pore size shape and connectivity in tills and their relationship to deformation processes this paper describes how till bulk porosity and pore shape size and connectivity relate to till deformation processes methods have been developed to examine till pores microscopically using thin section analysis scanning electron microscopy sem and x ray computed micro tomography ct porosity is quantified using digital image analysis of thin section images from the petrographic microscope and sem and from x ray ct these methods were applied to a selection of pleistocene tills with diverse properties the micromorphological techniques have allowed porosity to be related to other till microstructures most of the microstructures examined including the pores have been interpreted to be indicative of either plastic or brittle subglacial deformation and the type and extent of till deformation has been interpreted to affect bulk porosity pore type and pore connectivity

the micromorphology of last glacial maximum sediments in the southern north sea abstract the terrestrial ice limits of the last glacial maximum ice sheets are well understood but areas submerged during postglacial sea level rise have proved more difficult to accurately map fine grained diamicts in the southern north sea have been variously interpreted as glacial glacioaqueous or periglacial in origin implying different sedimentary environments this has resulted in contrasting opinions regarding the position of the last ice sheets in this area micromorphology is presented as a useful technique to aid the analysis of such sediments using systematic description of the physical characteristics of the sediments related to an interpreted seismic stratigraphy results indicate that the british ice sheet deposited glaciomarine sediments during an early advance and then advanced over an extensive part of the southern north sea as terrestrial ice

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

apatite in granitoids related to polymetallic mineral deposits in southeastern hunan province shi hang zone china implications for petrogenesis and metallogenesis abstract the area of southeastern hunan province china located within the southwestern part of the shi hang metallogenic zone is characterized by abundant cu pb zn w and sn polymetallic ore deposits that are closely associated with coeval late mesozoic granodiorite porphyries and biotite granites respectively here we present new major and trace element concentrations and 87 sr 86 sr ratios of apatites from six ore bearing granitic rocks as determined by electron microprobe laser ablation inductively coupled plasma mass spectrometry and thermal ionization mass spectrometer which allow us to determine the main controls on the formation of these different types of mineralization and to explore how these controls are reflected in variations in apatite chemical and isotopic compositions the apatite data indicate that granodiorite porphyry intrusions related to cu pb zn mineralization are oxidized and formed as a result of slab dehydration melting of the mantle wedge overlying a subducted slab and the partial melting of crustal material the release of abundant cl and h 2 o rich fluids from the slab triggered mantle melting and the extraction of metals that were precipitated within the deposits in comparison granites related to w and sn deposits are moderately oxidized to reduced and were generated by the partial melting of crustal material with only limited input from mantle derived magmas granites associated with the w and sn mineralization formed in an intra arc rifting related tectonic environment the fact that these numerous polymetallic ore deposits formed in the same area during two successive periods of mineralization the first from 180 to 160 ma and the second from 160 to 140 ma indicates that the tectonic environment of southeastern hunan province evolved from a continental arc associated with the subduction of the paleo pacific plate and the formation of cu pb zn deposits to a later intra arc rifting environment associated with the formation of w and sn deposits as a consequence of slab roll back and mantle upwelling during the late jurassic this study reveals that apatite compositions can be used as a proxy to reflect the differences between granitoids and their associated mineralization and identify regional metallogeny and tectonic evolution

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

a comparison of micro ct and thin section analysis of lateglacial glaciolacustrine varves from glen roy scotland abstract despite the prevalence of thin section analysis in studies of quaternary sediments there are limitations associated with the production of thin sections sediment modification and the inherently 2d view that a thin section affords non destructive and rapid scanning technologies such as x ray computed microtomography ct enable material samples to be visualised and analysed in 3d in a quaternary context however such techniques are in their infancy this paper assesses the optimum approach to ct analysis of quaternary sediments applying the method on lateglacial glaciolacustrine varves from glen roy scotland scan datasets are examined at each stage of the thin section process and comparisons are made between 2d ct images and thin sections for the recognition of 2d sediment features with further appraisal of 3d models to identify 3d sediment structures comparable sediment features are observed in 2d ct images and thin sections however the ct imaging resolution determines the precision of microfacies descriptions additional 3d structures are distinguished from volumetric models that are otherwise impossible to identify in thin section slides these 3d structures can locally alter sediment properties e g layer thickness as seen in 2d thin sections and or digital images although such variation cannot be detected with these media it has been demonstrated that clear benefits exist in understanding the 3d structure of quaternary sediments both prior to thin sectioning to avoid complicating e g deformation structures and after thin sectioning to establish the complex 3d context of 2d datasets it is recommended that ct and thin section techniques are applied in parallel in future studies which will profit from the integration of true 3d data it is also advised that samples are scanned soon after field sampling due to the significant modification of in situ sediment structures that can occur during thin section processing

