iron oxide copper gold iocg deposits through earth history implications for origin lithospheric setting and distinction from other epigenetic iron oxide deposits the iron oxide copper gold iocg group of deposits initially defined following discovery of the giant olympic dam cu u au deposit has progressively become too embracing when associated deposits and potential end members or analogs are included the broader group includes several low ti iron oxide associated deposits that include iron oxide p rich iron oxide f and ree rich fe or cu au skarn high grade iron oxide hosted au cu carbonatite hosted cu ree and f rich and iocg sensu stricto deposits consideration of this broad group as a whole obscures the critical features of the iocg sensu stricto deposits such as their temporal distribution and tectonic environment thus leading to difficulties in developing a robust exploration model the iocg sensu stricto deposits are magmatic hydrothermal deposits that contain economic cu and au grades are structurally controlled commonly contain significant volumes of breccia are commonly associated with presulfide sodic or sodic calcic alteration have alteration and or brecciation zones on a large commonly regional scale relative to economic mineralization have abundant low ti iron oxides and or iron silicates intimately associated with but generally paragenetically older than fe cu sulfides have lree enrichment and low s sulfides lack of abundant pyrite lack widespread quartz veins or silicification and show a clear temporal but not close spatial relationship to major magmatic intrusions these intrusions where identified are commonly alkaline to subalkaline mixed mafic even ultramafic to felsic in composition with evidence for mantle derivation of at least the mafic end members of the suite the giant size of many of the deposits and surrounding alteration zones the highly saline ore fluids and the available stable and radiogenic isotope data indicate release of deep volatile rich magmatic fluids through devolatization of causative mantle derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional scale fluid flow paths precambrian deposits are the dominant members of the iocg group in terms of both copper and gold resources the 12 iocg deposits with 100 tonnes t resources are located in intracratonic settings within about 100 km of the margins of archean or paleoproterozoic cratons or other lithospheric boundaries and formed 100 to 200 m y after supercontinent assembly their tectonic setting at formation was most likely anorogenic with magmatism and associated hydrothermal activity driven by mantle underplating and or plumes limited amounts of partial melting of volatile rich and possibly metal enriched metasomatized early precambrian subcontinental lithospheric mantle sclm fertilized during earlier subduction probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the iocg deposits preservation of near surface deposits such as olympic dam is probably due to their formation above buoyant and refractory sclm which resisted delamination and associated uplift most precambrian iron oxide p rich or magnetite apatite kiruna type deposits have a different temporal distribution apparently forming in convergent margin settings prior to or following supercontinent assembly it is only in the phanerozoic that iocg and magnetite apatite deposits are roughly penecontemporaneous in convergent margin settings the phanerozoic iocg deposits such as candelaria chile occur in anomalous extensional to transtensional zones in the coastal cordillera which are also the sites of mantle derived mafic to felsic intrusions that are anomalous in an andean context this implies that special conditions possibly detached slabs of metasomatized sclm may be required in convergent margin settings to generate world class iocg deposits it is likely that formation of giant iocg deposits was mainly a precambrian phenomenon related to the extensive mantle underplating that impacted on buoyant metasomatized sclm generally smaller and rarer phanerozoic iocg deposits formed in tectonic settings where conditions similar to those in the precambrian were replicated

fassaites in compact type a ca al rich inclusions in the ningqiang carbonaceous chondrite evidence for partial melting in the nebula fassaite is a major component of ca al rich inclusions cais of types b and c that crystallized from liquids in contrast this mineral is rarely reported in type a inclusions and has been much less studied in this paper we report highly ti al enriched fassaite that occurs as rims on perovskite in two compact type a inclusions from the ningqiang meteorite in addition one of the inclusions contains an euhedral grain of sc fassaite 16 4 wt sc2o3 isolated in melilite the occurrence and mineral chemistry of the fassaite rims can be explained by a reaction of pre existing perovskite with cai melts hence such rims may serve as an indicator for partial melting of type a inclusions the sc fassaite is probably a relict grain a third spherical cai contains several euhedral grains of v fassaite 4 8 5 4 wt v2o3 enclosed in a melilite fragment the high v content of fassaite cannot be related to any fremdlinge magnetite or metallic fe ni because these phases are absent in the inclusion in the same cai other fassaites intergrow with spinel and minor perovskite filling voids inside of the melilite and space adjacent to the wark lovering rim the fassaite intergrown with spinel is almost v free the coexistence of two types of fassaite suggests that this cai has not been completely melted

the formation of boundary clinopyroxenes and associated glass veins in type b1 cais we used focused ion beam thin section preparation and scanning transmission electron microscopy fib stem to examine the interfacial region between spinel and host melilite for spinel grains in type b1 inclusions from the allende and leoville carbonaceous chondrites boundary clinopyroxenes decorating spinel surfaces have compositions similar to those of coarser clinopyroxenes from the same region of the inclusion suggesting little movement after formation host melilite displays no anomalous compositions near the interface and late stage minerals are not observed suggesting that boundary pyroxenes did not form by crystallization of residual liquid allende spinels display either direct spinel melilite contact or an intervening boundary clinopyroxene between the two phases spinel melilite interfacial regions in a leoville b1 are more complex with boundary clinopyroxene as observed in allende but also variable amounts of glass secondary calcite perovskite and an mg al oh rich and ca si poor crystalline phase that may be a layered double hydrate one possible scenario of formation for the glass veins is that open system alteration of melilite produced a porous hydrated aggregate of mg carpholite or sudoite aluminous diopside that was shock melted and quenched to a glass the hydrated crystalline phase we observed may have been a shocked remnant of the precursor phase assemblage but is more likely to have formed later by alteration of the glass in the mantle boundary clinopyroxenes may have been crystallized from ti rich liquids formed by the direct dissolution of perovskite and an associated sc zr rich phase or as a reaction product between dissolving perovskite and liquid in the core any perovskite and associated ti enriched liquids that may have originally been present disappeared before the growth of boundary clinopyroxene and the observed boundary clinopyroxene may have nucleated and grown from the liquid along with the larger core clinopyroxene

crystal growth and disequilibrium distribution of oxygen isotopes in an igneous ca al rich inclusion from the allende carbonaceous chondrite abstract ts34 is a type b1 ca al rich inclusion cai from the allende cv3 chondrite consisting of spinel melilite ti al rich clinopyroxene fassaite and minor anorthite in an igneous texture oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in ts34 using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite the oxygen isotopic evolution of the cai melt was established oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line the spinel grains are uniformly 16o rich 17o 22 7 1 7 2sd while the melilite grains are uniformly 16o poor 17o 2 8 1 8 irrespective of their akermanite content and thus their relative time of crystallization the fassaite crystals exhibit growth zoning overprinting poorly developed sector zoning they generally grow from ti rich to ti poor compositions the fassaite crystals also show continuous variations in 17o along the inferred directions of crystal growth from 16o poor 17o 3 to 16o rich 17o 23 covering the full range of oxygen isotopic compositions observed in ts34 the early crystallized 16o poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously the correlation of oxygen isotopic compositions with ti content in the fassaite imply that the oxygen isotopic composition of the cai melt evolved from 16o poor to 16o rich during fassaite crystallization presumably due to oxygen isotope exchange with a surrounding 16o rich nebular gas formation of spinel the liquidus phase in melts of this composition predates crystallization of all other phases so its 16o rich composition is a relic of an earlier stage anorthite exhibits oxygen isotopic compositions between 17o 2 and 9 within the range of those of fassaite indicating co crystallization of these two minerals during the earliest to intermediate stage of fassaite growth the melilite and fassaite yield an 26al 26mg mineral isochron with an initial value of 26al 27al 0 5 003 0 075 10 5 corresponding to a relative age of 0 05 0 02 myr from the canonical al mg age of cais these data demonstrate that both 16o rich and 16o poor reservoirs existed in the solar nebula at least 0 05 myr after the birth of the solar system

halogen and ar ar age determinations of inclusions within quartz veins from porphyry copper deposits using complementary noble gas extraction techniques abstract extension of ar ar methodology has been used to determine mineralisation ages from mica inclusions and to simultaneously evaluate the noble gas and halogen composition of inclusion fluids within irradiated quartz vein samples from five porphyry copper deposits samples have been collected from the potassic and propylitic zones of bingham canyon utah and four arizonan deposits silverbell globe miami pinto valley and ray data obtained using three noble gas extraction techniques laser ablation in vacuo crushing and stepped heating are compared with each other laser ablation provides a means for the analysis of individual fluid inclusions but is limited by blank levels and detection limits stepped heating and in vacuo crushing are bulk extraction techniques that preferentially release gases from solid and fluid inclusion phases respectively and can be used in combination to obtain accurate and meaningful ages of mineralisation ages obtained for porphyry copper deposits are as follows bingham canyon 37 1 0 5 ray 65 3 1 5 globe miami 61 7 3 4 pinto valley 63 2 8 0 and silverbell 55 8 1 8 the age of mineralisation at ray is of particular interest as it enables a reported discrepancy in k ar ages to be understood halogen data for the bingham canyon samples gives insight into the partitioning of the heavy halogens br and i between solid and liquid phases

formation of an unusual compact type a refractory inclusion from allende we report the results of a study of ts2 an unusual compact type a inclusion from allende a distinctive major feature of this inclusion is that many of its melilite crystals have no dominant core rim zoning but instead consist of 50 200 m patches of mg rich melilite ak32 62 median ak51 set in or partially enclosed by and optically continuous with relatively al rich melilite ak25 53 median ak38 the al rich regions have jagged dendritic shapes but occur within crystals having straight grain boundaries another unusual feature of this inclusion is the size and spatial distribution of spinel in many places especially in the interior of the inclusion the aluminous melilite encloses numerous fine 0 5 5 m inclusions of spinel and minor perovskite and fassaite the latter phases also occur as isolated grains throughout the inclusion coarse grained spinel 50 150 m across occurs in clumps and chains enclosed in relatively mg rich melilite whereas none of the fine spinel grains are clumped together the sample also contains a spinel free palisade body 1 7 0 85 mm that consists almost entirely of ak rich 45 65 mol melilite within the palisade body are two grains of perovskite with extremely nb rich 4 8 wt nb2o5 cores and rims of typical composition all phases in this inclusion have chondrite normalized ree patterns that are consistent with crystal melt partitioning superimposed upon a bulk modified group ii pattern we suggest that ts2 had an anomalous cooling history and favor the following model for the formation of ts2 precursors having a bulk modified group ii pattern melted rapid growth of large dendritic nonstoichiometric melilite crystals occurred the melilite trapped pockets of melt and incorporated excess spinel components and tio2 bubbles formed in the residual melt as crystallization slowed coarse spinel grew some spinel grains collected against bubbles forming spherical shells and others formed clumps and chains relatively ak rich melilite crystallized from the residual melt between dendritic melilite crystals and from melt trapped in pockets and between arms of dendrites and incorporated the clumps and chains of coarse spinel bubbles broke and filled with late stage melt their shapes preserved by their spinel shells slow cooling or perhaps an episode of reheating allowed the early melilite to become stoichiometric by exsolving fine grains of spinel perovskite and fassaite and allowed the melilite to form smooth grain boundaries dendritic crystals are indicative of rapid growth and the melilite crystals in ts2 appear to be dendritic coarse dendritic melilite crystals have been grown from type b inclusion melts cooled at 50 100 c h if those results are applicable to type a inclusions we can make the first estimate of the cooling rate of a type a inclusion and it is outside the range 2 50 c h generally inferred for type b inclusions the rapid cooling inferred here may be part of an anomalous thermal history for ts2 or it may be representative of part of a normal thermal history common to types a and b that involved rapid cooling early at high temperatures as inferred for ts2 and slower cooling later at lower temperatures as inferred for type b inclusions we prefer the former explanation otherwise the unusual features of ts2 that are reported here would be common in type a inclusions which they are not

