Минеральный состав аподоломитового нефрита Кавоктинского месторождения, Средне-Витимская горная страна: залежь № 1 участка Прозрачный

A theoretical analysis shows that electrical conductivity along fractures in a saturated porous rock is a function of many factors: fluid and rock conductivities, initial fracture aperture and contact area, fracture surface geometry (asperity height distribution and tip curvature), elastic moduli of the rock, and confining pressure or normal stress acting across the fracture. The conductivity in the fracture plane decreases approximately in proportion to log pressure, but the conductivity is influenced by the increased contact area, and hence flow‐path tortuosity, along the fracture surface at elevated pressures. Electrical conductivity in fractures is more affected by flow‐path tortuosity than is permeability. The dependence on pressure was tested using laboratory measurements of conductivity through split cores containing ground, saw‐cut surfaces in a variety of rocks under confining pressures to 200 MPa. The conductivity decreased approximately in proportion to log pressure (there was little effect of increased contact area, and hence tortuosity), which suggests that the contact area may not exceed a few percent of the total apparent area. Measurements of gas permeability through the same split cores showed that when the asperity deformation remained largely elastic, permeability and conductivity had a power of 3 relationship. When asperity collapse occurred, as in a dolomitic marble, the powerlaw relation no longer held; permeability decreased more rapidly under pressure than did conductivity. The different influences of porosity and flow aperture may account for the different behaviors of the two transport properties. The theory suggests a number of ways in which fracture parameters may be extracted from field data. Some of the methods rely on the scale dependence and pressure dependence of the fractured‐rock conductivity; other methods require correlating between different physical properties, such as seismic velocity, which are influenced by the presence of fractures.

ABSTRACTThe angle of incidence of ion bombardment is an important processing parameter, which can strongly affect the shape, composition and microstructure of bombarded surfaces. We describe several phenomena directly related to the angle of ion incidence during ion beam etching and ion beam assisted deposition. First, the development of surface ripple topography during ion beam etching is modeled. Surface perturbations are shown to grow under ion bombardment, while surface selfdiffusion acts to select a characteristic wavelength. The orientation of these characteristic ripples changes by 90° as the angle of ion incidence is varied from near-normal to near-glancing angle. The second example is the effect of angle of incidence on the etching rate of Ta under mixed Ar-O2 ion bombardment. For pure Ar bombardment, the sputtering yield of Ta increases with angle of ion incidence slower than secθ, producing a maximum etch rate at normal incidence. Above a critical pressure of O2, however, the yield increases faster than secθ dependence, producing a maximum etch rate at a non-normal angle of incidence. The third example is the effect of angle of incidence on the preferential sputtering of Al relative to Cu in Al-5% Cu thin films. Films deposited by evaporation with simultaneous Ar ion bombardment at 500 eV show a depletion of Al relative to Cu. This composition change is enhanced by increasing the angle of incidence away from normal, resulting in a higher Cu concentration in a film deposited on a tilted surface. Finally, a mechanism is described for the generation of oriented microstructure in films deposited under simultaneous glancing-angle ion bombardment, demonstrated previously for Nb. Grain orientations are selected which allow channelling of the ion beam. These results show that the shape, composition and microstructure of films deposited under ion bombardment respond to changes in angle of incidence, and that these effects need further study and modeling.

