Fracture Fillings Research Articles

Compilation and Review of 87Sr/86Sr and Stable Isotopes from Groundwater, Calcite Fracture Fillings, Mineral, and Whole‐Rock Sampling at Äspö, Sweden

Integrated isotopic and hydrochemical studies of groundwater at Äspö, Sweden, support mixing models involving deep saline water, low-solute infiltration, and Baltic Sea water. Carbon, oxygen, and strontium isotope analyses of calcite fracture fillings indicate that paleohydrologic conditions were different than those of today in terms of the isotopic composition of water flowing through fractures. Sr isotopes of whole-rock and mineral (plagioclase, microcline, biotite, and epidote) samples are used to assess the effects of water-rock interaction. Biotite is a major reactant in the early stages of water-rock interaction. Strontium isotope systematics of groundwater from deep in the Hard Rock Laboratory, and underground research facility, and from low conductivity zones revealed a first order mixing line defined by a high-chloride saline component with 66 mg/L Sr and an ancient sea water component with approximately 4.5 mg/L. Dilution with low salinity recharge has produced groundwater with variable Sr contents and 87Sr/86Sr values between 0.7186 and 0.7160. Differences between Äspö and Laxemar groundwater are shown by trends in Sr concentrations plotted against 87Sr/86Sr. The Äspö trend shows increasing 87Sr/86Sr values with increasing concentrations of Sr, whereas the Laxemar groundwater trend shows little variability in 87Sr/86Sr with increasing Sr concentrations. These trends are controlled by the differences in 87Sr/86Sr composition of the saline end members in the two areas.

Percolation of diagenetic fluids in the Archaean basement of the Franceville basin

The Palaeoproterozoic Franceville basin, Gabon, is mainly known for its high-grade uranium deposits, which are the only ones known to act as natural nuclear fission reactors. Previous work in the Kiéné region investigated the nature of the fluids responsible for these natural nuclear reactors. The present work focuses on the top of the Archaean granitic basement, specifically, to identify and date the successive alteration events that affected this basement just below the unconformity separating it from the Palaeoproterozoic basin. Core from four drill holes crosscutting the basin–basement unconformity have been studied. Dating is based on U–Pb isotopic analyses performed on monazite. The origin of fluids is discussed from the study of fluid inclusion planes (FIP) in quartz from basement granitoids. From the deepest part of the drill holes to the unconformable boundary with the basin, propylitic alteration assemblages are progressively replaced by illite and locally by a phengite+Fe chlorite±Fe oxide assemblage. Illitic alteration is particularly strong along the sediment–granitoid contact and is associated with quartz dissolution. It was followed by calcite and anhydrite precipitation as fracture fillings. U–Pb isotopic dating outlines three successive events: a 3.0–2.9-Ga primary magmatic event, a 2.6-Ga propylitic alteration and a late 1.9-Ga diagenetic event. Fluid inclusion microthermometry suggests the circulation of three types of fluids: (1) a Na–Ca-rich diagenetic brine, (2) a moderately saline (diagenetic+meteoric) fluid, and (3) a low-salinity fluid of probable meteoric origin. These fluids are similar to those previously identified within the overlying sedimentary rocks of the Franceville basin. Overall, the data collected in this study show that the Proterozoic–Archaean unconformity has operated as a major flow corridor for fluids circulation, around 1.9Ga.

Red bed and basement sourced fluids recorded in hydrothermal Mn–Fe–As veins, Sailauf (Germany): A LA-ICPMS fluid inclusion study

