Bernhard Pracejus

<p>The Tethys-derived Semail Ophiolite had formed during the Cenomanien-Turonian. Along with deep-sea sediments, it was obducted onto the Arabian Plate as it was still young, hot and buoyant. Thrusting and loading triggered the formation of the Aruma Foreland system consisting of a foredeep, a forebulge and a backbulge basin.</p><p>The studied succession represents the uppermost part of the Permo-Mesozoic shallow marine shelf sequence of the Arabian Platform, which is blanketed at an angular unconformity by shales of the Late Cretaceous Muti Formation of the Aruma (foreland) Group. The structural position of the succession is on the forebulge which is characterized by eroded Cretaceous and Jurassic shelf formations of the Arabian Platform (Wasia-Aruma Break).    </p><p>We identified two forebulge successions. Both display repetitive lithofacies, beginning with (1) shallow subtidal massive/poorly bedded bioclastic wackestones to floatstones, followed by (2) peloidal grainstones, (3) ferruginous crusts and (4) shallow marine ferruginous oolites. From base to top, both successions record an overall shallowing-up trend. At the same time, the relative sedimentation rate decreases in the same direction. The coarse-grained massive facies may have been deposited on a regular slope which was well-supplied with bioclasts. The finer grained grainstone facies and their peloids indicate a lower sedimentation rate, reflecting the transition form a regular slope to a forebulge on which in the next step sediment condensation occurred (crusts) and chemical precipitation of ferruginous material (crusts and oolites). Each forebulge succession is capped by clayey material.</p><p>The similar facies development of the two successions suggests repetitively similar depositional and tectonic conditions. As both sequences occur at the same site, two vertical forebulge developments are concluded.</p><p>The ferruginous crusts formed under at least slightly reducing conditions, associated with minor water-deepening events. Both oolites contain chlorite, hematite, quartz, calcite and apatite. The nuclei of the ooids are often chlorite or hematite fragments, having most-likely derived from preexisting ferruginous crusts. Iron oxyhydroxides and clinochlore of the oolites reflect bathymetric changes to more oxidizing aqueous conditions, associated minor water-shallowing events.</p><p>Fe-rich anoxic to sub-oxic sea water of the marine foredeep was the Fe source for the crusts and oolites, coinciding with (1) a high rate of global Cretaceous oceanic crust production, (2) related hydrothermalism and (3) the regional proximity of an active spreading axis. Fe was likely stabilized in ocean water as Fe colloids and organic Fe complexes.</p>

The present study attempts to identify the sources of Cr(VI) in a coastal alluvial fan soil and soil from a chromite mine. In addition investigates the effect of photochemically oxidized organic matter in the Cr(VI) mobilization in soil. The alluvial bulk soil samples contain several evidence of weathered products of the ophiolite nappe like serpentine and amphiboles. For better characterization we separated different soil fractions with magnetic separation. The results showed that magnetic fraction exhibits high amount of serpentine. The XRF-analysis showed Mg and Cr to be enriched on average by 2.5 and 6 times, respectively. The produced fractions were mixed with glucose to simulate organic carbon and then leached with KH2PO4/Na2HPO4 for the exchangeable Cr in all fractions before and after the exposure of the samples in the sun for several days. The results showed that soils from chromite mine were influenced by oxidation of organic matter with 20-30% reduction in Cr(VI) release,...

