chemical and physical transfers in an ultramafic rock weathering profile part 1 supergene dissolution of pt bearing chromite chemical weathering and supergene dissolution processes of pt bearing chromite have been studied in a lateritic weathering profile developed on ultramafic rocks in new caledonia southwest pacific the chemical distributions of alkaline earth transition metals and precious metals including pt and pd were determined in a weathering profile varying from bedrock at the base upward through coarse and fine saprolites and capped by a mottled zone and a lateritic colluvial nodular horizon chemi cal analyses and mass balance calculations suggest that progressive weathering of the parent rock is characterized by an enrichment of fe co and mn a segregation of ni at the boundary between the bedrock and the coarse sapolite and in the lower part of the fine saprolite and a depletion of mg ca si al and cr the higher concentration of transition metals at the interface between the coarse and fine saprolite is due to vertical transfer and precipitation at the base of the weathering profile in such a lateritic environment the pt bearing chromite grains are progressively dissolved and the pt group minerals pgm are released in the weathering mantle with a preferential depletion of pd with regard to pt

thermoluminescence and nuclear particle tracks in alha 81005 evidence for a brief transit time thermoluminescence and nuclear particle track measurements were made on the antarctic meteorite alha 81005 no nuclear particle tracks were found in lithic fragments indicating that the clast material never resided at the very surface of the parent body the unusually low natural thermoluminescence of this material is interpreted as being due to a combination of anomalous fading and thermal decay the thermal decay could be due to very long terrestrial age or heating either during atmospheric entry in a near sun orbit or during a parent body impact event impact heating is considered the more likely of these possibilities for this meteorite if the impact heating interpretation is correct the thermoluminescence data constrains the space exposure time of the object to be less than 2 500 years such a brief earth transit time is consistent with a lunar origin for this meteorite

the antiquity indicator argon 40 argon 36 for lunar surface samples calibrated by uranium 235 xenon 136 dating several solar gas rich lunar soils and breccias have trapped 40ar 36ar ratios 10 although solar ar is expected to yield a ratio of 0 01 radiogenic 40ar produced in the lunar crust from 40k decay was outgassed into the lunar atmosphere ionized accelerated in the electromagnetic field of the solar wind and reimplanted into lunar surface material the 40ar loss rate depends on the decreasing abundance of 40k in order to calibrate the time dependence of the 40ar 36ar ratio in lunar surface material the period of reimplantation of lunar atmospheric ions and of solar wind ar was determined using the 235u 136xe dating method that relies on secondary cosmic ray neutron induced fission of 235u we identified the trapped fissiogenic and cosmogenic noble gases in lunar breccia 14307 and lunar soils 70001 8 70181 74261 and 75081 uranium and th concentrations were determined in the 74261 soil for which we obtain the 235u 136xe time of implantation of 3 25 0 38 0 60 ga ago on the basis of several cosmogenic noble gas signatures we calculate the duration of this near surface exposure of 393 45 ma and an average shielding depth below the lunar surface of 73 7 g cm2 a second recent exposure to solar and cosmic ray particles occurred after this soil was excavated from shorty crater 17 2 1 4 ma ago using a compilation of all lunar data with reliable trapped ar isotopic ratios and pre exposure times we infer a calibration curve of implantation times based on the trapped40 ar 36ar ratio a possible trend for the increase with time of the solar 3he 4he and 20ne 22ne ratios of about 12 ga and about 2 ga respectively is also discussed

lead isotope study of zn pb ore deposits associated with the basque cantabrian basin and paleozoic basement northern spain a total of forty three galena samples from syngenetic and epigenetic pb zn mineralizations emplaced in the lower cretaceous basque cantabrian basin and paleozoic basement of the cinco villas massif in the western pyrenees have been analyzed for pb isotopic composition galena from sedex mineralizations hosted in carboniferous clastic rocks in the cinco villas massif display an homogeneous lead isotopic signature 206pb 2044pb 18 43 207pb 204pb 15 66 208pb 204pb 38 69 suggesting a single lead reservoir these values are slightly more radiogenic than lead from other european hercynian deposits possibly reflecting the influence of a more evolved upper crustal source underlying paleozoic sediments are proposed as lead source for the cinco villas massif ores analyses from twenty six galena samples from the four strata bound ore districts hosted in mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition galena from the western santander districts e g reocin is characterized by more radiogenic isotope values 206pb 204pb 18 74 207pb 204pb 15 67 208pb 204pb 38 73 than those from the central and eastern districts troya legorreta central and western vizcaya 206pb 204pb 18 59 207pb 204pb 15 66 208pb 204pb 38 73 in all districts the most likely source for these mineralizations was the thick sequence of lower cretaceous clastic sediments the existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories in both sub basins isotopic ratios indicate an increase in crustal influence as the age of the ores decreases

