a sulfur carbon oxygen and strontium isotope study of the volcanic hosted el soldado manto type copper deposit chile the essential role of bacteria and petroleum strata bound manto type copper deposits of chile are a major source of copper and some deposits e g mantos blancos el soldado contain as much metal as do large porphyry copper deposits elsewhere el soldado 200 mt 1 35 cu the largest manto type copper deposit in the coastal cordillera of central chile is hosted by the rhyodacite basalt upper member of the marine lower cretaceous lo prado formation paragenetic studies indicate that the deposit formed in two stages the first was a low temperature stage stage 1 130 125 ma in which liquid petroleum migrated from underlying carbonaceous shales into the overlying host volcanic rocks and abundant framboidal pyrite developed in a paleopetroleum reservoir a later hydrothermal stage stage 2 ca 103 ma introduced copper and replaced earlier pyrite to form chalcopyrite bornite and chalcocite ores this study presents isotopic data that support bacterial sulfur reduction as the process that formed the essential precursor stage 1 pyrite and the participation of basinal fluids in the hydrothermal second stage a wide range of 34s values for early stage 1 pyrite 11 1 to 28 0 supports the hypothesis that low temperature incomplete sulfate reduction from connate seawater sulfate and fe enriched oil field brines took place in a compartmentalized petroleum reservoir by bacterial sulfate reduction with the exception of a small proportion of cu fe sulfides with 34s values between 2 0 and 2 0 per mil the bulk of stage 2 cu fe sulfides replaced earlier pyrite and mimic the broad range in 34svalues 12 7 and 19 0 of stage 1 pyrite sulfur from early pyrite was recycled with no significant homogenization fractionation or addition of new sulfur and indicates the essential role of hydrocarbons and bacteria in the formation of the deposit the 13c values of gangue calcite vary between 4 2 and 20 2 per mil and reflect a mixing of various proportions of oxidized pyrobitumen derived organic and inorganic carbon from the mineralizing fluid pyrobitumen in the ores has 13c values of 30 to 26 per mil consistent with it being a residue of the original liquid petroleum 18o values of k feldspar in both ore and barren samples are similar 12 0 12 7 and are compatible with the fluids being of metamorphic rather than magmatic origin the similar 18o ranges of calcite 2 7 and k feldspar 0 7 suggest that they formed from the same hydrothermal fluid and that the fluid was in equilibrium with the host rocks the 87sr 86sr ratios in calcite of 0 7041 to 0 7051 reflect isotopic ratios inherited from the subaerial andesitic rocks that overlay the deposit where the ore forming fluids are thought to have originated

sulfide formation in reservoir carbonates of the devonian nisku formation alberta canada an ion microprobe study the processes affecting sulfur during diagenesis in carbonates have been investigated by ion microprobe analysis of 34s values of pyrite marcasite and anhydrite from the devonian nisku formation in the western canada sedimentary basin pyrite and marcasite from three nisku wells have 34s ranging between 35 and 20 cdt most lie between 35 and 5 cdt the 34s values of sulfides are heterogeneous within individual thin section sized samples varying by as much as 25 the 34s values increase by up to 50 with increasing well depth in two different nisku wells and 34s also increases by up to 15 as grain size increases from 40 to over 100 m in individual samples the appearance of native sulfur is accompanied by an increase of up to 30 in pyrite 34s values bulk and ion probe analyses of anhydrite are relatively uniform 34s 22 to 30 cdt the predominately low 34s values of nisku sulfides indicate bacterial sulfate reduction textural relations indicate that fe sulfide formation in nisku carbonates may have occurred by two different mechanisms much of the sulfide has 34s values that suggest that it was associated with bacterial sulfate reduction although most fe sulfides did not form until after pervasive matrix dolomitization depths of 300 1000 m other sulfide may have formed later during deep 4 km burial via thermochemical sulfate reduction the range in 34s values in a single thin section and correlations between pyrite morphology and isotopic values suggest that sulfate reduction was a very localized process and that the sulfate reduction environment varied considerably on a small scale

influence of crude oil on the genesis of the lanjiagou porphyry molybdenum deposit western liaoning province china abstract the lanjiagou porphyry molybdenum deposit in western liaoning province china is hosted in fine grained jurassic granites la icp ms zircon u pb analyses indicate that the crystallization of the ore hosting granites took place 185 0 1 8 ma mswd 1 4 molybdenum mineralization in the deposit can be divided into three stages the stockwork quartz vein stage the planar quartz vein stage and the fissure filling quartz vein stage re os isotopic ages for the molybdenite from the stockwork quartz vein type ores yielded an isochron age of 188 8 9 9 ma mswd 3 0 while six samples from the planar quartz vein type ores yielded a similar isochron age of 185 6 1 2 ma mswd 0 5 re os isotopic ages for the molybdenite identical within error to zircon u pb isotopic ages indicate that the molybdenum mineralization is related to the host intrusions apart from primary inorganic fluid inclusions ifis a large number of primary organic fluid inclusions ofis are found in the latter two stages of vein quartz and minors found in the first stage the components and characteristics of ofis in the three stages of vein quartz differ from each other which is also true for the ifis ofis in stockwork vein quartz are characterized by halite bearing inclusions and organic liquids in the inclusions are brown and do not fluoresce under ultraviolet uv light homogenization temperatures t h for the primary ifis coeval with ofis of this stage ranges from 300 c to 450 c while the salinity varies from 10 to 53 wt nacl equiv in planar vein quartz ofis are predominately two phased liquid and gas and salt daughter minerals halite are absent organic liquids are light brown to colorless and show blue fluorescence under uv light the t h range for the ifis of this stage is 250 360 c and the salinity range is 3 17 wt nacl equiv finally ofis in fissure filling vein quartz are marked by liquid gas inclusions organic liquids are generally colorless and show yellow fluorescence under uv light the t h range for the primary ifis is 180 240 c and the salinity range is 4 11 wt nacl equiv organic geochemical analyses indicate that organic matter in the lanjiagou deposit was derived from mature crude oil we suggest that large volumes of crude oil bearing non magmatic fluids were flushed into the lanjiagou porphyry hydrothermal system during all phases of ore formation and likely played important roles in mineralization

development of framboidal pyrite during diagenesis low grade regional metamorphism and hydrothermal alteration distribution patterns microstructural relationships and compositional variations for framboidal pyrite in the paleozoic sedimentary host rocks to gold deposits on the northern carlin trend nevada and at fosterville in central victoria collectively demonstrate that it is not all of synsedimentary early diagenetic origin framboidal pyrite also nucleated in hydrothermal veins formed at several kilometers depth and along dissolution surfaces stylolites and crenulation cleavages formed during metamorphism at up to anchizonal grade i e prehnitepumpellyite facies there are no obvious differences in either the size range or internal morphology of framboids formed in these various settings suggesting that a single relatively simple crystallization path may operate over a wide depth range in the upper crust at fosterville anomalously metal rich including au framboidal pyrite is most abundant adjacent to laminated shear veins that developed by slip along bedding surfaces during folding of the sedimentary host rocks microstructural relationships and pb isotope compositions for the framboidal pyrite and other similarly distributed early formed sulfides support development in response to the localized episodic influx of metal enriched h 2s bearing hydrothermal fluids during regional deformation between 440 and 400 ma these findings may have implications for other similarly deformed metasedimentary successions where the discovery of au bearing framboidal pyrite has recently been cited as evidence for significant au enrichment during sedimentation 2009 society of economic geologists inc