Abstract This chapter provides the conclusions/outlines of the tectonics, affecting the Southeastern Oman Mountains, including the Jabal Akhdar and Saih Hatat domes. The main tectonic events include amongst others (1) Neoproterozoic rifting, (2) two distinct early Paleozoic compressive events, (3) large-scale open ‘Hercynian’ folding and formation of a pronounced unconformity during the late Paleozoic, (4) rifting preceding the opening of the Neo-Tethys Ocean during the late Paleozoic, (5) late Cretaceous obduction of the Semail Ophiolite and the response of the Arabian lithosphere as well as (6) post-obductional tectonics. Also of major geological significance are the three major glaciations (Sturtian, Marinoan and Late Paleozoic Gondwana glaciation) which have been recorded in the rocks of northern Oman. Moreover, major lithological, structural and metamorphic differences exist between the Jabal Akhdar and Saih Hatat domes. It appears likely that a major fault, striking parallel to the eastern margin of the Jabal Akhdar Dome, probably originating during Neoproterozoic terrain accretion, acted as a divide between both domes until present. This fault was multiple times reactivated and could explain the differences between the two domes. A catalogue of unanswered questions is included in chronological order to express that many geological aspects need further investigation and future research projects.

<p>The rocks of the Saih Hatat Dome (SHD) formed during and after two major geological events shaping Arabia: 1) Subduction of continental rocks in the course of the Late Cretaceous Semail Ophiolite obduction onto the Arabian Plate and 2) Exhumation of >16 km and high deformation/folding in the northeastern part of the SHD. The latter resulted in a ~20 km wide recumbent fold (Saih Hatat Fold Nappe). The sub-horizontal fold axis of this fold trends NNE in the northern SHD. The core of the SHD and the recumbent fold consist of dark Neoproterozoic meta-shales and meta-sandstones, while its margin (and upper/lower limbs of the recumbent fold) consist of Permian cliff-forming carbonates.</p><p>Within the northern SHD, numerous milky quartz veins occur. We structurally and mineralogical analyzed >500 of these veins, covering an area of ~200 km<sup>2</sup>. The veins vary in width from one centimeter to a few meters, while the length ranges between several decimeters to several decameters. Associated with the predominant milky quartz, are calcite, siderite, chlorite, albite, anorthite, actinolite, rutile, hematite, goethite, and pyrrhotite. Rare molybdenite aggregates seem to replace carbonate, in which it occurs exclusively. Quartz microstructures include bulging (BLG) recrystallization, sub-grain rotation (SGR) recrystallization, and undulose extinction. Sub-grains and triple junctions in quartz are common. The mineralogy and quartz microstructures indicate maximum peak temperature conditions of ~400-500°C.</p><p>At least two sets of veins can be distinguished. Both vein sets occur mostly in clusters and partly form vein swarms. The mineralogy and quartz microstructure of both vein sets is similar. The older set 1 has been folded by the Saih Hatat Fold Nappe. Thus, vein formation predates 76-70 Ma. Furthermore, veins of set 1 are often sub-parallelly oriented to the main foliation of the host rocks, and they may be boudinaged. They may form complicated vein structures. We assume that this vein set initially formed during the Permian Pangean/Tethys rifting. The second vein set is abundant, sub-vertically and strikes consistently E/W to ESE/WNW. These veins cut the overall moderately NW-dipping bedding surfaces of the ambient rocks. Set 2 veins either formed during exhumation of the dome (Late Cretaceous to early Eocene and late Eocene to Oligocene) or they are part of the NW-striking sinistral Hajar Shear Zone, which affected the entire eastern Oman Mountains during the Oligocene to early Miocene. Ongoing U-Pb dating of carbonates and further field survey will further contribute to the understanding of their age and tectonic setting.</p>