lunar highland meteorites and the composition of the lunar crust abstract major minor and trace element data obtained by neutron activation techniques and by spark source mass spectrometry ssms on two lunar meteorites mac88104 and mac88105 are reported both mac samples were also analysed for their contents and isotopic compositions of rare gases additional ssms data were obtained on four lunar highland meteorites previously found in antarctica alha81005 y791197 y82192 and y86032 mac88104 and mac88105 are very similar in chemistry suggesting that they are pieces of a single fall event the bulk chemical composition of mac88104 5 is not very different from the other lunar highland meteorites highly aluminous with relatively low contents of ree and siderophile element concentrations slightly above 1 of a ci chondritic level however mafic element concentrations mg cr mn etc are slightly lower in mac88104 5 than in the other lunar highland meteorites the contents of solar rare gases in the two mac samples are low indicating only a small regolith contribution in agreement with rare petrographically identifiable regolith components the mac samples and also y82192 and y86032 are classified as fragmental breccias with negligible regolith components in contrast to alha81005 and y791197 which are regolith breccias with high solar wind derived rare gas contents there is no correlation among lunar meteorites between peak shock pressures and solar gas contents indicating that peak shock pressures of up to 25 gpa do not lead to gas loss a low 26al activity vogt et al 1990 and high contents of cosmogenic rare gases in mac88104 5 suggest a long exposure 400 000 years in the lunar sub surface k ar ages are in excess of 3 9 by lunar highland meteorites and compositionally similar granulitic rocks from the apollo 16 and 17 landing sites contain about 1 of a ci chondritic component according to siderophile and volatile element contents but independent of the amount of regolith components apparently the major fraction of meteoritic elements in these rocks was not provided by micrometeorites impacting the regolith the abundances of siderophile e g ir and volatile elements may therefore reflect the last spike of accretion of the moon after the formation of the anorthositic crust lunar meteorites of highland origin are chemically different from the bulk of the apollo 16 highland samples in having higher fe mg ratios and lower contents and less fractionated patterns of incompatible and siderophile elements since lunar highland meteorites are associated with at least three but probably four different fall events and since they are not derived from chemically exotic front side terranes they may represent a better sampling of the average chemical composition of the lunar crust than previous estimates based on returned lunar samples and remote sensing data a comparison between an average highland composition derived by taylor 1982 and an estimate based on lunar highland meteorites shows that the taylor composition contains higher concentrations and more fractionated incompatible elements mainly because of a substantial amount of kreep a trace element rich highly fractionated component from the front side of the moon not present at the sites from which the lunar meteorites come

a new sulphur isotopic study of some iberian pyrite belt deposits evidence of a textural control on sulphur isotope composition the sulphide deposits of the iberian pyrite belt ipb represent an ore province of global importance our study presents 113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores measured 34s values range from 26 to 10 mostly for massive and stockwork ores in agreement with data previously published in situ laser 34s analyses reveals a close correlation of 34s with texture primary diagenetic textures are dominated by relatively low 34s 8 to 2 whereas stockwork feeder textures are dominated by higher 34s 3 to 5 intermediate textures mainly coarse textures in stratiform zones have intermediate 34s although they are mostly dominated by the high 34s component rare barite has a homogeneous 34s around 18 which is consistent with direct derivation from lower carboniferous seawater sulphate a dual source of sulphide sulphur in the ipb deposits has been considered a hydrothermal source derived from reduction of coeval seawater sulphate in the convective systems is represented by sulphide in the feeder zones here variations in 34s are caused by variations in the extent of the sulphate reduction which governs the so4 h2s ratio the second end member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface as reflected in the primary textures a distinct geographical variation in 34s and texture from sw more bacteriogenic and primary textures to ne more hydrothermal textures and 34s which reflects a variation in the relative input of each source was likely controlled by local geological environments given that the sulphur isotope characteristics of the ipb deposits are unlike most vms and kuroko deposits and noting the dominance of a mixed reduced sedimentary and volcanic environment we suggest that the ipb could represent an ore style which is intermediate between volcanic and sedimentary hosted massive sulphide types

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

geochemistry and petrography of the macalpine hills lunar meteorites abstract macalpine hills 88104 and 88105 are anorthositic lunar meteorites recovered from the same area in antarctica which are demonstrated to be paired samples of the same fall petrographic studies of matrix and clasts show that mac88104 5 is a polymict breccia dominated by impact melt clasts it contains a small amount of highland impact glass and very few regolith glass spherules it is better classified as a fragmental breccia than a regolith breccia the bulk composition is ferroan mg 63 and highly aluminous al 2 o 3 28 ree and other incompatible element concentrations are very low compositions of anorthositic granulitic and impact melt breccia clasts are very similar to but distinct from matrix composition mac88104 5 is very similar in composition to the other anorthositic lunar meteorites but each of the meteorites is distinct the anorthositic lunar meteorites especially mac88104 5 and y82192 3 86032 are very similar to north ray crater feldspathic fragmental breccias in compositon and petrography these fragmental lunar meteorites may have been ancient deeply buried breccias from the megaregolith comparisons of chemical petrographic features and exposure histories suggest that the twelve lunar meteorites were derived from two to nine but probably four to seven impacts onto the lunar surface discrepancies between the proportions of lunar meteorites and results of apollo missions may be due to unrepresentative sampling lunar meteorites provide valuable new information on the nature of the lunar crust

10be and36cl depth profiles in an apollo 15 drill core cosmic ray produced10be t1 2 1 6 106 years and36cl t1 2 3 0 105 years have been measured in the apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry from these experiments the half attenuation length for10be production and36cl production were calculated to be 120 g cm2 and 132 g cm2 150 400 g cm2 region the measured half attenuation length for10be is slightly longer than that predicted by the reedy arnold theoretical model the flatter and somewhat deeper maximum seen in the36cl profile compared to the10be 26al and53mn profiles can be explained by production from secondary thermal neutrons on35cl

