origin of lead from green glass of apollo 15426 a search for primitive lunar lead a major obstacle in lunar u pb chronology is the elusiveness of the primary pb isotopic composition and u pb ratio and therefore the pb evolution for the early history of the moon in an attempt to seek the primitive lunar pb isotopic composition green glass from lunar clod 15426 49 was studied for u th pb systematics because it is extremely mg rich and known to be the most primitive among sampled lunar volcanic rocks green glass and yellow impact glass were handpicked washed with water then washed in an acid mixture 0 3 n hbr 0 2 n hf and the washes and residues were analyzed in contrast to the pb from apollo 17 orange glass pb from the surface of the green glass spherules is totally different from that of the spherule interior but is similar to lunar surface lead data for the interior pb yield a 207pb 206pb age of 3 41 ga because of the low pb concentration and high u pb ratio observed for the interior the initial pb was poorly defined nevertheless the data indicate that lunar pb evolved in an environment with 238u 204pb 19 55 which is considerably lower than those for mare basalts around 300 but higher than values for the earth 6 8

examples of structural control of hydrothermal mineralization fault zones in epicontinental sedimentary basins a review by compiling data available from progressive geoscientific research and by complementary studies it seems possible for an increasing number of mineral districts to find indications of the regional structural control of hydrothermal ore deposits the relationship between hydrothermal mineralization faulting or fault reactivation and related processes can of course best be examined at the less deformed sedimentary record of ancient epicontinental sedimentary basins there is increasing evidence that the sediment hosted submarine hydrothermal zn pb ba mineralizations such as meggen rammelsberg howards pass and mcarthur river are spatially and genetically related to deep synsedimentarily active fault systems of intracontinental basins or stretched passive continental margins for long periods of basin development the faults provided favorable conduits for episodically released basin dewatering brines which precipitated the leached metals into third order basins situated next to these faults there are many similarities to epigenetic mineralizations which formed either pre syn or postorogenetically from brines leaching the meta sediments and associated magmatites and migrating along fault zones to their near surface trap structures

understanding the lunar surface and space moon interactions the surface of the moon is a critical boundary that shapes our understanding of the moon as a whole all geologic mapping and remote sensing techniques utilize only the outermost portion of the moon before leaving the moon for study in our laboratories all lunar samples that have been studied existed at or very near the surface with the exception of the deeply probing geophysical techniques our understanding of the interior of the moon is derived from surficial but not superficial information coupled with boundary of the lunar crust it is the lower boundary layer of the tenuous lunar atmosphere and constitutes both a source and a sink for atmospheric gases the surface is also where the moon interacts with the space environment causing changes in the physical nature of lunar materials and provides a laboratory for the study of processes that occur on all airless bodies the data obtained remotely by the galileo clementine and lunar prospector missions as well as data derived from lunar meteorites have resulted in major changes to our understanding of global distributions of chemistry and rocks this chapter summarizes the current understanding of this critical interface the surface of the moon in its role as the lower boundary of the lunar atmosphere the upper boundary of the crust and the window through which we view through remote sensing the composition of the crust and the history of the moon in this post lunar prospector time the view of the moon has changed lending new perspectives to lunar samples and lunar processes but the new view will likely remain in flux as we continue to digest the results from these recent space missions and move forward to a new era of lunar exploration despite the freshness of our perspective this is an important moment to capture

the polarity of the silurian magnetic field indications from a global data compilation silurian palaeomagnetic data from all continents are compiled in an attempt to define the polarity history of the earth s magnetic field during the period data sets from llandovery ludlow and pridoli strata often display evidence of field reversals i e the presence of both normal and reverse polarity magnetization directions despite the fact that the palaeomagnetic sample collections may cover only a limited stratigraphic range in each case palaeomagnetic data from rocks of wenlock age are exclusively of normal magnetic polarity a comparison of the available silurian data with published ordovician palaeomagnetic results suggests that the frequency of magnetic field reversals increased from ordovician to silurian times palaeomagnetic data sets are not yet available from a continuous silurian stratigraphic sequence of any great duration so the silurian magnetostratigraphy is still at a much more preliminary stage than that for the ordovician apart from the wenlock all silurian series have some intervals with frequent

