gold bearing mesothermal veins from the gubong mine cheongyang gold district republic of korea fluid inclusion and stable isotope studies the gubong deposit consists of five massive gold bearing mesothermal quartz veins that fill fractures oriented northeast and northwest along fault shear zones over an area of 14 km2 in precambrian metasedimentary rocks of the gyeonggi massif the veins are divided into three groups based on their orientation and location they have a ribbon texture that is interpreted to result from repeated hydraulic fracturing events mineral deposition was associated with hydrothermal fluid overpressuring within and below the active fault shear zones the vein mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes to be recognized separated by a major faulting event the ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes wall rock alteration minerals during stage i the main ore stage include sericite chlorite and minor pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena and argentite electrum also was deposited during stage ii mineralization in the one group of veins along with pyrite sphalerite chalcopyrite and galena but the second stage of deposition in other veins was barren petrographic examination of textural relationships among sulfides fluid inclusions microfracturing and quartz shows chronological and genetic relationships between gold deposition and fluid entrapment systematic studies of fluid inclusions in stage i vein indicate two contrasting events a relatively high temperature 203 432 c and pressure 943 2 098 bars event related to early sulfide deposition and associated with h2o co2 ch4 nacl n2 fluids less than about 13 4 wt nacl and a lower temperature 202 399 c and pressure 670 850 bars late sulfide depositional event involving h2o nacl fluids 3 9 17 3 wt nacl the h2o nacl fluid involved in ore related stage ii mineralization had a salinity of 0 4 to 4 2 wt percent nacl and a homogenization temperature of 201 to 378 c the calculated sulfur isotope compositions of hydrothermal fluids from the stage i veins 34sh2s 3 5 10 5 indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks the calculated and measured oxygen and hydrogen isotope compositions of the ore forming fluids stage i 18oh2o 1 1 9 0 d 92 to 21 stage ii 18oh2o 0 1 to 0 3 d 95 to 93 indicate that the fluids were derived from magmatic and or deep seated metasedimentary rocks stage i and evolved by mixing with local meteoric water stage ii by limited water rock exchange and by degassing during mineralization in uplift zones the h2o nacl fluids involved in the stage i development of these veins represent fluids that evolved either through unmixing of h2o co2 ch4 nacl n2 fluids following a decrease in fluid pressure or through mixing with deeply circulating meteoric waters possibly as a result of uplift and or unloading during mineralization the h2o nacl fluid involved in stage ii was derived from meteoric water early deposition of gold in stage i was caused by a decrease in sulfur fugacity h2s loss that accompanied the immiscible separation of carbonic vapor from h2o co2 ch4 nacl n2 fluids gold in late stage i and stage ii veins was precipitated from h2o nacl fluids by cooling and by dilution caused by mixing with meteoric water

fractured reservoirs with fracture corridors outcrop studies reveal a common occurrence of tabular zones of significantly increased fracture intensity affecting otherwise well lithified rocks these zones called fracture corridors can have a profound effect on multi phase fluid flow in the subsurface using standard geo modelling tools it is possible to generate 3d realizations of reservoirs that contain distributions of such fracture corridors that are consistent with observations including the vertical frequency in pseudo wells inserted into the model at random locations these models can generate the inputs to flow simulation the approach adopted here is to run the flow simulations in a single porosity representation where the flow effects of fractures are upscaled into equivalent cell based properties preserving a clear spatial relationship between the input geology and the resulting cellular model the simulated reservoir performance outcomes are very similar to those seen in real oilfields extreme variability between wells early water breakthrough disappointing recoveries and patchy saturation distributions thus a model based on fracture corridors can provide an explanation for the observed flow performance of a suitable field however the use of seismics to identify fracture corridors is not an easy task new work is needed to predict the seismic responses of fracture corridor systems to be able to judge whether it is likely that we can robustly detect and characterize these flow significant features adequately

comment on chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt by y h park s j doh and d suk summary a recent paper published in geophysical journal international reports that the late palaeozoic to early mesozoic sedimentary rocks in the northeastern okcheon belt of korea were remagnetized during the late cretaceous to early tertiary and argues that the remagnetization was triggered by fluids travelling more than 800 km from the subducting slab of the kula pacific plates based on available geological data however we suggest that the remagnetization was caused by thermal effects of a late cretaceous pluton intruding the sedimentary rocks and or associated short range hydrothermal fluids rather than by long range fluids

in situ measurements of rock mass deformability using fiber bragg grating strain gauges abstract in order to examine how the mechanical properties of a rock mass vary from the centimeter to meter scale we performed two field point loading tests 89 kn and 890 kn to determine the in situ modulus of deformation of a rock mass the experimental setup is analogous to plate jacking type tests but instead using a point load the experiments were done in the poorman formation on the 4100 level 1250 m underground of the sanford underground research facility surf at the site of the former homestake gold mine in lead sd for comparison with in situ values we also conducted laboratory mechanical tests and used two geotechnical classification systems to evaluate rock stiffness the in situ modulus of deformation increases with depth into the rock mass this increase in stiffness is a result of the differences in mechanical properties due to the effect of excavation of the underground space near the surface 0 1 2 m depth the rock is softest due to induced fractures and damage from blasting beyond this damaged zone is the stress relief zone 1 2 1 5 m depth where open joint sets affect rock stiffness and beyond that lies the undisturbed zone 1 5 m depth where the rock is the stiffest if done properly in situ measurements of rock stiffness are a valuable tool to fully characterize the gradient in stiffness of a rock mass which laboratory tests or geotechnical classification systems do not fully capture

