analysis of teleseismic body waves radiated from the loma prieta earthquake broad band data from iris and orfeus data centers the arcess array and scp station are analyzed to infer fault plane geometry and the character of rupture during the october 17 1989 loma prieta earthquake interference of p and sp seen in the p wave forms is consistent with the 18 km source depth inferred from local observations a minimum source depth of 14 km is inferred from interpretation of the s wave arrival time relative to instrument trigger using horizontal strong motion accelerations observed at corralitos california p sp s and ss polarities and relative amplitudes are used in a comprehensive grid search to infer that oblique right lateral faulting occurred on a steeply dipping 56 60 section of the san andreas fault with an equal amount of thrust component consistent with aftershock locations a suite of point moment tensor inversions for source depths spanning the observed depth of aftershock hypocenters yields similar mechanisms the best moment tensor in terms of wave form fit and minimum non double couple component occurs for a source depth of 8 km substantially shallower than the locally inferred hypocenter seismic moment for this model is 2 3 1026 dyn cm the slow growth of the p displacement pulse with time and impulsive sp suggests a working model for fault rapture where rupture initiates at 18 km and propagates upwards and outwards along the fault the p wave forms show the effects of variations in rupture along the plane through observation of a cascade of successively larger subevents

redistribution of dynamic stress during coseismic ruptures evidence for fault interaction and earthquake triggering we investigate the spatiotemporal evolution of dynamic stress outside a rupturing extended fault the dynamic stress variations caused by a coseismic rupture in a half space are computed by using the discrete wavenumber and reflectivity methods after a transient phase the stress time history evolves to the final static stress value we compare the static stress changes resulting from this model with those computed from a static dislocation model we have applied this method to study the interactions between the first two normal faults which ruptured during the 1980 ms 6 9 irpinia earthquake these two subevents are separated in time by nearly 20 s while the third and last subevent occurred 40 s after the rupture onset we compute the dynamic stress changes caused by the rupture of the first subevent our modeling results show that the dynamic stress peak on the second subevent fault plane is reached between 7 s and 8 s after the rupture initiation on the main fault on the average the static stress level on the second subevent 20 s fault plane is reached nearly after 14 s the dynamic rupture did not jump from a rupturing segment to the adjacent one immediately but the triggering of the 20 s subevent is delayed by roughly 10 s with respect to the instant of occurrence of the dynamic stress peak induced by the 0 s event the dynamic stress pulse propagates along the strike direction of the second subevent fault plane at an average velocity of nearly 3 4 km s the delayed triggering of the second subevent can be interpreted in terms of the frictional properties of the faults in particular rate and state dependent frictional law can explain a delayed instability after a sudden change in stress using the estimated values of the subevent triggering delay and the shear stress change we attempt to constrain the parameter a on the 20 s fault the values here inferred agree well with those resulting from previous studies

dynamical fault rupture processes in heterogeneous media abstract the fault rupture processes in a horizontally layered medium and also in a three dimensionally heterogeneous structure are investigated on three dimensional spontaneous dynamic shear crack models the wave equations for three dimensional space are solved numerically by a finite difference scheme under the appropriate boundary conditions and the finite stress fracture criterion the heterogeneous properties of the elastic medium particularly the existence of low velocity zones give remarkable effects on the rupture process yielding appreciably decelerated rupture velocities and large fault displacements in and around the zones and strong motions in the near field the large fault displacements are enhanced when the rupture breaks the ground surface the static seismic moment in the case with a low velocity zone is essentially the same as in a homogeneous half space an attempt is made to simulate the rupture process of a moderate size earthquake by applying the above shear crack model in a heterogeneous medium with depth dependent and laterally heterogeneous stress drop the model appears to explain the observed features to a satisfactory degree

dynamic nucleation process of shallow earthquake faulting in a fault zone two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes low frequency and low amplitude waves following the onset of a p wave p1 are interrupted by the arrival of the second impulsive phase p2 enriched with high frequency components this observation suggests that a large shallow earthquake involves two qualitatively different stages of rupture at its nucleation we propose a theoretical model that can naturally explain the above nucleation behaviour the model is 2 d and the deformation is assumed to be anti plane a key clement in our model is the assumption of a zone in which numbers of pre existing cracks are densely distributed this cracked zone is a model for the fault zone dynamic crack growth nucleated in such a zone is intensely affected by the crack interactions which exert two conflicting effects one tends to accelerate the crack growth and the other tends to decelerate it the accelerating and decelerating effects are generally ascribable to coplanar and non coplanar crack interactions respectively we rigorously treat the multiple interactions among the cracks using the boundary integral equation method biem and assume the critical stress fracture criterion for the analysis of spontaneous crack propagation our analysis shows that a dynamic rupture nucleated in the cracked zone begins to grow slowly due to the relative predominance of non coplanar interactions this process radiates the p1 phase if the crack continues to grow coalescence with adjacent coplanar cracks occurs after a short time then coplanar interactions suddenly begin to prevail and crack growth is accelerated the p2 phase is emitted in this process it is interpreted that the two distinct phases appear in the process of the transition from non coplanar to coplanar interaction predominance

long period and broad band teleseismic body wave modeling of the october 18 1989 loma prieta earthquake inversion of long period teleseismic body waves for the loma prieta earthquake yields a nearly double couple moment tensor corresponding to an oblique mechanism with strike 130 dip 73 and rake 146 the long period centroid depth of the source is 18 km and the seismic moment is 2 8 1019 nm the source time history consists of two pulses with a total duration of 8 9 sec preliminary forward modeling of broad band teleseismic body waves indicates the occurrence of at least two sub sources constraining the fault orientation to the long period inversion result the first source was located at 18 km depth and the second source was located updip at about 14 km depth the second source has a seismic moment 2 7 times that of the first and occurred 2 0 sec after the first the precise location of the second source will require further modeling

assessing geochemical anomalies using geographically weighted lasso abstract geochemical patterns in the surficial media are complex because of the various processes involved in their formation these processes may or may not relate to mineralization therefore geochemical anomalies identified are usually subject to uncertainty geographically weighted lasso gwl was adopted in this study to model the non stationary relationships between the geological geographical features and geochemical patterns in the surficial media the sparsity and reliability of regression coefficients in the gwl modeling renders it suitable for quantifying the controls that geological geographical features have on geochemical patterns this information can improve current knowledge about the complexity of geochemical patterns a case study in which the gwl model was established between geological geographical variables and the geochemical patterns of cu observed in stream sediments in the southwestern fujian province of china was presented the following findings were obtained 1 geological features show a major control on the geochemical patterns of cu in the studied area however the geochemical patterns of cu have been modified to some extent by secondary processes resulting in the relationships between geochemical signatures and mineralization becoming more complex and uncertain and 2 the gwl modeling can provide useful information for evaluating geochemical anomalies which can help reduce the uncertainty and benefit geochemical exploration at a later stage

