gold in porphyry copper deposits its abundance and fate abstract porphyry copper deposits are among the largest reservoirs of gold in the upper crust and are important potential sources for gold in lower temperature epithermal deposits whether gold remains in porphyry copper deposits is important both to their economic attractiveness and to the distribution of gold in the upper crust cu au atomic ratios of porphyry copper ore deposits form a continuous range from about 5000 to 5 000 000 with a median near 40 000 which separates gold rich and gold poor deposits gold is found in porphyry copper deposits in solid solution in cu fe and cu sulfides and as small grains of native gold usually along boundaries of bornite sims ion probe analyses of ore minerals from the gold rich batu hijau kingking and skouries porphyry copper deposits show that bornite contains about 1 ppm au whereas chalcopyrite contains about an order of magnitude less chalcocite and covellite contain 10 20 ppm au but are not abundant enough to account for a significant part of the gold endowment in many porphyry copper deposits the amount of gold presently in solid solution in cu fe sulfides is not adequate to account for all the gold in porphyry copper deposits and the remainder is present as micron scale grains of native gold experiments in the cu fe s au system show that bornite and chalcopyrite can contain about 1000 ppm gold at typical porphyry copper formation temperatures of 600 700 c and indicate that bornite and chalcopyrite in porphyry copper deposits were saturated with respect to gold at temperatures of only 200 300 c in contrast cu au ratios of bulk ore in porphyry copper deposits would require bornite and chalcopyrite to be saturated with respect to gold at temperatures similar to those at which primary potassic ore and alteration are thought to form this indicates that the maximum gold endowment of porphyry copper deposits is probably fixed by the amount of gold that will go into solid solution in cu fe sulfides when the deposit forms at high temperature and that gold is not commonly added later from other sources although it can be redistributed during cooling or later events the experimental data also suggest that high temperature 600 700 c vapors can extract considerably more gold from porphyry copper systems than can low temperature 300 c alteration comparison to cu au ratios of volcanic emissions suggests further that high temperature processes remove copper relative to gold from porphyry copper systems whereas low temperature processes remove gold preferentially and that this can account for deposits with extremely low and high cu au ratios respectively deposits with cu au ratios between about 20 000 and 100 000 however probably reflect different degrees of removal of gold or copper by immiscible sulfides

platinum group minerals in the skouries cu au pd pt te porphyry deposit the skouries deposit is a platinum group element pge enriched cu au porphyry system located in the chalkidiki peninsula greece with associated ag bi and te enrichment the deposit is hosted by multiple porphyritic monzonite and syenite intrusions which originated from a magma chamber at depth an initial quartz monzonite porphyritic intrusion contains a quartz magnetite chalcopyrite pyrite vein stockwork with intense potassic alteration the quartz monzonite intrusion is cross cut by a set of syenite and mafic porphyry dykes and quartz chalcopyrite bornite magnetite veins which host the majority of the cu and au mineralisation late stage quartz pyrite veins with associated phyllic alteration crosscut all previous vein generations electron microprobe and scanning electron microscopy shows that the pge are hosted by platinum group minerals pgm in the quartz chalcopyrite bornite magnetite veins and within potassic alteration assemblages the pge mineralisation in skouries is therefore part of the main high temperature hypogene mineralisation event platinum group minerals at skouries include sopcheite ag4pd3te4 merenskyite pd pt te bi 2 and kotulskite pd te bi with rare telargpalite pd ag 3te isomertieite pd11sb2as2 naldrettite pd2sb testibiopalladite pdte sb te and sobolevskite pdbi the most common platinum group mineral is sopcheite the pgm in skouries are small 52 m2 on average and occur as spherical grains on the boundaries between sulphides and silicates and as inclusions within hydrothermal quartz and sulphides these observations support a semi metal collector model whereby an immiscible bi te melt acts as a collector for pge and other precious metals in high temperature hydrothermal fluids this mechanism would allow the formation of pgm in porphyries without pt and pd fluid saturation

the lunar far uv albedo indicator of hydration and weathering 1 we present an analysis of lunar reconnaissance orbiter lro lyman alpha mapping project lamp measurements of the dayside lunar surface at far ultraviolet wavelengths we use the strong 165 nm h2o absorption edge to look for diurnal variations in hydration we find that diurnal variations in spectral slope are indeed present they are superimposed on latitudinal and spatial variations related to composition and weathering we use two different spectral regions 164 173 nm and 175 190 nm to separate out these effects highlands and mare regions have distinct reflectance spectra with mare regions being spectrally bluer than highlands regions a consequence of the greater abundance of opaque minerals in mare regions bright ray terrains and areas known to be young such as giordano bruno crater are found to be relatively spectrally flat or red in the far uv this is consistent with a lack of space weathering which tends to make the far uv spectrum bluer due to the spectral behavior of nanophase iron large scale latitudinal variations in fuv slope are distinct and are likely due to a gradient in space weathering the diurnal variation in hydration is consistent with a solar wind origin and with loss of h2o at temperatures above 320 k far uv spectroscopy is thus shown to represent a viable method for mapping aqueous alteration even on the dayside of the moon and potentially elsewhere in the solar system

clustered impacts experiments and implications impact by clusters of projectiles rather than a single projectile can result from several processes atmospheric breakup tidal breakup and ejecta from a large primary impact experiments have been performed in order to establish the characteristics of such events over a wide range of impact velocities 15 m s to 6 km s at very low impact velocities 15 200 m s clustered impacts were produced by launching a grouped projectiles of aluminum shot steel shot iron filings and sand at moderate to high velocities 0 8 6 km s pyrex spheres were shattered above the target during passage through aluminum foil or paper thereby forming a well defined cluster of fragments of overall radius rc the ratio of the overall radius rc of the cluster to the radius rs of a solid impactor of the same mass provides a measure of the cluster dispersion sand and compacted pumice targets were used in order to compare qualitatively the additional effect of slight differences in target strength the experiments reveal marked contrasts between impacts by clusters of projectiles and impacts by a single solid body tight clusters rc rs 20 displace a factor of 10 less mass this reduction in cratering efficiency is largely expressed as a shallow crater with an aspect ratio diameter depth as large as 30 for open clusters the size and velocity of the cluster as well as the density and strength contrast between the impactor and target can dramatically affect crater morphology open clusters impacting compacted pumice produce a flat hummocky floor with an incipient multiring pattern whereas a tight cluster impacting the same target produces a central floor mound oblique impacts by symmetrical clusters form a characteristic array of v shaped ridges pointing uprange the apex angle of the ridges depends on the cluster dispersion and impact angle inventories of postimpact projectile material reveal that the projectile is largely retained on the surface and spread downrange from the impact direction the amount of projectile material retained on the surfaces increases with decreasing impact angle from the horizontal and with increasing strength of the target relative to the projectile clustered impact craters and lunar secondary craters bear striking similarities over a broad range of morphologic features on this basis and on the basis of reasonable models of ejecta curtain structure we suggest that these experiments provide new clues for understanding ejecta emplacement around large lunar impact craters when the ejecta curtain around large impacts is viewed as a thick wall of debris and clustered impactors are viewed as a unit section of such a curtain then experimental results indicate that the continuous ejecta facies even for lunar craters larger than 100 km could contain as much as 90 primary material such a conclusion contrasts with many existing models that derive mixing ratios implicitly based on single noninteracting impact events beyond the continuous ejecta facies impacting clusters of ejecta provide a physical basis for understanding the wide variety of secondary morphologies and the large range in spectral signatures of primary material in crater rays

fluid inclusions reviews in mineralogy vol 12 edwin roedder 1984 mineralogical society of america 644 p u s 14

a magnetic anomaly associated with an albedo feature near airy crater in the lunar nearside highlands 1 we describe a strong crustal magnetic anomaly recently identified in lunar prospector magnetometer data that is associated with a previously unreported albedo feature near the crater airy in the lunar nearside highlands other workers have demonstrated a correlation between magnetic anomalies and the enigmatic bright markings known as lunar swirls we have used earth based telescopic spectra and clementine multispectral images to investigate the compositional and optical maturity characteristics of the airy swirl the airy albedo feature does not exhibit the complex sinuous structure of well known swirls such as the reiner gamma formation but does possess a bright loop and central dark lane another strong magnetic anomaly in the apollo 16 descartes region corresponds to a simple diffuse bright albedo spot on this basis we suggest that a continuum of swirl morphologies exists on the moon with the airy feature representing an intermediate or incipient swirl form

