recurrence behavior of short term slow slip and correlated nonvolcanic tremor episodes in western shikoku southwest japan 1 from the national research institute for earth science and disaster prevention hi net tiltmeter data we determine time dependent source processes of seven repeating short term slow slip events sse in the western shikoku region southwest japan over the period from 2002 to 2007 the tiltmeters record clear signals of sses characterized by a slow rise a week long duration and a magnitude on the order of 10 2 10 1 rad we apply a time dependent slip inversion method to the tilt records for the seven sses for each sse a slip area migrates in the strike direction of the subducting slab at a rate of 10 km d 1 comparing the slow slip area with epicenters of accompanying nonvolcanic tremors in subday time resolution we find that the two phenomena are located on a smaller area than previously reported and migrate as a group a moment rate function for each sse exhibits good correlation with the temporal change in tremor activity a comparison of the slip distributions of all of the analyzed sses shows that there is a patch of slow slip area 30 km in diameter that is shared by all of the episodes in addition the location of the slip patch is in good agreement with the epicenters of tremors and very low frequency earthquakes these lines of evidence suggest that the identified slip patch is one of the main slow slip patches in the region and a recurrence of sses may be controlled by the patch and that these slow earthquakes might be different manifestations of a single slip process on the deep plate interface

dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

dynamics of a velocity strengthening fault region implications for slow earthquakes and postseismic slip we consider the effect of permanent stress changes on a velocity strengthening rate and state fault through numerical simulations and analytical results on 1 d 2 d and 3 d models we show that slip transients can be triggered by perturbations of size roughly larger than lb gdc b where g is the shear modulus dc and b are the characteristic slip distance and the coefficient of the evolution effect of rate and state friction respectively and is the effective normal stress perturbations that increase the coulomb stress lead to the strongest transients but creep bursts can also be triggered by perturbations that decrease the coulomb stress in the latter case peak slip velocity is attained long after the perturbation so that it may be difficult in practice to identify their origin the evolution of slip in a creep transient shares many features with the nucleation process of a rate and state weakening fault slip initially localizes over a region of size not smaller than lb and then accelerates transiently and finally expands as a quasi static propagating crack the characteristic size lb implies a constraint on the grid resolution of numerical models even on strengthening faults that is more stringent than classical criteria in the transition zone between the velocity weakening and strengthening regions the peak slip velocity may be arbitrarily large and may approach seismic slip velocities postseismic slip may represent the response of the creeping parts of the fault to a stress perturbation of large scale comparable to the extent of the main shock rupture and high amplitude while slow earthquakes may represent the response of the creeping zones to a more localized stress perturbation our results indicate that superficial afterslip observed at usually seismogenic depths is governed by a rate strengthening rheology and is not likely to correspond to stable weakening zones the predictions of the full rate and state framework reduce to a pure velocity strengthening law on a timescale longer than the duration of the acceleration transient only when the triggering perturbation extends over length scales much larger than lb

assessment of undiscovered metal resources in finland this paper summarises the results of probabilistic estimates of the amounts of cu zn pb ni co pt pd au ag and mo in undiscovered orogenic au volcanogenic massive sulphide vms porphyry cu outokumpu type cu zn co synorogenic intrusion related ni cu komatiite related ni and layered intrusion hosted contact type and reef type pge deposits in finland the assessments were carried out down to the depth of one kilometre using the three part quantitative assessment method permissive areas tracts within which mineral deposits can exist based on their geological properties were delineated separately for each deposit type total number of tracts delineated was 188 and excluding overlap total area covered by the tracts is 190 700 km2 this means that 57 of the land area of finland holds potential for the discovery of new mineral deposits of the types included in the assessments orogenic au tracts cover the largest area 110 000 km2 and the contact type pge and talvivaara type tracts cover the smallest areas both 310 km2 the number of undiscovered deposits was estimated at several levels of confidence for each permissive tract the total expected number of undiscovered deposits across all permissive tracts is 309 deposits the largest expected numbers of deposits are associated with the orogenic au 90 synorogenic intrusion related ni cu 66 and vms 45 tracts statistical comparisons indicated differences in tonnage and grade values between fennoscandian and global data sets for several deposit types and between global precambrian and phanerozoic porphyry cu deposit data sets the reason for the differences is inconclusive but probably related to both global variations in exploration maturity and availability of grade and tonnage information due to the differences grade tonnage models were constructed using data from well known deposits within the fennoscandian shield for most of the assessed deposit types the orogenic au model was constructed using fennoscandian and north australian deposits and the porphyry cu model using global data on precambrian deposits the sum of median estimates of undiscovered resources across all the assessed deposit types is 9 7 mt cu 5 0 mt ni 1 8 mt zn 0 15 mt pb 0 10 mt mo 86 000 t co 12 000 t pd 5600 t pt 2100 t ag and 1400 t au layered intrusion hosted pge deposits and porphyry cu deposits are estimated to host the largest undiscovered resources containing the majority of the undiscovered cu ni pt pd and mo most of the undiscovered zn is in vms deposits and more than half of the undiscovered au is in orogenic au deposits comparison between discovered and estimated undiscovered resources indicates that practically all mo pt and pd resources and more than half of the au and cu resources in finland exist in undiscovered or poorly known deposits undiscovered resources of ni pb and ag are smaller than the discovered resources most of the total endowment of zn and co appears to be in discovered resources on a global scale the finnish resources are small the discovered resources and estimated total endowment for most of the metals assessed are 1 of the corresponding global identified resources platinum group elements ni co and possibly au might be exceptions to this at least on a european scale as a caveat to the results of this work we stress that a few potentially significant deposit types e g kevitsa and talvivaara types precambrian epithermal au were excluded from the assessments due to the lack of statistically reliable grade and tonnage data