Summary Dolomitic marbles from the Organi and Pandrosos areas of the ultrahigh-pressure (UHP) metamorphic Kimi complex in East Rhodope, N.E. Greece have the mineral as- semblage: Cal þ Dol þ Ol þ PhlDiHblSplTi-Chu þ retrograde Srp and Chl. Several generations of calcite and dolomite with variable composition and texture represent different stages of the P-T evolution: The first stage is represented by matrix dolomite (XMgCO3 ¼ 0.48) and relic domains of homogenous composition in matrix calcite (XMgCO3 ¼ 0.11-0.13); the second stage is evident from precipitation of lath- shaped and vermicular dolomite in matrix calcite. The third stage is represented by veinlets of almost pure CaCO3 and domainal replacement of prior calcite by nearly pure CaCO3 þ Ca-rich dolomite (XMgCO3 ¼ 0.34-0.43). Matrix dolomite adjacent to CaCO3 veinlets also becomes Ca-rich (XMgCO3 ¼ 0.42). In fact, Ca-rich dolomites with XMgCO3 in the range of 0.40-0.34 are reported for the first time from metamorphic marbles. Coexisting Ca-rich dolomite and Mg-poor calcite cannot be explained by the calcite- dolomite miscibility gap. This assemblage rather suggests that Mg-poor calcite was aragonite originally, which formed together with Ca-rich dolomite according to the reaction Mg-Cal ! Arg þ Dol (1) at ultrahigh pressures and temperatures above at least 850 � C, when dolomite becomes disordered and incorporates more Ca than coex- isting aragonite does in terms of Mg. The simplest explanation of these observations probably is to suggest two metamorphic events: The first one represented by relic matrix carbonates at relatively low to mod- erate pressures and temperatures of ca. 750 � C, and the second one limited by the mini- mum temperatures for dolomite disorder (ca. 850 � C) and in the aragonite þ dolomite

Mines Gaspe extracts copper and molybdenum from skarn and porphyry copper orebodies at Murdochville in the Gaspe Peninsula, Quebec. Both types of orebodies occur in the zoned Copper Brook aureole, which formed in calcareous Lower Devonian strata around the Copper Mountain plug, one of a group of small rhyodacite porphyry sills, dikes, and plugs of Upper Devonian to Mississippian age. Progressive metamorphism is marked by the alteration of diagenetic pyrite to pyrrhotite and the successive appearance of phlogopite, tremolite, diopside, and grossularitic garnet toward the plug. Diopside formation was accompanied by destruction of calcite, pyrrhotite, and carbonaceous material to form a bleached inner aureole. Similar metamorphic zones surround the nearby Porphyry Mountain plug and occur (without garnet) in the Porphyry Brook aureole. The three aureoles appear to coalesce some 1,200 to 1,500 m below surface.Crackle veinlets in the strata domed by eraplacement of the Copper Mountain plug were healed by quartz, feldspars, diopside, and grossularitic garnet, the same minerals that were formed in the metamorphosed wall rocks. Wollastonite partially replaced diopside in a ring around the plug. Iron metasomatism near the plug then replaced diopside with hedenbergitic pyroxene and replaced pale grossularitic garnet and wollastonite with darker andraditic garnet in veinlets and concretions. Massive skarn formed in some metamorphosed limestone units. The Porphyry Mountain plug also domed the surrounding sedimentary rocks. No crackle veinlets or wollastonite formed but andraditic garnet and hedenbergitic pyroxene were deposited in adjacent joints and bedding fractures. Metamorphism and metasomatism were followed, in some parts of the Copper Brook aureole, by formation of scapolite and a second generation of tremolite. Two major periods of mineralization followed.Early mineralization is characterized by pyrrhotite, minor chalcopyrite, and traces of sphalerite throughout the three aureoles. It is associated with alteration of Ca-Mg-Fe silicates to tremolite or actinolite, chlorite, and epidote or clinozoisite and with deposition of albite, calcite, and quartz. More intense mineralization formed replacement orebodies at Needle Mountain and Needle East, some distance from the Copper Mountain plug. These orebodies were cut by late 1 quartz veins containing chalcopyrite, pyrrhotite, fluorite, and traces of scheelite.Porphyry copper mineralization occurs as disseminations and in four sets of veins centered on the Copper Mountain plug. Late 2 veins, which contain quartz + anhydrite + K-feldspar with traces of chalcopyrite and magnetite, may be coeval with biotization and K-feldspar alteration in the plug. Late 3 veins, which account for most of the copper and molybdenum mineralization, contain quartz + or - anhydrite with chalcopyrite, pyrite, and molybdenite. They are variously associated with kaolinization, sericitization, and minor anhydrite alteration in the plug and adjacent intrusions and with formation of tremolite, epidote, chlorite, and minor anhydrite in the metasedimentary rocks. Late 4 veins contain calcite or dolomite, quartz + or - anhydrite, and pyrite, with traces of K-feldspar, chalcopyrite, sphalerite, and galena. They are associated with calcite + sericite + pyrite alteration of the plug and calcite, dolomite, and phlogopite alteration of the metasedimentary rocks. Late 3 and late 4 veins often occupy almost vertical fractures parallel to the local north-northwest joint trend. Late 5 veins contain calcite, quartz, laumontite, and apophyllite, with traces of K-feldspar, chlorite, molybdenite, chalcopyrite, and pyrite or pyrrhotite. Traces of scheelite occur in late 1, late 3, and late 5 veins and in quartz + garnet veins which predate all sulfide mineralization.A model is proposed whereby emplacement of a pluton generated a convective flow of water which metamorphosed the overlying strata to form the aureoles. The Copper Mountain and Porphyry Mountain plugs, apophyses of the pluton, intruded the metasedimentary rocks and superimposed further metamorphic and metasomatic effects on them. Early mineralizaotion, like the prograde metamorphism, is widespread throughout the aureoles (although very weak in most areas). Late mineralization, by contrast, is closely associated with the Copper Mountain plug. The succession of widespread and spatially restricted events suggests that the postulated pluton and the visible plugs alternately controlled the sequence of metamorphism, iron metasomatism, and early and late mineralization. The difference in zoning patterns between Mines Gaspe and other porphyry copper-skarn complexes was probably due to the fact that the Copper Mountain orebody formed in previously decarbonated wall rocks.