antiquity of aridity in the chilean atacama desert the atacama desert of northern chile and southern peru has one of the longest histories of arid conditions known although most studies have focused on the hyper aridity prevalent since the miocene all terrestrial sediments in the region from the late triassic onwards also record evaporitic and thus arid climates supergene mineralization in the region did not develop under a more humid climate conducive to deep weathering but under arid conditions these processes may have been facilitated by hydrological changes during miocene uplift and drainage incision but were operational prior to the uplift similarly global cooling and changes to oceanic circulation in the post miocene period only accentuated existing conditions a whole regolith perspective is vital to understanding the history of aridity in the atacama desert and its relevance to arid zone morphogenesis regolith formation and supergene mineralization in particular the long history of aridity raises the possibility that supergene mineralisation under the appropriate conditions form in arid environments instead of requiring humid conditions

composition of soils and ground waters at the pampa del tamarugal chile anatomy of a fossil geochemical anomaly derived from a distant porphyry copper deposit the pampa del tamarugal in northern chile is a gravel plain part of the hyperarid atacama desert soil geochemical surveys over the pampa using partial extraction analyses identified a large 100 km2 geochemical anomaly for cu subsequent analyses showed unusually high concentrations of elements that are associated with copper porphyry deposits mo as and se the soils are saline nacl and contain high concentrations of br and i which are abundant in ground waters from northern chile the anomaly lies west of one of the world s most important copper porphyry districts which includes the chuquicamata radomiro tomic and el abra deposits follow up drilling in the center of the anomaly through 300 m of piedmont gravel cover revealed barren andesitic basement rocks the soil anomalies were caused by ground water reaching the surface then evaporating both ground waters and soils share a common element assemblage with higher concentrations of mo as and se than cu the former dissolve as anions in ground water which can travel far from their source whereas dispersion of cu2 is restricted by adsorption the soil anomaly is interpreted to be a fossil anomaly preserved by the hyperarid climate to the south the anomaly is cut by an alluvial fan another nearby fan has been dated at 7 ma to the west the anomaly was eroded in the flood plain of the rio loa prior to the present 50 m deep incision of the rio loa the water table in the area of the anomaly may have been higher than the present depth of 33 to 55 m facilitating capillary rise of water to the surface we suggest that the source for the anomaly was the el abra deposit 75 km east and updrainage from the anomaly

local site effects on weak and strong ground motion abstract this is a review of the current state of the art in characterizing effects of local geology on ground motion a new horizon is clear in this aspect of strong motion studies non linear amplification at sediment sites appears to be more pervasive than seismologists used to think several recent observations about the weak motion and the strong motion suggest that the non linear amplification at sediment sites may be very common first on average the amplification is always greater at the younger sediment sites for all frequencies up to 12 hz in the case of weak motion while the relation is reversed for frequencies higher than 5 hz in the case of strong motion secondly the application of the amplification factor determined from weak motion overestimates significantly the strong motion at sediment sites observed during the loma prieta earthquake within the epicentral distance of about 50 km thirdly the variance of peak ground acceleration around the mean curve decreases with the increasing earthquake magnitude finally the above non linear effects are expected from geotechnical studies both in the magnitude of departure from the linear prediction and in the threshold acceleration level beyond which the non linearity begins

forecast model for moderate earthquakes near parkfield california earthquake instability models have possible application to earthquake forecasting because the models simulate both preseismic and coseismic changes of fault slip and ground deformation in the forecast procedure proposed here repeated measurements of preseismic fault slip and ground deformation constrain the values of model parameters the early part of the model simulation corresponds to the available field data and the subsequent part constitutes an estimate of future faulting and ground deformation in particular the time location and size of unstable faulting are estimates of the pending earthquake parameters the forecast accuracy depends on the model realism and parameter resolution the forecast procedure is applied to fault creep and trilateration data measured near parkfield california where at least five magnitude 5 5 to 6 earthquakes have occurred regularly since 1881 the last in 1966 the quasi static model consists of a flat vertical plane embedded in an elastic half space spacially variable fault slip of strike slip sense is driven by an increasing regional shear stress but is impeded by a relatively strong patch of brittle strain softening fault the field data are consistent with these approximate values of patch parameters radius of 3 km patch center 5 km deep and 8 km southeast of the 1966 epicenter and maximum brittle strength of 26 bars fluctuations in the available field data prevent estimating the earthquake time with any more precision than use of the 21 8 year recurrence interval however the model may later give a more precise estimate of the earthquake time if the fault slip rate near the inferred patch increases before the earthquake as predicted by the model

iodine rich waters involved in supergene enrichment of the mantos de la luna argentiferous copper deposit atacama desert chile recent studies have suggested the involvement of highly saline deep formation waters that modified preexisting cu assemblages to form atacamite during supergene oxidation of cu deposits in the atacama region in this report we document the occurrence of ag i inclusions hosted by supergene chalcocite from mantos de la luna an argentiferous upper jurassic stratabound cu deposit in the coastal range of northern chile the presence of this unusual mineral assemblage indicates that iodargyrite precipitated from reducing iodine rich waters suggesting that the fluids involved in supergene enrichment of cu deposits in the coastal range were more complex than previously thought this suggests the prevalence of hyperarid conditions during the latest stages of supergene enrichment of the mantos de la luna cu deposit in the atacama region supporting the notion that supergene enrichment processes in hyperarid areas are dynamic in nature and do not exclusively require the presence of meteoric water

a review of metal transfer mechanisms through transported cover with emphasis on the vadose zone within the australian regolith abstract there is a growing trend to try to make surface geochemistry effective for exploring areas of transported cover using sensitive techniques such as partial extractions of soil and gas analysis however these techniques have had mixed success in delineating buried ore bodies because the particular mechanisms and their effectiveness in transferring ore related metals upwards through transported cover are poorly understood this precludes discriminating null results a potentially ineffective technique from negative results no mineralization a review of mechanisms capable of transferring metals through barren transported cover to the surface identified those well documented and others not well studied but nonetheless promising the mechanisms are classified according to two main processes phreatic process involving groundwater flow convection dilatancy bubbles diffusion and electromigration and vadose processes involving capillary migration gaseous transport and biological transfer microbial metabolism affects the kinetics of many hydrochemical processes especially sulfide oxidation and other redox transfers and also impacts negatively and positively on the generation of gases throughout the entire cover sequence phreatic mechanisms require groundwater to transfer solutes and are most effective these have the most predictive capability where there are shallow water tables in the australian landscape groundwater occurs commonly more than 5 m below surface except in lower discharge landform sites and therefore other mechanisms biological capillary gaseous are necessary to transfer metals up from the water table thus much of the emphasis in this paper is on vadose processes an integrated approach is necessary combining different mechanisms with the nature and evolution of the transported cover and climatic settings regions and landforms of highly weathered transported cover with current or past water tables residing within the cover and long standing vegetation will favor combined mechanisms such as electrochemical plant uptake capillarity and bioturbation fresh relatively unweathered and thick 30 m transported cover may prove the most unlikely to develop surface geochemical anomalies gas e g co 2 h 2 s mechanisms may work provided that sufficient gases are generated from the oxidation of ore to produce a surface signature

