paleostress and statistical analysis using quartz veins from mineralized and non mineralized zones application for exploration targeting abstract quartz vein orientations thickness and spacing data are analyzed from 10 transects each of mineralized and non mineralized zones of gadag region which is a gold bearing terrain within the dharwar craton southern india paleostress analysis reveals that the veins emplaced when fluid pressure pf varied from pf 2 intermediate principle stress to pf 2 to pf

tensile rock mass strength estimated using insar 1 the large scale strength of rock is known to be lower than the strength determined from small scale samples in the laboratory however it is not well known how strength scales with sample size i estimate kilometer scale tensional rock mass strength by measuring offsets across new tensional fractures joints formed above a shallow magmatic dike intrusion in western arabia in 2009 i use satellite radar observations to derive 3d ground displacements and by quantifying the extension accommodated by the joints and the maximum extension that did not result in a fracture i put bounds on the joint initiation threshold of the surface rocks the results indicate that the kilometer scale tensile strength of the granitic rock mass is 1 3 mpa almost an order of magnitude lower than typical laboratory values

archaean gold mineralization synchronous with late cratonization of the western dharwar craton india 2 52 ga u pb ages of hydrothermal monazite and xenotime in gold deposits new zircon u pb ages for a felsic volcanic rock 2 588 10 ma and an intrusive granite 2 555 6 ma in the gadag greenstone belt in the western dharwar craton southern india are similar to dates for equivalent rocks in the eastern dharwar craton and indicates docking of the two cratons prior to this time the zircons in the intrusive granite are strongly overprinted and coexisting titanites yielded two different age populations the dominant group gives an age of 2 566 7 ma interpreted as the emplacement age whereas the minor group gives an age of 2 516 10 ma reflecting a hydrothermal overprint in situ u pb dating of monazite and xenotime in gold reefs of the gadag 2 522 6 ma and ajjanahalli 2 520 9 ma gold deposits reveal a previously undated episode of gold mineralization at 2 52 ga substantially younger than the 2 55 ga hutti deposit in the eastern dharwar craton the new dates confirm that both the younger greenstone belts and lode gold mineralization in the dharwar craton are about 100 120 my younger than in other well dated archaean cratons although gold mineralization across the craton postdates most of the magmatic activity and metamorphism at upper crustal levels widespread thermal reworking of the lower middle crust involving partial melting metamorphism and lower crustal granitoid intrusion occurred concurrently with gold mineralization it is likely that the large scale hydrothermal fluid flow that produced widespread gold deposition was also part of this tectono thermal event during the final stages of cratonization of the dharwar craton in southern india

vein development during folding in the upper brittle crust the case of tourmaline rich veins of eastern elba island northern tyrrhenian sea italy abstract detailed structural analysis of tourmaline rich veins hosted in the contact aureole of the 6 ma porto azzurro granite in southeastern elba island northern tyrrhenian sea is presented using geometric features of the veins the physical conditions at the time of vein formation are estimated namely the stress ratio 2 3 1 3 driving stress ratio r p f 3 1 3 and fluid overpressure p o p f 3 two vein sets a veins and b veins have been recognized based on orientation and thickness distributions and infilling material analysis of vein pole distributions indicates 0 57 and r 0 24 for the a veins and 0 58 and r 0 47 for the b veins and fluid pressures less than the intermediate stress magnitude analysis of geometric features of the veins gives estimated fluid overpressures of between 16 mpa a veins and 32 mpa b veins we propose a model for the tectonic environment of vein development in which formation of secondary permeability in the deforming thermal aureole of the porto azzurro pluton was controlled by ongoing development of fracture systems in the hinge zone of a regional nnw sse trending fold that favored transport and localization of hydrothermal fluids

fractal dimension and its translation into a model of gold spatial proxy abstract unraveling the spatial distribution of mineral deposits is an essential part of exploration and important for developing a better understanding of ore forming processes in this study gold assay results in g t of twelve boreholes completed from mysore block and eleven boreholes completed from nabhapur north block central lode system gadag gold field ggf india were analyzed using fractal analysis both the fractal correlation integral and rescaled range analysis were used to measure the fractal dimension from the gold concentration values the fractal dimension values obtained from the fractal correlation integral were used to better constrain the possible auriferous fluid flow pathways whilst results obtained from the rescaled range analysis were used to describe the behavior of auriferous veins across the boreholes the fractal dimension values were found to vary from 0 014 to 3 0 with the higher values taken to indicate the presence of well developed interconnected fault fracture networks representing steep permeable fluid flow pathways the lower fractal dimension values were taken to indicate unfavorable fluid flow pathways in other words higher grade gold ores were deposited along the structures represented by steep fractal gradients hurst exponent h values obtained from the rescaled range analysis were found to vary from 0 50 to 0 96 satisfying the condition 0 5

