scholarly journals Mineralogická charakteristika křemenné žíly se scheelitem a alpské žíly s prehnitem z lomu v Plaňanech u Kolína (kutnohorské krystalinikum)

2020 ◽  
Vol 28 (1) ◽  
pp. 74-85
Author(s):  
Zdeněk Dolníček ◽  
Jana Ulmanová
Keyword(s):  
Host Rock ◽  
Quartz Vein ◽  
Crystalline Complex ◽  
Host Rocks ◽  
Felsic Rocks ◽  
Hydrothermal Veins

Two new types of hydrothermal veins were found in the quarry at Plaňany. Both mineralizations are hosted by a lenticular body of amphibolites embedded in migmatites and gneisses of the Kutná Hora Crystalline Complex. The first type of mineralization is represented by subvertical scheelite-bearing quartz vein, which strikes WNW-ESE, perpendicularly to foliation planes of host rocks. In addition to quartz, the vein also contains a small amount of sulphides (especially chalcopyrite and molybdenite, less pyrite and sphalerite, rarely pyrrhotite and argentopentlandite), calcite, silicates [zoned amphibole (with compositions ranging from magnesiohornblende to actinolite), chlorite (clinochlore), plagioclase (andesine to albite) and prehnite] and scheelite, which forms up to 3 cm big nests in quartz. We cannot exclude the possibility that magnesiohornblende cores of amphibole crystals as well as andesine cores of plagioclases represent relics of host rock. Second type of mineralization is vein with prevailing prehnite, which is oblique to foliation of host amphibolites. Besides prehnite, it contains adularia, calcite and actinolitic amphibole. Both studied mineralizations represent retrograde-metamorphic mobilisates similar to the Alpine-type veins. Chlorite thermometry suggests that chlorite from scheelite-bearing quartz vein originated at temperatures between 253 and 298 °C. The source of Mo and W necessary for formation of molybdenite and scheelite is not clear, but one cannot exclude that these elements were transported by parent fluids from felsic rocks outside of the host amphibolite body.

scholarly journals Magma Mixing Genesis of the Mafic Enclaves in the Qingshanbao Complex of Longshou Mountain, China: Evidence from Petrology, Geochemistry, and Zircon Chronology

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 195 ◽  
Author(s):  
Wenheng Liu ◽  
Xiaodong Liu ◽  
Jiayong Pan ◽  
Kaixing Wang ◽  
Gang Wang ◽  
...  
Keyword(s):  
Host Rock ◽  
Inductively Coupled Plasma ◽  
Magma Mixing ◽  
Coarse Grained ◽  
Calc Alkaline ◽  
Quartz Crystals ◽  
Alkaline Rocks ◽  
Mafic Enclaves ◽  
Normal Zoning ◽  
Host Rocks

The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. In order to investigate the origin and formation of mafic enclaves observed in the Qingshanbao body and the implications for magmatic-tectonic dynamics, we systematically studied the mineralogy, petrography, and geochemistry of these enclaves. Our results showed that the enclaves contain plagioclase enwrapped by early dark minerals. These enclaves also showed round quartz crystals and acicular apatite in association with the plagioclase. Electron probe analyses showed that the plagioclase in the host rocks (such as K-feldspar granite, adamellite, granodiorite, etc.) show normal zoning, while the plagioclase in the mafic enclaves has a discontinuous rim composition and shows instances of reverse zoning. Major elemental geochemistry revealed that the mafic enclaves belong to the calc-alkaline rocks that are rich in titanium, iron, aluminum, and depleted in silica, while the host rocks are calc-alkaline to alkaline rocks with enrichment in silica. On Harker diagrams, SiO2 contents are negatively correlated with all major oxides but K2O. Both the mafic enclaves and host rock are rich in large ion lithophile elements such as Rb and K, as well as elements such as La, Nd, and Sm, and relatively poor in high field strength elements such as Nb, Ta, P, Ti, and U. Element ratios of Nb/La, Rb/Sr, and Nb/Ta indicate that the mafic enclaves were formed by the mixing of mafic and felsic magma. In terms of rare earth elements, both the mafic enclaves and the host rock show right-inclined trends with similar weak to medium degrees of negative Eu anomaly and with no obvious Ce anomaly. Zircon LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) U-Pb concordant ages of the mafic enclaves and host rock were determined to be 431.8 5.2 Ma (MSWD (mean standard weighted deviation)= 1.5, n = 14) and 432.8 4.2 Ma (MSWD = 1.7, n = 16), respectively, consistent with that for the zircon U-Pb ages of the granite and medium-coarse grained K-feldspar granites of the Qingshanbao complex. The estimated ages coincide with the timing of the late Caledonian collision of the Alashan Block. This comprehensive analysis allowed us to conclude that the mafic enclaves in the Qingshanbao complex were formed by the mixing of crust-mantle magma with mantle-derived magma due to underplating, which caused partial melting of the ancient basement crust during the collisional orogenesis between the Alashan Block and Qilian rock mass in the early Silurian Period.