from rifting to active spreading in the lau basin havre trough backarc system sw pacific locking unlocking induced by seamount chain subduction associated with pacific australia plate convergence the lau basin havre trough is an active back arc basin that has been opened since 5 5 ma by rifting and southward propagating oceanic spreading current back arc opening rates decrease from 159 mm yr 1 in the northern lau basin to 15 mm y 1 in the southern havre trough major tectonic changes occur at the transition between havre trough rifting and full oceanic spreading of the eastern lau spreading center elsc where the oblique to trench westward subducting louisville seamount chain lsc sweeps southwards along the tonga trench new swath bathymetry seismic reflection data and limited rock sampling in this area constrain a tectonic and kinematic back arc model that incorporates the effects of lsc subduction the elsc which extends southward to 24 55 s forms a deep rift valley propagating southward through older rifted arc basement present day seismicity and fresh and fractured pillow lavas at 23 42 s are consistent with rift valley neovolcanism conversely the northern havre trough has low seismicity and rifted volcanic basement ridges trending 25 45 oblique to the basin axis consistent with low levels of extensional tectonism and volcanism this latter structural fabric is interpreted as an early stage of rifting that is now locked due to compression on the arc exerted by lsc subduction while in the lau basin such effects have passed as the lsc swept along the tonga trench it is proposed that the lau havre back arc opening is controlled by tectonic constraints exerted at the limits of the system by the lsc subduction which determines the southward migration of the tonga arc pole of rotation and associated lau basin opening a discrete three stage back arc opening evolution is proposed comprising 1 an initial phase of back arc rifting along the whole length of the plate boundary beginning at 6 5 ma 2 a subsequent phase mostly present in the southern part of the back arc domain and still active in the havre trough of transpression and transtension starting at 4 ma in the north as the lsc starts to subduct and sweeps southward along the tonga trench and 3 a renewed opening phase in the northern segment of the back arc domain with rifting and spreading starting at 3 5 ma as subduction of the lsc along the northern tonga trench is progressively completed

deep low frequency microearthquakes in or around seismic low velocity zones beneath active volcanoes in northeastern japan abstract precise hypocenter relocations have been made for shallow intraplate microearthquakes beneath northeastern japan by applying source region station corrections the relocated hypocenter distribution shows that most of the events are confined to the upper 15 km of the crust which forms the brittle seismogenic zone in this volcanic arc it also shows that exceptionally deep microearthquakes well below the base of the seismic aseismic boundary occur at twelve locations of northeastern japan they occur in the lowermost crust or in the uppermost mantle where rheological properties of rocks are presumed to be in the ductile regime all the 153 events presently detected in the lowermost crust or in the uppermost mantle have anomalously low predominant frequencies 1 5 5 hz both for p and s waves in contrast to those 8 20 hz of normal shallow events in the brittle seismogenic zone the magnitudes of these events are small m 2 2 moreover all of these events are located beneath active volcanoes and or near p wave low velocity zones in the uppermost mantle the proximity of these events to the active volcanoes and other anomalous features suggest that these deep low frequency events are generated by magmatic activity of mantle diapirs in the uppermost mantle

the middle permian hongshanliang manto type copper deposit in the east tianshan constraints from geology geochronology fluid inclusions and h o s isotopes abstract the hongshanliang copper deposit hosted in the tuff of the lower carboniferous yamansu formation is a typical copper deposit in the aqishan yamansu belt east tianshan based on crosscutting relationships of veins textural relationships and mineral assemblages five alteration mineralization stages at hongshanliang have been established chlorite sulfide stage stage i quartz pyrite stage stage ii quartz polymetallic sulfide stage stage iii late veins stage iv and supergene process stage v stage i has mineral assemblage of chlorite pyrite chalcopyrite quartz sericite and is commonly characterized by euhedral pyrite with silicates e g chlorite quartz and sericite and or chalcopyrite as its pressure shadow indicating an early mineralization event with apparent deformation stage ii is characterized by quartz pyrite chalcopyrite or locally quartz gypsum anhydrite pyrite veins cutting stage i chlorite pyrite the main mineralization stage stage iii at hongshanliang has typical mineral assemblages of quartz chalcopyrite chlorite calcite sericite quartz chalcopyrite sphalerite galena pyrite and quartz sphalerite galena chlorite with veins veinlets disseminations and local massive ore types similar to manto type copper deposits regarding mineralization and ore structures detailed fluid inclusion study shows temperature of fluids decreased from stage ii 307 484 c through stage iii peak at 160 180 c consistent with quartz chlorite oxygen isotope geothermometer of 190 c to stage iv 129 169 c with corresponding salinities of 2 7 26 2 wt nacl equiv peak at 8 wt 2 1 12 3 wt nacl equiv peak at 8 wt and 0 5 7 7 wt nacl equiv peaks at 4 6 wt respectively indicating an evolved hydrothermal ore forming system such fluid evolution can also be supported by h o isotopes during water rock reaction from stage ii 18ofluid 6 3 8 3 and dfluid 77 to 64 through stage iii 18ofluid 1 7 to 7 0 and dfluid 82 to 58 to stage iv 18ofluid 2 5 to 2 1 and dfluid 77 to 73 with a magmatic hydrothermal origin furthermore sulfur isotopes suggest that fluids of the two mineralization stages stage i and iii are predominantly magmatic hydrothermal with other influx contribution into the ore forming system i e minor early carboniferous seawater in stage i 34sfluid varying from 3 5 to 6 1 with peak at 0 and minor organic materials in stage iii 34sfluid varying from 6 5 to 4 1 with peak at 0 1 and detection of ch4 and c2h6 from fluid inclusions in combination of alteration paragenesis nature and source of ore forming fluids and comparison with other typical deposits we proposed that the hongshanliang copper deposit underwent two mineralization events with the main mineralization similar to manto type copper deposits 40ar 39ar dating of sericite from a massive chalcopyrite ore indicates the hongshanliang main mineralization formed at 269 0 0 4 ma generally coeval with regional k feldspar granite emplacement ca 272 ma integrating the regional tectonic setting magmatism and metallogenesis of the aqishan yamansu belt and the east tianshan we suggest that the aqishan yamansu belt has potential of mineral prospecting for the middle permian manto type copper deposits

association of pyrobitumen with copper mineralization from the uchumi and talcuna districts central chile abstract pyrobitumen has been shown to be an essential component in formation of some chilean manto type strata bound copper deposits and its presence has been observed in a number of other deposits but has received limited investigation in this paper we present paragenetic and geochemical data from two central chilean manto type deposits from the uchumi and talcuna districts where solid pyrobitumen residual petroleum is intimately associated with copper sulfides pyrobitumen in the uchumi deposit occurs in pore space within the host conglomerates and is adjacent to a granitoid stock pyrobitumen predates bornite chalcocite mineralization and may have reduced subsequent mineralizing fluids pyrobitumen from the manto delirio deposit talcuna district fills the cores of early sphalerite veins and was partially replaced by later cu as mineralization pyrobitumen is petrographically intergrown with cu fe sulfides and light 13c values of gangue calcite indicates the interaction of pyrobitumen with the mineralizing fluid the presence of pyrobitumen within the ores of other manto type copper deposits in the lower cretaceous basin of chile suggests that degraded petroleum reservoirs in particular if biodegradation generated authigenic pyrite can be important controls for metallic mineralization derived from hydrothermal solutions of different sources

oxygen isotopic compositions of central andean plutonic and volcanic rocks latitudes 26 29 south abstract oxygen isotope data are reported for 27 igneous rocks of mesozoic to quaternary age from the central andes 26 29 s the plutonic rocks and most of the volcanics have 18 o values between 6 2 and 8 3 the whole rock 18 o values show a weak correlation with initial 87 sr 86 sr data this o sr array differs from documented trends for calc alkaline plutonic suites from california scotland and northern italy but overlaps with data for volcanic and plutonic rocks from ecuador northern chile and southern peru the oxygen isotope results indicate that the magmas evolved without significant contamination from supracrustal rocks e g rocks that experienced 18 o enrichment during surficial weathering the available o sr and pb isotopic data for these rocks are best explained by magma generation in the upper mantle or lower crust from the late mesozoic on the 87 sr 86 sr values were modified at depth by isotopic exchange between the magma and a continually thickening crust of plutonic rocks of late precambrian to early mesozoic age