The hydrothermal Mn–Fe–As vein mineralization at Sailauf (Germany) hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history. The mineralization is related to a major unconformity that separates Permian (Zechstein) sedimentary rocks from underlying Variscan crystalline basement. The hydrothermal veins contain two principal mineralization stages, which are Mn oxides associated with calcite and hematite associated with Mn-calcite. The fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography, microthermometry, and LA-ICPMS microanalysis, coupled with stable isotope geochemistry of carbonate and oxide minerals. The fluid inclusions are high salinity sodic–calcic brines and the bulk fluid properties show no major differences between the Mn oxide and the hematite stage. LA-ICPMS analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their K, Li, B, Pb and Zn concentrations. The fluid that precipitated the Mn oxide stage has anomalous Pb/Zn and Li/B ratios, which closely resemble fluids found in fracture fillings in red beds of the Permian Rotliegend basin. By contrast, the fluids associated with the hematite stage have Pb/Zn and Li/B ratios typical of crustal fluids that were derived from interaction with crystalline basement. Both fluids possess characteristic element ratios including Cl/Br, but variable absolute concentrations of most metals. This suggests that both fluids were modified by mixing with a common metal-depleted brine that had a similar Cl/Br ratio, most likely a formation water from the overlying Zechstein sedimentary rocks. The Sailauf mineralization provides insight into the protracted post-Variscan fluid evolution at the basement–cover interface. The compositionally anomalous fluid that precipitated the Mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of Kupferschiefer-type sediment-hosted Cu deposits. Conversely, the fluid that deposited the hematite mineralization resembles fluids that typically form basement- and sediment-hosted Pb–Zn deposits.

Effect of fracture fill on seismic attenuation and dispersion in fractured porous rocks

Effect of fracture fill on seismic attenuation and dispersion in fractured porous rocks

Multiple hydrocarbon charging events in Kuh‐e‐Mond oil field, Coastal Fars: evidence from biomarkers in oil inclusions

AbstractOil inclusions were retrieved from dolomite and calcite fracture fills in upper, middle and lower reservoir zones in Kuh‐e‐Mond Field, Zagros Basin, Iran. They are assumed to be persevered samples of primary oil; hence, their biomarkers were analysed to determine the maturity gradient and source facies of petroleum at the time of migration. A variety of specific parameters were obtained including n‐alkanes, hopanes, steranes from aromatic hydrocarbons in oil inclusions and reservoir hydrocarbons petroleum. The Pr/Ph ratio varies from 0.5 to 1, which is indicative of dominant reducing conditions during source rock deposition. The fluid inclusion oils with dibenzothiophene/phenanthrene ratios ranging from 0.68 to 1.4, Pr/Ph ratios from 0.8 to 1.2 and with C34/C35 ratios of homohopanes in the range from 1.1 to 1.76, suggest regional variations of organic facies in their source rocks. Biomarker parameters obtained from fluid inclusion oils differ slightly from those of reservoired oil. The biomarker data indicate that the reservoir oil in the Kuh‐e‐Mond Field was generated and expelled predominantly from carbonate–marly sources deposited in anoxic environments. A terrestrial material source seems plausible here, and the presence of C29/C27 ααα 20R steranes supports this finding. The maturity levels of fluid inclusion oils inferred from C12+ parameters are slightly higher in the dolomite and calcite cements from the upper reservoir zone, which may be due to continuous reservoir filling.

Rock slope stability and design in Arafat–Muzdalifa area, Saudi Arabia

The present contribution is a complete study extending before, during, and after the excavation of the mountain side that lying north of road 7. It includes slope stability analysis, rock cut design, and rockfall modeling for natural slope and rock cut face. Neoproterozoic granodiorite and biotite granite forming the slope body have medium to very high strengths. Mineral compositions and textures of these intact rocks control the strength values. These rocks are intensively dissected by fractures that are filled with montmorillonite and chlorite. The high plasticity and slippery nature of these filling materials represent the main problem that may face a rock cut designer because they damage the mechanical properties of these fractures. The problem begins with the selection of the rock mass classification that deals with the fracture fillings and extends during the stability analysis and the suggestion of mitigation and supporting measures. The rock masses building the natural slope are suffered by plane, wedge, and toppling failures. Therefore, two rock cut designs are suggested to avoid the hazards related to these failures and considering the construction cost as well. Rockfall modeling for the natural slope and rock cut designs was done to assess the hazards related to these falling of the blocks. The kinetic energy of falling blocks is represented on the roadway by the coverage distance and block rebound amplitude. Slope height has a positive effect on the values of these distance and amplitude, whereas the steepness of berm height has a negative effect on them. Coverage distance is a function to the location of rockfall barrier and to the width of road ditch, while the amplitude controls the barrier height.

