Physical Chemical Regime Research Articles

The “badland trilogy” of the Desierto de la Tatacoa, upper Magdalena Valley, Colombia, a result of geodynamics and climate: With a review of badland landscapes

The badlands of the “Desierto de la Tatacoa” (DDT) form part of the alluvial-fluvial system and are characterized by a landform trilogy: (1) gully zone, (2) wadi zone, (3) hillwash plain/mesa zone. This facies differentiation is controlled by the fluvial regimes and their degree of sinuosity of channels. The hydraulic and hydrographic systems of the badland trilogy depend on the geodynamic setting and climate (1st order) and on the bedrock lithology and tectonics (2nd order). Allogenic heavy minerals attest to two counteracting palaeogradients which interdigitate where the badlands evolved and authigenic heavy and light minerals furnish evidence of the physical-chemical regime to be governed by alkaline meteoric solutions and oxidizing conditions driven by the climate and the parent rocks. It is the high solubility of sulfates and chlorides and the differential expandability of smectite which impacted on the development of the individual badland zones. Large 1st order synclines plunging to the W and 2nd order fold structures account for the traps and conduits of the subsurface water system. The key to the hydraulic evolution of the badland lies within the hinterland hampering surface alteration and favoring the subsurface hydrogeological system to corrode the gully zone from below. The binary genetic model of the badlands in the DDT reveals, on a local scale, a “fight for dominance” of different fluvial drainage systems at the edge of the badlands as a hydrological consequence of neotectonics while, on a regional scale, badland formation is an upstream expression of a eustatic sea level oscillation in the Caribbean Sea. A review of true, false and pseudo-badlands concludes the study and underscores the reference character of the DDT badlands among the true badland series.

The physical-chemical regime of a sulfide-bearing semi-graphite mineral assemblage in metabasic rocks (SE Germany) – A multidisciplinary study of the missing link between impsonite and graphite

Along the western edge of the Bohemian Massif, SE Germany, graphitic carbon occurs in metabasic rocks plus calcsilicates, metabiolites, and paragneisses (graphite I), in pegmatites (graphite II) and in mineralized structure zones (semigraphite and impsonite) The current studies unveiled these graphitic carbon compounds are strikingly different with regard to their age and temperature of formation: Graphite I (≥324 Ma, 570 to 625 °C), graphite II (317 ± 3 Ma, >400 °C), semi-graphite (305 ± Ma, 225 to 400 °C), impsonite (<298 ± 4 Ma, 100 to 363 °C). Semi-graphite takes a special position among these graphitic carbon compounds because it links the different carbon modifications with regard to its age of formation, its structural position and its S- and C isotopes that point to a mantle and crustal influence on its formation in contrast to graphite (graphite I: crustal, graphite II: mantle) and impsonite (mantle). Semi-graphite precipitated in a fault zone which evolved from a zone of strong felsic mobilization in metabasic rocks spawning KNa feldspar-quartz pegmatoids/aploids. During conversion of a pre-existing zone of felsic mobilization into a brittle shearzone not only carbonaceous matter but also Ni-, Pb-, Cu-, Zn-, As-, Fe-, Hg- and Mo sulfides were concentrated. The semi-graphite-bearing mineralized zone is located near rare element pegmatites hosting graphite flakes. The C-bearing systems are useful pathfinders to locate structurebound mineral deposits hosting U or base metals in the Variscan orogen.The structurebound metalliferous semi-graphite mineralization in metabasic rocks can be taken as a reference type of dual-source hydrocarbon immigration into fault zones, syn- to postkinematically relative to the fault movement. The model can be applied to host rocks undergoing retrograde medium- to very-low-grade stage dynamo-metamorphic conditions.To elucidate the complex history of the various types of graphite and metamorphosed bitumen a multidisciplinary approach has been taken involving petrographic and geological field mapping combined with drill core examination, petrographic and ore microscopy supplemented by electron microprobe, X-ray diffraction and scanning electron microscopy with EDX, micro-Raman spectroscopy in addition to classical coal petrographic studies, and inorganic geochemistry of major and minor elements and isotope (carbon and sulfur) chemical analysis followed up by a statistical treatment of the various chemical datasets.