the nature of crater rays the copernicus example crater rays are formed during a cratering event as target material is ballistically ejected to distances of many crater radii forming narrow generally high albedo approximately linear features extending outward from the crater the nature of crater rays was examined for the lunar crater copernicus using new information on the composition of surface material from near ir reflectance measurements surface roughness from radar backscatter measurements and photogeologic data from available images part of the data analysis included use of mixing models to quantify the mixing systematics observed between primary ejecta and local substrate of the ray on the basis of compositional parameters from reflectance spectra primary material from copernicus can be detected in the surface material of rays in decreasing amounts with increasing radial distance e g 20 25 primary ejecta at six crater radii for distances greater than three crater radii the proportion of local material to primary ejecta observed from these compositional reflectance data is approximately equal to that predicted by previous laboratory and ballistic studies of craters within three crater radii the compositional data indicate a higher proportion of primary ejecta than predicted for extended areas along the ray that do not contain large secondary craters the primary ejecta is intimately mixed on the granular scale with local material throughout the regolith the relatively high albedo of the rays of copernicus is due to the feldspathic composition highland of the primary ejecta in rays emplaced on a mare substrate immature local substrate is only observed in copernicus s ray at large unmantied secondary craters or other areas with sufficient topographic slope to prevent the accumulation of mature soils crater rays are filamentous generally high albedo features that emanate nearly radially from young impact structures rays are narrow in relation to the crater radius extend distally for many crater radii and constitute a distinctive albedo feature around some of the largest and freshest lunar craters visible from earth synoptic views of ray systems figure la give the strong impression that the rays comprise bright material that has been excavated from the crater cavity and been emplaced beyond the continuous ejecta deposit if this visual impression is correct then the process that forms crater rays represents a significant mechanism for the lateral transport of primary material to great distances from its point of origin and particularly for craters larger than a let tens of kilometers in diameter constitutes a fundamental process for the regional mixing of crustal materials earth based telescopic images of the moon allowed the first studies and descriptions of rays and ray systems shoemaker 1962 described the arcuate and loop shaped streaks of the copernicus ray systems and showed that these patterns could be locally resolved into individual en echelon feather shaped elements 15 20 km in length with their long axes oriented approximately radially to the crater he noted the presence of elongate depressions or gouges in the ray system ranking in diameter from 8 km down to the limits of resolution and generally located at the proximal ends of the individual ray elements shoemaker observed that some of the gouges were

lunar optical maturity investigations a possible recent impact crater and a magnetic anomaly 1 we have used maps of the omat optical maturity parameter along with other clementine uv vis image products to study two interesting lunar features related to albedo and optical maturity examination of the region of a small crater whose formation has been suggested to be a candidate for the flash photographed in 1953 by stuart demonstrates that the candidate crater is not unusually fresh compared to other small craters in the vicinity therefore it is unlikely that the formation of this impact crater generated the observed flash an area of unusually high albedo in the descartes highlands is also known to be a magnetic anomaly it has been proposed that the presence of the magnetic anomaly has prevented the solar wind from reaching the surface for billions of years and therefore that the area has not undergone normal space weathering and preserved a high albedo the high albedo is caused only by maturity differences with the surroundings not by an exotic composition the fact that the albedo anomaly has not darkened or reddened to the extent expected may be the result of the surface texture as revealed in 3 8 cm radar images we suggest that the fresh appearance is largely caused by overlapping ejecta from two nearby craters and continual exposure of immature material by the erosion of 1 to 10 cm sized fragments within the deposit the magnetic shielding mechanism if operative probably plays only a minor role in producing the descartes albedo anomaly

porphyry copper mineralisation in the central srednogorie zone bulgaria the porphyry copper systems in the central part of the srednogorie zone bulgaria are represented by three major deposits elatsite medet and assarel and several smaller deposits and occurrences all of them within the panagyurishte ore district the hydrothermal systems are related to late cretaceous calc alkaline igneous complexes ore mineralisation is developed predominantly in the apical parts of subvolcanic and intrusive bodies as well as within the volcanic and basement metamorphic rocks several of the porphyry systems are spatially associated with shallow level intermediate and high sulphidation volcanic hosted epithermal deposits of economic importance such as the major gold copper mine at chelopech located 10 km from the elatsite porphyry copper deposit mineralisation processes in the porphyry deposits start with intensive hydrothermal alteration of the wall rocks k silicate alteration is characteristic for pre ore hydrothermal activity in all of them and it is located mostly in their central parts propylitic alteration is prominent in the medet and assarel deposits the assarel deposit is located in the central part of a palaeovolcanic structure and shows a large spectrum of pre ore alterations including propylitic sericitic and advanced argillic assemblages the initial stages of the hydrothermal systems are characterised by high temperatures 550 500 c and highly saline 50 20 wt nacl equiv and vapour rich fluids of likely magmatic origin the composition of the fluids gradually changes from h2o nacl fecl2 to h2o nacl kcl and h2o nacl dominated as the fluids cool react with wall rocks and may become diluted with meteoric water fe ti oxide mineral associations were formed early in all deposits later followed in the elatsite deposit by an assemblage of bornite chalcopyrite platinum group element pge phases co ni thiospinels ag and bi tellurides and selenides the main ore stage in all deposits is dominated by chalcopyrite pyrite associated with propylitic alteration at medet k silcate sericite alteration at elatsite and chlorite sericite alteration at assarel specific geochemical features of the ore systems are marked by precipitation of numerous fine grained mineral inclusions in chalcopyrite and pyrite palladoarsenide pd rammelsbergite cu ni sulpharsenides in elatsite co and ni pyrite carrolite vaesite sulvanite and colusite in medet enargite as sulvanite colusite goldfieldite wittichenite calaverite and aikinite in assarel native gold and electrum are observed as small grains except in elatsite where larger aggregates up to several millimetres are found molybdenite is present as small flakes within chalcopyrite or forms felted aggregates within thin quartz veinlets in the elatsite and medet deposits and very rarely at assarel thin veinlets of quartz galena sphalerite are found at the upper parts of the deposits supergene alteration of the primary sulphide minerals is developed in the assarel deposit where a thick blanket of secondary copper mineralisation chalcocite covellite has formed in the other two deposits secondary mineral associations cu and fe oxides and hydroxides are limited to near the surface differences in the deposits studied suggest that elatsite and medet are formed probably at deeper levels of the porphyry systems whereas assarel is developed at rather shallower and lower temperature conditions typical of the apical part of a subvolcanic body intruding its volcanic superstructure

platinum group elements in ores from the kalmakyr porphyry cu au mo deposit uzbekistan bulk geochemical and laser ablation icp ms data we studied primary ore samples from kalmakyr a giant cu au mo porphyry deposit in eastern uzbekistan disseminated and stockwork type high grade cu au mo mineralization showed average concentrations of 55 ppb pd 5 5 ppb pt 0 95 ppb rh 0 49 ppb ir and 4 1 ppm au n 8 this type of mineralization is characterized by the presence of pyrite chalcopyrite molybdenite and gold a peak pd content of 292 ppb was determined in a base metal rich quartz vein in granodiorite porphyry which contains galena sphalerite chalcopyrite tetrahedrite and gold palladium correlates with cu ag se and s mineralogical and laser ablation icp ms study confirmed that pd is homogeneously distributed in chalcopyrite which contains up to 110 ppm pd and tetrahedrite containing up to 20 ppm pd an assessment of the pd and pt budget at kalmakyr showed the potential of approximately 17 t of pd and 1 7 t of pt

feo and tio2 concentrations in the south pole aitken basin implications for mantle composition and basin formation we use newly developed spectroscopic methods for determining feo and tio2 abundances to study the huge 2500 km diameter south pole aitken basin the floor of this basin shows iron and titanium values which are weakly correlated and largely range from 7 to 14 wt feo and from 0 5 to 1 5 wt tio2 this composition is consistent with an approximate 1 1 mixture of lower crustal material like that found elsewhere on the moon and mantle rock containing 10 16 wt feo and 0 1 wt tio2 although mantle rock appears to compose about 50 of the floor deposits models of the formation of large impact basins predict that virtually all the floor materials ought to be derived from the mantle

subepithermal au pd mineralization associated with an alkalic porphyry cu au deposit mount milligan quesnel terrane british columbia canada at the mount milligan cu au porphyry deposit quesnel terrane british columbia canada barren and weakly mineralized late stage hydrothermal veins occur in volcanic rocks adjacent to zones of cu au porphyry mineralization and have overprinted the porphyry stage veins the earliest of the late stage hydrothermal veins are barren and consist of quartz pyrite carbonate chlorite tourmaline these veins are similar to transitional to late stage hydrothermal veins in other alkaline porphyry cu au deposits and we consider these to be the equivalent of transitional post porphyry pre epithermal quartz sericite pyrite veins in calc alkaline porphyry environments a later generation of volumetrically minor mineralized veins are composed of pyrite hg and as bearing quartz carbonate chlorite and contain early electrum arsenopyrite tetra hedrite tennantite platinum group element pge tellurides galena sphalerite barite and chalcopyrite as inclusions in pyrite and a later assemblage of electrum pge tellurides arsenides and antimonides galena sphalerite chalcopyrite and various au ag te bi minerals in annealed fractures and open space infillings in quartz and pyrite metal precipitation in these veins was temporally and spatially associated with the deposition and later recrystallization of pyrite primary fluid inclusions in quartz in the barren and weakly mineralized veins are two phase l v homogenize to liquid over a narrow range in t 170 270 c n 96 12 veins and show a wide range in salinity 4 2 wt nacl equiv to 28 7 wt cacl2 equiv when all samples are considered however individual veins show narrow ranges in salinity and homogenization temperature la icp ms analyses indicate that the fluids were highly enriched in as to 2 260 ppm sb to 230 ppm b to 5 400 ppm au 1 2 ppm and pd 0 5 1 ppm but depleted in cu 80 ppm compared to typical porphyry stage fluids metal ratios in the fluids overlap with bulk rock metal ratios in the mineralized veins the inclusions are interpreted to contain a contracted magmatic vapor produced by boiling that lost cu during the formation of porphyry stage veins at depth fluids show decreasing b as sb and increasing sr ca and salinity with time stable c o and h isotope analyses of vein minerals indicate that mixing of this magmatic fluid with meteoric water was not responsible for metal deposition rather metal precipitation was possibly the result of mixing of the magmatic derived fluid with a heated saline groundwater the precious and accessory metal mineralogy of the hydrothermal veins is similar to that found in low to intermediate sulfidation epithermal systems fluid inclusion microthermometry and chlorite thermometry constrain the approximate formation conditions of the veins between 200 and 1 500 bars and 240 and 280 c after the formation of the mineralized veins circulation of low salinity metal depleted fluids occurred these latest stage fluids may have formed by mixing of the saline magmatic fluid groundwater hybrid with meteoric water the results of this study suggest a genetic link between porphyry stage events and the deposition of au and pge in late stage veins in an alkalic igneous environment recognition of hydrothermal processes involving the transport of au pge as sb bi te b rich fluids in the subepithermal regimes implies that low sulfidation epithermal au deposits may have been present in the shallower parts of the magmatic hydrothermal complex and that there is potential for the discovery of pge rich epithermal veins in less deeply exhumed terranes on the other hand the formation of high grade low sulfidation epithermal au pge deposits may be prohibited if porphyry epithermal transitional fluids precipitate ore metals through mixing with groundwater prior to reaching the level where meteoric water mixing and epithermal boiling normally occur