Greenstone Metamorphism, Hydrothermal Alteration, and Gold Mineralization in the Genetic Context of the Granodiorite-Hosted Gold Deposit at Jonnagiri, Eastern Dharwar Craton, India

Abstract Gold mineralization at Jonnagiri is hosted in laminated quartz veins within sheared granodiorite in a typical Archean greenstone-granitoid ensemble. The greenstones and the intrusive granodiorite have been affected by two folding and shearing events, respectively. THERMOCALC-aided P-T calculations suggested that lower amphibolite-grade metamorphism affected the greenstones, involving peak conditions at ~5 kbar and 500°C. Gold mineralization is characterized by a chlorite + biotite-rich proximal alteration zone and a muscovite-dominant inner zone among laminated auriferous quartz veins. Whereas the proximal zone had significant gain in S, C, K, Si, and Rb and depletion of Ca, Mg, and Fe, the inner alteration zone is typified by major addition of Si, K, S, C, and Au. General depletion of rare earth elements in the altered granodiorites is ascribed to high ambient fluid/rock during hydrothermal alteration. Results of the computed (aMg2+/aH+2) vs. (aK+/aH+) and (aNa+/aH+) vs. (aK+/aH+) diagrams, along with an increase in carbonation and alkali enrichment indices in the altered rocks, explain the observed hydrothermal alteration-induced mineralogical changes and constrain the possible fluid composition. Gold occurs as fracture fillings in the quartz matrix and pyrite grains, together with other sulfides, and associated with the fS2-buffering assemblage pyrite + pyrrhotite. Arsenopyrite compositions in the pyrite-arsenopyrite assemblage yielded temperature and log fS2 ranges of 305° to 335°C and −10.9 to −8.6, respectively. These temperature estimates compare well with the published results of chlorite thermometry (263°–323°C). Mineral-fluid equilibrium computations place narrow constraints on the ore fluid fO2 (and aH2S). Gold precipitation was a consequence of postpeak metamorphic fluid phase separation involving immiscibility of gaseous spies, fluid-rock interaction, and decrease in fO2 of the fluid. Published δ34S values in pyrite fall in a narrow range of 1.4 to 7.1‰, and the calculated δ34SH2S varies from 0.2 to 5.8‰, at log fO2 = −32.6 and pH = 5.15 to 5.95; these imply that Au(HS)2− was the dominant gold complex. The narrow range of δ34SPy values is indicative of magmatic (± mantle) source, or involvement of fluid with an average crustal sulfur composition. The geologic events responsible for Jonnagiri started with accretion of the greenstone package at the subduction boundary between the eastern and western blocks of the Dharwar craton, followed by their deformation, shearing, and metamorphism, with subsequent emplacement of the Pagadarayi granodiorite and continued shearing, culminating with fluid flow focused along the shear fractures, which resulted in postpeak metamorphic hydrothermal alteration and precipitation of gold-bearing quartz lodes. From the observed craton-scale uniformity in the chemical and sulfur isotope compositions of the ore fluids, we propose a model involving contamination of an auriferous metamorphic fluid with crustal sulfur during its upward transport.

