dimensional threshold for fracture linkage and hooking fracture connectivity in rocks depends on spatial properties of the pattern including length abundance and orientation when fractures form a single strike set they hardly cross cut each other and the connectivity is limited linkage probability increases with increasing fracture abundance and length as small fractures connect to each other to form longer ones a process for parallel fracture linkage is the hooking where two converging fracture tips mutually deviate and then converge to connect due to the interaction of their crack tip stresses quantifying the processes and conditions for fracture linkage in single strike fracture sets is crucial to better predicting fluid flow in naturally fractured reservoirs for 1734 fractures in permian shales of the lodeve basin se france we measured geometrical parameters in 2d characterizing three stages of the hooking process underlapping overlapping and linkage we deciphered the threshold values shape ratios and limiting conditions to switch from one stage to another one the hook set up depends on the spacing s and fracture length lh with the relation s 0 15 lh once the hooking is initiated with the fracture deviation length l l 0 4 lh the fractures reaches the linkage stage only when the spacing is reduced to s 0 02 lh and the convergence c is 0 1 l these conditions apply to multi scale fractures with a shape ratio l s 10 and for fracture curvature of 10 20

fracture characterization of chalk in uniaxial and triaxial tests by rock mechanics fractographic and electromagnetic radiation methods abstract this study relates to fracture characterization of chalk in uniaxial and triaxial tests by combined application of rock mechanic fractographic and electromagnetic radiation emr methods we found high strength results 1 3 that ranged from 37 7 to 52 6 mpa we identified several key surface morphologies that were distinct from each other and expanded on their characterization according to tensile and shear categories tensile features include plumes or striae and stairs shear features include a sugary texture ridges and grooves and steps fracture surfaces induced by tension and shear show distinct morphologies longitudinal splitting domains can occur continuously on an axial tensile plane or adjacent parallel planes on the other hand shear failure into meso fractures up to about 10 cm in length is a process that combines a series of distinct domains on separate surfaces that slightly differ in curvature and orientation and are inclined to the sample axis four fracture sequences that initiated either in tensile or in shear surfaces were distinguished in the failed samples results obtained by rock mechanics and by emr methods are well correlated for microcracks and for meso fractures and may vary over five orders of magnitude in size and this correlation is partially supported by fractography in particular a very good linear relationship was obtained between the ratio of the time interval to reach emr pulse envelope maximum and the pulse frequency t and the largest fractures formed extrapolating this result enabled us to calculate fracture sizes when the value of t was known

alteration of the damiao anorthosite complex in the northern north china craton implications for high grade iron mineralization abstract the damiao type iron deposit is hosted in a typical proterozoic anorthosite complex in the northern north china craton the types of ores in damiao mainly comprise massive fe ores massive fe p ores and disseminated fe and fe p ores the disseminated fe and fe p ores formed by fractional crystallization are generally hosted in oxide apatite gabbronorite and account for 70 of the proven reserve of the damiao type iron ore the massive fe and fe p ores account for 30 of the proven reserve of the damiao type deposit iron ore and generally occur as irregular dykes or veins filling vertical fractures of the previously consolidated anorthosite showing typical features of hydrothermal mineralization the contact between the massive orebodies and wall rocks is sharp and straight the anorthosite comprises white and dark varieties with the former resulted by the alteration of the latter that occurs as relicts petrographic observation and electron microprobe analyses show abundant fe ti oxide inclusions in plagioclase which impart the dark color to the rock the similar spider diagram patterns between fresh and altered plagioclase and between dark and white colored anorthosite imply a genetic relationship between the dark and white types during the alteration of anorthosite cao and mgo were slightly decreased the sio2 al2o3 and na2o were significantly increased and the tfe2o3 and tio2 were significantly decreased the tfe2o3 and tio2 in the dark colored anorthosite have a range of 4 86 12 18 wt and 0 37 1 65 wt respectively however the tfe2o3 and tio2 in the white colored anorthosite have a range of 1 67 3 1 wt and 0 14 0 31 wt respectively these features suggest that the alteration of the anorthosite led the fe element by leaching from the dark colored anorthosite at highly oxidized condition and then precipitated within the fractures of the anorthosite thus forming the massive fe and fe p orebodies because the estimated amount of transported fe is much more abundant than the proven ore reserve we infer that there should be huge potential for prospecting damiao type iron ores

analogue modeling of overlapping spreading centers insights into their propagation and coalescence abstract the propagation and segmentation of mid ocean ridges is studied using centrifuged analogue models built with non linear materials the deformation of the brittle ductile model is controlled by diapiric uprise of buoyant analogous asthenospheric material induced by a centrifugal body force this linear upwelling laterally stretches the model mantle that in turn induces failure in the upper layer simulating the brittle crust arrays of fractures initiate within zones of high stress concentration above the diapir fractures propagate laterally in a direction perpendicular to the maximum tensile the minimum principal stress secondary tension cracks initiate in the vicinity of parent fracture tips through going fractures that crosscut the model surface develop by short fractures propagating toward each other and coalescing in different types of patterns the overlap overstep and inclination of fractures developed at the initial stage of extension control their subsequent growth and coalescence non overlapping sub parallel fractures propagate along nearly straight paths and coalesce to produce a single planar fracture if overlapping fractures are parallel they propagate towards each other along curved paths that enclose an intervening elliptical core of intact material fracture curvature in this case results from crack crack interaction and is similar to that of overlapping spreading centers oscs observed along mid ocean ridges overlapping non parallel fractures tend to coalesce by one of their tips propagating sub parallel to the spreading direction toward the other fracture such offsets can serve as models for the development of the orthogonal ridge transform fault patterns common along mid ocean ridges

emplacement and growth of alkaline dikes insights from the shonkinite dikes elchuru alkaline complex se india abstract the mesoproterozoic elchuru alkaline complex in the prakasam alkaline province pap eastern ghats belt se india is intruded by coeval shonkinite dikes magmas parental to both the host nepheline syenite and shonkinite dikes formed during ca 1350 ma continental rift related magmatism the shonkinite dikes show fine to medium grained equigranular to foliated textures with clinopyroxene biotite amphibole k feldspar perthite and nepheline as major mineral phases the dikes grew by inflation and coalescence of dike segments along intrusive steps anastomosis and subsequent coalescence and thermal mechanical erosion of the host rocks a few dikes resulted by filling the fractures created by shearing inflation of intrusive steps between magma segments by mode i opening is the major mechanism of shonkinite dike emplacement and growth however the shonkinite dikes also demonstrate the application of remote shear stress on the dike walls resulting in anastomosis entrapment and segmentation of tabular host rock xenoliths and in extreme cases brecciation of the host rocks under volatile rich and low viscous melt conditions fractal analysis of xenolith bearing dike further illustrates that thermal erosion was facilitated and accentuated by mechanical breakdown of host rock xenoliths due to interactions of tensile and shear forces cross cutting relationships between the shonkinite dikes suggest local deviation in the least compressive stress direction during dike emplacement the shonkinite dikes of elchuru demonstrate that spatially and temporally restricted high volatile low viscous alkaline magmas may have distinctly different styles of emplacement as controlled by interaction of near field magmatic tensile stress and far field tectonic shear stress in an evolving continental rift setting

breakage and shear behaviour of intermittent rock joints abstract the breakage and shear behaviour of intermittent rock joints have been investigated in a series of direct shear tests with a new shear device specifically designed for this purpose the tests have been performed on specimens of rock like material or hard rock respectively incorporating idealized non persistent joints made up of a number of short cracks in an en echelon arrangement along the central shear axis the shear behaviour of such a joint constellation has been found to be composed of different phases the first phase of shearing is that of the actual rupture initiated by the formation of wing cracks starting from the existing cracks and growing into the material bridges and concluded by the generation of additional new fractures connecting the initial cracks in the zone between the wing cracks the second phase of shearing is characterized by friction processes and volume increase in the then continuous shear zone finally the third phase of shearing reached after large shear displacements is determined by sliding processes inside the strongly fractured shear zone in a large number of shear tests the geometrical parameters of the discontinuous joints as well as the loading conditions have been found to influence the activated shear resistance in each phase of shearing to a noticeably different extent the orientation of the initial cracks and the normal stress however have been identified as the most influential parameters depending on the test conditions an initially discontinuous rock joint can activate the largest shear resistance not just before rupture but in one of the two subsequent phases of shearing as well the mechanisms which govern the different shear phases could be identified as 1 tensile rupturing 2 rolling and sliding friction of dilatant joint zones and 3 sliding within the joint filling composed of brecciated material

the yenefrito pb zn mine spanish central pyrenees an example of superimposed metallogenetic events three types of base metal deposits occur in the devonian of the central pyrenees accompanying and post dating the hercynian orogeny since spatial and temporal relationships between mineralization can be recognized in the yenefrito area they have been incorporated into a metallogenetic model sedex like ore composed of sphalerite with minor galena pyrite arsenopyrite and magnetite is enclosed within a carbonate siltstone succession containing volcanic sills crust type mineralization is linked to an unconformity landscape and made up by quartz and minor sphalerite pyrite and galena finally vein deposit cross cutting these deposit types contains galena sphalerite and pyrite sedex like and crust type deposits are linked to hercynian extensional tectonics which favoured the development of an unstable depositional environment mainly controlled by synsedimentary faults being sedex mineralizations developed prior to crust type both mineralization types suffered diagenesis and deformation during the hercynian the vein type was generated by extensional movements related to early alpine rifting

cuttability and drillability studies towards predicting performance of mechanical miners excavating in hyperbaric conditions of deep seafloor mining abstract the research program outlined in this paper starts with the assumption that if there is a significant relationship between drilling and cutting specific energies in atmospheric conditions there would also be a significant relationship between these variables in hyperbaric conditions five model rock samples having uniaxial compressive strength varying from 9 to 160 mpa were subjected to full scale laboratory drilling tests with polycrystalline diamond compact pdc drill bits and a core drill as well as laboratory full and small scale linear cutting tests with a conical and chisel cutter in atmospheric conditions as a result significant correlations between drilling and cutting specific energies were found for atmospheric conditions of laboratory pdc drill bits and core drill bit used in laboratory tests were also used in the subsea drilling operations under hyperbaric conditions in bismarck sea the conical cutter used in the laboratory tests are intended to be used on mechanical miners for subsea metal production core samples taken from bismarck undersea mineral deposits were also subjected to physical and mechanical property tests in the deck and separately in the laboratories of istanbul technical university and small scale linear cutting tests were also applied in the university significant correlations were also found between the results of small and full scale cutting test it is concluded that the capabilities of in situ measurements will permit to detect some physical and mechanical properties of undersea mineral deposits these properties interpreted with laboratory drilling and cutting tests would serve a basis to predict performance of mechanical miners to be used in hyperbaric conditions