hydrocarbon and ore bearing basinal fluids a possible link between gold mineralization and hydrocarbon accumulation in the youjiang basin south china the youjiang basin which flanks the southwest edge of the yangtze craton in south china contains many carlin type gold deposits and abundant paleo oil reservoirs the gold deposits and paleo oil reservoirs are restricted to the same tectonic units commonly at the basinal margins and within the intrabasinal isolated platforms and or bioherms the gold deposits are hosted by permian to triassic carbonate and siliciclastic rocks that typically contain high contents of organic carbon paragenetic relationships indicate that most of the deposits exhibit an early stage of barren quartz pyrite stage i a main stage of auriferous quartz arsenian pyrite arsenopyrite marcasite stage ii and a late stage of quartz calcite realgar orpiment native arsenic stibnite cinnabar dolomite stage iii bitumen in the gold deposits is commonly present as a migrated hydrocarbon product in mineralized host rocks particularly close to high grade ores but is absent in barren sedimentary rocks bitumen dispersed in the mineralized rocks is closely associated and or intergrown with the main stage jasperoidal quartz arsenian pyrite and arsenopyrite bitumen occurring in hydrothermal veins and veinlets is paragenetically associated with stages ii and iii mineral assemblages these observations suggest an intimate relationship between bitumen precipitation and gold mineralization in the paleo petroleum reservoirs that typically occur in permian reef limestones bitumen is most commonly observed in open spaces either alone or associated with calcite where bitumen occurs with calcite it is typically concentrated along pore vein centers as well as along the wall of pores and fractures indicating approximately coeval precipitation in the gold deposits aqueous fluid inclusions are dominant in the early stage barren quartz veins stage i with a homogenization temperature range typically of 230 c to 270 c and a salinity range of 2 6 to 7 2 wt nacl eq fluid inclusions in the main and late stage quartz and calcite are dominated by aqueous inclusions as well as hydrocarbon and co2 rich inclusions the presence of abundant hydrocarbon fluid inclusions in the gold deposits provides evidence that at least during main periods of the hydrothermal activity responsible for gold mineralization the ore fluids consisted of an aqueous solution and an immiscible hydrocarbon phase aqueous inclusions in the main stage quartz associated with gold mineralization stage ii typically have a homogenization temperature range of 200 230 c and a modal salinity around 5 3 wt nacl eq homogenization temperatures and salinities of aqueous inclusions in the late stage drusy quartz and calcite stage iii typically range from 120 c to 160 c and from 2 0 to 5 6 wt nacl eq respectively in the paleo oil reservoirs aqueous fluid inclusions with an average homogenization temperature of 80 c are dominant in early diagenetic calcite fluid inclusions in late diagenetic pore and fissure filling calcite associated with bitumen are dominated by liquid c2h6 vapor ch4 ch4 h2o and aqueous inclusions with a typical homogenization temperature range of 90 c to 180 c and a salinity range of 2 8 wt nacl eq it is suggested that the hydrocarbons may have been trapped at relatively low temperatures while the formation of gold deposits could have occurred under a wider and higher range of temperatures the timing of gold mineralization in the youjiang basin is still in dispute and a wide range of ages has been reported for individual deposits among the limited isotopic data the rb sr date of 206 12 ma for au bearing hydrothermal sericite at jinya as well as the re os date of 193 13 ma on auriferous arsenian pyrite and 40ar 39ar date of 194 6 2 ma on vein filling sericite at lannigou may provide the most reliable age constraints on gold mineralization this age range is comparable with the estimated petroleum charging age range of 238 185 ma and the sm nd date of 182 21 ma for the pore and fissure filling calcite associated with bitumen at the shitouzhai paleo oil reservoir corresponding to the late indosinian to early yanshanian orogenies in south china the close association of carlin type gold deposits and paleo oil reservoirs the paragenetic coexistence of bitumens with ore stage minerals the presence of abundant hydrocarbons in the ore fluids and the temporal coincidence of gold mineralization and hydrocarbon accumulation all support a coeval model in which the gold originated migrated and precipitated along with the hydrocarbons in an immiscible gold and hydrocarbon bearing basinal fluid system

deep earthquakes in the southwest pacific a tectonic interpretation this paper examines the spatial distribution of deep earthquakes in the tonga fiji new hebrides region of the southwest pacific our interpretation emphasizes the complex cenozoic tectonics of the pacific indo australian plate boundary as a primary control on the distribution and deformation of subducted lithosphere most deep earthquakes in the interarc region are associated with the contorted pacific plate lithosphere subducted at the tonga trench however anomalous groups of deep earthquakes located west of the tonga zone are unrelated to the present plate configuration tectonic reconstructions of the region to 8 m y b p provide circumstantial evidence that 1 the anomalous events west of the tonga zone occur in two pieces of detached lithosphere subducted at the vitiaz and proto new hebrides trenches during the late miocene 2 the flattening of the inclined seismic zone in northernmost tonga is related to the rapid opening of the lau basin since 4 m y b p and 3 the sharp westward curvature of the tonga seismic zone in this area coincides with a preexisting bend in the late miocene vitiaz arc the sharpness of its present curvature appears to be a secondary effect of shear flow in the lower mantle and compression between detached vitiaz and attached tonga lithosphere thus much of the contortion of the subducted lithosphere beneath tonga fiji may be produced by local tectonic interactions rather than collision of the slab with an impenetrable boundary in the midmantle

the role of bitumen in strata bound copper deposit formation in the copiapo area northern chile in northern chile between 27 and 33 s there are numerous deposits where residual petroleum is associated with cu ag mineralisation the most famous being el soldado all of these deposits are hosted by lower cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin this close relationship suggests that the generation migration and emplacement of hydrocarbons in the cretaceous volcanic units is a regional process associated with the evolution of the cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar cu ag deposits the present work analyses four small strata bound copper deposits located along a north south belt approximately 10 km east of copiapo in northern chile these deposits are typically hosted by pyrobitumen rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate pabellon formation the youngest formation within the chanarcillo group the strong genetic and spatial relationships between the pyrobitumen rich lavas and the mineral deposits allow us to define this volcanic belt as the ocoita pabellon metallotect two hydrothermal events can be distinguished based on the mineralogical textural fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum during the early event petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by fe rich hydrothermal fluids which precipitated pyrite as an early sulphide phase the second event is characterised by cu rich hydrothermal fluids which induced three successive sub stages of cu sulphide precipitation the hydrothermal fluids chemically and thermally altered the first stage bitumen transforming it into pyrobitumen the present work documents similarities between the ocoita pabellon metallotect and the el soldado ore deposit and emphasises important differences in the el soldado host rocks a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids the framboidal pyrite was formed by assistance of bacteria the s of the cu sulphides was inherited from the pyrite and the fluid source was basin connate metamorphic brine in the ocoita pabellon metallotect the hydrocarbons were mobilised into the host rocks by hydrothermal fluids the pyrite is epigenetic the 34s values of pyrite and copper sulphides are very different with distinctive light 34s signature of cu sulphides 34s between 44 7 and 17 9 and the calculated 18o of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system

isolated deep earthquakes and the fate of subduction in the mantle the locations of earthquakes with depth in the mantle provide direct evidence of the trajectory and state of stress of subducting lithosphere the occurrence over the last decade of isolated large deep earthquakes outside the main wadati benioff zones in the kurile izu bonin and chile deep seismic areas in addition to the observed flat distributions of deep seismicity beneath the banda sea and fiji plateau areas and the large number of deep earthquakes located away from the main slab in the tonga arc supports recent tomographic and other seismological studies leading to a reconsideration of slabs as simple planar structures sinking undeformed into the lower mantle the focal geometries of these isolated earthquakes which often exhibit near vertical compressional stresses are distinct from adjacent events in the main wadati benioff zone they are also different in orientation from events in the deflecting toe of the slab and from the stress orientation expected if the deflected slab acts as a stress guide these isolated mantle earthquakes are interpreted to take place in subducted lithosphere that has deflected to a horizontal posture at the base of the upper mantle conversely the deep seismicity in the adjacent wadati benioff zone is associated with the deflection of the subducting lithosphere

