proterozoic contraction extension tectonics of the southern sao francisco region minas gerais brazil the southern sao francisco region comprises the southern portion of the sao francisco craton which is underlain by archean basement and its fringing proterozoic orogenic belts included in this region are three geologic provinces the quadrilatero ferrifero qf the sao francisco basin and the cordilheira do espinhaco we synthesize preliminary results of ongoing structural analysis reconnaissance field studies and published reports to provide a concise review of the geology of the region and to propose a working tectonic model for its proterozoic evolution interpretation of superimposed folds faults and foliations leads to the conclusion that the southern sao francisco region records the effects of four principal tectonic events that occurred subsequent to deposition of the lower proterozoic minas supergroup the first event resulted in formation of a northwest verging fold thrust belt the second event led to development of high angle reverse faults open folds and basement uplift the third event is manifested in the qf by the formation of normal faults and by the intrusion of mafic dikes these extensional structures may be associated with formation of the sedimentary basins east and south of the sao francisco craton the final event resulted in formation of a west verging fold thrust belt that affected the qf the cordilheira espinhaco and the sao francisco basin the events that we describe can be tentatively associated with regionally recognized orogenic periods trans amazonian uruacuano brasiliano

origin of placer gold nuggets and history of formation of glacial gold placers gold creek granite county montana placer gold along the upper portions of gold creek near deer lodge montana occurs in pliocene fossil alluvial placers pleistocene till and alluvium the upper gold creek placers yielded an estimated 175 to 200 kg gold during 1890 to 1990 the gold probably originated in veins skarn or replacement deposits in paleozoic and mesozoic sedimentary units near the contact with late cretaceous granodiorite of the royal stock gold was initially concentrated in alluvial placers along the ancestral gold creek valley during late tertiary pliocene time pleistocene glaciers scoured the pliocene placers from most parts of the valley although the fossil placers were locally buried beneath till and gold was also incorporated into till that was deposited farther down valley gold from pliocene and pleistocene placers has locally been reconcentrated into alluvium as a result of postglacial stream incision the placer gold occurs as coarse sized oval to elongate grains characterized by rounded protuberances and inclusions of quartz and sulfide minerals in polished section the grains have alternating convex and concave borders interrupted by pits and embayments grain borders and interiors of embayments display supergene gold rims averaging 98 8 percent au microprobe analysis of cores indicate average compositions of 83 6 percent au and 16 5 percent ag and spectrographic data indicate a trace element signature enriched in cu pb and sb which is compatible with derivation from mesothermal plutonic lode deposits associated with the royal stock

the genesis of gold mineralisation hosted by orogenic belts a lead isotope investigation of irish gold deposits abstract lead isotope analyses have been performed on 109 gold and 23 sulphide samples from 34 irish gold occurrences including 27 placers and used to shed light on the sources of mineralising fluids and metals associated with gold mineralisation hosted by orogenic belts the pb isotope ratios of lode and placer gold range from 206pb 204pb 17 287 18 679 207pb 204pb 15 382 15 661 and 208pb 204pb 37 517 38 635 consistent with the pb isotopic data on previously reported irish sulphide mineralisation there is no evidence that gold mineralisation is associated with distinctive source regions and it appears to have been derived from similar sources to those responsible for the widespread sulphide mineralisation in ireland it is inferred that the principal controls on the au mineralisation are structural and not related to the distribution of au in their source rocks the range of pb isotope ratios favours the interaction of multiple source reservoirs predominantly during the caledonian orogeny c 475 380 ma underlying basement was the primary control on two key sources of pb gold occurrences located to the south east of the iapetus suture are characterised by pb compositions that derive predominantly from the late proterozoic crustal basement or overlying lower palaeozoic sediments whilst those located north west of the iapetus suture are characterised by less radiogenic pb signatures derived predominantly from late proterozoic or older crustal basement a third source relatively enriched in radiogenic pb also played a role in the formation of a number of irish gold occurrences and may have been associated with syn to post orogenic intrusives magmatic processes may therefore have played an important role in the formation of some orogenic gold occurrences

detailed rupture imaging of the 25 april 2015 nepal earthquake using teleseismic p waves we analyze the rupture process of the 25 april 2015 nepal earthquake with globally recorded teleseismic p waves the rupture propagated east southeast from the hypocenter for about 160 km with a duration of 55 s backprojection of both high frequency hf 0 2 to 3 hz and low frequency lf 0 05 to 0 2 hz p waves suggest a multistage rupture process from the low frequency images we resolve an initial slow downdip northward rupture near the nucleation area for the first 20 s stage 1 followed by two faster updip ruptures 20 to 40 s for stage 2 and 40 to 55 s for stage 3 which released most of the radiated energy northeast of kathmandu the centroid rupture power from lf backprojection agrees well with the global centroid moment tensor solution the spatial resolution of the backprojection images is validated by applying similar analysis to nearby aftershocks the overall rupture pattern agrees well with the aftershock distribution a multiple asperity model could explain the observed multistage rupture and aftershock distribution

styles of lode gold mineralization contributing to the placers of the indian river and black hills creek yukon territory canada as deduced from microchemical characterization of placer gold grains between 1978 and 2009 approximately 430 000 oz of placer gold were obtained from the indian river and black hills creek which equates to roughly 20 of the production for the entire yukon territory during that period the area is unglaciated exposure is poor and there are few known lode gold occurrences present the technique of microchemical characterization of placer gold grains has been applied to illuminate the style s of source mineralization and their relationship to placer gold from the klondike gold district immediately to the north a total of 2 613 placer gold grains from 22 localities were characterised in terms of the au ag cu and hg content of their alloy and associated suite of opaque mineral inclusions a combination of alloy and inclusion mineralogy was used to define gold signatures which augmented the previous classification of orogenic gold in the klondike gold type 3b 8 25 ag is the main component of the placers in lower dominion creek but is augmented and eventually replaced by type 3a gold 10 40 ag in placers in the main indian river valley probably through erosion of gold bearing veins in the valley floor type 4 gold exhibits highly variable ag which may contain hg to a maximum of 11 wt this gold type also hosts a distinctive inclusion assemblage of complex polymetallic sulphides tellurides sulfotellurides and sulfosalts and has previously been ascribed to local low sulfidation epithermal mineralization placer gold in drainages radiating from eureka dome exhibits various proportions of types 3 and 4 gold depending on location but type 3 gold forms the major component in black hills creek and northerly flowing tributaries of the indian river with the exception of eureka and montana creeks type 5 gold is found only in placers in the middle and lower indian river it is distinguished by slightly elevated 0 05 0 17 cu in the gold alloy together with low 5 9 ag contents inclusions of bi minerals cr bearing magnetite and molybdenite within type 5 gold suggest derivation from an intrusion related source candidates for such a source include undiscovered lode occurrences associated with cretaceous age intrusions to the south of the indian river or deformed cu au mo porphyry occurrences which are known to be present in the same area this analysis of placer gold has indicated that the contribution of low sulfidation epithermal gold from eureka creek to the larger placers of the indian river is minor consequently the placer gold inventory of the indian river is primarily orogenic in origin similarly the characterization of placer gold in blackhills creek strongly suggests an orogenic source this study has demonstrated for the first time that orogenic lode gold mineralization extends a considerable distance to the south of the southern klondike goldfield this information contributes to the regional models of gold mineralization in an area which is currently the focus of intensive exploration

chemical and mineralogical signatures of gold formed in oxidizing chloride hydrothermal systems and their significance within populations of placer gold grains collected during reconnaissance the close association of pd with au has been previously reported in highly oxidized chloride hydrothermal systems from several regions including australia brazil poland and the united kingdom the distinctive mineralization precipitated usually as a consequence of contact with reducing environments is characterized by au alloys containing low ag pd hg cu associated with selenides tellurides antimonides arsenides placer gold grains derived from this style of mineralization inherit these chemical and physical characteristics which are shown to be distinct from those placer grains derived from other styles of mineralization the discovery of placer gold grains of this type in areas remote from known in situ mineralization initiated the present project and provided a methodology for the study of a relatively large number of occurrences data describing alloy chemistry and mineralogy of polished sections of 957 placer grains from 19 localities in the united kingdom and 1 locality in the czech republic have augmented previously published data for 303 gold grains from 10 localities in the united kingdom six generic gold alloy types have been identified based on the relative proportions of au ag pd and hg mineralogical descriptions of similar gold alloys from localities worldwide usually conform to this classification but slight deviations are noted where p t conditions differ from those previously identified in devon alloy types may occur either as discrete grains or as phases within heterogeneous grains type 1 gold defined as 99 mass au type 2 gold au pd and type 3 gold au ag alloys with selenide inclusions are the most common compositions and occur at most localities although in different proportions type 4 gold is also an au ag alloy but contains sulfide and sulfarsenide inclusions gold alloys or intermetallics containing pd hg and or pd sb alloys type 5 and cu type 6 are found only at some localities as is a variety of type 3 gold selenide inclusions which contains hg the spatial arrangement of the main alloy types within heterogeneous gold grains shows a consistent precipitation order of type 1 type 2 and type 3 independent of locality interpretation of the chemical controls on alloy precipitation indicates that o2 controls whether type 1 or type 2 gold precipitates initially the formation of type 4 gold au ag alloys with sulfide inclusions is ascribed to a fall in o2 to around the hematite magnetite buffer where hs aq replaces cl aq as the aqueous gold complex types 3 and 5 gold commonly mantle earlier alloys and show evidence for aggressive replacement of the core this texture is interpreted as evidence for influx of a more oxidizing fluid which also accounts for the abundance of selenide and telluride mineral inclusions within this gold type this approach provides a plausible explanation of the complex heterogeneity within and between gold grains from the localities and accounts for the common sequence of alloy precipitation without invoking multiple episodes of hydrothermal activity to account for different alloys however the absence of thermodynamic data describing the au cu au ag cu and au ag pd hg systems prevents interpretation of the significance of some alloy types this study has demonstrated that gold mineralization associated with oxidizing strata is more widespread than currently appreciated the methodology described here not only permits identification of gold from this style of mineralization but allows initial evaluation of the economic potential of the source through the study of the alloy types this information may be gained at an early stage in the exploration process from gold grains collected during routine reconnaissance