paleoproterozoic gold deposits hosted by albite and carbonate altered tonalite in the chirano district ghana west africa paleoproterozoic birimian supergroup rocks of southwest ghana host numerous mesothermal lode gold deposits including the 38 million ounce moz ashanti deposit at obuasi and other multimillion ounce deposits at bogoso konongo prestea bibiani and in the yamfo sefwi region gold deposits of the chirano district are localized along the chirano lode horizon a 9 km segment of the chirano and related shear zones on the southeast margin of the sefwi bibiani belt economically significant mineralization at chirano is largely hosted by altered tonalite intrusions weaker alteration and subparts per million gold grades extend into adjacent birimian mafic igneous rocks and tarkwaian group sedimentary rocks pink albite alteration albite quartz pyrite hematite rutile leucoxene chalcopyrite gold and later pale carbonate alteration ankerite sericite quartz pyrite hematite gold fineness 910 940 ag au telluride characterize the gold deposits of the chirano district alteration assemblages and the bi te and mo contents of the mineralized rocks at chirano are more typical of lode gold deposits than orthomagmatic gold deposits alteration assemblages at chirano contrast with the graphite carbonate pyrite arsenopyrite pyrrhotite assemblages that dominate the lode gold deposits in southwest ghana which are hosted by graphitic shear zones and birimian sedimentary rocks differences between alteration assemblages at chirano and those in graphitic shear zones may reflect the different wall rock assemblages with which the hydrothermal fluid equilibrated rather than different fluid sources mineralization in the chirano district formed during a relatively late episode of small displacement brittle cataclasis on the chirano lode horizon after reverse ductile shearing associated with regional scale shortening this structural history is similar to that documented at the larger ashanti and bogoso deposits on the opposite side of the kumasi basin timing relationships are compatible with all three deposits forming during a single mineralizing event late in the eburnean 2 orogeny at chirano limited fault vein geometric relationships imply a component of reverse movement during mineralization whereas sinistral strike slip movement accompanied mineralization at ashanti and bogoso no consistent correlation was observed between the asymmetry of bends and splays in the strike of the chirano lode horizon and the location or style of individual gold deposits unlike at ashanti and bogoso the structural settings of deposits in the chirano district indicate that an exploration strategy which assumes mineralization occurred during sinistral offset in the host structures similar to relationships at ashanti and bogoso may result in significant targets being ignored

micromorphology of iceberg scour in clays glacial lake agassiz manitoba canada abstract icebergs plough through unconsolidated lake sea sediments gouging out kilometre long grooves 100s of metres wide and tens of metres deep although the surface morphology of iceberg scours is well documented little is known about what scours look like in stratigraphic section particularly where surface characteristics are absent e g through decay or burial this investigation establishes a definitive suite of diagnostic criteria for identifying iceberg scours in clays by macroscopically and microscopically 2d thin sections examining sediment deformation below iceberg scours in former glacial lake agassiz manitoba canada structures unequivocally attributed to iceberg scour in this investigation include sub horizontal microfabrics folds sheath folds augen shapes normal faults reverse thrust faults discrete shears partially destroyed clasts intraclasts type iii multiple domains water escape structures flow structures unistrial plasmic fabric dropstones realigned bedding and specific structural sequences this research will be particularly valuable in palaeoenvironmental reconstruction and in predicting glacial dynamics in addition it may eventually aid structural engineering on polar shelves which could be of great value to oil and gas companies

pore water controlled grain fracturing as an indicator for subglacial shearing in tills genetic classification of glacial deposits still proves to be highly controversial in many cases it remains unclear whether a particular sediment has been sub glacially deformed in the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations it is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism deformational mechanisms associated with the fracturing process are outlined and explained using a series of thin sections from wijnjewoude the netherlands