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

deformation and failure of the tymfristos tunnel greece the tymfristos tunnel a 1 365m long road tunnel with an 11m section diameter was excavated through the highly tectonized low strength flysch formation of central greece about 1 year after the completion of the excavation in 1995 convergence of up to 20 followed by failure of the support system was recorded a 501m long segment in which the failure occurred was reexcavated based on a more detailed study of the ground conditions however this second phase was also followed by an up to 6 convergence the detailed geodetic study of the three dimensional kinematics of the support shell in relation time ring closure delays and support measures reveals an unusual time history of convergence occasionally continuing even after the ring closure and a nonuniform distortion of the lining furthermore uncontrolled deformation of certain weak sections propagated bidirectionally to adjacent previously stabilized sections producing a chain effect responsible for destabilization and resumed convergence

gold rich mesothermal vein deposits of the republic of korea geochemical studies of the jungwon gold area gold vein deposits of the jungwon area are among the first documented examples of mesothermal gold deposition in the republic of korea the deposits are composed of massive quartz veins up to 1 0 m wide which occupy fault planes in precambrian gneiss k ar dating of alteration sericite 146 156 m y indicates a late jurassic age for ore mineralization similar to that of a nearby granodiorite the veins are gold rich and sulfide poor with ore shoots up to 200 m in horizontal and vertical extent ore grades average 10 2 g ton gold with an average gold silver production ratio of 6 1 fluid inclusion data indicate that gold was deposited between 375 degrees and 290 degrees c from relatively dilute fluids asymp 4 equiv wt nacl containing asymp 15 to 25 mole percent co 2 evidence of fluid unmixing co 2 effervescence indicates pressures of 1 200 to 1 500 bars gold deposition was likely a result of decrease of sulfur activity caused by sulfide deposition and or h 2 s loss accompanying fluid unmixing measured and calculated compositions of ore fluids in the jungwon area delta 18 o 5 0 to 7 7ppm delta d 78 to 113ppm indicate that gold was deposited from a highly evolved meteoric water that underwent extreme 18 o enrichment and moderate d enrichment mineralogy and ore fluid chemistry of the jungwon area deposits are similar to those of mesothermal gold vein deposits of the canadian cordillera canadian archcan greenstone belts and the mother lode district of california the diversity of host rocks in these deposits indicates that host rock petrology is not a controlling factor in the formation of mesothermal gold vein deposits these observations together with our geochemical studies of korean deposits may validate a more general application of meteoric water models for the formation of mesothermal gold vein deposits

the early cretaceous yangzhaiyu lode gold deposit north china craton a link between craton reactivation and gold veining the yangzhaiyu gold deposit is one of numerous lode gold deposits in the xiaoqinling district southern margin of the north china craton gold mineralization is hosted in neoarchean to early paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein proximal alteration zone ore related hydrothermal alteration is dominated by sericite quartz sulfide assemblages close to gold veins and biotite quartz pyrite chlorite epidote alteration generally distal from mineralization pyrite is the predominant sulfide mineral locally coexisting with minor amounts of chalcopyrite sphalerite and galena gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with au bearing tellurides mainly petzite and calaverite coexisting with hessite tellurobismuthite and altaite fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures 175 313 c from aqueous or aqueous carbonic fluids with moderate salinity 5 14 wt nacl equiv 34s values of sulfide minerals range mainly from 2 0 to 4 4 whereas auriferous quartz vein samples have 18o values of 12 4 to 9 6 with calculated 18oh2o values of 6 0 to 3 2 gold related pyrite grains yield elevated 3he 4he ratios 1 51 0 32 ra relative to crustal reservoirs and mantle like 20ne 22ne and 21ne 22ne ratios 9 90 9 68 and 0 029 respectively the stable and noble gas isotopes thus suggest deep seated most likely magmatic and mantle derived sources for the ore fluids sulfur and by inference other components in the ore system 40ar 39ar dating of ore related sericite and biotite separates indicates two episodes of gold genesis at 134 5 to 132 3 and 124 3 to 123 7 ma the mineralization ages overlap zircon u pb ages of 141 0 1 6 to 125 8 1 4 ma 2 for the wenyu and niangniangshan monzogranite plutons and a number of mafic to intermediate dikes intruding these plutons all being proximal to the yangzhaiyu gold deposit the synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur the geochronologic data also suggest that gold veining took place billions of years after the stabilization of the north china craton and associated metamorphism in the late archean to early paleoproterozoic this contrasts sharply to lode gold deposits in other precambrian cratons that formed predominantly in late archean to paleoproterozoic temporarily and genetically related to regional high grade metamorphism and compressional or transpressional tectonism available data have demonstrated that the north china craton was reactivated in the late mesozoic as marked by voluminous igneous rocks faulted basin formation high crustal heat flow and widespread metamorphic core complexes in the eastern part of the craton it is thus suggested that the yangzhaiyu gold deposit together with other deposits of similar ages in the xiaoqinling district were products of this craton reactivation event lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy fluid and sulfur required for the formation of the gold deposits

nature and ore formation of the erdaohezi pb zn deposit in the great xing an range ne china abstract the erguna metallogenic belt is a large erdaohezi epithermal polymetallic sulfide pb zn deposit in the northern great xing an range that is associated with andesitic porphyry mineralization mainly occurs at the edges of andesitic porphyry and adjacent jurassic quartz porphyry and volcanic strata hydrothermal alteration minerals mainly include quartz sericite adularia chlorite and calcite while ore minerals include pyrite galena and sphalerite with minor argentite chalcopyrite and tetrahedrite three hydrothermal mineralization stages are recognized three categories of fluid inclusions fis are distinguished in quartz fluorite and sphalerite veins liquid rich gas rich and a few h2o co2 inclusions the stage i fis include all three inclusion types and present high homogenization temperatures 197 233 and salinities 0 7 6 8 wt nacl eq the stage ii fis mainly comprise liquid rich inclusions with a few h2o co2 types and present higher homogenization temperatures 167 190 and slightly higher salinities 0 9 7 6 wt nacl eq than those of stage i stage iii only contains liquid rich inclusions and presents the lowest homogenization temperatures 120 157 and salinities 0 5 4 8 wt nacl eq the ore forming fluids have low temperatures and salinities in an h2o nacl co2 ch4 system the o h isotope data 2 2 to 5 0 and 160 0 to 152 5 respectively suggest that ore forming fluids gradually evolved from mantle primary water to meteoric water sulfur strontium and lead isotopes imply a mixed crustal and mantle source for the ore forming materials sulfide rb sr dating yields a well defined isochron age of 130 5 3 6 ma from the main mineralization stage which is similar to the zircon age of 134 9 0 9 ma for the andesitic porphyry related to mineralization we therefore proposed that erdaohezi is a low sulfidation epithermal pb zn polymetallic deposit and fluid immiscibility was the dominant mechanism of ore deposition mineralization occurred in an early cretaceous back arc extensional setting that was related to the subduction of the paleo pacific plate