sem image analysis for characterization of sand grains in thai paddy soils abstract this study presents a detailed characterization of sand grains in 34 samples of thai paddy soils mostly alfisols and ultisols that have formed from diverse parent materials computer analysis of sem images of thin sections provided a novel and reliable method to analyse the size and shape of quartz grains using the software imagej 1 34s sand grain size expressed as the feret value showed a log normal distribution for 16 samples whereas for the other samples the distribution was positively skewed a logit transformation of grain circularity values generated a normal distribution for 26 samples and eight samples had bimodal distributions these granulometric data indicate the diversity of the soil parent materials and the observed soil layers represent discrete sedimentary events with materials of different origins or different depositional energies pedogenesis including pedoturbation has not disrupted these sedimentary layers some sand grains consist of gold brass copper ilmenite zircon magnetite barite or monazite the diversity of these grains reflects the complex geology of the catchments providing the sediments and some anthropogenic materials may have been incorporated into the soils

kirchhoff image propagation seismic imaging processes are in general formulated under the assumption of a correct macrovelocity model however seismic subsurface images are very sensitive to the accuracy of the macrovelocity model this paper investigates how the output of kirchhoff inversion migration changes for perturbations of a given 3 d laterally inhomogeneous macrovelocity model the displacement of a reflector image point from a perturbation of the given velocity model is determined in a first order approximation by the corresponding traveltime and slowness perturbations as well as the matrix of the beylkin determinant the required traveltime derivatives can be calculated with ray perturbation theory using this result a new computationally efficient kirchhoff inversion migration technique is developed to predict in parallel a series of subsurface images for perturbations of a given macrovelocity model during a single inversion migration process applied to the unmigrated seismic data these images are constructed by su

complex rupture of the 13 november 2016 m w 7 8 kaikoura new zealand earthquake comparison of high frequency and low frequency observations abstract we apply a back projection analysis to determine the locations and timing of the sources of short period 0 5 to 2 s energy generated by the 13 november 2016 mw 7 8 kaikoura new zealand earthquake using data from australian and southeast asia the sources of strong short period energy are distributed northeast of the epicenter at distances of 70 to 80 km during the time period of 70 to 80 s after the initiation the locations of sources of long period energy derived from global seismic and local gps data are close to the northeastern edge of the source area and complementary to the areas of short period energy which occur in the converging region of the upper kowhal papatea and jordan thrust faults the obvious frequency dependence might be attributed to complexities in fault geometry possible rupture in the subduction interface or varying focal mechanisms during the earthquake

gold a tracer of the dynamics of tropical laterites laterites have developed essentially from long term exposure of cratonal rocks to the atmosphere and hydrosphere the properties of gold density and relative insolubility make residual gold particles tracers of surficial processes causing mineralized laterites gold particles are useful in distinguishing between in situ chemical weathering and physical transport in african lateritic systems developed on slowly eroding stable landforms in an equatorial rainforest setting chemical dissolution and translocation of fine particles are the dominant processes episodic alluvial and or colluvial transport appears to contribute to laterite formation in the subsahelian steppe the use of gold particles coupled with the examination of in situ 10 be from auriferous quartz indicates the applicability of such methods for examination of lateritic weathering dynamics of the tropical transcontinental lithosphere

using centroid time delays to characterize source durations and identify earthquakes with unique characteristics the relationship between m 0 and the rupture duration is often difficult to establish this is particularly true for large earthquakes for which the moment rate functions mrf generally have complicated shapes and the estimated durations can vary considerably depending on the methodology used to evaluate the mrf in this work we show that the centroid time delay c provides an alternative estimate of the source duration inverted mrfs often end gradually making the end of coseismic rupture difficult to detect in such cases when the rupture duration is not well defined the time delay c is a useful quantity to represent the first order temporal characteristics of the rupture process variations in stress parameter can be investigated by assuming a standard scaling relationship between the seismic moment m0m0 and c this simple scaling relationship can also be used to identify unusual earthquakes with unique source properties such as events involving complicated rupture processes or earthquakes characterized by unusual rupture velocities stress drops or aspect ratios

microstructures textures and deformation mechanisms in hematite abstract deformation and recrystallization of hematite in iron formations and high grade ore bodies of the caue formation from the quadrilatero ferrifero district minas gerais brazil resulted in several types of fabrics depending on the tectonic and metamorphic imprint the fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic mylonitic with local development of cataclastic features complete pole figures of the crystallographic planes 003 basal plane 110 prism and 104 rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types the configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore the analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active basal slip diffusion processes and anisotropic grain growth post tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation

a three stage structural evolution of the quadrilatero ferriifero consequences for the neoproterozoic age and the formation of gold concentrations of the ouro preto area minas gerais brazil abstract the quadrilatero ferrifero occurs in the southern part of the sao francisco craton brazil where three major proterozoic supracrustal units the rio das velhas minas and itacolomi supergroups are exposed together with archaean to palaeoproterozoic granito gneissic basement microtectonic and kinematic analyses have been undertaken in the area close to ouro preto in order to precise the tectonic evolution and to distinguish the tectonic features related to the transamazonian and brasiliano orogenies respectively 2000 and 600 ma three main tectonic events have been recognized the earlier event de is clearly expressed within basement rocks of the bacao complex and surrounding supracrustal units a stretching lineation le lineation roughly oriented n s can be observed numerous shear criteria such as drag folds and asymmetric pressure shadows indicate a top to the south sense of movement along the southern border of the bacao complex this event was developed within amphibolite facies conditions fact confirmed by quartz c axis fabrics this earlier deformation is related to plutonic activity and reactivation of the archaean basement expressed by the occurrence of scarce leucocratic granitoid rocks intruded within the bacao gneisses it is here attributed to the transamazonian orogeny in agreement with recent u pb dating 2000 ma the large scale folds i e mariana anticline dom bosco syncline which define the dominant structural geometry of the quadrilatero ferrifero were formed during this event the second tectonic event dm has been defined as a major thrusting towards the wnw related to the brasiliano cycle a well expressed stretching and mineral lineation oriented e w to nw se lm lineation and associated nw verging shear criteria characterize this event occurrence of muscovite biotite and more scarcely sillimanite indicate that deformation developed in upper greenschist lower amphibolite facies quartz c axis fabrics confirm the sense of shearing but the large scattering of several fabrics traduces a weak intensity of strain all supracrustal and gneiss formations were affected by the thrusting which is developed on a folded surface previously formed during the de event the third event dm is characterized by hangingwall down movement of the nappe pile in response to relaxation of the brasiliano compressional dm forces this event developed in greenschist facies is marked by the occurrence of metre scale drag folds sometimes associated to the development of a new lineation lm gold mineralization which occurs along the main mineralized contact located between the minas and rio das velhas supergroups is found within late veins which comprise large recrystallized quartz carbonate sulphide chlorite and tourmaline microscopic analysis and veins geometry allow us to conclude that the veins were emplaced mostly after the ductile dm deformation it is proposed that the veins were formed by filling of open cavities created during dm tectonics this study highlights that the northwest verging thrusting which is the main tectonic event of the quadrilatero ferrifero is only relevant of the brasiliano orogeny a model of structural evolution which involves plutonic activity at 2000 ma within the archaean bacao complex followed by neoproterozoic thrust tectonics brasiliano is proposed and discussed the age of gold concentration assumed to be achieved during the relaxation that occurred in response to the thrusting event is re interpreted and related to the late stage of the brasiliano tectonics

brittle microstructures in gold nuggets a descriptive study using backscattered electron imaging abstract gold nuggets from specular hematite rich sulphide free auriferous veins jacutinga at gongo soco an iron ore deposit in the quadrilatero ferrifero of minas gerais brazil have inclusions of palladium arseno antimonides isomertieite and mertieite ii and hematite both isomertieite and mertieite ii are commonly fractured and their fragments are displaced in relation to each other without any optically recognisable brittle failure of the host gold more rarely isomertieite has sub parallel s shaped intragranular microfractures terminating in angular edges hematite shows microfracturing and displacement as well as microgouge formation and slumping it occasionally exhibits deformation twins microcracking also occurs in gold itself goethite seals microcracks in gold with or without angular fragments of goethite crack sealing in nugget gold by hg pd enriched gold hematite kaolinite infill indicates recurrent fracturing and mineralisation although the microstructures are enigmatic two hypotheses are suggested for their formation i fluid pressure increase and its sudden seismogenic release could fracture erstwhile ductile gold ii the ductile gold transferred tectonic stresses to the harder mineral inclusions which deformed in a brittle manner