mineralization controls in island arc settings insights from philippine metallic deposits abstract a review of the gold copper volcanogenic massive sulfide and ultramafic hosted i e chromitite nickel sulfide platinum group minerals deposits in the philippines is presented it is critical that a thorough understanding of the spatial and temporal relationship among magmatism structures and mineralization must be gained if the correct evaluation of the economic potential of a particular deposit is to be done structural features conducive to precious and base metal mineralizations are associated with shear zones extensional jogs and collision zones in northern luzon alkali and adakitic magmatism are considered good markers for gold copper mineralization volcanogenic massive sulfide deposits are hosted by either ophiolites of marginal basin origin or metamorphic terranes exploration works on these deposits have been geared in determining the gold content of the massive sulfides chromitite deposits are related with ultramafic rock hosted deposits their occurrence is attributed to crystallization magma mixing and mantle melt interaction processes in subduction related settings the multiple stages of partial melting responsible for the formation of supra subduction zone ophiolites result in the generation of second to third stage melts that are enriched in nickel sulfides and platinum group minerals on the basis of structural geochemical and tectonic controls panay mindoro and central mindanao and the sierra madre leyte and samar are good exploration targets for precious and base metal deposition in the western and eastern sides of the philippines respectively

a mariner 10 color study of mercurian craters 1 we have used recalibrated mariner 10 color image data uv and orange to examine spectral trends associated with crater features on the incoming hemisphere of mercury spacecraft images of the moon galileo and clementine and lunar sample laboratory spectra provide a framework for interpreting the mercurian data two spectral parameter images were constructed one reveals opaque mineral abundance and the other provides a map of variations related to optical maturity and feo content the crater kuiper and its rays are bright mainly because they are fresh immature but also because kuiper has excavated material with a lower opaque content than the surroundings under the influence of space weathering kuiper will eventually lose its rays and evolve into a bright floored crater like lermontov lermontov and nearby smaller craters are examples of craters that are likely mature but remain bright because of the low opaque material exposed on their floors in this portion of the planet it appears that a surface layer with moderate opaque abundance overlies low opaque material found at depth on the basis of estimates of crater excavation depths we suggest that the moderate opaque surface layer is 3 4 km thick this two layer stratigraphy is reminiscent of the lunar highland crust and may have originated in similar magma ocean processes we also describe a feature that exposes dark material with a relatively high opaque content this feature could be a mercurian analog to a lunar dark halo impact crater or perhaps a pyroclastic deposit this implies that opaque rich possibly mafic magmas were generated in the interior and reached the surface through effusive or explosive activity

platinum group minerals in the santo tomas ii philex porphyry copper gold deposit luzon island philippines mineralized quartz diorites of the santo tomas ii porphyry copper gold deposit carry high au contents average 1 8 ppm as well as 160 ppb pd and 38 ppb pt values of other platinum group elements pge and rhenium are below the analytical detection limits there is a significant positive correlation between au and cu the highest pd values were detected in the most au and cu rich rocks platinum group minerals pgm occur exclusively as inclusions in chalcopyrite and bornite potential pd and pt contents in sulphide concentrates are estimated at 1 5 g t and 0 4 g t respectively the precious metal assemblages consist of merenskyite main pgm kotulskite moncheite native gold electrum hessite and petzite polyphase fluid inclusions in quartz veinlets associated with a pgm bearing bornite chalcopyrite magnetite assemblage are characterized by high salinity 35 to 60 eq wt nacl and high trapping temperatures between 380 and 520 c they may represent primary magmatic hydrothermal fluids which have been responsible for the transport of pd pt and au as chloride complexes

global occurrence trend of high ca pyroxene on lunar highlands and its implications we present details of the global distribution of high ca pyroxene hcp rich sites in the lunar highlands based on the global data set of hyperspectral reflectance obtained by the selene spectral profiler most hcp rich sites in the lunar highlands are found at fresh impact craters in each crater most of the detection points are distributed on the ejecta rim and floor of the impact craters rather than the central peaks while the central peaks are dominated by purest anorthosite pan this indicates that hcp rich materials originate from relatively shallower regions of the lunar crust than pan in addition while all ray craters with sizes larger than 40 km possess hcp rich materials small fresh craters with sizes less than 6 10 km do not indicating that the uppermost mixing layers in the lunar crust are not dominated by hcp based on these results we propose that in the upper lunar crust a hcp rich zone overlying the pan layer exists below the uppermost mixing layer this hcp rich zone may originate from interstitial melt during the formation of the flotation anorthositic cumulate while an impact ejecta origin impact melt origin and or magmatic intrusion into the upper lunar crust may also account for the occurrence of hcp rich sites in the highlands

the lunar rayed crater population characteristics of the spatial distribution and ray retention abstract the global statistics for young impact craters on the moon is used to unravel potential spatial asymmetries that may have been introduced by the particular orbital configuration of a synchronously rotating satellite only craters that exhibit bright ejecta rays extending for several crater radii were considered in this study this crater population is younger than about 750 ma the shape of the crater size frequency distribution does not show strong dependence on the target properties mare vs highlands however slightly lower frequencies indicate a shorter retention of the visibility of rays in mare units when their visibility is purely due to immaturity and not due to composition rays of small craters fade away much faster large old rayed craters sustain their visibility longer than the average crater population because of the compositional contrast between rays and mare material and thus obscure the cratering record when investigated for spatial variations using the existence of rays purely based on optical maturity instead of visibility as marker horizon for the copernican eratosthenian boundary suggests a shift from 1 1 ga to 750 ma the spatial distribution of lunar rayed craters namely the latitudinal and longitudinal frequency variations does not agree with previous analytical and numerical studies although there is an apparent hemispherical asymmetry centred close to the apex the density distribution is patchy and no predicted spatial pattern could be confirmed spatial distribution corrections accounting for the lower frequencies in the mare areas did not result in a better agreement with the analytical estimates density variations are less than 15 over vast parts of the lunar surface and the uncertainties for absolute surface ages are similar however variations of up to 50 are found even for the more numerous small craters these extreme values are located at high latitudes a combination of crater forming projectile flux distribution and micrometeorite bombardment which acts on maturation of the ray systems could prove as an explanation for the contradicting observed rayed crater distribution an analysis of the older craters is more challenging on the moon because earlier geological processes complicate the setting and the orbital configuration of the moon earth sun projectile system altered with time

geochemistry and 40ar 39ar geochronology of impact melt clasts in feldspathic lunar meteorites implications for lunar bombardment history we studied 42 impact melt clasts from lunar feldspathic regolith breccias macalpine hills mac 88105 queen alexandra range que 93069 dar al gani dag 262 and dag 400 for texture chemical composition and or chronology although the textures are similar to the impactmelt clasts identified in mafic apollo and luna samples the meteorite clasts are chemically distinct from them having lower fe ti k and p thus representing previously unsampled impacts the 40ar 39ar ages on 31 of the impact melts the first ages on impact melt samples from outside the region of the apollo and luna sampling sites range from 4 to 2 5 ga we interpret these samples to have been created in at least six and possibly nine or more different impact events one inferred impact event may be consistent with the apollo impact melt rock age cluster at 3 9 ga but the meteorite impact melt clasts with this age are different in chemistry from the apollo samples suggesting that the mechanism responsible for the 3 9 ga peak in lunar impact melt clast ages is a lunar wide phenomenon no meteorite impact melts have ages more than 1 older than 4 0 ga this observation is consistent with but does not require a lunar cataclysm

phase relations among tellurides sulfides and oxides pt ii applications to telluride bearing ore deposits data on telluride bearing mineral assemblages from various types of ore deposits are compiled and interpreted in terms of the prevailing fugacities of te 2 s 2 and the temperature during deposition in the majority of hydrothermal deposits the appearance of tellurides after initial deposition of sulfides reflects an increase in the f sub te 2 f sub s 2 ratio most likely due to input of h 2 te from a magmatic source in some vein deposits such as boulder county colorado initial deposition of native tellurium is followed by deposition of minerals with progressively lower tellurium content indicating a decrease in f sub te 2 over the course of telluride deposition this trend may reflect local isolation of early formed minerals from the hydrothermal fluids and or progressive depletion of tellurium at the source ore minerals in other deposits such as mahd adh dhahab saudi arabia reveal systematic temporal or spatial variations in mineralogy that are attributed to introduction of a tellurium rich fluid into a preexisting sulfide assemblage and subsequent buffering of f sub te 2 and f sub s 2 by reactions such as 2pbs te 2 2pbte s 2 this buffering may exert considerable control on vein minerals such as the presence and relative abundance of gold and calaverite and the presence or absence of native tellurium