u pb zircon calendar for namaquan grenville crustal events in the granulite facies terrane of the o okiep copper district of south africa s xvi geokongres geological society of south africa stellenbosch pp 160 163 van zyl d 1978 a petrological approach towards the ore bearing potentialities of the okiep basic intrusives in namaqualand in verwoed w j ed mineralization in metamorphic terranes geological society of south africa special publication 4 323 329 vellet v 1958 the geology of the copper district namaqualand cape province south africa unpublished report of the o okiep copper company 110 pp waters d j 1989 metamorphic evidence for the heating and cooling path of namaqualand granulites in daly j s cliff r a yardley b w d eds evolution of metamorphic belts geological society london special publication 43 357 363 williams i s claesson s 1987 isotopic evidence for the precambrian provenance and caledonian metamorphism of high grade paragneisses from the seve nappes scandinavian caledonides ii ion microprobe zircon u th pb contributions to mineralogy and petrology 97 205 217 clifford et al crustal events in o okiep district

quantitative evaluation of quaternary crustal deformation around the takayama basin central japan a paleomagnetic and numerical modeling approach abstract neotectonic crustal deformation in central japan is described quantitatively on the basis of paleomagnetic measurements and numerical modeling the welded part of the earliest quaternary nyukawa pyroclastic flow deposit npfd preserves stable remanent magnetization detailed paleo rock magnetic experiments reveal that remanence of the npfd near the takayama basin resides in unimodal titanomagnetite and comprises a component of thermoremanent magnetization trm and three components of thermoviscous remanent magnetization tvrm scatter in the untilted declinations of the syn depositional trm component represents differential rotation about vertical axes related to quaternary activity of three faults enako makigahora and harayama associated with the takayama basin the normal and reversed tvrm components probably acquired by warm water circulation near the active faults during the jaramillo subchron record a complicated rotational sequence since ca 1 ma dislocation modeling successfully simulates the spatial distribution of rotation and the uplift subsidence pattern around the takayama basin assuming strike slip motion on the enako and makigahora faults along the basin margin and vertical displacements on the harayama fault within the basin temporal changes in rotational motions recorded in the tvrms of near fault sites can be modeled by considering transition of active segments of the three faults which is geologically constrained

research on the geometry of shear fracture zones the geometry of brittle shear fracture zones has been studied by the examination of some strike slip faults and shear joints in china pinnate and en echelon deformational patterns are two fundamental arrangements of fractures within brittle shear fracture zones the pinnate angle is usually less than 25 and the en echelon is more than 25 the deformation in the rock bridge the area between two secondary fractures depends on the arrangements of secondary fractures and the sense of shear some tensile ruptures are formed at the terminations of both primary shear fracture zones and secondary fractures the direction of a tensile rupture is commonly parallel to the orientation of the principal compression along the direction of propagation of the shear fracture the horizontal displacement is large and the attenuation of displacements is slow the maximum horizontal displacement of the shear zone may be located in the region of the initial fracture under certain conditions the shear fracture zones may possess pivotal movement this type of movement may be expressed by the behavior of the fault or by the geomorphology of the fault zone

experimental investigations on deformation of soft rock during cutting abstract an experimental study has been made on the deformation of model soft rocks during orthogonal cutting through high resolution imaging of orthogonal cutting experiments under 2 d plane strain conditions and consequent image analysis using particle image velocimetry piv we present the evolution of deformation during the cutting process in addition to examining the deformation fields and by analysing force signatures we examine the effect of tool geometry and the depth of cut on the mechanics of cutting in porous brittle solids in tracking the deformation continuously we identify the process of fracture initiation and propagation as well as the corresponding formation of chips the cutting force was influenced by depth of cut in far more significant way at negative rake angles we further demonstrate two types of cutting mechanisms occurring with change in tool geometry and draw correspondence between initiation and propagation of fractures and the cyclic nature of force signatures in the case of machining at negative rake angle in addition to cyclic increase and decrease of the cutting force a clear development of a triangular dead zone at the tool tip is measured and the size of this zone also varies cyclically the volume change occurring in this dead zone formed at the tool corner during negative rake angle cutting is also tracked by using image analysis and isolating the geometry of the crack developed during the experiments we find that the length of crack propagated during cutting of porous brittle solids is a function of the deformation geometry the effect of rake angle being far more prominent than the depth of cut the experiments also show that the extent of surface and subsurface deformation during cutting is limited and the deformation is localized

ore forming process of the huijiabao gold district southwestern guizhou province china evidence from fluid inclusions and stable isotopes abstract the huijiabao gold district is one of the major producers for carlin type gold deposits in southwestern guizhou province china including taipingdong zimudang shuiyindong bojitian and other gold deposits occurrences petrographic observation microthermometric study and laser raman spectroscopy were carried out on the fluid inclusions within representative minerals in various mineralization stages from these four gold deposits five types of fluid inclusions have been recognized in hydrothermal minerals of different ore forming stages aqueous inclusions co2 inclusions co2 h2o inclusions hydrocarbon inclusions and hydrocarbon h2o inclusions the ore forming fluids are characterized by a h2o co2 ch4 n2 system with medium to low temperature and low salinity from early mineralization stage to later ones the compositions of the ore forming fluids experienced an evolution of h2o nacl h2o nacl co2 ch4 n2 h2o nacl ch4 co2 with a slight decrease in homogenization temperature and salinity the 18o values of the main stage quartz vary from 15 2 to 24 1 while the dh2o and calculated 18oh2o values of the ore forming fluids range from 56 9 to 116 3 and from 2 12 to 12 7 respectively the 13cpdb and 18osmow values of hydrothermal calcite change in the range of 9 1 to 0 5 and 11 1 23 2 respectively stable isotopic characteristics indicate that the ore forming fluid was mainly composed of ore and hydrocarbon bearing basinal fluid the dynamic fractionation of the sulfur in the diagenetic pyrite is controlled by bacterial reduction of marine sulfates the hydrothermal sulfides and the diagenetic pyrite from the host rocks are very similar in their sulfur isotopic composition suggesting that the sulfur in the ore forming fluids was mainly derived from dissolution of diagenetic pyrite the study of fluid inclusions indicates that immiscibility of h2o nacl co2 fluids took place during the main mineralization stage and caused the precipitation and enrichment of gold

cenozoic basin forming processes along the northeastern margin of eurasia constraints determined from geophysical studies offshore of hokkaido japan abstract the cenozoic evolution of a sedimentary basin on a long lasting deformation zone along the northeastern eurasian margin is investigated using geophysical studies analysis of seismic reflection data with detailed age assignments reveals that an offshore paleogene and early miocene basin around northwestern hokkaido developed as a typical pull apart depression at the right stepping part of n s trending dextral faults numerical modeling estimates the total slip on the paleogene strike slip faults is ca 12 km which matches the actual shape and volume of the basin the total displacement resulted from quite active 1 4 mm year dextral motions along the fault zone during the paleogene and early miocene deformation fields around the fault step also indicate a complicated pattern of vertical axis rotation the emergence of contraction tectonics in the middle miocene is suggested from the foreland type basin configuration observed the temporal variations of sedimentation rate through the cenozoic are estimated utilizing the depth converted seismic record and they confirm an accelerated subsidence implying a forearc foreland transition upon the eurasian margin

precursors to the shear failure of rock discontinuities active geophysical monitoring of potential failure along mechanical discontinuities in rock requires identification of precursory signatures to failure in geophysical signals active ultrasonic monitoring of shear failure along frictional discontinuities was performed to determine the signatures of potential failure an instrumented direct shear apparatus was used to apply a constant shearing rate to a discontinuity that was held under a constant normal stress transmitted and reflected compressional and shear waves were recorded during the shearing process ultrasonic precursors were identified as distinct maxima in the amplitude of transmitted shear waves as well as minima in the amplitude of reflected shear waves that occurred well before the peak shear strength of a frictional discontinuity the precursors are linked to changes in the local shear specific stiffness along the discontinuity while the discontinuity s macroscopic shear strength continues to increase prior to failure

stable isotope composition of f pb zn mineralization in the valle de tena spanish central pyrenees this study dealing with the stable isotope c o and s geochemistry of f pb zn deposits is part of an integrated metallogenetic study of the valle de tena central pyrenees the objective of this work is to place constraints on the origin of the mineralizing solutions and sources of sulphur and metals two types of mineralization have been identified 1 stratabound ores linked to an emersion episode that occurred during the namurian to westfalian transition portalet mines and 2 low temperature hydrothermal veins related to post hercynian extensional tectonics yenefrito and lanuza mines and tebarray occurrences stable isotopic study indicates that the source of mineralizing components was the local upper palaeozoic country rocks in the case of the stratabound portalet deposit biogenic sulphides and connate waters modified by some meteoric input through a karst surface in the case of vein deposits stable isotopes point toward either modified connate water or marine water as the mineralizing fluid with sulphur and metals derived from a mixture in different proportions of regional igneous and meta sedimentary country rocks

the development of continental crust through geological time the south african case nd isotopic compositions and147sm144nd ratios were measured in fifty eight south african shales and greywackes with depositional ages ranging from 0 2 to 3 3 b y elements such as the rare earths which are poorly soluble in water and not fractionated during exogeneous processes preserve the signature of the original crustal source the147sm144nd ratios appear to be approximately constant throughout the time interval sampled we calculated nd model ages of crustal differentiation knowing that the shales represent a true blend of different continental areas we consider these model ages representative of the mean ages of their primitive continental sources then using the inverse technique developed by alle gre and rousseau in 1984 we computed a growth curve for the continental crust in south africa two periods of important crustal genesis archaean and around 1 5 b y can be compared with the observed geology and with other continental crust growth curves obtained in previous studies in southern africa and in australia the observation of large variations in the mgo content and ni cr u and th concentrations between archaean south african shales and post archaean samples compared to the constancy of the147sm144nd ratios leads us to propose that the archaean crust was composed of both granite 70 5 and a mafic component 29 5 which could have been komatiite the small dispersion of 147sm 144nd ratios suggests that erosion and sedimentation processes yielded homogeneous archaean shales the present day continental crust is much more heterogeneous because it has undergone several episodes of recycling thus recent shales are characterized by more variable 147sm 144nd ratios