early weathering of palladium gold under lateritic conditions maquine mine minas gerais brazil since the 80 s studies have shown that au is mobile in supergene lateritic surficial conditions they are based either on petrological thermodynamic studies or experimental works in contrast few studies have been done on the mobility of the pt group elements pge moreover at the present time no study has addressed the diaerential mobility of au ag and pd from natural alloys in the supergene environment the aim of this study is to understand the supergene behavior in lateritic conditions of au ag pd alloys of the au ore locally called jacutinga at the maquinemine iron quadrangle minas gerais state brazil the field work shows that the host rock is a lake superior type banded iron formation bif and that the au mineralization originates from sulfide barren hydrothermal processes primary ag pd bearing au has developed as xenomorphous particles between hematite and quartz grains the petrological study indicates that the most weathered primary au particles with rounded shapes and pitted surfaces were found under the duricrust within the upper friable saprolite this layer however is not the most weathered part of the lateritic mantle but it is where the quartz dissolution resulting porosity is the most developed the distribution of au contents in the weathered rocks are controlled by the initial hydrothermal primary pattern no physical dispersion has been found most of the particles are residual and very weakly weathered this characterizes early stages of au particle weathering in agreement with the relatively low weathering gradient of the host itabiritic formations that leads essentially to the development of isostructural saprolite lateritic mantle limited dissolution of primary au particles issued from the friable saprolite induces pd ag depleted rims compared to primary au particle pd ag contents in addition limited very short distance in situ dissolution reprecipitation processes have been found at depth within the primary mineralization as illustrated by tiny supergene almost pure au particles the supergene mobility order pd ag au as reflecting early weathering stages of au ag pd alloys under lateritic conditions is proposed 1999 published by elsevier science ltd all rights reserved

microchemical characterisation of natural gold and artefact gold as a tool for provenancing prehistoric gold artefacts a case study in ireland the importance of au to ancient societies has encouraged many archaeologists to search for the sources exploited in antiquity these projects generally involve detailed studies of artefacts and comparison of their chemical characteristics with those reported for natural au however descriptions of natural au are frequently inadequate for provenancing studies and the compositional variability of the material is not widely recognised the present study describes a new approach to gold provenancing using the technique of microchemical characterisation in which populations of gold grains are classified according to the alloy compositions and the assemblages of microinclusions of other minerals this technique originally developed to identify sources of alluvial gold during au exploration has proved applicable to provenancing studies in four main areas firstly microchemical characterisation of artefacts grouped according to archaeological criteria can indicate the number of sources exploited in relation to time and artefact taxonomy secondly knowledge of the total variation in chemical characteristics of natural au from a particular region provides an excellent database for provenancing and reduces the need for exhaustive sampling thirdly it is possible to predict how au alloys were modified during fabrication as a consequence of assimilation of mineral inclusions finally identification of inclusion phases in artefact au can provide information on metallurgical practices these principles have been applied to the search for the source of au used for the unique traditions of prehistoric irish metalworking studies of 180 irish au artefacts belonging to four major metalworking traditions dating from the early bronze age 2400 bc to the iron age 150 bc show that each group exhibits distinctive ag and cu contents parallel studies of 2267 natural au grains from 58 alluvial localities and four bedrock localities throughout ireland reveal a broad pattern of alloy compositions consistent with style of mineralisation and host geology the ranges of ag contents of early bronze age and middle bronze age artefacts suggests that the au source lies within lower palaeozoic sedimentary rocks of the southern uplands terrane and significantly that the same source or sources were used in both periods a different source of relatively ag rich au most probably at croagh patrick co mayo was exploited in the late bronze age iron age artefacts have ag contents higher than natural irish au evidence for evolution of metallurgical practice during the bronze age is provided by the increasing cu content of the gold alloys to levels far in excess of natural gold and the nature of inclusions in artefacts of different ages elevated sn in cu rich alloys suggests deliberate or accidental alloying with bronze this approach has provided the first clear indication that only a few individual indigenous irish sources of au were used during the bronze age and that their relative importance changed over time future archaeological investigations may adopt a geographical focus that was not previously possible

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

silver isotope analysis of gold nuggets an appraisal of instrumental isotope fractionation effects and potential for high resolution tracing of placer gold abstract we describe a technique for high precision analysis of 109ag 107ag ratios in natural and archaeological gold 1 0 120 mg g ag with particular emphasis on the control of ag yield and effects of instrumental mass bias after dissolution of mg sized gold samples in aqua regia and conversion to chlorides a miniature column filled with the anion exchange resin ag 1 x8 was used for removal of au from the sample solutions in a second miniature column made of the triskem tbp resin ag was converted from the chloride to the nitrate form isotopic analyses on the mc icp ms employed the combination of pd doping and standard bracketing and considering the measurements of replicate dissolutions and chromatographic separations for srm978a and cezag reference solutions the combined analytical uncertainty 2 s of the analytical method is better than 0 016 a solution prepared from several gold nuggets was characterised isotopically cezag with 109ag 0 043 0 015 for use as a silver in gold reference material in ag isotope studies of natural and processed gold results for gold nuggets from three continents indicate a wide variation in ag concentrations 5 to 123 mg g and this is matched by an equally wide range in isotopic compositions 109ag 0 58 to 0 83 this is larger than the variation found so far in in native gold from primary deposits 0 42 to 0 5 although small isotopic effects to lower 109ag during strong ag loss are possible within a single grain most analysed nuggets are internally isotopically homogeneous this suggests preservation of the primary 109ag in the supergene environment and that gold was sourced from several distinct gold deposits in the catchment recent studies however indicate that even single primary deposits may be isotopically heterogeneous implying that ag isotope fractionation is caused by numerous deposition dissolution cycles in hydrothermal systems fine grained detrital gold from three placers along the rhine river in germany show only small differences in 109ag 0 005 0 047 to 0 124 0 007 despite being distributed along 480 km of river length this may indicate thorough mixing of gold grain populations during transport the small sample size required for ag isotope work on gold opens the way for detailed micro sampling approaches these may be used to further examine the potential for within grain isotopic variability related to fluviatile processing and can be used to correlate the composition of the placers with that of grains from primary sources

source inversion of w phase speeding up seismic tsunami warning w phase is a long period phase arriving before s wave it can be interpreted as superposition of the fundamental first second and third overtones of spheroidal modes or rayleigh waves and has a group velocity from 4 5 to 9 km s 1 over a period range of 100 1000 s the amplitude of long period waves better represents the tsunami potential of an earthquake because of the fast group velocity of w phase most of w phase energy is contained within a short time window after the arrival of the p wave at a distance of 50 w phase energy is contained within 23 min after the origin time which is the distinct advantage of using w phase for rapid tsunami warning purposes we use a time domain deconvolution method to extract w phases from the broad band records of global seismic networks the bandwidth of w phase is approximately from 0 001 to 0 01 hz and we bandpass filter the data from 0 001 to 0 005 hz in most cases having extracted w phase from the vertical component records we perform a linear inversion using a point source to determine mw and the source mechanism for several large earthquakes including the 2004 sumatra andaman earthquake the 2005 nias earthquake the 2006 kuril is earthquake and the 2007 sumatra earthquake w phase inversion yields reliable solutions and holds promise of the use of w phase for rapid assessment of tsunami potential

depth migration of imaged time sections none of the leading approaches to the migration of seismic sections the kirchhoff summation method the finite difference method or the frequency domain method readily migrates seismic reflections to their proper positions when overburden velocities vary laterally for inhomogeneous media the diffraction curve for a localized buried scatterer is no longer hyperbolic and its apex is displaced laterally from the position directly above the scatterer hubral observed that the kirchhoff summation method images seismic data at emergent image ray locations rather than at the desired positions vertically above scatterers in addition distortions in diffraction shapes lead to incorrect imaging i e incomplete diffraction collapse and hence to further displacement errors for dipping reflections the finite difference method has been believed to continue waves downward correctly through inhomogeneous media in conventional implementations however both the finite difference method and frequency domain a

the magnetic fabric of metasediments in a detachment shear zone the example of tinos island greece abstract we present a magnetic fabric study 12 sites in strongly deformed metasediments micaschists and calcschists from a well exposed detachment shear zone at tinos island cyclades greece a gradient of deformation is observed from the southwest side to the northeast side of tinos the detachment shear zone is contemporaneous with a greenschist retrogression episode ca 25 20 ma high pressure hp 45 ma metasediments are preserved in the southwest side of tinos we compared the anisotropy of magnetic susceptibility ams 158 samples to the anisotropy of isothermal remanent magnetization airm 40 samples ams is primarily dominated by phyllosilicates whilst airm reflects the contribution of mixture of ferromagnetic grains magnetite hematite goethite and pyrrhotite interestingly we observe the appearance of goethite feo oh is observed when approaching the detachment area the orientation of the ams and airm axes shows a general consistency on the other hand airm is more prolate and anisotropic than ams we document a close agreement between the ams magnetic foliation and the structural cleavage that has been measured from the core sample the magnetic lineation is generally parallel to the stretching lineation observed on the field however composite magnetic lineations suggest well preserved petrofabrics contemporaneous to the 45 ma hp episode an increase in the ams foliation anisotropy parameter is observed in micaschists when deformation increases unfortunately no quantitative estimate of finite deformation is possible using ams due to the dominant role of phyllosilicates and the complex ferromagnetic mineralogy

integrated seismic source model of the 2015 gorkha nepal earthquake we compared spatiotemporal slip rate and high frequency around 1 hz radiation distributions from teleseismic p wave data to infer the seismic rupture process of the 2015 gorkha nepal earthquake for these estimates we applied a novel waveform inversion formulation that mitigates the effect of green s functions uncertainty and a hybrid backprojection method that mitigates contamination by depth phases our model showed that the dynamic rupture front propagated eastward from the hypocenter at 3 0 km s and triggered a large slip event centered about 50 km to the east it also showed that the large slip event included a rapid rupture acceleration event and an irregular deceleration of rupture propagation before the rupture termination heterogeneity of the stress drop or fracture energy in the eastern part of the rupture area where aftershock activity was high inhibited rupture growth high frequency radiation sources tended to be in the deeper part of the large slip area which suggests that heterogeneity of the stress drop or fracture energy there may have contributed to the damage in and around kathmandu