crustal configuration of the dharwar craton india based on joint modeling of regional gravity and magnetic data abstract regional gravity and magnetic investigations were conducted along a 600 km transect across the northern part of the dharwar craton in the precambrian indian peninsular shield from vasco da gama latitude 15 23 40 n and longitude 73 48 55 e to jadcharla latitude 16 41 40 n and longitude 78 08 18 e joint modeling of the two data sets was carried out utilizing gm sys geosoft software assuming a four layer model a tectonic re classification of the craton is proposed prompted by the location of four inferred deep seated faults into the western and eastern dharwar blocks with an intervening upthrown block this classification is at variance with the current perceptions of the configuration of the dharwar craton some of which hold that the craton consists of only two sub cratons an eastern and a western divided by the chitradurga thrust fault however in the present study this thrust fault is found to extend no deeper than the basement peninsular gneisses furthermore according to the proposed classification the thrust fault falls within the intervening block that forms the divide between the sub units of the craton rather than representing a tectonic boundary in addition twenty six near surface geological members in the region supracrustals consisting mainly of schists and younger granites were identified along the transect and modeled for the representative near surface crustal configuration of the craton

tonnage cutoff model and average grade cutoff model for a single ore deposit abstract ore reserve estimation and resource prediction are important aspects of deposit exploration and mining the cutoff has great influence on the reserve and resource calculation despite this the study on the mathematical relationships of the tonnage average grade and cutoff is still scant according to the fractal distribution of element concentrations which are obtained from analysis of channel samples of constant length along exploration or mining works the tonnage cutoff and average grade cutoff models are constructed which are applicable in both exploration and operating mine environments via these models the relationships between ore tonnage metal tonnage and cutoff are obtained in terms of the fractal model of element concentrations moreover the thickness of the mineralized zone in each exploration or mining work follows a fractal model and assuming that the thickness is a continuous variable a model for calculating the mass of the mineralized zone in a single deposit is established given the mineralized zone mass the tonnage cutoff and average grade cutoff models can be utilized to calculate ore reserve and average grade especially when the cutoff changes a fault controlled disseminated and veinlet gold deposit in jiaodong gold province china is selected as a case study the estimates of the ore reserves obtained from these models are found to be consistent with the results obtained by the traditional geometric block method

parametric and non parametric statistical approaches to the determination of paleostress from dilatant fractures application to an early miocene dike swarm in central japan abstract several methods have been proposed for determining paleostress states from orientations of dilatant fractures such as dikes and veins recently a stochastic inversion method was invented to objectively estimate the principal stress axes and the stress ratio whether a fracture is dilated or not is controlled by the balance of the fluid pressure and the normal stress acting on it the magnitude of normal stress depends on the fracture orientation which causes anisotropic orientation distribution of dilatant fractures the inversion method assumes that the orientation distribution of fractures can be approximated by a bingham distribution an exponential probability distribution on the unit sphere of which symmetric axes are interpreted as the principal stress axes however it is unknown if the exponential type of distribution function is suitable or not here we examine the distribution functions and propose two improved methods one method uses the shifted power law function as the shape of probability distribution which is more flexible than the bingham distribution and is applicable to various shapes of orientation distributions furthermore an index of the driving fluid pressure can be estimated with a confidence interval the other is a non parametric distribution free method which can avoid the a priori assumption on the shape of distribution function without significantly losing accuracy or precision the new methods were applied to an early miocene dike swarm formed during the back arc opening of the japan sea a normal faulting stress regime with the minimum principal stress axis trending roughly perpendicular to the arc was obtained from the dikes a moderately high stress ratio and a high fluid pressure were also estimated

evolution of the grenada and tobago basins and implications for arc migration abstract the tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood this paper presents an integrated stratigraphic and tectonic evolution of late cretaceous to recent volcanic arcs and associated basins in the southeastern caribbean sea using seismic reflection data wide angle seismic refraction data well data and onland geologic data we propose a new tectonic model for the opening of the grenada and tobago basins and the 50 250 km eastward jump of arc volcanism from the late cretaceous aves ridge to the miocene to recent lesser antilles arc in the southeast caribbean based on the mapping of three seismic megasequences the striking similarity of the half graben structure of the grenada and tobago basins that flank the lesser antilles arc their similar smooth basement character their similar deep marine seismic facies and their similar paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single saucer shaped oceanic crust paleogene forearc basin adjacent to the now dormant aves ridge this single forearc basin continued to extend and widen through flexural subsidence during the early to middle eocene probably because of slow rollback of the subducting atlantic oceanic slab rollback may have been accelerated by oblique collision of the southern aves ridge and southern lesser antilles arc with the south american continent uplift and growth of the southern lesser antilles arc divided the grenada and tobago basins by early to middle miocene time inversion of normal faults and uplift effects along both edges of the lesser antilles arc are most pronounced in its southern zone of arc collision with the south american continent the late miocene to recent depositional histories of the grenada and tobago basins are distinct because of isolation of the grenada basin by growth and uplift of the neogene lesser antilles volcanic ridge

fractal analysis of a mineralised vein deposit curraghinalt gold deposit county tyrone quantitative description and prediction of vein hosted deposits using fractal statistics have been tested using data collected from the curraghinalt gold deposit sperrin mountains county tyrone n ireland goldbearing quartz veins are hosted by neo proterozoic dalradian southern highland group age psammites pelitic schists and graphitic schists veins trend e to ese and cross cut regional structures vein thickness z distributions closely approximate a power law distribution of the form n z cz d with an exponent d of 0 76 over three orders of magnitude vein spacing data approximate a log normal distribution with a mean of 2 92m numerical analysis indicates that the veins are more clustered than expected from a random distribution regions of high percentage extension and high vein density define vein clusters the vein clustering relationship may be combined with the power law thickness distribution and used in a predictive manner the data may be used to constrain the probability of intersecting veins of potentially mineable dimension

