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Panteleit B.,Geological Survey of Germany | Hamer K.,University of Bremen | Kringel R.,Federal Institute for Geosciences and Natural Resources | Kessels W.,Leibnitz Institute for Applied Geosciences | Schulz H.D.,University of Bremen
Environmental Earth Sciences | Year: 2011

Geochemical processes, occurring in a stable transition zone between saltwater and freshwater, were simulated in a 2D, multi-layer flow chamber experiment. Mixing, calcite dissolution, and oxidative degradation of organic matter were identified as the main controlling factors. The results of the chamber experiment were compared to field data and verified by thermodynamic modeling. Similarity in most ion distributions suggests the general applicability of the experimental method. Differences in the redox conditions between field and experiment were reflected by the oxidants involved in the mineralization of organic carbon; while field data show evidence of sulfate reduction, the presence of oxygen in the laboratory experiment resulted in the reoxidation of sulfides. © 2010 Springer-Verlag.

Dill H.G.,Federal Institute for Geosciences and Natural Resources | Melcher F.,Federal Institute for Geosciences and Natural Resources | Kaufhold S.,Federal Institute for Geosciences and Natural Resources | Techmer A.,Leibnitz Institute for Applied Geosciences | And 2 more authors.
Canadian Mineralogist | Year: 2010

As a result of the Late Miocene skarn-type Fe mineralization at Mega Livadi on the Isle of Serifos, Greece, arsenical copper mineralization of hydrothermal origin formed in calcareous roof-rocks of a granodioritic intrusion. The hypogene mineralization, with pyrite. As-rich tennantite-group minerals and arsenopyrite, underwent strong alteration during the Pliocene and Quaternary by descending meteoric waters. We subdivide the geogenic and anthropogenic processes responsible for this alteration into five mineralizing stages, differing from each other by their element budget, Eh and pH. The supergene stages I to III comprise a variegated assemblage of oxides, hydroxides and arsenates: stage I (goethite, mixture of fine-grained Fe-As-Sb-Cu minerals, pharmacosiderite), stage II (Sb-bearing beudantite, REE-bearing beudantite), stage III (arseniosiderite). The anthropogenic stages IV and V are characterized by a set of hitherto unknown K-Cu humates and oxalates (stage IV) and the common Cu carbonates malachite and azurite (stage V). Chemical weathering induced by the (sub)tropical climatic conditions during the Late Miocene and Pliocene was responsible for the supergene associations of stages I through III at Mega Livadi. In the course of this alteration, the content of Fe decreased and As increased. Anomalously high contents of LREE in beudantite are used as a "minerostratigraphic" tracer to correlate the mineralization of stage II with a phase of pervasive formation of laterite in the Aegean region during the Pliocene. After a hiatus, an anthropogenic episode of mineralization was triggered by ancient mining activities during the early Bronze Age, around 3325 to 2890 BC, when miners began exploiting the soft arsenical Fe and Cu ore at shallow depth. This mineralization evolved under more temperate climatic conditions as a result of ventilation during mining. Bronze-age K-Cu humate-oxalate aggregates and Cu carbonates precipitated from pedogenetic fluids as a function of variable redox conditions and a pH value fluctuating around neutral. This sequence of per descensum mineralization with arsenates, humates and carbonates at Serifos, Greece, is of importance in three ways. It offers an insight into the most recent weathering processes of base-metal mineralization in the Aegean Sea region. It gives an overview of mining activities across Europe from Cyprus, the "Cradle of Cu mining", to Great Britain during the Bronze Age. Also, the physicochemical results obtained from the study of this multistage alteration may be employed to explain the compositional variation under (sub)tropical through temperate climatic conditions in tailings derived from beneficiation of As-Cu ores elsewhere.

Dill H.G.,Federal Institute for Geosciences and Natural Resources | Techmer A.,Leibnitz Institute for Applied Geosciences | Botz R.,University of Kiel | Weber B.,Burgermeister Knorr Str. 8
Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften | Year: 2012