integration of detrital gold microchemistry heavy mineral distribution and sediment geochemistry to clarify regional metallogeny in glaciated terrains application in the caledonides of southeast ireland regional exploration for rare and precious metal enrichment traditionally uses multielement geochemical analysis of the fines 150 m fraction of stream sediments however these data can be misleading in glaciated regions with complex geology here we compare the spatial distributions of data from sediment fines with distributions of heavy mineral concentrates including detrital gold in the same region gold grains are characterized according to abundance and morphology plus a microchemical signature from the combination of alloy analysis and systematic identification of mineral inclusions revealed in polished sections these inclusions survive indefinitely and are indicative of hypogene mineralogy whereas the metal loadings of fines may be affected by weathering or anthropogenic activity all three approaches are mutually supportive sediment fines analyses provide a basis for more labor intensive targeted gold grain studies which in turn highlight specific gold element associations useful for interpretation of geochemical data sets spatial distributions of resistate heavy mineral suites constrain the directions and extents of glacial transport which facilitates more confident interpretations of placer lode relationships from gold grain studies characterization of 2 160 gold grains from 40 localities in the auriferous region of southeast ireland provided a clear indication of proximity of gold to source and identified gold derived from different episodes of mineralization a distinction is apparent between gold in the south of the region wexford likely derived from widespread stratabound au as fe s mineralization and that in the north wicklow where the historical placer mining district of the goldmines river yielded gold with inclusions exhibiting a distinctive pb bi as association the goldmines river placers formed by the efficient accumulation and preservation of detrital gold derived from several discrete intravalley sources we recommend that a combination of classic stream sediment geochemistry heavy mineral analysis and gold grain studies is used more widely to provide additional insights on the location and nature of gold mineralization and regional metallogeny in regions of poor exposure and complex geology

seismogeodesy of the 2014 mw6 1 napa earthquake california rapid response and modeling of fast rupture on a dipping strike slip fault real time high rate geodetic data have been shown to be useful for rapid earthquake response systems during medium to large events the 2014 mw6 1 napa california earthquake is important because it provides an opportunity to study an event at the lower threshold of what can be detected with gps we show the results of gps only earthquake source products such as peak ground displacement magnitude scaling centroid moment tensor cmt solution and static slip inversion we also highlight the retrospective real time combination of gps and strong motion data to produce seismogeodetic waveforms that have higher precision and longer period information than gps only or seismic only measurements of ground motion we show their utility for rapid kinematic slip inversion and conclude that it would have been possible with current real time infrastructure to determine the basic features of the earthquake source we supplement the analysis with strong motion data collected close to the source to obtain an improved postevent image of the source process the model reveals unilateral fast propagation of slip to the north of the hypocenter with a delayed onset of shallow slip the source model suggests that the multiple strands of observed surface rupture are controlled by the shallow soft sediments of napa valley and do not necessarily represent the intersection of the main faulting surface and the free surface we conclude that the main dislocation plane is westward dipping and should intersect the surface to the east either where the easternmost strand of surface rupture is observed or at the location where the west napa fault has been mapped in the past

rapid earthquake rupture duration estimates from teleseismic energy rates with application to real time warning 1 we estimate the seismic rupture durations from global large earthquakes moment magnitude 7 0 by characterizing changes in the radiated p wave energy and by introducing the time averaged cumulative energy rate tacer which approximates rupture duration based on the peak first local maximum of an earthquake s high frequency energy measured at teleseismic broadband seismometers tacer is particularly useful for real time evaluations including the identification of slow rupturing tsunami earthquakes in cases of long unilateral earthquake rupture and good azimuthal station distribution the per station behavior of tacer may identify the approximate rupture direction rupture velocity and length due to directivity effects we retrospectively analyze 93 earthquakes between 2000 and 2009 and analyze another 65 earthquakes using real time observations between january 2009 and december 2012 real time and retrospective results are comparable and similar to the duration expected from other studies where duration grows as the cubed root of seismic moment

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

the application of microchemical analysis of alluvial gold grains to the understanding of complex local and regional gold mineralization a case study in the irish and scottish caledonides terranes of the appalachian caledonian orogen north of the iapetus suture host gold mineralization in north america scotland and ireland to date commercial exploitation has been confined to the appalachian terrane of canada in scotland and ireland regional analysis of the types of gold mineralization has been handicapped by the relatively small number of bedrock gold occurrences available for study however there are a large number of alluvial gold localities a technique of microchemical characterization of gold grains has been applied to facilitate the classification of alluvial gold localities in terms of the style or styles of source mineralization thereby permitting a more complete interpretation of regional gold mineralization the technique of microchemical characterization used in this study classifies populations of gold grains from each locality in terms of the assemblage of opaque mineral inclusions enclosed within the gold grains and the concentration of minor alloying elements in the gold a total of 2 400 gold grains collected from 44 sites in ireland and scotland have been studied the microchemical signatures of populations of gold grains extracted from bedrock samples correlate closely with those from adjacent alluvial populations and furthermore our data are compatible with the descriptions of the vein mineralogy of bedrock mineralization reported by other workers this result has facilitated informed speculation on the type of source mineralization of other alluvial occurrences where the bedrock source remains undiscovered populations of alluvial gold from individual localities have been grouped into larger regional data sets on the basis of similarities in microchemical signature the signatures of these data sets were analyzed using the same criteria and 10 classes of gold were identified regional analysis of the distribution of the gold classes showed that the occurrence of the four major classes correlates strongly with host terrane irrespective of geographical location gold from the southern uplands terrane is characterized by inclusions of base metal sulfides and sulfarsenides with the silver content of the gold being less than 15 percent in contrast populations of alluvial gold from the grampian and highland terranes commonly exhibit median silver contents of over 20 percent and frequently contain silver telluride and bismuth telluride inclusions which are extremely rare in gold from the southern uplands terrane however in other cases the style of mineralization is controlled by specific host or source rocks and is independent of the terrane two examples are gold mineralization within porphyry systems and gold associated with red bed sediments the study has confirmed the value of the technique of gold grain characterization using information from both concentrations of alloying elements and inclusion assemblages as a powerful tool in interpreting complex local and regional gold mineralization

the relationship between placer gold particle shape rimming and distance of fluvial transport as exemplified by gold from the klondike district yukon territory canada a semiquantitative study of various physical features of approximately 2 700 gold particles from 21 lode deposits and 36 placer deposits in the klondike district yukon territory canada was undertaken the shape parameters of roundness and flatness were determined using a classification method there appears to be a systematic variation between these parameters and between the parameters and the distance of transport of the particle these relationships were confirmed by quantitative measurements on critical samples rim characteristics were also estimated they show a systematic relationship between one another with the particle shape and less clearly with the distance of transport gold particle shape data shows a smooth well defined relationship to distance of transport from the lode source of the gold both roundness and flatness show a rapid increase within the first 5 km from the lode source and a slower more linear increase beyond this relationship seems to apply worldwide the relationship between the shape of a gold particle and the rim characteristic supports the conclusion that rims are formed by the removal of ag hg and cu and not by the precipitation of au thus rim thickness and the associated high fineness is probably the result of the dynamic process of ag removal in stagnant sediments to create the rim and abrasion in active sediments to remove the rim the composition of the rims represents the stable composition of gold in normal surficial environments together these observations place limits on the occurrence of new gold hammering is the main cause of shape change in fluvially transported gold particles its principal effect is to flatten particles abrasion has its most marked effect on surface texture hammering and abrasion both decrease the mass size and increase the roundness of the gold particles it is therefore possible to make a connection between hydraulic conditions during gold particle transport and its shape change

the isochron ray in seismic modeling and imaging the isochron the name given to a surface of equal two way time has a profound position in seismic imaging in this paper i introduce a framework for construction of isochrons for a given velocity model the basic idea is to let trajectories called isochron rays be associated with iso chrons in an way analogous to the association of conventional rays with wavefronts in the context of prestack depth migration an isochron ray based on conventional ray theory represents a simultaneous downward continuation from both source and receiver the isochron ray is a generalization of the normal ray for poststack map migration i have organized the process with systems of ordinary differential equations appearing on two levels the upper level is model independent and the lower level consists of conventional one way ray tracing an advantage of the new method is that interpolation in a ray domain using isochron rays is able to treat triplications multiarrivals accurately as opposed to interpolation in the dep