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

crustal structure of the caribbean northeastern south america arc continent collision zone 1 we present the results of a 568 km long regional wide angle seismic profile conducted in the southeastern caribbean that crosses an active island arc a remnant arc two basins possibly floored by oceanic crust an allochthonous terrane of forearc affinity and the passive margin of northern south america the velocity structures of the late cretaceous aves ridge remnant arc and miocene and younger lesser antilles arc are remarkably similar which implies that magmatic processes have remained moderately steady over time crustal thickness is 26 km at the aves ridge and 24 km at the lesser antilles arc in comparison to the izu bonin and aleutian arcs the lesser antilles arc is thinner and has no evidence for a lower crustal cumulate layer which is consistent with the estimated low magma production rates of the lesser antilles arc crustal thickness beneath the grenada and tobago basins is 4 10 km and the velocity structure suggests that these basins could be floored by oceanic crust a decrease of 1 km s in average seismic velocity of the upper crust is observed from nw to se across the north coast fault zone we argue that this marks the suture between the far traveled caribbean arc and the passive margin of the south american continent current strike slip motion between the caribbean and south american plates is located 30 km to the south and thus material originally deposited on the south american passive margin has now been transferred to the caribbean plate

cenozoic tectonic history of the north america caribbean plate boundary zone in western cuba structural studies of well dated jurassic to lower miocene rocks in western cuba constrain the sequence of structural events affecting this oblique collisional zone between the late cretaceous island arc and the jurassic cretaceous north america passive margin in the southeastern gulf of mexico and straits of florida results of detailed mapping and collection of fault slip data at 34 sites define a regionally consistent five phase tectonic model for the period from the late paleocene to the post early miocene during the late paleocene to the early eocene the cuban island arc collided with the north american passive margin bahamas platform northwest ward overthrusting during the collision defines tectonic phase i a nne ssw compression concurrent with early eocene left lateral strike slip faulting along the pinar fault zone defines phase ii this result is consistent with structural mapping showing sinistral shear within the 065 striking pinar fault zone an ene wsw to e w compression defining phase iii overprinted phase ii faults in the lower eocene and older rocks post early miocene normal faulting characterizes phase iv inversion of fault slip data indicates two contemporaneous directions of tension of 120 and 170 strike slip faults that overprint phase iv normal faults yield a 120 compression phase v the direction of compression associated with the arc continent collision rotates clockwise from nw se in the late paleocene early eocene phase i to nne ssw phase ii and to ene wsw by the middle eocene phase iii the rotation in the compression direction occurred because the arc turned toward an oceanic area in the present day area of central and eastern cuba progressive collision led to complete subduction of the remnant oceanic crust by middle to late eocene time

an enriched finite element for simulation of groundwater flow to a well or drain abstract a new quadrilateral finite element has been developed to simulate a well or drain in two dimensional fluid flow through porous media it is an enriched four node element which models the logarithmic head distribution about a well located at its center the enriched element is compatible at its boundaries with unenriched elements and is capable of representing a head boundary condition at the well it permits accurate modelling of sparse well or drain arrays with a coarse mesh while accuracy is reduced for dense arrays of large diameter wells it still compares favorably with the accuracy attainable with fine meshes of unenriched elements

pegmatite dyke emplacement and the state of stress during cratonization an example from the dharwar craton south india abstract in this study we measured orientations of 797 pegmatite dykes intruding the 2 5 ga koppal pluton dharwar craton south india and use the data to evaluate the state of stress prevalent during dyke emplacement we infer that the dykes were emplaced synchronously with late d3 regional deformation that was controlled by nw se directed shortening dykes within the koppal pluton kp have a restricted range of orientations which is indicative of fluid pressure pf

the role of strain localization in magma injection into a transtensional shear zone variscan belt sw iberia this study deals with the interaction between deformation and magmatism in mid to deep crustal domains the relation is analysed between migmatites and shear zones and the spatial distribution of leucogranitoid veins and dykes running through a footwall migmatite system and reaching a transtensional shear zone operated under amphibolite to greenschist facies metamorphic conditions boa fe shear zone variscan belt sw iberia statistical results show that the frequency of width and spacing of the leucogranitoid dykes conform to power law distributions comparable with observations in volcanic systems the fractal geometry of the distribution of leucogranitoid dykes highlights the development of a dense framework of thinner weakly or non mineralized veins and dykes formed at higher nucleation growth ratios in the footwall migmatite system that contrasts with the emplacement of thicker dykes associated with strongly mineralized thinner veins within the shear zone the volume of injected leucogranitoid dykes in the shear zone is lower as compared with the footwall and is comparable with an expanding footwall shear zone with non coaxial flow and volume increase the boa fe shear zone seems to form a physical barrier to the transport of magma to the hanging wall