The Dead Sea Transform Fault, creating one of the most prominent rift basins on Earth, provoked freshwater limestones to develop in five stages: (I) 45 to 26 ka, (II) 26 to 15 ka, (III) 15 to 12 ka, (IV) 12 to 5 ka, (V) 5000 to 1500. Stages I and II represent periods of subaqueous limestone formation and stages III to V sedimentation of carbonate in a subaerial depositional regime. Kutnahorite, barite, halite, sylvite and kainite reflect the environmental conditions of the limestones caused by oxidising, slightly acidic to strongly alkaline fluids. The mineral succession reflects the solubility products of the minerals involved, coupled with an uplift-induced detrital runoff and a hydrothermal activity (temperatures 40-70 °C), leading to "white smokers". Si, Fe, Y, V and Zr are representative of the detrital input, S, Sr, F and Ba of newlyformed minerals in the freshwater limestones and negative Yb anomalies are interpreted as an evidence for hydrothermal activity. The C isotopes suggest mixed sources of the mineralising fluids. The crystal morphology of the minerals is controlled by the presence of cations heavier than Ca 2+ and organic compounds. The Ba-Mn-bearing calcareous rocks evolved in subaqueous to subaerial depositional environments under hypogene through supergene conditions. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.

Dill H.G.,Federal Institute for Geosciences and Natural Resources | Techmer A.,Leibnitz Institute for Applied Geosciences | Botz R.,University of Kiel | Dohrmann R.,Federal Institute for Geosciences and Natural Resources | Kaufhold S.,Federal Institute for Geosciences and Natural Resources
Journal of Volcanology and Geothermal Research | Year: 2012

The boundary between the Arabian and African plates, is marked in the Middle East by one of the most prominent deep-seated lineamentary structures, called the Dead-Sea-Transform Fault System (DSTFS). Structural and mineralogical processes related to the DSTFS were correlated with equivalent processes leading to the alteration of pyroclastic deposits of alkali-olivine basaltic to nepheline basaltic composition which formed during a time span of less than 0.5. Ma. The large deposit of Tell Rimah, Jordan, is operated for the exploitation of zeolites, tuffs, and as pozzolana raw material. Four discrete stages of mineralizations have been distinguished from each other within these volcanic-hosted mineral deposits.(1) Hypogene syneruptive alteration of pyroclastic rocks produced siliceous gels ("allophane"), smectite, analcime, and phillipsite in vesicles when the groundwater level was low in the rift basin of the DSTFS. The lake-level lowstand caused the fluid system in the pyroclastic cone to become self-sufficient and it has been considered as a closed hydrothermal system. (2) Periods of tectonic and magmatic quiescence grinded the detrital sedimentation in the rift basin to a halt, while triggering a supergene alteration in the eruptive cones on the adjacent Arabian Plate. (3) Epigenetic alteration affected the pyroclastic rocks in the distal part of the DSTFS as a result of a rising water level. The water gradually filled the pore space of the permeable pyroclastic deposits almost to completeness and caused meniscus and blocky cements of calcite, phillipsite and chabazite to develop. In the rift basin, contemporaneously with the alteration of the pyroclastic rocks, freshwater limestones formed on calcareous bedrocks. Ba and Mn minerals in these freshwater limestones were supplied by subaquatic brines. Subsequently, a drastic lowering of the lake water level in the DSTFS converted the system of subaquatic freshwater limestones into subaerial tufa and travertine. As long as the basal parts of the pyroclastic units at Tell Rimah were in the reaches of the saline groundwaters, calcite and faujasite developed in the pyroclastic host rocks. (4) Another lake level lowstand within the rift basin caused the pyroclastic host rocks to get emerged and forced zeolite-carbonate mineralization in the tuffs to a complete stillstand. Hypogene and supergene alteration in these phreatomagmatic-strombolian pyroclastic cones of the Pleistocene x were correlated with lake high- and lowstands in the adjacent rift basin along the DSTFS.The results obtained by current tectono-morphological studies of the rift-related alteration of pyroclastic rocks along the DSTFS may also be applied to basin-and-swell-topographies elsewhere in the world. The current studies involved microscopy supplemented by SEM-EDX, X-ray diffraction analysis, mid (MIR) and far (FIR) infrared spectroscopy. Major and trace elements were analyzed by X-ray fluorescence spectrometry (XRF). C- and O isotope analyses were conducted on carbonate minerals, which were also targeted on by radiocarbon dating. © 2012 Elsevier B.V.