ore genesis constraints on the idaho cobalt belt from fluid inclusion gas noble gas isotope and ion ratio analyses a reply the idaho cobalt belt is a 60 km long alignment of deposits composed of cobaltite co pyrite chalcopyrite and gold with anomalous nb y be and rare earth elements rees in a quartz biotite tourmaline gangue hosted in mesoproterozoic metasedimentary rocks of the lemhi group it is the largest cobalt resource in the united states with historic production from the blackbird mine all of the deposits were deformed and metamorphosed to upper greenschist lower amphibolite grade in the cretaceous they occur near a 1377 ma anorogenic bimodal plutonic complex the enhanced solubility of fe co cu and au as chloride complexes together with gangue biotite rich in fe and cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved the isotopes of b in gangue tourmaline are suggestive of a marine source whereas those of pb in ore suggest a u th enriched source the ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post ore minerals and metamorphic minerals such components can potentially be identified and distinguished by their relative abundances in contrasting samples therefore we obtained samples of co and cu sulfides gangue quartz biotite and tourmaline and post ore quartz veins as well as cretaceous metamorphic garnet and determined the gas noble gas isotope and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography the most abundant gases present in extracts from each sample type are biased toward the gas rich population of inclusions trapped during maximum burial and metamorphism all have co 2 ch 4 and n 2 ar ratios of evolved crustal fluids and many yield a range of h 2 ch 4 co 2 h 2 s equilibration temperatures consistent with the metamorphic grade cretaceous garnet and post ore minerals have high r h and r s values suggestive of reduced sulfidic conditions most extracts have anomalous 4 he produced by decay of u and th and 38 ar produced by nucleogenic production from 41 k in contrast some ore and gangue minerals yield significant so 2 and have low r h and r s values of a more oxidized fluid three extracts from gangue quartz have high helium r r a values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 ne in fluorite from u th decay two extracts from gangue quartz have estimated 40 k 40 ar that permit a precambrian age extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios na k nh 4 cl br f suggestive of a single fluid their na cl br ratios suggest this fluid was a mixture of magmatic and basinal brine na k ca temperatures 279 347 c are similar to homogenization temperatures of hypersaline inclusions the high k na of the brine may be due to albitization of k silicate minerals in country rocks influx of k rich brines is consistent with the k metasomatism necessary to form gangue biotite with high cl an extract from a post ore quartz vein is distinct and has na cl br ratios that resemble metamorphic fluids in cretaceous silver veins of the coeur d alene district in the belt basin the results show that in some samples for certain components it is possible to see through the cretaceous metamorphic overprint of great import for genetic models the volatiles trapped in gangue quartz have 3 he derived from a mantle source and 22 ne derived from fluorite both of which may be attributed to nearby 1377 ma basalt rhyolite magmatism the brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater the former requires a granitic intrusion that is present in the bimodal intrusive complex and the latter equatorial paleolatitudes that existed in the mesoproterozoic the results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the lemhi group while the inferred fluid sources in the idaho cobalt belt are similar in many respects to those in iron oxide copper gold deposits the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides

the primordial noble gases in the earth a key constraint on earth evolution models abstract we made an extensive compilation of noble gas data obtained from morb oceanic island basalts oib and diamonds on the basis of this data base we discuss the primordial noble gases in the earth and its implications on mantle evolution we conclude that in the contrary to a common assumption the primordial ne ar kr and xe in the earth are distinctly different from the solar noble gases the primordial noble gases were derived from the solar noble gas through rayleigh distillation like mass dependent fractionation the primordial ar kr xe are identical with the atmospheric components but ne observed in the mantle derived materials differs significantly from the atmospheric ne we suggest that ne was further fractionated in the atmosphere while the abundances of ar kr and xe in the mantle derived materials are well correlated to each other he and ne in morb is totally uncorrelated with the heavier noble gases this indicates that he and ne in morb is decoupled from the heavier noble gases in the mantle source he ne ar systematics indicate that he was open to the morb and oib mantle sources and ne in the morb mantle source while he is excess in the morb mantle source it is deficient in the oib mantle source relative to the closed system values however it is not known whether this apparent complementary characteristic corresponds to some fundamental mantle dynamics or accidental coincidence

u th pb and rb sr geochronology of middle proterozoic granite and augen gneiss salmon river mountains east central idaho coarsely porphyritic granite and augen gneiss in east central idaho have been dated by the u th pb zircon method when plotted on concordia diagrams the results give nonlinear data arrays that indicate the presence of at least one component of inherited radiogenic lead as well as postcrystallization probably recent episodic lead loss nevertheless a systematic relationship between zircon size and convergence of the 207 pb 206 pb ages for the 100 and 100 150 mesh fractions from several samples are interpreted to provide a valid age of about 1 370 m y for these plutons a single sample which is free of inheritance for all size fractions confirms this conclusion rb sr whole rock samples are highly enriched in radiogenic strontium but do not define an isochron probably because the system did not remain closed following crystallization of the plutons intrusive contacts of the granitic rocks indicate that deformation and regional metamorphism of the host yellowjacket formation occurred prior to 1370 ma rather than prior to 1500 ma as previously suggested by others this refinement of the geochronology 1 removes the necessity that the yellowjacket formation and overlying proterozoic metasedimentary rocks of central and east central idaho be pre belt in age 2 permits the traditional age correlation of the east central idaho metasedimentary sequence yellowjacket through lawson creek formations with the belt supergroup and 3 suggests that a re evaluation is in order for paleogeographic models of central idaho especially the proposed topographic high known as the salmon river arch

a petrologic and ion microprobe study of a vigarano type b refractory inclusion evolution by multiple stages of alteration and melting abstract usnm 1623 8 is a type b vigarano inclusion 6 mm in diameter consisting of melilite ak12 72 fassaite 17 23 a12o3 5 17 tio2 anorthite and spinel secondary alteration is negligible and consists of diopside and sparse nepheline melilite is normally zoned and contains up to 0 35 wt na2o higher than generally seen in melilite from other refractory inclusions a strong correlation between akermanite content and na2o in 1623 8 melilite suggests that the na was present during igneous crystallization rather than introduced later by diffusion anorthite in 1623 8 is coarse grained but commonly has an irregular border with neighboring melilite crystals many spinel grains enclosed within anorthite have selvages of melilite around them which in places are continuous with melilite exterior to the anorthite the anorthite appears to be replacing melilite ion microprobe analyses of anorthite in 1623 8 show that there is no detectable excess 26mg in nine anorthite crystals that have 27 al 24 mg as high as 970 implying an upper limit of 26 al 27 al 0 7 one crystal was found that has excess 26mg consistent with 26 al 27 al 0 3 10 6 melilite in the outer portion of the inclusion 27 al 24 mg 2 7 11 5 contains excess 26mg that considered together with spinel and pyroxene defines an isochron consistent with the canonical early solar system value of 26 al 27 al 0 4 5 10 5 melilite near an anorthite 27 al 24 mg 1 6 5 9 has 26mg values in excess of those predicted from 26 al 27 al 0 4 5 10 5 presumably caused by redistribution of radiogenic 26mg from adjacent anorthite the high na2o inferred to have been present in the melt suggests that the precursor solids were na bearing such as for example refractory material having an allende like overprint of feldspathoid bearing secondary alteration the melting event must have been brief in order that not all of the na was vaporized during melting the isotopic composition of the anorthite relative to melilite indicates a subsequent much later after the decay of most or all 26a1 episode of partial melting or solidstate recrystallization that did not affect the al rich melilite but reset most of the anorthite and some mg rich melilite near anorthite because the inclusion is both rimmed and slightly altered this late resetting event appears to have been a nebular one an assumption of homogeneously distributed 26a1 in the regions of the nebula where the inclusion formed and was later modified implies a several millionyear interval between condensation of the precursors and final melting of 1623 8

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

anorthite spinel rich inclusions in the ningqiang carbonaceous chondrite genetic links with type a and c inclusions many ca al rich inclusions cais were molten once and the question of what their precursors consisted of is controversial in this paper we report a new type of anorthite spinel rich inclusion asi in the ningqiang carbonaceous chondrite the modal and bulk compositions of the asis are similar to those of type c inclusions but with nonmolten textures the asis are proposed to be the precursors of type c inclusions the asis show alteration textures with melilite being replaced by anorthite and ca pyroxene furthermore compositions of the melilites and the calculated modal and bulk compositions of the possible precursors of the asis are close to those of the spinel rich type a inclusions in the ningqiang meteorite which suggests that asis formed by alteration of the latter in the solar nebula petrography and mineral chemistry of one type c inclusion in ningqiang are also reported

ungulate community richness grazer extinctions and human subsistence behavior in southern africa s cape floral region precipitation primary productivity and herbivore biomass are linked to ungulate richness the number of species in african ecosystems this study compares the richness of late middle to late pleistocene and holocene ungulate assemblages in southern africa s cape floral region cfr regression analysis demonstrates that pleistocene ungulate assemblages are significantly richer than their holocene counterparts elevated pleistocene ungulate richness is not explained by differential time averaging the presence of extinct taxa in pleistocene assemblages or by middle stone age msa to later stone age lsa technological change but instead by a greater number of grazing species in pleistocene faunal communities based on modern african analogs this implies that the pleistocene assemblages examined here sample time intervals characterized by elevated primary productivity particularly of grassland habitats greater ungulate biomass and altered rainfall regimes declining ungulate richness from the pleistocene to the holocene supports the hypothesis that the extinction of specialized grazers at the pleistocene holocene transition in the cfr was driven by declining productivity and availability of grassland habitats the contrast between rich pleistocene ungulate communities and impoverished holocene ungulate communities may also explain important differences in msa and lsa subsistence behavior it is proposed that intensified exploitation of fish shellfish tortoises and seabirds by lsa foragers during the holocene reflects an expansion of diet breadth in response to diminished ungulate biomass on the landscape rather than fundamental behavioral cognitive advances

petrographic studies of refractory inclusions from the murchison meteorite textural and mineral chemical data on freeze thaw disaggregated refractory inclusions from the murchison meteorite are reported the data were obtained with neutron activation analysis sem and spectroscopy the study revealed corundum bearing inclusions spinel hibonite aggregates and spherules and spinel pyroxene and elivine pyroxene inclusions one of the three spinel pyroxene forsterite rich inclusions had an amoeba shaped spinel pyroxene core implying vapor to solid condensation and therefore crystallization from a melt it is concluded that the meteorite formation encompassed diverse nebular materials and that further studies of the meteorite will enhance the data base on the planetary nebular processes

origins of mineral deposits belt purcell basin united states and canada an introduction the fill of the mesoproterozoic belt purcell basin which straddles the united states canada border within the rocky mountains of western north america fig 1 consists of marine and nonmarine clastic and carbonate strata 15 to 20 km thick three giant metal producing ore deposits or districts account for the bulk of the known metal endowment within the bounds of the belt purcell basin 1 the syndepositional sullivan pb zn ag deposit in southern british columbia total production pb 8 4 million tonnes mt zn 7 9 mt ag 0 0093 mt lydon 2000 2 the mesothermal pb zn ag veins of the coeur d alene district in northern idaho total production pb 7 5 mt zn 3 0 mt ag 0 052 mt long 1998 post 1997 data from usgs annual minerals yearbooks and 3 the cretaceous porphyry copper deposit and associated polymetallic veins in the butte district in montana total resource cu 35 mt zn 4 6 mt ag 0 044 mt long et al 1998 the sullivan mine closed in 2001 after more than 92 years of production mining of 26 major vein deposits in the coeur d alene district began in the 1880s and peaked about 1950 production in the coeur d alene district continues today from the galena and lucky friday mines the latter closed for 2012 to refurbish the mile deep vertical access shaft mining at butte began in 1875 with copper production peaking in 1917 mining continues today in the eastern upfaulted portion of the butte porphyry copper deposit at the continental mine fig 1 locations of major ore deposits within the belt purcell basin area along with other ore deposits and mineralized trends that are discussed in this issue deposit locations are plotted on a geologic map showing the distribution of five stratigraphic units within the belt purcell basin in the united states and canada lower belt formations include the prichard altyn appekunny chamberlain newland lahood