subsidence controls on foreland basin development of northwestern offshore cuba southeastern gulf of mexico we reviewed the tectonostratigraphic evolution of the jurassic cenozoic collision between the north american and the caribbean plate using more than 30 000 km 18 641 mi of regional two dimensional 2 d academic seismic lines and deep sea drilling project wells of leg 77 the main objective is to perform one dimensional subsidence analysis and 2 d flexural modeling to better understand how the caribbean collision may have controlled the stratigraphic evolution of the offshore cuba region five main tectonic phases previously proposed were recognized 1 late triassic jurassic rifting between south and north america that led to the formation of the proto caribbean plate this event is interpreted as half grabens controlled by fault family 1 as the east northeast south southwest striking faults 2 middle late jurassic anticlockwise rotation of the yucatan block and formation of the gulf of mexico this event resulted in north northwest south southeast striking faults of fault family 2 controlling half graben structures 3 early cretaceous passive margin development characterized by carbonate sedimentation sedimentation was controlled by normal subsidence and eustatic changes and because of high eustatic seas during the late cretaceous the carbonate platform drowned 4 late cretaceous paleogene collision between the caribbean plate resulting in the cuban fold and thrust belt province the foreland basin province and the platform margin province the platform margin province represents the submerged paleoforebulge which was formed as a flexural response to the tectonic load of the great arc of the caribbean during initial late cretaceous paleocene collision and foreland basin development that was subsequently submerged during the eocene to the present water depths as the arc tectonic load reached the maximum collision and 5 late cenozoic large deep sea erosional features and constructional sediment drifts related to the formation of the oligocene holocene loop current gulf stream that flows from the northern caribbean into the straits of florida and to the north atlantic

correlation between mineralization intensity and fluid rock reaction in the xinli gold deposit jiaodong peninsula china constraints from petrographic and statistical approaches abstract the jiaodong peninsula the most productive gold province in china is dominated by jiaojia type gold deposits that formed at ca 120 ma the deposits are characterized by widespread alteration and mineralization resulted from fluid rock reactions in the footwall of regional faults it is known that the interrupted appearance of continuous mineralization zones and barren zones along regional faults is controlled by changes in the dip direction and dip angle of these faults which can cause local dilational sense in the continuous mineralization zone intensive fluid rock reactions occurred yet whether and how the fluid rock reaction impacted on the mineralization intensity are not well constrained in this study we selected the xinli jiaojia type gold deposit associated sanshandao cangshang fault located on the northwest margin of the jiaodong peninsula to examine in detail the distribution of orebody parameters and to observe the mineralization occurrences we applied the number size fractal model and the lacunarity method to quantify the distribution of gold concentration along drifts with the goal of clarifying the ambiguities noted above the drifts in continuous mineralization zones can be divided into stable and unstable types according to lateral changes in the dip direction and dip angle of the sanshandao cangshang fault stable and unstable drifts share several common features 1 statistical results show that changes in the dip direction and dip angle of this fault bear almost no relationship to the thickness or grade thickness of the orebody 2 mineralization along drifts is most intense at some distance from the fault plane rather than at locations immediately adjacent to the fault plane where fracturing is most extensive and according to fluid infiltration theory would be the most likely regions of intense mineralization 3 gold bearing sulfide pods and veinlets in the alteration zone commonly possess irregular and corroded boundaries that are considered to be an indicator of fluid rock reactions 4 the threshold the gold concentration that divides a segment with a lower fractal dimension in a lower concentration range from one with a higher fractal dimension in a higher concentration range and the lacunarity the parameter that evaluates the evenness of high gold concentration distribution show positive and negative relationships respectively to the thickness and grade thickness of a drift we thereby argue on the basis of these features that fluid rock reactions were an important factor responsible for the mineralization upgrade in continuous mineralization zones an increase in the threshold and a decrease in the lacunarity indicate that fluid rock reactions causing gold precipitation are more intensive and more evenly distributed throughout the footwall for better mineralization these phenomena suggest that fluid rock reactions responsible for the gold precipitation possibly own the characteristics of spatial self organization mechanism which is widely developed in various geological fluid rock reaction processes

deep sea drilling project leg 77 southeastern gulf of mexico in january 1981 r v glomar challenger drilled five holes in the southeastern gulf of mexico to provide ground data for extensive seismic surveys and to document the pre tertiary history of the gulf holes 535 and 540 were drilled in a basinal terrane for maximum penetration of the cretaceous tertiary sequence rhythmic alternations of light bioturbated and dark laminated carbonaceous limestone represent the early cretaceous interval some of the dark layers are rich but immature oil source rocks the limestones resemble the blake bahama formation in the north atlantic but their stratigraphic age overlaps in part with the hatteras shale late cretaceous rocks are almost totally missing in the basin sites and the cenozoic section consists of chalk and marly carbonate ooze holes 536 537 and 538a were drilled on high standing fault blocks hole 537 recovered phyllite that records 40 ar 39 ar plateau ages of about 500 m y and is overlain by an early cretaceous deepening sequence of alluvial to littoral elastics and oolitic oncolitic limestones capped by a thin sequence of cretaceous and cenozoic pelagics in hole 538a basement consists of mylonitic gneiss and amphibolite intruded by several generations of diabase dikes that is transitional crust 40 ar 39 ar dates of hornblendes and biotite from the regional metamorphic rocks suggest a 500 m y pan african age with mild late paleozoic thermal overprint 40 ar 39 ar whole rock dates from the dikes suggest intrusions between 190 and 160 m y ago basement is covered by a thin layer of pelagic chalk followed by early cretaceous skeletal oolitic limestones and finally cretaceous tertiary pelagics the oolitic oncolitic limestones at both sites represent either parts of a shallow water carbonate platform or platform talus deposited in deep water hole 536 bottomed in shallow water dolomite jurassic or permian overlain by middle cretaceous skeletal limestones with shallow water biota and intercalations of pelagic chalk interpreted as cretaceous talus at the foot of the campeche bank cretaceous tertiary chalk and carbonate ooze cap the sequence among the most significant results of the leg are 1 recovery of transitional crust with early paleozoic pan african metamorphic rocks 2 recovery of early cretaceous deep water limestones with immature petroleum source beds 3 recovery of mid cretaceous platform talus resembling the reservoirs in the poza rica and probably some of the reforma fields of mexico and 4 discovery of a late cretaceous hiatus of 30 m y that corresponds approximately to the mid cretaceous unconformity recognized widely on seismic records in the gulf of mexico