typomorphic features of placer gold of vagran cluster the northern urals and search indicators for primary bedrock gold deposits abstract the vagran placer cluster is located on the eastern slope of northern urals during 100 years of gold mining history approximately 40 tons of gold have been extracted from the placer deposits bedrocks of the region consist of high metamorphic upper proterozoic and paleozoic terrigeneous terrigeneous volcanogenic and igneous rocks gold placer deposits are mostly alluvial genesis deposits and of quaternary to oligocene age the alluvial deposits consist of gravel with pebbles boulders and sandy clay covered by sandy silt and a soil layer the thickness of the alluvial sequence is usually 5 10 m and reaches 18 m in the main watercourses of the third order nearly all of the alluvial sediments are gold bearing but concentrations of economic importance prevail in the bottom part of the sequence above the bedrock there are four different types of gold particles i rounded and well rounded particles of high fineness and homogeneous inner structure ii rounded to sub rounded high fineness particles with a pure gold rim developed over a core iii crystallomorphic idiomorphic high fineness with a homogeneous inner structure and iv irregular angular and subangular particles of medium fineness with a significant content of ag 10 40 wt and elevated hg up to 1 15 wt the first type is prevalent and comprises up to 65 of the total gold particles it is uniformly distributed throughout the territory there are features with initially complicated dendritic and laminar shaped particles which were rounded during transportation the second and third types have a propensity for zones of the inherited erosion tectonic depressions apparently types i ii and iii are related with orogenic mesothermal gold sulfide quartz mineralization the differences of these types depend on the primary zonation of ore bodies and supergenic transformation of the alloys they were connected with middle depth ore bodies of an orogenic gold sulfide quartz formation the fourth type is evident of nearby transportation from primary sources and a short duration of supergenic influence it is controlled by a zone of nw se orientation diagonal to the main structures of ural fold belt the plot of au content vs coefficient of heterogeneity ratio of the au content in the core and in the rim of the grains is the distinguishing factor between the four types of gold grains both by primary hypogenetic characteristics and supergenetic features no corresponding lode occurrence of gold sulfide quartz mineralization has been identified to date in this region placer gold concentrations are related to the intermediate hosts of the mesozoic cenozoic surfaces of the ural peneplain uplift in the oligocene and eroded in miocene quaternary time this factor determines the widespread distribution of placer gold in the territory of the vagran cluster the large carlin type vorontsovsk gold deposit is located 60 km south east from the vagran area it has a shallow erosional level small size of native gold and its distal location from the placer deposits makes it an unlikely primary source for the vagran placers however mineralization of this type of deposit is noted within the cluster gold of the fourth type nearly resembles the gold of the vorontsovsk deposit and apparently the source is related to the same hydrothermal mineralization event icp ms analyses of the quartz sulfide lodes in the floor of gold bearing valleys revealed a gold content of 2 0 6 9 g t in the zone of type iv distribution therefore gold of the fourth type can be used as an indicator for the exploration of primary bedrock mineralization the geological setting and typomorphic features of this placer gold shows that the primary gold mineralization is similar to the vorontsovsk deposit and within the zone of distribution of the placer gold of the fourth type

mesothermal gold vein mineralization of the samdong mine youngdong mining district republic of korea mesothermal gold mineralization at the samdong mine 5 5 13 5 g ton au youngdong mining district is situated in massive quartz veins up to 1 2 m wide which fill fault fractures within upper amphibolite to epidote amphibolite facies precambrian banded biotite gneiss the veins are mineralogically simple consisting of iron and base metal sulfides and electrum and are associated with weak hydrothermal alteration zones 0 5 m wide characterized by silicification and sericitization fluid inclusion data and equilibrium thermodynamic interpretation of mineral assemblages indicate that the quartz veins were formed at temperatures between 425 and 190 c from relatively dilute aqueous fluids 4 5 13 8 wt equiv nacl containing variable amounts of co2 and ch4 evidence of fluid unmixing co2 effervescence during the early vein formation indicates approximate pressures of 1 3 1 9 kbars corresponding to minimum depths of 5 7 km under a purely lithostatic pressure regime gold deposition occurred mainly at temperatures between 345 and 240 c likely due to decreases in sulfur activity accompanying fluid unmixing the 34s values of sulfide minerals 3 0 to 5 3 and the measured and calculated o h isotope compositions of ore fluids 18o 5 7 to 7 6 74 to 80 indicate that mesothermal gold mineralization at the samdong mine may have formed from dominantly magmatic hydrothermal fluids possibly related to intrusion of the nearby ilmenite series kimcheon granite of late jurassic age

multi scale fracture network analysis from an outcrop analogue a case study from the cambro ordovician clastic succession in petra jordan abstract a regional multi scale fracture network is prominently exposed in the cambro ordovician sedimentary succession in south western jordan this succession consists of marine deposits overlain by heterogeneous deltaic sediments culminating in 500 m of massive to cross bedded fluvial sandstones a data set acquired from high resolution satellite imagery and field measurements enables the quantification of the geometry and spatial characteristics of the fracture network in three dimensions five directional fracture sets are identified from the satellite data with mean strikes of 000 040 065 120 and 145 large fracture zones longer than 600 m composed of tightly spaced joints confined in fracture swarms exhibit a log normal trace length distribution and the fracture swarms are regularly spaced the trace length distribution of intermediate fractures 40 600 m long exhibits power law characteristics and the fractures are clustered reflecting different fracture system styles and stratigraphic controls as a function of scale the small scale fracture network is strongly dependent on the distribution of bedding plane discontinuities throughout different parts of the succession the multi scale fracture network is categorized in a three tier hierarchical fracture model that reflects underlying stratigraphic controls in the study area this type of model can be used to improve the representation of fracture networks in fluid flow simulations of fractured reservoirs with hybrid models that combine elements of discrete fracture networks and continuum models

fracture corridors and fault reactivation example from the chalk isle of thanet kent england abstract fracture corridors elongated zones of narrowly spaced highly connected fractures can generate the main fluid flow pathways in natural reservoirs and can be responsible for an early water break through in hydrocarbon reservoirs understanding this fracturing is necessary for reservoir behaviour prediction an outcrop analogue of a chalk fractured reservoir from the isle of thanet in se england is used to understand the development of fracture corridors and to characterize their relationship with faulting and folding we show that fracture corridors are associated with strike slip reactivation on sub seismic faults in a context of polyphase deformation they nucleate on slip patch tips or on areas of stress concentration due to fault plane dip strike irregularities steps or fault intersections fracture corridors generated are oblique to the fault which they initiate on with increasing deformation fractures composing the corridor are sheared and a fault can develop within the fracture corridor the relationship between folding and fracture corridor development in this area is indirect both are localized by a pre existing basement fault that allows stress concentration and reorientation and promotes fault reactivation in the chalk cover this work emphases the importance of the distribution of sub seismic faults in fractured reservoirs as they can control the development of fracture corridors