the formation of chondrules petrologic tests of the shock wave model chondrules are millimeter sized rounded igneous rocks within chondritic meteorites their textures and fractionated mineral chemistries suggest that they formed by repeated localized brief minutes to hours melting of cold aggregates of mineral dust in the protoplanetary nebula astrophysical models of chondrule formation have been unable to explain the petrologically diverse nature of chondrites however a nebular shock wave model for chondrule formation agrees with many of the observed petrologic and geochemical properties of chondrules and shows how particles within the nebula are sorted by size and how rims around chondrules are formed it also explains the volatile rich nature of chondrule rims and the chondrite matrix

mineral thermometry and fluid inclusion studies of the pea ridge iron oxide apatite rare earth element deposit mesoproterozoic st francois mountains terrane southeast missouri usa mineral thermometry and fluid inclusion studies were conducted on variably altered and mineralized samples from the mesoproterozoic pea ridge iron oxide apatite ioa rare earth element ree deposit in order to constrain p t conditions fluid chemistry and the source of salt and volatiles during early magnetite and later ree mineralization scanning electron microscopy sem cathodoluminescence and sem backscatter electron images show that quartz and rutile precipitated before during and after magnetite and ree mineral growth ti in quartz and zr in rutile equilibration temperatures range from 350 to 750 c in the amphibole magnetite hematite and silicified zones where t increased during magnetite and quartz growth and dropped precipitously after fracturing and brecciation late drusy quartz cements within a ree rich breccia pipe record the lowest t 315 400 c liquid vapor rich and hypersaline hematite calcite fluid inclusions are common and liquid co 2 is present locally salinities define three populations saline 10 27 wt nacl equiv hypersaline 34 60 wt nacl equiv and dilute 0 10 wt nacl equiv the wide range of eutectic melting temperatures 67 to 19 c suggests that saline inclusions trapped variable proportions of a cacl mgcl fecl bearing fluid end member and an nacl kcl fluid end member homogenization temperatures and pressures of these saline inclusions suggest they were trapped when fluids unmixed into brine and vapor at t the na cl na k and cl br ratios of fluid inclusion extracts provide evidence for mixtures of magmatic hydrothermal fluids and evaporated seawater extracts from magnetite hematite and pyrite plot in the magmatic hydrothermal field indicating that fe was derived from a magmatic source their enrichments in mg and ca are consistent with a mafic magmatic source the positive correlation between na mg and na ca ratios may be due to halite saturation or albitization of igneous rocks extracts from barite in the ree rich breccia pipes are enriched in na and br and plot near the seawater evaporation trend he is highly enriched relative to ne and ar in fluid inclusion extracts which precludes air as a source of he although the he is mostly of crustal origin pyrite with a 3 he 4 he r r a of 0 1 contains up to 12 mantle he many extracts have low 20 ne 22 ne ratios due to nucleogenic production of 22 ne in high f o minerals such as fluorapatite or f biotite the arrays of data for 3 he 4 he r r a and 22 ne 20 ne suggest that volatiles were derived from two sources a moderate f mafic magma containing mantle he and a high f silicic magma with crustal he together with other evidence cited in this report these data 1 support a magmatic hydrothermal origin for the mesoproterozoic magnetite apatite deposit with ore fluids derived from a concealed mafic to intermediate composition intrusion 2 suggest that the ree minerals in breccia pipes were either derived from apatite or precipitated in response to decompression and cooling during breccia pipe formation 3 provide evidence for the influx of basinal brine magmatic fluids from granitic intrusions and meteoric water after breccia pipe formation and 4 show that pea ridge was relatively unaffected by the late paleozoic mississippi valley type mvt pb zn system in overlying cambrian sedimentary rocks

the nature and origin of type b1 and b2 caal rich inclusions in the allende meteorite abstract the type b ca al rich inclusions in the allende carbonaceous chondrite form a continuous range from the mineralogically concentrically zoned b1 subtype to the unzoned b2 subtype these subtypes differ in i structure texture grain size and shape ii mineralogical proportions and compositions iii accessory mineralogy iv relative abundance of spinel framboids v rim layering vi major element chemistry and vii degree of secondary alteration these differences together with observations on the crystallization of synthetic melts suggest that the b1 inclusions crystallised relatively rapidly from molten parental material while b2 types crystallised relatively slowly close to the solidus from material that had not been completely melted the same data are used to construct an evaporative residue model for the origin of the parental type b materials in the model dust in the protosolar nebula was heated with removal of more volatile elements leaving completely melted type b1 residues at the highest temperatures and incompletely melted less highly evaporated type b2 residues at lower temperatures

a caal4o7 bearing refractory spherule from murchison evidence for very high temperature melting in the solar nebula we have recovered a unique refractory spherule b6 from the murchison c2 chondrite approximately 170 m in diameter it is concentrically zoned with an outer rim sequence from outermost to innermost of aluminous diopside 10 m thick anorthite 3 m and melilite 3 m inside the melilite layer is a 7 m thick nearly pure layer of spinel inward from this layer is a 20 m wide zone of hibonite laths enclosed in spinel inward from this zone at the core of the inclusion is caal4o7 perovskite this is the first reported occurrence of caal4o7 in a murchison inclusion the sequence of mineral assemblages from the spinel shell inward parallels that expected for crystallization of a melt with the composition of this spherule 73 2 wt al2o3 17 7 mgo 6 5 cao and 2 5 tio2 from the bulk composition of the inclusion distribution of phases and spherical shape we conclude that the oxide phases in it including spinel crystallized from a liquid from calculated phase relations in the system al2o3 mgo cao we infer a melting temperature of 2100 c the highest ever inferred for a refractory inclusion evidence of a high temperature history is also seen in the spinel which unlike that in most cais contains 1 2 mol excess al2o3 relative to stoichiometric mgal2o4 at this temperature b6 should have been grossly out of equilibrium by 600 c with a gas of solar composition at 10 3 atm but no evidence of evaporative loss is seen the inclusion has a group ii ree pattern and a normal magnesium isotopic composition the latter observation requires a very brief cooling time on the order of several seconds this is consistent with cooling rates calculated for a liquid spherule of the size and composition of b6 undergoing radiative cooling in the solar nebula and constrains the heating mechanism to a small scale event we propose the following sequence for the formation of b6 condensation of solid precursors melting of those precursors in a hypervelocity collision which caused heating of the melt to 2100 c rapid formation of the spinel shell preventing evaporation of the melt fractional crystallization of the melt and addition probably by condensation of the silicate layers corundum and caal4o7 are very rarely found in murchison cais apparently most early formed corundum rich condensates continued to react with the solar nebula until hibonite perovskite and spinel had condensed forming aggregates which when melted gave rise to liquids too rich in tio2 mgo and cao to yield corundum or caal4o7 upon cooling

samarium neodymium chronology and rubidium strontium systematics of an allende calcium aluminum rich inclusion with implications for 146sm half life abstract calcium aluminum rich inclusions cais are primitive objects that formed within the protoplanetary disk surrounding the young sun recent pb pb chronologic studies have demonstrated that cais are the oldest solar system solids crystallizing 4567 ma ago amelin et al 2002 connelly et al 2012 the isotope systematics of cais therefore provide critical insight into the earliest history of the solar system although sm nd and rb sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early solar system previous studies of cais have revealed evidence for isotopically disturbed systems here we report new age data for allende cai al3s4 derived from both the long lived 147sm 143nd and short lived 146sm 142nd isotopic systems the 147sm 143nd chronometer yields an age of 4560 34 ma that is concordant with 207pb 206pb ages for cais and indicates that the sm nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes the slope of the 146sm 142nd isochron defines the solar system initial 146sm 144sm of 0 00828 0 00044 this value is significantly different from the value of 0 0094 determined by kinoshita et al 2012 ages recalculated from all published 146sm 142nd isochron data using the traditional 103 ma half life and the initial 146sm 144sm value determined here closely match pb pb and 147sm 143nd ages determined on the same samples in contrast ages recalculated using the 68 ma half life determined by kinoshita et al 2012 and either of the initial 146sm 144sm values are often anomalously old this is particularly true for the youngest samples with 146sm 142nd isochron ages that are most sensitive to the choice of 146sm half life used in the age calculation in contrast to the sm nd isotope system the rb sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 110 ma although the rb sr system in cais appears to be disturbed the initial 87sr 86sr value determined from the isochron is 0 698942 0 000008 and closely approximates estimates of the initial solar system value although this isochron may be a mixing line it might also record alteration on the allende parent body in which rb was added to the al3s4 cai that was initially largely devoid of rb

iron and chlorine as guides to stratiform cu co au deposits idaho cobalt belt usa the cu co au deposits of the idaho cobalt belt are in lithostratigraphic zones of the middle proterozoic yellowjacket formation characterized by distinctive chemical and mineralogical compositions including high concentrations of fe 15 30 wt percent fe2o3 cl 0 1 1 10 wt percent and magnetite or biotite 50 vol percent the cu co au deposits of the blackbird mine are stratabound in fe silicate facies rocks that are rich in biotite fe and cl but stratigraphically equivalent rocks farther than 10 km from ore deposits have similar compositions a lower lithostratigraphic zone containing magnetite and small cu co au deposits extends for more than 40 km the fe rich strata are probably exhalative units related to mafic volcanism and submarine hot springs but the origin of the high cl concentrations is less clear former chlorine rich pore fluids are suggested by the presence of supersaline fluid inclusions by cl rich biotite and scapolite as much as 1 87 percent cl in fe rich biotite and by high cl concentrations in rock samples chlorine is enriched in specific strata and in zones characterized by soft sediment deformation thus probably was introduced during sedimentation or diagenesis unlike some metasedimentary rocks containing scapolite and high cl the yellowjacket formation lacks evidence for evaporitic strata that could have been a source of cl more likely the cl reflects a submarine brine that carried fe k and base metals strata containing anomalous fe k cl are considered to be a guide to sub basins favorable for the occurrence of stratiform base metal deposits

re os systematics and geochemistry of cobaltite coass in the idaho cobalt belt belt purcell basin usa evidence for middle mesoproterozoic sediment hosted co cu sulfide mineralization with grenvillian and cretaceous remobilization we report the first study of the re os systematics of cobaltite coass using disseminated grains and massive sulfides from samples of two breccia type and two stratabound deposits in the co cu au idaho cobalt belt icb lemhi subbasin to the belt purcell basin idaho usa using a 185re 190os spike solution magnetic and non magnetic fractions of cobaltite mineral separates give reproducible re os analytical data for aliquot sizes of 150 to 200 mg cobaltite from the icb has highly radiogenic 187os 188os ratios 17 45 and high 187re 188os ratios 600 1800 but low re and total os contents ca 0 4 4 ppb and 14 64 ppt respectively containing 30 to 74 radiogenic 187os cobaltite from the icb is amenable to re os age determination using the isochron regression approach re os data for disseminated cobaltite mineralization in a quartz tourmaline breccia from the haynes stellite deposit yield a model 1 isochron age of 1349 76 ma 2 n 4 mean squared weighted deviation mswd 2 1 initial 187os 188os ratio 4 7 2 2 this middle mesoproterozoic age is preserved despite a possible metamorphic overprint or a pulse of metamorphic hydrothermal remobilization of pre existing cobaltite that formed along fold cleavages during the ca 1190 1006 ma grenvillian orogeny this phase of remobilization is tentatively identified by a model 3 isochron age of 1132 240 ma 2 n 7 mswd 9 3 initial 187os 188os ratio of 9 0 2 9 for cobaltite in the quartz tourmaline breccia from the idaho zone in the blackbird mine all mesoproterozoic cobaltite mineralization in the district was affected by greenschist to lower amphibolite facies garnet zone metamorphism during the late jurassic to late cretaceous cordilleran orogeny however the fine to coarse grained massive cobaltite mineralization from the shear zone hosted chicago zone blackbird mine is the only studied deposit that has severely disturbed re os systematics with evidence for a linear trend of mixing with metamorphic fluids the new re os ages and extremely high initial 187os 188os ratios of cobaltite reported here favor a magmatic hydrothermal genetic model for a multi stage ree y co cu au mineralization occurring at ca 1370 to 1349 ma and related to the emplacement of the big deer creek granite pluton at ca 1377 ma in our model deposition of paragenetically early xenotime and gadolinite was followed by an influx of mesoproterozoic evaporitic brines and magmatic hydrothermal fluids containing metals and reduced sulfur derived from mafic and oceanic island arc archean to paleoproterozoic rocks in the laurentian basement cobaltite mineralization occurred upon cooling of these fluids at an inferred temperature of 300 c or below