Geology, mineralogy, geochemistry, and zonation of the Bajiazi dolostone-hosted Zn–Pb–Ag skarn deposit, Liaoning Province, China

Zn-Pb-Ag ores at Nanisivik, northwest Baffin Island, are hosted by upper Proterozoic laminated dolostone of the Society Cliffs Formation. Sulfide orebodies containing pyrite, sphalerite, galena, sparry dolomite, and pyrite pseudomorphous after marcasite are characterized by well-banded ore textures considered to have resulted from the progressive replacement of carbonate wall rock. Textural and mineralogical variations enable the Main orebody to be divided into three vertical and four horizontal ore zones. The upper lens of the Main orebody may be further subdivided into six texturally distinct, laterally extensive mine units.In the eastern upper lens, where textural variations are best developed, fluid inclusions indicate that most ore mineralization took place over the temperature range of 165 degrees to 210 degrees C and involved a brine containing 20 to 38 wt percent NaCl equiv. The sulfur isotope compositions of main- and late-stage pyrite crystals range from (delta 34 S = 27.4 to 28.0 per mil. Iron contents of sphalerite vary from 14 to 0 mole percent FeS, corresponding to well-developed color zoning, and constrain the oxygen activity of the ore fluid to 10 (super -46) to 10 (super -41) at 200 degrees C during sphalerite precipitation. Interbanded primary marcasite and sparry dolomite gangue indicates that the ore fluid fluctuated around pH = 5.Ore formation is modeled based on processes involving in situ reduction of sulfate by hydrocarbons and minor H 2 S encountered at the site of ore deposition. The location and configuration of the orebodies was probably controlled in part by the former position of a horizontal fluid interface. Banding is likely the result of repetitive sulfate reduction, metal precipitation, wall-rock dissolution, and dolomite recrystallization in response to the pulsatory influx of ore fluid. Textural and mineralogic variations probably resulted from slight variations in the availability of reduced sulfur.

Tremolite and olivine reaction veins in dolomite marble inclusions in the Bergell granite formed by a crack-reaction-seal mechanism during the cooling history of the area. Brittle failure of stressed marble opened extension cracks that served as conduits for infiltrating silica-rich aqueous fluids. Reaction of the fluids at 450–550 °C with dolomite along the fracture walls resulted in partial replacement of dolomite by reaction products whose mineralogy was controlled mostly by temperature. Aqueous silica dissolved in the fluid in the central fracture was transported by diffusion from the fracture wall to the reaction front in the dolomite marble. The velocity of the replacement reaction'front in the marble itself was controlled by the slower of the two processes: the surface-reaction kinetics of the replacement reaction and the diffusion rate of silica to the reaction site. Reaction veins with very different reaction front morphologies occur. Tremolite veins always have straight reaction fronts parallel to the central fissure and formed at about 450°C. Olivine veins are typically bounded by highly irregular, wavy, undulating reaction fronts. O1 veins formed at about 550 °C. It is concluded that Trmolite-vein growth was controlled by surface-reaction kinetics, whereas diffusion kinetics controlled the growth of olivine veins. The difference in the morphology of the reaction front surface is probably a consequence of small scale texture variations in the deposited vein rock and associated porosity differences. Both types of veins formed in about 1000 years.