geochemistry and origin of cordierite orthoamphibole orthopyroxene phlogopite rocks from namaqualand south africa abstract a suite of cordierite orthoamphibole cordierite orthopyroxene and cordierite phlogopite gneisses are described from the amphibolite and granulite facies region of the western namaqualand metamorphic complex the gneisses are directly associated with underlying and overlying metapelitic rocks to which they show certain geochemical affinities using overall geochemical trends and comparisons between amphibolite and granulite facies samples particularly for na 2 o feo and tio 2 a residual origin by extraction of granite melt can be excluded and a premetamorphic origin proposed for the mg al rich bulk compositions the formation of these specific cordierite orthoamphibole orthopyroxene rocks by metamorphism of carbonate associated evaporite sequences is not supported by their field relationships or by their al fe rich character the bulk of the cordierite orthoamphibole orthopyroxene rocks have trace element contents that strongly resemble those of underlying mafic rocks an al rich group of cordierite phlogopite bearing rocks shows marked enrichment in zr ce and th suggesting residual concentration following weathering major element modelling of postulated premetamorphic constituents indicates that the majority of cordierite orthoamphibole orthopyroxene rocks comprise former mixtures of chlorite with lesser quartz and other minor clay components phlogopite rich rocks can be modelled as mixtures of chlorite illite and kaolinite the suite probably formed by weathering of mafic volcanic material and its local redeposition in an environment where relatively warm saline conditions favoured the development of chlorite rich assemblages

systematic variation in chemistry and nd sr isotopes across a caledonian calc alkaline volcanic arc implications for source materials abstract sr and nd isotope compositions and major and trace element chemistry are reported for 42 primitive calc alkaline lavas from the siluro devonian scottish old red sandstone northwestward increases in concentrations of sr ba k p and lree associated with northwest subduction of iapetus ocean crust 1 are not accompanied by change in rb th or ti group elements these relationships show that the spatial variation cannot be simply the result of change in the degree of partial melting with depth initial 143 nd 144 nd expressed as e nd at 410 ma shows a wide range from 6 4 to 3 7 and in contrast to e sr decreases markedly to the northwest samples from the midland valley show a strong anticorrelation between e nd and e sr with the correlation band offset to more radiogenic compositions than that defined by modern oceanic volcanic rocks the mantle array such an offset is common in modern volcanic arc magmas but cannot be explained by addition to the overlying mantle of a single component enriched in radiogenic sr derived from subducted lithosphere southwest highland lavas lie in a completely separate field on an e sr e nd diagram most fall within the mantle array but samples with highest concentrations of sr etc are offset to less radiogenic compositions consideration of the chemical and isotopic relationships with respect to several models of crustal contamination shows that the additional lree in the northwest cannot be derived from a crustal source the data imply the existence beneath scotland of a large region of mantle with time integrated lree enrichment parts of which may have anomalous nd sr isotopic compositions less radiogenic than the mantle array midland valley lavas are probably derived from a long term lree depleted mantle source modified by interaction with subducted oceanic lithosphere the coexistence of two mantle sources with differing histories is best explained by vertical stratification with deeper more lree enriched layers accessible only to magmas formed at great depth in a subduction zone the spatial variation probably in part reflects this mantle layering and in part the operation of some mantle zone refining process that permits efficient concentration of incompatible elements from large regions of mantle

an fe analogue of kinoshitalite from the broken hill massive sulfide deposit in the namaqualand metamorphic complex south africa micas with variable ba content in the interlayer sites occur in silicate rich bands within the high grade metamorphic banded iron formation enclosing massive sulfide bodies in the broken hill deposit namaqualand metamorphic complex south africa in those layers that contain neither potassium feldspar nor muscovite a green barian up to 17 wt o bao trioctahedral mica occurs that is similar to kinoshitalite in contrast to the originally described kinoshitalite however this mica is fe rich average xfe 0 65 suggesting the existence of an fe analogue of kinoshitalite not described to date ion chromatographic analysis indicates that about 8 1oof the total fe in this mica is present as fe3 and a typical formula is ba1 2k0 4 fel1 mno 2mg2 oalo 2fe6 t tio 2 ai3 osi5 o 02o oh l sf2 2 the unit cell parameters were determined as follows a 5 383 2 b 9 328 8 c 10 055 8 a j 100 44 5 0 with v 496 5 a3 and z 2 the space group is c21m the ba rich mica formed at the peak of metamorphism t 670 t 20 c p 4 5 t 1 0 kbar at a ph below the muscovite potassium feldspar buffer 102buffered by quartz fayalite magnetite and fs2between 10 5 and 10 7

geochemistry and isotopic characteristics of mafic phulad ophiolite and related rocks in the delhi supergroup rajasthan india implications for rifting in the proterozoic abstract regionally metamorphosed mafic rocks phulad ophiolite in the delhi supergroup n w india have tholeiitic compositions the data indicate that there are two independent rock suites phulad barr jetgarh pbj meta basalts with element abundances and ratios resembling midocean ridge basalts morb and ranakpur desuri r d meta basalts and meta gabbros with relatively high al2o3 and low tio2 for similar mgo and high lil element rb ba sr coupled with low hfs zr nb and ree sm nd abundances the compositions of these rocks are characteristic of ocean arc basalts dioritic rocks at ranakpur exhibit low k tholeiitic differentiation trends and have close chemical affinity with the spatially associated meta basalts ranakpur diorites define a sm nd whole rock isochron corresponding to an age of 1012 78 ma with an initial nd isotopic composition that is similar to bulk earth sm nd mineral isochrons for a meta gabbro diorite and quartz diorite at ranakpur correspond to ages of 838 36 835 43 and 791 43 ma respectively these younger ages reflect metamorphic re equilibration of isotope compositions during widespread granite and granodiorite emplacement in this region during the late proterozoic model sm nd ages for the meta basalts calculated relative to undepleted mantle vary between 1300 1700 ma the chemistry of both mafic rock suites indicates derivation from source regions which had been depleted during previous melting episodes so the model ages are a maximum age constraint ranakpur desuri mafic rocks have negative initial nd 1 0 to 4 5 and low sm nd ratios suggesting crustal contamination or reworking with a few exceptions the pbj meta basalts have positive initial nd 1 5 to 4 8 indicating that they were derived from heterogeneously enriched although longterm depleted mantle the chemical data support the hypothesis that the pbj meta basalts are fragments of proterozoic ocean crust

peraluminous metamorphic rocks from the namaqualand metamorphic complex south africa geochemical evidence for an exhalation related sedimentary origin in a mid proterozoic rift system abstract stratiform peraluminous rocks in western namaqualand mainly sillimanite rocks and sillimanite corundum rocks are intercalated into metapelites of the mid proterozoic bushmanland sequence exhalative concentrations of siliceous b rich zincian calcareous ferruginous and phosphatic composition coprecipitated locally during deposition of the peraluminous rocks as fluorine is a conspicuous component in most peraluminous rocks hydrothermal alteration was a primary process prior to transport premetamorphic al enrichment in these rocks was also partly due to transport as aluminous clays and hydroxides and to selective re deposition the most probable precursor rocks before al enrichment were pelites as shown with the aid of discrimination diagrams formation and distribution of the peraluminous rocks is thought to have occurred near hydrothermal vents during an intermediate stage of rifting that characterized the deposition of the bushmanland sequence this event preceded formation of a major stratiform base metal sulphide horizon

modeling fluid pressure effects when cutting saturated rock abstract the cutting of saturated rock is of importance to the deep sea mining dredging and drilling industries the presence of a fluid in the pores and surrounding the rock can significantly alter the cutting process compared to dry rock cutting through hydrostatic pressure and velocity effects the discrete element method dem is often used to model rock cutting processes because of its capability to deal simultaneously with deformation fracturing and fragmentation of the rock in this paper a numerical modeling technique to model the cutting of saturated rock is presented the methodology is based on the dem and is extended with a hydro mechanical coupling of a pore and ambient fluid the effects of the fluid pressure are modeled using a smoothed particle sp method linear rock cutting tests are simulated for various ranges of water depth and permeability of the rock these results are compared with the available experimental data the simulations show good resemblance with the experimental results

age and isotope geochemistry of the archaean pongola and usushwana suites in swaziland southern africa a case for crustal contamination of mantle derived magma the igneous rocks of the pongola supergroup ps and usushwana intrusive suite uis represent a case of late archaean continental magmatism in the southeastern part of the kaapvaal craton of south africa and swaziland u pb dating on zircons from felsic volcanic rocks of the ps yields a concordia intercept age of 2940 22ma that is consistent with a sm nd whole rock age of 2934 114ma determined on the ps basalt rhyolite suite the initial end of 2 6 0 9 is the lowest value so far reported for archaean mantle derived rocks rb sr whole rock dating of the ps yields a younger isochron age of 2883 69ma which is not significantly different form the accepted u pb zircon age an internal cpx opx plag whole rock isochron for a pyroxenite from the younger uis yields an age of 2871 30 ma and initial 143nd 144nd that lies off the chur growth curve by end 2 9 0 2 however sm nd whole rock data for the uis yield an excessively high age of 3 1 ga that conflicts with firm geological evidence showing the uis to be intrusive into the ps the negative deviations of initialend from the chondritic nd evolution curve suggest significant contamination of the ps and uis melts by older continental crust a mixing process with continental crust after magma segregation is supported by a high initial 87sr 86sr ratio of0 703024 24 for a clinopyroxene sample from a uis pyroxenite compared with an expected value of 0 701 for the 2 9 ga mantle we therefore interpret the linear array of data points for the uis gabbros as a mixing line between 2 87 ga old magma and older continental crust parallel lree enriched ree patterns negative nb ti anomalies a distinctive and uniform ratio of ti zr 46 and a narrow span of initial nd indicate a common source for both the ps and uis suites which is different from primitive mantle