A joint study in geomorphology, pedology and sedimentology of a Mesoeuropean landscape in the Meseta and Atlas Foreland (NW Morocco). A function of parent lithology, geodynamics and climate

The origin of the landscape spreading across NW Morocco (Meseta, Atlas Mts. Foreland) is geodynamically controlled by two collisional and one extensional regime, while climate changes had only a minor impact on the shaping the landscape. The existing landscape pertains to the series characterized by highly to partially eroded mountain blocks of Paleozoic and Early Mesozoic age which is represented at its best by the relics of the Variscan orogeny resultant in what is called “Mesoeurope”. The Mesoeuropean landscape in Morocco is described by four morphodynamic units.MD 1 (0.4–1.8 Ma/generation 3) has brought about landforms in a fluvial (-alluvial) depositional environment with a strong aeolian influence at its margins. Its drainage patterns feature a moderate to gentle dip of the palaeo-current with a predominantly meandering depositional regime. The major minerals are quartz, calcite, smectite, and smectite-illite mixed-layers (submature landscape).MD 2 (2.0–3.0 Ma/generation 2) involves coastal-marine processes of a microtidal environment. Only quartz warrants mentioning as major constituent (supermature landscape).MD 3 (Neogene/generation 1) is the core zone with extensive planation and chemical weathering which gave rise to amorphous silica and smectite-group minerals (mature landscape).MD 4 (Quaternary/generation 4) encompasses landforms typical of alluvial-fluvial environments evolving under a moderate to strong palaeo-current in the foothills of the Atlas Mts. Aside of quartz, calcite, chlorite, muscovite, illite, and feldspar, labile heavy minerals are as widespread as the calcitic carbocretes. Modern structural disturbances are accountable for the immature landforms and high preservation potential of labile mineral constituents.A morphodynamic comparison between the reference type of “Mesoeurope” and the current morphodynamic type under study in Morocco results into a binary classification scheme encompassing two phases, an older one called phase of planation and a younger one called phase of dissection, a sequence which reflects quiescence and relative stable geodynamic conditions succeeded by a period of tectonic mobility. There is one striking difference between the Moroccan landscape and the reference type in Mid-Europe; the reference type has no equivalent morphodynamic unit which was triggered by the opening of the Atlantic Ocean denoted by the lack of U/Pb data of supergene alteration minerals in the reference log. The most widespread soil types encountered in the Moroccan study sites are vertisols (MD 1, MD3), luvisols (MD 1, MD 2, MD 4) and cambisols. Second in abundance are planosols, which are confined to MD 2 and, locally, arenosol associated with plinthite (MD 1); kastanozem and chernozem (MD 3) are rare members of the topsoil. While the log activity of SiO2 varies in a narrow range, the pH of the meteoric water is considerable wide, from 4.2 to 9.4. The physical-chemical regime suggests a binary subdivision into a more acidic regime (MD1, MD2) in the N and an alkaline one (MD 3, MD4) in the S which goes along with the change in the redox ratios of organic matter (LER/HER) and the climate-zonation.

The Totumo mud volcano and its near-shore marine sedimentological setting (North Colombia) — From sedimentary volcanism to epithermal mineralization

The Holocene mud volcano exposed at Totumo (younger than 4150 ± 50 yr BP) lines up together with some other landforms of its kind along the Caribbean Coast in northern Colombia. It currently vents a mud of the silicate-phosphate-bearing sulfur-sodium chloride type. The mud volcanoes evolved in an active continental margin setting of the South American Cordillera with high seismicity and affected by pervasive neotectonic structural disturbances. During the Neogene and Quaternary linear terrigenous shoreline sediments alternating with delta deposits evolved on this mobile crustal segment between the Andes and ancient Precambrian cratons. Meso- to microtidal sedimentary settings during transgression and progradation created meta- to instable sedimentary and petrophysical conditions (e.g. overpressure and gas-bearing bubble sands), favorable for the formation of mud volcanoes, whose lithofacies is subdivided into (1) footwall facies (detritus from metabasic, -pelitic source rocks), (2) mud volcano plus lateral facies (material from deep-seated hydrothermal sources, hydrocarbon plays, and brine reflux from the sea), (3) hanging wall facies, sand characterized by a strong longshore drift. The sedimentary volcanism in the area is characterized by different temperatures of formation: (1) pre-stage (<100 °C) and (2) recent stage (≈25 °C). Heavy (pyroxene, amphibole, epidote-clinozoisite, Fe-Ti silicates and oxides, garnet, alumosilicates, tourmaline, zircon, barite, Fe sulfides and -sulfates), light (Ca sulfates, calcite, quartz, feldspar) and clay minerals (kaolinite, mica, pyrophyllite, chlorite, vermiculite) are efficient tools to determine the source of mud, to subdivide the mud volcano system as to its facies and describe its physical-chemical regime as to the temperature of formation, pH and Eh values. The mud volcano system of Totumo bridges the gap between sedimentary “volcanism” and epithermal hot spring deposits of intermediate to high sulfidation and forms a useful “guide” to hydrocarbon accumulation.

