Alkaline igneous rocks of the coastal belt, south of Luderitz, South West Africa : a petrological study

The Luderitz Alkaline Province, as it is at present known, comprises the subvolcanic central complexes of Drachenberg, Pomona, and Granitberg. An attendant dyke swarm strikes NE-SW and crops out between the latitudes of 27°00' and 27°30' S. Stratigraphic indications (now confirmed by a K/Ar age from Granitberg) are that the Luderitz Province is early-Cretaceous in age and therefore older than the Klinghardt phonolites (Eocene) as well as the smaller melilitite and nephelinite intrusions. Granitberg is a circular foyaite complex, in the centre of which is preserved a large fragment of sedimentary rocks that originally formed the roof of the intrusion. The foyaites have been emplaced into the feldspathic sandstones and dolomites of the Bogenfels Formation, and three major intrusive phases can be recognised. The first phase produced chilled nepheline syenites beneath the roof of the intrusion. These chilled rocks grade downwards into coarse-grained foyaites. The second phase was the emplacement of the Inner Foyaite which crystallized as a cylindrically zoned plug, capped by a zone of layered, laminated, and xenolithrich foyaites. The third phase was the emplacement of the Outer Foyaite, into which the Roof Zone and the Inner Foyaite foundered. The Outer Foyaite is zoned with a miaskitic core, and an agpaitic outer zone

Potential reactivity assessment of mechanically activated kaolin as alternative cement precursor

This work aims to assess the potential reactivity of a mechanically activated kaolin for its use as an alternative cement precursor. The mechanical activation was successfully achieved by grinding at different rotation speeds (250, 300, and 350 rpm) and times (60, 90, and 120 min), obtaining a highly amorphous and reactive material. The amorphization was monitored through XRD with amorphous content estimation and FTIR deconvolution. The potential reactivity was evaluated through chemical attacks, obtaining SiO2 and Al2O3 availabilities up to 95 wt% and 93 wt% of total SiO2 and Al2O3 content. XRD and FTIR also allowed the identification of the nonreactive phases on the insoluble residue after chemical attacks. NMR analysis revealed that part of the aluminium was in IV coordination, limiting the reactivity in the alkali activation process. This work demonstrated the effectiveness of mechanical activation as a greener treatment than thermal dehydroxylation to increase the raw kaolin's reactivity

A comparison betweenab initio calculated and measured Raman spectrum of triclinic albite (NaAlSi3O8)

Albite is one of the most common minerals in the Earth\u2019s crust, and its polymorphs can be found in rocks with different cooling histories. The characteristic spectrum of vibration of the albite mineral reflects its structural Si/Al ordering. In this study, we report on the comparison between the Raman spectrameasured on a natural and fully ordered (as deduced on the basis of single-crystal X-ray diffraction data) \u2018low albite\u2019, NaAlSi3O8, and those calculated at the hybrid Hartree\u2013Fock/density functional theory level by employing the WC1LYP Hamiltonian, which has proven to give excellent agreement between calculated and experimentally measured vibrational wavenumbers in silicate minerals. All the 39 expected Ag modes are identified in the Raman spectra, and their wavenumbers and intensities, in different scattering configurations, correspond well to the calculated ones. The average absolute discrepancy |\u394v| is ~3.4cm-1, being the maximum discrepancy |\u394v|max ~ 10.3 cm-1. The very good quality of the WC1LYP results allows for reliable assignments of the Raman features to specific patterns of atomic vibrational motion

The geology and the ore mineralization in the Keban area, east Turkey

The Keban mine is one of the most important lead and zinc producers in Turkey. It is located 54 km NW of Elazig County, Eastern Turkey. The Keban metamorphic massif consists of calc-schists, dolomite marble, phyllite and marble. It forms part of the eastern Taurid belt, a prolongation of the Alpine orogenic belt. The principal structural feature of the area is the northern extension of the Malatya-Keban anticline, a major recumbent fold with a NE-SW axis. Later movements acting in different directions gave rise to N-S, E-W, NW-SE and NE-SW directed folding and faulting over the previous anticline. Small bodies of quartz-syenite porphyry, of paleocene age, intrude the metasediments. Detailed study by chemistry, petrography and x-ray techniques on sanidine accounts for a composition range between Or65 Ab35 and Or99 Ab1. The ratio of Or to Ab tends to increase outwards from the central parts of the igneous body. Skarn zones have developed in association with the intrusion of quartz-syenite porphyry. These are located mainly within the metasediments. The magnatite deposit of Zereyandere, the scheelite deposit of Kebandere and the main sulphide deposit were formed as part of the process of skarn formation. Minor amounts of some manganese minerals and the minerals vanadinite and descloizite derived from the main sulphide deposit, are also found in the district. The main sulphide deposit of economic importance chiefly incudes sphalerite, galena, iron and copper sulphides and several sulfo-salts in subordinate amounts. Of the by-products, silver comes from galena, polybasite and tennantite. Arsenopyrite in addition to chalcopyrite contains trace concentrations of gold. All the evidence suggests that the quartz- syenite porphyry is the source of mineralization. The location of ore minerals is controlled by certain rock types and by major and minor structural elements. Variation of vapour fugacity and temperature during mineralization are indicated by more than one stage of formation for certain ore minerals. The presence of different gangue minerals marks the fluctuating nature of the ore forming fluids whose last stage is believed to be alkaline rather than acidic. The main sulphide deposit is accepted as a semi-metasomatic contact deposit, while the magnetite and scheelite deposits are classified as being metamorphic. Using various methods, a temperature range of formation between 620° and 78°C is estimated for the ore minerals of the main sulphide deposit. For the ore minerals of the magnetite and scheelite deposits the range is from 743°C down to 225°C