northwest africa 482 a crystalline impact melt breccia from the lunar highlands northwest africa 482 nwa 482 is a crystalline impact melt breccia from the moon with highlands affinities the recrystallized matrix and the clast population are both highly anorthositic clasts are all related to the ferroan anorthosite suite and include isolated plagioclase crystals and lithic anorthosites troctolites and spinel troctolites potassium rare earth element and phosphorus bearing kreep and mare lithologies are both absent constraining the source area ofthis meteorite to a highland terrain with little to no kreep component most likely on the far side of the moon glass is present in shock veins cutting through the sample and in several large melt pockets indicating a second impact event there are two separate events recorded in the 40ar 39ar system one at 3750 ma which completely reset the k ar system and one at 2400 ma which caused onlypartial degassing these events could represent respectively crystallization ofthe impact melt breccia and later formation of the glass or the formation of the glass and a later thermal event the terrestrial age of the meteorite is 8 6 1 3 ka this age corresponds well with the modest amount ofweathering in the rock in the form ofsecondaryphyllosilicates and carbonates based on terrestrial age and location lithology and chemistry nwa 482 is unique among known lunar meteorites

concentration of gold in in situ laterites from mato grosso the gold concentration studied is located in lateritic soils overlying precambrian schists of the cuiaba group in mato grosso brazil the following five horizons may be recognized from bottom to top 1 a gray blue altered schist horizon 2 a red argillaceous alterite 3 a horizon characterized by iron oxihydroxide rich pebbles and quartz fragments in an iron oxihydroxide rich matrix and clays 4 an iron crust and 5 the present soil the most significant gold content is found in the third horizon just below the iron crust according to geological study and morphological observations of the gold particles the gold ore mined today is the result of two combined processes i e the ferrallitic alteration of quartz lodes enclosed in schists and the effect of the red argillaceous alterite which acts as an impervious structure preventing the largest gold grains from migrating downward during their mechanical concentration

support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages lunar meteorites represent a more random sampling of lunar material than the apollo or luna collections and as such lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis within the lunar meteorite breccias mac 88105 que 93069 dag 262 and dag 400 seven to nine different impact events are represented with 40ar 39ar ages between 2 76 and 3 92 billion years ago ga the lack of impact melt older than 3 92 ga supports the concept of a short intense period of bombardment in the earth moon system at approximately 3 9 ga this was an anomalous spike of impact activity on the otherwise declining impact frequency curve

a basis for geochemical exploration models for tropical terrains abstract the principles and mechanisms of geochemical dispersion and the formation of anomalies govern the effective use of exploration geochemistry in any terrain the dispersion characteristics can be summarized in the form of geochemical exploration models that illustrate the nature of the surface expression of mineralization and that in turn should aid the planning execution and interpretation of future surveys in much of the tropics and sub tropics and in some areas in higher latitudes evidence of weathering under former seasonal tropical conditions is preserved these regions have similarities in landforms deeply weathered regoliths and hence geochemical dispersion patterns relating to such weathering conditions geochemical models can be based on these common features and their subsequent modification under different climatic regimes two model systems are described one in which the deeply weathered profile is preserved and the other in which the profile has been partially truncated these models can be used to compare and contrast the surface expression of mineralization under present day arid savanna and equatorial rainforest environments thereby in effect extending the data base for exploration of such areas

history of the paired lunar meteorites mac88104 and mac88105 derived from noble gas isotopes radionuclides and some chemical abundances abstract noble gas isotopes radionuclides and chemical abundances were studied in the lunar meteorites mac88104 and mac88105 collected in the macalpine hills area of antarctica the concentrations of the noble gas isotopes and the radionuclide activities in the two meteorites are essentially identical proving that the two meteorites are paired from 40k 40ar dating we obtain a gas retention age of 3550 400 ma typical for lunar surface material probably before breccia compaction the mac88104 5 material resided for 630 200 ma at an average shielding depth of 85 g cm 2 that is about 50 cm below the lunar surface in the lunar regolith as judged from the concentration of cosmic ray produced kr and xe isotopes although this duration of lunar regolith residence is relatively long mac88104 5 represent immature regolith material the concentration of solar wind implanted noble gases are two orders of magnitude lower than those in mature lunar soil the reason for that might be the relatively high average shielding the 40 ar 36ar ratio of the trapped component is 5 7 1 0 indicating an intermediate antiquity of the material we estimate that the solar wind and lunar atmospheric particles were implanted about 2000 ma ago the radionuclide activities allow us to derive the exposure history of the mac88104 5 material the duration of the moon earth transfer was 0 24 ma production of the radionuclides on the lunar surface immediately before ejection is possible but duration and shielding depth for such an exposure cannot be determined from our data we obtain a terrestrial age of 0 1 tterr 0 6 ma and an ejection time of mac88104 5 from the moon of 0 1 tejection 0 8 ma the exposure histories of the lunar meteorites discussed in this work indicate that at least two impact events are required for their ejection from the moon our first noble gas results for lunar meteorite yamato 793274 show that it represents mature lunar regolith material with relatively high concentrations of solar wind implanted noble gases and a duration of several hundred million years of exposure to cosmic rays