A laterite-hosted APS deposit in the Amazon region, Brazil: The physical-chemical regime and environment of formation

Several occurrences and deposits of aluminum-phosphate-sulfate (APS) minerals have been discovered during the last century, and most are closely related to lateritic weathering formations. These deposits have been found all over the world but are more common in the present intertropical climate zone. Only one such deposit is mined for phosphate. However, a second, the Bonito deposit, has recently started to be mined in the Amazon region. The deposit is located in one of the most important provinces for APS minerals in the world, the Gurupi region, which lies in the northeastern Amazon region and still remains relatively unexplored. The Bonito APS deposit comprises a complete mature laterite profile, and the APS minerals are exposed at the top of the profile in the form of an aluminum phosphatic-sulphatic crust and an aluminum phosphatic-sulphatic iron-oxyhydroxide crust. The phosphate-sulphatic ore is composed of crandallite-goyazite, woodhouseite-svanbergite, and wardite-millisite, as well as some quartz, kaolinite, hematite and goethite. The ore is high in phosphor (>18% P2O5) and is rich in SrO, BaO and LREEs. The mineralogy and geochemistry of the whole profile show a complete lateritic evolution, with increasing enrichment in Fe, Al, Ti, P, S, Ca, Na, Ba, Sr, REEs, Th, U, Zr, Hf, Y, Sc, V, Ga, As, Se, etc., upwards in the profile. The mineralogy, geochemistry, and chemical element contents indicate a lateritic phosphate-sulphate sequence derived probably from Ca-phosphate-bearing sedimentary rocks from the Paleozoic Parnaíba Basin.

Preface

“One of the finest natural areas yet discovered” was the way John McTaggart, a young British engineer, described Hamilton Harbour in 1827. By 1969, it was described in the Canadian Parliament as a “stinking rotten quagmire of filth and poisonous waste.” The “industrial heart of Canada” and “Steel City” are other descriptions that defined Hamilton and its harbour, setting the background for the image shared by most local and Canadian citizens. This image has persisted well past the turn of the 21st Century, even as things change.Hamilton Harbour is a special place for research precisely because it has absorbed and succumbed to urbanization and industrialization. It is a special place because as a community, citizens, industry, scientists and governments come together to reinvent this Harbour and remediate its ecosystem. The remediation process is not complete at the time of this publication, but it is within sight. Telling the story of progress to date is overdue; hence this special issue of the Journal of the Aquatic Ecosystem Health and Management Society (AEHMS). The science in Hamilton Harbour could not take place without the support of the community, and the remediation of this Harbour could not take place without the science to direct actions. There are 19 varied partner agencies in the Bay Area Implementation Team that directs and leads the remedial actions: ArcelorMittal DofascoBay Area Restoration CouncilCity of BurlingtonCity of HamiltonConservation HaltonEnvironment and Climate Change CanadaFisheries and Oceans CanadaGreen VentureHamilton Conservation AuthorityHamilton Halton Home Builders’ AssociationHamilton Harbour RAP OfficeHamilton Port AuthorityHamilton Waterfront TrustMcMaster UniversityOntario Ministry of the Environment and Climate ChangeOntario Ministry of Natural Resources and ForestryRegional Municipality of HaltonRoyal Botanical GardensU.S. Steel CanadaThe Hamilton Harbour Remedial Action Plan is a model for community, government and scientists collaborating to one end: the eventual delisting of the Harbour from the designation, under the Great Lakes Water Quality Agreement, as an Area of Concern.This special issue reports on some of the ongoing science under the topics: Physical-chemical regime, toxic contaminant dynamics, and biotic community dynamics. The Hamilton Harbour community knows these topics as water quality, toxics, and fish and wildlife. Major projects are underway to remediate the Cootes Paradise Marsh, clean up a toxic blob known as Randle Reef, and upgrade wastewater treatment systems. These are not insignificant undertakings. Randle Reef is the largest sediment remediation project on the Canadian side of the Great Lakes and the most contaminated site of its kind in Canada. Upgrades to our wastewater treatment plants will push their function to the highest level practically achievable in tertiary treatment. Cootes Paradise Marsh restoration is one of the most notable and innovative freshwater marsh restorations of its kind in North America. In the end, close to two billion dollars will have been invested in remedial actions, science, and monitoring to remediate Hamilton Harbour.It is important to recognize that this collaborative effort would not have occurred without the work of several key individuals. We wish to acknowledge the role of the following individuals who have led, but are now retired from, this remediation effort: Anne Redish, former Chair of the Hamilton Harbour Stakeholder Forum; Dr. Keith Rodgers, first RAP Coordinator and leader of the original science writing team; Murray Charlton, former Head of the Hamilton Harbour Technical Team; Victor Cairns, former Chair of Fish and Wildlife Restoration; Dr. Peter Rice and Len Simser, leaders of the Cootes Paradise Restoration; Ken Hall, former Executive Director of the Bay Area Restoration Council; and Kathy Trotter, former Administrative Assistant for the Hamilton Harbour Remedial Action Plan. Finally, a special acknowledgement to the late Dr. Brian McCarry, whose understanding of the issues and ability to explain them to anyone are greatly missed. These people set an example for the many scientists and community workers who continue and expand their efforts.Thanks are also due to to Dr. Mohi Munawar and the staff of the AEHMS who were instrumental in organizing this special issue.