chronological evidence that the moon is either young or did not have a global magma ocean a new age determination for a moon rock collected close to the site of the apollo 16 lander has yielded a surprisingly young age of around 4 360 million years this age would require either that the moon solidified some 200 million years after the formation of the solar system significantly later than is assumed by most lunar formation models or that the long held theory that the moon once had a primordial global magma ocean is flawed in the latter case much of the lunar crust could have been produced by non magma ocean processes such as serial magmatism chemical evolution of planetary bodies ranging from asteroids to the large rocky planets is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth1 2 3 the earth s moon is the archetypical example of this type of differentiation evidence for a lunar magma ocean is derived largely from the widespread distribution compositional and mineralogical characteristics and ancient ages inferred for the ferroan anorthosite fan suite of lunar crustal rocks the fans are considered to be primary lunar flotation cumulate crust that crystallized in the latter stages of magma ocean solidification according to this theory fans represent the oldest lunar crustal rock type2 3 4 attempts to date this rock suite have yielded ambiguous results however because individual isochron measurements are typically incompatible with the geochemical make up of the samples and have not been confirmed by additional isotopic systems5 6 7 8 9 by making improvements to the standard isotopic techniques we report here the age of crystallization of fan 60025 using the 207pb 206pb 147sm 143nd and 146sm 142nd isotopic systems to be 4 360 3 million years this extraordinarily young age requires that either the moon solidified significantly later than most previous estimates or the long held assumption that fans are flotation cumulates of a primordial magma ocean is incorrect if the latter is correct then much of the lunar crust may have been produced by non magma ocean processes such as serial magmatism10

lunar ferroan anorthosites mineralogy compositional variations and petrogenesis detailed petrologic study of a suite of lunar ferroan anorthosites indicates that their mineral compositional variations are generally consistent with derivation of these anorthosites from a common parent magma there are continuous compositional variations in major elements and smooth trends in minor elements mg fe in plagioclase al ti cr in pyroxene relict textures zoning and possible primary trends of mineral compositional variations are preserved in many of the anorthosites the presence of heterogeneous bimodal and or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks however they are composed entirely of ferroan anorthosite suite lithologies some aspects of the mineral composition data suggest that complex processes operated during formation of the ferroan anorthosites the lack of a well defined positive or negative trend of pyroxene mg mg fe versus plagioclase anorthite content the homogenization of mineral compositions in some anorthosites and the varied and apparently enriched mn contents of pyroxenes in some anorthosites suggest that original igneous compositional characteristics have been altered during and or after crystallization processes operative during anorthosite formation may have included some mixing of different melts trapping of variable amounts of intercumulus liquid postcrystallization redistribution of elements or perturbations both during adcumulus growth and subsequent to crystallization by impact events feo and mgo contents of the highly calcic plagioclase typical of these anorthosites suggest that the plagioclase melt distribution coefficients for these elements need to be reassessed