la icp ms trace element analysis of arsenopyrite from the samgwang gold deposit south korea and its genetic implications abstract the samgwang deposit previously classified as an orogenic gold deposit consists of several structurally controlled auriferous quartz veins hosted by metasedimentary rocks of the precambrian gyeonggi massif south korea the gold at samgwang occurs as electrum commonly associated with arsenopyrite laser ablation inductively coupled plasma mass spectrometry la icp ms coupled with ore microscopy was conducted on au and trace elements distributed in arsenopyrite grains contained in quartz vein and wall rock samples resulting profiles for au co ni and sb were relatively flat and showed little variability indicating that the elements were relatively homogeneously distributed and exchanged via substitution in arsenopyrite while variability and noisy depth profiles inferred that pb was present as tiny inclusions or discrete particles furthermore measured gold concentrations were typically higher in arsenopyrite grains from laminated quartz veins avg 2 07 ppm than in grains from massive quartz veins avg 0 26 ppm and wall rock samples avg 0 33 ppm in the case of wall rock and massive quartz vein samples arsenopyrite grains of euhedral shape illustrate an element distribution pattern whereby au concentrations tend to decrease towards the rims of the analyzed grains in contrast the rims of arsenopyrite grains in laminated quartz vein samples recorded much higher au concentrations of up to 20 1 ppm with increasing pb bi and ag particularly within domains of fractured or recrystallized arsenopyrite grains the newly acquired la icp ms data along with textural evidence may be interpreted in terms of the release and remobilization of invisible gold that was originally locked up in the arsenopyrite this release is linked to late deformation and hydrothermal event during which the remobilized invisible gold was redeposited as electrum in addition there is evidence for the introduction of additional gold and other precious and base metals by the late stage hydrothermal fluids based on the above and in contrast to previous genetic models we propose a more complex metallogenic concept for samgwang in which the economically important gold enrichment process was genetically related to intrusive activity during the waning stages of jurassic to early cretaceous daebo orogenesis

quantifying aperture spacing and fracture intensity in a carbonate reservoir analogue crato formation ne brazil abstract the characterization of fracture networks in carbonate reservoirs represents a primary approach to understand the processes of fluid flow the study of outcrop analogues has been used to enhance the understanding of the relative contribution of fracture networks to reservoir permeability the outcrop data can overcome scale limitations and or lack of consistency of subsurface datasets e g seismic well logs and cores this paper presents the fracture characterization of the aptian albian lacustrine laminites of crato formation araripe basin ne brazil which have been investigated as an analogue to some of the observed carbonate facies present in the pre salt reservoir sequence of the brazilian marginal basins in order to provide fracture attributes for discrete fracture network dfn modelling we investigate spacing and aperture distribution length and intensity of fractures based on the use of traditional scanline macro and microscale method the main fractures identified in the crato formation are shear and extensional fractures and with stylolites also present in this study we focused on vertical veins which strike in two principal directions nnw sse set 1 ne sw set 2 and are filled or partially filled by calcite or gypsum the relationship between length and aperture of vertical veins is linear apertures and spacings of fractures in both sets 1 and 2 follow power law and lognormal cumulative frequency distribution functions respectively fractures of set 2 are more likely to be clustered than are fractures of set 1 which have a wider kinematic aperture this structural database can be used to populate computational models that consider the widespread fracture system in the fluid flow simulation of carbonate reservoirs

the berezovsk giant intrusion related gold quartz deposit urals russia evidence for multiple magmatic and metamorphic fluid reservoirs abstract the berezovsk gold deposit in the middle urals has been mined for 270 years its endowment past production and gold reserves is estimated to be 490 t of gold the deposit is located in the greenschist metamorphosed silurian volcanogenic sedimentary rocks intruded by granitoid dykes to the north east of late carboniferous shartash granite massif mineralisation is represented by sulphide quartz veins in the granitoid dykes ladder veins and in the host rocks krassyk veins formed in the following four stages ankerite quartz quartz pyrite gold polymetallic and carbonate ore veins are accompanied by halos of gumbeite quartz orthoclase carbonate beresite quartz sericite ankerite pyrite and listvenite quartz fe mg carbonate fuchsite pyrite the veins mainly consist of quartz with sulphide minerals commonly 3 5 vol about 180 minerals have been identified in ores but the most abundant minerals are quartz calcite ankerite pyrite galena tennantite chalcopyrite aikinite native gold and sphalerite native gold was deposited during quartz pyrite au i and gold polymetallic au ii stages fineness of gold ranges from 863 to 984 and from 723 to 848 for au i and au ii respectively the mineral and metal zoning was identified relative to the roof of the shartash granite massif the fluid inclusion study revealed that the gold mineralisation at the berezovsk deposit was formed at 300 230 c and 0 3 2 3 kbar mostly 0 5 1 2 kbar from a h2o co2 nacl fluid with salinity of 7 3 18 2 wt nacl equiv the fluid was separated into h2o co2 nacl and co2 rich fluids due to temperature and or pressure drop at the deposition site calculated 18o and d values are 5 2 8 1 and 39 to 63 respectively for the fluid in equilibrium with alteration assemblages the average 13c value for the fluid equilibrated with carbonates from the inner zones of metasomatic halos is 5 3 the calculated 18o and 13c values are 3 0 9 6 and 3 to 9 respectively for ore forming fluids the 34s values are 1 4 12 9 and 1 6 to 11 7 for the fluid in equilibrium with early and late sulphides respectively in addition to the isotopic data the geological mineralogical and fluid inclusion data confirmed the predominant contribution of the magmatic fluid to formation of the berezovsk hydrothermal system the light c o and s isotope enrichment of the fluid was mainly caused by fluid phase separation fluids generated by decarbonation and dehydration reactions due to the contact metamorphism of the host rocks during the shartash massif emplacement were responsible for additional 34s input the ore forming fluid was enriched in the light 16o isotope on the deposit flanks indicating the mixing with heated meteoric water