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

trapped noble gases indicate lunar origin for antarctic meteorite the isotopic abundances of the noble gases he ne ar kr xe are reported for antarctic meteorite alha81005 it contains solar wind implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites alha81005 also contains a large excess 40ar component which is identical to the component in lunar fines implanted from the lunar atmosphere large concentrations of cosmogenic 21ne 82kr and 126xe in alha81005 indicate a total cosmic ray exposure age of 2 108 years the noble gas data alone are strong evidence for a lunar origin of this meteorite

mineralogy of the sulphide deposits at sulitjelma northern norway abstract the pyritic vms deposits at sulitjelma northern norway have been regionally metamorphosed at amphibolite facies during the caledonide orogen the deposits contain a wide diversity of sulphide sulphosalt and related minerals which are systematically discussed with reference to their occurrence paragenesis and mineral chemistry most of these minerals are however rare to absent within the massive deposits which are dominantly composed of pyrite with subordinate chalcopyrite sphalerite and pyrrhotite galena arsenopyrite cubanite molybdenite stannite and tetrahedrite occur in minor amounts syn metamorphic mobilisation has however resulted in the redistribution of a range of elements including cu pb sb as ni and au these elements have been reconcentrated into mobilised segregations where they have crystallised under retrograde conditions into a range of discrete phases ore mobilisation which took place along tectonically controlled pathways is however of a highly localised nature with a considerable range in mineral textures and parageneses observed in different samples typical associations within these mobilisates include a range of cu pb sb and cu pb as sulphosalts including bournonite meneghinite seligmannite and jordanite breithauptite nisbite costibite arsenopyrite and gudmundite co existing galena is characterised by elevated concentrations of ag bi and se argentian tetrahedrite 9 17 wt ag the chief ag carrier in the deposits as well as other ag bearing phases including pyrargyrite hessite and empressite are strongly enriched in the mobilisates gold as electrum 50 75 wt au and more rarely as aurostibite is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits a further range of minerals including native antimony native arsenic allargentum dyscrasite argentite mckinstryite jalpaite and native silver occur as low temperature breakdown products of earlier formed minerals preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution

geochemistry and mineralogy of platinum group elements at hartley platinum mine zimbabwe the main sulfide zone msz is the most prominent layer of the great dyke layered intrusion carrying economic platinum group element pge mineralization at the hartley platinum mine the msz is up to some meters thick and is composed of a basal pge rich subzone which overlaps slightly with a base metal sulfide rich subzone on top based on the degree of sulfide mineralization and pge ratios the subzones can be further divided into geochemically distinct layers stratigraphically upwards the msz displays metal profiles characterized by increasing cu ni pt pd and ppge ipge ratios accompanied by a general element decoupling in the order pd pt base metals more specifically ipge pd pt ni cu co s sulfides au te bi the fine structure of the msz is regarded to reflect primary magmatic features of consecutive batches of sulfide accumulation concomitant scavenging of pge and fractionation sulfide deposition was followed by a second limited subsolidus stage of pge redistribution mineralogically most of the pd and rh is hosted in pentlandite whereas pt is dominantly present in the form of discrete platinum group minerals pgm within the msz sequence sperrylite is present throughout the pge subzone of the msz cooperite braggite occur mainly in its basal part and the pt pd bismuthotellurides concentrate at the top these findings indicate that a large proportion of the pge primarily concentrated in sulfide under magmatic conditions was redistributed in the subsolidus stage and formed discrete pgm with available reactant partners chemical gradients and magmatic hydrothermal fluids probably led to small scale redistribution of pge within the msz

the natural thermoluminescence of meteorites iii lunar and basaltic meteorites natural thermoluminescence tl data have been obtained for the lunar meteorite macalpine hills 88104 5 and for 65 eucrites howardites diogenites and mesosiderites in order to investigate their recent thermal and radiation histories all these meteorites have low levels of natural tl compared to chondrites which is primarily because they display anomalous fading i e fading by non classical mechanisms however some have especially low natural tl 5 krad at 250 c in the glow curve which cannot be attributed to anomalous fading or thermal fading over especially large terrestrial ages and which must reflect heating within the last 105 106 y in some cases this heating may have been associated with shock e g lew85303 or regolith processes kapoeta but in most cases bununu lowicz the diogenites alha77256 alha84001 eet79002 and maybe others solar heating at perihelia 0 8 au may be responsible for the low tl values the fraction of basaltic meteorites thought to have had small perihelia about 20 is comparable to the fraction of chondrites with low natural tl and to the fraction of observed falls and fireballs with small perihelia this may imply ejection from the asteroid belt via similar mechanisms assuming plausible values for cosmic ray dose rate and that the natural tl of mac88104 5 was totally drained by ejection from the moon the parameters for tl decay determined in the present study suggest that the moon earth transit times for mac88104 and mac88105 were 2 000 and 1 800 y respectively compared with 19 000 and 2 500 y for y791197 and alha81005 respectively although they are clearly not paired the possibility that mac88104 5 and alha81005 were ejected from the moon by the same event should be considered since diverse rock types are found in close proximity on the lunar surface the natural tl data confirm most previous published pairings among basaltic meteorites and suggest others

macalpine hills 88104 and 88105 lunar highland meteorites general description and consortium overview abstract macalpine hills 88104 and 88105 are new lunar meteorites returned from antarctica by the 1988 1989 us meteorite collection team the two specimens were found in nearby locations and based on field and laboratory evidence are thought to be pieces of the same meteorite mac88105 is the largest lunar meteorite yet found 662g mac88104 5 is an anorthositic breccia consisting of numerous small clasts in a glassy matrix an origin on the moon is supported by the mineral bulk and oxygen isotope compositions a consortium of twenty research groups has studied these meteorites samples were prepared at the nasa johnson space center meteorite processing laboratory details of consortium plans and allocations are documented herein a summary list of lunar meteorites and an overview of consortium research is presented discussions in this and the following consortium papers involve the issue of paired meteorites and paired ejecta and what new information about the nature and evolution of the lunar crust is provided by the lunar meteorites