ABSTRACT Modern massive sulfide deposits are known to occur in diverse tectonic settings and it is generally expected that hydrothermal deposits of similar geological settings shall have more or less similar mineralogical and geochemical signatures. However, the Mount Jourdanne sulfide deposits along the super-slow spreading Southwest Indian Ridge deviate from this common concept. These sulfide precipitates are Zn-rich (up to 35 wt.%) and are characterized by high concentrations of Pb (≤ 3.5 wt.%), As (≤ 1.1 wt.%), Ag (≤ 0.12 wt.%), Au (≤ 11 ppm), Sb (≤ 967 ppm), and Cd (≤ 0.2 wt.%) which are unusual for a modern sediment-free mid-oceanic ridge system. Therefore, we have reinvestigated the sulfide samples collected during the INDOYO cruise in 1998, in order to explain their unusual mineralogy and geochemical composition. The sulfide samples are polymetallic and are classified as: a) chimneys, b) mounds, and c) hydrothermal breccias. The chimneys are small tube-like symmetrical bodies (30–40 cm high; ~ 10 cm diameter) and consist mainly of sphalerite and less chalcopyrite, set in a matrix of late amorphous silica. The inner wall shows a late-stage colloform sphalerite containing co-precipitates of galena and/or Pb–As sulfosalts. In contrast, the mound samples are dominated either by Fe-sulfides (pyrite) or by a mixture of pyrite and chalcopyrite with less sphalerite, pyrrhotite, amorphous silica and barite. Both, the chimney and mound samples, are characterized by layering and mineral zonation. The hydrothermal breccias are highly altered and mineralogically heterogeneous. They consist of silicified basaltic material that are impregnated with sulfides and contain cm-sized chimney fragments within a matrix of low-temperature minerals such as sphalerite and pyrite. The latter fragments mainly consist of chalcopyrite with isocubanite lamellae. In addition, these breccias contain late-stage realgar, boulangerite, galena, Pb–As sulfosalts and barite that are mostly confined to vugs or fractures. At least five mineralogical associations are distinguished that indicate different thermal episodes ranging from black smoker mineralization conditions to cessation of the hydrothermal activity. Based on the mineralogical associations and established literature in this regard, it is inferred that the mineralization at Mt. Jourdanne occurred mainly in three temperature domains. Above 300 °C, the chalcopyrite (with isocubanite)–pyrrhotite association formed whereas the sphalerite dominated assemblage with much less chalcopyrite and pyrite formed around and below 300 °C. The late-stage mineralization (below 200 °C) contains colloform sphalerite, galena, Pb–As sulfosalts, realgar and barite. The unusual mineralogy and trace element chemistry for this modern VHMS deposit could be explained assuming hydrothermal leaching of some felsic differentiates underneath the basaltic cover and subsequent zone refining processes.

The geology of the Oman Mountains, including the Jabal Akhdar and Saih Hatat domes, is extraordinarily well-exposed and diverse, spanning a geological record of more than 800 Ma. The area is blessed with first-class outcrops and is well known in the geological community for its ophiolite. The Oman Mountains have much more to offer; including, Neoproterozoic diamictites (“Snowball Earth”), fossil-rich Permo-Mesozoic carbonates and metamorphic rocks. The arid climate and deep incision of wadis allow for nearly complete rock exposure which can be investigated in all three dimensions. The diverse geology is also responsible for the breathtaking landscape. New roads and the nature of the friendly Omani people make fieldwork unforgettable.This Memoir provides a thorough state-of-the-art overview of the geology and tectonics of the Southeastern Oman Mountains, and is accompanied by an over-sized geological map and a correlation chart.

The Ore Minerals Under the Microscope: An Optical Guide, Second Edition, is a very detailed color atlas for ore/opaque minerals (ore microscopy), with a main emphasis on name and synonyms, short descriptions, mineral groups, chemical compositions, information on major formation environments, optical data, reflection color/shade comparison with four common/standard minerals of a similar color or grey shade, and up to five high-quality photos for each mineral with scale. In addition, the atlas contains a compilation from some of the prominent publications in the field of ore microscopy presented on a list of 431 minerals. * Concise, full-color pictorial reference for scientists and geologists* Explains how to describe and identify microscopic samples of minerals* Draws material from prominent literature yielding more than 400 different minerals