Variability of rock texture and morphology correlated with the clay‐bearing units at Mawrth Vallis, Mars

AbstractThe clay units at Mawrth Vallis have been well‐characterized in hyperspectral data; however, a similar study of high spatial resolution High Resolution Imaging Science Experiment (HiRISE) data has not been previously conducted. Here the textures of the clay units are described and related to mineralogy across the central Mawrth Vallis region. The nontronite‐bearing rocks appear tan in HiRISE COLOR data and are polygonally fractured with polygons 2–5 m across. In some cases, the fractures appear wider and/or have darker fill or the rocks are a darker brown. The montmorillonite‐bearing rocks appear blue with regular polygons 0.5–1.5 m across; sometimes, there are larger polygons surrounded by regular polygons, a square fracture pattern, or the color appears yellow or mottled blue‐yellow. Kaolinite‐rich rocks are the brightest outcrops and are nonpolygonally fractured. Regions with spectra consistent with hydrated silica or the ferrous mineral component do not have unique textures. Hydrated silica‐bearing rocks appear yellow or mottled with a regular polygonal texture or yellow with hummocky appearance with no polygons. It is also possible that dust/sand on the surface alters the montmorillonite spectrum to appear like that of hydrated silica. The ferrous component may be expressed as mottled coloring or as a bright fracture fill. The nontronite‐ and montmorillonite‐bearing units have remarkably consistent textures in this region, allowing them to be uniquely identified in the Mawrth Vallis region in nonhyperspectral data sets such as CTX and HiRISE. The morphology of the polygons in these two units suggests that their formation is likely dominated by desiccation and controlled by composition.

New records of Oligocene diffuse hydrocarbon seeps, northern Cascadia margin

Fossil methane seeps are preserved in late Eocene through Pliocene marine sedimentary units of the Cascadia margin of the northeastern Pacific. All Cascadia fossil seeps are situated in the uplifted accretionary wedge that overlies extensive Middle Eocene coal-bearing units and the Paleocene–Early Eocene Siletzia large igneous province. This study describes eight previously unrecorded Oligocene seeps, all of which are identified by small, scattered carbonates with or without accompanying characteristic seep macrofauna, from both inner and outer shelf depths. We interpret these deposits as reflecting spatially and temporally diffuse seepage of hydrocarbon-enriched fluids, sourced from various carbon sources within the actively deforming accretionary prism, and term them diffuse seeps. δ13C and δ18O values from foraminiferal carbonate from the studied stratigraphic units have broad variability. Authigenic carbonates occurring as nodules, blebs, burrow fill and fracture fill indicated microbial and thermogenic methane, and multiple fluid flow pathways from within the actively deforming accretionary wedge. It is apparent that the complex fluid-flow regime observed in modern seeps of the Cascadia margin is a continuation of one established in the late Eocene.

Experimental study of shortite (Na2Ca2(CO3)3) formation and application to the burial history of the Wilkins Peak Member, Green River Basin, Wyoming, USA

The temperature at which shortite (Na2Ca2(CO3)3) forms from pirssonite (Na2Ca(CO3)2·2H2O) and calcite using pure synthetic phases in the system Na2CO3–CaCO3–H2O has been experimentally determined. At ∼1atm pressure, shortite forms via the reaction Na2Ca(CO3)2·2H2O+CaCO3=Na2Ca2(CO3)3+2H2O above 55±2°C. This equilibrium temperature is lower than determined previously (90±25°C) by Bradley and Eugster (1969). The solution in equilibrium with synthetic shortite, pirssonite, and calcite approximates a binary H2O–Na2CO3 brine with 1.1m Na2CO3 (10.6wt% Na2CO3). The equilibrium temperature is lowered to 52±2°C with 5m NaCl added to the system, which shows that this reaction is weakly dependent on the activity of H2O, aH2O. This study suggests that shortite does not occur in surficial alkaline saline environments because temperatures are too low.Shortite is abundant in the Wilkins Peak Member (WPM) of the Eocene Green River Formation, Green River Basin, Wyoming, USA (>78million tons/km2), where it occurs as diagenetic displacive crystals, fracture fills, and pseudomorphous replacements of a precursor Na–Ca–carbonate. The large area over which shortite occurs in the WPM indicates that saline pore fluids once existed in the buried lacustrine sediments, and thus, at times, large Na–CO3-rich saline alkaline lakes or laterally extensive saline groundwaters existed in the Green River Basin during WPM time. The thermal stability of shortite, together with vitrinite reflectance data and inferred regional geothermal gradients, establish that the shortite-bearing intervals of the WPM were buried to maximum depths of ∼1000m in the Green River Basin, and since experienced ∼800m of erosional exhumation.