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

entering an immature exploration search space assessment of the potential orogenic gold endowment of the sandstone greenstone belt yilgarn craton by application of zipf s law and comparison with the adjacent agnew goldfield abstract the sandstone greenstone belt is an exploration immature regolith covered approximately 1000 sq km belt in the southern cross domain of the yilgarn craton in order to estimate potential endowment historical gold production and deposit resource estimates are required to be quantitatively analysed for calculation of natural and residual gold endowment the total residual gold endowment within the oxide zone of the sandstone greenstone belt is estimated by application of a zipf s law statistical assessment to be 2 3 moz this mineralisation is most likely contained in extensions of known deposits and several undiscovered deposits the fresh rock of the sandstone greenstone belt remains poorly explored however a conceptual endowment estimate can be made based on a minerals system comparison between the exploration immature sandstone greenstone belt and the well explored geologically similar agnew greenstone belt 100 km to the east it is possible that natural endowment at sandstone could total 21 3 moz with nine undiscovered deposits of 0 5 moz application of such a minerals system integrated endowment assessment represents an effective motivator to embark on a well resourced gold exploration campaign in the sandstone greenstone belt a currently immature exploration search space

supergene ore and hypogene nonore mineralization at the nagambie sediment hosted gold deposit victoria australia the nagambie gold deposit central victoria australia consists of approximately 7 million metric tons of ore averaging 1 2 g t gold mineralization is confined largely to east west and n 50 degrees e oriented shears and faults contained in a doubly plunging anticlinal dome of undifferentiated silurian and early devonian siltstones and shales ore is associated with an east west trending anticlinal axis and is particularly concentrated in two east northeast trending structural zones the central and 303 shear zones five stages of protore vein genesis have been identified the first two a b are barren crenulated massive quartz primary gold mineralization occurs in stibnite bearing quartz stockwork stringers which belong to the third c and fourth d quartz veining stages whereas the fifth consists of unmineralized small veins e fluid inclusion studies on the two gold mineralization stages c and d yield trapping temperatures and pressures of 280 degrees or 25 degrees c and 1 000 to 1 200 bars and 200 degrees or 30 degrees c and 700 to 1 000 bars respectively the mineralization fluids contain h 2 o co 2 0 69 mole ch 4 0 21 mole and trace n 2 with wt percent nacl equiv values in the range of 0 to 10 2 wt percent calculated delta 18 o values 15 0 6 8 and measured delta d data 88 to 99 of the hypogene fluids indicate a meteoric origin these fluids underwent extreme 18 o enrichment by reacting with country rocks metamorphic or igneous genesis of the ore as opposed to the protore is as secondary supergene enrichment accompanied by varying degrees of surficial limonite alteration ore mineralization occurs almost exclusively in limonitized fractures up to 60 m below the surface in and adjacent to major shears based on features such as the spatial distribution high purity 999 26 fine and the form of the gold and its close association with limonite it is proposed that the gold is mobilized by surficial leaching and concentrated near the water table vertical movement of the water table perhaps due to seasonal changes as well as erosion produces rapid dissolution of hypogene gold and or aurostibite from above or at the water table

modelling of short interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable stable transition regime summary recent high resolution observations of crustal movements have revealed silent slip events sses with propagation velocities of around 10 15 km d 1 and with intervals of 3 14 months along the deeper parts of the cascadia and nankai subduction zones this study develops 2 d and 3 d models of these short interval sses considering the frictional behaviour that was confirmed experimentally by shimamoto for the unstable stable transition regime to represent this frictional behaviour a small cut off velocity to an evolution effect is introduced in a rate and state dependent friction law when the cut off velocity to the evolution effect is significantly smaller than that to a direct effect steady state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities at the deeper cascadia and nankai subduction interfaces the pore pressure is inferred to be high because of the dehydration of materials in the descending plate under conditions where the pore fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small short interval sses with propagation velocities and slip velocities of 4 8 km d 1 and 2 4 10 7 m s 1 respectively can be reproduced the propagation velocity of short interval sses is in proportion to the slip velocity the results also show that during the nucleation process of large earthquakes the occurrence of short interval sses becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone our results suggest that monitoring of short interval sses might be useful for forecasting the main earthquakes

translating the mineral systems approach into an effective exploration targeting system abstract holistic mineral systems approaches are being increasingly adopted in the study of ore deposits but application in industry has been suboptimal because of the lack of a conceptual framework to help translate the mineral system understanding to practical application a four step process is proposed for linking the conceptual mineral system with data available to support exploration targeting these steps include translation from 1 critical processes of the mineral system to 2 constituent processes of the mineral system to 3 targeting elements reflected in geology and 4 targeting criteria used to detect the targeting elements directly or by proxy this translation process is illustrated using examples from komatiite hosted ni cu pge and orogenic au mineral systems ranking of targets must be at the critical process level rather than the current practice of mixing processes elements and proxies the significance of targeting elements and their mappable criteria changes as a function of the scale at which the critical processes operate and the availability of relevant geoscience datasets this scale dependence is rarely recognised in current practice sources of uncertainty when translating the mineral system understanding into an effective exploration targeting system include 1 resolution of a mappable criterion in a dataset 2 how well the targeting criterion reflects the targeting element 3 how well the targeting element reflects the critical process and 4 whether the process being mapped is critical for the genesis of a mineral deposit the first three sources of uncertainty collectively are termed the representativeness of the targeting criteria i e how representative is a mappable criterion of the constituent process for which it is a proxy the last source of uncertainty reflects our lack of understanding of the processes that control mineralisation and highlights areas for further research

melange and sediment hosted gold bearing quartz veins hodgkinson gold field queensland australia gold bearing quartz veins in the hodgkinson gold field are hosted in subgreenschist facies siluro devonian sandstone conglomerate carbonaceous shale clast in matrix rock chert and spilite mineralization occurs in brittle to brittle ductile shear zones which crosscut two previous deformations and melange vein systems are isolated in distinct structural and lithologic domains by postmineralization faulting scheelite quartz veins may locally overprint the gold quartz mineralization but stibnite gold quartz mineralization is restricted to separate domains the strongest mineralized areas define elongate elliptical ore shoots which plunge steeply down or across the dip of the host shear zones melange hosted lodes are parallel in strike but have opposite dips to the melange cleavage sandstone hosted shear zones lie within reactivated f 2 axial planes or are refracted through bedding planes splaying fissure intersections changes in attitude and lithologic contacts are the main ore shoot controls the gold quartz vein textural types are ribbon buck breccia assimilation textured and comb quartz multiple injection of quartz and multiple shear zone movement have produced complex zones of quartz separated by seams of gouge arsenopyrite galena sphalerite pyrite pyrrhotite and gold 600 840 fine constitute 5 percent of the ore shoots and occur as millimeter scale clusters in quartz fluid inclusions in quartz are liquid and liquid vapor types and give salinity ranges of 3 to 11 equiv wt percent nacl with a slight salinity decrease through time co 2 and other gases are not abundant homogenization temperatures of 170 degrees to 305 degrees c have been pressure corrected to 270 degrees to 355 degrees c based on estimated formation pressure of about 1 kbar measured and calculated stable isotope compositions of the fluid depositing gold quartz are delta 18 o 10 or 2 per mil delta d 100 or 20 per mil although meteoric water contributions cannot be discounted geologic characteristics isotopic data quartz types sulfide mineralogy and ore controls favor gold deposition from an upwardly migrating homogeneous metamorphic or distal magmatic fluid depletion of d is attributed to exchange reactions involving organic matter in the metasediments and reduced gas species rather than introduction of meteoric water gold mineralization accompanied brittle tectonism which was contemporaneous with regional plutonism and took place late in the evolution of the melange

