as well as for mesoperthite granulites indicates that peak temperatures were 900°C or higher throughout the belt and locally reached 1000-1050°C. It is, therefore, concluded that the other parts of the belt also witnessed UHTM, despite their lack of typical UHTM assemblages. Study of peak assemblages in metapelites in these parts is hampered by varying, but usually considerable retrograde metamorphism. The main mafic mineral in metapelites is coarse Mg-rich cordierite, accompanied by coarse sillimanite. Widespread occurrence of cordierite + sillimanite in metapelites is unusual for UHTM, the more so as UHTM assemblages are commonly formed at the expense of cordierite-bearing assemblages. In a small part of the metapelites cordierite is accompanied by coarse aluminous (up to 9 wt.%) orthopyroxene. Associated cordierite and orthopyroxene appear to have formed in equilibrium with each other. Only the presence of aluminous orthopyroxene (as well as the presence of mesoperthite) is typical for UHTM, but is limited to a small part of the metapelites. Peak P-T conditions for the cordierite-bearing part of the belt are estimated to have been similar to those in the NE area with its characteristic UHTM assemblages. Primary and secondary fluid inclusions in UHT quartz blebs in orthopyroxene consist of pure CO2 and have a high density. Raman spectroscopy indicated a considerable CO2 content in cordierite. Estimated from their birefringence, the CO2 content of most cordierites is in the range of 1-2 wt.% CO2. This corresponds to a substantial filling of the cordierite channels with CO2 and for the higher levels possibly near-saturation with CO2 according to the model of Harley and Thompson for the maximum level of CO2 in cordierite. Thermodynamic data for CO2-rich cordierite are poorly known. However, a high level of CO2 in cordierite has been considered to lead to a substantial expansion of its stability field, also into the field of UHTM, at T > 900°C. This is, therefore, assumed to be the explanation for the unusual, widespread occurrence of cordierite in the UHTM belt. A small part of the metapelite samples shows cordierite of a high birefringence, twice that of quartz. SIMS analysis of such cordierite showed 3.0 wt.% CO2, the highest level known from nature. The level is far too high to have formed at UHTM conditions according to the model of Harley and Thompson and would be possible only at conditions such as 700°C and 10 kbar. It is assumed that locally the CO2 level of cordierite changed after UHTM, by taking up additional CO2. Secondary fluid CO2 inclusions in UHT quartz have a higher density than the primary inclusions, indicating a near-isobaric cooling path down to 700-750°C. In these conditions cordierite probably could steadily re-equilibrate at decreasing temperature while taking up more and more CO2, up to 3 wt.% around 700°C. The heat source for the UHTM in the Bakhuis Granulite belt is considered to be asthenospheric upwelling or mafic underplating, but mafic magmatism of identical age to the UHTM has not yet been found. One mafic intrusion was found to be around 20 Ma older than the UHTM, whereas in the SW of the belt numerous mafic intrusions formed around 70 Ma after UHTM

Percentile reference values for anthropometric body composition indices in European children from the IDEFICS study

INTRODUCTION: To characterise the nutritional status in children with obesity or wasting conditions, European anthropometric reference values for body composition measures beyond the body mass index (BMI) are needed. Differentiated assessment of body composition in children has long been hampered by the lack of appropriate references. OBJECTIVES: The aim of our study is to provide percentiles for body composition indices in normal weight European children, based on the IDEFICS cohort (Identification and prevention of Dietary-and lifestyle-induced health Effects in Children and infantS). METHODS: Overall 18 745 2.0-10.9-year-old children from eight countries participated in the study. Children classified as overweight/obese or underweight according to IOTF (N = 5915) were excluded from the analysis. Anthropometric measurements (BMI (N = 12 830); triceps, subscapular, fat mass and fat mass index (N = 11 845-11 901); biceps, suprailiac skinfolds, sum of skinfolds calculated from skinfold thicknesses (N = 8129-8205), neck circumference (N = 12 241); waist circumference and waist-to-height ratio (N = 12 381)) were analysed stratified by sex and smoothed 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th and 99th percentile curves were calculated using GAMLSS. RESULTS: Percentile values of the most important anthropometric measures related to the degree of adiposity are depicted for European girls and boys. Age-and sex-specific differences were investigated for all measures. As an example, the 50th and 99th percentile values of waist circumference ranged from 50.7-59.2 cm and from 51.3-58.7 cm in 4.5-to < 5.0-year-old girls and boys, respectively, to 60.6-74.5 cm in girls and to 59.9-76.7 cm in boys at the age of 10.5-10.9 years. CONCLUSION: The presented percentile curves may aid a differentiated assessment of total and abdominal adiposity in European children

Data for: Trace element associations in hydrothermal pyrite at the Geita Hill gold deposit, Tanzania, revealed through LA-ICP-MS mapping

Database contains LA-ICP-MS data and data reduction techniques relevant to the submitted article &quot;Trace element associations in hydrothermal pyrite at the Geita Hill gold deposit, Tanzania, revealed through LA-ICP-MS mapping&quot;, along with a contents file.Appendix 1 contains the LA-ICP-MS spot analysis data cited in the articleAppendix 2 contains all LA-ICP-MS data processed for this research.Appendix 3 contains all La-ICP-MS transects processed for this research. All transects were ablated through pyrite grains.Appendix 4 contains the 9 LA-ICP-MS trace element images as a stand-alone ArcMap database file. Instructions for reading this file are included in the contents PDF.Appendix 5 contains the data reduction methodology used to create the trace element images.Appendix 6 contains the raw data underpinning the trace element images