fluid circulation in the upper brittle crust thickness distribution hydraulic transmissivity fluid inclusion and isotopic data of veins hosted in the oligocene sandstones of the macigno formation in southern tuscany italy abstract we present structural analysis fluid inclusion data on calcite and quartz and isotopic composition of calcite forming veins occurring in the upper crustal level and hosted in oligocene sandstone in southern tuscany italy the veins have been analysed in two sites few kilometres apart along well exposed coastal cliffs and in an abandoned quarry these two sites were at a different depths at the time of the vein formation with a h 100 m structural analysis of veins provided estimations of stress ratio 2 3 1 3 driving stress ratio r pf 3 1 3 and fluid overpressure po pf 3 at the time of vein formation the estimated po is in the range of 42 103 mpa 0 24 and r 0 45 indicating that fluid pressure was higher than the intermediate principal stress at the time of veins formation the veins thickness t shows a clear power law distribution d 1 8835 and r2 0 9762 in the lowermost site coast and a negative exponential distribution a 0 6943 and r2 0 9921 in the uppermost site abandoned quarry the vein thickness distributions have been used to compute the average transmissivity of the veins in the two sites the computed transmissivity for the vein formation is 10 4 m2 s 1 with higher values attained by the veins having negative exponential thickness distribution fluid inclusions studies highlighted that in both calcite and quartz water rich inclusions with salinities of 2 2 4 3 wt nacl equiv and methane rich inclusions were coevally trapped during fluid un mixing processes thermogenic origin from thermal maturation of organic matter present in the macigno formation is proposed for methane whereas the similarity between the 18o from 14 9 to 17 4 and 13c from 0 4 to 2 4 data of representative calcite veins and the isotopic composition 18o 16 1 13c 1 0 of host rock carbonate component indicates that the fluid which formed calcite was in isotopic equilibrium with the carbonates present in the oligocene sandstones the calculated pressure temperature conditions during the formation of these inclusions are prevalently within the 40 145 mpa and 160 260 c ranges the highest pressure values approximate the lithostatic pressure 120 mpa computed from geological data and are coherent with a geothermal gradient ranges of 35 45 c km whereas the lower pressure values are comparable with hydrostatic pressure conditions the pressure range indicated by fluid inclusion data is also comparable with the fluid pressure estimated from structural analysis the considerable pressure range can be related to pressure cycling between lithostatic and hydrostatic conditions as a consequence of fault valve actions and rock fracturing with subsequent pressure recover due to self sealing process

dehydration related deformation during regional metamorphism nw sardinia italy the relationship between deformation and dehydration has been investigated in hercynian regionally metamorphosed rocks exposed on nw sardinia two episodes of prograde mineral growth m1 m2 involving dehydration are recognized growth of chlorite phengite porphyroblasts at anchizone metamorphic conditions contemporaneous with the first phase of deformation d1 and growth of biotite from chlorite and phengite coincident with the second phase of deformation d2 deformation during both episodes of dehydration is characterized by penetrative axial planar foliations defined by well developed phyllosilicate preferred orientations quantified by xrd textural goniometry tight to isoclinal similar folds interlimb angles 40 low strain similar folds and minor brittle deformation systematic variations in macrofold interlimb angles with respect to the timing of mineral growth indicate that enhanced shortening c 80 occurred during dehydration microfabrics show that the onset of dehydration is associated with the transition from a crenulation cleavage to a penetrative foliation the presence of axial planar hydrofractures that formed coevally with dehydration and fabric development requires that supralithostatic fluid pressures and low differential stresses c 20 mpa accompanied dehydration these features demonstrate a connection between the timing of dehydration and the style of deformation

application of cantor s method for fractal analysis of fractures in the toyoha mine hokkaido japan cantor s method has been used for fractal analysis of fractures in the toyoha mine hokkaido japan the analyses were performed on a two dimensional area ranging from 30 cm2 to 220 km2 cantor s analysis predicts the probability of fracture occurrence in rocks in a given distance the probability of finding a fractured zone of length x is given by p x d where d is the fractal dimension in the toyoha mine the samples collected in sugo and izumo veins are characterized by d values of 0 25 and 0 10 0 24 respectively the distribution of fractures in galleries 200 m long is very similar d 0 17 at a kilometer scale the disposition of veins varies according to the directions of observation d 0 20 e w and 0 25 0 28 nw se at a larger scale landsat map the fault distribution appears very similar in all directions 0 22 d 0 25 in the vicinity of the toyoha mine the fracture disposition is fractal at all scales of observation despite a scale factor that can vary by 106 the distribution of fractures remains fractal with similar fractal numbers average d 0 25 moreover d values gradually change according to the distance from the toyoha mine suggesting that the type of rupture and consequently the nature of stress are different far from the toyoha mine