Dill H.G.,Federal Institute for Geosciences and Natural Resources | Pollmann H.,Institute for Geological science and Geiseltal Museum | Techmer A.,Leibnitz Institute for Applied Geosciences
Ore Geology Reviews | Year: 2013

The crust along the northern boundary of Gondwana, what is called today Jordan, Israel, Turkey and Egypt, is enriched in Mn. During the geodynamic evolution of this crustal part, lasting for 500. million years, the opening of the Paleo- and the Neotethys Oceans was accompanied by the emplacement of several medium- to small-sized Mn deposits in the Middle East region. Manganese concentration was linked in time and space closely to the evolution of triple junctions which mark the break-up of the crust in northern Gondwana and whose linear fault zones deeply penetrated into the upper mantle so that alkaline magmas in the Middle East and East Africa could use these plate boundaries as conduits for their ascent. The first triple junction on the Sinai Peninsula, active around 500. Ma ago, marked the beginning of rifting and Mn recycling at the northern edge of Gondwana, the second one in the Afar Region, Ethiopia, denotes factually the end of the first tectono-metallogenetic phase and the onset of another Mn cycle still being in its embryonic state. In the upper crust Mn was recycled by episodic rifting to form Mn deposits during the Cambrian, the late Paleozoic, the Paleogene and the Quaternary in the Middle East. Manganese mineralization is bound to siliciclastic rocks containing Mn oxides and hydrates, e.g., birnessite, pyrolusite, and manganite. Ba, K, Pb, Co and Ni act as chemical qualifiers in these oxidic minerals and allow for a more subtle subdivision of different stages of Mn mineralization (romanechite, cryptomelane, coronadite, asbolane). Concentration of Mn involved deposition in near-shore marine basins under diagenetic, epigenetic hydrothermal, roll-type and supergene conditions. It was mediated by Cu mineralization and microbial processes and, in places, accompanied by baryte concentration. The branches of the Middle East triple junctions were not equally operative through time:. (1)The Najd strike-slip zone was active during the Precambrian and Cambrian and was only re-activated after a long period of tectonic quiescence within the Red-Sea Graben(2)The N-trending Dead-Sea Transform Fault (DSTF) was active all the way till the Recent.(3)The third branch of the triple junction, the SW Egypt Rift was episodically active, e.g., during the mid-Permian-Jurassic period, leading to the late Permian Mn concentration. Its NE prolongation, the Palmyra Trough, gave rise to an embryonic Neo-Tethys Ocean and paved the way for Turkey to drift away from the Afro-Arabian Plate leading to a separate Mn province during the Cenozoic. By its drifting away, part of the Mn preconcentrated in the crustal section of Gondwana was also taken away and recycled later north of the Neo-Tethys in what is called today Turkey. During the late Mesozoic, advanced spreading in the Neo-Tethys Ocean generated oceanic crust and added another batch of Mn from the mantle to the crustal Mn cycle in form of Mn-bearing mud on top of the ophiolite sequences in the Troodos and Semail Ophiolites Cenozoic. Mn mineralization resulted from redeposition of an intracrustal Mn repository along the NW prolongation of the Red Sea Rift and along the N prolongation of the DSTF during the Eocene in Turkey and Egypt. Unlike many of the so-called giant Mn deposits located on stable cratons that owe their mineral wealth to their geodynamic persistence and in-situ re-working of Mn, Middle East rift-related Mn concentration was later subjected to considerable dilution by plate motion, leading to a number of Mn occurrences displaced around the former triple junction instead of one unique "giant deposit" on top of it. Mn concentration in the Middle East is confined to megasequence boundaries (AP1/AP2, AP5/AP6, AP10/AP 11), using sequence stratigraphic principles for a temporal subdivision. The crustal sections most productive for Mn concentration are those megasequences typical of maximum regression surfaces or, in other words, where conformities were correlative with unconformities. An important chemical factor of Mn enrichment related to these sequence stratigraphical changes can be microbial activity both in oxic Mn enrichments and anoxic, sulfidic environments. These geodynamic issues, described in terms of sequence stratigraphy and plate tectonics, directly translate into the physico-chemical regime, when the periods of a maximum contrast among the redox conditions fostered the complete sequence of tetra- to bivalent oxidic Mn minerals to evolve. In conclusion, the most fertile areas on the globe to concentrate Mn are crustal sections characterized by hot-spots at a triple-junctions, truncated by surfaces of maximum regression that provoked the strongest contrast of redox conditions and thereby gave rise to the precipitation of a wide range of oxidic Mn minerals. During subduction Mn previously preconcentrated in the oceanic crust will be consumed and, hence, active margins rank lower than passive ones when it comes to Mn accumulation. © 2013.

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