Quantifying noble gas contamination during terrestrial alteration in Martian meteorites from Antarctica

AbstractWe investigated exterior and interior subsamples from the Martian shergottite meteorites Allan Hills (ALH) A77005 and Roberts Massif (RBT) 04261 for secondary minerals, oxygen isotopes, Ar‐Ar, and noble gas signatures. Electron microprobe investigations revealed that RBT 04261 does not contain any visible alteration even in its most exterior fractures, whereas fracture fillings in ALHA77005 penetrate into the meteorite up to 300 μm, beyond which the fractures are devoid of secondary minerals. Light noble gases seem to be almost unaffected by terrestrially induced alteration in both meteorites. Thus, a shock metamorphic overprint of 30–35 GPa can be deduced from the helium measurements in RBT 04261. Oxygen isotopes also seem unaffected by terrestrially weathering and variations can easily be reconciled with the differences in modal mineralogy of the exterior and interior subsamples. The measurements on irradiated samples (Ar‐Ar) showed a clear Martian atmospheric contribution in ALHA77005, but this is less apparent in our sample of RBT 04261. Exterior and interior subsamples show slight differences in apparent ages, but the overall results are very similar between the two. In contrast, krypton and xenon are severely affected by terrestrial contamination, demonstrating the ubiquitous presence of elementally fractionated air in RBT 04261. Although seemingly contradictory, our results indicate that RBT 04261 was more affected by contamination than ALHA77005. We conclude that irrespective of on which planet the alteration occurred, exposure of Martian rocks to atmosphere (or brine) introduces noble gases with signatures elementally fractionated relative to the respective atmospheric composition into the rock, and relationships of that process with oxygen isotopes or mineralogical observations are not straightforward.

Trace element distribution in uraninite from Mesoarchaean Witwatersrand conglomerates (South Africa) supports placer model and magmatogenic source

The first systematic analyses of the trace and rare earth element (REE) distribution in uraninite from various gold-bearing conglomerates of the Mesoarchaean Central Rand Group in South Africa’s Witwatersrand Basin by in situ laser ablation-inductively coupled plasma-mass spectrometry confirms a placer origin for the uraninite and a magmatogenic provenance thereof. The chemistry of commonly rounded to sub-rounded uraninite is highly variable from grain to grain but generally marked by elevated Th, W, Bi, Mo, Ta, Y, REE contents and unusually high Au concentrations. Especially, the high Th contents and the chondrite-normalised REE patterns are incompatible with post-sedimentary hydrothermal genetic models for the U mineralisation and point to derivation of the detrital uraninite from a high-temperature, magmatogenic, presumably granitic to pegmatitic source. The elevated Au concentrations (of as much as 67 ppm) in this uraninite are unique to the Witwatersrand and hint at a granitic hinterland that was enriched in both U and Au, thus presenting a potential source domain for some of the detrital gold in the Witwatersrand conglomerates. Minute fracture fills of brannerite in close proximity to the larger, rounded uraninite grains are devoid of detectable Bi, Mo, REE and Au and have only very low concentrations of Th, W, Ta and Y. This is explicable by crystallisation from a low-temperature hydrothermal fluid. Thus, Witwatersrand U phases show, analogous to many other ore constituents, such as pyrite and gold, clear evidence of partial, short-range mobilisation of originally detrital particles by post-sedimentary fluids.