crustal architecture and geodynamics of north queensland australia insights from deep seismic reflection profiling abstract a deep crustal seismic reflection and magnetotelluric survey conducted in 2007 established the architecture and geodynamic framework of north queensland australia results based on the interpretation of the deep seismic data include the discovery of a major west dipping paleoproterozoic or older crustal boundary considered to be an ancient suture zone separating relatively nonreflective thick crust of the mount isa province from thinner two layered crust to the east farther to the east a second major crustal boundary also dips west or southwest offsetting the moho and extending below it and is interpreted as a fossil subduction zone across the region the lower crust is mostly highly reflective and is subdivided into three mappable seismic provinces but they have not been tracked to the surface in the east the greenvale and charters towers provinces part of the thomson orogen have been mapped on the surface as two discrete provinces but the seismic interpretation raises the possibility that these two provinces are continuous in the subsurface and also extend northwards to beneath the hodgkinson province originally forming part of an extensive neoproterozoic cambrian passive margin continuation of the thomson orogen at depth beneath the hodgkinson and broken river provinces suggests that these provinces which formed in an oceanic environment possibly as an accretionary wedge at a convergent margin have been thrust westwards onto the older continental passive margin the tasman line originally defined to represent the eastern limit of precambrian rocks in australia has a complicated geometry in three dimensions which is related to regional deformational events during the paleozoic overall the seismic data show evidence for a continental margin with a long history paleoproterozoic to early mesozoic but showing only limited outward growth by crustal accretion because of a repeated history of overthrust shortening during repeated phases of orogenesis

formation of gold deposits review and evaluation of the continuum model abstract the continuum model has been one of the more widely advocated genetic models for gold only deposits such as those found in archaean greenstone belts it postulates that hydrothermal gold deposits were formed throughout a 20 25 km vertical crustal profile from temperatures above 700 c to below 180 c and that the deposition occurred synchronous with the peak of metamorphism the continuum model is reviewed at this stage because we believe that it does not successfully account for many aspects of gold deposit formation the most obvious shortcoming is in considering ore deposits found in rocks of uppermost amphibolite and granulite facies domains where temperatures were appropriate for partial melting the main chemical condition that favours melting is access to h2o from either aqueous fluid or the breakdown of hydrous minerals a major gold forming hydrothermal event at the peak of high grade metamorphism as implied by the continuum model is incompatible with partial melting of wallrocks instead of forming a hydrothermal gold deposit an aqueous fluid introduced during partial melting would be consumed to produce further melt five gold deposits are documented from high metamorphic grade domains within four separate archaean cratons one is the type example used in the continuum model the other four have been significant producers partial melting has been recorded in the wallrocks adjacent to gold mineralisation at big bell hemlo challenger and renco gold deposits in the sulphide rich ore itself at challenger and hemlo deposits and as cross cutting dykes and migmatites at griffins find for these five deposits and indeed in general the continuum model does not easily account for aspects of the fluid source fluid composition gold transport and metal deposition the evidence that has been used to support deposit formation at the peak of high grade metamorphism as required by the continuum model is generally compatible with one or more alternative genetic models textural and structural siting of the gold high variance mineral assemblages proportion of various gold host rocks and relative element enrichments at high metamorphic grade can be accounted for by gold formation at greenschist facies conditions followed by progress of the deposit to high metamorphic grade metamorphic model moreover the type examples in the continuum model of deposits in sub greenschist facies domains appear to be incorrectly ascribed and are likely to be in greenschist facies domains the continuum model does not adequately explain archaean gold deposits

generation mechanism of slow earthquakes numerical analysis based on a dynamic model with brittle ductile mixed fault heterogeneity 1 various characteristics have been discovered for small slow earthquakes occurring along subduction zones which are deep nonvolcanic tremor low frequency earthquakes lfes and very low frequency earthquakes vlfs in this study we model these slow earthquakes using a dynamic model consisting of a cluster of frictionally unstable patches on a stable background the controlling parameters in our model are related to the patch distribution and the viscosity of both the patches and the background by decreasing patch density or increasing viscosity we observed the transition in rupture propagation mechanism that is from fast elastodynamic interactions characterized by an elastic wave propagation to slow diffusion limited by viscous relaxation times of traction on fault patches and or background some sets of these geometrical and frictional parameters collectively explain the moment rate functions source spectra and scaled energy of observed slow earthquakes in addition we successfully explain both parabolic and constant velocity migrations in the case of the diffusion limited rupture therefore the observed various characteristics of tremor lfes vlfs and potentially slow slip events may be essentially explained by our simple model with a few parameters describing source structures and frictional properties of brittle ductile transition zones along plate boundaries