new approach for the quantification of paleostress magnitudes application to the soultz vein system rhine graben france abstract quartz veins often appear in pre existing cracks and are the witnesses of paleofluid flows a new method of paleostress magnitude quantification is proposed in this paper based on the knowledge of i the geometrical distribution of vein poles ii empirical considerations of rupture criteria and iii the fluid pressure stress axis orientations deduced from the geometrical distribution of the vein poles define angular relations allowing the reduced stress tensor and the ratio characterization p f values quantified with fluid inclusion studies and intrinsic curves drawn with empirical relations depending on the rheologic properties of the pre fractured rock are combined to graphically fit the final mohr circle the resulting absolute stress magnitudes take into account the fluid pressure influence application of this method on the quartz vein system of soultz sous forets rhine graben france gives realistic magnitudes of the oligocene extension and are similar to those found in previous study with other methods

fractal models for ore reserve estimation abstract traditional geometric and geostatistic methods for reserve estimation in a single deposit are difficult to use with skewed distribution mineralization variables including grade orebody thickness and grade thickness a common characteristic of most deposits and require complex data processing it has been shown that the skewed mineralization variables can be described by the number size model in a fractal domain based on the number size model assuming that orebody thickness and grade thickness are continuous variables the fractal model for reserve estimation fmre in a single deposit can be established in the fmre ore tonnage can be estimated given the orebody area and the fractal parameters of orebody thickness distribution and metal tonnage can be estimated based on the orebody area and the fractal parameters of grade thickness distribution the reserve estimated by the fmre can denote actual ore tonnage and metal tonnage that can be mined out of the deposit the frme was applied to the dayingezhuang gold deposit in the jiaodong gold province in china the gold reserves via the fmre and the traditional geometric block method are similar with relative errors of 3 11 in ore tonnage and 0 29 in metal tonnage compared to traditional reserve estimation the fmre is much easier in calculation process and is more reasonable in dealing with the skewed distribution however this new method fails to calculate local reserve which can be derived via any of the traditional estimation methods

a plate tectonic model for the mesozoic and early cenozoic history of the caribbean plate abstract we present a model in which the caribbean plate is an intra american feature formed along the caribbean spreading center as opposed to the current model that considers the caribbean plate as a far travelled crustal segment that formed in the pacific region paleomagnetic data which cover an age range from jurassic through paleocene indicate the ophiolite complexes in costa rica and panama formed in an equatorial position the ophiolites did not fundamentally change their position relative to south america since their origin basaltic rocks of the lower part of the ophiolites are of mid ocean ridge type suggesting formation at a spreading center they are interpreted to have formed as part of the proto caribbean crust at a spreading axis in an intra american position during jurassic and early cretaceous times the upper part of the ophiolites is mainly built up by island arc and intraplate basalts the island arc basalts evolved at the central american landbridge which started in the middle cretaceous the intraplate basalts are related to the caribbean plateau basalt which thickened and stiffened the caribbean crust in middle cretaceous to probably campanian times changes in relative plate motions along the middle american convergent plate margin are reflected by orientations and time sequences of paleostress tensors calculated from fault slip data in southern mexico and costa rica kinematic indicators from mylonite zones display sinistral movement along secondary shear zones within the southern mexican crustal complexes and along the northern boundary of the chortis block in the motagua polochic fault system this reflects the eastward drift of the chortis block since the beginning of the cenozoic at this time the chortis block became part of the caribbean plate which moved more than 1000 km towards the east relative to the north and south american plates during the cenozoic

quantitative analysis of tin and tungsten bearing sheeted vein systems several methods are investigated for the quantitative analysis of a range of sn w sheeted vein systems from southwest england and spain the methods are based on fractal concepts and include the measurement of vein thickness and spacing distributions and the development of a multifractal interval counting method equivalent to box counting in two dimensions the results indicate that sets of subparallel veins are generally distributed randomly or with only slight clustering and develop from fracture systems in which the spacing of veins is homogeneous the opening of the veins is much more heterogeneous suggesting localization of subsequent deformation and flow this is especially true in mineralized areas and together with power law distributions of vein thickness can be used to characterize mineralized systems new data presented in this paper suggest that fracture evolution may play a fundamental role in defining the location and style of sn w mineralization observed greisen dominated and disseminated sn w systems develop where the initial fracture system dominates the fluid flow regime whereas sheeted vein systems are best developed where stress induced critical behavior of flow in fracture networks controls the permeability and fluid flow of the system

