a whiff of oxygen before the great oxidation event high resolution chemostratigraphy reveals an episode of enrichment of the redox sensitive transition metals molybdenum and rhenium in the late archean mount mcrae shale in western australia correlations with organic carbon indicate that these metals were derived from contemporaneous seawater rhenium osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 8 million years ago ma molybdenum and rhenium were probably supplied to archean oceans by oxidative weathering of crustal sulfide minerals these findings point to the presence of small amounts of o 2 in the environment more than 50 million years before the start of the great oxidation event

clay mineral evolution changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4 567 ga of planetary evolution in our solar system reflect evolving tectonic geochemical and biological processes clay minerals were absent prior to planetesimal formation 4 6 billion years ago but today are abundant in all near surface earth environments new clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in earth s evolution notably the formation of a mafic crust and oceans the emergence of granite rooted continents the initiation of plate tectonics and subduction the great oxidation event and the rise of the terrestrial biosphere the changing character of clay minerals through time is thus an important part of earth s mineralogical history and exemplifies the principles of mineral evolution

re assessing the surface cycling of molybdenum and rhenium we re evaluate the cycling of molybdenum mo and rhenium re in the near surface environment world river average mo and re concentrations initially based on a handful of rivers are calculated using 38 rivers representing five continents and 11 of 19 large scale drainage regions our new river concentration estimates are 8 0 nmol kg 1 mo and 16 5 pmol kg 1 re natural anthropogenic the linear relationship of dissolved re and so 2 4 in global rivers r 2 0 76 indicates labile continental re is predominantly hosted within sulfide minerals and reduced sediments it also provides a means of correcting for the anthropogenic contribution of re to world rivers using independent estimates of anthropogenic sulfate approximately 30 of re in global rivers is anthropogenic yielding a pre anthropogenic world river average of 11 2 pmol re kg 1 the potential for anthropogenic contribution is also seen in the non negligible re concentrations in precipitation 0 03 5 9 pmol kg 1 and the nmol kg 1 level re concentrations of mine waters the linear mo so 2 4 relationship r 2 0 69 indicates that the predominant source of mo to rivers is the weathering of pyrite an anthropogenic mo correction was not done as anthropogenically influenced samples do not display the unambiguous metal enrichment observed for re metal concentrations in high temperature hydrothermal fluids from the manus basin indicate that calculated end member fluids i e mg free yield negative mo and re concentrations showing that mo and re can be removed more quickly than mg during recharge high temperature hydrothermal fluids are unimportant sinks relative to their river sources 0 4 mo and 0 1 pre anthropogenic re we calculate new seawater response times of 4 4 10 5 yr smo and 1 3 10 5 yr sre pre

processes of selective grain transport and the formation of placers on beaches placers are found on many beaches of the oregon coast in the beach that is the focus of this study the principal placer minerals are ilmenite 22 0 epidote 20 0 garnet 18 7 augite 15 5 hypersthene 8 1 hornblende 5 8 and zircon 2 0 the ilmenite fraction actually being partly chromite a series of beach face sand samples was obtained along a profile when sand was being eroded from the upper beach and transported to offshore bars since the processes of grain selective sorting leading to placer formation were probably most active at such a time the landward most sample contained 96 heavy minerals being part of the placer this concentration systematically decreased offshore to a 6 heavy mineral content in the seaward most sample 54 m offshore determinations of individual heavy mineral concentrations revealed that although they all tended to become concentrated within the placer with light quartz and feldspar dominating the offshore transport the sorting processes were m

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

temporal record of osmium concentrations and 187os 188os in organic rich mudrocks implications for the osmium geochemical cycle and the use of osmium as a paleoceanographic tracer the final publication is available at elsevier via https doi org 10 1016 j gca 2017 06 046 2017 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

rhenium variations in molybdenite mos2 evidence for progressive subsurface oxidation abstract temporal trends in earth s near surface mineralogy correlate with major events in earth s geochemical and tectonic history new and published analyses of 422 molybdenite mos2 specimens from 135 localities with known ages from 2 91 billion years ga to 6 3 million years ma reveal two statistically significant trends first systematic increases in average and maximum trace concentrations of re in molybdenite since 3 0 ga point to enhanced oxidative weathering by subsurface fluids in addition episodic molybdenum mineralization correlates with five intervals of supercontinent assembly from 2 7 ga kenorland to 300 ma pangaea