a single late orogenic permian episode of gold mineralization in the hodgkinson province north queensland australia quartz hosted gold deposits in the hodgkinson province north queensland are widely distributed with the most heavily endowed areas comprising three separate spatially distant goldfields the west normanby goldfield the palmer river goldfield and the hodgkinson goldfield relationships among quartz vein and shear hosted deposits in each of the three goldfields indicate that the introduction of gold bearing quartz displays consistent structural timing relative to a regionally recognized deformation history gold was emplaced during the waning stages of d4 the main contractional phase of the permian triassic hunter bowen orogeny mineralization and structures have been structurally timed relative to isotopically dated plutons of the spatially associated syn d4 whypalla supersuite indicating emplacement of the mineralization in the early permian or later emplacement of gold bearing quartz veins in the fossiliferous permian normanby formation in the north of the province supports this contention the permian age is younger than the originally published carboniferous 300 ma age for gold mineralization in the hodgkinson province fluid generation and gold transport were related to regional scale devolatilization during province wide metamorphism the final distribution of fluids and contained gold was controlled by faults produced during the hunter bowen orogeny and by major late devonian shear zones that were reactivated during this orogeny heat from synchronously emplaced d4 granites focused enhanced fluid flow into spatially associated dilatant structures in these faults

phenomenology of deep slow earthquake family in southwest japan spatiotemporal characteristics and segmentation 1 the phenomenology of deep slow earthquakes including low frequency tremors very low frequency earthquakes and short term slow slip events on the subducting plate interface in southwest japan is investigated on the basis of their spatiotemporal characteristics the belt like distribution of tremors is divided into segments bounded by gaps the repetition of tremor episode depends on the magnitude of the episode which is defined by the number of detected tremors within each episode major tremor episodes with a large number of detected tremors recur at an interval of approximately 6 months accompanying the short term slow slip events in large segments in small segments tremor episodes with small numbers of tremors have recurrence intervals of a few months some of them occasionally accompany the slight ground tilting caused by a small size slow slip event even in the same segment there exist different recurrence intervals according to the magnitude of the tremor episode the migration pattern varies greatly in initiation termination direction and speed however the migration direction has a general tendency for each segment on both sides of the gap the tremor starts next to the gap and propagates to the other side assuming all tremor episodes are caused by slow slip events the equivalent moment and slip are estimated from the number of detected tremor counts and the area of each tremor episode the equivalent slip history estimated from all tremor episodes is almost constant in each segment this indicates that tremor activity is a good proxy for slow slips

discovered and undiscovered gold endowment of turkey a quantitative mineral resource assessment using gis and rank statistical analysis an assessment of the discovered and undiscovered gold endowment of turkey a prolific sector in the tethyan metallogenic belt is developed from a comprehensive geographic information system database containing 402 gold deposits and prospects the majority of the gold deposits and prospects are epithermal porphyry volcanic associated massive sulfides orogenic gold and skarn systems these five major deposit types form more than 90 of the known gold deposits and prospects just 87 corresponding to 21 6 of the deposits and prospects in the data set have current calculated gold reserve and or resources containing a total of 54 885 moz au current gold reserves of the country are 21 447 moz constituting 39 1 of the total gold resources of which 17 1 moz gold are contained in four deposits out of these 87 deposits and prospects only 27 contain significant gold reserve and or resources defined as equal to or more than 0 32 moz or 10 tons au and contain 91 8 of the total gold endowment of the country the cumulative frequency distribution model of the gold endowment of turkey abides by log normal distribution observed and estimated 10th 50th median and 90th percentiles of the data are 0 0046 moz 0 0045 moz estimated 0 1030 moz 0 0875 moz and 1 4969 moz 1 6938 moz respectively the 99th percentile of the data is 7 6444 moz 18 9636 moz the arithmetic mean of the known gold endowment is 0 657 moz and the swanson mean size is 0 492 moz the arithmetic mean of the 27 significant gold deposit or prospects is 1 94 moz zipf s law estimates of the undiscovered residual gold resources of turkey are based on the current size of the largest rank 1 gold deposit of turkey which is the kisladag porphyry deposit that has 17 481 moz gold endowment including past production zipf s law estimates a total of 88 261 moz natural or total gold endowment 57 133 moz or 65 of which has already been found this predicts at least 31 128 moz residual or undiscovered gold resources to be found in turkey though the lack of full delineation of the rank 1 deposit kisladag means that this figure is very conservative

a slow slip event triggered by teleseismic surface waves 1 in recent years slow slip events sse have been observed to occur at regular intervals on the deep portions of subduction zone interfaces these are accompanied by seismic tremor that occurs over their duration it has been observed that tremor activity shows transient modulations in response to earth tides and the passage of seismic waves from distant earthquakes here we show for the first time geodetic evidence for the triggering of an interplate sse itself by teleseismic surface waves this sse in southwest japan which had an equivalent magnitude mw 5 3 and duration of 1 5 days was triggered by the surface waves of a mw 7 6 earthquake in tonga this evidence was captured by a newly deployed sensitive strainmeter network the triggered sse occurred on a place on the plate interface where the recurrence time for such events had almost expired whereas other regions at up to 90 of the recurrence time were not triggered this provides information for the conditions for triggering and generation of sses and perhaps for regular earthquakes

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

rapid continuous streaking of tremor in cascadia nonvolcanic tremor is a recently discovered weak seismic signal associated with slow slip on a fault plane and has potential to answer many questions about how faults move its spatiotemporal distribution however is complex and varies over different time scales and the causal physical mechanisms remain unclear here we use a beam backprojection method to show rapid continuous slip parallel streaking of tremor over time scales of several minutes to an hour during the may 2008 episodic tremor and slip event in the cascadia subduction zone the streaks propagate across distances up to 65 km primarily parallel to the slip direction of the subduction zone both updip and downdip at velocities ranging from 30 to 200 km h we explore mainly two models that may explain such continuous tremor streaking the first involves interaction of slowly migrating creep front with slip parallel linear structures on the fault the second is pressure driven fluid flow through structurally controlled conduits on the fault both can be consistent with the observed propagation velocities and geometries although the second one requires unlikely condition in addition we put this new observation in the context of the overall variability of tremor behavior observed over different time scales