the crustal architecture of myanmar imaged through zircon u pb lu hf and o isotopes tectonic and metallogenic implications abstract the tethys margin in central and eastern asia is comprised of continental terranes separated by suture zones some of which remain cryptic determining the crustal architecture and therefore the geological history of the eastern tethyan margin remains challenging sited in the heart of this region myanmar is a highly prospective but poorly explored minerals jurisdiction a better understanding of myanmar s mineralization can only be realized through a better understanding of its tectonic history itself reflected in at least four major magmatic belts the eastern and the main range provinces are associated with the late permian to early triassic closure of palaeo tethys the mogok mandalay mergui belt and wuntho popa arc are a response to the eocene closure of neo tethys however magmatic ages outside these two orogenic events are also recorded we present new zircon u pb lu hf and o isotope data from magmatic rocks across myanmar which we append to the existing dataset to isotopically characterize myanmar s magmatic belts eastern province permian i type magmatism has evolved ehf 10 9 to 6 4 whilst main range province triassic s type magmatism also records evolved ehf 13 5 to 8 8 the mogok mandalay mergui belt is here divided into the tin province and the mogok metamorphic belt the tin province hosts ca 77 50 ma magmatism with evolved ehf 1 2 to 15 2 and 18o of 5 6 8 3 the mogok metamorphic belt exhibits a more complex magmatic and metamorphic history and granitoids record jurassic late cretaceous and eocene to miocene phases of magmatism all of which exhibit evolved ehf values between 4 6 and 17 6 and 18o between 6 3 and 9 2 from the tagaung myitkyina belt we report a magmatic age of 172 ma and ehf of 18 1 to 10 8 to accommodate the geological evidence we propose a tectonic model for myanmar involving a greater sibumasu where the documented zircon isotopic variations reflect compositional variations in magmatic source and invoke the role of a tengchong block the baoshan block and greater sibumasu were likely assembled on or before the triassic a former andean margin and suture which may lie across the northern shan plateau and reflected in isotopic differences between the northern and southern parts of the mogok metamorphic belt this contiguous sibumasu baoshan block then sutured onto the indochina margin in the late triassic we propose that a tengchong block within myanmar provides for a southerly termination of the meso tethys suture immediately north of the mogok area a discrete tengchong block may explain a discontinuous arc of late triassic to jurassic i type magmatism in central myanmar representing an andean type margin sited above a subducting meso tethys on the margin of sibumasu the tengchong block sutured onto greater sibumasu before the late cretaceous after which subduction of neo tethys drove the magmatism of the wuntho popa arc and ultimately that of the tin province the metallogenic character of granite belts in myanmar reflects the crustal architecture of the region which is remarkable for its prolific endowment of granite hosted sn w mineralization in two quite distinct granite belts related to sequential indosinian and himalayan orogenesis

geochemistry of hypersaline fluid inclusions from the starra fe oxide au cu deposit cloncurry district queensland studies of liquid vapor multisolid l v ns and liquid vapor halite fluid inclusions suggest that at least three fundamentally different brines were involved in the genesis of the proterozoic ironstone hosted starra au cu deposit element concentrations determined from proton induced x ray emission pixe analysis of groups of l v ns inclusions from the early barren magnetite ironstone stage 400 550 c and the younger mineralization stage 220 360 c covary over concentration ranges greater than the deduced analytical errors the l v ns inclusions in the two stages are very different with higher ratios of fe and k to ca mn cu zn sr ba and pb in the ironstone stage quite distinct pseudosecondary nacl cacl h o inclusions are abundant in mineralization stage quartz calcite and anhydrite high concentrations of cu ca 1 000 ppm are present in some l v ns inclusions of both stages and the data suggest that large amounts of cu mn zn as ba and pb passed through the starra system as it evolved cl br ratios in the inclusions are mostly less than 0 002 and clearly different from those of ore fluids of the giant sedimentary hosted copper orebody at mount isa this could reflect a major magmatic contribution to the salinity at starra that is consistent with the preferred origin of the water in published stable isotope studies ba concentrations of at least several wt percent in some mineralization stage l v ns inclusions are associated with oxidized sulfur bearing mineral parageneses given the low solubility of barite this suggests that a s2 f o2 relationships varied during mineralization

