Iron played a decisive part when uranyl phosphates (‘yellow U ores’) formed during supergene alteration of the aplitic and pegmatitic rocks of the Hagendorf Pegmatite Province. Three different supergene U mineral successions, referred to in the current study as pathways I to III, were identified. Pathway I began with the release of PO42– by the dissolution of rockbridgeite and ended after shortdistance transport under alkaline reducing or slightly acidic oxidizing conditions in the precipitation of bassetite. Pathway II is an advanced form of pathway I that did not stop with the precipitation of bassetite, but progressed by acidic Cu-bearing meteoric waters under oxidizing conditions up to the torbernite precipitation stage. Minor amounts of Mn or Ca may have led to a deviation from the normal pathway into the stability fields of lehnerite or autunite, respectively, both of which may occur either as solid solution series or in a layered intergrowth with torbernite. Limonite-cored torbernite has been described for the first time and only exists in pathway III. Unlike its counterpart pathways I and II, which appeared at the end of a complex polystage element recycling process of secondary Fe phosphates under fluctuating redox and pH conditions, limonite-cored torbernite resulted from a monostage transformation of primary ‘black Fe-U ore minerals’ under strongly oxidizing conditions and short-distance element transport. These restricted physicochemical conditions caused the immediate stabilization of the Fe-U-P system and by doing so the U-Pb ratios of the black ore progenitor were well preserved in the limoniticc ore. Torbernite was analysed for U, Th and Pb isotopes by laser ablation inductively coupled plasma mass spectrometry techniques. For one domain the data yielded a formation age of 4.55±0.02 Ma, which corresponds to Miocene-Pliocene weathering and geomorphological processes in the study area. A second domain gave a discordia with an upper intercept age of 549±12 Ma, interpreted to represent a thermal event at the Precambrian-Cambrian boundary. Ferrocolumbite is found exclusively in the mineralization of pathway III. Due to the proximity of ferrocolumbite to torbernite, limonite-cored torbernite probably inherited the 549 Ma age from ferrocolumbite during supergene alteration.

Electron microprobe analysis (EMPA) and microscopic investigations were performed on monazite grains from the black sand deposits of northern Sinai beach. Electron microprobe backscattered electron images, X-ray mapping and wavelength dispersive spectroscopy line scans showed some grains with sector zoning and others with thorite inclusions. Based on the EMPA data, the studied monazite is grouped into monazite-(Ce) and Th-rich monazite. Monazite-(Ce) is enriched in REE and P, whereas Th-rich monazite is enriched in Th, U, Ca, Y, Si and Fe. The compositional variations of monazite are governed by the substitution of REE by Th, U, Ca and Y. The monazite grains show enriched chondrite-normalized REE patterns represented mainly by LREE and only Gd from the HREE. These patterns demonstrate negative Nd and Euanomalies. The floods associated with the pluvial periods which prevailed in Egypt during the Pleistocene, were able to erode the source rocks and liberate heavy minerals including monazite. The mineral grains were transported through several wadis and tributaries to the main channel of the River Nile. At the confluence sites, these heavy minerals were mixed with Ethiopian and central African heavy mineral assemblages. The grains continued to move together downriver until being deposited in their current locations. The analytical results suggest that pegmatites and granites of the Eastern Desert are the most likely source of the monazite. However, due to the large area of the Nile watershed, other undiscovered sources are possible.

In order to better understand the formation and evolution processes of ultrahigh pressure (UHP) felsic rocks, we determined the ages of various domains of zircon and monazite crystals from the diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge. According to cathodoluminescence imagery and Th/U ratios, three zircon zones were distinguished. Each was dated using several spot analyses from a sensitive high-resolution ion microprobe analysing Pb, U and Th isotopes. The results were: (1) core zone – 21 analyses: Th/U ≤ 40.023 and 337.0±2.7 Ma (2σ, combined 206Pb/238U-207Pb/235U age); (2) diamond-bearing intermediate zone – 23 analyses: Th/U ≥ 50.037 and 336.8±2.8 Ma; and (3) rim zone – 12 analyses: Th/U = 0.015–0.038 (plus one analysis of 0.164) and 330.2±5.8 Ma. The U-Pb obtained ages are virtually concordant. Furthermore, two oscillatory zoned zircon cores (Th/U ≥ 50.8) yielded (~concordant) ages of ~400 Ma. Six SHRIMP analyses of monazites gave an age of 332.4±2.1 Ma. In addition, Pb, Th and U contents in monazite were analysed with an electron microprobe (EMP). A mean age of 324.7±8.0 (2σ) Ma was acquired from 113 analyses.