Compositional variation in the chevkinite group: new data from igneous and metamorphic rocks

2009 ◽  
Vol 73 (5) ◽  
pp. 777-796 ◽  
Author(s):  
R. Macdonald ◽  
H. E. Belkin ◽  
F. Wall ◽  
B. Baginski
Keyword(s):  
Electron Microprobe ◽  
Host Rock ◽  
Metamorphic Rocks ◽  
Compositional Variation ◽  
Temperature Range ◽  
Wide Range ◽  
Host Rocks ◽  
Cation Sites ◽  
Dominant Cation

AbstractElectron microprobe analyses are presented of chevkinite-group minerals from Canada, USA, Guatemala, Norway, Scotland, Italy and India. The host rocks are metacarbonates, alkaline and subalkaline granitoids, quartz-bearing pegmatites, carbonatite and an inferred K-rich tuff. The analyses extend slightly the range of compositions in the chevkinite group, e.g. the most MgO-rich phases yet recorded, and we report two further examples where La is the dominant cation in the A site. Patchily- zoned crystals from Virginia and Guatemala contain both perrierite and chevkinite compositions. The new and published analyses are used to review compositional variation in minerals of the perrierite subgroup, which can form in a wide range of host rock compositions and over a substantial pressure- temperature range. The dominant substitutions in the various cation sites and a generalized substitution scheme are described.

Competence and lithostratigraphy of host rocks govern kimberlite pipe morphology

2018 ◽  
Vol 55 (2) ◽  
pp. 130-137
Author(s):  
David E. Newton ◽  
Amy G. Ryan ◽  
Luke J. Hilchie
Keyword(s):  
Host Rock ◽  
Sedimentary Rock ◽  
Kimberlite Pipe ◽  
Crystalline Rock ◽  
Experimental Results ◽  
Compressed Air ◽  
Unconsolidated Sediments ◽  
Final Shape ◽  
Class 1 ◽  
Host Rocks

We use analogue experimentation to test the hypothesis that host rock competence primarily determines the morphology of kimberlite pipes. Natural occurrences of kimberlite pipes are subdivided into three classes: class 1 pipes are steep-sided diatremes emplaced into crystalline rock; class 2 pipes have a wide, shallow crater emplaced into sedimentary rock overlain by unconsolidated sediments; class 3 pipes comprise a steep-sided diatreme with a shallow-angled crater emplaced into competent crystalline rock overlain by unconsolidated sediments. We use different configurations of three analogue materials with varying cohesions to model the contrasting geological settings observed in nature. Pulses of compressed air, representing the energy of the gas-rich head of a kimberlitic magma, are used to disrupt the experimental substrate. In our experiments, the competence and configuration of the analogue materials control the excavation processes as well as the final shape of the analogue pipes: eruption through competent analogue strata results in steep-sided analogue pipes; eruption through weak analogue strata results in wide, shallow analogue pipes; eruption through intermediate strength analogue strata results in analogue pipes with a shallow crater and a steep-sided diatreme. These experimental results correspond with the shapes of natural kimberlite pipes, and demonstrate that variations in the lithology of the host rock are sufficient to generate classic kimberlite pipe shapes. These findings are consistent with models that ascribe the pipe morphologies of natural kimberlites to the competence of the host rocks in which they are emplaced.

scholarly journals Permeability Changes Resulting from Quartz Precipitation and Dissolution around Upper Crustal Intrusions