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

rise of atmospheric oxygen and the upside down archean mantle 1 the establishment of an oxygen rich atmosphere dramatically altered the evolution of life on earth most of the recent discussion of the topic has been focused on the timing of the event rather than on its mechanism here we draw upon recent developments in the understanding of earth s interior to propose that the rise of oxygen followed a geologically abrupt period of mantle overturn and or intense plume activity near the archean proterozoic transition 2470 2450 million years ago the magmatic event has already been linked to the widespread deposition of oxide facies banded iron formation and the rise of oxygen has been implicated as the trigger for iron deposition and earth s first major glaciation we argue that these events are all related to a change in redox state of volcanic gases brought about by deep seated late archean and earliest paleoproterozoic magmatism

primitive os and 2316 ma age for marine shale implications for paleoproterozoic glacial events and the rise of atmospheric oxygen abstract re os dating of synsedimentary to early diagenetic pyrite from carbonaceous shale that straddles the boundary between the rooihoogte and timeball hill formations transvaal supergroup south africa provides a precise isochron age of 2316 7 ma 4 statistical uncertainty if error on decay constant is excluded and a chondritic initial 187os 188os ratio of 0 1121 0 0012 these units were deposited between what are interpreted as the second and third of three paleoproterozoic global glacial events and thus provide minimum and maximum ages respectively for these events the rooihoogte formation is correlative with the duitschland formation which records previously undated carbon isotope excursions because the pyrite samples show no evidence of mass independent fractionation of sulfur and have highly negative 34s values the rise of atmospheric oxygen most likely began prior to 2 32 ga the chondritic initial 187os 188os ratio requires that primitive hydrothermal sources of os dominated the os budget of seawater at 2 32 ga os is mobile only under oxidizing conditions therefore the chondritic initial 187os 188os ratio may reflect atmospheric oxygen levels too low to introduce sufficient riverine flux of dissolved radiogenic os to offset the primitive hydrothermal magmatic flux even if atmospheric oxygen levels had increased significantly by 2 32 ga anoxic conditions throughout the archean most likely limited os enrichment in archean marine shales so that their subsequent exposure and weathering was unable to provide a significant amount of radiogenic os to paleoproterozoic seawater

the rise of atmospheric oxygen when did atmospheric oxygen rise to near present concentrations and what led to this rise as kasting explains in his perspective recent results have provided stronger than ever evidence that the switch from an anoxic to an oxic atmosphere occurred around 2300 millions years ago but researchers remain divided over the mechanism catling et al resurrect a previously proposed mechanism involving hydrogen escape to space with a couple of new twists whether their mechanism is viable depends on the oxidation state of the continental and oceanic crust at this crucial time of earth9s evolution

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

trace element concentrations in porphyry copper deposits from metaliferi mountains romania a reconnaissance study there are fifteen miocene intrusions with porphyry copper mineralization in the metaliferi mountains romania most are associated with epithermal au ag te bi se ge vein systems the investigation of fifty samples from six deposits rosia poieni bucium tarni a colnic rovina valea morii and bolcana indicated bulk rock mean values of 0 16 0 88 ppm au 1000 ppm in bornite in the porphyry type mineralization galena forms microinclusions in pyrite chalcopyrite and bornite and contains up to 3750 ppm ag 17 380 ppm se 1570 ppm ge and 780 ppm te galena and pyrite from the epithermal mineralization in the m gura bolcana troi a system contain concentrations of ag and se ten times lower than in the same minerals from the porphyry copper mineralization the present data show that te is a significant trace element in the potassic zone of the investigated porphyry systems the data also shows that this does not correlate with the presence or absence of ophiolitic basement or with variation in the chemistry of the host intrusions tellurium enrichment in porphyry type deposits of the metaliferi mountains supports their genetic relationship with the spatially associated epithermal systems