Data for: Trace element associations in hydrothermal pyrite at the Geita Hill gold deposit, Tanzania, revealed through LA-ICP-MS mapping

Database contains LA-ICP-MS data and data reduction techniques relevant to the submitted article &quot;Trace element associations in hydrothermal pyrite at the Geita Hill gold deposit, Tanzania, revealed through LA-ICP-MS mapping&quot;, along with a contents file.Appendix 1 contains the LA-ICP-MS spot analysis data cited in the articleAppendix 2 contains all LA-ICP-MS data processed for this research.Appendix 3 contains all La-ICP-MS transects processed for this research. All transects were ablated through pyrite grains.Appendix 4 contains the 9 LA-ICP-MS trace element images as a stand-alone ArcMap database file. Instructions for reading this file are included in the contents PDF.Appendix 5 contains the data reduction methodology used to create the trace element images.Appendix 6 contains the raw data underpinning the trace element images.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

The world-class gold deposits in the Geita greenstone belt, Northwestern Tanzania

The Geita mine is operated by AngloGold Ashanti and currently comprises four gold deposits mined as open pits and underground operations in the Geita greenstone belt, Tanzania. The mine produces ~0.5 Moz of gold a year and has produced ~8.3 Moz since 2000, with current resources estimated at ~6.5 Moz, using a lower cut-off of 0.5 g/t.The geologic history of the Geita greenstone belt involved three tectonic stages: (I) early (2820–2700 Ma) extension (D1) and formation of the greenstone sequence in an oceanic plateau environment; (II) shortening of the greenstone sequence (2700–2660 Ma) involving ductile folding (D2–5) and brittle-ductile shearing (D6), coincident with long-lived igneous activity concentrated in five intrusive centers; and (III) renewed extension (2660–2620 Ma) involving strike-slip and normal faulting (D7–8), basin formation, and potassic magmatism. Major gold deposits in the Geita greenstone belt formed late in the history of the greenstone belt, during D8normal faulting at ~2640 Ma, and the structural framework, mineral paragenesis, and timing of gold precipita-tion is essentially the same in all major deposits. Gold is hosted in iron-rich lithologies along contacts between folded metaironstone beds and tonalite-trondhjemite-granodiorite (TTG) intrusions, particularly where the contacts were sheared and fractured during D6–7 faulting. The faults, together with damage zones created along D3 fold hinges and D2–3 hydrothermal breccia zones near intrusions, formed microfracture networks that were reactivated during D8. The fracture networks served as conduits for gold-bearing fluids; i.e., lithologies and structures that trap gold formed early, but gold was introduced late.Fluids carried gold as Au bisulfide complexes and interacted with Fe-rich wall rocks to precipitate gold. Fluid-rock interaction and mineralization were enhanced as a result of D8 extension, and localized hydro-fracturing formed high-grade breccia ores. Gold is contained in electrum and gold-bearing tellurides that occur in the matrix and as inclusions in pyrrhotite and pyrite. The gold mineralization is spatially linked to long-lived, near-stationary intrusive centers. Critical factors in forming the deposits include the (syn-D2–6) formation of damage zones in lithologies that enhance gold precipitation (Fe-rich lithologies); late tectonic reactivation of the damage zones during extensional (D8) faulting with the introduction of an S-rich, gold-bearing fluid; and efficient fluid-rock interaction in zones that were structurally well prepared

Alteration paragenesis and the timing of mineralised quartz veins at the world-class Geita Hill gold deposit, Geita Greenstone Belt, Tanzania

The world-class Geita Hill deposit is one of the largest gold deposits located within the Geita Greenstone Belt in NW Tanzania. The deposit is hosted within a complexly deformed sedimentary package dominated by ironstone and intruded by diorite dykes. The gold mineralisation is spatially associated with the Geita Hill Shear Zone which, is a NE-trending, moderately NW dipping deformation zone consisting of a network of discontinuous shear fractures that record early thrusting overprinted by later strike-slip and normal events. The regional metamorphic assemblage in the meta-sediments is characterised by biotite +chlorite + actinolite +K-feldspar + magnetite ± pyrrhotite ± pyrite indicating upper greenschist facies conditions. The gold-related alteration overprints the regional metamorphic assemblage, and is characterised by silicification and sulfidation fronts that generally extend out from the mineralised zone by no more than one meter. The alteration assemblage includes sub-vertical, mineralised quartz veins that trend approximately E-W. The mineralised quartz veins are accompanied by alteration halos of quartz +biotite+ K-feldspar +pyrite which overprints the peak metamorphic assemblage. Gold is closely associated with secondary pyrite and occurs as free gold and gold tellurides (sylvanite, calaverite and nagyagite). It occurs mainly as inclusions in pyrite and as invisible gold in pyrite but also as gold inclusions in biotite and along quartz grain boundaries. Two distinct textural styles of auriferous pyrite can be distinguished: inclusion rich subhedral pyrite, hosting invisible gold, and inclusion free euhedral pyrite, hosting visible gold grains. It is common for the inclusions rich pyrite to have thick rims of inclusion free pyrite. The mineralising alteration is overprinted by barren, multiphase quartz-carbonate, and carbonate-chlorite veins. This alteration is characterised by the assemblage calcite +siderite +chlorite ± quartz ± pyrite ± barite. Palaeostress analysis of mineralised shear fractures along the Geita Hill Shear Zone are indicative of sigma 1 being vertical and sigma 3 trending N-S, indicating N-S extension, which is consistent with the orientation of the mineralised quartz veins