the evolution of a complex type b allende inclusion an ion microprobe trace element study abstract usnm 5241 is a type b1 refractory inclusion from allende first described by el goresy et al 1985 that consists of a 1 2 mm thick melilite rich and spinel poor mantle enclosing a 0 6 cm radius spinel rich core the inclusion contains xenoliths of spinel free fassaite melilite anorthite incorporated within the spinel rich core detailed ion microprobe analyses of individual phases in 5241 show that the rare earth element ree concentrations in mantle melilite vary irregularly with increasing distance from the rim of the inclusion at first decreasing immediately below the rim and then remaining constant between 0 4 and 1 0 mm more than 1 0 mm from the rim the ree concentrations again decrease although counterintuitive in the context of traditional fractional crystallization models these ree variations are in fact broadly consistent with such a model in light of recent experimental measurements of dree3 mel by beckett et al 1988 that show a strong inverse correlation of d with the akermanite content of the melilite local variations over distances of we interpret 5241 as having formed largely by fractional crystallization during the first 40 of its solidification this was followed by fractional crystallization xenolith assimilation during the last 60

n2 ar he compositions in fluid inclusions indicators of fluid source abstract a quadrupole mass spectrometer was used to measure bulk samples of conservative gas species n 2 ar and he in fluid inclusions from a variety of hydrothermal systems analyses of these tracer elements help determine 1 1 if gases extracted by bulk inclusion analyses can provide accurate measurement of n 2 ar he in active and fossil geothermal systems 2 2 if hydrothermal fluids associated with paleogeothermal systems in a continental setting follow n 2 ar he systematics similar to th the western pacific rim active geothermal systems specifically new zealand and 3 3 whether different deposit types systematically vary with regard to n 2 ar he the n 2 ar he ratios of fluid inclusion volatiles released from recently deposited minerals from the valles system are similar to those of present day valles thermal waters those inclusion samples from deep within the valles system below a regional aquitard increase in n 2 compositions for inclusions from the questa and copper flat porphyry deposits are n 2 rich similar to those of arc related volcanic gases whereas those from taylor creek sn deposit appear to be mixtures of magmatic and crustal components n 2 ar he ratios of the precambrian tribag deposit suggest a basalt source but significant levels of self generated he from u and th in the inclusion fluids are also possible inclusions from two epithermal deposits with low salinity inclusions have n 2 ar he ratios trending towards air saturated meteoric waters asw and those inclusions with higher salinities indicate minor to no asw component the n 2 ar he ratios in fresnillo and cochiti inclusions which have magmatic helium isotopic ratios indicate additions of magmatic gases to meteoric fluids inclusions from sediment hosted deposits that contain hydrocarbon bearing brines are he rich as are meteoric waters with a long residence time in the crust at relevant pressure temperature composition conditions henry s law constants of n 2 ar and he are similar and thus the relative amounts of these species trapped under boiling conditions will not vary appreciably from solubility controlled amounts in coexisting liquid furthermore there is no evidence of he loss or gain in inclusions by diffusion process data from the various systems that were examined indicate that fluid inclusion n 2 ar he compositions may be related to magmatic fluid sedimentary brine deep circulating meteoric fluid and shallow circulating meteoric fluid sources which we modified from those proposed by giggenbach 1986 relationships between the n 2 ar he tracer gases and other measurable quantities in fluid inclusions are indicated to be helpful in understanding fluid mixing processes in paleogeothermal systems

melt solidification and late stage evaporation in the evolution of a fun inclusion from the vigarano c3v chondrite vigarano 1623 5 is a forsterite bearing refractory inclusion in which oxygen magnesium and silicon show large degrees of mass dependent isotopic fractionation the core of 1623 5 consists of forsteritic olivine fassaite melilite ak89 and spinel all of which show isotopic mass fractionation averaging 30 6 amu for magnesium and 10 0 amu for silicon it is enclosed in a mantle consisting of aluminous melilite ak16 60 spinel perovskite and hibonite hibonite and spinel in the mantle are enriched in heavy isotopes of magnesium by 8 15 amu relative to the core 1623 5 originally formed by solidification of a magnesium rich melt the endemic isotopic mass fractionation may have been caused by evaporation of that melt or may reflect an earlier evaporation event affecting the reservoir from which the interior of 1623 5 formed later flash remelting of the outer part of the core and volatilization of sio2 and mgo from the melt so produced caused formation of a mantle that is in isotopic and petrologic disequilibrium with the core

a unique type b inclusion from allende with evidence for multiple stages of melting a large 7 mm in diameter allende type b inclusion has a typical bulk composition and a unique structure a fassaite rich mantle enclosing a melilite rich core the core and mantle have sharply contrasting textures in the mantle coarse 1 mm across subhedral fassaite crystals enclose radially oriented melilite laths about 500 m long that occur at the inclusion rim the core consists of blocky melilite grains 20 50 m across and poikilitically enclosed in anhedral fassaite grains that are optically continuous over 1 mm another unique feature of this inclusion is that melilite laths also extend from the core into the mantle fassaite in both the core and mantle is very rich in fine grained 1 10 m spinel the rim laths are normally zoned ak 30 70 inward from the rim of the inclusion with reverse zoning over the last 200 m to crystallize a very wide range of melilite compositions is found in the core of the inclusion where gehlenitic grains ak 5 12 occur these grains are enclosed in strongly zoned ak 15 70 overgrowths the gehlenitic cores and innermost parts of the overgrowths are na2o free but the outer parts of the overgrowths are not in the laths at the rim na2o decreases inward from the rim then increases fassaite in the core has the same range of ti contents as that in the mantle 29 wt tio2 ti2o3 two melting events are required to account for the features of this inclusion in the first event the precursor assemblage is heated to 1400 c and melts except for gehlenitic ak 5 12 melilite and some spinel these grains become concentrated in the core during cooling na2o free melilite nucleates at the rim of the inclusion and on the relict grains in the core after open system secondary alteration the inclusion is heated again but only to 1260 c melilite more gehlenitic than k40 does not melt during cooling na2o bearing melilite crystallizes as small blocky grains and laths in the core and as overgrowths on relict grains in the core and at the rim eventually melilite co crystallizes with fassaite leading to the reverse zoning observed in the laths the coexistence in this inclusion of na free and na bearing melilite plus a positive correlation between na2o and kermanite contents in melilite in an inclusion with a bulk mg isotopic composition that is mass fractionated in favor of the heavy isotopes are both consistent with at least two melting events several other recently described coarse grained inclusions also have features consistent with a sequence of early high temperature melting secondary alteration and remelting at a lower temperature suggesting that remelting of refractory inclusions was a common occurrence in the solar nebula

sulfur carbon hydrogen and oxygen isotope geochemistry of the idaho cobalt belt cobalt copper gold deposits of the idaho cobalt belt including the deposits of the blackbird district have been analyzed for their sulfur carbon hydrogen and oxygen isotope compositions to improve the understanding of ore formation previous genetic hypotheses have ranged widely linking the ores to the sedimentary or diagenetic history of the host mesoproterozoic sedimentary rocks to mesoproterozoic or cretaceous magmatism or to metamorphic shearing the 34 s values are nearly uniform throughout the blackbird district with a mean value for cobaltite coass the main cobalt mineral of 8 0 0 4 n 19 the data suggest that 1 sulfur was derived at least partly from sedimentary sources 2 redox reactions involving sulfur were probably unimportant for ore deposition and 3 the sulfur was probably transported to sites of ore formation as h 2 s hydrogen and oxygen isotope compositions of the ore forming fluid which are calculated from analyses of biotite rich wall rocks and tourmaline do not uniquely identify the source of the fluid plausible sources include formation waters metamorphic waters and mixtures of magmatic and isotopically heavy meteoric waters the calculated compositions are a poor match for the modified seawaters that form volcanogenic massive sulfide vms deposits carbon and oxygen isotope compositions of siderite a mineral that is widespread although sparse at blackbird suggest formation from mixtures of sedimentary organic carbon and magmatic metamorphic carbon the isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper so its significance for the ore forming event is uncertain from the stable isotope perspective the mineral deposits of the idaho cobalt belt contrast with typical vms and sedimentary exhalative deposits they show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes although the isotopic evidence for magmatic components is relatively weak

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

formation of epizonal gold mineralization within the latimojong metamorphic complex sulawesi indonesia evidence from mineralogy fluid inclusions and raman spectroscopy abstract the gold deposits within the latimojong metamorphic complex of sulawesi indonesia including awak mas and salu bulo are estimated to host 50 tonnes au with an average grade of 1 41 g t they are located within the metamorphic basement consisting of pumpellyite to greenschist facies metasedimentary and metavolcanic rocks where gold precipitated in quartz veins that fill north south striking normal faults and extensional fractures the mineral assemblage is dominated by pyrite chalcopyrite galena minor tetrahedrite tennantite and sphalerite gold is electrum with a low silver content au ag ratio of 8 5 to 9 1 albite dolomite ankerite siderite chlorite and white mica are the main alteration minerals quartz albite and carbonate veins hosting h2o bearing fluid inclusions with minor aqueous carbonic phases co2 n2 were detected mole fraction

bicarbonate rich fluid inclusions and hydrogen diffusion in quartz from the libcice orogenic gold deposit bohemian massif abstract unusual paleofluid composition is reported for the libcice orogenic type gold deposit located in the central bohemian plutonic complex cbpc czech republic unexpected bicarbonate rich fluids and their complex chemistry variations characterize primary fluid inclusions from the main gold bearing quartz vein a detailed microthermometry laser raman micro spectroscopy lrms and sem cathodoluminescence study was used to understand the complex chemistry and p t x history the results indicate the presence of h 2 o and h 2 o co 2 ch 4 n 2 h 2 s fluids the latter displaying variations of the co 2 ch 4 ratio in the gaseous phase from 6 8 to 0 06 variation of the ch 4 content across single grains and between different levels of the mine was recorded the presence of nahcolite h 2 up to 6 mol and ethane 0 0 2 mol in the fluids were also discovered by lrms potential models for the formation of different types of fluids present in the deposit are discussed including the genesis of hco 3 rich fluids as well as h 2 and c 2 h 6 presence in the primary fluid inclusions the potential influence of organic matter bearing sediments as well as the impact of the intrusion of cbpc re equilibration and or re speciation of fluid inclusions during the post entrapment history is considered to have the main impact on the complex paleofluid chemistry based on the thermodynamic modeling h 2 diffusion into the fluid inclusions was shown to be the main reason for the ch 4 variation on the scale of a single grain as well as across the whole vein although the exact processes of production formation of hco 3 and h 2 at the libcice deposit remain open to discussion reactions in the c o h system are considered to be a possible formation mechanism this work also contributes to our understanding of the importance of post entrapment modifications and reactions in the c o h system on interpretation deciphering the processes in orogenic type deposits