paleomineralogy of the hadean eon a preliminary species list the hadean eon encompassing earth9s first 550 million years was a time of significant planetary evolution nevertheless prebiotic earth9s near surface environment may have held no more than approximately 420 different rock forming or accessory mineral species that were widely distributed and or volumetrically significant this relative hadean mineralogical parsimony is a consequence of the limited modes of mineral paragenesis prior to 4 ga compared to the last 3 0 billion years dominant hadean eon mineralizing processes include the evolution of a diverse suite of intrusive and extrusive igneous lithologies hydrothermal alteration over a wide temperature range notably serpentinization authigenesis in marine sediments diagenesis and low grade metamorphism in near surface environments and impact related processes including shock mineralization creation of marginal hydrothermal zones and excavation of deep metamorphosed terrains on the other hand the hadean eon may have been notably lacking in mineralization generated by plate tectonic processes such as subduction zone volcanism and associated fluid rock interactions which result in massive sulfide deposition convergent boundary orogenesis and consequent extensive granitoid rooted continental landmasses and the selection and concentration of incompatible elements in complex pegmatites with hundreds of accompanying minerals the dramatic mineralogical consequences of life are reflected in the absence of hadean biomineralization for example the lack of extensive carbonate deposits and the associated restricted development of skarn and cave minerals prior to 4 ga most importantly it was not until after the establishment via photosynthesis of significant near surface redox gradients that supergene alteration redox controlled ore deposition and subaerial weathering in an oxidizing environment could diversify earth9s near surface mineralogy these post hadean processes may be responsible for over 4000 of the more than 4800 approved mineral species any scenario for life9s origins that invokes minerals as agents of molecular synthesis selection protection or organization must take into account the limited mineralogical repertoire of the time

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

sedimentology and palaeoenvironment of the southeast sicilian tertiary platform carbonates abstract a thick succession of shelf and shelf slope carbonates is developed in southeastern sicily sedimentological aspects of the oligocene to tortonian sequence including distribution and palaeoenvironmental factors are considered a new formation and four new members are proposed in the upper part of the succession the region comprises a western half typically exhibiting the principal deeper water planktonic facies including marls and an eastern area displaying typically inner shelf carbonates and an attenuated succession coralline algal limestones and calcarenites are more typical of this latter region but there are also some volcanic intercalations an attempt is made to relate the hyblean succession to that of the maltese islands which lie at the southern end of this tertiary carbonate platform

low rhenium molybdenite by metamorphism in northern sweden recognition genesis and global implications abstract re os dating of molybdenite is an accurate means to date intrusions and intrusion related ore deposits using the model age or isochron approach but molybdenite has a new niche in the greenschist to granulite facies metamorphic environment re os ages for metamorphic molybdenite may be used to construct regional metamorphic histories age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single petrographically characterized molybdenite occurrences in this study twelve geologically distinct molybdenite bearing samples from two small mo districts in northern sweden trace a 150 m y paleoproterozoic svecofennian metamorphic history from 1900 to 1750 ma these data reveal a little known widespread and protracted late svecofennian anatexis in northern sweden the kataberget mo cu f deposit is located in the moskosel granite batholith north of the economically renown skellefte district four different molybdenite samples from outcrop at kataberget indicate an intrusion age of 1895 6 ma with the formation of later pegmatite aplite at 1875 6 ma the allebuoda bjorntjarn and munka mo w deposits in the rappen district are represented by three outcrop and five drill core samples of molybdenite bearing aplite pegmatite granite these two deposits were previously described as intrusion related climax type mo mineralization re os ages for molybdenites from these deposits range from 1865 to 1750 ma and significantly re concentrations are markedly low extending to the sub ppm level age agreement within the deposits is conspicuously lacking whereas with one exception age agreement within any single sample geologic occurrence as established by analysis of additional molybdenite separates is very good these data together with fundamental geologic observations discussed in this paper suggest that mo w mineralization in northern sweden is not intrusion related but the local product of episodic melting of archean paleoproterozoic supracrustal gneisses related to the svecofennian orogeny petrographic traverses across the boundary between widespread foliation parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation dehydration breakdown of zircon rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine post deformational biotite plus sulfides oxides hydrothermal zircon and fluorite all associated with microcline dominant leucosomes this process has profound implication for the traditional leucogranite intrusion related genesis attributed to the broad classification of mo w sn base and precious metal mineralization e g south mountain batholith nova scotia okiep namaqualand south africa mactung yukon pogo liese tintina alaska carajas and goias rio tocantins brazil new england batholith nsw australia bergslagen sweden nevoria western australia alpeinerscharte austria erzgebirge germany sardinia corsica batholith in addition to biotite metallogenic contributions e g mo w sn u bi cu pb zn fe ni co au ag te as sb ree in various combinations may also be controlled by breakdown of amphibole in effect the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite in the absence of focusing structures e g shear zones sheeted vein development this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades low re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss mo w or muscovite schist sn w