baltica a synopsis of vendian permian palaeomagnetic data and their palaeotectonic implications torsvlk t h smethurst m a van der voo r trench a abrahamsen n and halvorsen e 1992 baltlca a synopsis of vendlan permmn palaeomagnetic data and their palaeotectonlc implications earth sci rev 33 133 152 in light of recent additions to the palaeozoic palaeo magnetlc data base particularly for the ordovlclan era a revised apparent polar wander apw path for baltica has been constructed following a rigorous synthesis of all late precambrlan perm lan data the apw path is characterized by two prominent loops firstly a late precambrlan camb rlan loop probably relating to a rifting event and secondly a younger loop relating to a mid silurian scandlan colhsion event these features imply major change in plate tectonic reconfiguratlon baltlca probably represented an individual continental unit m early palaeozoic times and was positioned m high southerly latitudes in an inverted geographic orientation in such a reconstruction baltlca was separated from the northern margin of gondwana by the tornqulst sea and from laurentla by the iapetus ocean the tornqulst zone is thus interpreted as a passive or dextral transform margin during the early palaeozoic while undergoing counter clockwise rotations up to 1 6 ma baltica drifted northward through most ol the palaeozoic except for a short period of southerly movement in late silurian early devonian times after colhslon with laurentla rapid movements in latitude up to 9 cm yr are noted m late precambrlan earl y palaeozoic times and slgmficant decrease in velocities throughout palaeozoic time probably reflect the progressive amalgamation of a larger continent by early devonian euramerlca and permian pangea times the tornqulst sea had a principal component of palaeo east west orientation hence it is difficult to be precise in the timing of when micro continents such as eastern avalonla and the european masslfs ultimately collided along the southwestern margin of baltica these micro continents are considered to have been peripheral to gondwana m high southerly latitudes during the early ordovlclan eastern avalonla clearly had rifted off gondwana by llanvlrn llanded o times and may have collided with baltlca during late ordovlclan times although the present available sdunan palaeomagnetlc data from eastern avalonia may suggest colhslon in late silurian times across the lapetus facing margin of baltica laurentla was s tuated in equatorml to southerly latitudes during most of the lower palaeozoic these continents collided in mid silurian times l e a first collision between southwestern norway and greenland scotla nd which gave rise to the early scandlan orogeny 425 ma in southwestern norway possible followed by a later but less dramatic scandlan event in northern norway at around 410 ma since baltlca was geographically reverted m early palaeozoic times the colhsional margin could not have been a margin that once rifted off laurentm as assumed in a number of plate tectonic models

water hydrogen in the lunar mantle results from petrology and magma ocean modeling abstract measurements of hydroxyl or water in lunar materials are being used to suggest that melting source regions within the moon contained tens to hundreds of ppm water the compositions of magmatic source regions in the moon can be calculated using magma ocean fractional solidification models given an initial bulk composition our magma ocean models demonstrate that to make a source region with 10 to 200 ppm water the bulk magma ocean must contain 100 to 1000 ppm water or more and in a 1000 km deep lunar magma ocean 1000 ppm water is equivalent to 5 of an earth ocean by weight as solidification of the magma ocean continues water and other incompatible elements are progressively enriched in the evolving liquids the final kreep like liquids would contain the greatest fraction of water we suggest that a bulk magma ocean with over 100 ppm water is prohibited by constraints on these kreep like final magma ocean liquids and by the thermodynamic equilibrium requirement with metallic iron in mare basalts we conclude that bulk lunar interior water contents must be at the low end of the range posited by recent observations

contribution to the genesis of the sedex type mineralizations of the rhenish massif germany implications for future pb zn exploration the meggen orebody and the number of subeconomic sediment hosted mineralizations at plettenberg affeln oberhundem and gunterod eastern rhenish massif are considered to be typical members of the large sedex family i e submarine hydrothermal zn pb orebodies examples such as howards pass canada mcarthur river and broken hill australia and navan ireland formed between the middle proterozoic and carboniferous as a consequence of slow continental extension long term elevated heat flow and basin dewatering enhanced and focused along deeply penetrating synsedimentary fault zones volcanic activity bound to these fractures has no direct genetic relationship to sedex mineralization based on structural and detailed stratigraphic correlation and facies analysis it can be shown that all sedex type mineralizations of the rhenish massif are bound to one and the same synsedimentary fault zone named here the balve oberscheld fault zone which was reactivated during variscan compressional and extensional movements the trend of this tectonic lineament termed menden oberscheld lineament can be even recognized on maps depicting crustal gravity patterns and the configuration of the moho illite crystallinity measurements in devonian shales along profiles crosscutting the lineament evidence increased variscan to early post variscan metamorphism in the fault system which already had promoted the synsedimentary heat flow indications were found that the metalliferous brines escaping into the meggen basin were bound to a synsedimentary fault situated at the western margin of the meggen basin the widespread zn pb ba mineralizations and anomalies in the middle to upper givetian shales in the plettenberg affeln area are likewise bound to horst and graben tectonism along the balve oberscheld fault zone based on data from economic and scientific research in the rhenish massif the application of paleostructural methods for future basemetal exploration is discussed