exposure history of the lunar meteorite elephant moraine 87521 abstract we report the noble gas concentrations and the 26al 10be 36cl and 41ca activities of the antarctic lunar meteorite elephant moraine 87521 although the actual exposure history of the meteorite may have been more complex the following model history accounts satisfactorily for the cosmogenic nuclide data a first stage of lunar irradiation for 1 ma at a depth of 1 5 g cm2 followed not necessarily directly by a second one for 26 ma at 565 g cm2 launch from the moon less than 0 1 ma ago and arrival on earth 15 50 ka ago the small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch eet 87521 spent k ar age in the range 3 0 3 4 ga which is typical for lunar mare basalts

mesozoic volcanogenic massive sulfide vms deposits in mexico abstract volcanogenic massive sulfide vms deposits are the most conspicuous type of deposits that formed during the mesozoic in mexico many mexican vms deposits display classical kuroko type mineral zonation and structure and some of them as cuale and la minita formed in shallow submarine environments the most prospective time window for the formation of vms deposits in mexico comprises the late jurassic and the early cretaceous vms stopped forming during the progressive continentalization of mexico since its metallotectonic processes dominated by extensive tectonics changed giving way to compression during the late early cretaceous new vms deposits did not form until after the opening of the gulf of california mesozoic vms deposits in mexico occur in submarine volcano sedimentary sequences that deposited essentially in association with back arc basins now found roughly along the boundaries between tectonostratigraphic terranes or within juvenile and slightly evolved arcs at the internal parts of the terranes while few others occur on the epicontinental seafloor and hinterlands of eastern mexico vms deposits are especially abundant in the guerrero composite terrane and are also present in the alisitos and parral terranes however new evidence referred in this paper indicate the western continental edge of the cratonic block of oaxaquia as a promising new prospective region for vms deposits interestingly no vms deposits are found in the northern part of the guerrero composite terrane despite the occurrence of marine volcano sedimentary sequences similar to those in the south such absence can be related to differential extensional unroofing much larger in the southern part of the guerrero composite terrane than in the northern part many vms deposits occur along or close to terrane boundaries especially around the guerrero composite terrane this distribution reflects the association between vms deposits and back arc basins which represented the frontal part of terranes or sub terranes that were ultimately accreted to the oaxaquia cratonic block as a consequence vms deposits usually display strong deformation and thrusting and their mineral and compositional zonation can be found overturned due to such common association between these deposits and terrane boundaries that reactivated during the cenozoic vms deposits are especially susceptible to overprinting by later metallogenic processes unrelated to vms producing environments this susceptibility may be held accountable for the complex mineral associations found in the francisco i madero deposit the inclusion fluids in the cuale la minita el rubi tizapa and campo morado deposits have salinities that range from 2 5 to 20 0 wt nacl equiv and temperatures of homogenization from 110 to 420 c although a particular fluid inclusion assemblage with daughter halite and sylvite from a stockwork at the tizapa deposit ranged salinities from 39 7 to 64 7 wt nacl and from 35 9 to 43 5 wt kcl and temperatures of homogenization from 440 to 550 c the general characteristics listed above may account for mineralizing fluids from magmatic marine and modified marine sources the entrainment of cool and oxidizing seawater within upwelling fluids increased as the paleohydrothermal systems waned the waning stages are normally represented by barite rich mineralizations and in the case of the la minita deposit this notoriously outlasted by mn oxide mineralization that reflects even more oxidizing conditions a similar evolution is deduced in cuale which is the only known mesozoic vms deposit in mexico that formed in a shallow submarine environment together with la minita the shallower the formation of vms deposits is the more quickly mineralizing fluids evolve into highly oxidized end members once the paleohydrothermal systems cooled down the extremely high salinity and hot inclusion fluids in tizapa despite the unavailability of further geochemical data are likely to represent magmatic brines that did not undergo significant mixing with seawater as for the temporal evolution of the studied deposits they generally exhibit 1 an increasing magmatic contribution from early to middle stages for both fluids as mineralizing fluids grew hotter and more saline and sulfur and 2 the waning of hydrothermal activity towards the last stages on mineralization which is characterized by the prevalence of seawater as fluids grew cooler and more diluted and oxidizing thus reflecting quite a typical evolution for most vms deposits elsewhere new 34s values for the same vms deposits reflect multiple sources of sulfur in the mineralizing fluids magmatic sedimentary metasedimentary and marine different degrees of dominance of either source for sulfur in these deposits and in their stages of mineralization have been inferred in a way that also responds to a schematic evolution from magmatic to seawater dominated paleohydrothermal systems

noble gas isotopic composition cosmic ray exposure history and terrestrial age of the meteorite allan hills a81005 from the moon we present a comprehensive study of the elemental and isotopic abundances of the noble gases he ne ar kr and xe in the meteorite allan hills a81005 from the moon in addition to a bulk sample five grain size fractions were analyzed chemical abundances relevant for the interpretation of the cosmic ray produced noble gases were determined and indicate that the grain size fractions are chemically uniform except for the fact that the trapped noble gas concentrations appear to be grain size correlated the isotopic and elemental pattern of the trapped solar wind noble gases in a81005 are very similar to those observed in lunar soils and breccias the a81005 material resided during 580 180 m y in the nuclear active zone of the lunar regolith at an average shielding depth of about 40 g cm2 from literature data we conclude that the moon earth transit time lasted less than a few million years finally a81005 was captured by the earth more than 140 000 years ago as obtained from the abundance of cosmic ray produced81kr