seafloor geomorphology and glacimarine sedimentation associated with fast flowing ice sheet outlet glaciers in disko bay west greenland fast flowing outlet glaciers currently drain the greenland ice sheet gis delivering ice meltwater and debris to the fjords around greenland although such glaciers strongly affect the ice sheet s mass balance their glacimarine processes and associated products are still poorly understood this study provides a detailed analysis of lithological and geophysical data from disko bay and the vaigat strait in central west greenland disko bay is strongly influenced by jakobshavn isbrae greenland s fastest flowing glacier which currently drains 7 of the ice sheet streamlined glacial landforms record the former flow of an expanded jakobshavn isbrae and adjacent gis outlets through disko bay and the vaigat strait towards the continental shelf thirteen vibrocores contain a complex set of lithofacies including diamict stratified mud interbedded mud and sand and bioturbated mud deposited by 1 suspension settling from meltwater plumes and the water column 2 sediment gravity flows and 3 iceberg rafting and ploughing the importance of meltwater related processes to glacimarine sedimentation in west greenland fjords and bays is emphasised by the abundance of mud preserved in the cores radiocarbon dates constrain the position of the ice margin during deglaciation and suggest that jakobshavn isbrae had retreated into central disko bay before 10 6 cal ka bp and to beyond isfjeldsbanken by 7 6 7 1 cal ka bp sediment accumulation rates were up to 1 7 cm a 1 for ice proximal glacimarine mud and 0 007 0 05 cm a 1 for overlying distal sediments in addition to elucidating the deglacial retreat history of jakobshavn isbrae our findings show that the glacimarine sedimentary processes in west greenland are similar to those in east greenland and that variability in such processes is more a function of time and glacier proximity than of geographic location and associated climatic regime

an intrusion related origin for cu au mineralization in iron oxide copper gold iocg provinces major cu au deposits of iron oxide copper gold iocg style are temporally associated with oxidized potassic granitoids similar to those linked to major porphyry cu au deposits stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions iocg deposits form over a range of crustal levels because co2 rich fluids separate from the magmas at higher pressures than in co2 poor systems thereby promoting partitioning of h2o cl and metals to the fluid phase at deep levels the magma fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the iocg deposits therefore form in a variety of fault related structural traps where the magmatic fluids may mix with other fluids to promote ore formation at shallow levels the iocg deposits form breccia and fracture hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry cu au deposits the fluids associated with iocg deposits are typically h2o co2 salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources in contrast fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids these different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and iocg deposits porphyry cu au deposits typically evolve through potassic sericitic and intermediate and or advanced argillic stages while iocg deposits typically evolve through sodic calcic potassic and carbonate rich stages and at deeper levels generally lack sericitic and argillic alteration the common association of porphyry and iocg cu au deposits with potassic oxidized intermediate to felsic granitoids together with their contrasting fluid compositions alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion related systems but that they are typically not directly related to each other

quartz microtextures and microstructures owing to deformation of glaciolacustrine sediments in the northern venezuelan andes glaciolacustrine sediments ranging in age from early to late merida wisconsinan in sections in the northern venezuelan andes near pedregal were studied to assess the effect of small scale folding and faulting on the surface microtextures of individual grains at site ped5 faulting of sediments beneath 35 m of middle to late merida glaciolacustrine glaciofluvial and probable till deposits has resulted in a maximum displacement of 1 m and many crushed sand grains are found along the shear zone these dominantly quartz particles are typically smoothed and or faceted with surface skins split from parent grains to produce adhering blade or wafer shaped coarse silts faulting with displacement of 40 cm occurs in late merida glaciolacustrine beds at sites ped13 and ped11 beneath ca 1 5 m of sediment and is thought to result from the removal of lateral support during valley erosion and possibly seismic disturbance associated sediments exhibit a greater incidence of small scale fold structures and convoluted bedding but with similar numbers and types of crushed grains all of the fault traces examined exhibit microstructural modifications including microfaulting folding and multiple domains associated with fluidisation and liquefaction the microtextures described are distinct from those produced by glacial or glaciofluvial transport processes and potentially may be used to infer glaciotectonic or other post depositional disturbance of sediments rare euhedral quartz grains with distorted crystallographic axes may derive from the shear zone of the regional trans form boconofault although many of these grains appear to be overprinted by glacial and or recent deformation processes copyright 2004 john wiley sons ltd