the nature and origin of rims on lunar soil grains abstract space weathering processes that operate in the lunar regolith modify the surfaces of lunar soil grains transmission electron microscope analysis of the lunar soil grains from the fine size fraction of several lunar soils show that most grains are surrounded by thin 60 200 nm thick rims the microstructure and chemical compositions of the rims can be used to classify rims into four broad categories amorphous inclusion rich multiple and vesicular amorphous rims are noncrystalline generally lack crystalline inclusions show evidence for preferential sputtering of cations and are produced largely by solar wind irradiation damage inclusion rich rims contain abundant nanometer sized grains of fe metal as randomly dispersed inclusions or as distinct layers embedded in an amorphous silica rich matrix inclusion rich rims are compositionally distinct from their host grains and typically contain accumulations of elements that are not indigenous to the host inclusion rich rims are formed largely by the deposition of impact generated vapors with a contribution from the deposition of sputtered ions a continuum in the chemical and microstructural properties exists between typical amorphous rims and typical inclusion rich rims multiple rims consist of a distinct radiation damaged layer up to 50 nm thick that is overlain by vapor deposited material of comparable thickness vesicular rims are compositionally similar to their hosts and are characterized by an abundance of small the formation of rims on lunar soils is complex and involves several processes whose effects may be superimposed from this study it is shown that one process does not dominate and that the relative importance of vapor deposition is comparable to radiation damage in the formation of rims on lunar silicate grains the presence of rims on lunar soil grains particularly those with nanometer sized fe metal inclusions may have a major influence on the optical and magnetic properties of lunar soils

monitoring the 1980 1982 eruptions of mount st helens compositions and abundances of glass the mount st helens eruptive sequence of 1980 through 1982 reflects the tapping of successively less water rich more highly crystallized and more viscous highly phyric dacitic magmas these changes reflect both syn and preeruption processes the decreasing water content points to a continued decline in the volume and intensity of explosive pyroclastic activity this decreasing water content appears to be composed of a long term trend established during a long period of repose about 130 years imposed on short term trends established during short periods about 7 to 100 days of repose between eruptions in the present eruptive cycle the last two eruptive cycles of this volcano the t a d 1800 and w cycles about a d 1500 exhibited similar trends these changes are inferred from a combination of petrographic bulk chemical and electron and ion microprobe analyses of matrix and melt inclusion glasses

an early cretaceous carbonate replacement origin for the xinqiao stratabound massive sulfide deposit middle lower yangtze metallogenic belt china stratabound massive sulfide deposits are widespread along the middle lower yangtze metallogenic belt mlymb and serve as an important copper producer in china two contrasting genetic models have been proposed interpreting the stratabound massive sulfide deposits as a carboniferous sedex protore overprinted by cretaceous magmatic hydrothermal system or an early cretaceous carbonate replacement deposit these two contrasting models have been applied to the xinqiao stratabound cu au sulfide deposit which is dominated by massive sulfide ores hosted in marine carbonates of the carboniferous chuanshan and huanglong formations with minor cu au skarn ores localized in the contact zone between the cretaceous diorite jitou stock and the carboniferous carbonate rocks new sims zircon u pb dating suggests that the jitou stock formed at 138 5 1 1 ma 2 mswd 0 6 pyrite re os dating yields an imprecise date of 142 47 ma 2 mswd 7 8 the geochronological data thus constrain the mineralization of the xinqiao deposit at early cretaceous fluid inclusions in prograde skarn diopside have homogenization temperatures of 450 600 c and calculated salinities of 13 58 wt nacl equiv quartz from the stratabound ores and pyrite quartz vein networks beneath the stratabound ores have homogenization temperatures of 290 360 and 200 300 c with calculated salinities of 5 12 and 2 10 wt nacl equiv respectively quartz from the skarn ores and veins beneath the stratabound ores have 18o values of 12 32 0 55 2 sd n 22 and 15 57 1 92 2 sd n 60 respectively corresponding to calculated 18o values of 6 22 1 59 2 and 6 81 2 76 2 for the equilibrated ore forming fluids the fluid inclusion and oxygen isotope data thus support a magmatic hydrothermal origin rather than a sedex system for the stratabound ores with the hydrothermal fluids most likely being derived from the jitou stock or associated concealed intrusion results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the mlymb