Development of calcium phosphate cement for the augmentation of traumatically fractured porcine specimens using vertebroplasty

The study aim was to develop and apply an experimental technique to determine the biomechanical effect of polymethylmethacrylate (PMMA) and calcium phosphate (CaP) cement on the stiffness and strength of augmented vertebrae following traumatic fracture. Twelve burst type fractures were generated in porcine three-vertebra segments. The specimens were randomly split into two groups (n=6), imaged using microCT and tested under axial loading. The two groups of fractured specimens underwent a vertebroplasty procedure, one group was augmented with CaP cement designed and developed at Queen's University Belfast. The other group was augmented with PMMA cement (WHW Plastics, Hull, UK). The specimens were imaged and re-tested . An intact single vertebra specimen group (n=12) was also imaged and tested under axial loading. A significant decrease (p<0.01) was found between the stiffness of the fractured and intact groups, demonstrating that the fractures generated were sufficiently severe, to adversely affect mechanical behaviour. Significant increase (p<0.01) in failure load was found for the specimen group augmented with the PMMA cement compared to the pre-augmentation group, conversely, no significant increase (p<0.01) was found in the failure load of the specimens augmented with CaP cement, this is attributed to the significantly (p<0.05) lower volume of CaP cement that was successfully injected into the fracture, compared to the PMMA cement. The effect of the percentage of cement fracture fill, cement modulus on the specimen stiffness and ultimate failure load could be investigated further by using the methods developed within this study to test a more injectable CaP cement.

Long‐term stability of fracture systems and their behaviour as flow paths in uplifting granitic rocks from the Japanese orogenic field

AbstractIn granitic rocks, fracture networks typically provide pathways for groundwater flow and solute transport that need to be understood to assess the long‐term performance of deep underground storage or disposal facilities such as radioactive waste repositories. However, relatively little is known about the long‐term processes of fracturing and/or the longevity of flow paths (FP) in granitic rocks distributed within orogenic belts. To clarify these issues, Japanese plutons of different ages and in situ fractures in granite at the Mizunami Underground Research Laboratory (MIU) located in central Japan were studied. Detailed structural characterization and geochemical analysis of in situ fracture fillings sampled from a depth of 300 m were carried out to clarify the relationship between fracturing and mineral infilling processes. Different plutons show identical episodes of fracturing and fracture filling, consisting of: brittle tensile fracturing, due to decreasing temperature through the ductile–brittle transition after plutonic intrusion (Stage I); relatively rapid uplifting (ca. a few mm/year) accompanied by hydrothermal water circulation, which produced uncrushed layered mineral fillings (Stage II); and a period of low‐temperature meteoric water circulation following exposure after uplift (Stage III). The parageneses of carbonate mineral fracture fillings and their carbon isotopic compositions (14C, δ13C) show that there were distinct episodes of carbonate mineral precipitation during the rapid uplifting of a pluton. The carbonate minerals that formed during each episode incorporated carbon from a distinct source. The evolution of fillings identified here enables development of a specific model of fracturing and persistence of fluid‐conducting systems in the plutons of the orogenic field.

Paleo water–rock interaction determined through isotopic tracing (Sr, O, C, U) in fracture-fill minerals: Evidence from the Vienne granitoids (France)

Based on the concepts (a) that the stable C and O isotopes combined with the Sr isotope ratios of fracture fills should reflect the source groundwater from which the solid phases precipitated and (b) that U-series disequilibria (USD) enable the calculation of residence time for the U by using Fe oxides as the best candidate, an “isotopic toolbox” was applied to fracture fill from the crystalline basement of the Vienne district. The fracture fills are formed mainly of carbonates, clays and Fe oxides. The isotope data indicate two main generations of carbonate that originated from hydrothermal circulation and equilibrium with present-day groundwaters but the Sr isotope ratios highlight another component with a higher 87Sr/86Sr ratio reflecting the complexity of the water–rock interactions.For the USD, the Fe-hydroxides located at 207m depth yield an age of 102±5ka (St. Germain I interglacial stage), whereas those located at 277m and 300m yield respective ages of 173±15ka and 181±10ka. These corresponding to the transition between the penultimate glacial period (isotopic stage 6) and the end of the preceding interglacial stage (isotopic sub-stage 7a). Investigating water–rock interaction (87Sr/86Sr, 18O, 13C, USD) in the fracture-fill minerals from the crystalline basement has shown that such an approach is relevant to developing an understanding of how the groundwater system has changed over time.