atacamite in the oxide zone of copper deposits in northern chile involvement of deep formation waters atacamite a copper hydroxychloride is an important constituent of supergene oxide zones of copper deposits in northern chile whereas in similar deposits elsewhere it is rare in chile it has generally been assumed to be a primary constituent of the supergene zones there are two difficulties with this supposition the first is that atacamite requires saline water for its formation whereas supergene oxidation was caused by percolating oxygenated meteoric water mainly rainwater the second is that atacamite dissolves rapidly or undergoes phase change when exposed to fresh water supergene enrichment of copper deposits in northern chile extended over a long period 44 to 9 ma being terminated by the onset of hyperaridity during this period there was at least intermittent rainfall exposing previously formed atacamite to dissolution or phase change furthermore atacamite bearing oxide zones in several deposits are directly overlain by thick miocene alluvial gravels the stream waters that transported these gravels would have permeated the oxide zones in some deposits atacamite bearing assemblages occur both in the oxide zones and in contiguous gravels we suggest that atacamite bearing oxide assemblages are more likely to have been a replacement of preexisting oxide phases after the onset of hyperaridity at about 9 ma a hyperarid climate made possible evaporation and concentration of chloride in meteoric waters in this paper we discuss another source of saline waters to modify oxide zones dewatering of the domeyko basin expelled brines along faults some of which had earlier guided the location of porphyry deposits at the spence porphyry copper deposit saline waters which d vs 18o isotope analyses identify as basinal brines are presently rising through the deposit then flowing away along the base of the covering gravels compositions of these waters lie within the stability fields of atacamite and brochantite the two minerals that comprise the oxide zone evidence is presented for other porphyry deposits radomiro tomic and gaby sur that basinal brines may have been involved in the late formation of atacamite

u series dating of co seismic gypsum and submarine paleoseismology of active faults in northern chile 23 s abstract the convergence of the nazca and south american plates along the subduction margin of the central andes results in large subduction earthquakes and tectonic activity along major fault systems despite its relevance the paleoseismic record of this region is scarce hampering our understanding about the relationship between the andes building and earthquake occurrence in this study we used the u series disequilibrium method to obtain absolute ages of paleoearthquake events associated with normal displacements along the active mejillones and salar del carmen faults in the coastal range of the atacama desert of northern chile the 230th 234u disequilibrium ages in co seismic gypsum salts sampled along the fault traces together with marine evidences indicate that earthquakes occurred at ca 29 7 1 7 ka 11 4 ka and 2 4 0 8 ka when coupled with paleoseismic marine and radiocarbon 14c records in the nearby mejillones bay evidencing large dislocations along the mejillones fault the geochronological dataset presented here is consistent with the notion that gypsum salts formed during large earthquakes as a result of co seismic dilatancy pumping of saline waters along the major faults based on maximum observed cumulative vertical offsets in the studied faults this phenomena could have occurred episodically at a rate in the order of 1 40 to 1 50 with respect to the very large subduction earthquakes during the latest pleistocene holocene period the results presented here reveal that the u series disequilibrium method can be successfully applied to date the gypsum salts deposited along faults during seismic events and therefore directly constrain the age of large paleoearthquakes in hyperarid and seismically active zones

stable isotopic composition of soil calcite o c and gypsum s overlying cu deposits in the atacama desert chile implications for mineral exploration salt sources and paleoenvironmental reconstruction abstract soils overlying two porphyry cu deposits spence gaby sur and the pampa del tamarugal atacama desert northern chile were collected in order to investigate the extent to which saline groundwaters influence soil chemistry in regions with thick miocene and younger sediment cover soil carbonate calcite was analyzed for c and o isotopes and pedogenic gypsum for s isotopes soil calcite is present in all soils at the spence deposit but increases volumetrically above two fracture zones that cut the miocene gravels including gravels that overlie the deposit the c isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the spence deposit all 13 c vpdb values fall within a narrow range 1 40 4 23 consistent with the carbonate having formed in equilibrium with atmospheric co 2 however 18 o vpdb for carbonate over both fracture zones is statistically different from carbonate elsewhere average 18 o vpdb 0 82 vs 2 23 respectively suggesting involvement of groundwater in their formation the composition of soils at the tamarugal anomaly has been most strongly affected by earthquake related surface flooding and evaporation of groundwater 13 c vpdb values 4 28 to 2 04 are interpreted to be a mixture of dissolved inorganic c dic from groundwater and atmospheric co 2 at the spence deposit soils only rarely contain sufficient so 4 for s isotope analysis the so 4 bearing soils occur only above the fracture zones in the gravel results are uniform 3 7 4 9 34 s cdt which is near the middle of the range for so 4 in groundwater 0 9 7 3 sulfur in soils at the gaby sur deposit 3 8 6 1 34 s cdt is dominated by gypsum which primarily occurs on the flanks and tops of hills suggesting deposition from so 4 rich fogs sulfate in gaby sur deposit gypsum is possibly derived by condensation of airborne so 4 from volcanic so 2 from the nearby andes at the gaby sur deposit and tamarugal anomaly pedogenic stable isotopes cannot distinguish between s from porphyry or redeposited so 4 from interior salars the three sites studied have had different histories of salt accumulation and display variable influence of groundwater which is interpreted to have been forced to the surface during earthquakes the clear accumulation of salts associated with fractures at the spence deposit and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process the interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism

earthquake core inferred from near field observations abstract the source processes of large shallow earthquakes are investigated based on the various field phenomena and on the seismograms recorded at short focal distances the results from coseismic and postseismic field surveys in some source regions strongly show that there must be a particular region characterized by a large dislocation large acceleration and extremely low aftershock activity this specific region seems to have a relatively small dimension compared with the length of the main fault the predominant short period waves on the strong motion seismograms are concentrated within the short intervals at the initial parts of p and s waves this fact also suggests that the rupture elements generating the predominant short period waves are not distributed over the entire surface of a single main fault but are concentrated in a small region we call this confined small region in the source area earthquake core the earthquake core is formed a little later than the start of smoothing dislocation and it may be located at some distance from the starting point of rupture