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

a survey of hydrous species and concentrations in igneous feldspars the hydrous components in 85 feldspars from various igneous environments spanning the range of naturally occurring compositions were examined with infrared spectroscopy the feldspars contain structural oh 0 512 ppm h 2o h 2o 0 1350 ppm h 2o and nh 4 0 1500 ppm nh 4 groups as well as fluid inclusions and alteration products although composition and structure do influence the type of hydrous species that can be incorporated into a particular feldspar mineral the concentration of these species is not controlled by major element composition coarse perthitic microclines have a heterogeneous distribution of hydrous species and contain h 2o or nh 4 in k rich lamellae and fluid inclusions in na rich areas the structural oh in plagioclase feldspars is not associated with twin boundaries or exsolution lamellae all of the possible structural hydrous species are found in pegmatite feldspars whereas volcanic feldspars contain only structural oh the variation in oh concentration within a given feldspar composition suggests that fluids in the geologic environment play a role in determining the hydrogen concentration of each sample the vast majority of plutonic feldspars have undergone partial or total equilibration with meteoric fluids during low temperature 400 150 c hydrothermal exchange obliterating any structural hydrogen and creating substantial concentrations of fluid inclusions up to 4000 ppm h 2o in the exchanged regions the amount of water stored as fluid inclusions within feldspars in the upper crust 1 10 19 kg is small compared to the 1 35 10 21 kg of water in the oceans but is roughly equivalent to the reservoir of water stored in hydrous minerals in the upper crust

oxygen isotope geochemistry of the sullivan massive sulfide deposit kimberley british columbia hydrothermal evolution of the deposit potential applications of isotopic analyses to exploration for stratabound stratiform pb zn ag deposits the deposit is hosted by the proterozoic aldridge formation the delta 18 o results for samples from the aldridge range from 10 0 to 13 1 per mil with an average of 11 4 or 1 0 per mil oxygen isotope results from the tourmaline alteration zone located in the footwall of the western proximal ores range from 10 7 to 13 1 per mil with an average of 11 9 or 0 8 per mil the similarity between values for the tourmalinite and the aldridge formation suggests that the fluids which produced the tourmalinite alteration did not significantly alter the primary 18 o 16 o of the host sedimentary units isotopic values for samples from the albite chlorite alteration zone located in the hanging wall of the proximal ores range from 6 1 to 7 7 per mil such values indicate that there is a distinct difference in the isotopic composition of the albite chlorite zone relative to unaltered country rocks the following sequence is proposed the first hydrothermal stage consisted of the migration of low temperature 100 degrees c boron rich fluids up permeable zones causing the development of the tourmalinite alteration zone subsequent to this event hotter approximately 150 degrees c pb zn fe bearing fluids rose through the same zone at sullivan and deposited sulfides on the sea floor the final hydrothermal event was the alteration of the tourmalinite ore and hanging wall sedimentary units to produce the albite chlorite alteration assemblage the fluids which produced the albite chlorite assemblage were most likely more saline than normal seawater and had a temperature of 250 degrees c or more modified journal abstract