geological and geochemical characteristics of the sawaya erdun gold deposit southwestern chinese tianshan the sawaya erdun gold deposit in the western segment of the south tianshan xinjiang china is a large low grade orogenic gold deposit an abundance of index fossils in the ore hosting strata including brachiopoda corals and schwagerina show that the fossil age of the country rocks ranges from late carboniferous to early permian whole rock rb sr and sm nd isochron ages ranging from 292 43 0 38 to 304 7 11 6 ma are concordant with a late carboniferous age gold mineralization is strictly controlled by a fault zone ore minerals are dominated by sulfides with gold inhomogeneously distributed within them gangue minerals are quartz siderite or calcite data suggest that the ore forming fluid was derived predominantly from an active meteoric groundwater system ore forming temperatures are estimated to have been within the range 110 to 220 c new 40 ar 39 ar isotope age determinations of auriferous quartz are in excellent agreement with rb sr ages obtained from fluid inclusions in quartz they suggest gold mineralization at 206 to 213 ma late indosinian such an age is consistent with the age of formation given for other gold deposits in the region such as bulong and dashankou combined with k ar geochronological data and observed geological features it is concluded that the indosinian metallogentic epoch represents a previously unrecognized major period of gold metallogeny in the southwestern chinese tianshan in some ways the sawaya erdun gold deposit can be compared with the muruntau gold deposit in uzbekistan with respect to geological setting host lithology mineralization style mineral assemblages geochemical association and metallogenic processes involved despite this the sawaya erdun gold deposit possesses a number of characteristics typical of only low temperature metallogenesis 2007 elsevier b v all rights reserved

some new data on the genesis of the linghou cu pb zn polymetallic deposit based on the study of fluid inclusions and c h o s pb isotopes abstract the linghou deposit located near hangzhou city of zhejiang province eastern china is a medium sized polymetallic sulfide deposit associated with granitic intrusion this deposit is structurally and lithologically controlled and commonly characterized by ore veins or irregular ore lenses in this deposit two mineralization events were identified of which the former produced the cu au ag orebodies while the latter formed pb zn cu orebodies silicification and calc silicate skarn type phyllic and carbonate alternation are four principal types of hydrothermal alteration the early cu au ag and late pb zn cu mineralizations are characterized by quartz sericite pyrite chalcopyrite bornite au ag minerals magnetite molybdenite and calcite dolomite sphalerite pyrite chalcopyrite galena respectively calcite clusters and calcite quartz vein are formed during the late hydrothermal stage the nacl h 2 o co 2 system fluid coexisting with nacl h 2 o system fluid and showing the similar homogenization temperatures 385 c and 356 c respectively and different salinities 16 89 21 68 wt nacl eqv and 7 70 15 53 wt nacl eqv suggests that fluid immiscibility occurred during the cu au ag mineralization stage and might have given rise to the ore metal precipitation the ore forming fluid of the pb zn cu mineralization mainly belongs to the nacl h 2 o co 2 system of high temperature 401 c and mid high salinity 10 79 wt nacl eqv fluids trapped in the quartz chalcopyrite vein cu au ag ores pb zn cu ores and calcite clusters yielded 18 o h2o and d values varying from 5 54 to 13 11 and from 71 8 to 105 1 respectively indicating that magmatic fluids may have played an important role in two mineralization events the 13 c pdb values of the calcite change from 2 78 to 4 63 indicating that the co 3 2 or co 2 in the ore forming fluid of the pb zn cu mineralization was mainly sourced from the magmatic system although dissolution of minor marine carbonate may have also occurred during the ore forming processes the sulfide minerals have homogeneous lead isotopic compositions with 206 pb 204 pb ranging from 17 958 to 18 587 207 pb 204 pb ranging from 15 549 to 15 701 and 208 pb 204 pb ranging from 37 976 to 39 052 indicating that metallic elements of the linghou deposit came from a mixed source involving mantle and crustal components based on geological evidence fluid inclusions and h o c s pb isotopic data the linghou polymetallic deposit is interpreted as a high temperature skarn carbonate replacement type two types of mineralization are both related to the magmatic hydrothermal system with the cu au ag mineralization having a close relationship with granodiorite

effect of high hyperbaric pressure on rock cutting process abstract when cutting rock hyperbaric two cases may occur the rock may encounter dilation or compaction due to shear dilation results in pore under pressures while compaction results in pore overpressures dilation will increase the cutting forces considerably while compaction may decrease the cutting forces in both cases the cutting process is supposed to be cataclastic to dimension cutting tools for deep sea mining the worst case should be investigated which is the dilatant case to understand the cutting mechanism experiments are carried out in a pressure tank simulating the hyperbaric conditions hyperbaric cutting appears to be very different from atmospheric cutting due to the pore water pressures the experiments have revealed that the cutting mechanism changes from a chip type mechanism under atmospheric conditions to a cataclastic crushed type under hyperbaric conditions resulting in higher cutting forces an analytical model is presented to estimate the cutting forces under high hyperbaric conditions the results obtained with the analytical model agree rather well with the experimental data

the stratigraphic interpretation of a highly deformed proterozoic region in central bushmanland south africa first correlation of structurally separated metasediments of the aggeneys subgroup abstract it is demonstrated that highly deformed and structurally separated proterozoic metasediments which have previously defied stratigraphic and sedimentological classification may be correlated and characterised this is done by using a multidisciplinary approach including stratigraphic and structural mapping and sedimentological interpretation developed during the geodynamics programme in western namaqualand 1975 1980 the metasediments under consideration belong to the economically important aggeneys subgroup which hosts stratabound massive sulphide deposits at aggeneys and gamsberg gams four isolated areas are considered and it is shown that the dabenoris kabas and pella formations and the lower part of the achab formation are equivalent to the lower part of the wortel formation and that the upper part of the stratigraphic column is composed of the upper units of the achab formation the gams formation and the blomhoek formation the zuurwater formation is for the most part equivalent to the lower portion of the wortel formation but the uppermost strata are correlated with the blomhoek formation these results illustrate that it is possible to obtain the information necessary for a palaeobasin analysis from even the most complex proterozoic regions

sm nd data for granitoids across the namaqua sector of the namaqua natal province south africa sm nd data for rocks of granitic composition in an east west traverse across the namaqua sector of the mesoproterozoic c 1 2 ga namaqua natal province of southern africa provide new evidence about the timing of crustal extraction from the mantle recent ion probe zircon dating has shown that contrary to previous indications that pre namaqua basement had been preserved in parts of the namaqua sector the majority of the magmatic rocks were emplaced during the 1 4 1 0 ga namaqua tectogenesis and very little u pb evidence of older precursors remains sm nd model ages show that mesoproterozoic crustal extraction did occur but was also strong in the palaeoproterozoic with local evidence for the existence of archaean crust the distribution of model ages generally corresponds with the established terranes subdivided using lithostratigraphic and structural criteria the northern part of the bushmanland terrane shows early palaeoproterozoic to archaean model ages and is clearly different from the southern part which has mesoproterozoic model ages this supports the previously published results of a north south traverse and justifies the separation of the garies terrane from the bushmanland terrane though further subdivisions are not supported the continuation of the richtersveld province east of pofadder is supported by one sample and the terrane boundary between the bushmanland and kakamas terranes is marked by an abrupt change from palaeoproterozoic to mesoproterozoic model ages model ages for the kakamas and areachap terranes do not distinguish them well they suggest a mesoproterozoic to late palaeoproterozoic origin for both terranes neither of which has a purely juvenile character the influence of palaeoproterozoic crust forming events is clear in the kaaien terrane to the east possibly reflecting reworking of the kaapvaal craton the namaqua sector of the province thus has a history of crustal extraction and evolution which reaches back locally to the archaean with major palaeoproterozoic and mesoproterozoic crust forming events this differs from the natal sector which has a largely juvenile character related to a mesoproterozoic wilson cycle attempts to reconstruct the mesoproterozoic supercontinent rodinia will have to take into account the extensive nd isotopic evidence for older crustal events in the namaqua sector

fracture coalescence as a mechanism for earthquakes observations based on mining induced microseismicity abstract microseismic events with magnitudes less than zero recorded within a volume at depth in an underground mine are used to evaluate failure conditions associated with a magnitude 2 9 event rockburst the approach incorporated several independent methods of analysis including the principal component analysis pca of seismicity focal mechanisms stress inversion underground in situ stress measurements and structural mapping and three dimensional numerical modelling derived stresses a good correlation was found between stress inversion and pca derived microseismic failure planes and structural mapping and between the in situ principal stress orientations and those obtained through stress inversion and numerical modelling a few days prior to the large event and during the aftershock sequence a change in microseismic failure plane orientation to a shallower dip angle than mapped underground was found to coincide with the numerical modelling derived plane of maximum slip potential this orientation along with measured fracture characteristics persistence and spacing and an increase in event clustering into the plane suggests that the formation of the large event plane of rupture was likely related to the coalescence of mapped fractures an observed reduction in stress release accompanying the increased tendency towards planarity prior to the large event indicates that the development of a large rupture surface occurred under an increased effective shear stress build up as part of the earthquake generation process and the process of coalescence can be considered as the breakage of barriers new fracture growth accompanied by an increase in the effective shear stress on the remaining asperities pre existing fractures

petrochemical evidence on the probable origin of ferriferous metasediments in western bushmanland the mineralized proterozoic metasediments of bushmanland are characterized by the presence of ferriferous rocks this includes banded and unbanded iron formations and various types of gossans these units are not laterally extensive and occur in different stratigraphic levels the prevalent minerals in the ferriferous rocks are hematite magnetite quartz garnet muscovite biotite and sillimanite but less common occurrences of graphite alunite plumbojarosite gahnite and dufrenite have been noted the chemical variation wt is extensive total fe2o3 1 3 93 5 sio2 4 93 al2o3 0 2 14 0 cao 0 02 20 7 mno 0 0 14 3 mgo 0 0 5 7 tio2 0 0 4 4 na2o 0 0 2 0 k2o 0 0 1 5 and p2o5 0 1 7 0 the preliminary nature of the data set precludes however firm conclusions regarding stratigraphic control of the chemical composition the trace element contents ppm extend over several orders of magnitude zn 0 7 000 ba 0 5 200 cu 0 1 400 pb 0 1 070 and ni 6 540 collectively the data indicate that most of the ferriferous rocks represent highly metamorphosed sediments