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

analysis of near source static and dynamic measurements from the 1979 imperial valley earthquake gross features of the rupture mechanism of the 1979 imperial valley earthquake ml 6 6 are inferred from qualitative analysis of near source ground motion data and observed surface rupture a lower bound on the event s seismic moment of 2 5 1025 dyne cm is obtained by assuming that the average slip over the whole fault plane equals the average surface rupture 40 5 cm far field estimates of moment suggest an average slip over the fault plane of 105 cm from which a static stress drop of 11 bars is obtained an alternative slip model consistent with the far field moment has 40 5 cm of slip in the upper 5 km of the fault and 120 cm of slip in the lower 5 km this model suggests a static stress drop of 39 bars from the lower estimate of 11 bars an average strain drop of 32 strain is derived this strain drop is four times greater than the strain that could have accumulated since the 1940 el centro earthquake based on measured strain rates for the region hence a major portion of the strain released in the 1979 main shock had been accumulated prior to 1940 unusually large amplitude 500 to 600 cm sec2 vertical accelerations were recorded at stations e05 e06 e07 e08 eda of the ei centro array and the five stations of the differential array near eda although the peak acceleration of 1705 cm sec2 at e06 is probably amplified by a factor of 3 due to local site conditions these large amplitude vertical accelerations are unusual in that they are evident on only a few stations all of which are near the fault trace and at about the same epicentral range two possible explanations are considered first that they are due to a direct p wave generated from a region about 17 km north of the hypocenter or second that they are due to a pp phase that is unusually strong in the imperial valley due to the large p wave velocity gradient in the upper 5 km of the imperial valley based on the distribution of both the horizontal and vertical offsets it is likely that the rupture went beyond stations e06 and e07 during the main shock by exploiting the antisymmetry of the parallel components of particle velocity between e06 and e07 and by examining polarization diagrams of the particle velocity at e06 and e07 an average rupture velocity in the basement of 2 5 to 2 6 km sec between the hypocenter and station e06 is obtained in addition several lines of evidence suggest that the imperial fault dips about 75 to the ne

evolution of hierarchical self similar geometry of experimental fault zones implications for seismic nucleation and earthquake size 1 the geometry of fault zones and its evolutionary trend were experimentally investigated for samples of calcareous siltstone nodule through a repetitive procedure of axial loading to grow faults a little close up photographing of faults that appeared on the side surface of the samples and axial loading again irrespective of their size fault zones are composed of three or four fault segments and compression type fault jogs smaller segment jog structures are nested in larger segments forming a hierarchical fault zone structure as a whole and they show self similarities fault zones grow keeping this self similar hierarchical structure on the basis of this fault zone geometry we successfully derived the gutenberg richter s law as well as the previously known relationship of seismic nucleation sizes to seismic moments these results suggest that fundamentally any seismic rupture nucleates at a smaller jog asperity of a lower hierarchical rank and terminates eventually at a larger jog barrier of a higher rank mimicking the hierarchical fault zone geometry

composition of groundwaters associated with porphyry cu deposits atacama desert chile elemental and isotopic constraints on water sources and water rock reactions abstract groundwaters were collected around the spence porphyry copper deposit atacama desert northern chile to study water porphyry copper ore bodies interaction and test hypotheses regarding transport of metals through thick overburden leading to the formation of soil geochemical anomalies the deposit contains 400 mt of 1 cu and is completely buried by piedmont gravels of miocene age groundwaters were recovered from the eastern up hydraulic gradient upflow margin of the spence deposit from within the deposit and for two kilometers down flow from the deposit water table depths decrease from 90 m at the upflow margin to 30 m 1 5 km down flow groundwaters at the spence deposit are compositionally variable with those upflow of the deposit characterized by relatively low salinities 900 7000 mg l and na so42 type compositions these waters have compositions and stable isotope values similar to regional groundwaters recovered elsewhere in the atacama desert of northern chile in contrast groundwaters recovered within and down flow of the deposit range in salinity from 10 000 to 55 000 mg l one groundwater at 145 000 mg l and are dominantly na cl type waters dissolved sulfate values are however elevated compared to upflow waters and 34scdt decreases into the deposit from 4 to 2 consistent with increasing influence of sulfur derived from oxidation of sulfide minerals within the deposit the increase in salinity and conservative tracers cl br li and na and the relationship between oxygen and hydrogen isotopes suggests that in addition to water rock reactions within the deposit most of the compositional variation can be explained by groundwater mixing with perhaps a minor role for evaporation a groundwater mixing scenario implies a deeper more saline groundwater source mixing with the less saline regional groundwater flow system flow of deeper more saline groundwater along pre existing structures has important implications for geochemical exploration and metal transport models

airborne sar stereo restitution in a mountainous area of costa rica first results this paper presents a fully digital method for the stereo extraction of planimetric and altimetric features from digital airborne sar data in stereoscopic mode the method uses a photogrammetric approach image analysis is done with a digital stereo workstation dvp using a low cost hardware pc to test the limits of the dvp system with actual data a challenging airborne sar stereopair was used from a mountainous area 2 000 m in the cordillera centrale costa rica from the sarex 92 mission compared with a 1 50000 topographic map the first results show a planimetric accuracy of 20 35 m for well identifiable features and an altimetric accuracy of 40 50 m these results have to be confirmed with more precise digital topographic data

tem observations of particles in groundwater and their prospecting significance in the bofang copper deposit hunan china abstract groundwater is an important medium in geochemical research due to its mobility and low elemental background values currently major ion and isotopic analyses are the methods that are most commonly used to examine elemental contents this paper aims to explore nanoparticles related to deep concealed ore bodies in the bofang deposit through discussions on their classification and origins and ultimately to provide recommendations for prospecting this research takes groundwater as the main medium for tem transmission electron microscope observations all particles in deep and shallow groundwater samples contain cu zn pb as fe and other metal elements that are related to the ore body cu bearing particles which are the focus of this study comprise the following main components cu bearing particles with carriers and those without carriers these two types of particles are discussed and classified then individual particles are selected among these particles the cu bearing particles that originated from concealed ore bodies comprise the following three types 1 cu occurring with and migrated by geochemical carriers 2 cu nanoparticles physically adsorbed and migrated by fe oh 3 3 cu migrating as single cu or cu o nanoparticles these individual particles and the geological information they provide about the bofang copper deposit suggest that metals that are captured by geochemical carriers in groundwater should be analyzed analysis of these particles combined with analyses of other important prospecting geological data could reduce the cost of drilling and narrow areas of interest