details of stress directions in the alaska subduction zone from fault plane solutions we used the cumulative misfit method to divide a data set with heterogeneous stress orientations into subsets with homogeneous stress directions we propose that slope changes of the cumulative misfit as a function of earthquake number pinpoint the boundaries of homogeneous stresses using a synthetic data set of 50 fault plane solutions composed of two halves corresponding to two incompatible stress tensors we tested the validity and efficacy of the cumulative misfit method our acceptance criteria for results of stress tensor inversions are 1 the directions must be well constrained that is the 95 confidence regions of the greatest and least principal stresses do not overlap and 2 there must be evidence for homogeneity in the sample that is the average misfit of the inversion is less than 6 we estimated stress directions in the alaska wadati benioff zone wbz using 470 fault plane solutions which we determined for earthquakes with ml 3 and 67 published fault plane solutions for earthquakes with ms 5 we succeeded in subdividing the data set of the small and large earthquakes into 25 and 3 subsets with the average misfit ranging from 3 2 to 5 5 the average misfits of the subsets we accept as satisfying the assumption of homogeneity are smaller than the average misfit of the overall data set f 10 by factors of 2 to 3 we estimated the stress fields at two scales along the alaska wbz the stress directions measured by the large earthquakes ms 5 were homogeneous over large volumes with extension downdip and the direction of greatest compression along strike this unusual orientation of the greatest principal stress is attributed to the bend of the slab under central alaska which generates compressive stresses along strike the stress orientations revealed by small earthquakes in contrast exhibited a great deal of heterogeneity as a function of space although their general trend confirms the overall stress directions obtained from the large events we propose that the ratio of the dimensions of the stress field sensed by earthquakes to the rupture dimensions is about 20 to 50 the estimated stress directions of the crustal earthquakes corresponded to the following mechanisms 1 strike slip faulting with the greatest principal stress oriented n s near fairbanks and 2 thrusting with the greatest principal stress oriented nw se near mount mckinley

a manto type cu deposit in the central asian orogenic belt the hongguleleng example xinjiang china abstract manto type cu deposits with relatively high grade up to 8 wt cu occurred widely around the pacific rim belt and along the himalayan tibetan belt however so far manto type cu deposits have not been reported in the central asian orogenic belt caob hongguleleng also called armuqiang located in the west junggar xinjiang china is the first recognized manto type cu deposit it is hosted in the late silurian early devonian volcano sedimentary sequence and associated with pale volcanic apparatus the cu bodies are restricted to particular porous units e g andesitic volcanic breccias amygdale basalt and andesite and are mostly controlled by the steep dipping fault zones the host volcanic rocks have been overprinted by three alteration assemblages and associated copper mineralization an early barren propylitic chlorite calcite assemblage is widespread and is overprinted by epidote chlorite assemblage associated with ores they are cut by barren calcite veins the major copper sulfides are chalcopyrite bornite and chalcocite that show disseminated amygdale filling breccias vein veinlet massive and replacement textures only two fluid inclusion types were recognized in quartz calcite and epidote liquid rich and vapor rich inclusions they have homogenization temperatures in the range 140 280 c sulfur isotope compositions from ores have a positive 34s values range from 0 5 to 3 4 suggesting a magma source from the geology alteration mineralization and fluid inclusion characteristics and sulfur isotopic compositions we propose that the hongguleleng deposit is classified as a typical manto type copper deposit

mechanisms of sulfate removal from subsurface calcium chloride brines heletz kokhav oilfields israel abstract the evolution of the ca chloride brines in the heletz formation lower cretaceous in the southern coastal plain of israel was reconstructed through the study of its sulfate concentration and isotopic composition particular emphasis was given to the brine oil interaction in the oilfields and to the sulfate depletion and lower so4 cl ratio in brines in contact with hydrocarbons oil brines relative to oil free from dry wells in the same oilfields a method is presented for a calculation of the amount of sulfate removed from the original seawater in the various stages of its evolution to ca chloride brine these stages include evaporation dolomitization and sulfate reduction in different stages of its evolution from early diagenetic processes to the contact with crude oil in the present study based on the 34sso4 and so4 cl ratio it was found that in the heletz brines most of the sulfate 80 94 was removed from the original seawater prior to their interaction with the hydrocarbons and only a negligible fraction of few percent of the sulfate was removed during the crude oil water contact the ca chloride brines evolved from messinian upper miocene seawater that underwent evaporation during the desiccation of the mediterranean sulfate was removed from messinian lagoon s during gypsum precipitation due to evaporation and dolomitization bacterial sulfate reduction further depleted the brine in sulfate and changed its isotopic composition from its original miocene seawater composition of 34sso4 20 o 26 o overall some 50 of the original sulfate as normalized to chloride was removed from the original lagoon through the above processes mostly by gypsum precipitation eastward migration of the messinian ca chloride brine into the heletz formation was accompanied by dolomitization of the country rock final depletion of sulfate from the brines took place and possibly still occurs in the presence of crude oil in the oilfields the two oil producing fields heletz and kokhav occupy different areas on a rayleigh distillation diagram sulfate depletion in both fields is accompanied by an increase in 34sso4 which reaches a maximum value of 59 o the above correlation is explained by bacterial sulfate reduction facilitated by the contact with the crude samples collected from the same boreholes at time intervals of several months show two opposing trends sulfate concentration decrease accompanied by increase in 34sso4 and vice versa while the first can be explained as in situ bacterial sulfate reduction the latter attest to subsurface brine migration as would be expected in oil producing fields

deep earthquakes in real slabs deep earthquakes shouldn9t happen yet they do at depths greater than about 50 kilometers rock begins to flow rather than fracture and fracture is the phenomenon associated with seismic activity in their perspective stein and rubie discusses the highlights of a recent conference on subduction the geological process whereby one lithospheric plate is pushed under another deep earthquakes can take place in subducting slabs owing to the complex phase transformations that occur as minerals are heated and put under pressure as they are pushed deeper conference participants debated current models of deep seismic activity and their limitations

evidence for transformational faulting from a deep double seismic zone in tonga double seismic zones planes or earthquakes parallel to the dip of a subducting slab and separated by 20 40 km provide important clues about the earthquake generating mechanisms and strain distribution inside subducting slabs double seismic zones have been found at intermediate depths 70 200 km in many subduction zones1 6 but have not been previously reported in deep slabs here by relocating earthquakes with a hypocentroidal decomposition technique7 and visualizing the earthquake positions and uncertainties in three dimensions we identify a double seismic zone at depths of 350 460 km in the tonga subduction zone source parameters of the earthquakes determined by waveform analysis suggest different stress orientations for the two zones with in plane compression in the lower zone and in plane tension in the upper zone the double zone may be due to transformational faulting as olivine along the edges of a metastable olivine wedge becomes warmer and transforms to spinel8 11