<p>The Jabal Akhdar Dome of the Hajar Mountains (northern Oman) has long been considered to have had no significant thermal overprinting since the start of its doming (Eocene, ~40 to 30 Ma). Only the Semail Ophiolite, obducted during the Late Cretaceous, metamorphosed the overridden sedimentary rocks at its base. However, this is stratigraphically well above the positions of the rocks discussed here. Our findings describe the first evidence for an increased metamorphic alteration of Late Permian, Jurassic and Lower Cretaceous shelfal limestones. Two independent sites were identified, where calcite was either replaced by wollastonite or sulfides.<span> </span></p><p> </p><p>The calc-silicates, which occur southeast of the Saiq Plateau (stratigraphically above the plateau), contain up to centimeter-sized wollastonite crystals. The conversion into marble has been interrupted, as indicated by relict fossils and ooliths of Jurassic and Lower Cretaceous limestones. So far, the outcrop has been mapped over a length of ~1.2 km. It is dissected by several NW-striking dextral faults in a difficult terrain and, thus, the occurrence may be significantly wider. Wollastonite concentrates in sub-horizontal to gently SE-dipping limestone layers, neighbouring strata may be almost void of it. In places, strong and coarse-grained dolomitisation coincides with decreased wollastonite content. The area is cross-cut by irregular quartz-wollastonite-rich veins.</p><p> </p><p>Adjacent to the outcrops are younger quartz-siderite veins, which have almost completely replaced limestone layers (encased wollastonite-carrying limestone relicts). Distal to the mineralisations, the limestones contain decimeter-sized chert nodules. This entire silica-dominated system must have reached 450 ºC in order to form the well crystallised wollastonite. The mostly oxidising character of the environment during overprinting is reflected by fine euhedral hematite grains throughout the examined profile. However, slightly reducing settings promoted the formation of very rare and tiny crystals of erdite (NaFeS<sub>2</sub>·2H<sub>2</sub>O) in two places.</p><p> </p><p>Sulfides in finely laminated Permian carbonates, which contain fine as well as very coarse-grained black carbonates, occur on the northwestern side of the Saiq Plateau in no longer accessible excavation materials. So far, the search for another outcrop failed, due to the sub-vertical wadi walls near-by. The strongly dominating pyrite is accompanied by trace amounts of sphalerite and less galena. Collectively, sulfides replaced carbonate laminae with fine crystalline impregnations and concentrated in up to decimeter-large lensoid concretionary shapes. Dark carbonaceous laminae and recrystallised coarse-grained materials contain finest graphite flakes. This again indicates temperatures of ~450 ºC, at which the graphite formation started during decarbonisation, also promoting a reducing regime (the sulfides show no signs of oxidation).</p><p> </p><p>Our working hypothesis is that the thermal overprint (>450 ºC) coincided with the late Eocene to Oligocene doming event, leading to multiple mafic intrusions. Similar intrusions are known from the Muscat and Batain area and have the same age.</p>

... AND DEVELOPMENT OF SUPERGENE MANGANESE DEPOSITS, GROOTE EYLANDT, NORTHERN TERRITORY, AUSTRALIA BERNHARD PRACEJUS, BARRIE R. BOLTON ... silts, siltstones, disordered in laterites clayey sands and pipes, rare layers in vugs, as impregnation ...

... to medium-scale crossbedding and massive Laterally extensive, underneath soils, vugular Lateral, underneath manganiferous laterite, vugular Planar, regionally up to 50 m thick, sometimes layered, mostly irregular in laterites and pipes, rarely layers in vugs, as impregnation in ...

... AND ANDREAS M',d. RTEN Labor fiYr Bau-und Werkstoffchemie, Universit•it Siegen, Paul-Bonatz-Strasse, ... The arc consists of a nonvolcanic outer arc (Pa-leozoic and Cenozoic sedimentary rocks), forming the main island chain and representing an elongated piece of the ...