atacamite formation by deep saline waters in copper deposits from the atacama desert chile evidence from fluid inclusions groundwater geochemistry tem and 36 cl data the presence of large amounts of atacamite in oxide zones from ore deposits in the atacama desert of northern chile requires saline solutions for its formation and hyperarid climate conditions for its preservation we investigated the nature and origin of atacamite forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data high resolution mineralogical observations and chlorine 36 36cl data in atacamite from the mantos blancos and spence cu deposits in both deposits the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes the average salinity of fluid inclusions in atacamite for the mantos blancos and spence deposits 7 9 and 2 3 wt nacleq respectively are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits total dissolved solids 5 9 and 1 3 wt nacleq respectively this correlation is confirmed by transmission electron microscopy observations of atacamite bearing samples revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale 36cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry cu deposits from the atacama desert all atacamite samples show very low 36cl to cl ratios 11 10 15 to 28 10 15 at at 1 comparable to previously reported 36cl to cl ratios of deep formation waters and old groundwaters in addition 36cl to cl ratios in atacamite correlate with u and th concentration in the host rocks but are independent from distance to the ocean this trend supports an interpretation of the low 36cl to cl ratios in atacamite as representing subsurface production of fissiogenic 36cl in secular equilibrium with the solutions involved in atacamite formation therefore 36cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old 1 5 ma but that atacamite formation occurred more recently 1 5 ma than suggested in previous interpretations our data provide new constraints on the origin of atacamite in cu deposits from the atacama desert and support the recent notion that the formation of atacamite in hyperarid climates such as the atacama desert is an ongoing process that has occurred intermittently since the onset of hyperaridity

summary of exploration geochemical and mineralogical studies at the giant pebble porphyry cu au mo deposit alaska implications for exploration under cover exploration geochemical and mineralogical studies by the u s geological survey at the pebble porphyry cu au mo deposit were designed to 1 determine whether the concealed deposit can be detected with surface samples 2 better understand the processes of metal migration from the deposit to the surface and 3 test existing methods for assessing concealed mineral resources and or develop new ones surface water ponds streams and springs pond and stream sediment soils subjected to various leaching techniques and glacial till samples were collected the tilted nature of the undisturbed orebody varying depth of cover and later glacial processes strongly influence the geochemical responses and processes active on the various sample media the multimedia approach aids in identifying possible processes that caused the significant geochemical variations within and among the various media these processes include the following 1 in the pebble west zone thin cover and local exposure of the orebody have facilitated the oxidation of pyrite and other sulfides and associated ferrous ferric iron reactions resulting in the local natural acidification of ponds observed in the west zone and in associated metal anomalies in waters sediments and soils 2 in contrast the east zone is concealed by both glacial deposits and underlying thick cover rocks which precludes the oxidation of sulfides in the underlying orebody low level geochemical anomalies in circumneutral spring and pond waters from the east zone are discernible only by using high resolution inductively coupled plasma mass spectrometry with lower limits of determination two and perhaps three orders of magnitude lower than traditional methods a variety of partial leaches of soils over the east zone reveal geochemical anomalies in a similar suite of elements that may be related to upwelling waters from depth along graben bounding faults 3 the indicator minerals gold jarosite and andradite in till reveal a displaced mineralogical anomaly to the west and south of the pebble orebody as ore related minerals were scraped from the orebody and deposited in till downice of the deposit geochemical anomalies in pond water and sediment over the displaced till are attributed to the ore related minerals in till this orientation study demonstrates the strong control of local geologic and geochemical settings on the effectiveness of different traditional and newer reconnaissance geochemical exploration techniques and thus has important implications for exploration

supergene enrichment of copper deposits since the onset of modern hyperaridity in the atacama desert chile supergene enrichment of cu deposits in the atacama desert has played a critical role in making this the prime cu producing province of the world previously this has been believed to have occurred exclusively over a long period from the middle eocene to the late miocene which ended when climatic conditions changed from arid to hyperarid here we report u series disequilibrium ages in atacamite bearing supergene assemblages that provide a new conceptualization on both the supergene enrichment process and the onset of extreme hyperaridity in the atacama desert 230th 234u ages of gypsum intergrown with atacamite in supergene veins from cu deposits cluster at 240 ka chuquicamata 130 ka mantos blancos spence and 80 ka mantos de la luna michilla when coupled with previous data these results indicate that supergene enrichment of cu deposits did not cease after the onset of hyperaridity we propose that supergene enrichment in the atacama region developed in two main stages the main phase caused by downward circulation of meteoric waters in a semi arid setting was active from 45 until 9 ma with a last pulse ca 5 ma in the southern atacama desert during this phase atacamite bearing supergene assemblages were not preserved because atacamite requires saline water for its formation and rapidly dissolves when contacted by meteoric water this was followed by a second stage starting at 2 1 5 ma and continuing until at least the late pleistocene when deep formation waters derived from the basement passed up through and modified the pre existing supergene cu oxide minerals atacamite has then been preserved in the prevailing hyperarid climate

exploring for deeply covered mineral deposits formation of geochemical anomalies in northern chile by earthquake induced surface flooding of mineralized groundwaters northern chile is a major producer of copper from porphyry deposits most ores worked to date were exposed near the surface exploration is now focused on deposits along a basement unconformity buried under piedmont gravels deposited by ca 10 ma two recent discoveries the spence and gaby sur deposits are covered by gravel soils above these deposits have anomalies for elements present in saline mineralized groundwaters the anomalies occur above fracture zones in the gravels believed to represent the upward propagation of basement faults that guided emplacement of the porphyries we propose that during earthquakes in this seismically active region there was pumping of saline basement waters up the faults and fracture zones entraining mineralized groundwaters from the deposits after surface flooding and evaporation elements were redistributed by infrequent rains sampling shows that surface active cations such as cu 2 1 were adsorbed and retained in the top few centimeters of soil whereas nacl and porphyry indicator elements that dissolve as anions se re and as are not adsorbed and are removed to 40 cm depth given the 10 m y interval since the gravels were deposited and the hyperarid climate of the atacama desert anomalies may have formed by repeated episodes of seismically induced flooding company geochemical surveys show that such features are numerous in northern chile producing linear zones of saline soils plus other constituents of local groundwaters e g b and i where faults controlling these features intersect mineralization elements specific to the mineralization are also present saline zones may be outlined in the field by measuring the conductivity of soil plus water slurries sampling for full geochemical analyses can be limited to areas so defined anomalies may be generated along fault lines in other seismically active wetter climates but only for elements that are adsorbed on soil minerals although the context of the study is mineral exploration the process may be relevant to the formation of geochemical features of environmental interest above major faults

using iodine isotopes to constrain supergene fluid sources in arid regions insights from the chuquicamata oxide blanket although iodine is rare in crustal settings previous studies have documented its occurrence in the supergene zones of base and precious metal ore deposits in arid environments in this report we present a novel application of the iodine 129 129i isotope tracer to iodine rich samples from the world s largest supergene cu profile at the chuquicamata deposit in northern chile where anomalous concentrations of this element have been reported all supergene marshite cui samples from chuquicamata and iodine rich soil above the mansa mina deposit have 129i i isotope ratios 190 560 10 15 that are significantly lower than those of surface waters i e 1 500 10 15 indicating that iodine was most likely derived from a reservoir of marine origin rather than a meteoric and or atmospheric source geochemical modeling shows that the long term dilution of iodinerich deep formation waters by meteoric water during the main stage of supergene alteration 40 10 ma resulted in fluid 129i i ratios that are within the range of mineral soil 129i i ratios observed at chuquicamata strongly suggesting that iodine was remobilized from the lower jurassic to mid cretaceous marine basement results from this study show that iodine isotopes can be successfully applied to trace the origin and nature of supergene fluids in iodine rich oxide blankets leach caps and soils above buried cu deposits and also to constrain the timescales of fluid circulation during supergene enrichment