genetic environment of germanium bearing gold silver vein ores from the wolyu mine republic of korea the wolyu mine is one of the largest vein type gold silver bearing epithermal systems in the youngdong district and is the first gold silver deposit in korea found to contain significant germanium in the form of argyrodite ag8ges6 mineralized veins 78 9 1 2 ma crosscutting late cretaceous hostrock tuff and quartz porphyry 81 5 1 8 ma consist of three stages of quartz and carbonates the first of which contains pyrite basemetal sulfides and au ag minerals stage i au ag ge mineralized veins show a systematic variation of mineral assemblage with time 1 quartz pyrite 2 quartz pyrite sphalerite electrum argentite 3 carbonate quartz sphalerite electrum argentite 4 carbonate native silver argentite ag sulfosalts argyrodite sphalerite calculated values of temperature and sulfur activity are assemblage 1 360 280 c and 10 7 10 10 2 280 210 c and 10 10 10 14 3 210 180 c and 10 14 10 16 4 180 155 c and 10 17 10 18 these data the frequent association of gold with sulfides and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time within the main ag au ge mineralization d and 18o values decrease with the transition from quartz to carbonate deposition from 78 and 2 8 to 90 and 8 7 respectively indicating increasing involvement mixing of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow 370 600 m wolyu epithermal system

multi scale fracture network characterisation on carbonate platforms abstract characterisation of fracture networks at different scales is challenging and important to many fields of geoscience especially when access to multiple resolution datasets is limited here we develop an integrated analysis of fracture networks on carbonate platforms using three scales of observation small outcrop intermediate airborne lidar and large 3d seismic statistical analyses and ternary diagrams of geometrical and topological data from cariatiz south east spain and pernambuco east brazil are used to understand the relationships and distribution of fracture networks between multi scale datasets a variety of fracture types at each scale of observation reveal how complex fracture networks are on carbonate platforms our results demonstrate that fracture network properties behave differently depending on the fracture size and that transitional scale gaps between datasets constrain fracture characterisation airborne lidar maps show that intermediate sized fractures appear to have a better controlled orientation and a lower connectivity than smaller fractures from the same area in cariatiz fracture branch length distributions fit a negative exponential or log normal distribution for massive non stratabound units this work is important as it demonstrates that the use of outcrop data is a good approach to understand fracture complexity of carbonate platforms understanding sub seismic fracture networks is therefore critical in quantifying fluid flow and permeability in carbonate reservoirs

lateral variations of strain in experimental forced folds abstract packages of rock layers deformed under confining pressure by the uplift and rotation of a steel block forcing assembly translate both towards and away from the margin of the principal uplifted block the resulting asymmetric forced folds and especially their long planar limbs exhibit along layer variations in strain alternations of layer elongation and contraction occur along profiles extending away from the antiform synform couplet layer normal strains are mostly nil so the longitudinal strains largely equate to volume strains in these plane strain models spaced anomalies in outcrops indicating either increased cementation or erosional weakness may suggest that similar processes operate in nature to produce variations in damage caused during the flexural slip process two non exclusive explanations are offered to account for the patterns of strain observed in the experiments 1 they may be caused by decaying wavetrains of small scale flexural deflections and their local strain patterns related to the bending of the major forced folds or 2 they may be caused by a patchy development of layer parallel slip and the consequent spatial variability in displacements

fluid inclusion microthermometry and the p t evolution of gold bearing hydrothermal fluids in the niuxinshan gold deposit eastern hebei province ne china niuxinshan is a typical example of the numerous mesothermal gold deposits formed during mesozoic tectono magmatic reactivation of the archean north china craton in eastern hebei province gold occurs in quartz sulfide lodes in archean amphibolites and also in greisen zones in the mesozoic niuxinshan granite stock four mineralization stages can be recognized from early to late 1 quartz k feldspar 2 quartz pyrite 3 quartz polysulfide and 4 quartz carbonate gold mineralization mainly occurs in stages 2 and 3 fluid inclusions in quartz and fluorite from greisen zones in the niuxinshan granite and inclusions in vein quartz and sphalerite from stages 1 to 3 in the amphibolites have been studied by microthermometry three compositional types of inclusions are recognized type 1 tp1 are h2o co2 bearing inclusions and include primary tp1 p and secondary tp1 s inclusions these are found in quartz and fluorite from the greisen zones as well as in vein quartz and sphalerite from stages 1 to 3 the tp1 p inclusions are considered to represent the gold bearing hydrothermal fluids type 2 tp2 s are secondary h2o co2 solid phase inclusions in fluorite from the greisen zones type 3 tp3 s are secondary aqueous inclusions with a solid phase which coexist with the tp2 s in fluorite from the greisen zones the tp1 p inclusions show variable vco2 commonly 0 3 to 0 6 and xco2 values mainly 0 1 to 0 4 the salinities of inclusions cluster around 3 to 11 wt nacl equivalent and their homogenization temperatures to the liquid phase th l fall dominantly in the range of 260 to 360 c the compositional variations of inclusions in stage 1 probably result from exsolution of magmatic fluids at various stages immiscibility or boiling of the fluids can be ruled out the compositional variations of inclusions in the greisen zones and in vein stages 2 and 3 are attributed to cooling mixing dilution and necking down of the fluids the tp1 s and tp2 s inclusions show salinities of 3 to 6 wt nacl equivalent and xco2 values of 0 04 to 0 17 th l clusters at 240 to 260 c the tp3 s inclusions have salinities of 3 to 6 wt nacl equivalent and th l of 170 to 240 c isochoric reconstructions combined with oxygen and sulfur isotope geothermometry of mineral pairs give trapping p t conditions for the gold bearing fluids the greisen zones formed at 310 to 460 c and 1 3 to 3 7 kbar stage 1 veins at 300 to 430 c and 1 2 to 3 7 kbar stage 2 veins at 290 to 380 c and 1 to 3 kbar stage 3 veins at 250 to 350 c and 1 to 3 kbar h2o co2 fluids with low to moderate salinities and moderate to high densities 0 66 to 1 01 g cm3 dominated at early mineralization stages and evolved towards h2o richer and co2 and less saline fluids through time the retrograde p t evolution probably resulted from regional uplift and cooling of gold bearing hydrothermal fluids the gold bisulfide complex was dominant in the fluids during mineralization and gold deposition was mainly induced by decreases of temperature and pressure as well as destabilization of the bisulfide complex during sulfidization of wall rocks