MINERALOGY OF SPODUMENE PEGMATITES AND RELATED ROCKS IN THE TIN-SPODUMENE BELT OF NORTH CAROLINA AND SOUTH CAROLINA, USA

The Tin–Spodumene Belt (TSB) along the border of North and South Carolina, southeastern USA, is composed of hundreds of en echelon dikes intruded into amphibolite-facies mica schist and amphibolite. The spodumene pegmatites are unzoned and consist of medium- to very coarse-grained spodumene, plagioclase, K-feldspar, quartz, muscovite, and accessory amounts of beryl, manganoan fluorapatite, triphylite, and cassiterite. The pegmatitic fabric is replaced by a fine-grained saccharoidal albite– quartz fabric that also heals fractures in spodumene and feldspar. Plagioclase (Ab95–96) in the pegmatite is only slightly less sodic than that (Ab98–99) in the replacement albite–quartz assemblage. Rare, nonperthitic K-feldspar is slightly sodic (Or95–99). Spodumene typically contains about 1% iron oxide, giving the mineral a light green color. Muscovite contains 1–2 wt% FeO and a trace of sodium (0.2–0.6 wt% Na2O). A Mn-bearing fluorapatite (altered to low-F and low-Mn apatite) and triphylite (altered to fairfieldite) occur within the pegmatite fabric and appear to be primary phosphate minerals. Secondary phosphate minerals, including several species first described from the TSB, are associated with fracture fillings in sheared pegmatite. Pre-tectonic plagioclase – quartz – muscovite – garnet (Alm71Sps26Prp3) pegmatites are folded and sheared. Muscovite and Mn-bearing fluorapatite compositions are similar to equivalent phases in the spodumene pegmatites. The spodumene pegmatites are sheared, especially in proximity to regional shear-zones, but are not folded. Post-tectonic plagioclase – quartz – K-feldspar – muscovite – biotite pegmatites have Mn-poor fluorapatite, unlike the spodumene pegmatites. The pre-tectonic pegmatites may represent a precursor to the spodumene pegmatites.

Features of fractures forming flow paths in granitic rock at an LPG storage site in the orogenic field of Japan

The biggest underground storage facility for Liquefied Petroleum Gas (LPG) in the world has been constructed in sub-seabed Cretaceous granitic rock located in the Seto inner-sea area of western Japan. This LPG facility is being operated using a ‘water curtain system’ in order to control the flow of groundwater and pore pressure and thereby ensure long-term safe LPG storage. To design this ‘water curtain system’ it was essential to understand the hydrological and structural features of flow-path (FP) fractures in the granitic host rock. Therefore, detailed FP mapping, structural characterization and grouting after hydrological examination were carried out. As a result, two types of FP were distinguished in the host granitic rock. One is a ‘planar type’ fracture, which constitutes a major FP at the site. Hydrologically, the fractures of this type are well-connected and readily controlled by grouting. The other type is a ‘micro-sheeting type’ fracture, which is characterized by an assemblage of micro-fractures. Fractures of this second type were formed under an unloading stress field while the granitic body underwent uplift. However, these fractures have quite low groutability owing to the poor connectivity of their micro-pores. The physical characteristics of the fracture fillings (e.g. calcite) within both kinds of FPs reflect the processes of FP formation and evolution of the host rock. The structural and mineralogical features of the FPs can be explained by the development of fractures and fluid circulation due to the relatively rapid uplift of the granite during orogenesis. The two kinds of FP can be considered typical of groundwater conductive features in an orogenic stress field. Inevitably such features will be encountered in other plutons formed at continental margins.