propagation dynamics of seismic and aseismic slip governed by fault heterogeneity and newtonian rheology 1 slow earthquakes called episodic tremor and slip ets events propagate over 100 km at low average velocities 10 km per day along several plate interfaces accompanying seismic and aseismic slip these low propagation velocities differentiate slow earthquakes from ordinary earthquakes and thus understanding their propagation processes is fundamental to understanding the poorly constrained physics governing the diversity and universality of earthquakes we show that rheological heterogeneity on faults primarily governs ets propagation on the basis of comprehensive modeling and observations that correlate migration patterns with the energetics of tremor on a plate bounding fault in southwest japan the fault has persistent small scale segmentation in which ets events started propagating energetically in relatively brittle sections and decelerated generally with a parabolic pattern in relatively ductile sections simulated spontaneous ruptures that are based on these parabolic tremor migration patterns constrain the cause of ductility to newtonian plastic flow or perhaps dilatant strengthening but reject large scale fluid flows we discuss possible elementary processes underlying the newtonian rheology this model is also consistent with the observed seismicity migration pattern before the 2011mw9 0 tohoku oki earthquake suggesting delayed triggering by themw 7 3 foreshock

link between gold provinces low salinity high temperature 200 degrees c reducing fluids are poorly represented in ore forming processes yet appear to account for 90 percent of the primary gold mined to date such fluids have been implicated in the formation of many archcan greenstone witwatersrand slate belt and epithermal gold deposits these low salinity auriferous fluids occur in variable time space lithological sequence and tectonic settings and are most easily explained by metamorphic devolatilization of mafic and or graywacke successions metamorphism of chlorite calcite albite quartz assemblages e g mafic or graywacke at the greenschist amphibolite facies boundary occurs around 480 degrees or 20 degrees c for 3 5 kbars and produces large volumes of low salinity h 2 o co 2 fluid similar in composition to those recorded in many gold deposits widespread pyrite in the above assemblage typically leads to elevated levels of dissolved sulfur such conditions are ideal for gold transport as a molecular au s complex and can lead to deposits rich in gold relative to silver and base metals deposition of gold occurs in the temperature range of 250 degrees to 400 degrees c and can be facilitated by lower temperature lower sulfur activity and changes in oxygen activity lower sulfur activity is most readily achieved by fluid interaction with fe rich host rocks with the formation of pyrite or pyrrhotite whereas lower oxygen activity is readily achieved by interaction with carbonaceous metasediments low salinity fluids produced by metamorphic devolatilization provide a common theme embracing the formation of many archcan greenstone slate belt witwatersrand and potentially epithermal gold deposits it involves the common features of high geothermal gradient low salinity fluid high au ag high au base metals and broad synchroneity with metamorphism it also accounts for the considerable variability in hosting structures detailed timing relations host rocks alteration assemblages and geologic age of different deposits interestingly the similarities are explained by deeper processes the differences by processes at or near the depositional sites

brittle and ductile friction and the physics of tectonic tremor 1 observations of nonvolcanic tremor provide a unique window into the mechanisms of deformation and failure in the lower crust at increasing depths rock deformation gradually transitions from brittle where earthquakes occur to ductile with tremor occurring in the transitional region the physics of deformation in the transition region remain poorly constrained limiting our basic understanding of tremor and its relation to earthquakes we combine field and laboratory observations with a physical friction model comprised of brittle and ductile components and use the model to provide constraints on the friction and stress state in the lower crust a phase diagram is constructed that characterizes under what conditions all faulting behaviors occur including earthquakes tremor silent transient slip and steady sliding our results show that tremor occurs over a range of ductile and brittle frictional strengths and advances our understanding of the physical conditions at which tremor and earthquakes take place

striations duration migration and tidal response in deep tremor deep tremor in subduction zones is thought to be caused by small repeating shear slip events on the plate interface with significant slow components it occurs at a depth of about 30 kilometres and provides valuable information on deep plate motion and shallow stress accumulation on the fault plane of megathrust earthquakes tremor has been suggested to repeat at a regular interval migrate at various velocities and be modulated by tidal stress here i show that some time invariant interface property controls tremor behaviour using precise location of tremor sources with event duration in western shikoku in the nankai subduction zone japan in areas where tremor duration is short tremor is more strongly affected by tidal stress and migration is inhibited where tremor lasts longer diffusive migration occurs with a constant diffusivity of 10 4 m 2 s 1 the control property may be the ratio of brittle to ductile areas perhaps determined by the influence of mantle wedge serpentinization on the plate interface the spatial variation of the controlling property seems to be characterized by striations in tremor source distribution which follows either the current or previous plate subduction directions this suggests that the striations and corresponding interface properties are formed through the subduction of inhomogeneous structure such as seamounts for periods as long as ten million years

spatial data analysis of mineral deposit point patterns applications to exploration targeting abstract systematic spatial analysis of mineral deposit point patterns can reveal significant spatial properties of mineral systems with major implications for regional mineral prospectivity modelling for valid results a study area needs to be clearly defined taking into account permissiveness of the geological units for a particular mineral system and effects of cover standard statistical tests assuming an isometric contiguous study area with regionally homogeneous distribution of deposits are likely to produce invalid results analysis of regional uniformity of spatial deposit density is required for adequate design and interpretation of tests for clustering spatial distribution of orogenic gold deposits in the hodgkinson province in queensland and the western lachlan orogen in victoria australia indicates the presence of significant regional linear metallogenic zones probably controlled by deep crustal domain boundaries oblique and not related to any recognised major faults within the metallogenic zones in both regions individual gold occurrences are strongly clustered into ore fields but the distribution of ore fields is random

mossman orogenic gold province in north queensland australia regional metallogenic controls and undiscovered gold endowment the hodgkinson and broken river provinces of the mossman orogen in north queensland host numerous orogenic gold deposits and still remain under explored this paper discusses regional metallogenic controls and results of a probabilistic quantitative assessment of undiscovered gold potential in the region significant orogenic gold deposits in the region occur only within relatively small well endowed metallogenic zones likely to be controlled by the eastern margin of the paleoproterozoic continental crust underlying the western mossman orogen three distinct styles of primary orogenic gold deposits are present in the area gold quartz veins refractory gold associated with quartz pyrite arsenopyrite veins and stockworks and stibnite quartz gold veins refractory gold deposits are estimated to have the highest potential for significant undiscovered resources in the region the hodgkinson province is estimated to host between one and ten significant undiscovered refractory gold ore fields with a 50 probability of at least 20 t of total contained gold and a 90 probability of at least 1 t the broken river province is estimated to host up to five significant undiscovered refractory gold ore fields with a 50 probability of at least 12 t of contained gold