The Southeastern Oman Mountains are dominated by two major culminations: the Jabal Akhdar and Saih Hatat domes, surrounded by allochthonous and/or neo-autochthonous rocks. In the cores of both domes, folded autochthonous and par-autochthonous pre-Permian metasedimentary rocks are exposed, subjacent to the ‘Hercynian’ Unconformity. Above the unconformity are Permo--Mesozoic shelfal sedimentary rocks, characterized by carbonates. These sedimentary rocks were openly folded. The open folds are large-scale elongate structures that define the shapes of both domes. The main elongation direction is NW--SE. Doming is syn- to post-obductional. Most margins of the domes are marked by major post-obductional, extensional faults. Reactivated basement faults along the eastern margin of the Jabal Akhdar Dome may be responsible for the straight NNE-striking eastern margin which is perpendicular to the main elongation direction of the domes. The deep structure of both domes is poorly known. However, ...

The Angudan Orogeny affected Cryogenian to earliest Cambrian sedimentary rock formations of the Jabal Akhdar Dome of the Oman Mountains. These rocks were folded and cleaved at 525 ± 5 Ma. We studied the Cambro-Ordovician (Terreneuvian to Darriwillian) Amdeh Formation of the neighboring Saih Hatat Dome to see whether this formation was also affected by the Angudan Orogeny. The Angudan deformation within the Jabal Akhdar Dome is known for its folds and cleavage. Due to age considerations (see above), we studied the folds and cleavages within the two oldest members of the Amdeh Formation (Am 1 and Am 2) in order to compare them with the ones that are known from the Jabal Akhdar Dome to possibly detect Angudan-related deformation in Am 1 and Am 2. Angudan folds of the Jabal Akhdar Dome display fold axes that are oriented NE/SW, but the two lowest members of the Amdeh Formation reveal one set of folds with subhorizontal fold axes that trend NW-NNW/SE-SSE. The lack of Angudan-related fold...

The role and significance of microorganisms in environmental recycling activities marks geomicrobiology one of the essential branches within the environmental biotechnology field. Naturally occurring microbes also play geo-active roles in rocks, leading to biomineralization or biomobilization of minerals and metals. Heavy metals, such as chromium (Cr), are essential micronutrients at very low concentrations, but are very toxic at higher concentrations. Generally, heavy metals are leached to the environment through natural processes or anthropogenic activities such as industrial processes, leading to pollution with serious consequences. The presence of potentially toxic heavy metals, including Cr, in soils does not necessarily result in toxicity because not all forms of metals are toxic. Microbial interaction with Cr by different mechanisms leads to its oxidation or reduction, where its toxicity could be increased or decreased. Chromite contains both Cr(III) and Fe(II) and microbial ...

This study presents a new approach for detection and mapping of ancient slag heaps using 16-band multispectral satellite imagery. Understanding the distribution of slag (a byproduct of metal production) is of great importance for understanding how metallurgy shaped long-term economic and political change across the ancient Near East. This study presents results of slag mapping in Oman using WorldView-3 (WV3) satellite imagery. A semi-automated target detection routine using a mixed tuned matched filtering (MTMF) algorithm with scene-derived spectral signatures was applied to 16-band WV3 imagery. Associated field mapping at two copper production sites indicates that WorldView-3 satellite data can differentiate slag and background materials with a relatively high (>90%) overall accuracy. Although this method shows promise for future initiatives to discover and map slag deposits, difficulties in dark object spectral differentiation and underestimation of total slag coverage substant...

Wadi Fizah ophiolite in Oman has widespread ultramafic rocks, particularly in the basal dunite and harzburgite unit ofthe mantle section. This paper presents a research study to evaluate the discrimination and occurrence of chromites bearing mineralized zones within Oman ophiolites by analyzing the capabilities of Landsat TM and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data; using a number of selected methods including decorrelated stretching, different band rationing and Principal Component Analysis image processing techniques. The study results show that the processed VNIR and SWIR spectral wavelength regions are promising in detecting the areas of potential chromite bearing mineralized zones within the ophiolite region, and proved to be successful for mapping of serpentinized harzburgite containing chromites.