cretaceous epithermal gold silver mineralization and geodynamic environment korea abstract epithermal precious metal mineralization in the korean peninsula mainly occurred along nne trending major strike slip fault systems that are associated commonly with formation of pull apart basins and major volcanic activity during the cretaceous sedimentation in the basins was initiated in the hauterivian and continued into the albian whereas much of the volcanism occurred sporadically from ca 110 to 50 ma with a major episode between ca 90 and 70 ma epithermal au ag mineralization in korea took place between approximately 100 and 70 ma overlapping with the shallow magmatic activity styles of epithermal au ag deposits in korea include those of the mugeug type found in sediment dominant basins in the central portion and the haenam type in volcanic dominant basins in the southwest epithermal au ag deposits associated with the volcanic dominant basins in the southern korea generally formed at very shallow crustal levels

karst dissolution along fracture corridors in an anticline hinge jandaira formation brazil implications for reservoir quality abstract folded fractured and karstified structures have been recognized in several carbonate reservoirs however they are rarely fully identified from seismic or well data and have been poorly described the present study investigates the geological and structural controls that regional anticlines may exert on solution enlarged fracture corridors and epigenic karst concentrations in folded fractured carbonate units we performed regional mapping based on 106 2d seismic lines 51 well logs unmanned aerial vehicle uav imagery of four major outcrop sites i ii iii and iv and field investigations to parameterize fracture and karstic features density spacing length and aperture the study area is potiguar basin brazil where we identified the gentle ne trending apodi fold 10 km wide and 20 km long the fold formed along an inverted extensional fault during the latest miocene quaternary stress field and the envelope of the meandering trend of the apodi river coincides with the ne trending fold axis the fracture pattern in the fold hinge zone consists of two orthogonal syn folding fracture sets a ne sw striking hinge parallel set and an orthogonal nw se striking set these fractures and superposed karstification are mostly concentrated in the hinge zone along fracture corridors in an area 1 5 km wide and 20 km long we conclude that fracture corridors in anticline hinges are likely sites to have high fracture densities and wide apertures these corridors provide reservoir spaces that are favorable for the formation of karst cavities with significant increases in permeability and porosity along the fracture sets these features act as important fluid pathways and storage areas where matrix porosity is low the findings can be used for first order prediction in karstified carbonate reservoirs

line sampling of fracture swarms and corridors abstract scanlines across a range of fracture networks are analysed using cumulative frequency plots spacing distribution and correlation integral plots synthetic samples from known distributions are used to distinguish uniform and random positioning of fractures from various types of clustering and the results used to interpret fracture corridors from the bergen area norway the kuiper test provides a means of establishing the statistical significance of clustering and the correlation integral allows assessment of clustering at different scales a simple workflow is proposed that uses quantitative measures for the definition and characterisation of the spatial organisation of fractures the form of fracture networks is shown to vary from uniform or random distributions through the development of simple corridors to clustering at various scales

porosity estimation and geometric characterization of fractured and karstified carbonate rocks using gpr data in the salitre formation brazil three dimensional distribution of karstic zones and estimated porosity were obtained in fractured carbonate units of the salitre formation brazil from gpr data low amplitude shadow gpr zones could be associated with mineral dissolution halos that developed around fractures and bedding planes gpr volumes show a 3d mazelike geometry of the vertical karstified carbonate zones similar to the set of passages controlled by n s and e w oriented fracture systems observed on the surface in unmanned aerial vehicle images measurements in plug samples indicate that the mineral dissolution caused bulk density and dielectric permittivity decline and incipient increase in porosity from 0 95 to 1 01 these changes in the rock properties affect the em impedance contrasts between carbonate bedding causing loss of the reflected gpr signal the correlation between dielectric permittivity and porosity could be analyzed using the complex refractive index model crim which is used to convert the relative dielectric permittivity into porosity the crim porosities are somewhat lower than plug sample porosities due to different estimation methodologies and measurement scales however the fact that porosity is slightly higher in the dissolved carbonates was maintained in addition gpr amplitude and frequency instantaneous attributes were used to estimate spatial variability in porosity throughout the whole gpr data volume the crossplot of these two gpr attributes show that altered zones generally cluster in narrow ranges of instantaneous gpr amplitude and in broad range of instantaneous gpr frequency assuming empirical correlation between physical properties and gpr attributes two predicted porosity volumes were established for the karstified carbonates in the studied area

spatial arrangement of faults and opening mode fractures spatial arrangement is a fundamental characteristic of fracture arrays the pattern of fault and opening mode fracture positions in space defines structural heterogeneity and anisotropy in a rock volume governs how faults and fractures affect fluid flow and impacts our understanding of the initiation propagation and interactions during the formation of fracture patterns this special issue highlights recent progress with respect to characterizing and understanding the spatial arrangements of fault and fracture patterns providing examples over a wide range of scales and structural settings five papers describe new methods and improvements of existing techniques to quantify spatial arrangement one study unravels the time evolution of opening mode fracture spatial arrangement which are data needed to compare natural patterns with progressive fracture growth in kinematic and mechanical models three papers investigate the role of evolving diagenesis in localizing fractures by mechanical stratigraphy and nine discuss opening mode fracture spatial arrangement two papers show the relevance of complex cluster patterns to unconventional reservoirs through examples of fractures in tight gas sandstone horizontal wells and a study of fracture arrangement in shale four papers demonstrate the roles of folds in fracture localization and the development spatial patterns one paper models along fault friction and fluid pressure and their effects on fault related fracture arrangement contributions address deformation band patterns in carbonate rocks and fault size and arrangement above a detachment fault three papers describe fault and fracture arrangements in basement terrains and three document fracture patterns in shale this collection of papers points toward improvement in field methods continuing improvements in computer based data analysis and creation of synthetic fracture patterns and opportunities for further understanding fault and fracture attributes in the subsurface through coupled spatial size and pattern analysis

seismic dispersion and attenuation in saturated porous rocks with aligned fractures of finite thickness theory and numerical simulations part 1 p wave perpendicular to the fracture plane when a seismic wave travels through a fluid saturated porous reservoir containing aligned fractures it induces oscillatory fluid flow between the fractures and the embedding background medium although there are numerous theoretical models for quantifying the associated seismic attenuation and velocity dispersion they rely on certain assumptions such as infinitesimal fracture thickness and dilute fracture concentration which usually do not hold in real reservoirs the objective of this work is to overcome some of these limitations and therefore improve the applicability of the available theoretical models to do so we extend existing models to the finite fracture thickness case for p waves propagating perpendicular to the fracture plane using the so called branching function approach we consider three types of fractures namely periodically and randomly spaced planar fractures as well as penny shaped cracks the extended unified model is then tested by comparing with corresponding numerical sim