thermal and metamorphic environment of subduction zone episodic tremor and slip 1 episodic tremor and slip ets have been detected in the cascadia and southwest japan subduction zones where the subducting crust is relatively warm because of the young incoming lithosphere 20 ma and modest plate convergence rates 40 60 mm a in the southwest japan subduction zone low frequency earthquakes occur on the plate interface at depths of 30 35 km beneath shikoku where finite element thermal models predict temperatures of 425 c in the subducting oceanic crust and at depths of 30 40 km beneath the kii peninsula where predicted temperatures are 325 c warmer temperatures of 575 c are predicted at ets depths beneath southern vancouver island in the cascadia subduction zone but here tremor also occurs within the overlying fore arc crust where temperatures are lower in the southwest japan and cascadia subduction zones subducting oceanic crust passes through the blueschist greenschist and amphibolite metamorphic facies where mineral dehydration reactions are complex the different temperatures predicted for the two subduction zones suggest that ets does not coincide with a specific temperature or metamorphic reaction several lines of evidence indicate that a free h2o rich fluid is present at least transiently in subducting oceanic crust and fluids released by prograde metamorphic dehydration reactions may help trigger or enable ets within the subducting plate less clear is the role h2o may play in tremor observed in the cascadia fore arc crust where free h2o may exist locally in faults and fractures but retrograde hydration reactions are expected to consume h2o

a role for data richness mapping in exploration decision making abstract exploration programs involve long multi branched decision pathways with many potential outcomes from a single starting point critical decisions along this pathway include the choice of the area s in which to explore and the choice to acquire new data sets to assist in exploration included in this is a factoring of risks including the technical risks associated with imperfect data and the value relative to cost of collecting more data in our experience it is not common practice to explicitly assess and quantify the impact of data on exploration decisions a better understanding of the opportunity provided by data has the potential to improve the quality and or ease of decision making in this study we explore the potential role of data richness mapping as part of a decision making workflow we outline a method to quantitatively assess data richness following a four level hierarchy namely presence of data l1 quality of data l2 and attributes of data l3 measures of these are combined across several data sets to give an overall estimate of data richness l4 using this data richness map along with past exploration records and a prospectivity model we conduct an illustrative case study for gold exploration in the bryah sub basin yerrida basin region of western australia the first application is to produce a simple data based classification of regions with different technical risk characteristics the second application is to combine this with a prospectivity model to better understand exploration potential the third application uses data richness mapping to understand which data sets are most likely to have an impact on regional exploration in each case we show how an understanding of data richness can help support exploration decision making

undiscovered orogenic gold endowment in northern victoria australia abstract the northern part of the victorian gold province australia is covered by cainozoic sediments and remains poorly explored this contiguous covered area of over 44 000 km 2 is highly prospective for orogenic gold deposits this paper discusses results of probabilistic quantitative assessments of undiscovered gold potential in the northern covered parts of the western lachlan orogen the stawell bendigo and melbourne zones for the bendigo and stawell zones quantitative estimates were only made for undiscovered mesozonal orogenic gold quartz vein deposits the predominant type of gold mineralisation in that region for the northern part of the bendigo zone under cover 10 000 km 2 the mean estimate is approximately 1000 t with a 90 probability of at least 290 t of gold in undiscovered mesozonal orogenic gold deposits for the northern covered area of the stawell zone 30 000 km 2 the mean estimate is 1200 t with a 90 probability of at least 200 t of undiscovered gold the northern part of the melbourne zone 4400 km 2 is considered prospective for epizonal orogenic gold deposits associated with quartz pyrite arsenopyrite veins and stockworks or with quartz stibnite gold veins the mean estimate for that area is 90 t with a 90 probability of at least 10 t of gold in undiscovered epizonal orogenic gold deposits

rank statistical analysis of nickel sulphide resources of the norseman wiluna greenstone belt western australia estimating the undiscovered mineral resources of a terrane is a challenging yet essential task in mineral exploration we apply zipf s law rank statistical analysis to estimate the undiscovered nickel sulphide resources in the norseman wiluna greenstone belt western australia the analysis suggests that about 3 0 to 10 0 mt of nickel sulphide resources are yet to be discovered in this belt compared to the currently known total nickel sulphide endowment of 10 8 mt this undiscovered nickel sulphide endowment is likely to be hosted by incompletely delineated deposits and undiscovered deposits in less explored komatiites in the belt using the more detailed data subset of the kambalda domain this study manipulates zipf s law to estimate the sizes of undiscovered deposits in addition to the domain s total nickel sulphide endowment estimate importantly regression analysis shows that the gradient of the line of best fit through the logarithmic rank size plot for the detailed kambalda data subset is 1 this gradient which is the key zipf s law constant k has the value of 0 92 for the norseman wiluna greenstone belt which is collectively less mature than the kambalda domain this result corroborates the use of k 1 in zipf s law predictive analyses of mineral resources for deposit populations for which the value of k 1 has not yet been attained due to exploration immaturity

variations of fluid pressure within the subducting oceanic crust and slow earthquakes 1 we show fine scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high pressure fluids released by progressive metamorphic dehydration reactions in the subducting philippine sea plate in tokai district japan these zones have a strong correlation with the distribution of slow earthquakes including long term slow slip ltss and low frequency earthquakes lfes overpressured fluids in the ltss region appear to be trapped within the oceanic crust by an impermeable cap rock in the fore arc and impede intraslab earthquakes therein in contrast fluid pressures are reduced in the lfe zone which is deeper than the centroid of the ltss because there fluids are able to infiltrate into the narrow corner of the mantle wedge leading to mantle serpentinization the combination of fluids released from the subducting oceanic crust with heterogeneous fluid transport properties in the hanging wall generates variations of fluid pressures along the downgoing plate boundary which in turn control the occurrence of slow earthquakes

plagioclase preferred orientation in layered mylonites evaluation of flow laws for the lower crust thesis s m joint program in marine geology and geophysics massachusetts institute of technology dept of earth atmospheric and planetary sciences and the woods hole oceanographic institution 2008

spatiotemporal distribution of seismic energy radiation from low frequency tremor in western shikoku japan 1 the spatiotemporal patterns of the radiated seismic energy from low frequency tremor associated with slow slip events in western shikoku japan have been estimated a spatially decaying mean square amplitude and differential traveltime measurement from envelope correlations observed at hi net stations were used to locate tremors and to estimate their seismic energies tremor amplitude was corrected for the site amplification factors estimated using the coda normalization method the location of the tremor is estimated as the position where both the decay of the observed energy and the differential travel times are well explained the temporal pattern of the total energy released agrees very well with the observed tilt records although the spatial patterns of the energy radiation vary strongly among the six slow slip events sses in western shikoku the region where they overlap always radiates relatively high levels of energy the estimated band limited energy rate of the tremor for a 2 to 10 hz bandwidth was typically between 105 and 106 j min though there is temporal variation of the radiation energy the released total energy associated with the sses whose magnitude is 5 9 6 1 is on the order of 108 j within the duration of sses of 8 13 days this is quite small energy radiation compared to the moment release of accompanying sse the scaled energy which is the ratio of the seismic moment and the seismic energy for the slow slip and a very low frequency earthquake was estimated to be 5 orders of magnitude smaller than that of a regular earthquake