iron and titanium abundance and maturity degree distribution on the lunar nearside new digital images of the lunar nearside albedos at 0 42 0 65 0 75 and 0 95 m derived from telescopic data were used to map the abundance and distribution of iron titanium and maturity degree on the lunar nearside developing the approach by p luceyet al 1995 science268 1150 a method of separating contributions of the fe and ti abundance and maturity degree to spectral properties of the lunar surface is presented the main objective of the method is an analysis of the 3d correlation diagram of optical characteristics of regolith material with the aim of choosing a coordinate system providing the best correlations of these characteristics with fe and ti abundance data for the surveyor luna and apollo landing sites and with maturity degree laboratory measurements of lunar samples by e fischer and c pieters e g 1996 j geophys res 101 2225 to find the coordinates a geometrical optics model of light scattering in particulate media enabling to calculate the absorption coefficient from albedo measurements is used an analysis of the correlation diagram feo tio2provides two maps characterizing optical types of the lunar nearside in particular the maps show that the basalts of mare serenitatis and mare tranquillitatis are not widely extended on the lunar nearside the maturity degree parameteris feo was also mapped regions withis feo 50 are young craters surrounded by ray systems whereas the conditionis feo 70 corresponds to regions associated with copernicus ejecta western boundaries of mare tranquillitatis and mare serenitatis and a portion of the south highland the new map of feo distribution on the lunar nearside was used to study a correlation between iron content and distribution of remanent magnetism over the lunar surface the relationship obtained has a reverse behavior the lower the iron content the higher the magnetism

precious metal distribution and fluid inclusion petrography of the elatsite porphyry copper deposit bulgaria the elatsite porphyry copper deposit occurs in an island arc setting hosted by late cretaceous monzonitic monzodioritic porphyry stocks which were emplaced into precambrian cambrian phyllites trace element data of the late cretaceous intrusive rocks suggest that they are i type volcanic arc granitoids two main ore mineral assemblages are distinguished 1 magnetite bornite chalcopyrite and 2 chalcopyrite pyrite the first one is linked to potassic propylitic and the second to phyllic argillic alteration minor ore minerals are hematite molybdenite sphalerite pyrrhotite marcasite hessite and solid solutions of linnaeite siegenite carrollite tetrahedrite tennantite clausthalite galena gold electrum and merenskyite moncheite precious metal contents are relatively high throughout the deposit but au pd and pt are concentrated more strongly in the magnetite bornite chalcopyrite assemblage average grades of au ag pd and pt calculated for the 0 33 cu ore body are 0 96 0 19 0 007 and 0 002 g t respectively analyses of flotation concentrates revealed 25 6 cu and ag au pd and pt contents of 33 0 13 6 0 72 and 0 15 g t respectively the copper mineralisation at elatsite took place at pressures of 120 to 300 bar corresponding to depths of formation of 1 to 3 km under hydrostatic conditions the precious metals were probably transported jointly as chloride complexes in highly saline magmatic hydrothermal solutions the fluids had temperatures of 340 to 700 c and salinities of 28 to 64 nacl and mixed with meteoric water

mineral chemistry and sources of fluid and sulfur at the katbasu gold deposit in south tianshan nw china abstract katbasu is a gold and copper deposit located in an arc on the southern margin of the ili central tianshan micro continent an in situ method was conducted to acquire trace element concentrations to elucidate the origins and chemistry of the fluid in the katbasu deposit this included oxygen isotopes in quartz as well as sulfur isotopes and trace elements concentrations in pyrite trace elements in gold deficient veins have higher concentrations compared to those in the gold bearing veins the 18o values of gold deficient veins are between 3 9 and 8 1 which imply a magmatic oxygen isotope signature in contrast oxygen isotopes in gold bearing veins range between 1 3 and 5 8 indicating the involvement of meteoric water in the mineralization system this data combined with evidence from alteration style and metal assemblages shows that the ore forming fluids at the katbasu gold deposit is of a magmatic origin the data also indicates that meteoric water diluted the magmatic fluid and caused an oversaturation of gold causing precipitation of native gold grains trace elements in pyrite show no difference among the veins analyzed however they have distinctly different trace element patterns of pyrite from orogenic gold deposits based on the 34s values of pyrite 8 3 12 9 and the lack of coeval regional metamorphism we conclude that the enriched 34s at the katbasu gold deposit is derived from a subducted slab during the late carboniferous

optical maturity of ejecta from large rayed lunar craters lucey et al 2000 have developed a methodology for extracting an optical maturity parameter omat from multispectral clementine images the omat parameter characterizes the overall maturity of lunar soils and crater ejecta by changes in reflectance spectra using these omat images we surveyed large craters 20 km diameter on the moon that had previously been mapped as possessing or possibly possessing rayed ejecta we generated average radial profiles of omat values for rays of these large craters from these profiles we classified the craters into three relative age groups 1 older than copernicus inferred age of 810 myr 2 intermediate and 3 as young or younger than tycho inferred age of 109 myr we suspect that there is a bias to our classification scheme such that the omat profiles of smaller craters look like that of larger but older craters nevertheless some large craters such as eudoxus 67 km and aristillus 55 km are now known from this study to have optically mature ejecta and therefore are suspected to be older than copernicus this is consistent with an age of 1 3 gyr suggested for aristillus by ryder et al 1991 such craters were included by mcewen et al 1997 when estimating the density of craters younger than or contemporaneous with copernicus therefore the case for a modest increase in the cratering rate in the past 800 myr versus the previous 2 4 gyr indicated from that work has been weakened grier and mcewen 2001 given current constraints on dating large and recent lunar craters we cannot support or disprove the hypothesis that there has been a significant increase in the rate of large terrestrial impact events in the past 100 400 myr

mapping the feo and tio2 content of the lunar surface with multispectral imagery the derivation of quantitative elemental concentrations from multispectral imaging of the moon has long been a goal of lunar remote sensing concentration maps at the spatial resolutions available from the recent clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust lucey et al 1995 presented a method for extracting the concentration of fe from multispectral imaging of the moon this paper examines and quantifies important aspects ofthat technique left unexamined by lucey et al which had the potential to severely limit its utility these aspects include the effects of maturity grain size mineralogy shading due to topography and the presence of glass we also present a new algorithm for derivation of tio2 from multispectral imaging of both mare and highland units we find that both techniques are only weakly sensitive to maturity and that they have about 1 wt accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by blewett et al 1997 we also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by pieters and coworkers and hapke and coworkers we find the view of hapke and coworkers to be more consistent with our observations using a global mosaic of clementine multispectral data and these element derivation algorithms we find that the global modal abundance of feo is 4 5 wt 1 wt and the global modal abundance of tio2 is 0 45 wt 1 wt

on the diversity of the pge content in chromitites hosted in ophiolites and in porphyry cu systems controlling factors abstract the present study on the diversity of the platinum group elements pge content in chromitites and porphyry cu deposits from greece and everywhere literature data aims to define factors controlling precious metal enrichment in ophiolite complexes and the unknown pd and pt potential in porphyry cu systems through an integrated set of mineralogical and geochemical approaches the pge content in chromitites associated with ophiolite complexes is commonly low a few 100 s of ppb however a significant pge enrichment up to 10 s of ppm is a feature of relatively small chromite occurrences regardless their major element composition plots of the pd ir versus normalized pt pt ratios defined separate fields corresponding to various chromitite types large chromite deposits exhibit low pd ir values reflecting low degree of fractionation primitive magmas negative pt pt partial melting of already depleted mantle and increasing partial melting trend from high al towards to high cr deposits the association with hydrous silicates cr bearing hydrogrossular chlorite and serpentine and texture features of os ir ru rich compatible or ipge minerals coupled with very low pd ir and negative pt pt values were attributed to an origin by partial melting of already depleted mantle and increased partial melting degree during a subsequent crustal mantle recycling stage via fluid driven processes assuming that the increasing pd ir reflects a fractionation trend of parent magma a significant enrichment in pt and pd incompatible or ppge occurring in small occurrences either high cr or high al type may be a sensitive fingerprint for the orientation in the mantle sequence of the ophiolites and exploration for chromite commonly the pge content in porphyry cu mo au deposits is less than 10 ppb however elevated pd pt contents over 6 ppm in sulfide rich samples are a characteristic feature of certain porphyry cu au alkaline intrusions evidence of a favorable tectonic setting post collisional for the origin of porphyry cu au pd pt elevated porphyry deposits include elevated up to hundreds of ppm contents in cr co ni and re and elevated 187 os 188 os ratios reflecting mixing and contribution to the magma composition the oxidized nature of parent magmas abundant magnetite and the evolved mineralized fluid system in porphyry deposits are considered to be critical requirements for the transportation and deposition of sufficient au and pge elevated pd pt and au contents in porphyry deposits combined with the association of the major pd mineral merenskyite with bornite and chalcopyrite major cu minerals are encouraging economic factors for the contribution to the global pd pt production

the phanerozoic impact cratering rate evidence from the farside of the moon the relatively recent 1 b y flux of asteroids and comets forming large craters on the earth and moon may be accurately recorded by craters with bright rays on the moon s farside many previously unknown farside rayed craters are clearly distinguished in the low phase angle images returned by the clementine spacecraft some large rayed craters on the lunar nearside are probably significantly older than 1 ga rays remain visible over the maria due to compositional contrasts long after soils have reached optical maturity most of the farside crust has a more homogeneous composition and only immature rays are visible the size frequency distribution of farside rayed craters is similar to that measured for eratosthenian craters up to 3 2 b y at diameters larger than 15 km the areal density of farside rayed craters matches that of a corrected tabulation of nearside copernican craters hence the presence of bright rays due to immature soils around large craters provides a consistent time stratigraphic basis for defining the base of the copernican system the density of large craters less than 3 2 b y old is 3 2 times higher than that of large farside rayed craters alone this observation can be interpreted in two ways 1 the average cratering rate has been constant over the past 3 2 b y and the base of the copernican is 1 ga or 2 the cratering rate has increased in recent geologic time and the base of the copernican is less than 1 ga we favor the latter interpretation because the rays of copernicus 800 850 m y old appear to be very close to optical maturity suggesting that the average copernican cratering rate was 35 higher than the average eratosthenian rate other lines of evidence for an increase in the phanerozoic 545 ga cratering rate are 1 the densities of small craters superimposed on copernicus and apollo landing sites 2 the rates estimated from well dated terrestrial craters 120 m y and from present day astronomical observations and 3 the proterozoic rate suggested by the crater record of australia the hypothesis most consistent with several key observations is that the cratering rate has increased by 2x during the past 300 m y