Calc-silicate assemblages from the Kerala Khondalite Belt, southern India: implications for pressure-temperature-fluid histories

In this contribution, we report the metasomatic characteristics of a lamprophyre dyke–marble contact zone from the Hongseong–Imjingang belt along the western Gyeonggi Massif, South Korea. The lamprophyre dyke intruded into the dolomitic marble, forming a serpentinized contact zone. The zone consists of olivine, serpentine, calcite, dolomite, biotite, spinel, and hematite. Minor F and Cl contents in the serpentine and biotite indicate the composition of the infiltrating H2O-CO2 fluid. SiO2 (12.42 wt %), FeO (1.83 wt %), K2O (0.03 wt %), Sr (89 ppm), U (0.7 ppm), Th (1.44 ppm), and rare earth elements (REEs) are highly mobile, while Zr, Cr, and Ba are moderately mobile in the fluid. Phase equilibria modelling suggests that the olivine, spinel, biotite, and calcite assemblage might be formed by the dissolution of dolomite at ~700 °C, 130 MPa. Such modelling requires stable diopside in the observed conditions in the presence of silica-saturated fluid. The lack of diopside in the metasomatized region is due to the high K activity of the fluid. Our log activity K2O (aK2O)–temperature pseudosection shows that at aK2O~−40, the olivine, spinel, biotite, and calcite assemblage is stable without diopside. Subsequently, at ~450 °C, 130 MPa, serpentine is formed due to the infiltration of H2O during the cooling of the lamprophyre dyke. This suggests that hot H2O-CO2 fluids with dissolved major and trace elements infiltrated through fractures, grain boundaries, and micron-scale porosity, which dissolved dolomite in the marble and precipitated the observed olivine-bearing peak metasomatic assemblage. During cooling, exsolved CO2 could increase the water activity to stabilize the serpentine. Our example implies that dissolution-reprecipitation is an important process, locally and regionally, that could impart important textural and geochemical variations in metasomatized rocks.

Oxygen isotope ratios measured from microdrilled calcite in limestone wall rocks at the Banshee Carlin-type Au deposit show marked depletion proximal to Au mineralization, indicating isotopic exchange between wall-rock calcite and hydrothermal fluids. Isotopic alteration is spatially coincident with mineralization and puts minimum constraints on hydrothermal fluid infiltration outside of visible indicators (i.e., carbonate dissolution and silicification). Additionally, 18 O depletion is nearly homogeneous at hand-specimen scale indicating near-complete alteration of limestone protolith. The primary mechanism of isotopic exchange is coupled dissolution- precipitation leading to pseudomorphic replacement of calcite during hydrothermal fluid infiltration. Surface reactions between calcite and the hydrothermal fluids are evidenced by textural and chemical variations between altered and unaltered calcite in wall-rock limestone and limestone breccia. Cathodoluminescence (CL) reveals distinct changes in the luminescence of altered calcite relative to unaltered equivalent calcite, and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) data from altered and unaltered calcite show that observed CL responses are due to changes in calcite mineral chemistry. Altered samples exhibit bright CL responses in calcite with increases in Mn and Fe. In addition to wall-rock calcite alteration, calcite veins without clear paragenetic relationships can be related to hydrothermal alteration owing to 18 O depletion, CL response, and positive Eu* anomalies. Together, isotopic alteration of wall-rock calcite and evidence of hydrothermal calcite veins define the distal expression of low-temperature hydrothermal alteration in calcite-bearing rocks at the Banshee deposit.