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

appraisal of the usgs three part mineral resource assessment through estimation of the orogenic gold endowment of the sandstone greenstone belt yilgarn craton western australia regional scale ground selection presents a significant risk in mineral exploration targeting as any exploration search space contains a finite and fixed number of ore bodies selection of barren or depleted search spaces incurs wasted exploration expenditure by defining regions of estimated high mineral endowment via generation of quantitative information as to the value of potential discoveries mineral exploration effectiveness project acquisition and exploration portfolio management can be improved the three part mineral resource assessment developed by the united states geological survey usgs is a methodology designed to assist in this process here two separate assessments are applied to estimate the orogenic gold endowment of the sandstone greenstone belt in the yilgarn craton western australia first the results of a global regression assessment median endowment of 33 t 1 16 moz au mean of 130 t 4 59 moz au based on an available but outdated global grade tonnage model for low sulfide gold quartz vein deposits suggest that most outcropping and shallow orebodies in the sandstone greenstone belt have been discovered and fully delineated in contrast an expert assessment median endowment of 210 t 7 41 moz au mean of 220 t 7 76 moz au using expert derived grade and tonnage distributions specific to the sandstone greenstone belt predicts that significant gold mineralization remains to be discovered largely beneath cover the contrasting assessments imply a step change in exploration focus from surficial deposits at the time of the usgs global grade tonnage model to those buried under cover at the present time the expert assessment in contrast to the global regression assessment implies the potential for deeper exploration targets within the sandstone greenstone belt based on the predicted total number of deposits much of the undiscovered mineral endowment is likely to be distal to known ore bodies beneath cover and at greater depths within the belt

orogenic gold mineral systems of the western lachlan orogen victoria and the hodgkinson province queensland crustal metal sources and cryptic zones of regional fluid flow abstract orogenic gold mineral systems in the western lachlan orogen victoria and the hodgkinson province queensland produced gold provinces characterised by vastly different scales of gold endowment and strongly uneven distribution of gold mineralisation within each province the volume of hydrous pyrite bearing rocks undergoing metamorphic devolatilisation during thermo tectonic events driving orogenic gold mineral systems represents a fundamental first order constraint on the total gold endowment and its broad spatial distribution both between and within the provinces most of the largest gold deposits in both regions occur in linear richly endowed metallogenic zones oblique to the dominant regional structures and related to deep crustal domain boundaries these boundaries with only subtle surface expressions were the major regional structural controls which promoted focused near vertical flow of mineralising metamorphic fluids above the outer margins of cratonic blocks in the lower crust recognised major faults represented only more local scale and often indirect controls on the focused fluid flow particularly effective above the deep cratonic block boundaries overlain by relatively thick crustal source rocks

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

migration properties of non volcanic tremor in shikoku southwest japan 1 based on the precise locations of deep non volcanic tremor in southwest japan which show a depth dependent behavior we clarified characteristic properties of tremor migration major tremor swarms are mainly initiated at deep levels of the tremor zone corresponding to areas of frequent minor tremor and migrate up dip along the subduction interface in central and eastern shikoku tremor occurs in two clusters separated by a small gap with the timing of tremor activity in the clusters differing by 1 or 2 days the time evolution of tremor activity in western shikoku reveals that the migration front of tremor propagates continuously and radially even in the case of a tremor gap these findings indicate that the rupture front of slow slip events propagates continuously and radially from the deep levels through the area without tremor activity the occurrence of tremor may depend on the existence of inhomogeneous patches upon the plate interface

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

the palaeozoic tectono metallogenic evolution of the northern tasman fold belt system australia interplay of subduction rollback and accretion abstract the tasman fold belt system in eastern australia provides a record of the palaeozoic geological history and growth of the australian continent along the proto pacific margin of gondwana inboard of an extensive and long lived subduction system the hodgkinson and broken river provinces represent prominent geological elements of this system and together form the northern tasman fold belt system geochronological age dating of the timing of gold formation in the amanda bel goldfield in the broken river province and the hodgkinson goldfield in the hodgkinson province provides constraints on the occurrence of a deformation and mineralisation episode in the late devonian early carboniferous integration of these newly obtained data with petrogenetic constraints and a time space evaluation of the geological evolution of the hodgkinson and broken river provinces as well as other terranes in the northern tasman fold belt system allows for the development of a geodynamic model for the palaeozoic evolution of the northern tasman fold belt system our model indicates that three cycles of extension contraction occurred during the palaeozoic evolution of the northern tasman fold belt system episodes of extension were controlled by rollback of the subduction system along the proto pacific margin of gondwana whereas episodes of contraction resulted from accretion following the arrival of positively buoyant segments i e micro continental blocks oceanic plateaus at the subducting trench our composite interpretative model on the geodynamic evolution of the northern tasman fold belt system integrates the timing of the development of mineral deposits throughout this part of the system and provides a significant advancement in the understanding of palaeozoic geodynamics along the margin of gondwana in northeast australia and allows comparison with the southern part of the tasman fold belt system