Features of Coal Pore &amp; Fracture in Chuandong and their Relationship with Extra-Low Permeability

The comparative datas from home and abroad indicate that extra-low permeability of coal seam is the basic reason why the gas outbursts obviously demonstrate three features in Chuandong. Further analysis on the microstructure of coal pore and fracture show that, firstly，the quantity of micro pores is much more than that of macro pores; the total volume of the pores is large while the volume of interconnected pores is small. This is helpful to gas storage but going against gas flow. Secondly, fracture density varys with magnification; there are many short fractures but only a few long fractures; all of the fractures are similar in width and in the form of zigzag; the directivity of fracture extension is irregular. Thirdly, fracture fillings are mainly hard inorganic matters. It is put forward that both pressure sensitive effect and water sensitivity effect exist in the coal seam and they are "double-edged swords" to permeability. In order to increase the permeability, it is necessary to change passive exhausting into active driving, remove gas reservoir and provide the passageway for gas dissipation.

Fracture mapping using seismic amplitude variation with offset and azimuth analysis at the Weyburn CO2 storage site

Cap rock integrity is an essential characteristic of any reservoir to be used for long-term [Formula: see text] storage. Seismic AVOA (amplitude variation with offset and azimuth) techniques have been applied to map HTI anisotropy near the cap rock of the Weyburn field in southeast Saskatchewan, Canada, with the purpose of identifying potential fracture zones that may compromise seal integrity. This analysis, supported by modeling, observes the top of the regional seal (Watrous Formation) to have low levels of HTI anisotropy, whereas the reservoir cap rock (composite Midale Evaporite and Ratcliffe Beds) contains isolated areas of high intensity anisotropy, which may be fracture-related. Properties of the fracture fill and hydraulic conductivity within the inferred fracture zones are not constrained using this technique. The predominant orientations of the observed anisotropy are parallel and normal to the direction of maximum horizontal stress (northeast–southwest) and agree closely with previous fracture studies on core samples from the reservoir. Anisotropy anomalies are observed to correlate spatially with salt dissolution structures in the cap rock and overlying horizons as interpreted from 3D seismic cross sections.

Fracture aperture and fill characterization in a limestone quarry using GPR thin‐layer AVA analysis

The detection and characterization of fractures is important in many engineering practices e.g., rock fall assessment, quarry rock quality determination and mine roof and tunnel stability. Fractures may provide suitable contrasts in electrical properties for detection by GPR instruments. Their ability to reflect radar waves and the dependence of this reflectivity on fracture properties (aperture and fill) makes the GPR method a promising tool for rock fracture characterization. Doing so successfully requires quantification of the reflectivity, reflection coefficient, R, of individual fractures and its variation with incidence angle (AVA), or in practice, offset. Measuring the full AVA response using Common Mid Point (CMP) surveys enables simultaneous estimation of fracture aperture and fill permittivity, difficult to achieve with Common Offset (CO) profiling which does not evaluate angle dependence. This paper reports on AVA analysis carried out on CMP data acquired with 500 MHz antennae over Carboniferous Limestone with horizontal bedding plane fractures in Yorkshire, United Kingdom. Using the transverse electric (TE) polarization mode, data were collected at a sampling interval of 0.05 ns for offsets at 0.04 m steps from 0.37–16.05m.The recorded amplitude is related to the reflection coefficient but is also influenced by other factors we eliminated by making some simplifying assumptions and amplitude corrections. We assume frequency‐independent electrical properties, constant antenna coupling with the ground surface, constant losses associated with transmission losses through any interfaces above the target reflection for the range of offsets considered and a flat homogeneous surface over which measurements are made. Amplitudes were corrected for conductive attenuation, spherical spreading and antenna patterns, which we measured through transillumination surveys across limestone boulders and numerical modelling using the GprMax 3D modelling code. To constrain fracture aperture and fill permittivity, we use the least squares fit of normalized reflection coefficient curves to corrected CMP amplitudes. The analysis allowed characterization of the (bedding plane) fracture fill relative permittivity (~7.8) and aperture (~0.043 m, ~0.2 at 500 MHz). The values obtained are consistent with field observations of fracture fill, corresponding to a mixture of clays and calcite.