porphyry gold copper mineralisation in the cadia district eastern lachlan fold belt new south wales and its relationship to shoshonitic magmatism the cadia porphyry gold copper district is the largest hydrothermal intrusion related gold deposit in eastern australia discovered in 1992 by newcrest mining limited pre mine resources in the district were in excess of 585 t au and 2 35 mt cu the cadia district lies within shoshonitic subaqueous volcanic rocks of the late ordovician molong volcanic belt in the eastern lachlan fold belt lfb of new south wales an island arc tectonic setting is envisaged for the formation of these volcanic rocks but the nature of the arc basement and geometry of the subduction zone s is debated mineralisation occurs in four principal porphyry deposits cadia hill cadia ridgeway cadia east cadia far east and cadia quarry as sheeted and stockwork quartz sulfide veins and locally as broadly stratabound disseminated mineralisation cadia east and skarn big cadia and little cadia all of the porphyry deposits show a close spatial association with shoshonitic monzodiorite to quartz monzonite dykes and stocks of the cadia intrusive complex cic gold copper mineralisation is hosted by these intrusions and also by the enclosing forest reefs volcanics frv wall rocks hydrothermal alteration associated with mineralisation is potassic which is overprinted by selectively pervasive propylitic and silica albite assemblages petrological studies and major and trace element analysis of rocks of the cic and frv as well as of other intrusions in the cadia district that appear unrelated to mineralisation have been conducted unaltered samples from the cic are characterised by high k2o contents up to 6 5 wt and molecular k na ratios consistently 1 confirming the alkalic and shoshonitic nature of the complex the cic samples also fall just within the shoshonite field on ce yb ta yb and th yb ta yb plots although immediately adjacent to the calc alkaline field the frv are geochemically similar to the cic although lower in p2o5 and ce lree dacitic and hornblende porphyry intrusions from within the district but spatially unrelated to mineralisation have a distinctive geochemical signature and are not shoshonitic in composition the close spatial association between gold copper mineralisation and the shoshonitic monzonitic cic argues strongly for a genetic link between the two a similar association occurs at the economic goonumbla porphyry gold copper deposits in the eastern lfb while sub economic gold copper mineralisation at cargo and copper hill is associated with calc alkaline quartz diorite and dacitic intrusions the cadia district is considered to be an excellent example of the association of alkaline potassic magmas and gold copper porphyry style mineralisation

micromorphological evidence for polyphase deformation of glaciolacustrine sediments from strathspey scotland a combination of field investigation and micromorphological analysis has been applied to polydeformed late devensian rhythmites and glacigenic diamicton exposed in strathspey scotland this provided information on the geometry kinematics and relative ages of ductile and brittle structures and records a complex subglacial deformation history the deformation is interpreted as resulting from a single progressive event associated with over riding of proglacial lake sediments by wet based ice the earliest deformation d1 resulted from compaction loading pure shear and imposed a bedding parallel s1 fabric throughout the rhythmites s1 was subsequently deformed by kink bands and minor ductile shearing during d2 a later d3 event characterized by soft sediment deformation and fluidization of matrix poor sands was accompanied by an increase in pore water pressure this lead to hydrofracturing of the rhythmites the most intense deformation d4 which resulted from simple shear was partitioned into the upper part of the sequence it produced folding thrusting and brittle microfaulting in response to nnw directed ice push these findings indicate that in general subglacial deformation is not homogeneous and can extend to depths of 3 m below the presumed ice sediment interface

geology geochemistry and pb pb zircon geochronology of the paleoproterozoic magmatism of vila riozinho tapajos gold province amazonian craton brazil abstract pb pb zircon geochronologic data define two different periods of intense igneous activity in the vila riozinho region tapajos gold province tgp south central amazonian craton at 2 00 1 97 ga the vila riozinho volcanic sequence 2000 4 ma 1998 3 ma and the older sao jorge granite 1981 2 ma 1983 8 ma were formed at 1 89 1 87 ga the younger sao jorge 1891 3 ma jardim do ouro 1880 3 ma and maloquinha 1880 9 ma granites and the moraes almeida volcanic sequence 1890 6 ma 1881 4 ma 1875 4 ma were emplaced similar age intervals are registered throughout the tgp that is thus a little younger than the paleoproterozoic terranes of the maroni itacaiunas province in the guiana shield geochemical and geochronologic data demonstrate that the sao jorge pluton is composed of two different granitoids the older and younger sao jorge granites these as well as the jardim do ouro granite are i type and magnetite series the sao jorge granites are high k calc alkaline and show significant geochemical variation the jardim do ouro granite is more iron rich and less oxidized the vila riozinho formation is calc alkaline to shoshonitic and geochemically similar to the sao jorge granites the maloquinha granite and the moraes almeida formation differ from the other studied rocks in petrographic and geochemical characteristics have aluminous a type affinities and were probably derived by low temperature crustal melting the volcanic sequences of the studied area formerly included into the iriri group of the uatuma supergroup are divided into the vila riozinho and moraes almeida sequences the presence of these two sequences in the same tectonic domain demonstrates the heterogeneity of the uatuma supergroup the tgp registers accretionary processes related to the formation of the atlantica supercontinent at 2 00 ga this was followed at 1 88 ga by an intracontinental taphrogenic event that lasted throughout the mesoproterozoic the tectonic setting of the tgp was thus transitional between a subduction related magmatic arc and a stable continental block undergoing extension