Oxidized and reduced kaolin fan deposits: Their sedimentological–mineralogical facies and physical–chemical regime (North-Bavarian Kaolin Mining District, Germany)

The kaolin-fan deposits under consideration are sedimentary in origin and they bridge the gap between residual kaolin deposits proximal to the fan apex in crystalline basement rocks and syn(dia)genetic sandstone-hosted kaolin deposits on the fan apron. The “kaolin ore beds” on the other hand, developed in an arenaceous braided-river drainage system (bed load>>>suspended load deposits), reworking into secondary kaolin deposits that took place either intraformationally during the evolution of the kaolin fan deposits or epigenetically after unroofing of the kaolin deposits in high-sinuosity drainage systems passing, locally, into ephemeral lakes and mud flats (suspended load>bed load deposits). The reference type for kaolin fan deposits has been studied in terrigeneous sediments which are largely mined at Hirschau–Schnaittenbach, along the Western edge of the Bohemian Massif, SE Germany.The fan deposits formed under alternating wet and dry subtropical climatic conditions during the early Triassic. Different intensities of uplift in the hinterland and the frequency of tectonic quiescence to tectonic pulse had a strong impact on the paleogradient, facies and hydrography of the kaolin fan deposits, resulting in the build-up of oxidized kaolin fans (OKF) and reduced kaolin fans (RKF). The OKF provide favorable conditions for the accumulation and preservation of kaolin deposits of economic potential, due to a low paleogradient and a continuous rate of uplift. The opposite is the case in the RKF that formed more proximal to the initial residual kaolin deposits and, more basinward, grade into sandstone-hosted (non)-sulfidic faciesbound Pb deposits that were targeted upon during exploration campaigns in the study area.The mineral association of the kaolin fan deposits has been categorized as follows: the allochthonous heavy minerals are zircon, tourmaline, apatite, monazite, xenotime, rutile, garnet, titaniferous magnetite, and ilmenite. They do not significantly vary between OKF and RKF. The autochthonous heavy minerals show strong contrasts in their heavy mineral suites. The RKF are enriched in sulfides and arsenides, which can be deleterious for the kaolin raw material and exclude its use for special final products (anatase, hematite, galena, sphalerite, marcasite, pyrite, bravoite (Ni pyrite), “limonite”, goethite, Ag–Cu–Ni–As sulfides, and barite). The OKF are rather poor in accessory minerals and contain anatase, hematite, and APS minerals. The latter are geo-acidometers (marker minerals for low pH) and considered as an ore guide to high-potential target areas for kaolin. The allochthonous light minerals quartz and K feldspar are common to both fan types and were only in parts affected by kaolinization, whereas plagioclase has been decomposed to completeness. Autochthonous light minerals quartz, chalcedony (carnelian), and calcite are exclusive to the RKF, where silcretes and calcretes evolved in those stratigraphic units which in the OKF only brought about Ca, Fe and Ti anomalies. The OKF have a significant edge over the RKF in terms of kaolin quality and kaolin exploitation (providing less mechanical wear on LHD [load–haul–dump machinery] machinery). Allochthonous phyllosilicates have a more widespread occurrence in the RKF with muscovite, biotite and chlorite most common in the lowermost kaolin beds. By quality there is not much difference among the autochthonous phyllosilicates of the OKF and RKF. Kaolinite-group minerals, illite, smectite, and an illite–smectite mixed-layer are present in both types, but kaolinite-group minerals prevail in the OKF, with a downward-increasing trend of dickite. By contrast the amount of smectite and smectite–illite mixed layers increases at the expense of kaolinite upward in the stratigraphy.The evolution of the kaolin fan deposits can be subdivided into six stages. Each stage is representative of a peculiar process which translates into concentration, preservation and destruction of kaolin: stage 1 weathering and the formation of a kaolin regolith (constructive), stage 2 transport, deposition synsedimentary to early-diagenetic kaolinization (constructive+preserving), stage 3 synsedimentary to early-diagenetic smectitization of kaolin (faciesbound Pb mineralization only in the RKF) (preserving+destructive), stage 4 late-diagenetic kaolinization and formation of dickite (preserving+constructive) (not in RKF), stage 5 epigenetic unconformity-related Cu–Ag–Ni–As–Ba mineralization (vaguely expressed in the OKF) (preserving), and stage 6 unroofing, erosion and redeposition of kaolin (only in the OKF) (destructive).During the study a PIMA device has proven in this type of kaolin deposit to be an efficacious tool for capturing digital data in the field of exploitation and exploration of industrial minerals for the identification and quantification of clay minerals (quality control).