a distinctive pd hg signature in detrital gold derived from alkalic cu au porphyry systems abstract this study comprises the first systematic classification of native gold geochemistry within alkalic porphyry cu au systems and the placer expression of such systems the geochemistry and mineral associations of gold from four alkalic porphyry deposits in british columbia canada afton mount milligan mount polley and copper mountain have been compared to comment on the likely detrital gold expression of similar systems globally populations of gold grains collected from in situ hypogene mineralization as well as fluvial deposits downstream of these deposits have been characterized in terms of their alloy composition au ag cu hg and pd and associated mineral inclusions these data are combined to generate a microchemical signature gold compositions vary according to the alteration zone within a porphyry system previous compositional studies of gold in porphyry systems have focused on the most economically important ore associated with potassic alteration wherein native gold hosted either by bornite or chalcopyrite comprises tiny blebs typically 5 20 m containing detectable cu in the gold alloy to a maximum of around 5 but quite variable 2 30 wt ag the presence of such grains have been confirmed in hypogene ore from the four systems studied but they have been shown to be compositionally distinct from detrital gold collected from nearby fluvial placers which exhibit a strong pd and hg signature both in the alloy and as mineral inclusions several workers have described late stage veins associated with alkalic porphyries which contain distinctive pd hg bearing minerals in association with other sulphides and sulphosalts this unusual mineralogy has been observed in the mineral inclusion suites of populations of detrital gold grains collected in the environs of the porphyry systems we conclude that whilst the micron scale cu rich gold grains formed in potassically altered rocks are in general too small to be recovered during routine sediment sampling those formed in later stage hydrothermal systems are larger and exhibit a distinctive microchemical signature which may be differentiated from those of gold formed in other mineralizing systems consequently compositional studies of detrital gold could underpin a mineral indicator methodology in the exploration for alkalic porphyry cu au deposits

mineralogy of the lunar crust results from clementine received 1997 december 5 accepted in revised form 1998 september 15 abstract the central peaks of 109 impact craters across the moon are examined with clementine ultraviolet visible uvvis camera multispectral data the craters range in diameter from 40 to 180 km and are believed to have exhumed material from 5 30 km beneath the surface to form the peaks including both upper and lower crustal rocks depending on whether craters have impacted into highlands or basins representative five color spectra from spectrally and spatially distinct areas within the peaks are classified using spectral parameters including key ratio which is related to mafic mineral abundance and spectral curvature linked to absorption band shape which distinguishes between low and high ca pyroxene and olivine the spectral parameters are correlated to mineralogical abundances related in turn to highland plutonic rock compositions the derived rock compositions for the various central peaks are presented in a global map from these results it is evident that the lunar crust is compositionally diverse both globally and at local 100 m scales found within individual sets of central peaks although the central peaks compositions imply a crust that is generally consistent with previous models of crustal structure they also indicate a more anorthositic crust than generally assumed with a bulk plagioclase content of 8 1 evolving from pure anorthosite near the surface towards more mafic low ca pyroxene rich compositions with depth comparable to anorthositic norite evidence for mafic plutons occurs in both highlands and basins and represent all mafic highland rock types however the lower crust is more compositionally diverse than the highlands with both a greater range of rock types and more diversity within individual sets of central peaks

mesozoic porphyry cu au mineralization and associated adakite like magmatism in the philippines insights from the giant atlas deposit the atlas porphyry cu au deposit is located in central cebu island in the philippines with a proven mineral reserve of 1420 mt at 0 45 cu 0 24 g t au 0 018 g t mo and 1 8 g t ag it is associated with the lutopan quartz diorite porphyry stock that was emplaced into the cretaceous volcano sedimentary sequences of the cansi formation two stages of hypogene alteration have been identified at atlas stage i quartz magnetite chalcopyrite pyrite veins associated with potassic and propylitic alteration and stage ii anhydrite pyrite chalcopyrite specularite veins associated with phyllic alteration supergene gypsum veins are also present mineralization is mainly associated with the stage i and stage ii veins the lutopan quartz diorite porphyry yielded a zircon u pb age of 108 5 1 6 ma and is characterized by high sr y 54 69 with the corresponding magma having high oxygen fugacity avg fmq 2 7 avg ce4 ce3 of zircon 439 and h2o concentrations presence of amphibole and biotite phenocrysts and low magmatic temperatures avg ti in zircon thermometry 706 c the relatively low la yb ratios 9 11 listric shaped normalized ree patterns with weak or absent eu anomalies together with zircon ehf t values of 3 4 to 10 0 whole rock isr values of 0 70373 0 70382 end t values of 2 4 3 4 and mg numbers of 49 53 suggest that the lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts that evolved to adakite like trace element compositions through amphibole fractionation stage i veins yielded a pyrite re os isochron age of 110 2 5 6 ma making atlas the only mesozoic porphyry deposit discovered in the philippines

probable age of autolycus and calibration of lunar stratigraphy 39 ar 40 ar analyses of three petrographically distinct shocked apollo 15 kreep i e high k rare earth element p and other trace element contents basalt samples demonstrate that a major impact event affected all three samples at about 2 1 ga the copernican system craters aristillus and autolycus are to the north a ray from one of them crosses the landing site and had been suggested prior to the apollo 15 mission as a source of material that could be used to date these craters autolycus the older of the two is in a particularly appropriate terrain and is the most likely source of the 2 1 ga heating and delivery event with this calibration point and if autolycus really is a copernican crater the copernican system lasted twice as long as has previously been suggested furthermore the moon was not subjected to a constant cratering rate over the past 3 b y the average rate in the preceding eratosthenian must have been twice that in the copernican

imaging of lunar surface maturity the physical evolution of the lunar surface with exposure to the space environment is termed maturation and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure several quantitative measures or indices of maturity have been proposed and employed including the abundance of solar wind gas abundance of various types of agglutinates various measures of grain size and is feo among the changes attendant with space exposure are striking changes in the optical characteristics of soils mature lunar soils are dark red and exhibit reduced spectral contrast relative to immature soils this paper presents an optical maturity index that quantifies the spectral effects of maturation we show that this optical maturity index correlates with other maturity indices about as well as the accepted maturity indices correlate among themselves and is only weakly coupled to composition the modest correlations among maturity indices suggest important controls on individual maturity indices other than age uncorrelated variations in the rates of accumulation of individual indicators or variations in depths over which indicators are emplaced in addition to mixing these effects conspire to reduce the equivalence of maturity and duration of surface exposure optical maturity illustrates some of these effects showing that ejecta of large and small craters mature at different rates and that the interiors and ejecta of large craters exhibit systematically different optical maturities the same or analogous effects are likely to influence other maturity indices

abundance and distribution of iron on the moon the abundance and distribution of iron on the moon is derived from a near global data set from clementine the determined iron content of the lunar highlands crust 3 percent iron by weight supports the hypothesis that much of the lunar crust was derived from a magma ocean the iron content of lower crustal material exposed by the south pole aitken impact basin on the lunar farside is higher 7 to 8 percent by weight and consistent with a basaltic composition this composition supports earlier evidence that the lunar crust becomes more mafic with depth the data also suggest that the bulk composition of the moon differs from that of the earth9s mantle this difference excludes models for lunar origin that require the earth and moon to have the same compositions such as fission and coaccretion and favors giant impact and capture

composition and exposure age of the apollo 16 cayley and descartes regions from clementine data normalizing the optical effects of space weathering in order to quantitatively assess the composition of the lunar surface from reflectance spectroscopy it is necessary to be able to differentiate between the optical effects due to composition and those due to exposure to space weathering processes laboratory analyses of returned lunar soils are used to show that limited quantitative compositional information and the exposure age of the lunar surface can be determined using straightforward calculations from remotely acquired reflectance data sampled with a small number of spectral channels exposure age approximated by is feo where is is the characteristic ferromagnetic signal from single domain iron metal is estimated using a ratio of the reflectance at a wavelength outside of the 1 m ferrous iron absorption band to the reflectance at a wavelength within the band the iron plus titanium content of a soil can then be calculated from its is feo and reflectance these combined techniques are applied to clementine uvvis multispectral data of the lunar highlands in the vicinity of the apollo 16 landing site the is feo and feo tio2 contents are calculated for this region materials associated with recently formed impact craters and recent and or ongoing downslope movement are easily detected as nonmature the feo tio2 content of the descartes mountains is found to be 1 2 wt less than the cayley plains west of the apollo 16 landing site localized areas of compositional heterogeneity associated with some small impact events are also revealed a model for normalizing the optical contribution due to exposure to space weathering processes is applied to the clementine uvvis data in order to bring the data to an equivalent mature exposure state this approach allows residual spectral differences between the observed materials to be confidently interpreted as being due to compositional differences alone rather than to differences both of composition and of exposure the exposure normalized data reveal that this region of the highlands is characterized by limited large scale compositional heterogeneity that is detectable by a small number of spectral bandpasses the descartes mountains are identified as being more anorthositic than the cayley plains units most small impacts in the region excavated material compositionally similar to material surrounding them with the notable exceptions of the impacts that created south ray crater and an unnamed crater on the floor of abulfeda