the bright spot of an earthquake abstract umeda y 1992 the bright spot of an earthquake in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 13 22 field surveys in the source region for some large shallow earthquakes reveal that there is a special spot characterized by high acceleration aftershock gap and parallel faults system this spot is called an earthquake bright spot which occupies a relatively small region compared to the final rupture region at least two kinds of phases p1 and p2 which are responsible for the rupture initiation and the bright spot formation can be identified on the broad band seismograms for large earthquakes duration times of preliminary waves p1 p2 are proportional to the earthquake magnitudes by using this evidence from the field and seismograms a model having three rupture stages is proposed for a growth process of large earthquakes the 1st stage is an initiation and propagation of rupture the 2nd stage is formation of the bright spot which produces the high frequency seismic waves in the 3rd stage smooth dislocations again propagate in bi laterally and radiate the long period seismic waves

high accelerations produced by the western nagano prefecture japan earthquake of 1984 many boulders were thrown out of their former sockets by the western nagano prefecture japan earthquake of 1984 mjma 6 8 the anomalous high accelerations of 4 16 g were estimated from the displacement of thrown out boulders assuming that the seismic waves had a frequency range of 5 10 hz almost all of the thrown out boulders were found on the mountain tops ridges and saddles the topographic amplifications of seismic waves were estimated using five aftershocks recorded on the mountain top and at the foot average amplitude ratios mountain top foot of seismic waves are 2 7 in the frequency range concerned the high acceleration area defined by the distribution of thrown out boulders is very small 1 3 km compared with the length 12 km of the assumed main fault many cracks were also found in this limited small area which is characterized by extremely low activity of aftershocks and relatively large dislocation

beginnings of earthquakes in the mexican subduction zone on strong motion accelerograms abstract the guerrero mexico accelerograph network has recorded at short distances earthquakes with magnitudes from 3 0 to 8 1 in this article the initial 3 5 sec of the p waves on the vertical component are compared in addition to unfiltered accelerograms several causal bandpass filters are applied we do not see significant differences in either original or filtered records between the initial e g 0 5 sec seismograms of moderate and large earthquakes in the original and 2 to 5 hz passband the main differences among events with magnitudes over about 4 5 is in the duration of shaking the initial ground motions of all the large events have very small amplitudes which gradually get larger at lower frequencies seismograms of the largest events show a complex series of multiple pulses assumed related to failure of numerous asperities in our lowest frequency band 0 2 to 0 5 hz most of the large events that we examined begin with rupture of asperities that are not necessarily larger and are sometimes smaller than the asperities that fail during smaller events the observations are consistent with a model of faulting in which the largest asperities are located at random on the eventual fault plane and fail when the rupture front propagating from the hypocenter reaches them this allows the largest asperities to occasionally be at the hypocenter and to fail immediately but for a large fault it is more likely that they will be located elsewhere and fail later

remobilized geochemical anomalies related to deep gold zones carlin trend nevada a near vertical fracture set in miocene carlin formation tuffaceous sediments occurs approximately 800 m above a deep carlin type gold ore zone of eocene age at the ren property on the northern carlin trend nevada the fractures 0 2 to 2 cm wide are filled with brown montmorillonite clays and contain a distinctive carlin type geochemical assemblage including au as sb hg tl and s these young in situ geochemical anomalies are thought to originate from a paleogeothermal event that may have been seismically triggered by yellowstone plume bulge relaxation dynamics the passage of the plume immediately north of the carlin trend would have provided increased heat flow which coupled with crustal extension may have allowed metal charged geothermal vapor to be released from depth the hydrothermal remobilization filled dilational fractures in surficial units with vapor phase alteration clays containing the geochemical signature of the deep gold ore zone such fractures if found in other areas of northern nevada s great mineral trends may provide important exploration guidance for deep ore systems

middle miocene climatic change in the atacama desert northern chile evidence from supergene mineralization at la escondida geochronology and paleotopographic reconstruction of the porphyry copper deposit at la escondida chile are used to calculate long term erosion rates and to deduce the timing of tertiary climatic change for a portion of the atacama desert region hypogene hydrothermal alteration and protore mineralization at la escondida took place between 33 7 1 4 and 31 0 1 4 ma based on k ar dating of hydrothermal biotite and sericite supergene weathering and copper sulfide en richment processes were active from 18 0 0 7 to 14 7 0 6 ma based on k ar dating of supergene alunite distinguished from hypogene alunite by grain size color and sulfur isotopic composition reworked lenses of volcanic ash in the vicinity of la escondida provide useful time stratigraphic markers at 8 7 0 4 6 5 0 2 and 4 2 0 2 ma within present soil profiles long term average rates of erosion are determined by these age dates and quantitative calculation of eroded leached capping thickness at la escondida using mass balance analysis of geochemical profiles coupled with an estimate of unmineralized lithocap thickness based on alteration petrology and fluid inclusion geobarometry at similar deposits the observed trend of decreasing long term average erosion rates with time is consistent with arid to semiarid conditions in the early miocene changing to hyperarid conditions during the middle miocene this climatic desiccation caused termination of significant supergene copper suffide enrichment at la escondida and elsewhere in the atacama region and preservation of surficial features including the ash horizons and the leached capping middle miocene climatic desiccation in northern chile and southern peru was probably related to a pronounced decrease in temperature of coastal waters supplied by an ancestral humboldt current and an increase in upwelling intensity as the antarctic ice cap became established at approximately 15 to 13 ma the central andes cordillera which now provides a rain shadow protecting the atacama region from precipitation from the east must have attained at least half its present elevation prior to about 15 ma to have played a similar role in the middle miocene

weathering profile of the cerro de maimon vms deposit dominican republic textures mineralogy gossan evolution and mobility of gold and silver abstract cerro de maimon in the central dominican republic is currently the only vms deposit under production in the caribbean region it is hosted in the maimon formation of early cretaceous age which is part of the oldest and chemically most primitive island arc in the caribbean from bottom to top this deposit can be divided into i a primary sulfide zone ii a supergene enrichment zone and iii an oxidized zone this study reports new data on the textural and mineralogical characteristics of the oxidized zone gossan leached capping zone with emphasis in the au ag bearing phases the mineral paragenesis of the oxidized zone is essentially composed of goethite hematite quartz and barite botryoidal cellular and brecciated textures can be distinguished botryoidal and brecciated textures dominate in the upper parts of the oxidized zone whereas cellular textures are more common in the intermediate and lower parts however the weathering profile is very heterogeneous the leached capping profile shows evidence of both transported and indigenous gossans gold in the oxide paragenesis is extremely pure 99 au suggesting that chemical refining took place silver occurs mainly as iodargyrite agi and minor agbr agcl in botryoidal aggregates particles of au ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents chemical and biochemical that may exist simultaneously in the presence of halides gold and silver can be leached and transported in a wide range of ph eh conditions especially if iodine is present silver is leached more rapidly and over a broader range of ph eh conditions and is preferentially transported as iodine complexes than other halides the presence of iodargyrite in the cerro de maimon gossan fully developed under tropical conditions suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors iodargyrite occurrence would rather point to the presence of saline halide rich groundwater in oxide deposits