The physical–chemical regime of argillaceous interseam sediments in the Emet borate district, Turkey: A transition from non-metallic volcano-sedimentary to metallic epithermal deposits

Among the world-class borate deposits, the borate deposits at Emet Espey and Hisarık in Western Anatolia, Turkey, stand out by their enrichment in As-bearing minerals realgar and orpiment. In terms of abundance these Turkish deposits are on a par with the world-class borate deposits in North America. In Turkey As-bearing base and precious metal deposits of epithermal low-sulfidation type developed adjacent to these non-metallic deposits under consideration. The borate deposits formed during the Miocene under arid climatic conditions within intermontane basins. The latter were filled with volcano-sedimentary series, which host a playa lake at the center. If we use the non-borate minerals, mainly phyllosilicates, as marker minerals and as a link to the equivalent shallow metal deposits, we can distinguish six paragenetic mineral associations (PAS). They reflect the following intrabasinal processes responsible for the formation of the deposits: (1) siliciclastic detrital input into the depocenter, (2) basic volcanic input into the depocenter, (3) felsic volcanic input into the depocenter, (4) evaporation in the depocenter, (5) hot brine activity in the depocenter and at its rim, and (6) oxidation. The physical–chemical regime of the various stages, including the temperature of formation, and the Eh and pH conditions are discussed in the current study indicating the interaction of intrabasinal and extrabasinal fluids:PAS-1: The alluvial–fluvial drainage systems delivered siliciclastics into the playa lake, which is a result of the weathering and denudation from the crystalline footwall rocks. The phyllosilicate association may be described as “kaolinite-in” and “pyrophyllite-out” bearing witness of a true supergene siallitic weathering, unaffected by hydrothermal activity (Eh>0, pH<7, T≈30°C).PAS-2: The phyllosilicate association which features chlorite and saponite is indicative of a reducing environment during smectitization. A moderate activity of basinal hot brines can be recognized, affecting the mineralogical input derived from basic magmatic rocks into the Neogene borate basin (Eh<0, pH6–7, T=30°–100°C).PAS-3: The alteration within the felsic tuffaceous rocks is marked by two discrete trends, the Mg trend with smectite as the diagnostic mineral (pH>7, T<100°C), and the K trend with sanidine and zeolite (clinoptilolite) being typical of this trend (pH>5.5, T<100°C). The temperature of alteration in the tuffaceous interseam pyroclastic deposits was higher than during alteration of stage (2).PAS-4: The borate minerals resulted from the combined action of evaporation and hydrothermal activity. The temperature of formation increased relative to the afore-mentioned processes. As far as the phyllosilicates are concerned, muscovite can be considered a marker mineral of this stage (pH=7–13, T≪100°C) (≪ means significantly lower than).PAS-5: Although dominated by As sulfides, the sheet silicate muscovite can be referred to as a marker for stage 5. This mineral association most strikingly shows the genetic relationship between the low-sulfidation epithermal metal and volcano-sedimentary non-metallic deposits, which developed within an ephemeral lacustrine environment of deposition (Eh<0⇒>0, pH=3–7, T≈100°C).PAS-6: A side-effect of a rising Eh is also observed among the Fe-bearing phyllosilicates. Nontronite, the diagnostic element acts like an umbrella, which covers the low-sulfidation epithermal metal and volcano-sedimentary non-metallic deposits (Eh>0, pH>5.5, T<100°C).A comparison of non-metallic and metallic shallow or epithermal systems reveals that the borate–smectite–muscovite system is the distal or non-metallic part of the low-sulfidation-type epithermal system when it comes to the accumulation of precious and base metals in a region under semi(arid) climatic conditions. Both systems show the largest overlap in stages (5) and (6). At the opposite end of this metallic–non-metallic catena, the alunite (APS mineral)–pyrophyllite–kaolinite system takes a position similar to the borate–smectite–muscovite system for the high-sulfidation metallic epithermal system.