absolute model ages from lunar crater morphology the degradation state of an impact crater is an indicator of its age previous workers have used crater degradation states to estimate ages of surfaces or geomorphological features one example is the degree of freshness method developed by pohn and offield 1970 here we attempted to produce an empirical calibration that yields absolute model ages based upon the degree of freshness technique for craters 8 20 km in diameter to produce the calibration we first selected 15 craters with degree of freshness values ranging from 2 5 to 6 3 next we used the kaguya terrain camera data to measure crater density on the ejecta of these craters from which absolute model age could be calculated the resulting absolute model ages ranged from 0 9 to 4 0 ga we used two linear regressions to describe the relationship between the absolute model age and degree of freshness of the craters we fitted each trend with two linear least squares regressions where the first regression represents craters with a degree of freshness from 0 0 to 4 9 and the second regression from 5 0 to 7 0 the 95 confidence belt shows that the calibrations are accurate to 0 5 ga to 1 1 ga for the fresh crater regression 5 0 7 0 and slightly more accurate to 0 3 ga to 0 1 ga for the degraded crater regression 0 0 4 9 however the degraded crater regression is likely based upon craters with continuous ejecta that are crater saturated thus implying that craters with a degree of freshness 3 8 ga

the ridgeway gold copper deposit a high grade alkalic porphyry deposit in the lachlan fold belt new south wales australia ridgeway is a high grade gold copper porphyry deposit 54 mt at 2 5 g t au and 0 77 cu related to an alkalic intrusive complex of monzonitic composition the deposit occurs within the cadia district of new south wales australia which consists of a cluster of four late ordovician gold copper porphyry deposits and two iron copper gold skarn deposits with a combined gold resource in excess of 574 metric tonnes t the deposits lie on a 7 km long northwest oriented corridor of alteration and mineralization transverse to the axis of the postulated volcanic arc alteration and mineralization at ridgeway are zoned around a vertically attenuated intrusive complex of monzodioritic to quartz monzonitic composition distinct styles of veining and alteration are related to different intrusive phases of the monzonite complex with the intensity of alteration and grade of mineralization decreasing from early to late mineral intrusions early mineral intrusions are associated with intense actinolite magnetite biotite calc potassic alteration and up to four stages of high grade quartz magnetite sulfide veining bornite is the most abundant sulfide formed during early stage alteration and correlates well with gold moderate to weak intensity orthoclase biotite plus or minus magnetite potassic alteration accompanies the inter and late mineral intrusions this alteration being associated with chalcopyrite and pyrite rich quartz orthoclase veins propylitic and sodic albite pyrite alteration assemblages are peripheral to and locally overprint the potassic alteration phyllic alteration is restricted to the margins of late stage faults the fluid inclusion assemblage comprises one and two salt bearing brine inclusions in addition to aqueous liquid vapor inclusions of low to moderate salinity no low density vapor rich inclusions are present indicating that the fluids from which the quartz veins precipitated did not enter the liquid vapor field of the h2o nacl system the brine inclusions undergo final homogenization to liquid via halite dissolution this phenomenon in addition to the absence of low density vapor inclusions suggests that the mineralizing fluids at ridgeway were nonboiling hypersaline brines that exsolved directly from the crystallizing magma the presence of mineralized aplitic vein dikes and comb quartz layering are interpreted to indicate that the early and transitional stages of mineralization at ridgeway formed at the transition between magmatic and hydrothermal conditions

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

gold in porphyry copper deposits experimental determination of the distribution of gold in the cu fe s system at 400 to 700 c experiments in the system au cu fe s were carried out at temperatures of 400 to 700 c to determine how much gold could be accommodated by bornite and chalcopyrite the two most common ore minerals in porphyry copper gold deposits our results show that for all temperatures bornite contains one order of magnitude more gold than chalcopyrite or intermediate solid solution iss its high temperature equivalent the range of gold concentrations in bornite and chalcopyrite or iss decreases with decreasing temperature from 1 280 to 8 200 ppm au in bornite and 100 to 125 ppm au in iss at 600 c to 235 to 364 ppm au in bornite and 5 to 16 ppm au in chalcopyrite or iss at 500 c and to 13 to 80 ppm au in bornite and 2 to 4 ppm au in chalcopyrite or iss at 400 c the amount of gold in bornite is also strongly dependent on the composition of bornite being highest in stoichiometric bornite compositions cu5fes4 and decreasing toward cu rich and cu poor compositions phase equilibrium constraints for solutions with geologically reasonable reduced sulfur contents indicate that high temperature porphyry copper gold deposits will contain bornite and magnetite whereas lower temperature deposits whether primary or overprinted by phyllic alteration will contain chalcopyrite and pyrite if gold is present in the ore forming solutions more of it will be deposited in high temperature porphyry copper gold deposits where it will be closely associated with bornite coexisting magnetite in these deposits should generate magnetic anomalies lower temperature deposits will contain less gold which is hosted by pyrite as well as chalcopyrite and will lack magnetic anomalies comparison of the amount of gold hosted by natural porphyry copper gold ores to that hosted by bornite and chalcopyrite in our experiments suggests that significant amounts of gold can be lost from these deposits into surrounding hydrothermal systems

pge geochemistry of the fengshan porphyry skarn cu mo deposit hubei province eastern china abstract the fengshan cu mo deposit is located in the western part of the jiurui cu au mo district in the late mesozoic middle lower yangtze river metallogenic belt yrmb eastern china the mineralization is spatially associated with the fengshan granodiorite porphyry stock 149 138 ma where two types of ore bodies porphyry skarn occur the fengshan deposit is located on the yangtze craton i e in an intracontinental extensional environment a geological setting not considered by previous studies of pge abundance and distribution in porphyry systems for the present investigation the pge geochemistry of fourteen samples of the granodiorite ore and flotation concentrates were determined by icp ms after preconcentration by the lead fire assay technique from large 30 g samples a maximum of 32 ppb pd and 81 2 ppb pt is reported for the molybdenum flotation concentrate cu au pt pd contents from flotation concentrate samples are almost 1 to 2 orders of magnitude higher than those reported for ore samples this is especially true for the pt content covariant diagrams of cu and mo with noble metals au ag pt and pd reveal weak correlation between cu vs au ag and mo vs pt also au shows a slightly positive relationship with pt and pd it is apparent that pd and pt contents of flotation concentrate from the fengshan deposit are considerably lower than those reported for porphyry deposits in an island arc setting however au and ag appear to be elevated in the fengshan deposit the intrusion derived from an enriched mantle source high oxygen fugacity fo2 and liberation of mantle sulfates during partial melting are the first steps for pge enrichment in porphyry cu deposits however the fengshan granodiorite was most likely generated by partial melting of enriched mantle that was previously metasomatized by slab melts related to an ancient subduction system au pt and pd in potassic alteration zones and or endocontact zones are transported as an aqueous chloride complex in high temperature hypersaline fluid in contrast au pt and pd would be transported by bisulfide complex in low temperature intermediate salinity fluid in phyllic alteration zones and or exocontact marble that is distinctly different from the porphyry cu deposits in an island arc environment where intrusion derived directly from slab melting and pd and pt are transported only as chloride complexes

speciation and solubility of palladium in aqueous magmatic hydrothermal solutions combining thermodynamic data at 25c and 1 bar with correlation algorithms enables prediction of equilibrium dissociation constants for aqueous platinum group element pge complexes at high pressures and temperatures we used these data 1 to calculate the speciation of pd ii in nacl solutions at temperatures to 750c pressures to 2 kbar and values from 3 to 8 and 2 to predict the solubility of palladium at 2 kbar as a function of temperature oxygen fugacity f sub o2 ph and total chloride concentration m sub t cl sup minus calculations indicate that as ph increases there is a sharp transition from chloride to hydroxide complex dominance at all chloride concentrations this shift occurs at or below neutral ph in dilute solution but at m sub t cl sup minus ge 1 0 pd ii chloride complexes account for the majority of dissolved pd ii well into alkaline conditions solubility of palladium increases with increasing temperature m sub t cl sup minus and f sub o2 at 700c 2 kbar and the f sub o2 set by the fmq buffer palladium solubility in a 3 0 m nacl solution is approximately 0 3 ppm at a ph of 4 and one unit ph variation can change palladium solubility by two orders of magnitude these results suggest that pge can be transported as chloridemore complexes in cl rich magmatic hydrothermal solutions like those inferred from petrologic studies of the stillwater and bushveld complexes less