scaling relationship of initiations for moderate to large earthquakes 1 we investigate the initiation sizes of earthquakes over a wide range of moderate to large events using the model of sato and kanamori which is based on griffith crack theory for a circular fault we estimate the initial crack sizes of earthquakes using high quality data recorded at close hypocentral distances taking into account the local attenuation and the dynamic stress drop of the earthquakes we estimate trigger factors and initial crack radii for 35 events in japan and taiwan with magnitudes of 3 5 to 7 9 our results show that all of the earthquakes can be explained with a small trigger factor and initial crack sizes of 12 96 m for the large range of earthquake sizes this is a small range of initial crack sizes there does not appear to be a clear scaling relationship between initial crack size and final earthquake size instead our results show that all the moderate to large earthquakes initiate with initial crack radii on the order of tens of meters

geochemical challenges of diverse regolith covered terrains for mineral exploration in china abstract in recent years mineral exploration has concentrated on concealed deposits in regolith covered terrains in china the regolith covered landscapes mainly include desert windblown sand basins desert peneplains semi arid grassland loess plateaus forestry land alluvial plains and laterite terrains these diverse regolith covered areas represent geochemical challenges for mineral exploration in china this paper provides an overview of recent progress on mechanisms of metal dispersion from the buried ore deposits through the transported cover to the surface and penetrating geochemical methods to detect the anomalies case studies show that in arid and semi arid desert sand covered terrains sampling of fine fraction 120 mesh

controls on supergene enrichment of porphyry copper deposits in the central andes a review and discussion the central andes host some of the world s largest porphyry copper deposits the economic viability of these deposits is dependent on the size and quality of their supergene enrichment blanket published models that have strongly influenced exploration policy suggest that supergene enrichment ceased at 14 ma due to an increase in aridity here we discuss these models using published geochronological geomorphological and geological data geochronological data indicate that supergene oxidation and enrichment has been active between 17 and 27 s across the forearc of northern chile and southern peru from 44 to 6 ma and on the bolivian altiplano and eastern cordillera of argentina from 11 ma to present there is evidence for cessation at 20 14 and 6 ma however a major problem is that as more geochronological data become available the age ranges and periods of enrichment increase this suggests that the full spectrum of enrichment ages may not have been sampled the relationship between supergene enrichment and the age of regional pediplain surface development is not well constrained only in two areas have surfaces related to enrichment been directly dated southern peru and south of 26 s in chile and suggest formation post 14 ma sedimentological data indicate that a fluctuating arid semi arid climate prevailed across the atacama desert until between 4 and 3 ma climatic conditions that are thought to be favourable for supergene enrichment the balance between uplift erosion burial and sufficient water supply to promote enrichment is complex this suggests that a simple model for controlling supergene enrichment is unlikely to be widely applicable in northern chile general models that involve climatic desiccation at 14 ma related to rainshadow development and or the presence of an ancestral cold upwelling humboldt current are not supported by the available geological evidence the integration of disparate sedimentological geomorphological and supergene age data will be required to fully understand the controls on and distribution of supergene oxidation and enrichment in the central andes

characterization of metal bearing particles in groundwater from the weilasituo zn cu ag deposit inner mongolia china implications for mineral exploration abstract nanoparticles in groundwater have important implications for facilitating the transportation of metals in groundwater and to a certain extent can reveal the geochemical conditions of the groundwater therefore there is an increasing interest in analytical techniques that allow for in depth characterization of nanoparticles in the groundwater and utilize these characteristics for geochemical prospecting metal bearing particles in groundwater samples from deep lying orebodies referred to as deep groundwater of the weilasituo zn cu ag deposit inner mongolia china and the groundwater from motor pumped wells of a catchment basin around weilasituo were chosen to study using high angle annular dark field scanning transmission electron microscopy haadf stem and transmission electron microscopy tem coupled with energy dispersive x ray spectrometer eds individual particles were characterized based on the tem compositional and structural investigation ag pb cu zn sn as and mo bearing particles were observed in the groundwater samples collected in the deep ore and the catchment basin these metal bearing particles are compositionally and structurally similar to the ore mineral metal bearing particles observed in the ore bodies and can directly reflect the ore forming elemental characteristics e g metallogenic element assemblage and mineralization type of the weilasituo deposit the result indicates that the metal bearing particles originating from the concealed ore bodies migrate via the groundwater flow and discharge to the catchment basin this finding implies that the metal bearing particle phases have great significances in facilitating the transportation of ore related species and forming the geochemical anomalies in the groundwater this field scale study demonstrates that by applying the analytical transmission electron microscopy the nanocharacteristics of metal particles can be utilized to improve the accuracy and sensitivity for geochemical mineral exploration

chlorine isotope fractionation recorded in atacamite during supergene copper oxidation abstract in the atacama desert of northern chile large amounts of the copper hydroxy chloride mineral atacamite cu2cl oh 3 are formed in the supergene oxidation zone of cu deposits since atacamite requires saline water to form and is commonly preserved under hyperarid conditions it has been proposed as a climate sensitive mineral marker that can also provide relevant geochemical information regarding halogen in particular chlorine fluid sources during supergene cu oxidation however chlorine stable isotope data for atacamite in cu deposits are scarce and no experimental data for chlorine isotope fractionation between atacamite and water are currently available that could provide constraints on the possible mechanisms of fractionation in this study we report 37cl values of atacamite along a thick 100 m and well developed supergene enrichment profile at the barreal seco iron oxide copper gold iocg deposit in the atacama desert the 37cl values of atacamite along this profile range from 2 1 to 0 6 mean 0 4 0 7 median 0 3 and show a distinct trend with depth characterized by higher 37cl values towards the top of the profile with lower values at the bottom in addition the chlorine isotope compositions of experimentally synthetized atacamite crystals and coexisting cucl2 solutions were determined at room temperature 23 c the per mil fractionation factor 37clatacamite cl was determined at 0 75 showing that the heavy isotope 37cl is preferentially incorporated into atacamite we used numerical models to test two possible scenarios that might explain the observed 37cl profile at barreal seco a first scenario involves lowering of the water table with concomitant precipitation of atacamite which removes cl from solution following a rayleigh fractionation process this model qualitatively fits our observations but does not explain the full magnitude of the observed 37cl shift along the supergene profile in contrast a model that simulates cl diffusion following the upward injection of a deep brine that overlies fresh groundwater reproduces well the observed 37cl data suggesting that seismic pumping of basinal brines followed by cl diffusion is a feasible mechanism to explain the formation of atacamite at barreal seco these data are a first step towards interpreting 37cl profiles of atacamite in cu deposits in the atacama desert and exploring the potential use of stable chlorine isotopes to monitor cu weathering and enrichment in supergene environments