coalescence of fractures under shear stresses in experiments a series of uniaxial compression tests were performed on gypsum specimens with preexisting fractures to study the failure mechanism of fractures and rock bridges in fractured rock masses the coalescence mechanism of two parallel and offset fractures was investigated by monitoring the process of fracture initiation and propagation with a video camera the tests showed that two inclined parallel fractures can coalesce by shear failure and or tensile failure under a uniaxial load the coalescence path and mechanism mainly depend on the relative position of the two fractures for instance when the two fractures are coplanar or slightly offset coalescence is generated by shear failure when they are overlapping in the loading direction coalescence is generated by mixed shear and tensile failure two types of preexisting fractures one without initial surface contact and hence frictionless and another with surface contact and friction were used to study the influence of fracture contact conditions on the coalescence path and load it was found that coalescence of fractures with surface contact and friction requires loads as much as 35 higher than that for coalescence of fractures without contact and friction a stress analysis was conducted in this study to explain the different coalescence mechanisms the analytical work indicated that different fracture geometries produce significantly different stress fields in the rock bridge area and hence result in different failure modes

tourmalinites from the stratiform peraluminous metamorphic suite of the central namaqua mobile belt south africa tourmalinites as proximal fades equivalents of stratiform peraluminous metamorphic rocks occur stratigraphically below base metal deposits and above thick metarhyolite horizons their premetamorphic protoliths are believed to have originated by tourmaline precipitation from exhalative b f and w rich brines also transporting aluminous clay colloids and dissolved silica tourmaline chemistry is used as an effective petrogenetic sensor the tourmalines are al saturated alkali deficient dravite schorl solid solutions which are in the compositional range of tourmalines originated by exhalative processes f substitution in tourmalines is governed by fe f avoidance f is relatively enriched in the tourmalines and can potentially be used as a tracer for the source of primary hydrothermal solutions ti is introduced into the tourmalines by the substitution scheme ti aliv aly si the high ti contents of the tourmalines as well as those of coexisting muscovites represent evidence of high temperature metamorphism many tourmalines exhibit continuous zoning which can partly be attributed to external fluid influx near peak metamorphic conditions

composition age and tectonic setting of amphibolites in the central bushmanland group western namaqua province southern africa abstract the western namaqua province wnp of southern africa is composed of several supracrustal assemblages and intrusive granitoid suites that were formed during the mid proterozoic 2 0 1 0 ga ago the bushmanland group bg has been the subject of intense study recently because of its considerable strategic metal potential hosting several giant stratiform base metal deposits e g gamsberg and aggeneys the bg contains amphibolites which represent metamorphosed tholeiitic basalts with mgo 9 4 and enriched in ni relative to modern basalts a feature reminiscent of archaean tholeiites post depositional mobility of elements is probably widespread and hampers recognition of parental magma composition and source region characteristics however the amphibolites have yielded a sm nd isochron age of 1649 90 ma nd t 0 48 0 89 which is interpreted as the time of extrusion of the basalt precursors and by inference a minimum sedimentation age for the underlying metalliferous bg sequence it follows that the bg sequence evolved during an intermediate period in the history of the namaqua province after major crustal stabilisation around 2 0 1 9 ga and before the last major tectonothermal event around 1 2 1 1 ga results of a parallel rb sr and u th pb study of the bg amphibolites indicate strong metamorphic resetting 1 2 1 1 ga ago thereby confirming earlier work on the wnp characteristics of the source region to the bg basalts have been inspected with morb normalised trace element abundances with the salient result being the bg basalts require derivation from a source that experienced variable geochemical modification similar to that proposed for the mantle wedge overlying modern subduction zones such a process is currently preferred over crustal contamination since the sm nd isochron for the bg amphibolites is remarkably linear but independent confirmation of the sm nd age is still required before this alternative model can be discounted to reconcile the requirement of subduction related metasomatism in the source to tholeiitic basalts erupted within what appears to be a cratonic sedimentary basin we suggest that back are continental extension could provide a satisfactory tectonic setting as such an environment is intrinsically linked to subduction

geochronology of the deep profile through archean basement at vredefort with implications for early crustal evolution the presence of archean granite forming the core of an updomed and overturned sequence of strata at vredefort south africa has been known for over 70 years recent geophysical geochemical and geological evidence has given rise to the proposal that the basement granite core has also been overturned presenting a section of the earth s granitic crust to view and that radial traverses in the vredefort basement penetrate through a 15 km thick section of the archean crust when moving from the contact of collar strata to the center of the dome the upper levels of the vredefort crust are dominated by a relatively homogeneous outer granite gneiss ogg displaying marked gradients in large ion lithophile elements these rocks grade inward into the deeper levels which occur in granulite facies metamorphism the deeper levels of the vredefort crust exposed in the central parts of the dome consist predominantly of felsic inlandsee leucogranofels ilg which occurs interleaved with inclusions of mafic metavolcanic and metasedimentary rocks termed steynskraal metamorphic zone smz a comprehensive isotopic study using four decay schemes 87rb 232th 238u and 235u on this crustal section is now reported the results permit unique and direct tests on the theories of archean crust forming processes in the upper vredefort crust whole rock isochron ages of 3050 m y are obtained from the four decay schemes and almost all evidence of an extended crustal history prior to 3050 m y has been obliterated establishment of strong vertical gradients in rb sr ratio shortly before setting of rb sr whole rock systems has wide implications for the interpretation of sr initial ratios although the vredefort upper levels of the crust has a low 87sr 86sr initial ratio of 0 7019 0 0002 it probably participated in a crustal prehistory for at least 500 m y in the deeper levels of the vredefort basement the geochronology is much more complex rb sr and th pb isochrons of 3500 m y are recorded in the mafic granulite relicts a companion paper welke and nicolaysen this issue provides evidence for an early crust forming event in this sector 3800 m y ago from 3500 m y onward these deeper crustal levels did not undergo addition of new archean crust forming material on a major scale nevertheless a most important younger archean event affected these levels 2800 m y ago cessation of high grade metamorphism is recorded by setting of the rb sr isotopic system in the felsic rocks and zircon u pb ages an episode of strong uranium depletion affected both the felsic and mafic rocks of this sector 2800 m y ago the inlandsee leucogranofels is evidently a rock unit with a long and complex history beginning with the emplacement as a crustal unit at least 3800 m y ago since then it has been subject to reworking and resetting of isotopic systems which terminated 2800 m y ago in the deeper crust there is scant evidence of a 3050 m y event similarly there is no record of a 2800 m y old imprint in the upper vredefort crust thus the last major events that affected the geochemical constitution of the vredefort upper and deeper crustal sectors differed in time and nature nevertheless they brought about isotopic setting in a downward moving sequence while the overlying crust remained cooler rigid and unaffected these events probably reflect significant discontinuities in the cooling of the archean crust

fluid evolution of the wushan skarn dominant copper deposit in the middle lower yangtze river metallogenic belt eastern china abstract the wushan copper skarn deposit 1 37 mt at 1 17 cu is located in the middle lower yangtze river polymetallic belt skarn orebodies mainly occur in the carboniferous and permian carbonates adjacent to early cretaceous granodiorite porphyries 148 138 ma ore deposition underwent two episodes of metallogenic events involving hydrothermal evolution followed by skarn formation and porphyry related mineralization the skarn episode formed massive disseminated veinlet and breccia style mineralization at the contact zone whereas porphyry mineralization is characterized as disseminated and veinlet style only various types of fluid inclusions daughter mineral bearing co2 bearing vapor and aqueous vapor are classified based on their fluid composition and phase assemblages the hydrothermal fluids are mainly derived from a magmatic origin which exsolves during the melt fluid differentiation primary fluid in endoskarn is interpreted as representing two immiscible phases evolving from a low salinity initial fluid the initial supersaturated fluid has a relative low salinity and the wide range of th values 433 626 c implies heterogeneous trapping corresponding to pressures of 371 646 bars and hydrostatic depth of 3 7 6 5 km primary fluid inclusions trapped in syn ore quartz show the coexistence of s type inclusions 30 0 wt nacl equiv with vapor rich and liquid rich inclusions indicating fluid immiscibility and phase separation from heterogeneous trapping the homogenization temperatures 347 434 c of primary vapor rich inclusions represent the trapping temperatures corresponding the trapped pressures range from 152 to 374 bars and a hydrostatic depth of 1 5 3 7 km copper mineralization in episode porphyry occurs on a very small scale and have a clear trend of decreasing temperatures and salinities during fluid evolution a similar scenario occurred during the porphyry episode in which fluid immiscibility led to copper mineralization significant trends of decreasing temperatures and salinities for both mineralization episodes reflect the change from a magmatic fluid dominated system to a mixed source fluid that incorporated formation water from the country rocks and or meteoric water controlled by the chemical transition of the fluid this mixing process produced a relatively cool fluid system with lower salinities which enhanced the precipitation of cu fe sulfides h o c isotope signatures further indicate that both the fluid and metal are predominantly derived from magmatic sources and that multiple fluid pulses contributed to form skarn minerals and sulfides in the wushan deposit

first results regarding the influence of mineralogy on the mechanical properties of seafloor massive sulfide samples abstract seafloor massive sulfides sms are increasingly accepted as important marine raw material resources for the future in particular because of their polymetallic character many industrial nations are researching not only on the scientific importance of these deposits but also on their economic value regarding the current state of the international exploration mainly two dimensional surface close observations are accessible whereas only some core data and measurements are publicly available to date in fact there are few successful drilling campaigns containing information about the size and shape which also give information on the structure and content of modern massive sulfide ore bodies in their third dimension regarding the mechanical properties of sms samples only few data are available geotechnical data of these deposits are important in order to develop an efficient mining technology for exploitation in this research 12 sms samples from two different locations were investigated based on the mineralogical characterization of the studied samples the geotechnical properties were preliminary correlated with the mineralogical results the comparative study indicates how far the geotechnical data are controlled by mineral type and composition including the porosity a regression relation between compressive strength and the porosity based on the mineralogy shows a distinct relation between these parameters therefore the geomechanical and mineralogical features have a strong importance for deep sea mining applications and this should be kept in mind considering the hyperbaric effects on the rock cutting