Diffraction beams for normal incidence on the (100) faces of copper and silver crystals.---Previous results for a copper crystal are checked and extended, by using another crystal of exceptionally pure copper. All of the expected diffraction beams which are x-ray analogues in the two principal azimuths and in the range below 325 volts are found. These beams require values of refractive index greater than unity, but the associated values of inner potential are not constant. Another class of weak beams is found characteristic of the copper lattice, but which require a refractive index of approximately unity for the first order beams of the two principal azimuths. These weak beams accompany the main beams on the high voltage side as satellites. Conditions for orders higher than the 1st are more complicated and indicate that the above method of classification is not sufficient. For a silver crystal the number of experimental maxima is considerably greater than the number of theoretical beams in the low-voltage range. These maxima cannot be classified as main beams requiring a refractive index greater than unity, and weak satellites requiring unit refractive index as in case of a copper crystal, but whenever two or more experimental maxima are to be associated with a given theoretical beam, they are, in general, grouped as components of fine structure of a single diffraction beam.Intensity measurements on diffraction beams as a function of angle of incidence.---For copper, as the angle of incidence is changed by only a few degrees from normal, large intensity changes of the various diffraction beams are observed. Some beams increase while others decrease in intensity for a given change in angle of incidence. Primary voltage and collector angle are adjusted for each observation. For silver, as the angle of incidence is changed from normal the relative intensities of the components associated with a particular beam change rapidly. Some components may disappear and others appear at different voltages, as the incident angle is changed a few degrees. The plane grating formula is approximately satisfied over considerable ranges in the angle of incidence, but there are other ranges for which it is not satisfied. The above variations for various beams do not correspond; neither do those for the beams associated with different orders of reflection from the same set of Bragg planes. Intensity measurements are given for most of the beams in the two principal azimuths below 350 volts for ranges in the angle of incidence, including normal incidence, through which the beams are observable.Regular reflection of electrons from the (100) set of planes.---For copper, with angle of incidence equal to angle of reflection, curves obtained by measuring collector current as a function of primary voltage show many irregularities. For silver, the curves contain many irregularities which do not correspond to those for a copper crystal under similar conditions. For the same angle of incidence and the same set of reflecting planes, the results are not the same for the plane of reflection in the (100) and the (111) azimuths, respectively.Diffraction beams due to a surface gas lattice on the (100) faces of copper and silver crystals.---For copper, "additional" beams which were formerly reported have since been found to decrease in intensity after prolonged heat treatment of the copper crystal at temperatures near its melting point. These beams indicate a simple-cubic, single-spaced lattice with the same constant as that for the copper lattice. They require values of refractive index greater than unity. When the surface gas lattice becomes thin it changes in structure from a simple-cubic, single-spaced lattice to a face-centered, double-spaced lattice. The beams characteristic of the latter structure require unit refractive index. Hydrogen also forms in either of the above two lattices on a copper crystal, depending on the pressure of the hydrogen while the lattice is formed. The lattice which is characteristic of the thicker layer is very unstable and soon changes to that of the thinner layer after the pressure is removed. For silver, only a few very weak beams due to a surface gas lattice are found below 50 volts after heating the crystal a short time at red heat. They indicate a double-spaced, face-centered structure.Inner potential. The measured value of the inner potential is neither constant nor a continuous function of the voltage. It is found to change discontinuously, by several volts in some cases, as the angle of incidence is varied. Results for the crystals of copper and silver which have the same lattice structure are found to differ widely. Hence they appear to be a function of the type of atom.Surface action. Experimental methods of distinguishing between effects due to surface action and those due to a space lattice are discussed.