Provenance analysis and thermo-dynamic studies of multi-type Holocene duricrusts (1700 BC) in the Sua Salt Pan, NE Botswana

Multi-type duricrusts, composed of silcretes, calcretes, halcretes and sulcretes developed during the Holocene at the northern rim of the Sua Salt Pan, NE Botswana. They were investigated for their light (quartz/chalcedony, feldspar, analcime, clinoptilolite, calcite, kaolinite/halloysite, illite–smectite mixed-layers, halite) and heavy minerals (baryte, clinozoisite–epidote s.s.s., amphibole, corundum, tourmaline, ilmenite, rutile, sphene, kyanite, andalusite, staurolite, garnet, zircon, apatite, monazite, cassiterite, garnet, biotite) using petrographic microscopy, X-ray fluorescence and diffraction analyses, radio-carbon dating, scanning electron microscopy equipped with an EDX-system, cation exchange capacity and infrared spectroscopy. Detrital minerals predominantly derived from the erosion of rocks belonging to the Archaean Basement Complex, the Stormberg Volcanites and the Kalahari sediments. Of particular interest to exploration geologists, geikielite-enriched ilmenite fragments are a hint to kimberlitic pipes. Biodetritus was derived from invertebrates and from vertebrates (fish bones?). A man-made impact on the heavy mineral suite has to be invoked from small fragments of cassiterite fragments that derived from processing of sulfidic and pegmatitic Sn-bearing ore. In the salt-pan-derived duricrusts mainly the aeolian and to a lesser degree fluvial inputs were responsible for the concentration of clasts in these multi-type duricrusts. Moreover, their variegated mineralogy enables us to constrain the physical–chemical regime, prevalently as to the pH and the chemical composition of the major constituents. All duricrusts developed in a self-sufficient chemically closed system where quartz and feldspar provided the elements Si, Na, K, Ca, and Ba to produce the encrustations. The spatial and temporal trend in the Sua Salt Pan rim encrustations may be described as follows: (1) sulcrete–silcretes, (2) silcretes with kaolinite-group minerals towards more recent stages at the rim and smectite-illite mixed-layers and clinoptilolite towards the basin center, (3) calcretes with analcite towards the basin center, (4) halcretes (and soda ash at a more central position). In the sulcrete–silcrete facies the pH decreases from pH 14 down to 4. In the calcretes and halcretes it increases from pH 8 to pH>13. marking a chemical hiatus between stages 1 plus 2 and stages 3 plus 4. Mineral assemblages forming more basinward tend to have derived from more alkaline fluids than those near the edge of the salt pan.

Capturing digital data of rock magnetic, gamma-ray and IR spectrometry for in-situ quality control and for the study of the physical–chemical regime of residual kaolin deposits, SE Germany