geochronology and ore genesis of the shuangjianzishan ag polymetallic deposit inner mongolia china abstract the newly discovered shuangjianzishan ag polymetallic deposit is in the southern part of the great xing an range of inner mongolia in ne china and is china s largest ag deposit with a 21 665 t silver reserves three types of hydrothermal mineralization are evident relatively early disseminated and stringer mineralization succeeded by a breccia hosted and younger vein type mineralization preliminary studies show that the deposit might represent a mixed ore system where the early disseminated and stringer mineralization is overprinted by the breccia hosted and vein type mineralization muscovite ar ar and laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of zircon and geochemical analyses were completed at the deposit the zircon u pb dating for the argentiferous quartz veins yield a crystallization age of 148 1 ma and muscovite coexisting with sulfides yields an ar ar plateau age of 147 2 ma both dates being the same within error indicate that the mineralization is ca 148 ma which is a date that coincides with a wide spread ca 159 144 ma magmatic event in the region stable isotopic data 18 o h2o and d collected from fluid inclusions from the quartz vein type mineralization are characterized by systematic and small variation and this difference reflects the higher fluid fluxes and smaller amount of rock buffering for the quartz veins the 13 c values of 10 6 to 14 3 and 18 o values of 0 to 5 1 for calcite from the veins indicate that the carbon in the mineralizing fluid had a mixed magmatic and highly evolved meteoric fluid source in addition the 34 s values of 28 sulfides range from 4 70 to 1 40 which are values markedly close to that of granitic rocks and the mantle indicative of a magmatic source lead isotopes values for sulfides are indicative of a mixed mantle and crustal source many features of intermediate sulfidation epithermal deposits are present at shuangjianzishan which is therefore interpreted as an intermediate sulfidation deposit derived from a mixed source during a phase change in temperature and pressure interpreted as being related to fluid mixing and boiling

geochemistry of late proterozoic basaltic rocks from southeastern new brunswick canada late proterozoic volcanic rocks of the coldbrook group 630 600 ma from the avalon zone of the appalachians in southeastern new brunswick canada are predominantly bimodal and occur in three belts fault blocks eastern central and western the basaltic rocks were emplaced in a convergent plate margin setting and range from incompatible element depleted island arc tholeiites in the eastern belt to calc alkalic types of the western belt the distinct compositional zonation of the basaltic rocks resembles the across arc variation observed in recent volcanic arc systems the trends include an increase of the lile and hfse abundances and the zr sio2 th sio2 la yb th nb th hf and zr y ratios from the eastern belt in the southeast through the central belt to the western belt in the northwest the zonation of the coldbrook group is attributed to a northwest dipping subduction zone during late proterozoic time it is suggested that some of the late proterozoic basins in the avalon zone of the northern appalachians reached a stage of oceanization

the kibaran of southern africa tectonic evolution and metallogeny abstract the tectono magmatic and metallogenic evolution of the 1100 ma late kibaran high grade namaqua natal metamorphic belt is reviewed and compared with that of the grenville province and the kibaran belts of central and eastern africa in namaqualand 1300 1600 ma supracrustal rocks are recognised including arc related sequences in the east and extensional foreland basin sequences in the west these were laid down either on a heterogeneous basement of eburnian 2000 ma age or on juvenile oceanic crust prior to late kibaran deformation metamorphism and multiple plutonic intrusion the pre namaqua basement infrastructure has been recognised largely in the eastern and nw parts of the orogen adjacent to areas of exposed eburnian crust and probably only the areachap terrane in the east comprises juvenile kibaran crust in natal 1400 ma predominantly metavolcanic supracrustal gneisses were extensively intruded by voluminous plutonic batholiths during the 1050 ma tectonothermal event the northern terrane is interpreted as an ophiolitic assemblage obducted to the ne onto the kaapvaal craton whereas the southern domains are predominantly arc related no older basement is recognised and the entire belt comprises juvenile crustal material none of which is apparently older than 1400 ma the kinematic evolution of the entire namaqua natal belt is comparable in both areas early sw and ne d directed thrusting and nappe emplacement during collision were followed by pervasive steep transcurrent ductile shearing in natal the later shearing event gave rise to major wnw trending oblique sinistral transcurrent steep belts whereas the same event in namaqualand is manifested as major subvertical nw trending dextral transcurrent shear zones the difference in dominant sense of movement in the two regions can be attributed to changes in orientation of the adjacent archaean craton margin within a progressive consistently oriented ne sw directed zone of plate convergence in eastern namaqualand and namibia the transcurrent shearing gave rise to a north propagating stricke slip rift system in which the volcano sedimentary koras sinclair ghansi sequences were deposited mineral cooling ages of 950 ma reported from throughout the belt are considered to signal the end of the kibaran cycle in southern africa the metallogenic evolution is discussed in the light of the tectono magmatic model presented economically important stratiform volcanic and sedimentary exhalative base metal occurrences are extensively associated with early supracrustal sequences throughout the belt other metal deposits and occurrences are predominantly related to the voluminous granitoid and more restricted metabasic suites which characterise the younger rocks in both natal and namaqualand the metallogenesis of the dominantly convergent collisional namaqua natal belt is similar to that seen in the grenville province but distinct from and younger than the lower grade strike slip basin related kibaran belt of central and eastern africa

fracture initiation growth and effect on stress field a numerical investigation a numerical investigation was made of the relationships between fracture initiation growth stress field and boundary conditions two dimensional plane strain continuum models were used in which fractures appeared as zones of strain localization developed through application of a strain softening mohr coulomb constitutive model r and r fractures developed first followed by y fractures at larger strains the models showed that equal development of conjugate r and r fractures is easily changed to favor one or the other set by minor variations in model initial conditions strength loss in fractures caused stress field rotations in regions bounded by fractures altering the orientation of subsequent fractures the amount and sense of stress field rotation is dependent on the strength loss during displacement on the fractures the orientation of fractures and on the boundary conditions y oriented fractures could be explained on the basis of a mohr coulomb failure criterion provided that stress field rotation is accounted for monitoring of fracture slip activity showed that under conditions of constant boundary velocity slip was discontinuous in time alternating on fractures throughout the model

the sm nd age of kambalda volcanics is 500 ma too old although sm nd isotopic analyses of volcanics from kambalda western australia form a 3 2 ga linear array pb pb analyses of the same suite give an isochron age of 2 73 0 03 ga and a 2 7 ga model age for the associated sulphides we suggest that the 3 2 ga age is incorrect and that the sm nd array results from mixing between depleted mantle and either older continental crust or enriched mantle

apatite nodules as an indicator of depositional environment and ore genesis for the mesoproterozoic broken hill type gamsberg zn pb deposit namaqua province south africa nodules consisting of fluorapatite are concentrated as a discrete band in the polymetallic sulfide ore of the gamsberg deposit in central bushmanland south africa their shape zonal features and geochemistry in particular rare earth element ree abundances are similar to authigenic francolite concretions that precipitate during diagenesis in organic rich muds as a result the apatite nodules are regarded as primary the nodules have a strong lithostratigraphic control occurring at the transition of siliciclastic hosted pyrite sphalerite graphite mineralization to calc silicate hosted pyrrhotite sphalerite mineralization mineralogical and chemical evidence indicates that this transition also corresponds to a paleo redox boundary that separates sediments deposited under oxygen deficient conditions from those that developed in a more oxygenated environment the apatite nodules can morphologically and chemically clearly be distinguished from coarse apatite grains that occur in oxide facies iron formations stratigraphically above the ore horizon however similar ree profiles and in particular positive eu anomalies in both types of apatite are indicative of a close genetic relationship between the two units and favor a common hydrothermal origin of the p the contrasting morphologies and chemical signatures of the two occurrences can rather be attributed to differences in behavior of the phosphates during precipitation within the contrasting host sediments chemical versus fine grained clastic taking modern phosphorites as an analogue these results are used to postulate a genetic model for the deposition of the sulfide ore and associated iron formations the model envisages differentiation of the depositional basin into oxygen deficient basin facies hosting the sulfide ore and oxygenated shelf facies which are composed of manganiferous iron formations the intimate association of sedimentary apatite with base metal sulfides indicates that basin conditions were conducive to the precipitation of both phases this relationship might act as a potential exploration guide in similar basins elsewhere

hydrothermal fluid evolution of the jintingling gold deposit in the jiaodong peninsula china constraints from u pb age cl imaging fluid inclusion and stable isotope abstract the jintingling gold deposit located in the jiaodong peninsula north china contains vein dissemination and stockwork style ores hosted in the jurassic linglong granitic pluton hydrothermal activities in this deposit are divided into seven stages including pre ore massive k feldspar alteration specularite quartz vein v1 milky quartz sulfide vein v2 quartz pyrite vein v3 massive quartz sericite pyrite alteration and gold mineralization quartz polymetallic sulfide vein v4 and quartz calcite vein v5 rhenium osmium dating was conducted on molybdenite from v2 yielding an isochron age of 123 3 3 6 ma la icp ms zircon u pb dating yielded 121 5 1 5 ma 1 mswd 0 010 for a pre ore diorite porphyrite dyke and 117 6 1 2 ma 1 mswd 0 018 for a post ore diorite porphyry dyke respectively thus gold mineralization occurred at 122 118 ma four types of fluid inclusions were identified in quartz veins including co 2 h 2 o ch 4 inclusions type i pure co 2 inclusions type ii mineral bearing inclusions type iii and aqueous inclusions type iv fluid inclusion studies demonstrate that the primary ore forming fluids contain co 2 rich vapor 357 420 c 7 2 11 3 wt nacl equivalent and critical fluids 368 400 c the two phases were likely formed by immiscibility of magmatic hydrothermal fluids later on the fluids evolved to a h 2 o co 2 nacl ch 4 system which had temperatures of 300 364 c and salinities of 2 0 9 7 wt nacl equivalent the h 2 o co 2 nacl ch 4 fluid system may experience phase separation forming coexisted co 2 h 2 o ch 4 inclusions homogenized to vapor or liquid at temperature of 265 309 c and 265 287 c salinities of 3 1 7 1 wt and 4 3 7 1 wt nacl equivalent respectively and aqueous inclusions homogenized to liquid at temperature of 255 294 c and 3 7 7 6 wt nacl equivalent along with further evolution the fluids shifted to a h 2 o nacl system with temperatures of 163 258 c and salinities of 0 5 9 0 wt nacl equivalent pyrite from the jintingling deposit has 34 s values 5 5 6 1 similar to those of pyrite from other gold deposits in the jiaodong district indicating that they were related to the same hydrothermal ore forming system the 13 cpdb values of calcite 4 5 to 5 4 in v5 are generally located in the range of magmatic derived carbon fluids of v2 v3 v4 have d from 64 4 to 87 1 and 18 o from 8 4 to 0 2 located in the compositional fields between magmatic water and meteoric water collectively microthermonetric results and isotopic data indicate that the primary ore forming fluids were most probably magmatic in origin with incorporation of meteoric water in the later ore forming stage precipitation of gold was triggered by cooling of fluids fluid immiscibility and decrease of sulfur in the fluids