platinum group element and gold contents in the skouries porphyry copper deposit chalkidiki peninsula northern greece the skouries porphyry copper deposit is located in the eastern chalkidiki peninsula northern greece along with several other porphyry copper occurrences this deposit establishes the northeastern part of the servomacedonian zone as a porphyry copper region amphibolite mica schist and two mica gneiss are the predominant rock types exposed in the skouries area these rocks have been intruded by the skouries porphyry stock which is of subalkaline composition and is tertiary in age 18 ma the skouries porphyry intrusion and the surrounding country rocks are strongly fractured and intensely altered by hydrothermal fluids in addition to intense silicification a prominent alteration type is potassic whereas phyllic and propylitic types are less common mineralization mainly includes chalcopyrite pyrite bornite chalcocite and magnetite in the form of veins stockworks and disseminations native gold and electrum commonly are present as small inclusions in chalcopyrite although lateral zoning is not defined clearly a vertical zoning in terms of both metal mineralogy and overall metal content is apparent a zone of oxidation azurite malachite covers the upper part of the ore and is underlain by a zone of reduced rock rich in covellite and chalcocite which in turn is underlain by the most important ore type including a chalcopyrite pyrite bornite magnetite assemblage both weakly and intensively altered porphyry samples from the deposit were analyzed for major oxides trace elements and all platinum group elements pge the stock exhibits high levels of cu au ag b bi co se and te barium and sr contents are also high while rb is low resulting thereby in high k rb and low rb sr ratios palladium concentrations range from less than 2 to 480 ppb ruthenium content ranges from 8 to 41 ppb and pt from 2 to 10 ppb osmium ir and rh content is below detection limit the average au ag ratio is 0 87 which is consistent with the range of several worldwide porphyry copper deposits on the basis of factor analysis of selected geochemical data a strong positive interelement correlation r or 0 83 between au ag pd nd te coupled with their association with silica appears to support a correlation of these precious metals with silicification rather than potassic type alteration such a relationship may suggest similar behavior of these metals and a common origin a positive correlation of cu with iron r 0 86 which is consistent with the association of chalcopyrite with magnetite and the low correlation of te and pd with cu may suggest that these metals and to a lesser extent copper have been redistributed during a late stage of evolution of the skouries porphyry system furthermore the close association of te with precious metals combined with the relatively low temperature for telluride minerals stability may indicate that at least partly precious metal tellurides have been formed in a relatively shallow and less hot environment

geomorphologic mapping of the lunar crater tycho and its impact melt deposits abstract using selene kaguya terrain camera and lunar reconnaissance orbiter camera lroc data we produced a new high resolution 10 m pixel geomorphological and impact melt distribution map for the lunar crater tycho the distal ejecta blanket and crater rays were investigated using lroc wide angle camera wac data 100 m pixel while the fine scale morphologies of individual units were documented using high resolution 0 5 m pixel lroc narrow angle camera nac frames in particular tycho shows a large coherent melt sheet on the crater floor melt pools and flows along the terraced walls and melt pools on the continuous ejecta blanket the crater floor of tycho exhibits three distinct units distinguishable by their elevation and hummocky surface morphology the distribution of impact melt pools and ejecta as well as topographic asymmetries support the formation of tycho as an oblique impact from the w sw the asymmetric ejecta blanket significantly reduced melt emplacement uprange and the depressed uprange crater rim at tycho suggest an impact angle of 25 45

a new indicator mineral methodology based on a generic bi pb te s mineral inclusion signature in detrital gold from porphyry and low intermediate sulfidation epithermal environments in yukon territory canada porphyry epithermal and orogenic gold are two of the most important styles of gold bearing mineralization within orogenic belts populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein ag cu and hg in the gold alloy may vary across the full range exhibited by natural gold this paper describes a new methodology whereby orogenic and porphyry epithermal gold may be distinguished according to the mineralogy of microscopic inclusions observed within detrital gold particles a total of 1459 gold grains from hypogene eluvial and placer environments around calc alkaline porphyry deposits in yukon nucleus revenue casino sonora gulch and cyprus klaza have been characterized in terms of their alloy compositions au ag cu and hg and their inclusion mineralogy despite differences in the evolution of the different magmatic hydrothermal systems the gold exhibits a clear bi pb te s mineralogy in the inclusion suite a signature which is either extremely weak or most commonly absent in both yukon orogenic gold and gold from orogenic settings worldwide generic systematic compositional changes in ore mineralogy previously identified across the porphyry epithermal transition have been identified in the corresponding inclusion suites observed in samples from yukon however the bi te association repeatedly observed in gold from the porphyry mineralization persists into the epithermal environment ranges of p t x conditions are replicated in the geological environments which define generic styles of mineralization these parameters influence both gold alloy composition and ore mineralogy of which inclusion suites are a manifestation consequently we propose that this methodology approach can underpin a widely applicable indicator methodology based on detrital gold

galileo observations of post imbrium lunar craters during the first earth moon flyby copernican age craters are among the most conspicuous features seen on the far side and western limb of the moon in the galileo multispectral images acquired in december 1990 among the new morphologic observations of far side craters are bright rays continuous ejecta deposits and dark rings associated with probable impact melt veneers these observations suggest that the mapped age assignments of several large far side craters ohm robertson and possibly lowell and lenz need revision new crater size frequency measurements on lunar orbiter images suggest the following age reassignments hausen 170 km diameter pythagoras 120 km and bullialdus 61 km from eratosthenian to upper imbrian and carpenter 60 km and harpalus 39 km from copernican to eratosthenian colors and albedos of craters away from impact melt veneers are correlated with their geologic emplacement ages as determined from counts of superposed craters these age color relations are used to estimate the emplacement age time since impact event for other copernican age craters these age color relations indicate a probable copernican age for 27 far side or western limb craters larger than 10 km diameter that were not previously mapped as copernican the apparent deficiency of copernican craters on the far side compared with the near side in published geologic maps is not present in our data age color trends differ between mare and highland regions and between the interiors and continuous ejecta of the craters similar trends are established for color and albedo versus soil maturity indices for the returned lunar samples with distinct trends for mare and highland soils however the mare versus highland offsets are reversed in the two comparisons these relations can be explained by variations in regolith thicknesses and rates of mixing with relatively fresh crystalline ejecta therefore the soil maturity trends represent longer geologic time periods in regions with thinner regoliths such as the maria

characterization of lunar swirls at mare ingenii a model for space weathering at magnetic anomalies 1 analysis of spectra from the clementine ultraviolet visible and near infrared cameras of small immature craters and surface soils both on and adjacent to the lunar swirls at mare ingenii has yielded the following conclusions about space weathering at a magnetic anomaly 1 despite having spectral characteristics of immaturity the lunar swirls are not freshly exposed surfaces 2 the swirl surfaces are regions of retarded weathering while immediately adjacent regions experience accelerated weathering 3 weathering in the off swirl regions darkens and flattens the spectrum with little to no reddening which suggests that the production of larger 40 nm nanophase iron dominates in these locations as a result of charged particle sorting by the magnetic field preliminary analysis of two other lunar swirl regions reiner gamma and mare marginis is consistent with our observations at mare ingenii our results indicate that sputtering vapor deposition implanted solar wind hydrogen and agglutination share responsibility for creating the range in npfe0 particle sizes responsible for the spectral effects of space weathering

near infrared spectroscopy of probable impact melt from three large lunar highland craters abstract the composition of small areas within three large lunar highland craters are compared using near infrared earth based telescopic data spectra from many areas in the walls and central peaks of the craters indicate the presence of crystalline components which include olivine two types of pyroxene and sometimes fe bearing feldspar spectra from other regions suspected of being impact melt deposits located on the floors and walls of the three craters have remarkably similar yet anomalous features these features are interpreted to indicate the presence of pyroxene fe bearing glass and fe bearing feldspar pyroxene and feldspar are believed to occur primarily in the form of lithic clasts and rapidly recrystallized impact melt the fe bearing glass is interpreted as impact melt glass

pin pricking the elephant evidence on the origin of the ontong java plateau from pb sr hf nd isotopic characteristics of odp leg 192 basalts age corrected pb sr and nd isotope ratios early aptian basalt from four widely separated sites on the ontong java plateau that were sampled during ocean drilling program leg 192 cluster within the small range reported for three earlier drill sites for outcrops in the solomon islands and for the nauru and east mariana basins hf isotope ratios also display only a small spread of values a vitric tuff with end t 4 5 that lies immediately above basement at site 1183 represents the only probable example from leg 192 of the singgalo magma type flows of which comprise the upper 46 750 m of sections in the solomon islands and at leg 130 site 807 on the northern flank of the plateau all of the leg 192 lavas including the high mgo 8 10 wt kroenke type basalts found at sites 1185 and 1187 have end t between 5 8 and 6 5 they are isotopically indistinguishable from the abundant kwaimbaita basalt type in the solomon islands and at previous plateau nauru basin and east mariana basin drill sites the little fractionated kroenke type flows thus indicate that the uniform isotopic signature of the more evolved kwaimbaita type basalt with 5 8 wt mgo is not simply a result of homogenization of isotopically variable magmas in extensive magma chambers but instead must reflect the signature of an inherently rather homogeneous relative to the scale of melting mantle source in the context of a plume head model the kwaimbaita type magmas previously have been inferred to represent mantle derived largely from the plume source region our isotopic modelling suggests that such mantle could correspond to originally primitive mantle that experienced a rather minor fractionation event e g a small amount of partial melting approximately 3 ga or earlier and subsequently evolved in nearly closed system fashion until being tapped by plateau magmatism in the early aptian these results are consistent with current models of a compositionally distinct lower mantle and a plume head origin for the plateau however several other key aspects of the plateau are not easily explained by the plume head model the plateau also poses significant challenges for asteroid impact icelandic type and plate separation perisphere models at present no simple model appears to account satisfactorily for all of the observed first order features of the ontong java plateau the geological society of london 2004