age of mineralization by basinal fluids at the el soldado manto type copper deposit chile 40ar 39ar geochronology of k feldspar abstract manto type copper deposits of the southern central andes are strata bound epigenetic mineral concentrations hosted by bimodal volcanic and volcaniclastic rock suites they are economically important but since they are not obviously related to intrusions their genesis has been controversial to some extent because it has proven difficult to date the ore forming event and distinguish it from the age of low grade regional metamorphism el soldado the largest manto type copper deposit in central chile is hosted by marine volcanic and subvolcanic intrusive rocks of the lower cretaceous extensional arc to discriminate between regional metamorphism and mineralization we dated 11 samples of k feldspar by the stepwise heating 40 ar 39 ar method hydrothermally precipitated k feldspar associated with copper sulfides precipitated at temperatures of 300 c and range in age from 100 5 1 5 to 106 1 1 1 ma mean 103 1 6 ma n 8 syn mineralization k feldspar gave an age of 102 5 2 0 which is interpreted to be the age of mineralization k feldspar unrelated to ore yields older ages between 109 4 1 1 and 112 2 ma mean 110 3 1 4 ma n 3 is variably reset by the younger ca 103 ma mineralization episode the above ages are interpreted to represent the age of alkali redistribution and crystallization due to burial metamorphism of the host sequence fission track dating of apatite in the host rocks yields an age of ca 90 ma indicating fast cooling of the system to less than ca 100 c after mineralization time temperature modeling of fission track length data are compatible with initial fast exhumation followed by slow exhumation and cooling to surface temperatures high levels of atmospheric ar were detected in all k feldspar samples and are tentatively attributed to connate meteoric fluids incorporated into the basinal metamorphic mineralizing fluids

extremely negative and inhomogeneous sulfur isotope signatures in cretaceous chilean manto type cu ag deposits coastal range of central chile abstract chilean manto type cmt cu ag hydrothermal deposits share a characteristic association of volcano sedimentary jurassic to lower cretaceous host rocks style of mineralization ore and associated mineralogy and geochemistry with ore grades typically 1 cu that make this family of deposits significant and interesting both academically and economically although often stratabound geological evidence supports an epigenetic origin for these deposits we present a detailed stable isotope study of la serena and melipilla naltahua lower cretaceous deposits central chile which reveals extremely negative 34 s values to 50 which are among the lowest values found in any ore deposit in addition the range of 34 s values from sulfides in the two areas is very wide 38 3 to 6 9 in la serena and 50 4 to 0 6 in melipilla naltahua these new data significantly extended the reported range of 34 s data for cmt deposits co existing sulfates range from 7 9 to 14 3 and are exclusive to la serena deposit the wide sulfide isotopic range occurs at deposit and hand specimen scale and suggests a polygenic sulfur source for these deposits where bacteriogenic sulfide dominates while sulfur isotope data for the bulk of jurassic cmt deposits northern chile suggests a predominant magmatic source in their origin mean 2 7 1 9 1 contributions of a magmatic component is only likely to be involved at melipilla naltahua deposit the 13 c values obtained for calcites associated with the mineralization range from 20 1 to 0 2 also suggesting polygenic carbon sources with the likely strong involvement of degradation of organic matter and leaching of limestone two different genetic models with involvement of hydrocarbon are proposed for both areas for melipilla naltahua a two step model can be developed as follows 1 framboidal pyrite growth with very low 34 s formed by bacterial sulfate reduction in an open system and with diagenetic degradation of oil related brines leaving pyrobitumen 2 cu bearing stage replacing of framboidal pyrite inheriting depleted sulfur as low as 50 4 together with sulfides directly precipitated from a hydrothermal fluid with 34 s close to 0 for la serena a single step model fits best without framboidal pyrite generation cu bearing sulfides were precipitated mainly in veins where cu plus base metal bearing hydrothermal fluids mixed with h 2 s generated by bacterial sulfate reduction in the host rocks isotopic evidence clearly illustrates that bacterial activity perhaps enhanced by hydrothermal activity was fed by hydrocarbon brines and sulfate remobilized from continental evaporites it is possible that variable ecological conditions led to different extents of isotopic fractionation adding to the typical sulfur isotopic heterogeneity of such bacterial systems for both areas the cu bearing stage occurred during the peak to waning stages of the very low grade metamorphism that affected the lower cretaceous sequence

a classification of mineral systems overviews of plate tectonic margins and examples of ore deposits associated with convergent margins abstract in this contribution i presents definitions of mineral systems followed by a proposed classification of mineral deposits the concept of mineral systems has been tackled by various authors within the framework of genetic models with the aim of improving the targeting of new deposits in green field areas a mineral system has to be considered taking into account by and large space time patterns or trends of mineralisation at the regional scale their tectonic controls and related metallogenic belts this leads to a suggested classification of mineral systems together with a summary of previous ideas on what is without doubt a kind of mine field because if a classification is based on genetic processes these can be extremely complex due to the fact that ore genesis usually involves a number of interactive processes the classification presented is based on magmatic magmatic hydrothermal sedimentary hydrothermal non magmatic and mechanical residual processes an overview of plate tectonics convergent and divergent margins is discussed next convergent plate margins are characterised by a tectonic plate subducting beneath a lower density plate convergent plate margins have landward of a deep trench a subduction accretion complex a magmatic arc and a foreland thrust belt an important feature is the subduction angle a steep angle of descent is exemplified by the mariana or tonga kermadec subduction systems conducive to porphyry high sulphidation epithermal systems whereas in an intra arc rift systems with spreading centres is conducive to the generation of massive sulphide deposits of kuroko affinity a shallower subduction zone is the domain of large porphyry cu mo and epithermal deposits the implications of this difference in terms of metallogenesis are extremely important continent continent arc continent arc arc amalgamation of drifting microcontinents and oceanic collision events are considered to be a major factor in uplift the inception of fold and thrust belts and high p metamorphism examples are the alpine himalayan orogenic belt formed by the closure of the tethys oceanic basins and the great central asian orogenic belt caob a giant accretionary collage of island arcs and continental fragments the closing of oceanic basins and the accretion of allochthonous terranes result in the emplacement of ophiolites by the obduction process divergent plates include mid ocean ridges passive margins and various forms of continental rifting at mid ocean spreading centres magma chambers are just below the spreading centre once the oceanic crust moves away from the ridge it is either consumed in a subduction zone or it may be accreted to continental margins or island arcs spreading centres also form in back arc marginal basins transform settings include transtensional with a component of tension due to oblique divergence transform or strike slip sensu stricto and transpressive with a component of compression due to oblique convergence strike slip faults that form during extensional processes lead to the formation of pull apart basins mineral systems that form at convergent margins the topic of this special issue are succinctly introduced in table 1 table 2 table 3 table 4 table 5 table 6 table 7 as follows principal geological features of selected mineral systems at convergent plate margins and back arcs table 1 their recognition criteria table 2 principal geological features of selected ore deposits of back arc basins and post subduction rifting table 3 and of subduction related magmatic arcs table 4 their respective recognition criteria table 5 accretionary and collisional tectonics and associated mineral systems table 6 principal geological features and associated mineral systems of transform faults table 7

unraveling the origin of the andean iocg clan a re os isotope approach the andean iocg clan in the coastal cordillera of northern chile comprises the iron oxide cu au sensu stricto the iron oxide apatite ioa and the stratabound cu ag deposits also known as manto type cu ag deposits iocgs and manto type deposits constitute the second source of copper in chile after porphyry cu mo systems whereas ioas are an important source of iron regardless of their economic importance little is known about their formation and contrasting genetic models have been proposed i e an origin from magmatic hydrothermal fluids exsolved from a cooling intrusion or formation from non magmatic basinal brines heated by plutonic bodies here we report re os data for five iocg deposits candelaria mantoverde casualidad diego de almagro and barreal seco three ioas los colorados el romeral carmen and two manto type deposits altamira and franke calculated re os ages for some of these deposits are consistent with previously published geochronological data and indicate an early to late cretaceous age the calculated ages for the altamira manto type cu deposit yield a 90 ma age indicating that the cretaceous manto type cu belt of central chile extends further north than previously thought additionally the calculated initial os ratios using reported ages show that iocgs have a more radiogenic signature 2 0 2 4 than ioas 1 0 1 2 and manto type cu deposits 1 1 a comparison with previously published os initial ratios for the mantoverde 0 2 and candelaria 0 4 iocgs suggests that the mineralization in chilean iocgs is the result of different events with metals derived from diverse sources i e the magmatic hydrothermal system and basement host rocks rhenium and os concentrations for the various studied deposits vary over a wide range of values at the ppb and ppt level respectively with many sulfides and magnetite bearing appreciable no common os the re and os contents in sulfides pyrite chalcopyrite from iocgs are low ranging from 2 to 149 ppb re and up to 49 ppt os pyrite from ioa deposits show re and os concentrations ranging from 10 8 to 214 ppb re and os 156 ppt whereas magnetite has lower re and os contents 0 7 129 ppb re 0 2 3 6 ppt os however rhenium and os concentrations in magnetite might be attributed to small sulfide inclusions chalcocite from manto type cu deposits shows the widest range and highest re and os concentrations 15 to 253 ppb and 34 to 639 ppt respectively the os present in all these deposits is dominated by radiogenic 187os a comparison of re and os data from different deposit types show that andean iocg and ioa deposits have similar characteristics to chilean porphyry cu mo systems with low to moderate re content 90 osr and variable initial os ratios our data supports the idea that andean iocg and ioa deposits formed by magmatic hydrothermal processes with little involvement of basinal brines in contrast published re os information from iocgs in china and australia argue for the involvement of a much more radiogenic crustal source possibly related to non magmatic oxidized saline brines that leached basement rocks we conclude that andean iocg and ioa deposits in northern chile were formed mainly by magmatic hydrothermal processes related to the formation and emplacement of plutonic rocks with moderate contribution from leaching of basement and or volcanic host rocks surface or basin derived brines as well as sediments appear to play only a minor role in the formation of the chilean iocg clan