new insights into the geology of the namaqua tectonic province south africa from ion probe dating of detrital and metamorphic zircon abstract an ion microprobe study in the western part of the namaqua natal tectonic province of south africa provides new insights into ages of sedimentation magmatism and metamorphism in the bushmanland terrane concordant u pb ages and discordia regressions are reported for three samples and in combination with secondary electron microscope images th u ratios and rare earth element analyses of different zircon age domains are used to distinguish several igneous and metamorphic events detrital zircon grains from the tectono stratigraphic lowermost part of the kamiesberg subgroup louisrus formation yielded ages between 1200 and 1250 ma and formed before a first tectono thermal event at 1187 ma in contrast detrital zircon grains from a metapelitic granulite from the top of the subgroup bitterfontein formation were deposited during a previously unrecognized sedimentation stage after 1157 ma and after this first tectono thermal event therefore at least parts of the supracrustal rocks in the bus

juvenile vs recycled crust in ne china zircon u pb geochronology hf isotope and an integrated model for mesozoic gold mineralization in the jiaodong peninsula abstract the continental crust of the north china craton ncc is a major reservoir of mineral resources with imprints of secular changes in tectonics and metallogeny the jiaodong peninsula located in the eastern margin of the north china craton ncc is currently one of the largest gold producers over the globe and preserves the records of multiple magmatic and metamorphic events here we characterize the timing and tectonics of the major mesozoic magmatism and the associated gold metallogeny in this region through a comprehensive u pb geochronological and hf isotope investigation of zircons in a suite of granitoids mafic magmatic enclaves melanocratic dikes and melted basement rocks the linglong granite hosting one of the major gold deposits in jiaodong shows emplacement ages between 150 and 160 ma and the dominantly negative e hf t values 34 0 to 23 8 of zircons from this intrusion suggest magma derivation from recycled components in the archean basement the guojialing granodiorite and its mafic magmatic enclaves show similar ages between 123 and 127 ma with negative e hf t values 19 3 to 16 8 corresponding to crustal magma source the melanocratic dikes belonging to pre and syn mineralization stages with u pb age range of 126 to 166 ma display large variation in their zircon e hf t values 25 7 and 2 3 suggesting the involvement of both recycled crustal and juvenile mantle components zircons in the melted basement rocks with ages in the range of ca 127 132 ma also display both positive and negative e hf t values 44 6 and 9 8 indicating a mixture of recycled ancient crust and juvenile magmas our study shows that although the peak of gold metallogeny coincided with the tectonics associated with pacific plate subduction which mobilized and concentrated the ores the source materials of gold mineralization and magmatism had multiple origins including from the precambrian basement rocks mesozoic granitoids and mantle derived mafic magmas with extensive mixing of crustal lithosphere mantle and asthenospheric components a combination of delamination mantle upwelling subduction related metasomatic enrichment and recycling of ancient components facilitated the gold metallogeny in this region our study provides a typical case of juvenile and recycled components in the formation and evolution of continental crust and associated mineral resources

the grid work texture of authigenic microcrystalline quartz in siliceous crust type sct mineralized horizons siliceous crust type sct formations are pervasive silicified horizons associated with fluoritebarite polymetallic sulfide mineralization in carbonate rocks they almost invariably show a peculiar grid work texture formed by microcrystalline quartz the mineralogical and textural features of several sct samples from italy spain france china and brazil were investigated by optical and electron microscopy and x ray and neutron powder diffraction the resulting 001 pole figures exhibit two main components of orientation of the crystallographic c axis with respect to the normal to the sample surface one located at about 35 and the other in the range 60 85 the observed textural features are seen in all samples and they appear to be independent of the age and geographical location of the sct formation the observed grid work texture is tentatively interpreted as forming by nucleation of quartz seeds on specific faces of surrounding crystals the observed morphology and the regularly oriented populations of crystals are consistent with simultaneous growth of quartz crystals having well defined reciprocal orientations the grid work texture of quartz in sct horizons is similar to the type reported for magadi type cherts which are commonly interpreted as formed by magadiite mediated silica precipitation processes since the genesis of sct deposits is totally unrelated to alkaline lake genetic processes it is concluded that cherts showing strongly textured patterns of microcrystalline quartz may have a different origin than magadi type deposits

simulating hydro mechanical effects in rock deformation by combination of the discrete element method and the smoothed particle method abstract the discrete element method dem has been used successfully to simulate rock failure however when considering the deformation of fluid saturated rock the dem lacks the contribution of the fluid pressure the presence of a pore fluid can affect the effective stress state which might result in a change in some of the mechanical properties of the rock e g strength and modulus additionally saturated rock is more susceptible to strain rate effects an extension to dem is presented in which the effective stress theory is embedded by coupling the dem with a pore pressure diffusion process this is achieved by interpolating the discrete properties of the dem to a continuum by using a smoothed particle approach sp the model is able to predict the strengthening weakening of a rock with respect to the amount of fluid drainage that has been allowed to demonstrate the validity of the model several simulations of tests under different loading conditions are conducted and the results are compared with experimental data from literature the agreement between theory and experiment is very good

the chemistry and origin of zincian spinel associated with the aggeneys cu pb zn ag deposits namaqualand south africa zincian spinel or gahnite zn fe mg al2o4 occurs in metamorphosed sulphide rich rocks garnet quartzites quartz magnetite rocks aluminous metasediments barite magnetite rocks quartz veins and pegmatites associated with the aggeneys base metal deposits namaqualand south africa zincian spinel in sulphide bearing rocks is considered to have formed predominantly by desulphurization reactions involving a member of the system fe s o and sphalerite with sillimanite or garnet gahnite in sulphide free garnet quartzites quartz magnetite rocks and barite magnetite rocks probably formed from zn and al that were hydrothermally derived whereas gahnite in aluminous metasediments was derived from the metamorphism of metalliferous shales in which zn may originally have been linked to organic material gahnite is zn rich in sulphide bearing rock but is fe rich in sulphide free garnet quartzites and quartz magnetite rocks although zn rich spinels represent guides to ore in the aggeneys area and elsewhere in the namaqualand metamorphic complex fe rich spinels should not be discounted because zn rich and fe rich spinels occur within metres of sulphides at aggeneys

an integrated mineral system model for the gold deposits of the giant jiaodong province eastern china abstract the giant jiaodong gold province with more than 5000 t of proven gold resources is unique in that its mesozoic gold deposits are hosted in a precambrian basement block there has long been debate on the source of gold the mechanism for its extreme enrichment and a holistic genetic model for these spectacular deposits in order to improve understanding of these factors a mineral system model is proposed for the jiaodong gold deposits for the first time it is based on a detailed review of the architecture and composition of the underlying mantle lithosphere the geodynamic setting at the time of gold mineralization the geological and geochemical features of the deposits themselves and mechanisms of their preservation regional geodynamic reconstructions combined with the nature of mesozoic magmatic systems show that late mesozoic breakoff of the subduction slab and rollback of the paleo pacific plate caused asthenosphere upwelling and lithosphere extension and thinning robust geochronological studies demonstrate that the jiaodong gold deposits formed at ca 120 ma during a change of subduction direction of the paleo pacific plate and the synchronous transition of tectonic regime from regional compression to transpression or transtension prior to peak extension caused by thinning of the lithosphere geophysical exploration data and hf nd isotope mapping of the jiaodong peninsula reveal a relatively simple ancient crustal structure cut by near vertical shear or fault zones including the lithosphere scale tan lu and wulian yantai faults that provided the first order architecture for emplacement of mantle magmas and sub crustal fluids in terms of fertility the significant older pre mineralization crustal metamorphism combined with sulfur lead and strontium isotope ratios indicate a dominant sub crustal source for the ore components for the jiaodong gold deposits consistent with evidence for volatile and gold fertilized metasomatized mantle lithosphere beneath the north china block helium ar and c o isotope ratios implicate mantle sources of ore fluids with contamination by crustal components en route to crustal depositional sites in terms of crustal architecture combined geophysical structural mineralogical fluid inclusion and geochemical studies show that the deeply sourced ore fluids and metals advected upwards through lithosphere scale faults to deposit gold via sulfidation and phase separation in crustal scale nne ne trending fault systems at mid to upper crustal levels preservation of disseminated to stockwork style deposits and auriferous quartz pyrite vein deposits was enhanced by deep crustal formation combined with limited uplift and exhumation of the province the jiaodong gold deposits although commonly hosted in granite intrusions clearly post date them on the basis of robust and reliable geochronology the spatial but non temporal relationships of gold deposits with granites their strong structural control and their other characteristics clearly place them in the orogenic gold group it is suggested because of their uniqueness that they be termed jiaodong type orogenic gold deposits

multi stage structural and kinematic analysis of a retrogressive rock slope instability complex preonzo switzerland abstract large catastrophic rock slope failures are difficult to predict because the underlying mechanisms causing slope accelerations are difficult to study under in situ conditions for slope failures with compound basal rupture planes not only fracture propagation and slip in the basal rupture surface but also within the landslide body control the displacement evolution and time to failure the preonzo instability complex in southern switzerland failed several times since 2002 and offers a unique opportunity to study these mechanisms under in situ conditions the largest failure at preonzo occurred in may 2012 and was conditioned by large slope parallel nne ssw fracture zones which are intersected by ne and sw and e w striking faults creating diverging lateral boundaries whereas in the head scarp region oblique and flexural toppling along pre existing fracture sets is the prevailing mechanism sliding of either planar or wedge type is the preferred kinematic mode facilitated by the new discontinuities developed within the basal rupture surfaces these dominating mechanisms leading to a classical rock slope collapse could only be revealed in retrospect we compare fracture patterns in stable ground tectonic and unloading fractures with new fractures related to rock slope failure observed on basal rupture surfaces and in the head scarp simplified mechanical and kinematic analyses show that old pre existing tectonic fractures cannot accommodate substantial deformations under the in situ stress conditions and propagate connect through curved wing cracks forming at high angles this situation favors the development of new nearly slope parallel fractures which are interpreted as synthetic p shears along localized shear zones fractographic markings on these fractures indicate a continuous and relatively fast formation which presumably has taken place during a period of about 60 years prior to catastrophic failure this detailed description of the multi stage evolution of slope failure at preonzo represents a unique data set for future numerical studies of progressive failure in crystalline rocks