geochemical characterization of source rocks crude oils and gases of northwest cuba abstract in order to characterize the cuban petroleum system we analyzed source rocks as well as crude oils and gases from carbonate producing reservoirs from northwest onshore cuban fields the geochemical oil and gas characterizations were based on bulk analyses chromatography liquid and gas mass spectrometry and mass spectrometry coupled to stable carbon isotope ratio determination analyses of sampled source rocks intervals were performed with rock eval 6 and provided valuable data for the appraisal of the active petroleum system in northwest cuba our paper focused on the genetic semblance between carbonate reservoired crude oils and source rocks to assess the offshore extension of the onshore cuban carbonate petroleum system crude oils source rocks and crude oils offshore dsdp source rocks were correlated to a common type of carbonate depositional environment an understanding of the geochemical compositions of carbonate crude oils grouped in families including heavy sulphur rich oils light or mixed and biodegraded fluids helped to underline the different processes operating in the reservoirs today the high degree of anoxicity during the organic matter deposition in the upper jurassic and lower cretaceous was confirmed we observed low hydrocarbon cracking levels and non biodegraded fluids of type ii iis organic matter in upper jurassic and lower cretaceous reservoirs while shallower tertiary reservoirs although more mature were altered by microbial biodegradation there reservoirs with temperatures below 80 c provided a good habitat for aerobic anaerobic bacteria and the possibility of hydrocarbon biodegradation

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

fractal distributions of veins in drill core from the hellyer vhms deposit australia constraints on the origin and evolution of the mineralising system statistical analysis of the vein thickness distributions of veins in the cambrian hellyer volcanic hosted massive sulfide deposit australia indicates that the vein thickness data conform to power law distributions characterised by fractal dimensions d the most intensely mineralised vein type is characterised by a low fractal dimension whereas weakly mineralised or barren vein types have elevated d values the observed differences in the fractal dimensions suggest that the study of vein thickness distributions may provide a tool in exploration it is also shown that the field observations can be explained by a model linking the fractal dimensions of the vein thickness distributions with the mechanisms responsible for the formation and evolution of the vein systems

topological characterization of a polyphased gold bearing vein network abstract it is challenging to evaluate the connectivity of metal bearing hydrothermal vein systems i e the degree to which fractures or veins are connected within a network moreover many ancient ore bearing vein networks have been deformed and metamorphosed which hinders the reconstruction and quantification of their primary characteristics here we explore the reliability and limitations of the network distribution and topologic classification of vein terminations into i y and x nodes approaches to study deformed and metamorphosed mineral deposits we focus on the cheechoo gold deposit located in the eeyou istchee james bay area of quebec canada archean superior province this gold deposit shows a complex hydrothermal and magmatic polyphased gold bearing vein system hosted in a granodioritic tonalitic intrusion the cheechoo deposit is composed of quartz feldspar diopside qtz fsp di and quartz qtz veins that underwent ductile deformation and amphibolite facies metamorphism the high grade metamorphism led to the modification of vein shape relative position and spacing making these parameters unreliable for the characterization of the cheechoo vein system and similar metamorphosed networks however the number of veins per length unit and topology are reliable tools to characterize such networks in the gold bearing cheechoo system the gold mineralization appears to be mainly controlled by i the number of qtz and qtz fsp di veins per length unit and by ii the connectivity of these networks as shown by the increase of both parameters with the gold grade furthermore we introduce the y i ratio as a simple topological parameter to quantify the connectivity of two dimensional i y dominated systems this parameter is positively correlated with the number of connections per branch cb used to quantify network connectivity and ultimately represent the development of a fault or fracture zone

thickness and spatial distribution of veins in a porphyry copper deposit rosia poieni romania abstract a statistical analysis of the vein thickness distributions of veins in the rosia poieni porphyry copper deposit romania indicates that vein thickness data conform to a power law distribution whereas the spatial distribution of veins follows a negative exponential law a high clustering of the veins is indicated by both the spacing distribution and the cv values the similar vein densities observed at the open pit scale are representative of a saturation level of vein nucleation differences in the spacing distribution and in the mean vein thickness are explained by different initial nucleation rates in the deepest and the lowest parts of the porphyry copper the highly clustered organization of the system is explained by vein linkage processes during their growth and modification of the fluid pressure and local stress during the hydrofracturing

lithofacies associations and structural evolution of the archean rio das velhas greenstone belt quadrilatero ferrifero brazil a review of the setting of gold deposits abstract the rio das velhas greenstone belt is located in the quadrilatero ferrifero region in the southern extremity of the sao francisco craton central southern part of the state of minas gerais se brazil the metavolcano sedimentary rocks of the rio das velhas supergroup in this region are subdivided into the nova lima and maquine groups the former occurs at the base of the sequence and contains the major au deposits of the region new geochronological data along with a review of geochemical data for volcanic and sedimentary rocks suggest at least two generations of greenstone belts dated at 2900 and 2780 ma seven lithofacies associations are identified from bottom to top encompassing 1 mafic ultramafic volcanic 2 volcano chemical sedimentary 3 clastic chemical sedimentary 4 volcaniclastic association with four lithofacies monomictic and polymictic breccias conglomerate graywacke graywacke sandstone graywacke argillite 5 resedimented association including three sequences of graywacke argillite in the north and eastern at greenschist facies and in the south at amphibolite metamorphic facies 6 coastal association with four lithofacies sandstone with medium to large scale cross bedding sandstone with ripple marks sandstone with herringbone cross bedding sandstone siltstone 7 non marine association with the lithofacies conglomerate sandstone coarse grained sandstone fine to medium grained sandstone four generations of structures are recognized the first and second are archean and compressional driven from nne to ssw the third is extensional and attributed to the paleoproterozoic transamazonian orogenic cycle and the fourth is compressional driven from e to w is related to the neoproterozoic brasiliano orogenic cycle gold deposits in the rio das velhas greenstone belt are structurally controlled and occur associated with hydrothermal alterations along archean thrust shear zones of the second generation of structures sedimentation occurred during four episodes cycle 1 is interpreted to have occurred between 2800 and 2780 ma based on the ages of the mafic and felsic volcanism and comprises predominantly chemical sedimentary rocks intercalated with mafic ultramafic volcanic flows it includes the volcano chemical sedimentary lithofacies association and part of the mafic ultramafic volcanic association the cycle is related to the initial extensional stage of the greenstone belt formation with the deposition of sediments contemporaneous with volcanic flows that formed the submarine mafic plains cycle 2 encompasses the clastic chemical sedimentary association and distal turbidites of the resedimented association in the eastern sector of the quadrilatero ferrifero it was deposited in the initial stages of the felsic volcanism cycle 2 includes the coastal and resedimented associations in the southern sector in advanced stages of subduction in this southern sedimentary cycle it is also possible to recognize a stable shelf environment following the felsic volcanism cycle 3 comprises sedimentary rocks of the volcaniclastic and resedimented lithofacies associations largely in the northern sector of the area the characteristics of both associations indicate a submarine fan environment transitional to non marine successions related to felsic volcanic edifices and related to the formation of island arcs cycle 4 is made up of clastic sedimentary rocks belonging to the non marine lithofacies association they are interpreted as braided plain and alluvial fan deposits in a retroarc foreland basin with the supply of debris from the previous cycles