evolution of caal rich bodies in the earliest solar system growth by incorporation abstract many type b ca al rich inclusions cai s in the allende carbonaceous chondrite contain two types of spinel structures framboids and palisades framboids are clumps of spinel grains generally in situ by solid state growth processes palisades are texturally different and consist of ovoid shells of spinel grains that appear in thin sections as long arcs or rings with diameters ranging from 50 m up to 2 cm no in situ formation process seems able to explain the variety of sizes and morphologies of palisades nor the different compositions and textures of the enclosed and enclosing materials we therefore suggest that palisades are the spinel rims of smaller earlier formed type b cai s that were incorporated into other cai material in various ways by capture into liquid drops by solid condensate overgrowths and by the partial melting or welding of agglomerates containing the bodies as some type b bodies have been found inside type a host material it appears that in at least some regions and probably generally type a cai s formed after type b we propose that type b cai s are residues from the heating and incomplete evaporation of interstellar dust during the accretion of the protosolar nebula and that type a cai s are later condensates from completely evaporated dust whose exotic 16 o rich component became more diluted in the gas phase

strata bound fe co cu au bi y ree deposits of the idaho cobalt belt multistage hydrothermal mineralization in a magmatic related iron oxide copper gold system mineralogical and geochemical studies of strata bound fe co cu au bi y rare earth element ree deposits of the idaho cobalt belt in east central idaho provide evidence of multistage epigenetic mineralization by magmatic hydrothermal processes in an iron oxide copper gold iocg system deposits of the idaho cobalt belt comprise three types 1 strata bound sulfide lenses in the blackbird district which are cobaltite and less commonly chalcopyrite rich with locally abundant gold native bismuth bismuthinite xenotime allanite monazite and the be rich silicate gadolinite y with sparse uraninite stannite and bi tellurides in a gangue of quartz chlorite biotite muscovite garnet tourmaline chloritoid and or siderite with locally abundant fluorapatite or magnetite 2 discordant tourmalinized breccias in the blackbird district that in places have concentrations of cobaltite chalcopyrite gold and xenotime and 3 strata bound magnetite rich lenses in the iron creek area which contain cobaltiferous pyrite and locally sparse chalcopyrite or xenotime most sulfide rich deposits in the blackbird district are enclosed by strata bound lenses composed mainly of cl rich fe biotite some deposits have quartz rich envelopes whole rock analyses of 48 co and or cu rich samples show high concentrations of au up to 26 8 ppm bi up to 9 16 wt y up to 0 83 wt rees up to 2 56 wt ni up to 6 780 ppm and be up to 1 180 ppm with locally elevated u up to 124 ppm and sn up to 133 ppm zn and pb contents are uniformly low 821 and 61 ppm respectively varimax factor analysis of bulk compositions of these samples reveals geochemically distinct element groupings that reflect statistical associations of monazite allanite and xenotime biotite and gold detrital minerals chalcopyrite and sparse stannite quartz and cobaltite with sparse selenides and tellurides significantly cu is statistically separate from co and as consistent with the general lack of abundant chalcopyrite in cobaltite rich samples paragenetic relations determined by scanning electron microscopy indicate that the earliest y ree be mineralization preceded deposition of co cu au and bi allanite xenotime and gadolinite y commonly occur as intergrowths with and inclusions in cobaltite the opposite texture is rare monazite in contrast forms a poikiloblastic matrix to cobaltite and thin rims on allanite and xenotime reflecting a later metamorphic paragenesis allanite and xenotime also show evidence of late dissolution and reprecipitation forming discordant rims on older anhedral allanite and xenotime and separate euhedral crystals of each mineral textural data suggest extensive deformation of the deposits by folding and shearing and by pervasive recrystallization all during cretaceous metamorphism sensitive high resolution ion microprobe u pb geochronology by aleinikoff et al 2012 supports these paragenetic interpretations documenting contemporaneous mesoproterozoic growth of early xenotime and crystallization of megacrystic a type granite on the northern border of the district these ages are used together with mineralogical and geochemical data from the present study to support an epigenetic iocg model for fe co cu au bi y ree deposits of the idaho cobalt belt a sulfide facies variant of iocg deposits is proposed for the blackbird district in which reducing hydrothermal conditions favored deposition of sulfide minerals over iron oxides this new model includes mesoproterozoic vein mineralization and related fe cl metasomatism that formed the biotite rich lenses a predominantly felsic magmatic source for metals in the deposits given their local abundance of y rees and be and a major sedimentary component in the hydrothermal fluids based on independent sulfur isotope and boron isotope data for sulfides and ore related tourmaline respectively

fractionation of rare earth elements in refractory inclusions from the ningqiang meteorite origin of positive anomalies in ce eu and yb abstract ion microprobe analyses of rare earth elements rees ba and hf were performed for various types of refractory inclusions including amoeboid olivine aggregates aoas from the ningqiang ungrouped carbonaceous chondrite to search for possible relationships between ree abundance patterns and bulk chemical compositions of the inclusions four types of ci normalized ree patterns were recognized 1 nearly flat unfractionated pattern with or without eu and yb anomalies groups i iii or v 2 depletions of ultrarefractory heavy rees hrees relative to light rees lrees and depletions of eu and yb group ii but without depletion of yb in some cases 3 depletions of ultrarefractory hrees with positive anomalies in ce eu and yb modified group ii and 4 nearly flat pattern with positive anomalies in ce eu and yb modified group i no systematic correlation was found between bulk chemical compositions and ree patterns of the inclusions this suggests that the observed ree fractionations occurred prior to condensation of major elements e g mg and si which defined bulk chemical compositions of the inclusions it is remarkable that 7 out of 19 inclusions show positive anomalies in ce yb and in some cases eu as well modified group i and modified group ii suggesting that such anomalies are rather common among inclusions in the ningqiang and possibly in other primitive meteorites two possible mechanisms are considered for the formation of modified group ii and modified group i patterns in model 1 modified group ii is formed by a process similar to that produced group ii but removal of ultrarefractory dust occurred at slightly lower temperatures where not only ultrarefractory hrees but some fraction of lrees had been condensed and removed from the system modified group i may be explained by addition of an unfractionated component to the modified group ii component or alternatively by partial removal of ultrarefractory dust from the system in model 2 modified group ii is formed by later addition of ce eu and yb onto fine grained dust or inclusions having hree depleted group ii like ree patterns similarly modified group i is explained by later addition of ce eu and yb onto those with almost unfractionated ree patterns the observed ree data show that both the degree of hree depletion e g er depletion and that of fractionation among hrees e g depletion in the er gd ratio for modified group ii are very similar to those for group ii model 1 predicts almost complete removal of ultrarefractory hrees from the system resulting in much higher hree depletion for modified group ii which is not consistent with the present observations addition of an unfractionated component may explain moderate depletion of hrees in modified group ii but it will diminish fractionation among hrees which is not consistent with the present observations in contrast model 2 predicts no correlations between ce eu yb enrichment and hree depletion or between ce eu yb enrichment and fractionation among hrees consistent with the present observations hence model 2 seems more likely if this is the case at least two distinct regions with different ree characteristics are required for the formation of modified group ii inclusions one is a high temperature region where group ii like hree depleted inclusions or their precursors are formed by condensation from a fractionated gas after removal of ultrarefractory dust and another is a low temperature region enriched in ce eu and yb in the gas phase abundant occurrence of positive ce eu yb anomalies suggests that migration of solid materials from one region to another occurs rather frequently in the solar nebula the most likely place satisfying such conditions for the formation of these inclusions may be the innermost part of the protoplanetary disk

two unusual type b refractory inclusions in the ningqiang carbonaceous chondrite evidence for relicts xenoliths and multi heating abstract two type b refractory inclusions consisting mainly of melilite fassaite and spinel anorthite were found in the anomalous ningqiang carbonaceous chondrite the composition of melilite varies from ak4 15 near the diopside rims to ak80 90 in the centers of these inclusions in addition melilite exhibits intergrowths with fassaite and or anorthite in the centers of the inclusions these observations suggest that both inclusions were once molten the na2o content of melilite is positively correlated with the ak content for ak beyond crystallization from melts the ningqiang type b refractory inclusions contain possible relict fassaite fragments these fragments are embedded in gehlenitic melilite and have corroded outlines surrounded by highly tio2 enriched fringes as distinguished from the fassaites intergrown with melilite in the centers of the inclusions in inclusion nqj331 most grains of anorthite occur as irregular coarse grained fragments distinct from those intergrown with melilite toward these anorthite fragments melilite shows a steep decrease in ak content we propose that these anorthite fragments are xenoliths and were probably injected into the host while the latter was crystallizing palisades occur only in nqj331 and are probably relicts too distinctly low v2o3 concentrations of the spinels from the palisade bodies and the presence of palisade bodies consisting of one or more corroded crystals of fassaite anorthite are new lines of the evidence for a relict origin of palisades the other type b refractory inclusion nqj354 contains a spherule consisting of a grossite core and a spinel mantle enclosing laths of hibonite the modal abundance and mineral chemistry of the spinel hibonite spherule are distinctly different from the host inclusion we propose that the spinel hibonite spherule crystallized from a sio2 poor melt at a very high temperature and was injected into the type b host before the latter was completely solidified this grossite bearing spinel hibonite spherule may be related to the spinel hibonite spherules in cm2 chondrites

fluorite u th he thermochronology constraints on the low temperature history of yucca mountain nevada abstract fluorite is one of the secondary minerals precipitated in pore spaces at the future nuclear waste repository site at yucca mountain nevada the authors have conducted u th he dating of this fluorite in an attempt to constrain the temperature and timing of paleo fluid flux into the site repeated analysis of colourless fluorite yielded a weighted average age of 9 7 0 15 ma 2 younger than previously determined sanidine 40ar 39 ar ages 12 8 ma for deposition of the tuff laboratory he diffusion experiments conducted on the yucca fluorite yield a preliminary he closure temperature tc of 90 10 c cooling rate of 10 c ma and previous studies have determined that the fluorite precipitated from warm fluids 65 80 c at depths of it was observed that the purple coloured outer portion of the fluorite nodule yielded non reproducible and invariably older ages than colourless fluorite several possible reasons are suggested

correlated study of initial sr 87 sr 86 and al mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the allende meteorite we have studied a suite of six coarse grained ca al rich inclusions cais from the allende meteorite applying in concert detailed petrographic and chemical characterization ion probe mass spectrometric analyses of the al mg isotopic system to determine the abundance and distribution of 26a1 and thermal emission mass spectrometric analyses of the rb sr system to determine initial 87sr86sr ratios the simplest inclusion is a type bl usnm 3529 z that shows evidence of minor alteration and recrystallization since solidification from a melt droplet e g some of the coarse grained anorthite in the inclusion especially near the inclusion rim apparently formed by recrystallization or melting of fine grained secondary anorthite that had replaced melilite four other type bs contain evidence of more widespread recrystallization in addition to evidence of local replacement of melilite by coarse anorthite e g melilite zoning is complex and not igneous in origin and in one inclusion usnm 3529 21 melilite and pyroxene crystals enclose relicts of an earlier generation of the same phases the sixth inclusion usnm 3898 is a type a whose properties appear to be largely metamorphic in origin all six inclusions show variations in mg isotopic compositions indicating that they incorporated 26a1 in 3529 z the relative abundance of 26a1 26al27al 4 0 0 1 10 5 is close to the canonical value 26al27al 5 10 5 for cais but both anorthite and melilite show minor departures from a strict isochron relationship between mg and al in particular the coarse anorthite near the inclusion rim has initial 26al27al ratios of 1 2 10 5 implying formation at least 1 5 million years after the first generation anorthite the other four type bs exhibit larger disturbances of the al mg system that can be understood in terms of local recrystallization and isotopic exchange primarily between anorthite and melilite only 3898 is consistent with a strict al mg isochron relationship but this cai lacks primary anorthite and the small range of al mg among the phases analyzed may preclude resolution of any small isotopic disturbances the rb sr isotopic system also typically indicates some level of disturbance some of which must have been relatively recent nevertheless phases characterized by very low rb sr permit precise identification of initial 87sr86sr our al mg and sr data are largely consistent with a simple chronological interpretation of both systems i e the 26al results suggest that all the initial 87sr86sr ratios should have the same value and with one exception our initial 87sr86sr ratios are consistent with a single value this value is somewhat higher than the primitive value all reported by gray et al 1973 however also with one exception the very low rb sr cai data reported by gray et al 1973 are consistent with the same value the exception is the same inclusion in both studies our analysis of usnm 3898 yields an initial 87sr86srhigher than that of the other cais while gray et al 1973 obtained an initial 87sr86srlower than that of the other cais for the same inclusion labeled as d7 on which all is based neither result can be readily explained as a chronological aberration since 3898 has nearly canonical 26al27al the present data are the first which establish a firm association between primitive 26al27al and primitive 87sr86sr by analysis of both isotopic systems in the same inclusions the comparison of both isotopic systems interpreted as simple nebular chronometers does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of 26al