a progressive ductile shear model for the proterozoic aggeneys terrane namaqua mobile belt south africa abstract recent structural and stratigraphic study results indicate that the namaqua orogenesis ca 1 2 ga involved relative movement of lozenge shaped suspect terranes detailed study of one of the terranes the aggeneys terrane provided important information concerning the deformation process the principal process was differential shear which produced complex structures such as interference folds and thrust faults all the observed deformational structures can be explained by a single long lived compressional event

a new chronostratigraphic paradigm for the age and tectonic history of the mesoproterozoic bushmanland ore district south africa a discussion sir the authors are to be congratulated for their contribution to the greater understanding of the aggeneys gamsberg district and bushmanland group through the addition of new detrital zircon age data we trust that these data will ultimately contribute to a better understanding of the depositional age of the bushmanland group as well as the tectonic evolution for this portion of the namaqualand metamorphic province fig 1 while we concur with the authors interpretation that deposition of the bushmanland group and associated base metal sulfide deposits of the aggeneys gamsberg district must be younger than 1650 ma as previously concluded by mcclung 2006 and bailie 2007b we would like to raise some fundamental objections to the contribution by cornell et al 2009 our objections center on the poor and possibly erroneous lithostratigraphic position of the samples analyzed by the authors much of this uncertainty is due to the absence of proper geologic descriptions or convincing evidence to support the assumed stratigraphic position uncritical use of an inadequate lithostratigraphic column for the bushmanland group and the lack of appropriate referencing of recent contributions relevant to this region of the na maquland metamorphic province our most important objection to the communication by cornell et al 2009 relates to the stratigraphic column endorsed the authors present a modified version of the stratigraphic column that was originally described and proposed by praekelt et al 1997 and reiterated in several subsequent publications by the same group of authors e g colliston and schoch 1998 2002 2003 2006 colliston et al 2008 this stratigraphic column is however not widely accepted as it is in direct conflict with the results of regional and local field based investigations of the lithostratigraphy of the bushmanland group fig 2 joubert 1974 1986 rozendaal

evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a proterozoic continental rift sequence at broken hill australia 1 low pressure p high temperature t metamorphism previously attributed to crustal thickening accompanying nappe emplacement in the paleoproterozoic willyama supergroup at broken hill is reinterpreted as a response to crustal extension d1 and bimodal magmatism commencing circa 1700 ma d1 deformation occurred under amphibolite granulite facies conditions producing layer parallel fabrics s1 and metapelitic mineral assemblages in which andalusite dominated over sillimanite crustal extension ceased soon after 1640 ma to be followed by crustal thickening higher pressure metamorphism and northeast vergent recumbent folding d2 attendant on inversion of the original d1 extensional structures d2 recumbent folding has previously gone unrecognized but probably peaked around 1600 ma before further amphibolite facies metamorphism between 1600 and 1590 ma accompanying upright folding and northwest directed thrust faulting d3 in the light of this revised tectonothermal history geodynamic models erected to explain elevated thermal gradients and low p high t granulite facies metamorphism in tectonically thickened crust may not be as relevant to broken hill as once thought above average crustal temperatures and low p high t metamorphism in the willyama supergroup more likely occurred in response to voluminous magmatic intrusion accompanying crustal thinning mantle upwelling and emplacement and unroofing of midcrustal rocks along a major detachment surface a second major structural and or stratigraphic break in the willyama supergroup is indicated by the absence of d1 fabrics from the uppermost part of the sequence

calc alkaline and tholeiitic dyke swarms of tandilia rio de la plata craton argentina u pb sm nd and rb sr 40ar 39ar data provide new clues for intraplate rifting shortly after the trans amazonian orogeny abstract the tandilia system argentina southernmost part of rio de la plata craton rlpc is intruded by two paleoproterozoic unmetamorphosed dyke swarms which are i intermediate i and acid a and ii basic b1 and b2 in composition the latter dykes have tholeiitic characteristics while for both i and a dykes major minor and trace elements including ree e g the higher values of sio2 k2o and ba compared to tholeiitic dykes are characteristic of calc alkaline suites the calc alkaline dykes i and a yielded 40ar 39ar step heating plateau ages of emplacement of 2020 24 and 2007 24 ma these ages are within error in agreement with a rb sr errorchron of 1956 110 ma 1 initial 87sr 86sr 0 7038 0 0025 mswd 19 an upper intercept u pb age on two baddeleyites from a tholeiitic b1 dyke places the intrusion at 1588 11 ma the tholeiitic dykes b1 and b2 have k ar whole rock ages from 803 14 to 1193 18 ma and a 40ar 39ar plateau age of 811 36 ma 2 on plagioclase these discordant apparent ages suggest variable ar loss of the mineral systems calc alkaline dykes mainly trend e w and were emplaced during the transtensional stage of the trans amazonian orogeny during which the plutonic rocks of the tandilia system were formed such a scenario has similarities with the eburnean evolution of the richtersveld plutonic arc complex of the southern african subcontinent namaqualand that faces the rlpc in the west gondwana reconstruction the significantly younger tholeiitic dykes of tandilia 1 59 ga trend mainly nw se their presence constrains the time of crustal extension at the paleo mesoproterozoic boundary during which basin formation tectonics and anorogenic magmatism took place worldwide within a stabilized paleoproterozoic lithosphere such an intraplate regime for the emplacement the youngest dykes of tandilia is consistent with transcontinental scale diachronous extensional episodes within the south american continent which initiated shortly after the trans amazonian orogeny as illustrated by the 1 73 ga florida tholeiitic dyke swarm and coeval anorogenic granitoids scattered across the rlpc uruguay and tandilia paleoproterozoic geologic features of the rlpc namely the occurrence of plutonic arc rocks 2 14 2 07 ga succeeded by emplacement of anorogenic granitoids and mafic dykes 1 73 1 59 ga allow direct correlation with the postulated gondwana counterpart mirrored by broadly contemporary plutonic rocks of the richtersveld and bushmanland subprovinces of namaqualand the broad picture reinforces the idea that the trans amazonian eburnean orogenies played an important role for juvenile crustal accretion within the southern south america and its southern africa counterpart which was followed by a tendency to dispersion of the stabilized continental fragments during the mesoproterozoic preceding the assembly of the rodinia supercontinent

the relationship of mantle derived fluids to gold metallogenesis in the jiaodong peninsula evidence from d o c s isotope systematics abstract the largest gold district in china is the jiaodong peninsula where three types of gold deposits are recognized quartz vein fracture altered and breccia types the first two developed along a group of ne trending faults and are hosted by granitic intrusions dated at 160 to 150 ma biotite granite and 130 to 126 ma granodiorite and by metamorphic rocks of the precambrian crystalline basement the breccia type gold system is mainly located around the northern margin of the jiaolai cretaceous basin where mineralisation is controlled by both detachment fractures and ne trending faults this study is based on stable isotope determinations from ten gold deposits including linglong jiaojia sanshandao cangshang wang ershan dayigezhuang denggezhuang pengjiakuang fayunkuang and dazhuangzi as well as the linglong jurassic biotite granite guojialing cretaceous granodiorite and archean gneiss the stable isotope systematics reflect the style of the three types of gold deposits but also show that they belong to the same metallogenic system in which the hydrothermal fluids were derived from a mantle fluid reservoir and mixed with crustal fluids the ore forming age is later than both the jurassic biotite granite and cretaceous granodiotite but overlaps with the 121 to 114 ma ages of lamprophyre and diabase dykes the hydrothermal fluids that were responsible for both gold mineralisation and the retrograde alteration of the diabase and lamprophyre dykes are similar and represent a co 2 and potassium rich system this fluid system is interpreted to be the consequence of cretaceous lithospheric thinning asthenospheric upwelling and mantle degassing in eastern china

studies on the formation of discontinuous rock fragments during cutting operation abstract a rock fragmentation process is simulated during mechanical cutting of rock using an explicit finite element code ls dyna in the simulation a cutting tool is orthogonally moved against stationary rock materials made of sandstone and limestone rock material properties have been incorporated using an advanced damage constitute material model simulations were performed for various rake angles at different cutting velocities and cutting depths the variation of cutting forces stresses rock fragment morphology and the character of fragment formation have been investigated overall the results indicate that the explicit fem is a powerful tool for simulating rock cutting and the fragmentation process more specifically the separation of rock fragments from the base rock slab was accurately predicted using the numerical model the cutting forces and rock fragment characteristics were strongly influenced by rake angle when compared to cutting tool velocities for a given depth of cut this information is shown to be highly pertinent to better understanding cutting rates and tool wear

numerical simulation of progressive rock failure and associated seismicity in this paper a numerical approach to modeling progressive failure leading to collapse in rock and associated seismicity is reported in the first part a newly developed numerical code rfpaz rock failure process analysis is introduced the program allows modeling of the observed evolution of damage and associated seismic events due to progressive failure leading to collapse in brittle rock there are three features distinguishing the approach from conventional numerical methods such as fem 1 by introducing heterogeneity of rock parameters into the model rfpaz can simulate non linear behavior in rock using a linear method 2 by introducing elastic modulus reduction for failed elements rfpa2d can process discontinuum mechanics problems by a continuum mechanics method and 3 by recording the event rate of failed elements the seismicities associated with the progressive failure in rock can be simulated in the second part of the paper the applications of rfpa2d in simulating geological process and in solving mining design problems are illustrated numerical simulation of a fault initiation process indicates that some of the important phenomena such as coalescence of microfracture the nucleation and growth of crack clusters fault initiation and development elastic rebound dilatation uplift and seismic behavior etc can be simulated with this numerical code the simulation of progressive failure leading to collapse in underground openings demonstrates the capacity of this code in solving mining design problems