By combining the defined ages with previously published P-T conditions, minimum velocities for burial and exhumation were estimated. In addition, we present a likely geodynamic scenario involving age data from the literature as well as this study: beginning 340 million years ago, gneisses at the base of a thickened continentalcrust (~1.8 GPa, 650ºC) were transported to depths of at least 130 km, possibly as deep as 250 km. Here they were heated (>1050ºC) and partially melted and as a result began to rise rapidly. The burial and subsequent ascent back to a depth of 50 km, where zircon rims and monazite formed, took only a few million years and perhaps significantly less.

The atomic structure of ammoniojarosite,[(NH4)Fe3(SO4)2(OH)6], a = 7.3177(3) Å, c = 17.534(1) Å, space group Rm, Z = 3, has been solved using single-crystal X-ray diffraction (XRD) to wR 3.64% and R 1.4%. The atomic coordinates of the hydrogen atoms of the NH4 group were located and it was found that the ammonium group has two different orientations with equal probability. Hydronium commonly substitutes into jarosite group mineral structures and samples in the ammoniojarosite–hydronium jarosite solid-solution series were synthesized and analysed using powder XRD and Rietveld refinement. Changes in unit-cell dimensions and bond lengths are noted across the solidsolution series. The end-member ammoniojarosite synthesized in this study has no hydronium substitution in the A site and the unit-cell dimensions determined have a smaller a dimension and larger c dimension than previous studies. Two natural ammoniojarosite samples were analysed and shown to have similar unit-cell dimensions to the synthetic samples. Short-wave infrared and Fourier transform infrared spectra were collected for samples from the NH4–H3O jarosite solid-solution series and the differences between the end-members were significant. Both are useful tools for determining NH4 content in jarosite group minerals.

Geochemical processes and mineralogical transformations in the spontaneously combusting coal waste pile of the Kukla mine in Oslavany, Czech Republic, were investigated. The aims of the study were: (1) the characterization of secondary minerals; and (2) determination of processes which influence the mobility of elements in the pile. The pile burned from the late 19th century until the 1990s and has acquired a zoned nature, with original black material in the core of the pile, red material produced by burning close to the pile slopes and grey and white efflorescent salts precipitated on the pile top and slopes. Several mineral assemblages have been identified including (1) primary minerals in the black material including bituminous coal to anthracite, micas, pyrite and goethite; (2) hematite, spinels and corundum in the red materialproduced by pyrometamorphism; and (3) hydrated sulphates of magnesium including hexahydrite, konyaite and picromerite in efflorescent precipitates on the slopes of the pile. A conceptual model of geochemical processes in the pile includes seasonal changes with mineral dissolution during the wet season and precipitation of efflorescent salt minerals during the dry season. Formation of secondary minerals such as hematite, which is resistant to weathering and immobilizes hydrolysable Fe, may have a positive environmental impact in the long term.

Agates from a 430 Ma host at Stockdale Beck, Cumbria, England have been characterized. The crystallite size of the Stockdale Beck agates was found to be ~60% greater than any other agates from five regions aged 400–1100 Ma. Raman spectroscopy identified moganite in all agates tested except those from Stockdale Beck. Infrared spectroscopy showed that the silanol content of the Stockdale Beck agates was near zero. The properties of agates from Stockdale Beck and the 1.84–3.48 Ga metamorphosed hosts found in Western Australia were similar but different from agates found in other hosts aged 400–1100 Ma. Cathodoluminescence demonstrates further differences between agates from hosts aged 13–1100 Ma and those from Stockdale Beck and Western Australia. Agates from the latter areas have a lower proportion of defects causing a red emission band (~660 nm) but an increased proportion of defects causing blue (~470 nm) and orange (~640 nm) emission bands. Agates found in hosts aged 13–1100 Ma are also differentiated from the Stockdale Beck and Western Australian agates in a ternary plot of the relative intensities of violet to blue to orange emission bands. Single scans producing this combination of colours are only found in the Stockdale Beck and Western Australian agates. The properties shown by the Stockdale Beck and Western Australian agates demonstrate that an agate or chalcedony infill can be used to identify post-deposition palaeoheating within a host rock.