a calcium aluminum rich inclusion from the essebi cm2 chondrite evidence for captured spinel hibonite spherules and for an ultra refractory rimming sequence abstract an unusual refractory inclusion was discovered in the essebi cm2 chondrite the inclusion has high concentrations of refractory lithophile and siderophile elements with strong enrichments of the most refractory elements lu sc hf in one part of the inclusion the inclusion consists of a melilite rich core partially surrounded by a very refractory rim which in turn is covered by a mantle enriched in si al fe mn cl and s melilite compositions vary from ak 10 26 in the core to ak 0 12 in the rim the core contains several complex framboids consisting of spinel fassaite or spinel hibonite these framboids are probably spherules of the types reported from murchison and were possibly captured by the molten inclusion before it solidified these findings may indicate a genetic link between framboids in cai s and the spinel rich spherules in murchison the rim sequence consists of the following five layers from inside to outside 1 1 hibonite spinel melilite 2 2 hibonite perovskite spinel melilite melilite in this layer is altered to sodalite nepheline calcite 3 3 a hibonite corundum solid solution 4 4 a spinel corundum solid solution as much as 0 1 mole fraction al 2 67 o 4 5 5 sc rich fassaite as much as 6 2 wt sc 2 o 3 spinel al 2 o 3 solid solution al rich diopside pt rich metal crystals occur only in the rim some of these metal crystals contain minor amounts of zr and hf indicating that they formed under reducing conditions the bulk mineral chemistry and texture of the essebi inclusion indicates a complex history involving capture of solid spinel and spinel hibonite spherules similar to the murchison type by a refractory melt droplet solidification of the droplet without obliteration of the spherule textures transportation of the composite object to hotter regions of the solar nebula where the very refractory rim condensed alteration of melilite to sodalite nepheline minor calcite and finally burial in the essebi parent body the cl s bearing mantle probably formed by reactions between the inclusion and liquid and gaseous phases in the parent body

replacement textures in cai and implications regarding planetary metamorphism textural and chemical features of five coarse grained calcium aluminum rich inclusions from the allende meteorite indicate that some of the melilite in these inclusions was formed by a secondary metamorphic event and not by primary crystallization from a melt or by a sequential nebular condensation process these inclusions contain embayed pyroxene surrounded by melilite physically separated pyroxene crystals are often in optical continuity indicating that they were once part of larger single crystals that have been partly replaced by melilite other evidences of metamorphism include reaction textures between melilite and spinel and metamorphic textures such as kink band like features lobate sutured grain boundaries and 120 triple points this type of metamorphic process requires the addition of ca which we propose came from calcite or by introduction of a fluid phase we believe that the most likely environment for this metamorphic process is on a small planetary body and not in the solar nebula the results of this study are compatible with oxygen isotopic heterogeneities within cai and provide a mechanism for producing lower temperature alteration phases and the rim phases found in these inclusions we conclude that planetary processes must thus be considered in the formation history of cai and that it is necessary to reconsider the classification system of these objects in light of the replacement process proposed here

differential recovery of pacific island fish remains the effects of differential recovery have been documented and discussed for almost a century screening experiments using comparative collections are one avenue for understanding recovery bias because they develop expectations about what is likely to be recovered in this study modern reference specimens of pacific island fish were screened through 1 4 inch 6 4 mm and 1 8 inch 3 2 mm mesh recovery rates are examined across taxa body size and element type the experimental recovery rates are then compared to those from an archaeological fish assemblage from the moturakau rockshelter aitutaki cook islands to examine how well the data derived from screening experiments are able to predict archaeological recovery patterns the experimental data is able to accurately predict the taxa recovered in the moturakau sample the impact of differential recovery on a variety of interpretations utilizing archaeological fish remains is then discussed

crystal chemical effects on the partitioning of trace elements between mineral and melt an experimental study of melilite with applications to refractory inclusions from carbonaceous chondrites the partitioning behavior of the trace elements be sc ba la ce and tm between melilite and liquid has been determined using stepwise integration of a rayleigh fractionation equation for ion microprobe analyses of synthetic zoned melilite crystals distribution coefficients between melilite and liquid d mel l i were determined over the entire range of melilite spinel crystallization for one bulk composition corresponding to that of an average type b inclusion from the allende c3v carbonaceous chondrite beryllium is incompatible in gehlenitic meliliters e g d mel l b e 0 5 for x ak 0 3 but compatible in akermanitic melilites e g d mel l b e 1 9 for x ak 0 75 barium d mel l b a 0 04 0 05 sc d mel l s c 0 01 0 02 la d mel l l 0 07 0 29 ce d mel l c e 0 05 0 21 and tm d mel l t m 0 03 0 14 are all incompatible in melilites in the range ak25 ak75 variations in d mel l i as a function of x ak are explicable in terms of a simple thermodynamic treatment of trace element partitioning based on crystal chemical considerations characteristic trace element zoning patterns are predicted for early crystallizing melilite from meliliterich type b inclusions for example concentrations of the rees in melilite should continually decrease with increasing degrees of crystallization opposite the behavior normally expected of an incompatible element concentrations of be should rise with increasing degrees of crystallization even when the element is compatible again opposite the behavior normally expected of compatible elements in general zoning patterns of trace elements in melilite from type b inclusions are consistent with those predicted for fractional crystallization from a melt in a closed system trace element zoning patterns in meteoritic melilite crystals constrain the origin and thermal histories of ca al rich inclusions from carbonaceous chondrites

part ii evaluation of 40ar 39ar quartz ages implications for fluid inclusion retentivity and determination of initial 40ar 36ar values in proterozoic samples the argon isotope systematics of vein quartz samples with two different k reservoirs have been evaluated in detail potassium is hosted by ultra high salinity fluid inclusions in quartz samples from the eloise and osborne iron oxide copper gold iocg deposits of the mt isa inlier australia in contrast k is hosted by accidentally trapped mica within lower salinity fluid inclusions of a sample selected from the railway fault 13 km south of the mt isa copper mine australia imprecise apparent ages have been obtained for all of the samples studied and conclusively demonstrate that quartz fluid inclusions are retentive to ar and have not leaked over billions of years iocg samples that host k in fluid inclusions only have k cl values of 1 and the ages obtained represent the maximum ages for mineralization in contrast the railway fault samples that include accidentally trapped mica have k cl values of 1 excess 40 are plus cl hosted by fluid inclusions and radiogenic 40 arr plus k are strongly correlated in these samples and define a plane in 3d 40 ar 36 ar k cl space in this case the plane yields an excess 40 are corrected age of 1030 ma that is 100 s of ma younger than nearby cu mineralization at mt isa the age is interpreted to reflect 40 ar loss from the accidentally trapped mica into the surrounding fluid inclusions and is not related to the samples age of formation the initial 40 ar 36 ar value of fluid inclusions is widely used to provide information on fluid origin for the iocg samples that host k in fluid inclusions only the initial 40 ar 36 ar values are close to the measured values at every temperature of stepped heating experiments for samples that include accidentally trapped mica the correction for post entrapment radiogenic 40 arr production is significant furthermore because 39 ark present in accidentally trapped mica crystals is released at different temperatures to radiogenic 40 arr lost to the surrounding fluid inclusions intra sample 40 ar 36 ar variation cannot be reliably documented the results demonstrate that noble gas analysis is readily applicable to proterozoic or older samples but that if k mineral impurities are present within quartz the abundance of k must be determined before calculation of mean 40 ar 36 ar values that are

uranium in iron oxide copper gold iocg systems the olympic dam iron oxide copper gold iocg deposit is currently the world s largest producer of uranium other iocg deposits generally have anomalous though uneconomic uranium grades the fluids that generate iocg deposits are thought to be saline and highly oxidized and would be capable of leaching and transporting significant uranium the reasons for uranium enrichment in certain iocg deposits remain speculative but could include the composition of mineralization related magmas of the wall rocks altered by hydrothermal fluids or of the fluids mixing at the site of mineralization there is sparse data available on uranium abundance in iocg ores there is even less reliable data on the uranium content of unaltered wall rocks for the deposits however the data that is available suggest that the uranium grade of iocg deposits may be primarily related to the uranium content of their unaltered host rocks many iocg deposits appear to have approximately 10 to 40 times enrichment in the ore compared to unaltered host rocks this suggests that exploration for uranium rich iocg deposits should focus on areas with anomalously high uranium contents in host rock sequences

petrology and mineralogy of the ningqiang carbonaceous chondrite we report detailed chemical petrological and mineralogical studies on the ningqiang carbonaceous chondrite ningqiang is a unique ungrouped type 3 carbonaceous chondrite its bulk composition is similar to that of cv and ck chondrites but refractory lithophile elements 1 01 x ci are distinctly depleted relative to cv 1 29 x ci and ck 1 20 x ci chondrites ningqiang consists of 47 5 vol chondrules 2 0 vol ca al rich inclusions cals 4 5 vol amoeboid olivine aggregates aoas and 46 0 vol matrix most chondrules 95 in ningqiang are mg rich the abundances of fe rich and al rich chondrules are very low al rich chondrules arcs in ningqiang are composed mainly of olivine plagioclase spinel and pyroxenes in arcs spinel and plagioclase are enriched in moderately volatile elements cr mn and na and low ca pyroxenes are enriched in refractory elements al and ti the petrology and mineralogy of arcs in ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes we found 294 cals 55 0 type a 39 5 spinel pyroxene rich 4 4 hibonite rich and several type c and anorthite spinel rich inclusions and 73 aoas in 15 ningqiang sections equivalent to 20 cm 2 surface area this is the first report of hibonite rich inclusions in ningqiang they are texturally similar to those in cm ch and cb chondrites and exhibit three textural forms aggregates of euhedral hibonite single crystals fine grained aggregates of subhedral hibonite with minor spinel and hibonite al ti diopside spinel spherules evidence of secondary alteration is ubiquitous in ningqiang opaque assemblages formed by secondary alteration of pre existing alloys on the parent body are widespread in chondrules and matrix on the other hand nepheline and socialite existing in all chondritic components formed by alkali halogen metasomatism in the solar nebula

