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Höhn Stefan Koglin Nikola Klopf Lisa Schüssler Ulrich Tragelehn Harald Frimmel Hartwig E. Zeh Armin Brätz Helene 《International Journal of Earth Sciences》2018,107(1):359-377
International Journal of Earth Sciences - Stratigraphically well-defined volcanic rocks in Palaeozoic volcano-sedimentary units of the Frankenwald area (Saxothuringian Zone, Variscan Orogen) were... 相似文献
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Alexandre Raphael Cabral Nikola Koglin Harald Strauss Helene Brätz Rogerio Kwitko-Ribeiro 《Mineralium Deposita》2013,48(7):805-816
The distribution of mineral deposits, characterised as barite deposits, hematite-rich auriferous deposits and auriferous tourmaline–sulfide deposits, displays a regional sulfate–hematite–sulfide zoning along the thrust-delineated limbs of the Mariana anticline, in the south-eastern part of the Quadrilátero Ferrífero of Minas Gerais, Brazil. Cross-cut relationships of barite veins and sulfide lodes indicate that sulfidation occurred in a late-tectonic context, which is here attributed to the collapse of the ～0.6-Ga Brasiliano thrust front. Reconnaissance S-isotopic data from barite and pyrite (Antônio Pereira barite deposit and its adjacent gold deposit, respectively), and arsenopyrite (Passagem de Mariana gold deposit), suggest a new interpretation for the hydrothermal fluid overprint in the Mariana anticline. The Antônio Pereira barite has Δ33S values that are near zero, constraining the sulfate source to rocks younger than 2.45 Ga. The barite-δ34S values are between +19.6 and +20.8?‰. The Passagem arsenopyrite and tourmaline have Co/Ni ratios that define a positive linear trend with the Antônio Pereira pyrite. The latter has homogenous δ34S values, between +8.8 and +8.9?‰, which are compatible with thermochemical reduction of aqueous sulfate with the S-isotopic composition of the Antônio Pereira barite. 相似文献
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Combined U–Pb and Lu–Hf isotope analyses of detrital zircon grains from the auriferous Eldorado Reef conglomerate, upper Central Rand Group, reveal new insights into the provenance of the sediments and thus, by implication, possibly also into that of the gold. Most of the detrital zircon grains, which are of magmatic origin, yielded Mesoarchaean ages clustering around 2.94 and 3.06 Ga. A subordinate zircon population gave ages with maxima at 3.28 and 3.44 Ga. The Mesoarchaean zircon grains mostly show super-chondritic ?Hft of up to +5.2, whereas the Palaeoarchaean zircon grains have nearly chondritic composition with ?Hft between −1.3 and +2.0. The new dataset of the Mesoarchaean zircon populations provides the first unambiguous evidence of the formation of juvenile crust not only at 3.06 but also at 2.94 Ga. As the analysed zircon grains are from the ruditic fraction, they must be derived from a comparatively proximal source in close vicinity to the Central Rand Basin. Based on currently available data, this source was most likely a magmatic arc that existed at the northern edge of the Witwatersrand Block at 3.06 Ga. An additional source might be the 2.94 Ga magmatic rocks of the Kraaipan Greenstone Belt that occurs to the west of the Witwatersrand Block. The minor fraction of Palaeoarchaean zircon grains in the Eldorado Reef perhaps stem from sources that are isotopically similar to the Barberton Greenstone Belt and the Limpopo Belt but were more proximal to the Central Rand Basin. 相似文献
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Cenozoic sediments deposited in graben‐like basins in the Quadrilátero Ferrífero, southern São Francisco craton, Brazil, have anomalous contents of Hg and Sb. Two localities have been studied: the topaz deposit of Antônio Pereira, and the remains of the old opencast workings at Cata Preta, one of the earliest Au mines of Minas Gerais that dates back to about 1690. At Cata Preta, a brecciated wad‐like rock exhibits geochemical fingerprints that point to fractionation of Pt and Pd from Ag. This metal fractionation, reflected in the Au ingots produced in the region, genetically links Cata Preta to the near‐surface bonanza ore of Serra Pelada, which formed as a result of a Late‐Cretaceous hydrothermal overprint in the Amazon craton. Here, we propose that anorogenic hydrothermal activity in cratonic terrains prepared the ground for the enrichment in precious metals that gave rise to two of the most important Au rushes in Brazilian history. 相似文献