Residual kaolin deposits are operated on a worldwide basis. The majority of them is derived from chemical weathering of felsic rocks during the Cenozoic. This is true for the kaolin deposits on the western edge of the Bohemian Massif. Here this type of deposit provides industrial minerals for the ceramic industry in SE Germany. This raw material formed under tropical climatic conditions during the Miocene and Pliocene across a vast peneplain. Only within the Naab-Wondreb Depression, however, were economic accumulations preserved from erosion. Here near Tirschenreuth, kaolin has been mined since its discovery in 1830. The semi-consolidated regolith is composed of quartz and opaline material, alkaline feldspar, different types of kaolinite, muscovite–illite, a variegated spectrum of 14Å phyllosilicates, Fe–Mn oxide–hydroxides and minor heavy minerals, mainly containing Ti. A precise determination of the mineralogical composition of the ceramic raw material has so far solely relied on laboratory techniques, e.g., XRD, XRF, and spectroscopic methods. To the contrary, this study takes a different approach, capturing digital data in the field to determine its mineralogical composition. Gamma spectrometry (K, U, Th), measuring the susceptibility of and analyzing short-wave infrared spectra, allows for an in-situ quality control of the run-of-mine raw material. It further assists in mapping the monotonous lithology and enables the authors to constrain the physico-chemical regime throughout formation of the kaolin deposit. The benefit for technical mineralogy and applied economic geology, and the strong points of capturing digital data in the field, is the easy and cost-efficient handling of the various methods; methods that were applied in this way for the first time. The in-door calibration and test measurements as well as the data acquisition during the field survey are presented and the data are correlated with the enhancing or deteriorating impacts of the inferred minerals on the firing behavior of the ceramic product.Collecting digital data can also help constrain the physico-chemical regime during formation of the argillaceous deposit and improve further exploration through fine-tuning the genetic model of residual kaolin accumulation. The late Carboniferous granites around Tirschenreuth underwent strong supergene alteration in the pH range of 2.5–7 at log a SiO2(aq) −2.5 to −3.5, which resulted in a thick kaolinitic regolith. Illite formed under slightly increased pH, between 4 and 7, attests to a change from tropical to more temperate humid conditions in the area. The chlorite-group phyllosilicates and nontronitic members of the smectite group came into existence when the pH increased to a pH interval of 7 to 11. This considerable change in the pH of the meteoric solutions occurred at the end of the Neogene between 4.55Ma and 3.99Ma.The different field methods compensate for each others' weak points. Neither method is successful on its own, but the current configuration can easily be expanded to include additional methods as there are neutron- and micro-resistivity and air- and space-borne approaches to cover more swiftly a larger exploration or study area.

U/Pb age and origin of supergene uranophane-beta from the Borborema Pegmatite Mineral Province, Brazil

Uranophane-beta of supergene origin formed in the Borborema Pegmatite Mineral.Province, which is situated in the north-easternmost part of Brazil. The sampling site lies in the topmost parts of the Quintos Pegmatite, about ten kilometers north of the town of Equador. The uranyl silicate was investigated for its age and physical chemical regime of formation. Age dating yielded a U/Pb age of 6.77 ± 0.61 Ma. Uranophane has been derived together with autunite from weathering of brannerite in a tropical climate under alternating wet and dry seasons, when the pH was below 8. This canary-yellow well-crystallized uranyl silicate can be used as a physical chemical marker as well as a clock for supergene alteration.

Copper-bearing encrustations: a tool for age dating and constraining the physical–chemical regime during the late Quaternary in the Wadi Araba, southern Jordan

The alluvial–fluvial drainage system in the Wadi Araba, southern Jordan, incised into Cambrian clastic sedimentary and felsic igneous rocks giving rise to a disseminated Cu–(Mn) mineralization of diagenetic and epigenetic origin along the southern branch of the Dead Sea Transform Fault (=DSTF). During the Late Pleistocene and Holocene, the primary Cu sulfides were replaced by secondary minerals giving rise to hypogene to supergene encrustations, bearing Cu silicates, Cu carbonates, Cu oxychlorides and cupriferous vanadates. They occur in fissures, coat walls and developed even-rim/meniscus and blocky cements in the arenites near the surface. The first generation cement has been interpreted in terms of freshwater vadose hydraulic conditions, while the second-generation blocky cement of chrysocolla and malachite evolved as late cement. The Cu–Si–C fluid system within the Wadi Araba drainage system is the on-shore or subaerial facies of a regressive lacustrine regime called the “Lake Lisan Stage”, a precursor of the present-day Dead Sea. Radiocarbon dating (younger than 27,740 ± 1,570 years), oxygen-isotope-based temperature determination (hot brine-related mineralization at 60–80 °C, climate-driven mineralization at 25–30 °C) and thermodynamical calculations let to the subdivision of this secondary Cu mineralization into four stages, whose chemical and mineralogical composition was controlled by the variation of the anion complexes of silica and carbonate and the chlorine contents. The acidity of the pore water positively correlates with the degree of oxidation. The highest aridity and most intensive evaporation deduced from the thermodynamical calculations were achieved during stage 3, which is coeval with late Lake Lisan. Geogene processes causing Cu-enriched encrustations overlap with man-made manganiferous slags. The smelter feed has been derived mainly from Cu ore which developed during Late Pleistocene in the region.