ore metamorphism in sulfide mineralizations from the cinco villas massif western pyrenees spain massive stratiform and vein type zn pb fe f ba mineralizations associated with namuro westfalian metasediments occur in the cinco villas paleozoic massif these mineralizations were previously considered to be the result of the precipitation of hydrothermal fluids liberated by the aya granitic intrusion however the orebodies show several metamorphic features typical of similar mineralizations described in the geologic literature suggesting a preintrusive genesis of probably exhalative sedimentary nature the sedimentary sequence consists of two formations 1 the aranaz limestones dated as namurian and 2 a westphalian schistose formation composed of pelitic semipelitic and psammitic rocks with some conglomeratic tuffs albite rich laminae tourmalinites and interlayered basic sills these materials have been affected by the hercynian deformation and a low pressure regional metamorphism ranging from anchizone to biotite zone mesoscale structural data and microscopical observations suggest three periods d 1 d 2 and d 3 of progressive deformation accompanied by fracturing and shearing phenomena d 2 the main deformation developed isoclinal to recumbent folds and a regional foliation s sub 0 2 the more important metamorphic traits are produced during this deformation and at the same time the aya granitoid intrusion was emplaced the orebodies exhibit a lenticular to tabular morphology concordant with host rocks or forming a variable angle with s sphalerite galena and different proportions of pyrite pyrrhotite and chalcopyrite represent the major sulfide minerals quartz carbonates fluorite and barite are the main gangue minerals regional deformation and metamorphism have caused uneven but important effects on the geometry and primary textures of the orebodies however there is evidence of some premetamorphic textures such as debris flow breccias slump folds and particularly in pyrite framboidal relicts and colloform textures folding foliation transposition shearing durchbewegung and vein type ores are common metamorphic features in ore layers where the sulfides and gangue minerals have responded differently to deformation thus textures in pyrite denote a fundamentally brittle behavior but in some cases there is evidence of cataclastic flow kinking deformation bands and recrystallization in contrast sphalerite galena chalcopyrite and pyrrhotite exhibit different textures indicating that dislocation glide and creep mechanical twinning and recrystallization have generally been important mechanisms these processes suggest deformation under temperatures 400 degrees c which is consistent with the degree of metamorphismon in the host rocks micro and mesoscale remobilization of gangue and ductile sulfides due to a mixture of both mechanical and chemical processes is a generalized phenomenon in all deposits probably a major scale remobilization has been operative this would explain the existence of important vein type mineralizations in this region

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

geochemical comparison of impact glasses from lunar meteorites alha81005 and mac88105 and apollo 16 regolith 64001 abstract most glasses that occur in lunar highland regolith are quenched droplets of impact melt the chemical compositions of these glasses are equivalent in the absence of volatile losses to the original target materials the compositional range of impact glasses in a regolith reflects the chemical diversity that existed throughout the region up to the time of system closure e g breccia formation since these glasses are a product of widespread and random sampling both in terms of space and time they can be used for geochemical exploration of the moon the major element compositions of impact glasses occurring in three samples of lunar feldspathic regolith alha81005 mac88105 apollo 16 64001 have been determined by electron microprobe the glass populations among these three unrelated samples are compositionally distinct while most of the impact glasses within each of these three samples are compositionally similar to the regolith in which they are found up to 40 of the impact glasses are different some of the compositionally exotic glasses were ballistically transported from other areas of the moon and thereby provide information about the compositional range of regoliths that exist elsewhere since the geological setting of the apollo 16 region is well known compared to the source areas of the lunar meteorites the apollo 16 glasses provide a ground truth for interpretations the thirty four impact glasses in meteorite alha81005 overlap the compositional range of feldspathic regoliths represented by all of the lunar highland meteorites i e y86031 y82192 y791197 mac88105 alha81005 and are compositionally distinct from highland regoliths sampled by apollo 14 apollo 16 apollo 17 and luna 20 a small proportion of alha81005 glasses contain a mare component no kreep glasses were observed due to their scarcity only ten impact glasses in lunar meteorite mac88105 were analyzed the spherules occur in two broadly defined compositional groups one group of glasses is similar to the bulk composition of mac88105 whereas the other group is more mafic all of these glasses are distinct from highland regoliths sampled by apollo 14 apollo 16 and apollo 17 and luna 20 a low ti mare glass was also analyzed in mac88105 no kreep glasses were observed the two hundred and fifty three aluminous impact glasses analyzed in apollo 16 regolith 64001 display a prominent grouping of compositions equivalent to the local regolith in addition about 10 of the glasses in 64001 are distinct from the local regolith and chemically resemble the lunar highland meteorites alha81005 mac88105 these glasses may record the chemical composition of an ancient regolith that occurred in the apollo 16 region prior to the arrival of kreep and mare components twentythree percent of the glasses in 64001 have high ti mare affinities these mare glasses are clearly exotic to the apollo 16 site and have been transported from distances of at least 300 km