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

subevent location and rupture imaging using iterative backprojection for the 2011 tohoku mw 9 0 earthquake summary knowledge of the rupture speed and spatial temporal distribution of energy radiation of earthquakes is important for earthquake physics backprojection of teleseismic waves is commonly used to image the rupture process of large events the conventional backprojection method typically performs temporal and spatial averaging to obtain reliable rupture features we present an iterative backprojection method with subevent signal stripping to determine the distribution of subevents large energy bursts during the earthquake rupture we also relocate the subevents initially determined by iterative backprojection using the traveltime shifts from subevent waveform cross correlation which provides more accurate subevent locations and source times a bootstrap approach is used to assess the reliability of the identified subevents we apply this method to the mw 9 0 tohoku earthquake in japan using array data in the united states we identify 16 reliable subevents in the frequency band 0 2 1 hz which mostly occurred around or west of the hypocentre in the downdip region analysis of tohoku aftershocks shows that depth phases can often produce artefacts in the backprojection image but the position and timing of our main shock subevents are inconsistent with depth phase artefacts our results suggest a complicated rupture with a component of bilateral rupture along strike the dominant energy radiation between 0 2 and 1 hz is confined to a region close to the hypocentre during the first 90 s a number of subevents occurred around the hypocentre in the first 90 s suggesting a low initial rupture speed and repeated rupture or slip near thehypocentre therupturereachedthecoastalregionabout106kmnorthwestofthehypocentreat43sandtheregionabout110kmnorthofthehypocentreat105swithanorthwardrupture speed 2 0 kms 1 at 60 110 s after 110 s a series of subevents occurred about 120 220 km southwest of the hypocentre consistent wit ha3k ms 1 along strike rupture speed the abundant high frequency radiation in the downdip region close to the coast suggests intermittent rupture probably in the brittle ductile transition zone the lack of high frequency radiation in the updip region suggests the rupture near the trench was more continuous probably due to more homogeneous frictional properties of the shallow slab interface the lack of early aftershocks in the updip region indicates that most of the accumulated slip in the updip region during the interseismic period was probably released during the main shock

linking of regional and local hydrothermal systems in the mid crust by shearing and faulting abstract the concentration of mass during regional metamorphism and metallogenesis requires interactions between regional and local hydrothermal systems that are scale and time dependent during regional low to medium temperature metamorphism in which fluid flow is driven by broad thermal or mechanical gradients fluid flow rates are on average 8 m s and are limited by restricted permeabilities and gentle gradients in hydraulic head in contrast coseismic fluid flow rates in major fault zones may reach 10 2 m s as a consequence there may be a limited capacity for individual faults to substantially control fluid flow in the region because of the large contrast in flow rates and permeabilities between faults and low permeability rocks to produce a major epigenetic ore deposit in overpressured crust fluid flow systems with such diverse flow rates must interact in such a way that metal dissolution and transport from regional fluid flow systems culminate in focused fluid flow with metal deposition this is best achieved through two steps one in which km scale hydrothermal systems channel into 100 m scale ductile shear zones largely by reaction and deformation enhanced permeability in the shear zone and a second one in which rapid fluid pressure changes accompanying brittle faulting or intense shearing within the broader shear zones causes metal deposition and ore genesis

rapid determination of mw from broadband p waveforms we analyze broadband seismograms for magnitude 5 to 7 earthquakes which occurred in and around japan to develop a technique to determine moment magnitude from first arrival p waveforms we theoretically consider displacements of the p wave portion on broadband seismograph record as an approximate source time function and integrate them to obtain scalar moments at each station we show that a combination of multiple records will give a good estimation of moment magnitude without correcting for the source mechanism this technique is quite simple and robust so it will be effective for a rapid evaluation of the tsunami potential of a large earthquake

distribution characteristics and genesis of high fineness gold placers ninemile valley central western montana the high gold fineness geographic distribution and general lack of bedrock lode sources make the ninemile district of west central montana one of the most interesting gold placer localities in montana analysis of the distribution of the gold bearing gravels and the petrography and geochemistry of the gold grains leads to the conclusions that the gold is detrital of very high original purity and derived from lode deposits hosted by proterozoic age belt supergroup rocks located within the ninemile valley the limited known lode occurrences type and metamorphic grade of bedrock in the ninemile valley and gold grain characteristics are compatible with slate hosted type gold bearing quartz veins the lode deposits based upon relationships noted in the ninemile valley and elsewhere in the region were probably emplaced during laramide age felsic plutonism the gold however may ultimately have been derived from the prichard formation the basal unit of the belt supergroup which underlies the entire area and hosts gold bearing quartz veins elsewhere in the belt basin the stratigraphic interval encompassing the middle belt carbonate through the lower part of the missoula group may also have been the source for some of the vein gold we speculate that the distribution of placer deposits resulted from dextral offset of lode sources by the northwest striking ninemile fault during the tertiary this fault may have displaced the northeast half of the formerly circular to ellipically shaped lode district up to 15 km to the southeast

real time centroid moment tensor determination for large earthquakes from local and regional displacement records summary we present an algorithm to rapidly determine the moment tensor and centroid location for large earthquakes employing local and regional real time high rate displacement records from gps the algorithm extracts the coseismic offset from the displacement waveforms and uses the information to invert for the moment tensor the green s functions for a layered earth are obtained numerically from open source code edgrn to determine the centroid multiple inversions are simultaneously performed within a grid of inversion nodes and the node with the smallest misfit is then assigned the centroid location we show results for two large earthquakes replayed in simulated real time mode using recorded 1 hz gps displacements the 2003 mw 8 3 tokachi oki and the 2010 mw 7 2 el mayor cucapah earthquakes we demonstrate that it is feasible to obtain accurate cmt solutions within the first 2 3 min after rupture initiation without any prior assumptions on fault characteristics demonstrating an order of magnitude improvement in latency compared to existing seismic methods for the two earthquakes studied this methodology is useful for rapid earthquake response tsunami prediction and as a starting point for rapid finite fault modelling

texture microstructure and strength of hematite ores experimentally deformed in the temperature range 600 1100 c and at strain rates between 10 4 and 10 6 s 1 abstract polycrystalline hematite samples cored perpendicular and parallel to the foliation i e perpendicular and parallel to a weak c axis maximum respectively were deformed in triaxial compression experiments at confining pressures of 300 and 400 mpa temperatures t between 600 and 1100 c and strain rates between 10 4 and 10 6 s 1 the measured strength of hematite ranges from 890 to 67 mpa the grain size of the main starting material is up to 175 m grain boundaries are intensely serrated at t 800 c the grain boundaries become increasingly lobate and the number of r twins decreases dynamic recrystallization starts above 800 c and a foam structure with grain sizes up to 150 m develops at t 900 c neutron diffraction measurements show a distinct change of the preferred orientation texture in compression parallel to the foliation below 800 c a 300 maximum developed due to a m slip at 800 and 900 c a c axis maximum evolved probably due to c a slip the original texture is preferentially preserved but with lower densities at t 1000 c presumably caused by increasing diffusional flow processes perpendicular to the foliation only minor changes of the texture occurred the experimentally determined textures allow a better understanding of the natural preferred orientation of hematite ores the extrapolation of experimental strength data of hematite quartz and carbonates to geological conditions are compatible with field observations

pressure fluctuations phase separation and gold precipitation during seismic fracture propagation gold mineralization at croagh patrick western ireland occurs in quartz veins associated with three synchronous oblique tensile shear systems the veins evolved by progressive thickening of isolated en echelon lensoid tensile fractures that show a power law relation between their length and thickness a change in power law exponent marks the linking of the en echelon arrays by large oblique tensile veins fluid inclusion data show that gold was deposited due to unmixing of an h 2 o co 2 nacl fluid at 320 240 c and 160 30 mpa primarily due to decreases in fluid pressure evidence for phase separation is only observed in the large linking veins and is abundant close to intersections of the vein arrays these sites are where high gold grades occur the distribution of gold is believed to reflect both spatial and temporal variations in fluid pressure fluctuation during seismic fracture propagation controlled by the vein growth mechanism and zones of maximum dilation

variation in placer style gold morphology and gold particle behavior down gravel bed load rivers an example from the shotover arrow kawarau clutha river system otago new zealand gold eroded from quartz veins on the slopes of actively uplifting and physically weathering tributary catchments is transported to the fluvial system with little modification by mass movement mechanisms gold concentrates initially in the bed load component of spatially limited high grade primitive placers in moderate to high gradient incised juvenile valleys in which the rivers flow on or near bedrock interglacial and or uplift induced downcutting events and major floods periodically reconcentrate gold into lags on bedrock maximum gold particle size increases for the first few kilometers of primitive placers then decreases progressively downstream coarse gold 3 mm 0 5 g and gold with low flatness index 10 and is well rounded and commonly folded flattening progressively increases both the surface area to volume ratio and the entrainment potential of gold particles a reliable relationship between fluvial transport distance and flatness index maxima throughout the river system defines a critical flatness index above which gold is entrained and below which gold is not transported at given values of river gradient velocity and bed roughness both entrainment and retention of gold in primitive placer valleys are controlled by shape and mass characteristics that are largely inherited from the primary sources in transition and trunk placer valleys gold entrainment is controlled by flattening of particles to a critical flatness index state whereas gold retention is controlled by flatness index reduction to sub critical state by particle folding as well as input of relatively proximal locally derived primary or paleoplacer gold with subcritical flatness index or mass

lode and placer gold composition in the klondike district yukon territory canada implications for the nature and genesis of klondike placer and lode gold deposits we have determined the major and trace element composition of approximately 2 700 gold particles from 21 gold bearing mesothermal quartz veins and 35 placer gold samples from the klondike district in western yukon territory measured au ag cu and hg contents were used to define a characteristic geochemical signature or fingerprint for each of the vein samples these signatures were then compared with the various compositional populations that we have distinguished within each of the placer samples preliminary conclusions derived from the study include 1 placer gold in both recent stream deposits and in the pliocene to pleistocene white channel gravels is detrital in origin 2 the placer gold is mainly if not entirely derived from mesothermal quartz veins 3 all lode sources for the placer gold have not yet been located and 4 gold composition data can be used to identify the lode signature for placer gold and if it has not been removed by erosion help locate and link placer gold to its specific lode source