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

molybdenum isotope variations in molybdenite vapor transport and rayleigh fractionation of mo molybdenum isotopes in 20 molybdenite samples dated by the re os method and representing a range of geologic settings show mass dependent fractionation spanning 0 63 per atomic mass unit amu previous mo isotope data for molybdenite reveal variations in fractionation of 0 5 amu interpretation of these data is hampered however by limited sample numbers in each study lack of a common standard for interlaboratory comparison and limited range of geologic settings here we show that mo isotope compositions of molybdenites do not correlate with crystallization temperature age geographic distribution or geologic conditions rather rayleigh distillation may explain variations of as much as 0 34 amu in a single molybdenite occurrence exceeding the proposed variability in average continental crust vapor transport and rapid precipitation of mo in propagating fractures may account for isotope fractionation of mo and perhaps other metals at very small scales if so the average isotopic composition of mo at each molybdenite occurrence may be representative of bulk crust our results suggest that the isotopic composition of mo delivered to the oceans is uniform geographically and through geologic time

mineral evolution and earth history the field of mineral evolution a merger of mineralogy and earth history coalesced in 2008 with the first of several global syntheses by robert hazen and coworkers in the american mineralogist they showed that the cumulative abundance of mineral species has a stepwise trend with first appearances tied to various transitions in earth history such as the end of planetary accretion at ca 4 55 ga and the onset of bio mediated mineralogy at ca 2 5 ga a global age distribution is best established for zircon observed abundance of zircon fluctuates through more than an order of magnitude during successive supercontinent cycles the pulse of the earth is also recorded albeit imperfectly by the 87sr 86sr composition of marine biogenic calcite the sr isotopic ratio of this mineral reflects the balance of inputs of primitive strontium at mid ocean ridges and evolved strontium that drains off the continents a global mineral evolution database currently in the works will greatly facilitate the compilation and analysis of extant data and the expansion of research in mineralogy outside its traditional bounds and into more interdisciplinary realms

onset of plate tectonics the further back we look into the geological past the more obscured the view masked by an increasingly fragmentary geological record this has resulted in a controversy on the rates and mechanisms of early continental crust formation and whether plate tectonics the dominant crust forming process over at least the past 2 5 billion years operated the same way or even at all during early earth history 1 2 on page 434 of this issue shirey and richardson 3 shed light on this issue by looking at it from a new angle from the bottom up they investigated the composition of a suite of minerals occurring as inclusions in diamonds dredged up by young kimberlite volcanoes these diamonds derive from great depths 125 to 175 km within the ancient lithospheric mantle keels that underpin the stable continental crustal regions known as cratons because the minerals can be precisely dated they can provide a snapshot of the subcontinental lithospheric mantle sclm composition at the time when the crust was being formed

isotopic evidence for massive oxidation of organic matter following the great oxidation event the stable isotope record of marine carbon indicates that the proterozoic eon began and ended with extreme fluctuations in the carbon cycle in both the paleoproterozoic 2500 to 1600 million years ago ma and neoproterozoic 1000 to 542 ma extended intervals of anomalously high carbon isotope ratios 13c indicate high rates of organic matter burial and release of oxygen to the atmosphere in the neoproterozoic the high 13c interval was punctuated by abrupt swings to low 13c indicating massive oxidation of organic matter we report a paleoproterozoic negative 13c excursion that is similar in magnitude and apparent duration to the neoproterozoic anomaly this shunga francevillian anomaly may reflect intense oxidative weathering of rocks as the result of the initial establishment of an oxygen rich atmosphere

multiple age components in individual molybdenite grains abstract re os geochronology of fractions composed of unsized coarse and fine molybdenite from a pod of unusual monazite xenotime gneiss within a granulite facies paragneiss hudson highlands ny yielded dates of 950 5 2 5 953 8 2 6 and 941 2 2 6 ma respectively these dates are not recorded by co existing zircon monazite or xenotime sem bse imagery of thin sections and separated grains reveals that most molybdenite grains are composed of core and rim plates that are approximately perpendicular rim material invaded cores forming irregular contacts probably reflecting dissolution reprecipitation epma and la icp ms analyses show that cores and rims have different trace element concentrations for example cores are relatively enriched in w on the basis of inclusions of zircon with metamorphic overgrowths we conclude that molybdenite cores and rims formed after high grade regional metamorphism the discovery of cores and rims in individual molybdenite grains is analogous to multi component u pb geochronometers such as zircon monazite and titanite thus molybdenite should be carefully examined before dating to ensure that the requirement of age homogeneity is fulfilled