characterization of graphite alteration and bitumen genesis in the cigar lake deposit saskatchewan canada bitumens collected in the east zone of the cigar lake deposit have been analyzed by c 13 nuclear magnetic resonance pyrolysis gas chromatography rock eval and c h and 0 methods carbon and hydrogen isotopic compositions and uranium contents have been determined results indicate that the bitumens consist mainly of aromatic structures f a almost equal to 60 and have undergone a late oxidation process similarities in carbon isotopic composition 27 5 part per thousand deltac 13 28 2 parts per thousand between barren bitumens u 300 ppm and graphite collected in the basement gneisses as well as evidence for progressive disorganization of graphite along a basement profile suggest a genetic relationship between graphite and bitumens from the mineralized areas the presence of amorphous carbon in pit structures inside graphite flakes close to the unconformity supports this assessment significant differences in geochemical and isotopic characteristics of the cigar lake barren bitumens and the cluff lake mineralized bitumens suggest that there are two possible mechanisms for their formation barren c enriched bitumens could have formed directly by hydrogenation of amorphous carbon whereas mineralized isotopically light bitumens from cluff lake deltac 13 almost equal to 48 parts per thousand may result from the polymerization of light hydrocarbons around uraninite grains

are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle in a number of subduction zones earthquakes at 50 200 km depth define two dipping planes separated by 20 40 km that appear to merge downdip upper plane earthquakes are inferred to occur within the subducting oceanic crust whereas lower plane earthquakes occur in the subducting oceanic mantle beneath northeast japan the results of a new finite element heat transfer model suggest that the lower seismic plane cuts across isotherms at a shallow angle lower plane earthquakes occur at 550 800 c at 100 km depth and at 350 600 c at 160 km depth these conditions coincide with the dehydration reaction antigorite serpentine forsterite enstatite h 2 o which suggests that lower plane earthquakes may be triggered by dehydration embrittlement which in turn suggests that the subducting oceanic mantle is partially hydrated serpentinization may occur in the trench outer rise region where faulting may promote infiltration of seawater several tens of kilometers into the oceanic lithosphere if this hypothesis is correct current subduction zone h 2 o budgets may significantly underestimate the amount of bound h 2 o entering the subduction factory

genesis and evolution of bitumen in lower cretaceous lavas and implications for strata bound copper deposits north chile small strata bound copper sulfide deposits are found associated with bitumen in lower cretaceous basaltic andesite flows of the pabellon formation near copiapo north chile the physical characteristics of the bitumen and hydrocarbon biomarkers provide clues to the genesis evolution and possible role during copper mineralization biomarker analysis reveals a predominantly bacterial origin with minor contributions from phytoplankton and higher plants which were deposited in a shallow marine environment an expulsion temperature between 64 and 87 c was determined typical for low maturity petroleum this petroleum was altered during migration by mixing with brines increasing its viscosity by aromatization and sulfurization at the moment of the accumulation the temperature of the brine was under 150 c the viscous oil filled the primary and secondary porosity of the basaltic andesite which acted as an oil trap after the oil accumulation a hotter hydrothermal influx resulted in thermal alteration of the petroleum and a further decrease of light alkane concentrations high sulfur concentrations in the hydrothermal fluids led to further aromatization of the organic compounds generating highly alkylated benzonaptho and dinaphthothiophenes copper in the sulfur rich solutions was reduced triggering the precipitation of bornite chalcopyrite digenite chalcocite and covellite through thermochemical sulfate reduction the bitumen interacted with metals by virtue of its inherent reducing characteristics activated carbon and was itself oxidized to form a pyrobitumen residue

assessing the role of bitumen in the formation of stratabound cu ag deposits insights from the lorena deposit las luces district northern chile abstract stratabound cu ag deposits located in north central chile have been grouped into two ns parallel belts according to the age of their volcanic and volcanoclastic host rocks deposits from the cretaceous belt are characterized by an unusual assemblage of cu sulfides with migrated hydrocarbons whereas the presence of organic matter has not yet been recognized in deposits from the jurassic belt here we report the first evidence of pyrobitumen in a jurassic stratabound cu ag deposit and evaluate its role in ore formation we present a micro analytical study of pyrobitumen associated with cu fe sulfides in the lorena deposit located in northern chile our approach involved a combination of surface and drill core sample characterization fe sem observations empa and xrf mapping of pyrobitumen in addition we determined the speciation of sulfur in pyrobitumen by using synchrotron xanes two main events of hypogene mineralization were identified at lorena deposit i e a pre ore and a main cu ore stage the pre ore stage is characterized by globularly shaped pyrobitumen and minor pyrite and a widespread albite alteration of the andesite host rock pre ore pyrite was replaced by chalcopyrite bornite and chalcocite providing evidence for a late cu inception in the main cu ore stage chalcocite is often associated with sharp edged angular pyrobitumen most likely indicating remobilization or a later pulse of hydrocarbons empa data show that pyrobitumen at lorena is enriched in fe 0 02 1 74 wt cu 0 02 0 87 wt s 0 01 0 43 wt and cl 0 01 0 4 wt other elements detected include v co ni cr sb as ag and au both ag and au were only detected in a few spots with au reaching up to 600 ppm desktop and synchrotron xrf mapping shows that s is homogeneously distributed within pyrobitumen with lower s concentrations observed at grain rims on the other hand empa wds x ray maps show that cu precipitated on pyrobitumen grain surfaces filling fractures and forming veinlets in addition textures showing the presence of micro to nano sized pyrobitumen inclusions within both pre ore pyrite and main ore chalcocite grains point unequivocally to the interaction of hydrothermal fluids with hydrocarbons during the formation of this deposit the high s concentrations measured in pyrobitumen and the presence of organosulfur compounds detected by xanes can be attributed to an organic source the pre ore assemblage is interpreted as formed from a petroleum aqueous fluid connate waters mixture that migrated from the sedimentary source rock into the jurassic host rocks where pyrite and pyrobitumen precipitated in the andesite late cu bearing hydrothermal fluids interacted with this pyrobitumen pyrite assemblage to form cu sulfides either by replacement of pyrite or precipitation we conclude that some of the s contained in pyrobitumen could have been released during interaction with the cu bearing hydrothermal fluid contributing at least partially to the s budget required for sulfide mineralization in the main ore stage our results provide evidence supporting pyrobitumen fluid interaction as a key process in the formation of the lorena deposit and possibly other stratabound cu ag deposits in chile