gold nugget morphology and geochemical environments of nugget formation southern new zealand abstract gold nuggets centimetre scale have formed in a supergene alteration zone on hydrothermal gold deposits and occur intergrown with quartz and iron oxyhydroxide pseudomorphs after sulphide minerals and along fractures in quartz and host rocks the supergene alteration was driven by groundwater driven water rock interaction near to a regional unconformity beneath fluvial sediments and involved clay alteration and oxidation that extended up to 50 m below the unconformity oxidation of pyrite and arsenopyrite produced temporary thiosulphate ligands that mobilised microparticulate gold encapsulated in the sulphide minerals the nuggets have some crystalline form and internally they consist of anhedral grains elongated gold plates and intimate intergrowths of gold and iron oxyhydroxide nugget surfaces have further micron scale overgrowths of microparticulate gold gold plates and gold crystals nuggets were eroded and recycled into nearby proximal miocene quartz pebble conglomerates where they concentrated in placers near the basal unconformity later recycling transferred gold into pleistocene fluvial channels gold dissolution and redeposition as plates and crystals occurred on the exterior surfaces of placer gold particles with little change in mass all groundwater maintained high ph throughout the geological history because there was sufficient calcite in the basement rocks to neutralise any acid generated by pyrite oxidation hence gold mobility in sediments was driven by thiosulphate complexes as for the in situ nuggets albeit with lower dissolved sulphur concentrations despite aridification of the climate in the late cenozoic with resulting localised high dissolved chloride concentrations chloride complexation did not contribute to gold mobility

the tectonic evolution of the quadrilatero ferrifero minas gerais brazil abstract the structural framework of the quadrilatero ferrifero is the result of two main deformational events the first is an extensional event of palaeoproterozoic age between 2 100 and 1700 ma the transamazonian event which resulted in the formation of archaean granite gneiss domes and the nucleation of regional synclines in the overlying rio das velhas and minas supergroups strata such regional synclines are continuous with each other and are bordered by structural granite gneiss highs at the contact between these units ductile brittle to ductile extensional shear zones are developed representing the dislocation surfaces of archaean blocks this tectonism is probably related to the evolution of a metamorphic core complex formed in the hinterland to the west of a transamazonian collision zone which structured the paramirim craton the second event is compressive and associated with the closure of the pan african brasiliano proto ocean 650 500 ma situated to the east of quadrilatero ferrffero qf during this event a west verging fold and thrust belt ftb developed causing inversion amplification translation and rotation of the basinal synclines the ftb affected mainly the eastern portion of qf and obliterated many of the tectonic features of the extensional event

what is a seismic reflector like the spatial region that is in the vicinity of an interface and actually affects the interface response and hence the reflected wavefield is of particular interest for the characterization of reflectors from a seismic viewpoint this region is represented by a volume of integration of medium properties above and below the interface whose maximum lateral extent corresponds to the lateral extent of the interface fresnel zone and whose maximum vertical extent is equal to a thickness we evaluate approximately for subcritical incidence angles for a plane interface as well as for curved interfaces of anticline and syncline type the maximum vertical extent might be larger than the seismic wavelengths for subcritical incidence angles close to the critical angle and for a strong impedance contrast at the interface although the part of the reflector volume lying below the interface and affecting traveltime measurements actually is smaller than described in previous studies the whole part of the reflector volume that affects the amplitude of the reflected wavefield is larger than estimates in previous studies which considered only the spatial region below the interface for a syncline respectively an anticline it is larger respectively smaller than described for a plane interface in addition to providing more physical insights into the wave reflection process this study might have significant implications for seismic interpretation using amplitude variation with angle methodologies

event oriented velocity estimation based on prestack data in time or depth domain1 a 2d reflection tomographic method is described for the purpose of estimating an improved macrovelocity field for prestack depth migration an event oriented local approach of the layer stripping type has been developed where each input event is defined by its traveltime and a traveltime derivative taken with respect to one of four coordinates in the source receiver and midpoint half offset systems recent work has shown that the results of reflection tomography may be improved by performing event picking in a prestack depth domain the authors adopt this approach and allow events to be picked either before or after prestack depth migration hence if events have been picked in a depth domain such as the common shot depth domain or the common offset depth domain then a depth time transformation is required before velocity estimation the event transformation may for example be done by conventional kinematic ray tracing and with respect to the original depth migration velocity field by this means they expect the input events for velocity updating to become less sensitive to migration velocity errors an interactive updating approach is used based on calculation of derivatives of event reflection points with respect to velocity the event reflection points are obtained by ray theoretical depth conversion andmore reflection point derivatives are calculated accurately and efficiently from information pertaining to single rays less

proterozoic crustal extension and the generation of dome and keel structure in an archaean granite greenstone terrane archaean granite greenstone terranes1 3 in which narrow belts of greenstone ultramafic and mafic volcanics and overlying sedimentary rocks occur in association with broad provinces of granite granitic igneous rocks gneiss and migmatite have long puzzled geologists because of the lack of any clear modern analogues not only is there uncertainty about how the greenstone formed in the first place4 6 but there is continuing debate about how and when the terranes developed their distinctive structural and metamorphic architecture many granite greenstone terranes display a dome and keel geometry in which belts of supracrustal volcanic and sedimentary rocks occur as structural troughs wedged between dome shaped bodies of the granite gneiss migmatite complex a metamorphic aureole typically occurs in the supracrustals adjacent to their contact with the domes and the contact itself is a shear zone here we report the results of field studies of a granite greenstone terrane in brazil showing that this architecture originated during the proterozoic more than 500 million years after extrusion of the greenstone we suggest that the thermal regime and deformation kinematics necessary to create this architecture could be generated during an episode of crustal extension when hot basement rocks were transported upwards along a transcrustal normal fault system to the base of the supracrustals

survey of 2011 tohoku earthquake tsunami inundation and run up 1 at 14 46 local time on march 11 2011 a magnitude 9 0 earthquake occurred off the coast of northeast japan this earthquake generated a tsunami that struck japan as well as various locations around the pacific ocean with the participation of researchers from throughout japan joint research groups conducted a tsunami survey along a 2000 km stretch of the japanese coast more than 5300 locations have been surveyed to date generating the largest tsunami survey dataset in the world on the sendai plain the maximum inundation height was 19 5 m and the tsunami bore propagated more than 5 km inland along the ria coast from about 50 to 200 km north of sendai the narrow bays focused the tsunami waves generating the largest inundation heights and run ups the survey data clearly show a regional dependence of tsunami characteristics

teleseismic p wave imaging of the 26 december 2004 sumatra andaman and 28 march 2005 sumatra earthquake ruptures using the hi net array 1 seismograms from a dense high quality seismic network in japan are used to investigate the characteristics of the 26 december 2004 sumatra andaman and the 28 march 2005 sumatran earthquakes the onset of the p waveforms are aligned through cross correlation and a simple concept of back projecting seismic energy to a grid of potential source locations is applied the waveform alignment removes the effects due to lateral variations in wave speed between the hypocenter and each station to better approximate the effects of three dimensional heterogeneity for paths originating from grid points away from the hypocenter cross correlation results of the p waveforms from aftershocks are introduced this additional information leads to improved resolution of smaller scale features near many of the aftershocks by reducing wavefront distortion the back projection analysis provides a quick assessment of the spatiotemporal extent and variability of relative high frequency energy release which can be translated into an estimate of the moment magnitude as well as an unparalleled view of high frequency rupture propagation the results are in general consistent with those obtained from more involved source inversion methods the 2004 sumatra andaman earthquake released most energy in a region northwest of the sumatra island and the rupture extended to the northern andaman islands about 1300 km from the epicenter this northern portion of the rupture radiated a considerable amount of energy but there is little evidence of slow slip the 2005 event is imaged to have bilateral rupture with northwestern slip occurring for about 50 s before it moved to the southeast of the epicenter

genesis of itabirite hosted au pd pt bearing hematite quartz veins quadrilatero ferrifero minas gerais brazil constraints from fluid inclusion infrared microthermometry bulk crush leach analysis and u pb systematics fluid inclusions hosted in quartz and specular hematite from auriferous jacutinga and barren veins in the quadrilatero ferrifero qf have been studied using conventional and near infrared microscopy respectively the mineralization consists of veins that cross cut metamorphosed iron formation itabirite of the paleoproterozoic itabira group the sample suite comprises hematite from veins from the low strain domain in the w and sw of the study area as well as hematite samples from the eastern high strain domain in the central and ne parts of the qf halogen ratios of fluid inclusions in quartz and hematite from all studied deposits are consistent with a fluid evolved from dissolving and reprecipitating halite that was subsequently diluted fluid inclusions hosted in quartz and hematite are characterized by consistent na k ratios and considerable so4 contents and suggest similar formation conditions and perhaps fluid origin from a common source na k and na li fluid mineral geothermometers indicate water rock interaction at approximately 340 40 c hematites from the high strain domain contain fluid inclusion assemblages of high temperature aqueous carbonic and multiphase high salinity high temperature aqueous inclusions probably due to fluid immiscibility in the system h2o nacl co2 fluid inclusions hosted in hematite from barren veins in the low strain domain as well as in hematite from jacutinga type mineralization from the central part of the qf only host multiphase aqueous fluid inclusions all showing narrow ranges of salinity 7 2 11 7 wt nacl equiv and homogenization temperatures 148 to 229 c lower homogenization temperatures and the absence of co2 rich inclusions in specular hematite from these occurrences are attributed to carbonate precipitation and or co2 escape due to cooling during fluid migration from the high to the low strain domain pb pb and u pb systematics of gold hematite and hematite hosted fluid inclusions in combination with geochemical evidence indicate distinct sources for pd au and pb the formation of specular hematite veins may be related to retrograde metamorphic fluids being released during the brazilian orogenic cycle 600 700 ma the pb isotopic characteristics of all samples are readily reconciled in a simple model that involves two different paleoproterozoic or archean source lithologies for lead and reflects contrasting depths of fluid percolation during the brasiliano orogeny