gold mineralization in the okanagan valley southern british columbia fluid inclusion and stable isotope studies two styles of precious metal vein mineralization epithermal and mesothermal occur in the okanagan valley of southern british columbia the epithermal deposit dusty mac is composed of quartz stockwork mineralization in eocene volcanic and volcaniclastic rocks the mesothermal deposits fairview and oro fino consist of thick 1 10 m quartz veins in paleozoic and mesozoic metamorphic rocks fluid inclusion and stable isotope studies indicate that two distinct hydrothermal fluids were responsible for the mineralization events at dusty mac the epithermal fluid had a relatively low temperature 230 degrees 250 degrees c extremely low salinity 18 o 7 to 9ppm and delta d 133ppm values at fairview and oro fino the mesothermal fluids had higher temperatures 280 degrees 330 degrees c significant co 2 contents and higher salinities 3 6 equiv wt nacl stable isotope data show that the mesothermal fluids had low delta d 121 to 148ppm and delta 13 c 8 5ppm values but high delta 18 o 4 to 6ppm values the data indicate that the fluids involved in both styles of mineralization are 18 o shifted meteoric water with shallow circulation responsible for the epithermal deposits and deep circulation involved in the formation of the mesothermal deposits although both styles of mineralization occur in the same tectonic regime it appears that they are not temporally or genetically related to each other

mineralogical fluid inclusion and stable isotope constraints on mechanisms of ore deposition at the samgwang mine republic of korea a mesothermal vein hosted gold silver deposit the samgwang mine is located in the cheongyang gold district cheonan metallogenic province of the republic of korea it consists of eight massive gold bearing quartz veins that filled ne and nw striking fractures along fault zones in precambrian granitic gneiss of the gyeonggi massif their mineralogy and paragenesis allow two separate vein forming episodes to be recognized temporally separated by a major faulting event the ore minerals occur in quartz and calcite of stage i associated with fracturing and healing of veins hydrothermal wall rock alteration minerals of stage i include fe rich chlorite fe fe mg ratios 0 74 0 81 muscovite illite k feldspar and minor arsenopyrite pyrite and carbonates sulfide minerals deposited along with electrum during this stage include arsenopyrite pyrite pyrrhotite sphalerite marcasite chalcopyrite galena argentite pyrargyrite and argentian tetrahedrite only calcite was deposited during stage ii fluid inclusions in quartz contain three main types of c o h fluids co2 rich co2 h2o and aqueous inclusions quartz veins related to early sulfides in stage i were deposited from h2o nacl co2 fluids 1 500 5 000 bar average 3 200 with thtotal values of 200 c to 383 c and salinities less than about 7 wt nacl equiv late sulfide deposition was related to h2o nacl fluids 140 1 300 bar average 700 with thtotal values of 110 c to 385 c and salinities less than about 11 wt nacl equiv these fluids either evolved through immiscibility of h2o nacl co2 fluids as a result of a decrease in fluid pressure or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization or both measured and calculated sulfur isotope compositions 34sh2s 1 5 to 4 8 of hydrothermal fluids from the stage i quartz veins indicate that ore sulfur was derived mainly from a magmatic source the calculated and measured oxygen and hydrogen isotope compositions 18oh2o 5 9 to 10 9 d 102 to 87 of the ore forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water rock exchange and by partly degassing in uplift zones during mineralization while most features of the samgwang mine are consistent with classification as an orogenic gold deposit isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the jurassic to cretaceous daebo orogeny

hypogenic origin geologic controls and functional organization of a giant cave system in precambrian carbonates brazil abstract this study is focused on speleogenesis of the toca da boa vista tbv and toca da barriguda tbr the longest caves in south america occurring in the neoproterozoic salitre formation in the sao francisco craton ne brazil we employ a multidisciplinary approach integrating detailed speleomorphogenetic lithostratigraphic and geological structure studies in order to reveal the origin of the caves their functional organization and geologic controls on their development the caves developed in deep seated confined conditions by rising flow the overall fields of passages of tbv and tbr caves represent a speleogenetically exploited large ne sw trending fracture corridor associated with a major thrust this corridor vertically extends across the salitre formation allowing the rise of deep fluids in the overall ascending flow system the formation of the cave pattern was controlled by a system of sub parallel anticlines and troughs with nne ssw dominant orientation and by vertical and lateral heterogeneities in fracture distribution three cave stratigraphic stories reflect the actual hydrostratigraphy during the main phase of speleogenesis cavities at different stories are distinct in morphology and functioning the gross tree dimensional pattern of the system is effectively organized to conduct rising flow in deep seated confined conditions cavities in the lower story developed as recharge components to the system a laterally extensive conduit network in the middle story formed because the vertical flow from numerous recharge points has been redirected laterally along the highly conductive unit occurring below the major seal a scarcely fractured unit rift like and shaft like conduits in the upper story developed along fracture controlled outflow paths breaching the integrity of the major seal and served as outlets for the cave system the cave system represents a series of vertically organized functionally largely independent clusters of cavities developed within individual ascending flow cells lateral integration of clusters occurred due to hydrodynamic interaction between the flow cells in course of speleogenetic evolution and change of boundary conditions the main speleogenetic phase during which the gross cave pattern has been established and the caves acquired most of their volume was likely related to rise of deep fluids at about 520 ma or associated with rifting and the pangea break up in triassic cretaceous this study highlights the importance of speleogenetic studies for interpreting porosity and permeability features in carbonate reservoirs

a comparison of predicted and actual tunnel behaviour in the istanbul metro turkey abstract the empirical method proposed by hoek and brown is combined with rock mass classifications to predict the deformation behaviour of istanbul metro the rock mass was assessed using both bieniawski s rmr 89 and its strength was estimated from the formula of hoek and brown for the rmr 89 system the applicability and validity of the proposed procedure has been checked by comparing the predictions with actual observations it is found that the predictions agree well with observations in the intact rock although there are some differences between predictions and observations in the faulted rock these probably reflect the inevitable inaccuracies in empirical approaches and differences in behaviour of the actual support system that is assumed in modelling in addition anisotropy features like faults which are not accounted properly in the hoek et al equation that assumes isotropic behaviour