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Enrichments in platinum-group elements were found in clausthalite, PbSe, which occurs in carbonate–hematite veins hosted in black shale of Upper Wenlockian age in the eastern Harz, Germany. Spot measurements by laser ablation–quadrupole inductively coupled plasma mass spectrometry (LA–QICPMS) show that the clausthalite has Pt contents that average 0.459?ppm and range from 0.003 to 2.83?ppm. Other noble metals quantified in the present work include Au (0.226?ppm, 0.109–0.451?ppm), Ru (0.061?ppm, 0.006–0.264?ppm), Ir (0.071?ppm, 0.010–0.185?ppm), Pd (0.046?ppm, 0.017–0.107?ppm) and Os (0.010?ppm, <0.003–0.024?ppm). Elemental ratios of Au/Ir, Pd/Ir and Pt/Ir, the average values of which are respectively 4.6, 0.8, and 4.9, suggest that Au, Pd and Pt are poorly fractionated from Ir. The resulting Ir enrichment is unusual and should reflect a particularly soluble (and stable) aqueous complex of Ir in a highly oxidizing, low-temperature, Se-rich solution. 相似文献
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Fiona A. Harrison Finn E. Christensen William Craig Charles Hailey Wayne Baumgartner C. M. H. Chen James Chonko W. Rick Cook Jason Koglin Kristin-Kruse Madsen Michael Pivavoroff Steven Boggs David Smith 《Experimental Astronomy》2005,20(1-3):131-137
Hard X-ray/soft gamma-ray astrophysics is on the verge of a major advance with the practical realization of technologies capable of efficiently focusing X-rays above 10 keV. Hard X-ray focusing telescopes can achieve orders of magnitude improvements in sensitivity compared to the instruments based on coded apertures and collimated detectors that have traditionally been employed in this energy band. Compact focal planes enable high-performance detectors with good spectral resolution to be employed in efficient, low-background configurations. We have developed multilayer coated grazing incidence optics and solid state Cadmium Zinc Telluride focal plane systems for the High Energy Focusing Telescope (HEFT) balloon-borne experiment, and for the Nuclear Spectroscopic Telescope Array (NuSTAR) Small Explorer satellite. In this paper we describe the technologies, telescope designs, and performance of both experiments. 相似文献
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Nikola Koglin Hartwig E. Frimmel W. E. Lawrie Minter Helene Brätz 《Mineralium Deposita》2011,46(7):839-840
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Trace-element characteristics of different pyrite types in Mesoarchaean to Palaeoproterozoic placer deposits 总被引：7，自引：0，他引：7
Nikola Koglin Hartwig E. Frimmel W. E. Lawrie Minter Helene Brätz 《Mineralium Deposita》2010,45(3):259-280
A comparative in situ LA-ICP MS trace-element study on pyrite from three different, variably auriferous, Archaean to Palaeoproterozoic
palaeoplacer deposits in the Ouro Fino Syncline (Quadrilátero Ferrífero; Brazil), the Elliot Lake area north of Lake Huron
(SE Canada) and several deposits within the Witwatersrand Basin (South Africa) revealed systematic differences between morphologically
different pyrite types and between the various palaeoplacer deposits. Especially the Ni and Au concentrations as well as Co/Ni
and Mo/Ni ratios were found to be systematically different in detrital compact, detrital porous and post-sedimentary/hydrothermal
pyrite grains from different source areas. High Co/Ni ratios and low Au concentrations are typical of post-sedimentary pyrite,
which is hydrothermal in origin. In contrast, relatively low Co/Ni ratios and high Au contents characterise detrital porous
banded and concentric pyrite grains (Au > 1 ppm), which are syn-sedimentary in origin. In the Elliot Lake area and the Witwatersrand
Basin, detrital compact rounded pyrite is characterised by high Co/Ni ratios, which is in agreement with derivation from a
hydrothermal source. Low Au concentrations in this pyrite type support the contention of the gold and the pyrite in these
deposits coming from different source rocks. In contrast, derivation from an originally diagenetic pyrite is suggested for
the detrital compact pyrite in the Ouro Fino Syncline because of low to intermediate Co/Ni ratios. High Au contents may indicate
a genetic relationship between pyrite and gold there. Systematic differences exist between the three areas with respect to
Au, Ni, Co, Mo and Cu distributions in detrital pyrite, which reflects differences in the provenance. A predominantly mafic/ultramafic
source is indicated for the Ouro Fino, a felsic source for the Elliot Lake, and a mixed felsic–mafic provenance for the Witwatersrand
pyrite populations. Independently of pyrite type, the higher Au endowment of the studied Witwatersrand and Ouro Fino conglomerates
are also reflected by an overall higher Au concentration in the respective pyrite grains compared to the relatively Au-poor
samples from Elliot Lake. In general, a strong positive correlation between Au and Pb levels in the various pyrite grains
is noted. Analogous to Pb, which is well known for not being easily accommodated in the pyrite crystal lattice but occurring
as discrete PbS phases, Au is considered to be present mainly in the form of discrete Au phases in minute pores and interstices
of the pyrite grains rather than within the pyrite lattice. 相似文献