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-19 ◽  
Author(s):  
Samuel W. Scott ◽  
Thomas Driesner
Keyword(s):  
Host Rock ◽  
Permeability Reduction ◽  
Rock Permeability ◽  
Permeability Changes ◽  
Order Of Magnitude ◽  
Porosity And Permeability ◽  
Fluid Convection ◽  
Flow Heat ◽  
Primary Porosity ◽  
Host Rocks

It has long been recognized that quartz precipitation from circulating hydrothermal fluids may reduce porosity and permeability near intrusions. However, the magnitude of permeability changes and potential feedbacks between flow, heat transfer, and quartz precipitation/dissolution remain largely unquantified. Here, we present numerical simulations of fluid convection around upper crustal intrusions which explicitly incorporate the feedback between quartz solubility and rock permeability. As groundwater is heated to ~350°C, silica dissolves from the host rock, increasing porosity and permeability. Further heating to supercritical conditions leads to intensive quartz precipitation and consequent permeability reduction. The initial host rock permeability and porosity are found to be main controls on the magnitude and timescales of permeability changes. While the permeability changes induced by quartz precipitation are moderate in host rocks with a primary porosity ≥ 0.05, quartz precipitation may reduce rock permeability by more than an order of magnitude in host rocks with a primary porosity of 0.025. Zones of quartz precipitation transiently change locations as the intrusion cools, thereby limiting the clogging effect, except for host rocks with low initial porosity. This permeability reduction occurs in timescales of hundreds of years in host rocks with initial high permeability and thousands of years in host rocks with intermediate permeability.

scholarly journals Characterizing mineralogy and redox reactivity in potential host rocks for a UK geological disposal facility

2015 ◽  
Vol 79 (6) ◽  
pp. 1353-1367 ◽  
Author(s):  
J. Quirke ◽  
C. M. B. Henderson ◽  
R. A. D. Pattrick ◽  
K. M. Rosso ◽  
A. Dent ◽  
...  
Keyword(s):  
Iron Content ◽  
Host Rock ◽  
Azo Dye ◽  
Total Iron ◽  
Geological Disposal ◽  
Potential Host ◽  
Fine Grained ◽  
Reducing Conditions ◽  
Redox Reactivity ◽  
Host Rocks

AbstractGeological disposal facilities (GDF) are intended to isolate and contain radioactive waste within multiple protective barriers, deep underground, to ensure that no harmful quantities of radioactivity reach the surface environment. The last line of defense in a multi-barrier GDF is the geosphere, where iron is present in the host rock mineralogy as either Fe(II) or Fe(III), and in groundwater as Fe(II) under reducing conditions. The mobility of risk-driving radionuclides, including uranium and technetium, in the environment is affected significantly by their valence state. Due to its low redox potential, Fe(II) can mediate reduction of these radionuclides from their oxidized, highly mobile, soluble state to their reduced, insoluble state, preventing them from reaching the biosphere. Here a study of five types of potential host rocks, two granitoids, an andesite, a mudstone and a clay-rich carbonate, is reported. The bulk rocks and their minerals were analysed for iron content, Fe(II/III) ratio, and for the speciation and fine-grained nature of alteration product minerals that might have important controls on groundwater interaction. Total iron content varies between 0.9% in clays to 5.6% in the andesite. X-ray absorption spectroscopy reveals that Fe in the granitoids and andesite is predominantly Fe(II), and in mudstones, argillaceous limestone and terrestrial sandstone is predominantly Fe(III). The redox reactivity of the potential host rocks both in the presence and absence of Fe(II)-containing 'model' groundwater was investigated using an azo dye as a probe molecule. Reduction rates as determined by reactivity with the azo dye were correlated with the ability of the rocks to uptake Fe(II) from groundwater rather than with initial Fe(II) content. Potential GDF host rocks must be characterized in terms of mineralogy, texture, grain size and bulk geochemistry to assess how they might interact with groundwater. This study highlights the importance of redox reactivity, not just total iron and Fe(II)/(III) ratio, when considering the host rock performance as a barrier material to limit transport of radionuclides from the GDF.