geology mineralization and sulfur isotopes geochemistry of the mari cu ag manto type deposit northern zanjan iran abstract the eocene volcano sedimentary sequence northern zanjan consist of 1 5 km of shallow marine sediments these include sandstone lapilli tuff andesite basalt and felsic volcanic rocks the mari deposit is strata bound that hosted by the eocene andesite rocks the major copper sulfides are bornite chalcocite and chalcopyrite associated mainly with pyrite that show open space filling disseminated vein veinlet and replacement textures the abundances of cu and ag in the ore bearing andesite are up to 40 000 and 70 ppm respectively wall rock alterations include carbonatization chloritization epidotization and sericitization sulfur isotope compositions have a negative range from 34 s 2 7 to 3 4 suggesting the presence of a reducing environment resulting from activation of sulfate reducing bacteria mineralization formed two stages stage one include volcanic activity and eruption of andesitic lava in this stage syngenetic disseminated pyrites formed in the second stage increasing of the thickness of sediments basin subsidence and burial diagenesis accompanied with the entry of metal rich fluids into the reduced host rock caused the replacement of the first stage pyrites by copper sulfides the geology ore mineralogy alteration characteristics and sulfur isotopic compositions suggest the mari deposit may be classified as a manto type deposit

the world s lead zinc mineral resources scarcity data issues and opportunities abstract lead and zinc keep humanity powered and sheltered yet a comprehensive understanding of pb zn resources in known mineral deposits has been lacking leading to uncertainty over when we might expect the supply of these metals to face potential constraints addressing this we compile an extensive database of the world s known pb zn mineral deposits and provide in depth analyses of their contained resources ore grades economic value by products and geological settings our data indicate that at least 226 1 mt pb and 610 3 mt zn are present within 851 individual mineral deposits and mine waste projects from 67 countries and one in international waters at an average grade of 0 44 pb and 1 20 zn the identified resources are dominantly present within sediment hosted pb zn deposits 490 6 mt pb zn cu which contain the equivalent of vms skarn porphyry epithermal and mixed sediment hosted deposits combined and 49 of these resources are reported in australia russia peru and canada alone the reported pb zn resources appear to be sufficient to meet global demand for both pb and zn until 2050 although this estimate is most certainly a minimum as our case studies indicate a prevailing trend of deposits cumulatively producing well beyond their reported resources over time indeed despite increasing historical production of pb and zn estimated reserves and resources have also increased and this is expected to continue we also present an analysis and review of additional aspects affecting the future sustainability of pb zn resources including an account of the history of pb zn mining case studies and trends in reporting classifications of the dominant pb zn mineral deposit types analysis of reported by product companion metals review of tailings resource potential and case studies on the numerous challenges in environmental management historically faced for pb zn mining these analyses alongside our comprehensive resource data indicate that the future supply of pb and zn is likely to be governed by prevailing economic social and environmental factors much more so than sheer resource constraints

organic petrology chemical composition and reflectance of pyrobitumen from the el soldado cu deposit chile solid pyrobitumen residual petroleum is found intimately associated with sulfides in several manto type strata bound cu deposits of central chile el soldado lat 32 38 8 s long 71 06 7 w is one of the largest deposits of this type 130 mt 1 5 cu and is hosted by volcanic and subvolcanic rocks of the cretaceous lo prado fm detailed organic petrology of authigenic sulfide inclusions degassing vesicles and anisotropic pyrobitumen and graphitic carbon allowed the elucidation of a complex diagenetic history of a biodegraded reservoir in faulted volcanic and subvolcanic rocks due to the overmaturity of the host sequence biomarker techniques aliphatic and aromatic were unsuitable to investigate the composition of the pyrobitumen however microprobe and laser ablation inductively coupled plasma mass spectrometry la icpms analyses rock eval pyrolysis and 13 c nmr techniques were used to ascertain the composition of the pyrobitumen spatial variations in the maturity of the pyrobitumen were assessed using both random reflectance r o and rotational reflectance r omax and r omin the data are consistent with the following evolution for el soldado as a result of burial in the cretaceous back arc basin petroleum was generated from organic rich shales in the underlying lower lo prado fm and migrated into primary and structural porosity in the host rocks the predominantly volcanic upper lo prado fm low temperature 90 c biodegradation of petroleum developed an early assemblage stage i assemblage of pyrite sphalerite chalcopyrite geopetal structures related to pressure degassing of semisolid petroleum suggest that migration occurred while the strata were horizontal at ca 130 ma continued basinal burial led to thermal degassing increased maturation and contraction of the petroleum into pyrobitumen around 20 ma later an influx of high temperature ca 250 350 c cu rich fluids induced by regional granitoid intrusion stage ii assemblage replaced preexisting pyrite and pyrobitumen the mineralizing fluids altered the pyrobitumen physically and chemically a increasing r o to greater than ca 5 in the core of the orebodies against a background level of ca 3 b developing anisotropy nongranular fine to coarse mosaic and coarse flow mosaic within the pyrobitumen and locally graphitized the pyrobitumen developing graphitic carbon and c incorporating cl cu fe into the pyrobitumen during the development of anisotropy

earthquakes plate subduction and stress reversals in the eastern aleutian arc plate subduction beneath the 1500 km long segment of the eastern aleutian arc between kodiak and atka islands 154 w and 176 w longitude is studied with observations from teleseismic data the primary data base consists of hypocenters of earthquakes for the period 1965 1975 carefully selected from the bulletins of the international seismological centre and of 44 new focal mechanism solutions the principal results of this study are that hypocenters of intermediate depth earthquakes in the eastern aleutians appear to define a weakly developed double seismic zone at depths between 70 and 170 km additional evidence for a double seismic zone comes from focal mechanisms which generally show downdip directed p axes for earthquakes in the upper zone and downdip directed t axes in the lower zone major features of the double zone can be explained by thermoelastic stresses in the downgoing plate the observed predominant downdip stress polarity at intermediate depths in the descending plate reverses along strike of the arc this stress reversal coincides in map view with a change from a continental to an oceanic arc the coincidence may result from spatial differences either in the coupling between the plates at shallow depths or in the rheology of the surrounding oceanic versus continental mantle alternatively the stress reversal may be related to the time since the last great earthquake if the observed stress polarity relates to the elapsed time since the last great earthquake it may be a significant observation for long to intermediate term prediction of great thrust earthquakes in subduction zones portions of the eastern aleutian arc where downdip tension predominates contain one or more seismic gaps that appear to have a high probability for great earthquakes in the next few decades a moderate sized bathymetric feature in the pacific plate the amlia fracture zone modifies subduction and produces a bend or offset in the downgoing plate as well as an offset in the line of active volcanoes in the upper plate subduction of the fracture zone appears also to cause formation of summit basins on the arc platform and some aseismic behavior of a 100 km long segment of the main thrust zone

seismicity and state of stress within the overriding plate of the tonga kermadec subduction zone 1 to reassess the main tectonic units and to quantify the slip partitioning within the overriding plate of the tonga kermadec subduction zone a seismotectonic study was performed using global seismicity and focal mechanisms catalogs 1 new tectonic features were identified within the lau basin and the volcanic arc by remarkable shallow hypocenters alignments 2 the centroid moment tensor solutions catalog was processed in order to map the stress tensor variation in the upper plate we found the tectonic features characterized by a diffuse seismicity are subjected to a composite stress regime and they are interpreted as diffuse immature plate boundaries controlled by the high thermal anomaly lying beneath the lau basin 3 we quantified the margin parallel rates of motion using the azimuth of the maximum compressive stress component computed within the interplate zone the results highlight a major tectono kinematic segmentation related to the subduction of the louisville seamount chain