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

water in lunar anorthosites and evidence for a wet early moon water has been detected on the lunar surface and attributed to delivery by impacts and the solar wind to a dry early moon spectroscopic detections of water in lunar anorthosites from the apollo collection suggest that a significant amount of water is indigenous to the moon

paleomagnetic and rock magnetic data from the silurian succession of the dniester basin ukraine abstract paleomagnetic and rock magnetic data from silurian sedimentary rocks from west ukraine comprised of limestones and dolomites of the yaruga malinovtsy and rukshin series of wenlock to downton age have been obtained the rock magnetic data revealed magnetite as the main magnetic carrier the rocks are characterized by pervasive permian and carboniferous remagnetization demonstrated by the permian p direction which yields a pole position of 52 s 356 e identified in all the rocks and the late carboniferous c direction only found in rukshin series with a pole position of 29 s 356 e the third magnetization s is considered primary or early diagenetic origin and yields a pole position of 15 s 350 e which corresponds to the silurian part of the apwp for baltica

mineralogical change and self reversed magnetizations in pyrrhotite resulting from partial oxidation geophysical implications abstract low field thermomagnetic studies performed on natural and synthetic pyrrhotite samples showed that a very low oxygen fugacity is already sufficient to start the transformation into magnetite at 500 c the quantity of magnetite produced is a function of the oxidation time during which the temperature is maintained the remanent magnetization acquired by the magnetite during its formation in the applied field is a chemical remanent magnetization crm in the case of partial oxidation the close coexistence of pyrrhotite and magnetite in a single grain may produce a self reversed thermoremanent magnetization in pyrrhotite upon cooling in zero field if the initial pyrrhotite is hexagonal oxidation is necessary to obtain the transformation into the monoclinic variety which may also show the self reversed trm in contrast to the natural samples in synthetic pyrrhotite the magnetite produced by oxidation carries a crm but shows no self reversal upon cooling to room temperature a model for a self reversal and structural change processes following oxidation is presented in which the size and the shape of pyrrhotite grains play an important role the consequences for palaeomagnetism and magnetic anomaly interpretation are discussed

a new devonian palaeomagnetic pole for the russian platform and baltica and related apparent polar wander summary of published palaeomagnetic data from the russian platform and britain for mid palaeozoic times places an ocean between the two of the order of 2000 km latitudinal width this contradicts geological evidence which favours contiguity between the two continental units by devonian times we propose that this discrepancy can be attributed to the incorrect dating of palaeomagnetic remanence we strove to remedy this situation by conducting a new palaeomagnetic investigation of silurian and devonian sediments in west ukraine ussr latitude 48 7 n longitude 26 e that investigation uncovered a pervasive upper palaeozoic remagnetization corresponding to a palaeomagnetic pole at lat 45 8 s long 348 2 e dpldm 1 6 3 1 n 25 sites reversed polarity a second primary or near primary devonian remanence was identified with pole at lat 3 7 n long 325 5 e dpldm 5 2 8 7 n 25 samples mixed polarity the age determination for this devonian result is based on its dual polarity evidence for a detrital remanent mode and early host mineral phase haematite the new devonian result for the russian platform is conformable with the devonian parts of the british apparent polar wander paths and therefore eliminates the aforementioned discrepancy between palaeomagnetic and geological evidence for the timing of assembly of the old red continent

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

geology and ore enrichment factors at the radiore mine quebec the radiore cu zn massive sulfide deposit occurs in archean metavolcanic rocks of the abitibi greenstone belt in northwestern quebec the ore forms a stratiform lens between a massive rhyolite flow and a unit of mixed basaltic and intermediate flows intrusions of thick dykes of gabbro diorite quartz diorite and granodiorite and of the bell river igneous complex closely surround the ore lens all the volcanic rocks the quartz diorite grandiorite and the igneous complex are tholeiitic whereas the gabbro diorite is of calc alkaline affinity sedimentary structures are prevalent in the ore and heavily chloritized and biotitized rocks form a stratiform alteration zone mainly below the ore indicating a distal type deposit