Lenses of dedolomitized marble occur interspersed with Precambrian cataclastic rocks of the northeast-trending Mullen Creek-Nash Fork shear zone in the east-central portion of the Medicine Bow Mountains of southeast Wyoming. Eight lenses of tremolite marble (dolomitic) and one small body of serpentinized forsteritic marble (calcic) were observed. The Mullen Creek-Nash Fork shear zone separates a thick sequence of low grade metasedimentary rocks, including two locally siliceous dolomitic marble (metadolomite) units of the Nash Fork Formation, from a higher grade felsic and amphibolitic complex. The marble lenses that occur within the shear zone are considered to be fault slices of the dolomitic units that were dedolomitized during mylonitization. The formation of tremolite and forsterite in the lenses was probably facilitated by the presence of a water-rich fluid in the shear zones. Minor occurrences of talc-dolomite-calcite-quartz and tremolite-dolomite-calcite-quartz assemblages in the main sequence of Nash Fork Formation metadolomite are probably also a function of reactions in zones locally enriched in fluids. The presence of assemblages of Tc + Dol + Cc + Q and Tr + Dol + Cc + Q without the intermediate assemblage Tc + Tr + Dol + Cc + Q in the Nash Fork Formation and Tr + Dol + Cc and Fo + Cc + Dol without Tr + Fo + Cc + Dol in shear zone marble slices suggests that each set of reactions may have been controlled by different fluid paths. The stable talc and forsterite assemblages apparently formed under conditions of higher than the tremolite assemblages. Parent dolomite in the marble slices, although recrystallized, only partly decomposed to form tremolite; the tremolite-dolomite ratio increasing with increasing silica content. Under local conditions of higher tremolite apparently reacted with much of the excess dolomite to form forsteritic olivine (). Both tremolite and olivine have since been partially altered to talc and antigorite respectively (most pseudomorphically). This alteration represents a secondary or late retrogressive event superposed upon the upper greenschist or lowermost almandine amphibolite grade dedolomitization process that accompanied the development of the mylonites.

Graphite occurs in two distinct textural varieties in syntectonic granitoids of the New Hampshire Plutonic Series and in associated metasedimentary wall rocks. Textural characteristics indicate that coarse graphite flakes were present at an early stage of crystallization of the igneous rocks and thus may represent xenocrystic material assimilated from the wall rocks. The range of δ 13C values determined for flake graphite in the igneous rocks (−26.5 to −13.8‰) overlaps the range for flake graphite in the wall rocks (−26.0 to −16.7‰), and spatial correlation of some δ 13C values in the plutons and wall rocks supports the assimilation mechanism. The textures of fine-grained irregular aggregates or spherulites of graphite, on the other hand, indicate that they formed along with secondary hydrous silicates and carbonates during retrograde reactions between the primary silicates and a carbon-bearing aqueous fluid phase. Relative to coexisting flake graphite, spherulitic graphite shows isotopic shifts ranging from 1.9‰ higher to 1.4‰ lower in both igneous and metasedimentary samples. The observed isotopic shifts and the association of spherulitic graphite with hydrous silicates are explained by dehydration of C-O-H fluids initially on or near the graphite saturation boundary. Hydration of silicates causes dehydration of the fluid and drives the fluid composition to the graphite saturation surface. Continued dehydration of the fluid then requires coprecipitation of secondary graphite and hydrous silicates and drives the fluid toward either higher or lower CO2/CH4 depending upon the inital bulk composition. Isotopic shifts in graphite formed at successive reaction stages are explained by fractionation of 13C between secondary graphite and the evolving fluid because 13C is preferentially concentrated into CO2 relative to CH4. Epigenetic graphite in two vein deposits assiciated with the contacts of these igneous rocks is generally enriched in 13C (−15.7 to −11.6‰) relative to both the igneous and wall-rock δ 13C values. Values of δ 13C vary by up to 3.4‰ within veins, with samples taken only 3 cm apart differing by 2.0‰ These variations in δ 13C correlate with textural evidence showing sequential deposition of different generations of graphite in the veins from fluids which differed in proportions of carbon species or isotopic composition (or both).

Optimization of the position of the acetabulum in a ganz periacetabular osteotomy by finite element analysis

The thermal contact resistance between the balls and the inner and outer rings of a space-use deep groove ball bearing is analyzed assuming that heat transfer between smooth contacting elements occurs through the elastic contact areas. It is also assumed that the stationary bearing sustains axial and/or radial loads under steady-state temperature condition. The shapes and sizes of the contact areas are calculated using the Hertzian theory. The thermal analysis is based on an isolated isothermal elliptic contact area supplying heat to an insulated half-space. The formulation of the resistance is given as a function of a geometric factor of the contact area and the thermal conductivity of the bearing. In particular, an expression for the axial load is derived with careful consideration of changes in contact angle induced by elastic deformation at the contact area.