dome emplacement and formation of kilometre scale synclines in a granite greenstone terrain quadrilatero ferrifero southeastern brazil the quadrilatero ferrifero is a portion of the brazilian precambrian shield containing a granite greenstone terrain characterized by granite gneiss domes encircled by kilometre scale synclines integration of porphyroblast matrix microtextures c axis fabrics analysis and strain analysis with outcrop scale structural relationships indicates that the main phase of domes and synclines evolution occurred during the westerly directed 0 8 0 6 ga pan african brasiliano regional shortening this tectonic event has produced the single pervasive foliation observed in the folded supracrustal sequences of the quadrilatero ferrifero dip slip ductile shear zones developed at the dome supracrustal interface are synchronous with dome evolution during the pan african brasiliano deformation as indicated by contemporaneous growth of aureole porphyroblasts in the shear planes these shear zones facilitated steeply directed downward flow of country rock material around the granite gneiss domes the marked density contrast between granite gneiss material and the iron rich supracrustals provided a gravitationally favourable environment for downward wallrock flow variations in shear zone kinematics away from the domes combined with kilometer scale viscous drag contributed to produce kilometre scale synclines in the supracrustal rocks constrained between upward moving domes

the 2012 mw 8 6 sumatra earthquake evidence of westward sequential seismic ruptures associated to the reactivation of a n s ocean fabric 1 the 11 april 2012 mw 8 6 earthquake offshore sumatra is the largest of the rare great intraplate earthquakes of the instrumental era this major strike slip event occurred in the diffuse zone of deformation that accommodates differential rotation between indian and australian plates we perform a back projection analysis calibrated with well located aftershocks of short period teleseismic p waves recorded by the european array to image the rupture process during the mainshock in complement a love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio temporal extent the combined analysis reveals a complex rupture pattern characterized by three main episodes of energy release the latest being located 370 km west of the epicenter on the ninety east ridge with a delay of 120 s we interpret the 11 april 2012 mw 8 6 offshore sumatra earthquake as a complex westward propagating sequence of dynamically triggered strike slip fault ruptures associated to the reactivation of the inherited nne striking sea floor fabric the dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids

automated determination of magnitude and source length of large earthquakes using backprojection and p wave amplitudes fast estimates of magnitude and source extent of large earthquakes are fundamental for disaster mitigation however resolving these estimates within 10 20 min after origin time remains challenging here we propose a robust algorithm to resolve magnitude and source length of large earthquakes using seismic data recorded by regional arrays and global stations we estimate source length and source duration by back projecting seismic array data then the source duration and the maximum amplitude of the teleseismic p wave displacement waveforms are used jointly to estimate magnitude we apply this method to 74 shallow earthquakes that occurred within epicentral distances of 30 85 degrees to hi net 2004 2014 the estimated magnitudes are similar to moment magnitudes estimated from w phase inversions usgs with standard deviations of 0 14 0 19 depending on the global station distributions application of this method to multiple regional seismic arrays could benefit tsunami warning systems and emergency response to large global earthquakes

gold in the southwest of the iberian peninsula during the 3rd millennium bc abstract in the southwest of the iberian peninsula one of the main gold mining regions in western europe the presence of the first gold products are noted in the archaeological records of 3rd millennium bc megalithic tombs at some distance from the mining districts the lack of systematic programmes to analyse such archaeological gold finds has led them to being identified as ornamental finds of undetermined chronology linked to a simple manufacturing technology of hammering gold nuggets of an uncertain origin or from the eastern mediterranean as well as items with a purely symbolic or prestige value in the funerary practices of simple group oriented or collaborative chiefdoms but however the first documentation radiocarbon dating and systematic analysis of these products in settlement contexts has altered this interpretation the presence of gold manufactures during the third quarter of the 3rd millennium bc c 2500 2350 cal bc in the contexts of a settlement specialised in copper production such as cabezo jure in the south western mining region huelva spain and in the contexts of a huge central site such as valencina de la concepcion in the agrarian region of the lower guadalquivir basin seville spain points to the widespread social use of gold in the period of maximum expression of the inter settlement hierarchisation in the southwest of the iberian peninsula its link with the social spaces of inequality expression and their relationship with a complex production system geochemical characterization by la icp ms lead isotopes analysis by mc icp ms and metallographic study suggest two differentiated and independent supplies of raw material systems fluvial placers vs mines and local vs regional scale with at least four source areas the regional circulation of raw material or products and a manufacturing by a metallurgical technology linked to the copper production

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

estimation of multivalued arrivals in 3d models using wavefront construction part i1 a new 3d wavefield modelling approach based on dynamic ray tracing is presented this approach is called wavefront construction and it can be used in 3d models with constant or smoothly varying material properties s and p velocity and density separated by smooth interfaces wavefronts consisting of rays arranged in a triangular network are propagated stepwise through the model at each time step the differences in a number of parameters are checked between each pair of rays on the wavefront new rays are interpolated whenever this difference between pairs of rays exceeds some predefined maximum value a controlled sampling of the wavefront at all time steps is thus obtained receivers are given multiple event values by interpolation when the wavefronts pass them the strength of the wavefront construction method is that it is robust and efficient

w phase source inversion for moderate to large earthquakes 1990 2010 rapid characterization of the earthquake source and of its effects is a growing field of interest until recently it still took several hours to determine the first order attributes of a great earthquake e g m w 7 5 even in a well instrumented region the main limiting factors were data saturation the interference of different phases and the time duration and spatial extent of the source rupture to accelerate centroid moment tensor cmt determinations we have developed a source inversion algorithm based on modelling of the w phase a very long period phase 100 1000 s arriving at the same time as the p wave the purpose of this work is to finely tune and validate the algorithm for large to moderate sized earthquakes using three components of w phase ground motion at teleseismic distances to that end the point source parameters of all m w 6 5 earthquakes that occurred between 1990 and 2010 815 events are determined using federation of digital seismograph networks global seismographic network broad band stations and sts1 global virtual networks of the incorporated research institutions for seismology data management center for each event a preliminary magnitude obtained from w phase amplitudes is used to estimate the initial moment rate function half duration and to define the corner frequencies of the passband filter that will be applied to the waveforms starting from these initial parameters the seismic moment tensor is calculated using a preliminary location as a first approximation of the centroid a full cmt inversion is then conducted for centroid timing and location determination comparisons with harvard and global cmt solutions highlight the robustness of w phase cmt solutions at teleseismic distances the differences in m w rarely exceed 0 2 and the source mechanisms are very similar to one another difficulties arise when a target earthquake is shortly e g within 10 hr preceded by another large earthquake which disturbs the waveforms of the target event to deal with such difficult situations we remove the perturbation caused by earlier disturbing events by subtracting the corresponding synthetics from the data the cmt parameters for the disturbed event can then be retrieved using the residual seismograms we also explore the feasibility of obtaining source parameters of smaller earthquakes in the range 6 0 mw 6 5 results suggest that the w phase inversion can be implemented reliably for the majority of earthquakes of mw 6 or larger

microchemical studies of placer and lode gold in the klondike district yukon canada 1 evidence for a small gold rich orogenic hydrothermal system in the bonanza and eldorado creek area orogenic gold camps are commonly associated with placer deposits although in many cases the relationship between placer and lode source may be unclear placer gold deposits in bonanza and eldorado creeks in the northern klondike district goldfield yukon canada probably yielded more than 2 million ounces moz from a small geographic area but known occurrences of gold bearing orogenic style veins from which the placers were derived accounted for only a few thousand ounces the alloy chemistry and mineralogy of opaque mineral microinclusions microchemical signatures within these gold grains were compared to that of samples collected during a detailed placer gold sampling program collection of placer samples from the headwaters of watercourses in this unglaciated area allowed identification of microchemical signatures within gold populations from proximal sources which augmented information from lode gold sources to facilitate characterization of local gold mineralization a total of 1 163 gold grains from 18 lode sources and 2 777 grains from 27 placer localities within the bonanza and eldorado creek drainages were characterized in terms of the ag and hg content of the alloy together with the associated inclusion suite and two main compositional ranges along with several subtypes were identified type 1 gold is a simple au ag alloy but various subtypes have been identified on the basis of different ranges of ag and or specific inclusion assemblages type 2 gold is an au ag hg alloy composition the spatial arrangement of the gold types shows a systematic change in microchemical signature the lowest ag gold occurs in the lone star ridge area and the ag content increases both in the northeast and southwest the appearance of te bearing mineral inclusions in populations coincides with increasing ag and argentite inclusions are present only in high ag gold toward the periphery of study area type 2 gold is absent at lone star ridge and all localities to the east but is progressively more abundant in sample localities to the west the geographic distribution of gold types correlates well with placer abundance inferred from the production from previous mining activity and the study area is bounded by creeks and gulches in which there was insufficient placer gold for economic extraction we conclude that the lone star ridge area represents the epicenter of a single hydrothermal system in which spatial and temporal fluid evolution has generated compositional zonation variation in ag is ascribed to decrease in au ag aq following preferential au deposition in the center of the system controls on hg contents within au alloy are unclear but may be a consequence of mineralization temperature the complex but consistent signatures of placer gold samples from the eldorado creek drainage represents liberation of types 1 and 2 gold grains which coexist in some lode occurrences the different proportions of types 1 and 2 gold observed in placer and lode samples from west of lone star ridge reflect both temporal and spatial evolution of the hydrothermal system the main eldorado creek placers exhibit a signature most similar to lode gold from the buckland and nugget zones on lone star ridge placer gold in upper bonanza creek is distinguished by a relatively narrow ag range and the small but consistent presence of hessite in the inclusion suite no corresponding lode occurrence for this gold type has been identified to date this is the first time that the compositional signatures of major placer gold deposits derived from orogenic gold vein systems has been studied in this detail and the application of basic chemical principles to fluid evolution and electrum precipitation has allowed demarcation of an area in which extremely rich gold mineralization was formerly present while simultaneously identifying the most promising areas for further exploration for undiscovered lode gold