oxygen isotope ratios of feo poor chondrules in cr3 chondrites influence of dust enrichment and h2o during chondrule formation abstract we present detailed electron microprobe analyses and oxygen three isotope measurements by high precision secondary ion mass spectrometry on 45 type i feo poor chondrules fragments and 3 type ii feo rich chondrule fragments from meteorite hills 00426 and queen alexandra range 99177 two of the most primitive cr3 chondrites type i chondrules fragments have mg s defined as the mg of constituent olivine and or low ca pyroxene ranging from 94 2 to 99 2 type ii chondrule fragments have mg s of 53 63 oxygen three isotope measurements plot on the slope 1 primitive chondrule mineral pcm line within chondrules 17 o 17 o 0 52 18 o values of coexisting olivine pyroxene and plagioclase are homogeneous with propagated uncertainties of 0 3 this indicates each phase crystallized from the final chondrule melt and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt among type i chondrules there is a well defined increase in 17 o from 5 9 to 1 as mg s decrease from 99 2 to 96 type ii chondrule fragments are comparatively 16 o poor 17 o 0 2 0 6 the relationship between mg and 17 o among type i chondrules confirms that addition of a 16 o poor oxidizing agent to the highest mg chondrule precursors resulted in forming lower mg cr chondrules using aspects of existing equilibrium condensation models and a mass balance we estimate that type i cr chondrules formed at dust enrichments of 100 200 from dusts with 0 0 8 times the atomic abundance of ice relative to ci dust the type ii chondrule fragments are predicted to have formed at ci dust enrichments near 2500

type of faulting and orientation of stress and strain as a function of space and time in kilauea s south flank hawaii earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of kilauea volcano hawaii are used to infer the state of stress and strain as a function of time and space we have determined 870 fault plane solutions from p wave first motion polarities for events with magnitudes m l 2 5 and depth ranging between 6 and 12 km faulting is characterized by a mixture of decollement reverse and normal faults most large earthquakes with magnitude m 7 rupture the decollement plane since it is the only surface large enough to generate magnitude 7 or larger earthquakes the percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972 1983 the percentage of decollement type focal mechanisms becomes dominant after 1983 this pattern of faulting activity suggests that pressure was building up within kilauea s rift zone prior to the 1983 puu oo eruption overall a single stress orientation with the maximum compressive stress oriented se perpendicular to the rift and dipping at 45 is compatible with the coeval existence of decollement reverse and normal faults however in a crustal volume east of longitude 155 10 w we find a change of the orientation of 1 from nearly horizontal to plunging 45 se occurring in 1979 this stress rotation suggests magma movements within the aseismic part of kilauea s east rift zone the strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed we observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements while stress stays constant or by a rotation of stress while strain remains constant assuming that the model of a noncohesive coulomb wedge is appropriate for kilauea s south flank we find that high pore pressures are prevalent along the decollement and within the wedge for a coefficient of friction equal to 0 85

the role of organic matter in the genesis of the el soldado volcanic hosted manto type cu deposit chile solid bitumen residual petroleum occurs intimately associated with sulfides in several manto type cu deposits of central chile el soldado 32 degrees 38 s 71 degrees 04 w is one of the largest manto type deposits 130 million metric tons1 5 cu and is hosted by rhyolites and andesites of the lower cretaceous lo prado formation as a result of basinal burial in the early cretaceous back arc basin petroleum was generated from organic rich shales in the underlying lower lo prado formation and migrated into primary and structural porosity in the upper lo prado formation migration was controlled by extensional basinal faults low temperature 90 degrees c biodegradation of petroleum developed an early stage i assemblage of mostly framboidal pyrite or sphalerite or chalcopyrite geopetal structures related to pressure degassing of semi solid petroleum suggest that migration occurred while the strata were horizontal at ca 130 ma continued basinal burial led to thermal degassing increased maturation and solidification of the petroleum low grade regional pumpellyite prehnite metamorphism of the sequence was followed at ca 110 to 103 ma by the influx of high temperature ca 300 degrees c cu rich fluids concurrently with emplacement of the cretaceous batholith into the basin basinal fluids were focused into a now tilted sequence by a brittle shear north south to north northwest fault system copper sulfides stage ii assemblage replaced preexisting pyrite and bitumen forming zoned orebodies with a central chalcocite hematite zone followed outward by bornite chalcocite chalcopyrite bornite and pyrite chalcopyrite zones the mineralizing fluids altered the bitumen thermally and chemically as follows 1 reflectance r o increased up to ca 5 percent in the core of the orebodies against a background of ca 3 percent 2 anisotropy nongranular microscale and domain developed and the bitumen was locally graphitized 3 chlorine or cu or fe was incorporated into the bitumen affecting its reflectance the source of cu was most likely the overlying oxidized volcanic pile the cu was transported as chloride cucl complexes precipitating where the cucl rich solutions reacted with bitumen adsorption reduction and pyrite from the stage i assemblage the study demonstrates that in the lower cretaceous basin of chile degraded petroleum reservoirs can be important controls for metallic mineralization derived from hydrothermal solutions of different sources particularly if biodegradation generated pyrite

seismological evidence for tearing of the pacific plate at the northern termination of the tonga subduction zone we present seismological evidence for tearing of the pacific plate at the northern termination of the tonga subduction zone seismicity cross sections indicate 1 abrupt termination of intermediate depth seismicity along an east west trending zone coincident with the northern termination of the subduction zone and 2 shoaling of the subducted slab at its northern termination earthquake distribution and source mechanism determinations indicate progressive downwarping and tearing of the pacific plate as it enters the northernmost segment of the tonga subduction zone source mechanisms for 57 events located along a narrow belt of high seismicity in northernmost tonga indicate dip slip faulting along near vertical planes oriented 285 coinciding with the observed direction of plate convergence precisely determined depths for 21 events 18 57 km suggest that the plate is downwarped 15 km prior to initiation of tearing depths of the 7 april 1995 m s 8 event and aftershocks suggest tearing of the plate may extend through the entire thickness of the oceanic lithosphere

seismological evidence for a slab detachment in the tonga subduction zone abstract the tonga wadati benioff zone is characterized by a large seismicity gap beneath the lau basin that raises the question of the slab continuity between the shallow to intermediate part 60 300 km and the deep part 400 700 km to address this problem we investigated the wadati benioff zone geometry and stress regime through a detailed analysis of the spatial distribution of moment tensors and variation of the stress tensor using the global seismicity engdahl e van der hilst r buland r 1998 global teleseismic earthquake relocation with improved travel times and procedures for depth determination bull seism soc am 88 722 743 and the centroid moment tensor solutions cmt catalogs dziewonski a m chou t woodhouse j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 the stress tensors were computed using the gephart s program gephart j w forsyth d 1984 an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence j geophys res 89 9305 9320 the stress inversion results indicate that between 21 s and 27 s and depths down to 700 km the slab is under homogeneous down dip compressional stress regime while north of 21 s we found strong variations of the stress orientations between the intermediate and deep portions of the slab we also show that between 14 and 19 s the stresses at intermediate depth 60 300 km can be resolved into two slab parallel domains a thin upper part of the slab that is under downdip compression and the lower part that is under downdip extension this pattern of two zones with opposite mechanical behavior is characteristic of a subducted plate with a free lower limit that does not interact with the 670 km depth boundary these results together with the large seismicity gap within the slab argue for a slab detachment

evidence for a contribution from two mantle plumes to island arc lavas from northern tonga lavas from the islands of tafahi and niuatoputapu at the northern end of the active tonga kermadec arc in the southwest pacific were erupted at a convergent plate margin yet they can be shown to contain a contribution from two different mantle plumes high concentrations of nb relative to other high field strength elements in these lavas compared to other tonga lavas reflect an ocean island basalt component in the mantle wedge derived from the nearby samoa mantle plume pb isotope compositions indicate that most of the pb in these lavas is derived from the oceanic crust of the plume generated louisville seamount chain which is being subducted beneath the tonga arc these two plume components were thus introduced into the arc lavas in very different ways and provide insight into upper mantle dynamics and magma generation processes occurring in an active arc back arc system