41ca in iron falls grant and estherville production rates and related exposure age calculations recent technical developments in accelerator mass spectrometry have enabled us to measure routinely and with a precision of 5 7 the41ca 1 2 104 ky contents of extraterrestrial samples weighing approximately 100 mg in essence these advances have elevated41ca to the role of a new and potent cosmogenic radioisotope with wide ranging applications we present here the results from the first phase of our41ca cosmogenic studies program aimed at establishing baseline concentrations and trends in selected meteorites and the use of41ca in estimating exposure ages and pre atmospheric meteorite radii the average41ca saturation activity recorded in four small iron falls is 24 1 dpm kg this result together with measurements at the center and surface of the large iron grant indicates that production of41ca from spallation on iron is weakly dependent on shielding to depths as large as 250 g cm2 we estimate the41k 41ca exposure age of grant to be 330 50 my and an upper limit to its terrestrial age of 43 15 ky a comparison of the41ca contents of stony and metallic material separated from the mesosiderite estherville identifies low energy neutron capture on native ca as a second important channel of production we find that the41ca signal in the stone phase from three meteorites correlates with their size and that the inferred low energy neutron fluxes vary by a factor of at least 20

exposure histories of lunar meteorites alha81005 mac88104 mac88105 and y791197 the cosmogenic radionuclides sup 41 ca sup 36 cl sup 26 al and sup 10 be in the allan hills 81005 macalpine hills 88104 macalpine hills 88105 and yamato 791197 meteorites were measured by accelerator mass spectrometry ams sup 53 mn in allan hills 81005 and yamato 791197 was measured by activation these four lunar meteorites experienced similar histories they were ejected from near the surface of the moon ranging in depth down to 400 g cm sup 2 and had very short transition times less than 0 1 ma from the moon to the earth a comparison of the cosmogenic nuclide concentrations in macalpine hills 88104 and macalpine hills 88105 clearly indicates that they are a pair from the same fall

history of lunar meteorites queen alexandra range 93069 asuka 881757 and yamato 793169 based on noble gas isotopic abundances radionuclide concentrations and chemical composition we investigated the characteristics and history of lunar meteorites queen alexandra range 93069 yamato 793169 and asuka 881757 based on the abundances of all stable noble gas isotopes the concentrations of the radionuclides 10be 26al 36cl and 81kr and the abundances of mg al k ca fe cl sr y zr ba and la based on the solar wind and cosmic ray irradiations que 93069 is the most mature lunar meteorite studied up to now the 40ar 36ar ratio of the trapped component is 1 87 0 16 this ratio corresponds to a time when the material was exposed to solar and lunar atmospheric volatiles 400 ma ago on the other hand yamato 793169 and asuka 881757 contain very little or no solar noble gases which indicates that these materials resided in the top layer of the lunar regolith only briefly or not at all for all lunar meteorites we observe a positive correlation of the concentrations of cosmic ray produced with trapped solar noble gases the duration of lunar regolith residence for the lunar meteorites was calculated based on cosmic ray produced 21ne 38ar 78kr 83kr and 126xe and appropriate production rates that were derived based on the target element abundances and the shielding indicator 131xe 126xe for que 93069 yamato 793169 and asuka 881757 we obtained 1000 400 ma 50 10 ma and 1 ma respectively both asuka 881757 and yamato 793169 show losses of radiogenic 4he from u and th decay and yamato 793169 also 40ar loss from k decay for asuka 881757 we calculate a k ar gas retention age of 3100 600 ma and a 244pu 136xe fission age of 4240 170 ma this age is one of the oldest formation ages ever observed for a lunar basalt the exposure history of que 93069 after ejection from the moon was derived from the radionuclide concentrations ejection 0 16 0 03 ma ago duration of moon earth transit 0 15 0 02 ma and fall on earth 0 015 ma ago this ejection event is distinguished temporally from those which produced the other lunar meteorites we conclude that six to eight events are necessary to eject all the known lunar meteorites

lunar meteorite regolith breccias an in situ study of impact melt composition using la icp ms with implications for the composition of the lunar crust dar al gani dag 400 meteorite hills met 01210 pecora escarpment pca 02007 and macalpine hills mac 88104 88105 are lunar regolith breccia meteorites that provide sampling of the lunar surface from regions of the moon that were not visited by the us apollo or soviet luna sample return missions they contain a heterogeneous clast population from a range of typical lunar lithologies dag 400 pca 02007 and mac 88104 88105 are primarily feldspathic in nature and met 01210 is composed of mare basalt material mixed with a lesser amount of feldspathic material here we present a compositional study of the impact melt and impact melt breccia clast population i e clasts that were generated in impact cratering melting processes within these meteorites using in situ electron microprobe and la icp ms techniques results show that all of the meteorites are dominated by impact lithologies that are relatively ferroan mg 10 and have low incompatible trace element ite concentrations i e typically 10 ppm sm high magnesium suite typically 70 mg or high alkali suite high ites sc sm ratios 2 target rocks instead the meteorite mafic melts are more ferroan kreep poor and sc rich and represent mixing between feldspathic lithologies and low ti or very low ti vlt basalts as pca 02007 and mac 88104 05 were likely sourced from the outer feldspathic highlands terrane our findings suggest that these predominantly feldspathic regions commonly contain a vlt to low ti basalt contribution

exposure histories of the lunar meteorites mac88104 mac88105 y791197 and y86032 four lunar meteorites macalpine hills mac 88104 macalpine hills 88105 yamato y 791197 and yamato 86032 were analyzed for the cosmogenic radionuclides 10be 26al 36cl and 41ca from these and published data histories of exposure to cosmic rays were modelled in terms of two stage irradiations each with a long first stage on the moon lasting a time t2 5 ma at a burial depth d2 gcm2 followed by a second stage in space i e the transit time between the moon and the earth lasting a time t4 ma in a body of typical meteoroidal size the terrestrial age tt ma gives the time elapsed between meteorite fall and recovery in antarctica the following sets of parameters were obtained mac88104 5 390 d2 500 0 04 t4 0 11 0 10 tt 0 19 y791197 d2 1000 t4 10 2 0 08 tt 0 12 from the number and exposure histories of lunar meteorites we infer a production rate on the order of 5 ma 1 and an arrival rate worldwide of about 3 106 meteorites ma 1 these results suggest that each impact event large enough to produce lunar meteorites sends a large number of them to the earth