experimental studies of trace element partitioning in ca al rich compositions anorthite and perovskite using electron probe and ion probe techniques experimental crystal liquid partition coefficients d have been measured in meteoritic ca al rich inclusion cai compositions for mg zr y and rees in anorthite and perovskite partitioning data for ti in anorthite and al in perovskite are also reported where cross comparisons are possible between electron and ion probe data agreement is good concentration variations in anorthite for many elements are beyond what can be explained by fractional crystallization but show well defined interelement correlations which could reflect the temperature dependence of the d values or could result from liquid boundary layers for anorthite our d values for rees are lower and they decrease more rapidly with decreasing ionic radius than most in the literature most of the older ree d patterns for plagioclase in the literature are too flat because of insufficient purity of mineral separates or because of analytical problems new ion probe data for minor and trace elements in anorthite from type b cais permit detailed comparisons with fractional crystallization models based on the measured d values for most comparisons models and observations do not agree for amounts of crystallization less than 90 it is possible that anorthite does not appear until after 95 crystallization compared to about 40 which would be expected from isothermal equilibrium crystallization experiments the lrees are highly compatible elements in perovskite but d values drop sharply for the hrees y and zr d values for rees increase strongly from air to highly reducing conditions as coupled ree ti 3 substitutions become possible model calculations show that ree patterns in igneous perovskites from cais will reflect the d pattern and the models can explain some ree patterns from compact type a cais however there are other sets of trace element data for perovskite in cais that cannot easily be explained by igneous processes

structural controls and evolution of gold silver and ree bearing copper cobalt ore deposits blackbird district east central idaho epigenetic origins the cu co au ag ni ree ore deposits of the blackbird district east central idaho have previously been classified as besshi type vms sedex and iocg deposits within an intact stratigraphic section new studies indicate that across the district mineralization was introduced into the country rocks as a series of structurally controlled vein and alteration systems quartz rich and biotite rich veins and alteration zones and minor albite and siderite veinlets maintain consistent order and sulfide mineral associations across the district both early and late quartz veins contain chalcopyrite and pyrite whereas intermediate stage tourmaline biotite veins host the cobaltite barren early and late albite and late carbonate generally siderite form veins or are included in the quartz veins ree minerals principally monazite allanite and xenotime are associated with both tourmaline biotite and late quartz veins the veins are in mineralized intervals along axial planar cleavage intrafolial foliation and shears mineralized intervals are hosted by a variety of metasedimentary rocks including three phyllitic units of mesoproterozoic age and two schistose units all of these units are s tectonites in the footwall of a regional thrust fault specifically the district lies within an oblique thrust ramp containing a series of structural horses three domains in a duplex system the deposits span the three domains and are hosted by metamorphic rocks that range from lower amphibolite facies in the structurally upper domain to lower middle greenschist facies in the lower domain an inverted metamorphic sequence early quartz and biotite veins were introduced during progressive folding and prolonged peak metamorphic conditions and they underwent late tectonic retrograde recrystallization and metamorphic mineral growth to the same extent as the country rocks in each domain where little subsequent deformation occurred early veins are discordant to bedding but where folding was polyphase and fabrics are penetrative mineralized zones are concordant with metamorphic compositional layering late quartz veins in the zones are associated with retrograde minerals and textures and are only locally deformed 40 ar 39 ar dating of unoriented muscovite from the selvage of a late quartz vein yields a late cretaceous age of about 83 ma the time of retrograde metamorphism associated with introduction of late quartz veins textural data at all scales indicate that the host sites for veins and the tectonic evolution of both host rocks and mineral deposits were kinematically linked to late cretaceous regional thrust faulting heat fluids and conduits for generation and circulation of fluids were part of the regional crustal thickening the faulting also juxtaposed metaevaporite layers in the mesoproterozoic yellowjacket formation over blackbird district host rocks we conclude that this facilitated chemical exchange between juxtaposed units resulting in leaching of critical elements cl k b na from metaevaporites to produce brines scavenging of metals co cu etc from rocks in the region and finally concentrating metals in the lower plate ramp structures although the ultimate source of the metals remains undetermined the present cu co au ag ni ree blackbird ore deposits formed during late cretaceous compressional deformation

crystallization sequences of ca al rich inclusions from allende an experimental study the equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of type b ca al rich inclusions from the allende meteorite is spinel 1550 c melilite 1400 c ak22 anorthite 1260 c ti al rich clinopyroxene 1230 c ti fassaite the melilite becomes increasingly akermanitic with decreasing temperature the pyroxene is similar in composition to fassaites from type b inclusions preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron wustite buffer the results of these experiments have been integrated with available phase equilibrium data in the system cao mgo al 2o 3 sio 2tio 2 and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse grained ca al rich inclusions has been developed available bulk compositions of coarse grained inclusions form a well defined trend in terms of major elements extending from type a and bl inclusions near the spinel melilite join to more pyroxene rich type b2 inclusions the trend deviates from the expected sequence of solid condensates from a nebular gas at p 10 3 atm if pure diopside is assumed to be the clinopyroxene that condenses the type a b1 end of the trend is similar in composition to calculated equilibrium condensates at 1202 1227 c and the trend as a whole parallels the sequence of condensates expected from diopside condensation at 1170 c the trend is consistent to first order with the condensation of solid ti rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense partially molten condensates may be likely in this case or if the nebular pressure is higher than 10 3 atm

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

mantle derived and crustal he and ar in the ore forming fluids of the xihuashan granite associated tungsten ore deposit south china abstract the xihuashan tungsten ore deposit in the central nanling region south china is a vein type hydrothermal deposit associated with the late jurassic granitoids that were previously thought to be the products of crustal anatexis alone in this study we use helium he and argon ar isotopes of fluid inclusions entrapped in pyrite and arsenopyrite to determine the origin of the ore forming fluids the 3he 4he ratios of the crushed fluid inclusions vary from 0 15 to 1 16 ra with a mean of 0 72 ra ra the atmospheric 3he 4he ratio of 1 4 10 6 indicating the presence of mantle derived noble gasses in the fluids the amounts of the mantle derived noble gasses are estimated to be between 2 and 17 the 40ar 36ar ratios of the fluid inclusions vary from 306 to 1023 with an average of 440 these ratios are significantly higher than the average crustal value indicating the presence of air saturated water in the volatiles released from the mineral separates the results from this study indicate that the associated coeval granitoids which is believed to provide the ore forming fluids during magma evolution are not the products of pure crustal melts mantle derived volatiles and heat was also involved in the genesis of the host granite pluton

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

diet breadth adaptive change and the white mountains faunas abstract drawing on faunal data from high elevation sites in the white mountains of eastern california usa grayson journal of archaeological science 18 483 506 1991 tested implications of the bettinger baumhoff american antiquity 47 485 503 1982 model of late prehistoric human adaptive change in the great basin madsen journal of archaeological science 20 321 329 1993 challenges the validity of these tests and raises a number of arguments concerning the testing of diet breadth models in archaeological settings we argue that the tests presented by grayson are valid and that many of the critiques posed by madsen apply only to the bettinger baumhoff model we also explore the issues madsen raised concerning archaeological tests of foraging models

fassaite composition trends during crystallization of allende type b refractory inclusion melts fassaite is a major phase in type b refractory inclusions and its wide compositional variability makes it an excellent recorder of crystallization induced changes in liquid composition traverses across zoned crystals with electron and ion microprobes show that ti v sc zr and hf decrease from core to rim while mg si rees and other trace elements increase fassaite liquid distribution coefficients derived from the compositions of early fassaite and calculated parent liquid compositions are higher than previously reported fassaite ds e g 0 2 0 8 vs 0 08 0 5 for the trivalent rees possibly due to the high ti and al contents of the fassaite we analyzed log log plots of concentrations of elements vs those of sc give linear relationships with slopes of dixl l 1 dscxl l 1 where dixl l is the bulk crystal liquid distribution coefficient for element i from this relationship we derive effective fassaite liquid ds of 2 8 for sc 1 5 for hf 1 1 for zr 0 52 for y 0 34 for ta 0 29 for nb and 0 31 0 48 for trivalent rees the effective ds are applicable to fassaite crystallizing from melts having the compositions and thermal histories of allende type b refractory inclusions and incorporate any equilibrium and kinetic effects that modify ds during the course of crystallization observed fassaite ree contents can be reproduced by a fractional crystallization model in which the effective ds are used ti3 is more compatible in fassaite than ti4 and without equilibration of the residual liquid with an external reducing gas ti3 titot ratios where titot ti3 ti4 should decrease from core to rim in fassaite crystals comparison of profiles of ti3 titot ratios in several crystals with those calculated for fractional crystallization suggests that the trend in one crystal was controlled by fractional crystallization alone but in two others the virtually constant ti3 titot ratios may imply that the liquids in these inclusions were able to maintain equilibrium with the solar nebular gas throughout crystallization attempts to determine the o2 of fassaite crystallization on the basis of ti3 titot ratios must be based on fassaite grains which are not zoned with respect to ti3 titot the range of observed ree abundances in subliquidus fassaite 7 800 cl for la and 30 2000 cl for lu now encompasses those in grains previously identified as relict removing a major reason for their identification as such rounded fassaite grains with fairly sharp mg rich rims and ti rich cores poikilitically enclosed in mantle melilite in ts34 are candidates for relict grains the grains are so scrich that they would require extreme prior crystallization of spinel and melilite which is inconsistent with their very low ree contents e g la at 3 7 cl we suggest that the cores of these grains are relict and were trapped with liquid during formation of the mantle

anatomy of an allende coarse grained inclusion inclusion 5241 is a petrographically complex coarse grained cai from the allende meteorite containing a core with two petrographically and chemically distinct units the core is surrounded by a melilite mantle similar to that described for allende type b1 inclusions which consists of large millimetersized crystals the two different units of the core are 1 spinel free islands consisting of melilite fassaite and minor anorthite 2 spinel rich areas with major fassaite and reversely zoned melilite in this unit spinel occurs in fassaite melilite and in densely packed belts surrounding the spinel free islands mineral chemistries of melilite and fassaite in the spinel free islands are different from those in the spinel rich areas melilite in the spinel free islands is unzoned and displays a very narrow chemical variation 10 mol within individual crystals ranging between ak 52 and ak 68 in all islands they also contain considerable amounts of na melilite molecule as much as 2 7 mol in contrast melilite in the spinel rich areas is reversely zoned and barren of na melilite the composition varies between ak 43 and ak 62 with the lowest ak content within a zone decorated with fassaite and spinel inclusions zoning in individual melilite crystals in the mantle is not continuous as in allende type b1 inclusions but is rhythmic outwards from ak 30 to ak 35 near the core mantle boundary followed by a continuous decrease with the lowest value near the center of the melilite crystals ak 25 the ak content rises again and reaches a value of ak 28 at the rim of the inclusion fassaite in the spinel free islands is typically concentrically zoned with ti al rich cores and ti al poor rims the concentration of ti 3 in some fassaite crystals in the islands appears to be lower than in the spinelrich areas zoning of fassaite in the spinel rich areas is nonsystematic and the tio 2 variations are considerable 2 12wt bulk compositions of the spinel free islands plot inside the type b cai field but considerably below the fo an ge plane because they are spinel deficient in contrast compositions of the spinel rich areas plot outside the type b cai field close to pyroxene saturated compositions stolper 1982 textural relations and mineral chemistries in the spinel free islands spinel rich areas and melilite mantle cannot be explained by gas solid condensation simple stage crystallization from a refractory silicate liquid or evaporative loss by distillation but suggest a series of complex events including the capture of solid spinel free bodies by a refractory liquid the melilite mantle may have formed by crystallization from a liquid which enveloped the complex core

a primitive dark inclusion with radiation damaged silicates in the ningqiang carbonaceous chondrite a petrologic and tem study of a remarkable dark inclusion di in the ningqiang cv3 chondrite reveals that it is a mixture of highly primitive solar nebula materials the di contains two lithologies the first lithology a contains micron sized olivine and pyroxene grains rimmed by amorphous materials with compositions similar to the underlying crystalline grains the second lithology b appears to preserve the mineralogy of lithology a before formation of the amorphous rims overall the ningqiang di appears to record the following processes 1 formation condensation and fe enrichment of olivine crystals in the nebula with compositions of fo42 62 2 irradiation resulting in amorphitization of the olivine and pyroxene to varying degrees 3 partial annealing resulting in formation of fairly large euhedral olivine and pyroxene grains with remnant amorphous sharply bounded rims 4 in some cases prolonged annealing resulting in the formation of microcrystalline olivine or pyroxene rims the latter annealing would have been a natural consequence of irradiation near the critical temperature for olivine and 5 mixture of the above materials lithology a with nebular condensate high ca pyroxene and olivine which escaped nebular processing to become lithology b we suggest that the amorphous rims in lithology a formed in an energetic solar event such as a bi polar outflow or fu orionis flare

a once molten coarse grained ca rich inclusion in allende a compact spheroidal type b inclusion in allende contains melilite laths that project radially inward from the inclusion edge which show interference growth textures the combined textural and chemical features of this object cannot be explained by independent vapor solid condensation of grains in space followed by random aggregation of these grains into an inclusion rather it probably formed from a once molten droplet that crystallized in response to radiative cooling from its outer surface the crystallization sequence in this and another similar inclusion in which oxygen isotopes have been measured is melilite spinel anorthite fassaite this sequence supports the idea that oxygen isotopic heterogeneities in coarse grained inclusions were formed after complete solidification of these objects by partial exchange with a less16o rich gas and not during or before a melting event