fractal analysis of fractures in rocks the cantor s dust method abstract the cantor s dust method of fractal analysis has been used to describe the regularity of fracture patterns in geological materials seen on a two dimensional surface this linear method of analysis is well adapted to a determination of two dimensional phenomena the determination of the fractal dimension d indicates that it varies regularly as a function of the orientation of the analysis direction this is taken to indicate that there is a relation unexplained as yet between the regularity of the fracture pattern and the forces which produced it the use of the cantor s dust method on naturally fractured materials ranging in dimension from 3 mm to 45 m in maximum dimension indicates the fractal nature of the fractures found in natural materials the analysis method can also be used to identify local variations in the stress field which caused failure such as the fractures in a feldspar compared to those in the host granite etc the method appears to be a sensitive descriptive measure of the failure patterns in rocks

truncated fractal frequency distribution of element abundance data a dynamic model for the metasomatic enrichment of base and precious metals abstract the frequency distributions of elements in rocks and ore deposits do not conform to a universal scaling law but vary in dependence of the mechanism of element enrichment in the present contribution a dynamic model is proposed that describes element enrichments taking place by metasomatic processes causing the formation of hydrothermal ore deposits it is shown that metasomatic element enrichment can result in a fractal distribution of element abundance data in the low concentration region with a smooth truncation at higher concentration values due to the existence of physical upper concentration limits imposed by the mineralogical nature of the ore the developed model is tested on the basis of base and precious metal concentration data determined on diamond drill core samples collected from the waterloo massive sulfide deposit australia it is shown that the frequency distributions of zn pb cu and ag conform relatively well to truncated power law relationships as predicted by the model in contrast the frequency distribution of the au data was found to be better described by the log normal law presumably due to syn genetic processes of element redistribution that have not been modeled by the proposed dynamic model

dikes emplaced into fractured basement timna igneous complex israel dikes are usually envisioned as arrays of parallel segments dilated perpendicular to the direction of the least compressive stress we describe here four dikes of highly irregular shape intruded in the fractured basement in the timna igneous complex southern israel the dikes include a doleritic dike 2 3 km long and 1 6 m to 32 m thick and three andesitic dikes up to 1 5 km long and 8 m thick the dikes each display significant variations of dip up to 60 strike up to 160 and thickness the thickness variations correlate better with the segment attitude than with the position along the dikes we show that the irregular shapes of the timna dikes are the result of emplacement into fractured host rock under different paleostress states and driving pressures three dilation styles that differ by the geometry of the initial cracks are analyzed an array of randomly oriented cracks style a a single linear crack style b and an array of interconnected nonparallel cracks style c the analysis of style a provides the stress state during dike emplacement including the orientations of the three principal stresses 1 2 3 the stress ratio 2 3 1 3 and the normalized driving pressure r pm 3 1 3 the stress ratio indicates the shape of the stress ellipsoid and it ranges from 0 for 2 3 prolate ellipsoid to 1 for 1 2 oblate ellipsoid the normalized driving pressure r indicates the relative magnitude of the internal magma pressure pm with respect to the tectonic stresses and it ranges from r 0 for pm 3 to r 1 for pm 1 we found that for three dikes in timna 0 25 indicating small differences between the two horizontal principal stresses and for one dike 0 9 indicating a large difference between the two horizontal principal stresses the normalized driving pressure r is about 0 08 in two horizontally propagating dikes and about 0 25 in two vertically propagating dikes style b predicts an elliptical thickness profile along the dike due to dilation of a linear crack this prediction agrees with the profile of one of the dikes the predicted thicknesses due to dilation of the interconnected array of cracks style c are in good agreement with the thickness variations of the doleritic dike and in fair agreement with two of the andesitic dikes deviations from the ideal geometry suggest separate stages of propagation and dilation in some of the dike segments