2D thermo-mechanical-chemical coupled numerical models of interactions between a cooling magma chamber and a visco-elastic host rock

2020 ◽  
Author(s):  
Dániel Kiss ◽  
Evangelos Moulas ◽  
Lisa Rummel ◽  
Boris Kaus
Keyword(s):  
Magma Chamber ◽  
Host Rock ◽  
Numerical Models ◽  
Bulk Composition ◽  
Inertial Forces ◽  
Volume Changes ◽  
Consistent System ◽  
Host Rocks ◽  
2D Numerical Model ◽  
Crustal Magma

<p>A recent focus of studies in geodynamic modeling and magmatic petrology is to understand the coupled behavior between deformation and magmatic processes. Here, we present a 2D numerical model of an upper crustal magma (or mush) chamber in a visco-elastic host rock, with coupled thermal, mechanical and chemical (TMC) processes. The magma chamber is isolated from deeper sources of magma and it is cooling, and thus shrinking. We quantify the mechanical interaction between the shrinking magma chamber and the surrounding host rock, using a compressible visco-elastic formulation, considering several geometries of the magma chamber.</p><p>We present a self-consistent system of the conservation equations for coupled TMC processes, under the assumptions of slow (negligible inertial forces), visco-elastic deformation and constant chemical bulk composition. The thermodynamic melting/crystallization model is based on a pelitic melting model calculated with Perple_X, assuming a granitic composition and is incorporated as a look-up table. We will discuss the numerical implementation, show the results of systematic numerical simulations, and illustrate the effect of volume changes due to crystallization on stresses in the host rocks.</p>

Structural evolution of sulphide tectonites and their host rocks, Stratmat mine, New Brunswick

1996 ◽  
Vol 33 (3) ◽  
pp. 472-492 ◽  
Author(s):  
Adrian F. Park
Keyword(s):  
Grain Size ◽  
New Brunswick ◽  
Shear Zone ◽  
Quartz Vein ◽  
Structural Evolution ◽  
Fluid Migration ◽  
Soft Sediment ◽  
Polyphase Deformation ◽  
Fine Grain ◽  
Host Rocks

The sulphide orebodies at the Stratmat mine in New Brunswick are treated as tectonites, because their primary characteristics have been so modified by deformation, recrystallization, and vein injection that most of their original features have been obscured. Pb–Zn–Cu sulphide orebodies at the Stratmat mine consist of sulphide and sulphide–silicate tectonites, gneisses, schists, phyllites, and slates produced by the mixing of two sulphide precursors and silicate host rocks by polyphase deformation, much of which relates to progressive non-coaxial deformation. Quartz-vein injection during and after this period of deformation, and the intermixing of nonsulphide lithotypes, led to dilution of the initial ore composition. Both the deformation of the orebodies and fluid migration, manifested by vein injection, reflect processes that were operative in a major shear zone. No indisputable primary characteristics of the orebodies are preserved, although a number of tectonic and (or) tectonically modified features mimic depositional features, e.g., quartz mylonites resemble "cherts," festoon veinlets resemble dismembered stockwork veins, sulphide mylonites resemble rock with an original fine-grain size and "extra" fold phases that could be mistaken for soft sediment folds.

scholarly journals Emplacement of the Nain anorthosite: diapiric versus conduit ascent

2000 ◽  
Vol 37 (8) ◽  
pp. 1195-1207 ◽  
Author(s):  
K R Royse ◽  
R G Park
Keyword(s):  
Shear Zone ◽  
Host Rock ◽  
Border Zone ◽  
Crystal Mush ◽  
Mafic Rocks ◽  
Outer Border ◽  
Host Rocks ◽  
Nain Plutonic Suite

Estimation of settling velocities of large orthopyroxene megacrysts, found within anorthosite intrusions, are calculated and compared with ascent rates achieved by diapirism and conduit propagation. Calculations suggest that diapirism is far too slow to be an appropriate ascent mechanism for anorthositic crystal mush and favour conduit emplacement. The intrusions of the Nain Plutonic Suite (NPS) are located along the Abloviak shear zone, which marks the boundary between the Nain and Churchill provinces, and within the zone of juxtaposition of the Saglek and Hopedale blocks of the Nain Province. These crustal weaknesses have probably controlled the emplacement and distribution of the intrusions. Contact relations between intrusions of anorthosite and their gneissic host rock provide evidence for two emplacement styles within the NPS, the first typified by strongly deformed and recrystallized rocks, and the second by an outer border zone of mafic rocks. It is proposed that these differences in intrusive style are due to differences in ductility contrast between the magma and its surrounding host rocks, such that those intrusions emplaced into the thermally softened shear zone have deformed margins, whereas those intruded into the cooler Archaean crust have undeformed margins.