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a reply

the petrogenesis of type b1 ca al rich inclusions the spinel perspective minor element variations in mgal 2o 4 spinel from the type b1 calcium aluminum rich inclusion cai allende ts 34 confirm earlier studies in showing correlations between the minor element chemistry of spinels with their location within the inclusion and with the chemistry of host silicate phases these correlations result from a combination of crystallization of a liquid produced by re melting event s and local re equilibration during subsolidus reheating the correlation of the ti and v in spinel inclusions with the ti and v in the adjacent host clinopyroxene can be qualitatively explained by spinel and clinopyroxene crystallization prior to melilite following a partial melting event there are however difficulties in quantitative modeling of the observed trends and it is easier to explain the ti correlation in terms of complete re equilibration the correlation of v in spinel inclusions with that in the adjacent host clinopyroxene also cannot be quantitatively modeled by fractional crystallization of the liquid produced by re melting but it can be explained by partial re equilibration the distinct v and ti concentrations in spinel inclusions in melilite from the edge regions of the cai are best explained as being affected by only a minor degree of re equilibration the center melilites and included spinels formed during crystallization of the liquid produced by re melting while the edge melilites and included spinels are primary the oxygen isotope compositions of ts 34 spinels are uniformly 16 o rich regardless of the host silicate phase or its location within the inclusion similar to other type b1 cais clinopyroxene is 16 o rich but melilite is relatively 16 o poor these data require that the oxygen isotope exchange in ts 34 melilite occurred subsequent to the last re melting event

formation of spinel hibonite rich inclusions found in cm2 carbonaceous chondrites we report petrography mineral chemistry bulk chemistry and bulk isotopic compositions of a suite of 40 spinel rich inclusions from the murchison cm2 carbonaceous chondrite seven types of inclusions have been identified based on mineral assemblage spinel hibonite perovskite spinel perovskite pyroxene spinel perovskite melilite spinel hibonite perovskite melilite spinel hibonite spinel pyroxene and spinel melilite anorthite hibonite bearing inclusions have ti poor spinel compared to the hibonite free ones and spinel hibonite perovskite inclusions have the highest average bulk tio 2 contents 7 8 wt the bulk cao al 2 o 3 ratios of the inclusions range from 0 005 to 0 21 well below the solar value of 0 79 hibonite spinel rich inclusions consist of phases that are not predicted by condensation calculations to coexist in the equilibrium sequence hibonite is followed by melilite which is followed by spinel therefore hibonite melilite or melilite spinel inclusions should be dominant instead one explanation for the missing melilite is that it condensed as expected but was lost due to evaporation of mg and ca during heating and melting of spherule precursors if this theory were correct melilite poor spherules would have isotopically heavy mg and ca assuming rayleigh fractionation accompanied evaporation except for one inclusion with f mg 4 3 2 6 amu and another with isotopically light ca f ca 3 4 2 0 amu however all the inclusions we analyzed have normal isotopic compositions within their 2 uncertainties thus we found no evidence for significant mass dependent fractionation conditions necessary for non rayleigh evaporation are unlikely if not unrealistic and our preferred explanation for the general lack of melilite among hibonite spinel bearing inclusions is kinetic inhibition of melilite condensation relative to spinel because of similarities between the crystal structures of hibonite and spinel it should be easier for spinel than for melilite to form from hibonite

complexly zoned chromium aluminum spinel found in situ in the allende meteorite in addition to the mg al 16o rich spinels that are known to occur in refractory inclusions the murchison meteorite contains cr rich 16o poor spinels most of whose sources are unknown because they are rarely found in situ here we report the in situ occurrence in allende of cr rich spinels found in 13 chondrules and 4 olivine rich objects the allende spinels exhibit major and minor element contents isotopic compositions and zoning of cr2o3 contents like those of the cr spinels from murchison some chondrules contain patchy zoned spinel simon et al 1994 which suggests that such grains did not form by sintering but perhaps by formation of overgrowths on relic grains unlike the olivine rich objects phases in all three chondrules that were analyzed by ion microprobe have uniform near normal o isotopic compositions one olivine rich object alsp1 has a huge 1 mm fragment of chevron zoned spinel this spinel has near normal o isotopic compositions that are quite distinct from those of adjacent forsteritic olivine which are relatively 16o rich and plot on the calcium aluminum inclusion cai line like some isolated forsterite grains found in allende the spinel and olivine in this object are therefore not genetically related to each other another olivine rich object alsp11a contains a rectangular 150 s 100 m homogeneous spinel grain with 50 wt cr2o3 and 23 wt feo in a vuggy aggregate of finer grained 5 90 m feo rich fo47 55 olivine the magnesian core of one olivine grain has a somewhat 16o rich isotopic composition like that of the large spinel whereas the feo rich olivine is relatively 16o poor the composition of the spinel in alsp11a plots on the cai line the first cr rich spinel found to do so chevron zoned spinel has not been observed in chondrules and it is unlikely that either alsp1 or alsp11a were ever molten calculations show that a spinel with the composition of that in alsp1 can condense at 1780 k at a ptot of 10 3 atm and a dust gas ratio of 100 relative to solar the cr rich spinel in alsp11a could condense at 1420 k but this would require a dust gas enrichment of 1000 relative to solar the data presented here confirm that as in murchison the coarse cr rich spinels in allende are relatively 16o depleted and are isotopically distinct from the 16o enriched mgal2o4 from cais sample alsp11a may represent a third population one that is cr rich and plots on the cai line that the o isotopic composition of alsp1 is like those of cr rich spinels from chondrules indicates that o isotopic compositions cannot be used to distinguish whether grains from such unequilibrated objects are condensates or are fragments from a previous generation of chondrules

zoning patterns of fe and v in spinel from a type b ca al rich inclusion constraints on subsolidus thermal history we obtained two dimensional concentration maps for the minor elements fe and v in 21 spinel crystals in the allende type b1 inclusion ts 34 with a 4 5 m resolution locally high concentrations of fe occur along at least one edge of the spinels and decrease toward the center of the grains enrichment in v can also occur along edges or at corners in general there is no overall correlation of the fe and v distributions but in local regions of two grains the v and fe distributions are correlated strongly suggesting a local source for both elements in these two grains opaque assemblages are present that appear to locally control the v distributions this coupled with previous work suggests that prior to alteration ts 34 contained v rich metal oxidation of this metal during alteration can account for the edge corner v enrichments but provide only minor feo contributions explaining the overall lack of correlation between fe and v most of the feo appears to have been externally introduced along spinel boundaries during alteration these alteration phases served as sources for diffusion of feo into spinel feo distributions in spinel lead to a mean attenuation length of 8 m and using literature diffusion coefficients in isothermal and exponential cooling approximations for peak temperatures in the range 600 700 c this leads to a time scale for calcium aluminum rich inclusion cai alteration in the range of decades to centuries

the source and significance of argon isotopes in fluid inclusions from areas of mineralization argon isotopes in fluid inclusions in quartz veins associated with granite hosted tungsten mineralization in the southwest and north of england have been investigated in detail by the40ar 39ar technique the natural argon is present as a number of discrete components which can be identified through correlations with39ar 38ar and 37ar induced by neutron bombardment of potassium chlorine and calcium the potassium correlated component arises principally from in situ decay of potassium in solid phases in the inclusions in the case of the hemerdon tungsten deposit of southwest england the phases responsible are small 25 m captive authigenic micas which are shown to have been deposited from a fluid 268 20 ma ago shortly after the emplacement of the host granite the chlorine correlated component is present in the brines which constitute the fluid phase of the inclusions the argon in these hydrothermal fluids is made up in part of parentless or excess 40ar leached from surrounding crustal rocks and in part of dissolved ancient atmospheric argon absolute concentrations of both atmospheric and excess components in the brine can be estimated from 40arcl ratios and independent determinations of the salinity of the inclusions the absolute concentrations of the atmospheric argon are close to those found in modern meteoric water while those of the excess component can be interpreted in terms of the degree of interaction betwen the circulating fluids and country rock a calcium correlated component with a much higher ratio of excess to atmospheric argon than that in the brine was found to be a dominant phase in one sample from the hemerdon deposit indicating the presence of a solid phase probably a caso4 daughter mineral inclusions of this composition represent fluids which have had a more prolonged interaction with crustal rocks the results obtained from this study provide a systematization and a framework for future multi component argon studies of fluid inclusions together with an indication of the wide range of information which can be inferred

the origin and significance of reverse zoning in melilite from allende type b inclusions in many type b allende inclusions melilite is reversely zoned over restricted portions of each crystal textural relationships and the results of dynamic crystallization experiments suggest that the reverselyzoned intervals in these type melilites result from the co precipitation of melilite with clinopyroxene from a melt prior to the onset of anorthite precipitation when clinopyroxene begins to precipitate the al mg ratio of the melt rises causing the crystallizing melilite to become more gehlenitic an effect which is negated by crystallization of anorthite because the equilibrium crystallization sequence in these liquids is anorthite before pyroxene melilite reverse zoning can occur only when anorthite nucleation is suppressed relative to pyroxene this has been achieved in our experiments at cooling rates as low as 0 5 c hour our experiments further indicate however that reverse zoning does not form at cooling rates 50 c hour probably because the clinopyroxene becomes too al rich to drive up the al mg ratio of the liquid type inclusions with reversely zoned melilites must have cooled at rates greater than those at which anorthite begins to crystallize before clinopyroxene but 50 c hour such rates are far too slow for the type droplets to have cooled by radiation into a nebular gas but are much faster than the cooling rate of the solar nebula itself one possibility is that type b s formed in local hot regions within the nebula where their cooling rate was equal to that of their surrounding gas other possibilities are that their cooling rates reflect their movement along nebular temperature gradients or the influence of a heat source the sun or viscous drag on inclusions as they moved through the nebular gas are potential candidates for such heat sources

measuring foraging efficiency with archaeological faunas the relationship between relative abundance indices and foraging returns abstract in western north america models from foraging theory have been used to address subsistence change using archaeological faunas several studies have argued that return rates from foraging declined in a variety of late holocene contexts and support this position by applying a method involving the computation of a relative abundance index ai of large bodied animals to the sum of large and small ones we present the results of a series of computer simulations devised to identify the relationship between changes in such indices and changes in a forager s average return rate and discuss the implications of these simulations in light of our current work in the little boulder basin area of north central nevada these include 1 the importance of using knowledge of both post encounter return rates and changes in ai s to make inferences about changes in overall return rates 2 the fact that there are good reasons to expect ai values to be low and 3 what factors might contribute to the high ai values observed at archaeological sites