the early cretaceous weilasituo zn cu ag vein deposit in the southern great xing an range northeast china fluid inclusions h o s pb isotope geochemistry and genetic implications abstract the weilasituo vein type deposit hosted in hercynian middle to late paleozoic quartz diorite and palaeozoic gneiss occurs on the western slopes of the southern great xing an range in this paper we present results from fluid inclusion and isotope h o s pb investigations on the weilasituo deposit we identify three stages during the ore formation a barren pre ore stage stage 1 a main ore stage with economic grade cu zn ag mineralization stage 2 and a barren post ore stage stage 3 fluid inclusion and mineral thermometry constrain temperature intervals of approximately 243 to 333 c 192 to 425 c and 141 to 261 c for the three stages respectively fluids in the main ore stage are characterized by complex nacl h 2 o ch 4 co 2 low salinity 3 55 to 8 68 wt nacl equiv with isotopic signatures consistent with a magmatic source these fluids evolved by mixing with local meteoric water 18 o fluid 1 15 to 5 15 d fluid 139 4 to 88 2 measured and calculated sulfur isotope compositions of hydrothermal fluids 34 s fluid 3 0 to 3 4 indicate that the ore sulfur was derived mainly from a magmatic source the lead isotope ratios from the ores show mean values of 18 326 15 553 and 38 242 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb respectively indicating a mantle source our study shows that fluid mixing and or dilution played an important role in copper zinc and silver mineralization in the weilasituo deposit the weilasituo and bairendaba deposits represent a linked ore system genetically related to the late mesozoic magmatism the ore forming fluids associated with the early cretaceous mineralization in the southern great xing an range are of magmatic in origin and evolved by mixing with local meteoric water these deposits preserve the signature of a mantle source for lead however the deposits formed at ca 177 160 ma possess a dominantly magmatic signature with less radiogenic lead

late mesozoic metallogeny and intracontinental magmatism southern great xing an range northeastern china abstract mineral deposits are typically tied to plate margin processes such as accretion or rifting however some major deposits occur in plate interiors e g deposits in the southern great xing an range lacking a clear association with the supercontinent cycle intrusive activity in the southern great xing an range peaked in late mesozoic i e 155 120 ma simultaneously with large scale mineralization in this area in addition the late mesozoic granitoids show initial nd and hf isotopic signatures of depleted mantle possibly newly underplated basaltic materials with variable contamination from older crust and with model ages younger than 1 0 ga fluid inclusion waters extracted from ore minerals pyrite galena sphalerite and chalcopyrite associated with the late mesozoic mineralization have elevated 3he 4he ratios indicating a contribution of mantle derived helium stable isotopes of fluid inclusion waters hydrogen and oxygen and of sulfide minerals sulfur confirm a magmatic source for these components lead isotope data of ore minerals indicate a significant mantle lead contribution from the newly underplated material thus the southern great xing an range is best described as a typical late mesozoic intracontinental metallogenic belt related to magmatism with a significant mantle contribution the magmatism and mineralization took place in a setting of lithospheric extension and resulted because of the break off of the southerly dipping mongol okhotsk oceanic slab at depth during closure of the mongol okhotsk ocean which also restricted the westward movement of the paleo pacific oceanic plate this interplay between plate tectonic events and mantle dynamics provides a good example of the evolution of magmatism and hydrothermal activity in intracontinental settings

formation of oreshoots in mesothermal gold quartz vein deposits examples from queensland australia abstract mesothermal gold quartz vein deposits in granitoid hosted and melange sediment hosted goldfields contain oreshoots in areas of structural dilation the environment of formation is localized at depths of 2 5 km in brittle to brittle ductile shear zones which have stick slip seismic movement lithologic contacts and fissure intersections affect the shape and geometry of the oreshoots mineralizing fluids in these shear zones range between 3 and 10 wt nacl equiv with 18 o values of about 5 8 fluids are locally co 2 bearing with formation temperatures of between 220 and 350 c fluid source is either of deep magmatic or metamorphic origin and can rarely be correlated directly with nearby plutonism fluid transport is via single pass flow in high permeability conduits such as mylonites in granitoids or melange cleavage in sediments complex mixtures of mineralized quartz gouge fault rocks and altered wall rock reflect the environment of formation comb ribbon buck and breccia quartz and microscopic textures indicate different processes and stages of oreshoot formation quartz deposition is due to changes in silica solubility resulting from temperature and pressure fluctuations local pressure changes are due to reduced velocity of the fluid in dilated zones according to bernoulli s equation at restricted or dilated portions of the fissure throttling and adiabatic cooling are common and result in quartz deposition and channel choking which lead to pressure and temperature build ups and faulting the long dip lengths in many mesothermal oreshoots may also account for substantial pressure and temperature reductions in the fluid from bottom to top the venturi effect in connecting fissures may also affect quartz deposition microscopic textures indicate that multiple generations of quartz have been involved in cracking stress corrosion and dissolution due to porosity changes and dilation prior to and during faulting gouge and clay seams stabilize fault movement and may have acted as impermeable barriers and pressure seals which channelled fluid flow and if hydrated may have expelled concentrated brines when compressed by faulting hydrothermal alteration indicates early diffusive transport and chemical and ph gradients away from the oreshoots four main stages of oreshoot formation occur from the outside to the inside of oreshoots as 1 ground preparation and nucleation 2 reinjection and sheeting 3 major fault movement channeling of fluid flow local dissolution and cracking and 4 consolidation and oreshoot growth including fluid stagnation and ponding

evidence for temporally changing mechanical stratigraphy and effects on joint network architecture previous studies of jointing in sedimentary rocks have shown that joint network archi tecture is controlled by mechanical stratigraphy which is described by 1 the thickness and rigidity of stratigraphic units and 2 the nature of interfaces between beds using joint pattern to infer rigidity contrast between beds is complicated by the possibility that material properties of the beds may change between fracturing events observation of both an early bed contained joint set and a differently oriented late throughgoing joint set in the same beds of growth strata in the oliana anticline in the spanish pyrenees may reflect changing mechanical properties i e via diagenesis during the folding process using a schmidt hammer we assess the rigidity contrast between the individual units and show that the present day contrast is not great enough to terminate joints at interfaces this result is consistent with an interpretation that the late stage throughgoing joints formed in strata with conditions similar to those of the present day and that the early bed contained joints formed when the rigidity contrast between beds was significantly greater than that of the present day for example differential diagenesis rates between layers of differing grain size would produce temporally changing mechanical stratigraphy we propose that changes in mechanical stratigraphy may have previously been unrec ognized in other stratigraphic sections and that these changes affect joint network archi tecture and subsequent fluid flow pathways