lunar swirls examining crustal magnetic anomalies and space weathering trends 1 we have used multispectral images from clementine and data from lunar prospector s magnetometer to conduct a survey of lunar crustal magnetic anomalies prominent lunar swirls and lesser known swirl markings to provide new information on the nature of swirls and their association with magnetic anomalies we find that all swirls and swirl like albedo patterns are associated with areas of magnetized crust but not all areas of magnetized crust are colocated with swirl like albedo anomalies all observed swirls exhibit spectral characteristics similar to immature material and generally have slightly lower feo values compared with their surroundings as determined with a multispectral iron mapping method we discuss these results in relation to the various hypotheses for swirl formation the comet impact hypothesis for lunar swirls would not predict a difference in the spectrally determined feo content between swirls and nearby ordinary surfaces the compositional difference could be explained as a consequence of 1 magnetic shielding of the surface from the solar wind which could produce anomalous space weathering little darkening with limited reddening and potentially alter the predictions of the multispectral iron mapping algorithm while the compositional contrast could be enhanced by delivery of lower feo ejecta from outside the swirl and 2 accumulation of fine plagioclase rich dust moving under the influence of electric fields induced by solar wind interactions with a magnetic anomaly therefore we cannot at present clearly distinguish between the solar wind shielding and electrostatic dust accumulation models for swirl formation we describe future measurements that could contribute to solution of the puzzle of swirl origin

palladium platinum and gold distribution in porphyry cu mo deposits of russia and mongolia the porphyry cu mo deposits in the southern siberian craton and northern mongolia including subduction collision and rift related igneous series of early paleozoic to mesozoic age are all characterized by varying crustal contribution to their parent magmas and the presence of explosive breccias precious metal and associated element contents are reported for mineralized samples sulphide concentrates and chalcopyrite molybdenite flotation concentrates from porphyry cu mo intrusions of russia sora aksug and zhireken and mongolia erdenetiun obo average pge contents in rocks are 17 ppb pd and 22 ppb pt in the aksug deposit 13 ppb pd and 10 ppb detection limit pt in the sora 14 ppb pd and 21 ppb pt in the erdenetuin obo and 18 ppb pd and 28 ppb pt in the zhireken deposit average gold content in rocks is 61 ppb in the aksug deposit 17 ppb in the sora 21 ppb in the erdenetuin obo and 30 ppb in the zhireken deposit the highest average 2 3 ppm ag was recorded in the rocks of the sora deposit in general the precious metal distribution in the studied deposits has no apparent relationship with the alteration types the molybdenum content in rocks ranges between 1 and 128 ppm mo in the aksug deposit from 1 to 5400 ppm mo in the sora deposit from 2 to 755 ppm mo in the erdenetuin obo deposit and from 3 to 1530 ppm mo in the zhireken deposit the average copper content in rocks is 1540 ppm in the aksug deposit 460 ppm in the sora deposit 1460 ppm in the erdenetuin obo deposit and 220 ppm in the zhireken deposit the cu mo ratios are highest in the aksug and erdenetuin obo deposits and lowest in the sora and zhireken deposits the correlation matrix for selected major and trace element data on mineralized samples and sulphide concentrates 34 samples indicates that precious metals are associated with either chalcopyrite or molybdenite copper shows a strong positive correlation with au and pd r 0 91 while mo shows a strong positive correlation with pt r 0 98 in addition mo exhibits a strong positive correlation with w r 0 94 an interelement positive correlation between precious metals is 0 57 ag au the pd and pt contents of both chalcopyrite and molybdenite in flotation concentrates are low varying from 9 to 83 ppb pd and from 10 to 110 ppb pt the highest values recorded are 924 ppb pd in sulphide concentrates from the aksug deposit and 684 ppb pd and 299 ppb pt in sulphide concentrate from breccia of the zhireken deposit the highest gold content 5450 ppb au is in chalcopyrite flotation concentrate from the aksug deposit whereas in the majority of concentrates the gold content is in the order of a few hundreds parts per billion the relatively low contents and limited variation of the precious metal contents in the individual deposits of russia and mongolia point to the essential role of the composition of the source and composition of parent magmas

galileo multispectral imaging of the north polar and eastern limb regions of the moon multispectral images obtained during the galileo probe s second encounter with the moon reveal the compositional nature of the north polar regions and the northeastern limb mare deposits in these regions are found to be primarily low to medium titanium lavas and as on the western limb show only slight spectral heterogeneity the northern light plains are found to have the spectral characteristics of highlands materials show little evidence for the presence of cryptomaria and were most likely emplaced by impact processes regardless of their age

clementine images of the lunar sample return stations refinement of feo and tio2 mapping techniques clementine uvvis images of the lunar sample return sites have been processed and used to produce refined calibrations for the iron and titanium determination algorithms of lucey et al 1995 1996 the high spatial resolution of the clementine data permits individual sampling stations to be resolved at the apollo 15 16 and 17 landing sites we find an excellent linear correlation between the spectral fe and ti parameters and the average feo and tio 2 contents of soils sampled at each site or station this correlation demonstrates that these techniques can confidently be applied to other areas of the moon the luna 24 site does not fit the ti relation found for other sites suggesting that either its sample is nonrepresentative or the reported landing coordinates are incorrect

multispectral images of mercury from the first messenger flyby analysis of global and regional color trends abstract we have analyzed messenger multispectral images of mercury in order to gain information on the nature of materials present on the planet s surface the quantitative analysis tools of lucey which are built on the hapke conceptual framework for the reflectance of a silicate regolith allow us to derive spectral parameter images that are sensitive to the abundance of ferrous iron in silicates the abundance of opaque phases and the state of maturity of the surface consistent with previous estimates we conclude that the silicate portion of mercury s surface is low in ferrous iron with a small range of variation the spectral changes that accompany regolith maturation on mercury are consistent with lunar style space weathering via the accumulation of nanophase iron the spectral character of mercury s major surface units high reflectance plains intermediate terrain and low reflectance material can be attributed to variations in the abundance of an opaque phase s a class of minor color unit the red spots occurs in at least three morphological varieties two of which are associated with deposits interpreted to be of pyroclastic origin the bright crater floor deposits a second type of minor unit have extremely shallow blue spectral slopes that are unrelated to the presence of immature material

palladium platinum and gold concentration in porphyry copper systems of greece and their genetic significance compilation of new and published data on precious metal and associated trace element contents in mineralized porphyry copper intrusions of greece indicates that the pd content in the potassic propylitic zone of the skouries deposit is relatively high ranging between 60 and 200 ppb average 110 ppb whereas in the porphyry copper intrusions of gerakario and pontokerasia it is very low 3 ppb pd the oxidized zone of fissoka op 65 exhibits low pd and cu contents but higher au te as pb and zn contents the pt content is much lower than pd in the porphyry copper intrusions studied the pd pt ratio in the skouries deposit ranges from 9 to 60 while it is much lower 2 in the mineralized samples from fissoka gerakario and pontokerasia a decrease of the pd content and pd pt ratio with increasing te as pb and zn content may indicate that the pd distribution in porphyry copper systems is effected by the evolution of the magma hydrothermal system also mineralogical and geochemical data on the skouries deposit coupled with textural relations between base metal sulphides pgm and au ag tellurides indicate that the main pd bearing mineral merenskyite is associated with the vein type chalcopyrite or bornite and was deposited during the main stage of mineralization the high magmatic oxidation state and the magmatic features of the hydrothermal system limited participation of meteoric portion in the skouries intrusion may be a strong control of its pd potential assuming that pd is mainly associated with chalcopyrite in the porphyry copper deposits the calculated pd from measured pd contents in chalcopyrite average 3300 ppb pd are relatively high and comparable to that in the chalcopyrite concentrate made after the processing of large composite drill hole samples 2400 ppb pd to 21 wt cu it is considered to be an encouraging economic factor for pd as a by product probably along with au although the main product is cu

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

understanding the geologic evolution of northern tibetan plateau with multiple thermochronometers abstract the early onset of deformation following the india asia collision neogene expanse of uplift and complex systems that comprise strike slip faults thrust faults and intermontane basins characterize the cenozoic tectonism of northern tibetan plateau and raise two prominent questions in orogenic geodynamics 1 what mechanism s control s the transfer of stress related to the india asia collision across the distance of 2000 km and 2 why the development of high topography was delayed in the northern tibetan plateau and what does it reveal about how the internal forces and external boundary conditions evolved to address these two questions we reconstruct a holistic spatial temporal deformation history of the northern tibetan plateau by using a range of thermochronometers with closure temperature spanning from 350 c to 60 70 c this multi thermochronometer study reveals three stages of faulting related cooling in the early cretaceous in paleocene eocene and in middle late miocene we observe that paleocene eocene deformation was spatially restricted and mostly occurred on reactivated cretaceous structures indicating a control of pre existing weakness on early cenozoic deformation extensive neogene deformation contrasts with restricted paleocene eocene deformation and relatively quiescent shortening during the oligocene early miocene which implies a change in the regional tectonics regime global plate reconstructions show that this tectonic reorganization is coeval with an increase in pacific asia plate convergence rates we argue that this change in regional tectonics is a result of increasing constrictive environment of the eastern plate boundary which changed the behavior of the altyn tagh fault the boundary fault of northern tibetan plateau causing it to change from feeding slip into structures out of the plateau to feeding slip into structures at plateau margins

relative and absolute ages of individual craters and the rate of infalls on the moon in the post imbrium period abstract this paper contains a reasonably successful attempt to determine relative ages and then absolute ages of individual craters younger than imbrium and the rate of infalls onto the moon as a function of time after the tail of the massive premare bombardment became depleted before 3 aeons 1 aeon 109 years ago there was a period of minimal numbers of infalls the rate of infalls increased rather steadily from this minimum to the present the rate in the geologically recent past 0 3 aeon was about two times that found for the period immediately after the last of the major lave outpourings 3 2 aeons absolute ages were determined for large craters 8 km from crater counts on the surfaces within and on the rims of the large craters key dates were 0 and 0 3 aeon for terrestrial meteoritic craters 3 2 3 5 3 8 and 3 82 aeons for the various mare surfaces according to the determinations of d e wilhelms 1980 geologic history of the moon u s geol surv prof pap and 3 85 aeons from the formation of imbrium