the geology and geochronology of the waifangshan mo quartz vein cluster in eastern qinling china abstract the waifangshan mo quartz vein cluster occurs at the northernmost margin of the qinling orogen the orebodies occur as quartz veins and are controlled by low angle faults we identify three hydrothermal stages characterized by veinlets of quartz pyrite quartz molybdenite pyrite chalcopyrite galena sphalerite and quartz carbonate assemblages respectively the early stage quartz veins were structurally deformed brecciated and filled by non deformed middle or late stage veinlets suggesting that the mineralization is associated with a tectonic transition from compression to extension five molybdenite separates from the zhifang mo deposit yield individual re os ages from 241 2 1 6 to 247 4 2 5 ma with a weighted mean age of 243 8 2 8 ma individual re os isotope ages of four molybdenite samples from the badaogou mo deposit range from 238 9 2 1 to 255 8 2 2 ma with a weighted mean age of 246 10 ma four analyses of molybdenite separates from the xiangchungou mo deposit yield individual re os isotope ages of 243 8 8 8 to 247 7 4 4 ma with a weighted mean age of 246 0 1 1 ma all of these data yield a weighted mean age of 241 9 1 9 ma coeval with the accretionary orogeny we thus conclude that the waifangshan mo quartz veins formed during a transition from continental arc to back arc setting the waifangshan mo quartz veins share similar geological geochemical and geochronological features with the orogenic type systems we propose that the waifangshan mo quartz veins are an orogenic type mo mineralization and possibly represent the deepest member in the crustal continuum model of the orogenic type mineral systems the molybdenite samples from the mo quartz veins in the waifangshan area have low re contents 1 457 to 39 16 ppm suggesting a continental crust dominated source

sedimentology and palaeoecology of a miocene coralline algal biostrome from the maltese islands abstract a large coralline algal biostrome 20 km 5 km 16 m thick is well exposed in western malta and eastern gozo the biostrome is composed of limestones largely constructed by in situ coralline algae or transported algal debris some sediments are dominated by rhodoliths and others by crustose coralline frameworks six facies are distinguished crustose algal marl crustose algal wackestone rhodolith pavement algal branch packstone crustose pavement and algal crust packstone each facies is characterised by different rhodolith morphologies and coralline crusts which are constructed mainly bymesophyllum commune the coralline morphogenesis is related to the palaeoenvironmental conditions the biostrome is thought to have developed from a series of relic sand ridges to form a low relief platform of moderate depths containing a mosaic of sedimentary facies the sequence is affected by growth faulting which divides the biostrome into eight units

anomalous supply of bioessential molybdenum in mid proterozoic surface environments granites aged 1 9 ga to 1 5 ga exhibit molybdenite mineralization globally sandstones deposited during the mid proterozoic have a provenance dominated by 1 9 1 7 ga basement the mid proterozoic surface environment was consequently receiving detritus from the molybdenum rich granites thus there was a supply of molybdenum available in terrestrial or shallow marine environments at a time when molybdenum was required to support the evolution of multicellular life

trace element geochemistry of molybdenite from the shapinggou super large porphyry mo deposit china abstract the shapinggou deposit located in the dabie orogenic belt eastern china is one of the largest mo only porphyry deposits in the world alteration types associated with shapinggou include silicic potassic silicic phyllic propylitic and argillic the phyllic alteration can be subdivided into quartz and sericite mainly muscovite phases whereas the argillic alteration is distinguished by poorly crystallized kaolinite kaolinite px muscovite and phengite the ore forming event can be divided into quartz k feldspar quartz molybdenite quartz sericite and quartz fluorite gypsum stages with molybdenite deposited in the first three stages but mainly in the second the molybdenites in shapinggou represent either the 2h1 and or the 2h1 3r polytype and can be subdivided into two groups group one and group two group 1 is associated with stage 1 alteration whereas group 2 is found with stages 2 and 3 there is an increase in the re values from group one to group two with the re contents likely controlled by both the crustal metal source and temperature with decreasing temperature the contents of re and the ratios of mo cu in molybdenites in shapinggou decrease gradually whereas the contents of cu and w sn and the ratios of re cu co ni increase the pb zn values in molybdenite are higher in the porphyry mo deposit associated with pb zn deposits than in porphyry cu mo mo deposits not associated with pb zn deposits the ratios of cl f so2 h2s and h k in the shapinggou fluids increasing over time suggest that the fluids became more oxidised the initial ore forming fluid was 500 c carried ions of mo ca na k cl f s and caused potassic silicic alteration with deposition of only small amounts of molybdenite as the temperature dropped down to 400 c the amounts of mo k cu and cl ions in the fluid decreased leading to silicic sericitic and propylitic alteration and the deposition of the majority of the molybdenite as the temperatures decreased to 300 c the fluid contained ions of ca and f and pb zn was deposited distally around the main mo ore body