a time series audit of zipf s law as a measure of terrane endowment and maturity in mineral exploration controversy has surrounded the application of zipf s law as a potential exploration tool since it was first proposed by folinsbee in 1977 the current study empirically assesses with the wisdom of hindsight the realism of predictions that could have been made at various times in the past about the number and size of lode gold deposits yet to be discovered in the archean yilgarn craton of western australia the size distribution of gold deposits predicted by the zipf curve at any point in time represents an estimate of the original natural endowment for this terrane based on the knowledge available at the time predicted gold deposits not matched by known deposits by contrast represent the residual endowment for deposits yet to be discovered the study concludes that a zipf curve based on the size distribution of gold deposits known in 1973 1989 2003 and 2008 would have provided remarkably realistic predictions of the size and number of the gold deposits that were discovered subsequently or of the degree to which known deposits have grown in size in subsequent years as a result of better delineation because lode gold orebodies are notoriously difficult to fully delineate and their resources tend to grow with time initial zipf predictions generally prove conservative predictions are particularly sensitive to the accuracy of the resource inventory of the largest rank 1 deposit on which the zipf curve is based in our case the kalgoorlie golden mile which has virtually doubled in size during the period covered by the study from 36 to 72 moz of contained gold nevertheless the degree of exploration maturity could have consistently been estimated with a high degree of accuracy as 17 percent of predicted gold endowment discovered in 1973 33 percent in 1989 62 5 percent in 2003 and 75 percent in 2008 in conclusion application of zipf s law would have represented an effective motivator to embark into a well resourced gold exploration campaign in the yilgarn craton

a fluid inclusion study of the fosterville mine a turbidite hosted gold field in the western lachlan fold belt victoria australia abstract gold mineralisation at fosterville occurs in association with disseminated arsenopyrite and pyrite adjacent to a complex series of quartz carbonate veins along two nnw trending fault zones quartz carbonate veins which have formed in dilational fractures within the sulphide ore zone have 18 o values between 16 0 and 17 6 and contain the following types of fluid inclusions type ia two phase liquid rich inclusions with less than 10 vol vapour and no detectable gases type ib two phase inclusions with approximately 10 vol co 2 rich vapour type ii co 2 bearing inclusions with 30 vol vapour and type iii liquid h 2 o and liquid plus vapour co 2 inclusions with variable h 2 o co 2 ratios raman microprobe analysis showed that types ib ii and iii contain co 2 with variable amounts of n 2 and ch 4 in some inclusions type 1a aqueous inclusions from stage 4 of the paragenesis have salinities ranging from 5 to 7 wt nacl equivalent whereas the co 2 bearing inclusions in the same stage have average salinities around 3 5 4 0 wt nacl equivalent the co 2 bearing inclusions exhibited two different types of homogenisation behaviour vapour rich type ii and iii inclusions either homogenised to vapour or showed near critical behaviour by gradual fading of the meniscus with homogenisation temperatures from 234 to 384 c and a mode at 270 c liquid rich co 2 bearing inclusions homogenised to the liquid phase with a bimodal distribution the majority of inclusions homogenised between 243 c and 314 c with a mode around 270 c but a secondary mode occurs around 180 c this mode corresponds fairly closely to the mode observed for the aqueous type 1a inclusions at 170 c the variable salinities coexisting liquid and vapour rich inclusions and the overlap of the homogenisation temperatures suggest that phase separation has occurred during vein formation and the resulting depth of mineralisation is estimated to be between 2 6 and 5 7 km gold precipitation resulted from the partitioning of h 2 s into the vapour phase during fluid unmixing which was enhanced both by the decreasing pressure as fluid flowed from the faults and veins into the host rocks and by the addition of n 2 and ch 4 comparisons with available fluid inclusion data for the western lachlan fold belt indicates that the fosterville gold field formed at lower temperatures and at a higher crustal level than the quartz reef style of gold deposits in the bendigo ballarat zone the fluids at fosterville also contain greater amounts of n 2 and ch 4 suggesting that the mineralising fluids penetrated further into the host rocks and reacted either directly with carbonaceous matter or with reduced fluids contained within the host rocks

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

enhanced detection capability of non volcanic tremor using a 3 level vertical seismic array network va net in southwest japan 1 this study evaluates a method that enhances detection of non volcanic low frequency tremor nvt using va net a 3 level vertical seismic array network that was recently constructed in southwest japan the method employs semblance analysis for continuous vertical array records and calculates semblance coefficients as a function of time and apparent vertical velocity the sign of the best apparent velocity provides information about propagation direction either upward or downward allowing easy discrimination between seismic signals of natural origin and unwanted noise such as man made vibrations we applied the method to a nvt episode that occurred beneath the kii peninsula during november 2008 to demonstrate that nvt signals can be detected using only the 3 level array furthermore we demonstrate that the method enables us to detect minor nvt activity which is not detected by a conventional envelope cross correlation method resulting in a dramatic improvement in detection capability

speculations on the petroleum geology of the accretionary body an example from the central aleutians abstract in the 300 km wide adak amlia sector of the central aleutian trench 36 000 km 3 of offscraped trench fill makes up the wedge shaped mass of the aleutian accretionary body within this wedge seismic reflection profiles reveal an abundance of potential hydrocarbon trapping structures these structures include antiforms thrust and normal faults and stratigraphic pinchouts maximum closure on these features is 2 km in addition the silt and possibly sand size sediment within the offscraped turbidite deposits and the porous diatomaceous pelagic deposits interbedded with and at the base of the wedge may define suitable reservoirs for the entrapment of hydrocarbons potential seals for these reservoirs include diagenetically altered and produced siliceous and carbonate sediment the organic carbon input into the central aleutian trench based on carbon analyses of dsdp legs 18 and 19 core samples suggests that the average organic carbon content within the accretionary body is approximately 0 3 0 6 heat flow across the aleutian terrace indicates that at present the oil generation window lies at a depth of 3 6 5 km at depths of 8 km which corresponds to the maximum depth the offscraped sediment has been seismically resolved beneath the lower trench slope the probable high 170 180 c temperatures prohibit all but gas generation the dewatering of trench sediment and subducted oceanic crust should produce an abundance of fluids circulating within the accretionary body these fluids and gases can conduct hydrocarbons to any of the abundant trapping geometries or be lost from the system through sea floor seepage in the aleutian accretionary body all the conditions necessary for the formation of oil and gas deposits exist the size and ultimate preservation of these deposits however are dependent on the deformational history of the prism both during accretion and after the accretion process has been superceded by subsequent tectonic regimes