petrology chemistry and isotopic compositions of the lunar highland regolith breccia dar al gani 262 lunar meteorite dar al gani 262 dg 262 found in the libyan part of the sahara is a mature anorthositic regolith breccia with highland affinities the origin from the moon is undoubtedly indicated by its bulk chemical composition radionuclide concentrations noble gas n and o isotopic compositions and petrographic features dar al gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to queen alexandra range que 93069 about 52 vol of the studied thin sections of dar al gani 262 consist of fine grained 100 m constituents and 48 vol is mineral and lithic clasts and impact melt veins the most abundant clast types are feldspathic fine grained to microporphyritic crystalline melt breccias 50 2 vol includes recrystallized melt breccias whereas mafic crystalline melt breccias are extremely rare 1 4 vol granulitic lithologies are 12 8 vol intragranularly recrystallized anorthosites and cataclastic anorthosites are 8 8 and 8 2 vol respectively and devitrified glasses are 2 7 vol impact melt veins 5 5 vol of the whole thin sections cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 gpa because the bulk rock never experienced a higher peak shock pressure mafic crystalline melt breccias are very rare in dar al gani 262 and are similar in abundance to those in que 93069 the extremely low abundance of mafic components and the bulk composition may constrain possible areas of the moon from which the breccia was derived the source area of dar al gani 262 must be a highland terrain lacking significant mafic impact melts or mare components on the basis of radionuclide activities an irradiation position of dg 262 on the moon at a depth of 55 85 g cm3and a maximum transit time to earth 0 15 ma is suggested dar al gani 262 contains high concentrations of solar wind implanted noble gases the isotopic abundance ratio 40ar 36ar 3 is characteristic of lunar soils the terrestrial weathering of dg 262 is reflected by the occurrence of fractures filled with calcite and by high concentrations of ca ba cs br and as there is also a large amount of terrestrial c and some n in the sample which was released at low temperatures during stepped heating high concentrations of ni co and ir indicate a significant meteoritic component in the lunar surface regolith from which dg 262 was derived

relationships between the occurrence of accessory ge minerals and sphalerite in variscan pb zn deposits of the bossost anticlinorium french pyrenean axial zone chemistry microstructures and ore deposit setting abstract the presence of unique accessory ge minerals containing up to 70 wt ge is a widespread phenomenon in pb zn deposits of the variscan pyrenean axial zone paz such a mode of occurrence is however rare worldwide with germanium more typically occurring as a trace component of sulfides notably sphalerite

determination of the half life of41ca from measurements of antarctic meteorites abstract using accelerator mass spectrometry ams we have determined the half life of41ca from the decrease of its concentration with terrestrial age in five antarctic meteorites and a recent fall the meteorites were selected on the basis of their36cl concentrations measured on the same aliquots as used here which showed a span of terrestrial ages of 600 ka and on the basis of other cosmogenic nuclide concentrations which indicated that the meteorites had small pre atmospheric sizes so that the samples were negligibly shielded from primary cosmic rays and sufficiently long irradiation times in space that the concentrations of41ca and36cl were in secular equilibrium prior to the meteorites fall to earth based on the decrease of41ca relative to36cl t12 301 2 ka we infer that the half life of41ca is103 7 ka

platinum group element oxides from the pirogues ophiolitic mineralization new caledonia origin and significance a number of platinum group element pge oxides and hydroxides have been discovered in a pge mineralization in the new caledonia ophiolite complex they include pt fe oxides containing variable amounts of oxygen 5 50 at ir fe rh oxides metal oxygen approximately 3 fe rh pt oxides and pt ir fe rh oxides metal oxygen 1 and an ru mn fe phase with a very low metal oxygen ratio interpreted as hydroxide these minerals have been found either as inclusions in chromite crystals from chromitite or as discrete grains from alluvial concentrates pt fe oxides are characterized by unusual textures including zoning and symplectite optical and scanning electron microscope descriptions of all the pge oxides are given together with electron microprobe analyses including the quantitative determination of oxygen the pge oxides may result from the alteration of magmatic pgm alloys and from primary crystallization of oxides in lateritic conditions their presence indicates the existence of mechanisms of transport and crystallization of pge as oxide in surface conditions mechanisms contributing to the redistribution and enrichment of pge in laterite

chemical and physical transfers in an ultramafic rock weathering profile part 2 dissolution vs accumulation of platinum group minerals the chemical weathering of ultramafic rocks has resulted in eluvial concentration of pt group minerals pgm in lateritic weathering profiles of southern new caledonia the pt mineralization interpreted as being primary consists of pt group minerals included within chromite crystals the oc currence of pgm as free particles in the weathering profile results from the supergene dissolution of pt bearing chromite traore et al 2008 following their release in the profile supergene dissolution processes variably affect the pgm particles the behavior of pt group elements in the weathering profile is characterized by significant loss of pd and relative enrichment of pt indicating that pd is more mobile than pt in the exogenous cycle unstable pt fe cu pd alloys and pge oxides undergo chemical and mineralogical changes to acquire the chemical configuration of isoferroplatinum pt3fe which is the most stable pt phase in a lateritic environment the isoferroplatinum phase may also be dispersed throughout the weathering mantle and or accumulated in the lower parts of profiles ac cording to a translocation mechanism of residual pt rich fine particles driven by percolation of water through the connected pore spaces