scholarly journals Tectonic Influence on Speleogenesis of Sea Caves on Biševo Island (UNESCO Global Geopark Vis Archipelago, Adriatic Sea, Croatia)

Geosciences ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 341
Author(s):  
Ivan Mišur ◽  
Marko Budić ◽  
Tomislav Kurečić ◽  
Tvrtko Korbar
Keyword(s):  
Host Rock ◽  
Adriatic Sea ◽  
Strike Slip ◽  
Main Channel ◽  
Fault System ◽  
Quaternary Sediments ◽  
Tidal Zone ◽  
Tectonic Regime ◽  
Side Channels ◽  
Host Rocks

A geological and speleological investigation was conducted in the famous Blue Cave (Modra špilja) and the Monk Seal Cave (Medvidina špilja) on Biševo Island (Croatia) to promote the island’s geoheritage through the new Visitor Centre. The island is mainly composed of Cretaceous to Paleogene neritic carbonates, which form the bedrock, whereas parts of the island are covered with thin Quaternary sediments. The caves are of small dimensions and a simple layout, composed of the main channel and few shorter side channels, all positioned in the tidal zone. Thus, the caves are semi-submerged sea caves located along the coastline. The Blue Cave and the Monk Seal Cave developed within the bedrock limestones and dolostones, respectively, within a zone of left-lateral NNE–SSW striking strike-slip faults that belong to the Biševo fault system. Conjugated discontinuities within the carbonate bedrock indicate a specific strike-slip tectonic regime. Additionally, the host rocks were probably also deformed and fractured during the rise of salt diapirs that characterise this part of the Adriatic foreland. Tectonic and bedding discontinuities form the fragments of the host rock, that combined with the impacts of the strong southern waves, significantly influenced the genesis of the caves.

scholarly journals Mineral stability, brine development and rock-fluid reaction at repository-relevant temperatures (<i>T</i> < 200 °C) in the potential host rock rock salt

2021 ◽  
Vol 1 ◽  
pp. 101-102
Author(s):  
Michael Mertineit ◽  
Michael Schramm
Keyword(s):  
Melting Point ◽  
Rock Salt ◽  
Site Selection ◽  
Host Rock ◽  
Mineralogical Composition ◽  
Confining Pressure ◽  
Maximum Temperature ◽  
General Importance ◽  
Host Rocks ◽  
The Impact

Abstract. For a repository of heat generating radioactive waste, the thermal behaviour of the host rock and the impact of temperature increase on rock properties is of general importance. In the German Site Selection Act (2017), the maximum temperature of the container surface is preliminarily limited to 100 ∘C but this limit might change in the future based on scientific and technological findings. Rock salt, as one of the possible host rocks, consists predominantly of halite with varying amounts of accessory minerals (e.g., Hudec and Jackson, 2007); however, some lithological units within a salt deposit, e.g. potash seams, show a different mineralogical composition with high amounts of potash minerals. Most of them are not very stable regarding temperature resistance and stress, contain water in the crystal lattice, and therefore react sensitively to changes in the environment. The melting point of most evaporated minerals is higher than the expected temperatures in a repository but dehydration and partial melting might occur at relevant temperatures, depending on the confining pressure. For example, the temperature of dehydration of carnallite is ca. 80 ∘C at 0.1 MPa confining pressure but increases to ca. 145 ∘C at 10 MPa confining pressure (Kern and Franke, 1986). The melting point of carnallite increases from ca. 145∘C/8MPa to ca. 167∘C/24MPa, which corresponds to a depth of ca. 1000 m. Depending on the mineral paragenesis and composition of saline solutions, different minerals develop with increasing temperature. For instance, a salt rock with an initial composition of kieserite + kainite + carnallite + solution R (25 ∘C) reacts solely to kieserite and solution R, when the temperature increases to 78 ∘C. A rock with a composition of kieserite + carnallite + bischofite + solution Z (25 ∘C) reacts to kieserite + carnallite from 25 to 50 ∘C, from 50 to 73 ∘C only kieserite is stable, and at temperatures >73 ∘C kieserite and bischofite develop (Usdowski and Dietzel, 1998). For the construction of an underground repository, the mineralogical composition of the host rocks and fluids have to be evaluated carefully and play an important role for the site selection and design of the underground facility.

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