migrating around in circles part ii this paper proposes 1 simulating a zero offset zo section from common offset co sections of different offsets and 2 a possibility to find the best velocity to do this simulation more precisely the paper discusses the kinematic aspects of a common reflection point crp stack for an unknown velocity model

geological and geochemical controls on the silver content fineness of gold in gold silver deposits abstract a compilation of microprobe fineness data and a re evaluation of bullion production fineness data suggest that the gold fineness model of fisher 1945 can be updated and applied to a wide range of gold mineralised environments the major deposit classes are characterised by the overall average or range of deposits averages and total range of gold fineness values as follows archaean 940 780 1000 slate belt 920 800 1000 plutonic 825 650 970 porphyry 700 1000 650 1000 volcanogenic 650 850 520 870 epithermal 440 1000 0 1000 the archaean including witwatersrand slate belt and plutonic classes are characterised by a high and consistent average fineness and a narrow fineness range there is no clear subdivision within these classes according to deposit style or inferred genesis the porphyry volcanogenic and epithermal classes have a variable average deposit fineness and a wide total range of fineness values within these three classes higher fineness is typical of deposits in andesitic rather than rhyolitic volcanic settings deposits with cu au rather than cu mo or pb zn element associations and deposits with telluride or selenide minerals solubility calculations indicate that in all these environments gold and silver form the same aqueous species with agcl 2 dominating for silver and au hs 2 dominating for gold in all the environments the fluids transport an equal amount of gold and silver in the form of their bisulphide complexes therefore the observed gold fineness values can not be explained by the transporting mechanism only low silver in the ores and higher gold fineness values observed in the archaean plutonic and slate belt environments can be attributed to sulphidation as the dominant mechanism of ore deposition sulphidation of wall rocks destabilises only the bisulphide complexes of gold and silver in contrast epithermal volcanogenic and porphyry environments are characterised by a diversity of ore depositing mechanisms cooling boiling mixing which act alone or in combination and destabilise chloro and bisulphide complexes of gold and silver the high silver concentration in the ores low fineness values and large variation in the fineness values in these environments can be attributed to the complexities in the ore depositing mechanisms

imaging short period seismic radiation from the 27 february 2010 chile mw 8 8 earthquake by back projection of p pp and pkikp waves 1 teleseismic short period 0 5 5 s p waves from the 27 february 2010 chile earthquake mw 8 8 are back projected to the source region to image locations of coherent short period seismic wave radiation several receiver array configurations are analyzed using different p wave arrivals including networks of stations in north america p japan pkikp and europe pp as well as a global configuration of stations with a broad azimuthal distribution and longer period p waves 5 20 s coherent bursts of short period radiation from the source are concentrated below the chilean coastline along the downdip portion of the megathrust the short period source region expands bilaterally with significant irregularity in the radiation comparison with finite fault slip models inverted from longer period seismic waves indicates that the regions of large slip on the megathrust are located updip of the regions of short period radiation a manifestation of frequency dependent seismic radiation similar to observations for the great 2011 tohoku earthquake mw 9 0 back projection of synthetic p waves generated from the finite fault models demonstrates that if the short period energy had radiated with the same space time distribution as the long period energy back projection analysis would image it in the correct location updip we conclude that back projection imaging of short period signals provides a distinct view of the seismic source that is missed by studies based only on long period seismic waves geodetic data and or tsunami observations

trace elements in native gold by solution icp ms and their use in mineral exploration a british columbia example abstract an elegantly simple aqua regia based icp ms analytical procedure is used to compare the trace element composition of density separated alluvial native au from seven stream silt samples with three samples of geographically associated au from a prospective ore deposit in central british columbia not all of the alluvial au could have come from the ore deposit based on present drainage the silt sample au averaging four alluvial grains and totaling 12 250 g per sample generally yielded measurable concentrations for v fe cu as pd ag sb pt and bi the bedrock au samples represent the three dominant rock types in the showing their au trace element compositions largely bracket the alluvial au multidimensional scaling exploratory statistics shows that trace elements in the native au form lithophile chalcophile and siderophile groupings this indicates that a small set of geochemical processes formed all the au in one geologic environment previous work shows that au from individual deposits has distinct assemblages of detectable elements given these observations and that detectable elements are the same in both the deposit and alluvial au and that concentrations in the former bracket those of the latter it is concluded that the source of the alluvial au has probably been identified apparently neither mineral inclusions nor weathering impaired fingerprinting of the au the simplicity of the approach indicates that this is a useful exploration tool for determining the bedrock source of alluvial au the study also shows that silt sample exploration in glaciated terrains must recognize that paleo ice movement and paleo stream directions can yield geographic distributions of alluvial au that cannot be explained by present day drainage patterns thus this simple analytical exploration technique is potentially very useful to the exploration industry

rapid estimation of rupture extent for large earthquakes application to the 2004 m9 sumatra andaman mega thrust 1 rapid estimation of the rupture extent of large earthquakes is critical for tsunami warning and emergency response the hypocenter of a distant earthquake is determined from the first seismic p waves within about 15 minutes after the event however methods for determining the size and rupture extent of very large earthquakes rely on long period recordings and aftershock locations which are not available until several hours or more after the event here we introduce a method for rapid estimation of the rupture termination location for large earthquakes based on short period p wave recordings available about 30 minutes after an event the hypocenter and the rupture termination location provide estimates of the extent of rupture and the event size application to the 2004 m9 sumatra andaman earthquake gives a rupture termination location near the andaman islands about 1100 km north of the hypocenter and a rupture duration of about 8 minutes

a platform for kirchhoff data mapping in scalar models of data acquisition kirchhoff data mapping kdm is a procedure for transforming data from a given input source receiver configuration and background earth model to data corresponding to a different output source receiver configuration and background model the generalization of nmo dmo datuming and offset continuation are three examples of kdm applications this paper describes a platform for kdm for scalar wavefields the word platform indicates that no calculations are carried out in this paper that would adapt the derived formula to any one of a list of kdms that are presented in the text platform formulae are presented in 3d and in 2 5d for the latter the validity of the platform equation is verified within the constraints of high frequency asymptotics by applying it to a kirchhoff approximate representation of the upward scattered data from a single reflector and for an arbitrary source receiver configuration the kdm formalism is shown to map this kirchhoff model data in the input source receiver configuration to kirchhoff data in the output source receiver configuration with one exception the method does not map the reflection coefficient thus we verify that asymptotically the ray theoretical geometrical spreading effects due to propagation and reflection including reflector curvature are mapped by this formalism consistent with the input and output modelling parameters while the input reflection coefficient is preserved in this sense this is a true amplitude formalism as with earlier kirchhoff inversion a slight modification of the kernel of kdm provides alternative integral operators for estimating the specular reflection angle both in the input configuration and in the output configuration thereby providing a basis for amplitude versus angle analysis of the data

multistage deformation of au quartz veins laurieras french massif central evidence for late gold introduction from microstructural isotopic and fluid inclusion studies abstract the relative chronology of fluid migration quartz and au deposition in a silicified fault from the main au district laurieras st yrieix district from northern french massif central has been determined from microstructural fluid inclusion isotopic and ore mineral evidences three main stages of fluid circulation microfracturing and quartz crystallization and ore deposition were distinguished on the basis of textural relationships and the pressure temperature and composition of the palaeo fluids 1 a series of early fluid events was responsible for the localized drainage of retrograde metamorphic fluids along the main fault and the subsequent sealing by milky and microcrystalline quartz preceeded the main au ore stages early fluids were aqueous carbonic trapped under lithostatic to sublithostatic pressures at temperatures in the range 350 500 c subsequently several types of microstructures were developed in the early quartz matrix 2 ns microfractures filled by clear quartz arsenopyrite and boulangerite i contain significant refractory gold concentrations clear quartz formed from aqueous carbonic fluids of lower densities than those of the earlier fluids significant pressure drops down to pressures around 55 mpa were responsible for a local immiscibility of the aqueous carbonic fluids at temperatures of 340 20 c 3 the main ore stage is characterized by the formation of dense sets of sub vertical ew microfractures healed fluid inclusion planes in quartz and filled by ore minerals native gold galena and boulangerite ii when they crosscut earlier sulfides the fluids are aqueous with low and decreasing salinity and probable trapping temperatures around 230 c isotopic data obtained on microfissured quartz indicate these dilute aqueous fluids may be considered as meteoric waters that deeply infiltrated the crust late microfissuring of a mesothermal quartz vein originally barren only with pyrite and arsenopyrite appears to be the main factor controlling gold enrichment it can be related to late hercynian deformational stages disconnected from the early fault formation and silicification these late stages which affected the hercynian basement during its uplift are of critical importance for the formation of au ores we concluded that this type of au ore formed under rather shallow conditions is distinct from those generally described in most mesothermal au veins