pleistocene recycling of copper at a porphyry system atacama desert chile cu isotope evidence we present cu isotope data of hypogene and supergene minerals from the late paleocene spence cu mo porphyry in the atacama desert of northern chile chalcopyrite displays a restricted range of 65cu values within the values reported for primary porphyry cu sulfides 0 28 to 0 34 n 6 supergene chalcocite samples show heavier and remarkably homogeneous 65cu values between 3 91 and 3 95 n 6 consistent with previous models of cu leaching and enrichment in porphyry systems secondary cu minerals from the oxide zone show a wider range of composition varying from 1 28 and 1 37 for chrysocolla n 6 to very light cu isotope signatures reported for atacamite between 5 72 to 6 77 n 17 these data suggest redox cycling of cu during supergene enrichment of the spence cu deposit characterized by a first stage of supergene chalcocite formation from acidic isotopically heavy leach fluids of meteoric origin down flowing in a semi arid climate 44 to 15 9 ma reworking of the initial supergene copper assemblage during the pleistocene by rising neutral and chlorine rich deep formation waters under well established hyper arid climate conditions lead to the formation of atacamite with extremely fractionated cu compositions essentially coeval chrysocolla formed by dissolution of atacamite during short episodes of wetter climatic conditions occurring in the latest pleistocene

high amplitude seismic waves radiated from the bright spot of an earthquake abstract in the source region of a large shallow earthquake there is likely to be a small spot characterized by the production of high accelerations and a gap in the aftershocks on the seismograms of most large shallow earthquakes and on some seismograms of moderate main shocks two types of p waves may be detected the relatively low amplitude waves following phase p 1 and the predominant high frequency waves following phase p 2 the duration of the seismic waves following phase p 1 the p 1 p 2 time increases proportionately with the earthquake magnitude this fact strongly suggests that the preliminary rupture period is closely related to the radiation of the predominant high frequency seismic waves to explain the above observation the shear strain waves radiated from a moving rupture are calculated because the seismic wave velocity is generally higher than the rupture propagation velocity maximum shear strains by seismic waves usually precede the rupture front if the total shear strain which is equal to the static pre earthquake shear strain plus dynamic shear strain excited by seismic waves exceeds the critical shear strain 10 4 the secondary ruptures break out in the forward direction from the initial rupture the rupture processes of large or moderate earthquakes occur in two stages one is the initiation of rupture corresponding to phase p 1 and the other is the development of secondary ruptures triggered by seismic shear strain waves the latter process generates an earthquake bright spot which radiates high amplitude seismic waves

nanoparticles in groundwater of the qujia deposit eastern china prospecting significance for deep seated ore resources abstract the characterization of nanoparticles in groundwater is recognized as an important tool that can be applied to mineral exploration in this paper we investigate the concealed orebodies of the qujia gold deposit in the jiaojia orefield of eastern china by analyzing ore related nanoparticles in groundwater using transmission electron microscopy the nanoparticles contain variable amounts of ore related elements e g ag cu zn la ce pb pt and s some of these elements are rarely found in natural settings unrelated to orebodies or mineral extraction but are strongly linked to concealed orebodies in the study area these nanoparticles which are diverse in their shapes aggregated features and degrees of crystallinity can be grouped in terms of composition as i native metal nanoparticles ii metal based nanoparticles and iii carrier nanoparticles associated with trace elements we propose that these three main types of nanoparticles enable the efficient transport of ore forming elements in groundwater the results of this study provide insights into the migratory behaviour of ore related nanoparticles in groundwater and our methods could be applied for detecting deep seated mineral deposits

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits

sources sinks and long term cycling of iodine in the hyperarid atacama continental margin abstract the atacama region in northern chile hosts the driest desert on earth and is the world s premier iodine production province the origin of iodine enrichment in atacama is controversial and fundamentally different processes have been invoked over the years that involve marine eolian and more recently deep sedimentary fluid and groundwater sources as a result of the very limited geochemical iodine data in atacama and the western south american margin the origin of iodine enrichment in this region still remains elusive in this study we present a comprehensive survey of iodine concentrations and isotopic ratios 129i i of different reservoirs in the atacama desert of northern chile including nitrate soils supergene copper deposits marine sedimentary rocks geothermal fluids groundwater and meteoric water nitrate soils along the eastern slope of the coastal cordillera are found to have mean iodine concentrations of at least three orders of magnitude higher than the mean crustal abundances of 0 12 ppm with a mean concentration of 700 ppm soils above giant copper deposits in the central depression are also highly enriched in iodine 100 s of ppm range and cu iodide and iodate minerals occur in the supergene enrichment zones of some of these deposits further east in the precordillera jurassic sedimentary shales and limestones show above background iodine concentrations the latter averaging 50 ppm in the southern portion of the study area the highest iodine concentrations in fluids were measured in groundwater below nitrate soils in the coastal range 3 5 10 ppm and in geothermal waters 1 3 ppm along the volcanic arc although highly variable the iodine isotopic ratios 129i i of jurassic marine sedimentary rocks 300 600 10 15 nitrate soils 150 1500 10 15 and waters 215 10 15 are consistently low

the role of the antofagasta calama lineament in ore deposit deformation in the andes of northern chile during the late jurassic early oligocene interval widespread hydrothermal copper mineralization events occurred in association with the geological evolution of the southern segment of the central andes giving rise to four ns trending metallogenic belts of eastward decreasing age late jurassic early cretaceous late paleocene early eocene and late eocene early oligocene the antofagasta calama lineament acl consists of an important dextral strike slip ne trending fault system deformation along the acl system is evidenced by a right lateral displacement of the late paleocene early eocene metallogenic belts furthermore clockwise rotation of the early cretaceous mantos blancos copper deposit and the late paleocene lomas bayas porphyry copper occurred in the late eocene early oligocene metallogenic belt a sigmoidal deflection and a clockwise rotation is observed in the acl the acl is thought to have controlled the emplacement of early oligocene porphyry copper deposits 34 37 ma toki genoveva quetena and opache whereas it deflected the late eocene porphyry copper belt 41 44 ma esperanza telegrafo centinela and polo sur ore deposits these observations suggest that right lateral displacement of the acl was active during the early oligocene we propose that the described structural features need to be considered in future exploration programs within this extensively gravel covered region of northern chile