The fluorite deposits NE of Regensburg, SE Germany—A mineralogical and chemical comparison of unconformity-related fluorite vein-type deposits

A world-class fluorite mining district was located NNE of Regensburg at Nabburg-Wölsendorf, Germany. Together with some smaller mining sites near Bach a.d. Donau, Germany, it provided the main part of the domestic fluorite supply until the late 1980s when the last mines were shut down in NE Bavaria. Both fluorite mining districts are separated from each other by the Bodenwöhr Halbgraben and their mineral assemblages are controlled by deep-seated fault zones. The NW–SE-running “Pfahl”, also called the “Great Bavarian Quartz Lode” (=quartz dyke along a deep-seated shear zone), is of structural control for the vein-type U-, Pb-, Zn-, Cu-, Bi, -Co-, Ni-, As-, and Se mineralization in the Nabburg-Wölsendorf District. Another prominent fault structure, the NNW-trending boundary fault of the NE Bavarian Basement, controls vein-type fluorite deposits with minor Cu-, Zn- and Pb sulfides in the Donaustauf District.Concluding from the REE distribution, primary fluorite mineralization was sourced from granitic and gneissic aquifers or intrastratal solutions, giving rise in both fluorite mining districts to similar mineral assemblages. Two fluorite mineralizations can be distinguished from each other in both mining districts. The primary fluorite mineralization evolved in the aftermaths of the granite intrusion, during the Late Carboniferous and the early Permian, whereas the secondary mineralization or remobilization of fluorite took place until post-Middle Jurassic times. Remobilization, related to the paleogeography of each mineral district, was more intensive in the northern district, because of a moderate erosion. In the southern district, erosion cut deeply into the fluorite mineralization and left behind only relics of minerals indicative of fluorite remobilization.The physical–chemical regime of the fluorite mineralization was interpreted, making use of the common phase diagrams which show Eh and pH along the x- and y axes. The temperature of formation was as high as 200°C in both districts. The fluid regime became more acidic and more oxidizing from the north toward the south. This physical–chemical change well accords with the paleogeographic situation when the fluorite mineralization took place during the Permo-Mesozoic and with the supergene alteration during the Miocene and Pliocene when the southern part of the basement was undergoing stronger uplift than the northern part. Gangue minerals, e.g., ferroan carbonate and sulfate minerals are proximity indicators marking the distance of the vein-mineralization relative to the horizontal reference plain and implying a depth zonation (unconformity), whereas minerals and elements originating from the hypogene alteration are proximity indicators relative to the vertical reference plains (veins related to deep-seated lineamentary fault zones).

Cryptomelane: A tool to determine the age and the physical–chemical regime of a Plio-Pleistocene weathering zone in a granitic terrain (Hagendorf, SE Germany)

Cryptomelane, a K–Mn-bearing oxide, is widespread in the lowermost part of the weathering/supergene alteration zone of the Hagendorf Pegmatite, SE Germany. This supergene Mn mineral has been used in the present study for K/Ar dating of weathering and paleohydraulic processes as young as Plio-Pleistocene. Different cryptomelane age data found in the same weathering and paleohydraulic system resulted from continuous hydraulic processes in the weathering system rather than from a stepwise uplift that shaped the landscape in the granitic area of the NE Bavarian Basement. An almost pure cryptomelane mineralization is indicative of the basal zone of supergene alteration, because a complete separation of Mn from Fe can favorably be achieved only in the infiltration zone under slightly reducing conditions or in the percolation zone under slightly oxidizing conditions. Cryptomelane is precipitated under slightly oxidizing conditions from alkaline solutions in the percolation zone and cast as a marker for fluctuating (paleo)water levels. Manganese oxides, uranyl phosphates and silicates were found at different depths in the weathering zone of this granitic terrain. They were dated by different dating methods (K/Ar and U/Pb) and yielded the same age of formation. Consequently, the 4 Ma signal of both groups of supergene minerals has geomorphological and paleohydraulic connotation and is related to a unique geomorphological process, the Pliocene peneplanation. Gradual hydraulic adjustments gave rise to the younger Pleistocene age found at shallow depth in the weathering zone.

Constraining the physical–chemical conditions of Pleistocene cavernous weathering in Late Paleozoic granites

Cavernous weathering such as tafoni, alveoles and honeycomb structures have been recorded from a great variety of bedrocks and landforms. In the present study cavernous weathering from late Variscan granites was discussed as to its physical–chemical regime of formation. U/Pb dating yielded a maximum age of 1.52 ± 0.03 Ma. Supergene U mineralization is accompanied by kaolinite, nontronite and Fe(III) phosphates. Based upon Eh–pH diagrams calculated for U–Fe–P mineralization the physical–chemical conditions may be described as oxidizing with pH values fluctuating around neutral at near-ambient temperatures of 25 °C. Alteration occurs in two stages: dissolution of rock-forming minerals and neoformation of hydrosilicates under mildly acidic conditions, followed by phosphate precipitation under near-neutral conditions.