miocene sn polymetallic mineralization in the tethyan himalaya southeastern tibet a case study of the cuonadong deposit abstract the cuonadong deposit is located in the cuonadong gneiss dome of the eastern tethyan himalaya and is characterized as a large to superlarge scale sn polymetallic deposit in the himalaya orogen the mineralization pattern includes skarn w sn mineralization in the strong shear zone of the dome mantle hydrothermal sn w veins controlled by north south trending rifts nstrs and be rb mineralization in pegmatitic leucogranite the results of this study show that the zircon u pb age of undeformed postkinematic leucogranites is 15 5 0 1 ma n 28 mswd 1 4 the cassiterite u pb age of the vein type sn w orebody is 14 3 0 5 ma n 40 mswd 3 2 and the muscovite ar ar age of beryl bearing pegmatitic leucogranite is 15 2 0 2 ma mswd 1 5 the isotopic dating results demonstrate that the cuonadong sn w be rb mineralization has a close genetic relationship with the miocene ca 16 14 ma leucogranite magmatic hydrothermal activity in the cuonadong dome the deformed synkinematic two mica granite 18 ma was cut by the sn w ore veins 14 ma faulted by nstrs indicating that the e w trending extension of the nstrs initiated at ca 18 14 ma the himalaya leucogranite belongs to a highly fractionated granite with high sn content 15 ppm in conclusion the himalaya leucogranite is considered to be tin granite in this study and therefore the himalaya presents high potential for sn polymetallic mineralization prospecting

geology mineralization and fluid inclusion characteristics of the koitash redox intermediate w mo skarn and w au stockwork deposit western uzbekistan tien shan the koitash w mo skarn deposit in the tien shan gold belt contained resources of 60 kt wo3 in altered skarn averaging 0 56 wo3 and 0 029 mo and an additional 42 kt wo3 in separate zones of phyllic alteration averaging 0 30 wo3 0 97 g t au 0 67 cu and 0 02 bi it is related to an early permian multiphase granodiorite granite leucogranite pluton that is composed of medium to high k transitional metaluminous to peraluminous weakly oxidized weakly reduced ilmenite titanite series granitoids the pluton was emplaced in a tectonic domain with inferred ancient continental crust the latter coupled with possible ascent of hot asthenospheric material has likely defined a distinct w mo au metallogenic assemblage forming in a post collisional environment the deposit includes redox intermediate prograde and retrograde pyroxene garnet skarns partially overprinted by propylitic and phyllic alteration assemblages comprising scheelite molybdenite cu bi ag te sulfides and sulfosalts as well as native bi and au compositional similarities between w mo deposits containing au w cu bi mineralization in late alteration assemblages and coeval intrusion related au dominant with minor w bi etc deposits in the region support their possible genetic links fluid inclusion data indicate the involvement of carbonic free moderately saline 10 5 15 0 to 8 0 11 7 wt nacl eq high pressure 2000 to 1500 bars hot 550 600 c aqueous fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid was followed by moderately saline ca rich 14 16 wt nacl 19 21 wt cacl2 lower pressure 800 bars fluids toward the retrograde skarn stage with the deposition of scheelite in association with pyrrhotite and molybdenite locally with minor fluorite propylitic quartz amphibole chlorite oligoclase calcite with scheelite pyrrhotite locally molybdenite assemblages formed from boiling high methane aqueous carbonic fluids at temperatures of 370 400 c and pressures of 950 1000 bars phyllic quartz sericite fe carbonate locally with albite fluorite chlorite scheelite molybdenite and other sulfides also bi and au minerals alteration assemblages initially formed from homogeneous and then from boiling aqueous carbonic low salinity fluids at temperatures of 365 370 to 300 315 c and pressures of 2000 bars 34s increases from retrograde skarn 34s 2 0 to 2 3 through propylitic 34s 3 0 to 3 4 to phyllic alteration 34s 4 2 to 4 7 stages

chemistry origin and evolution of mineralized granites in the lachlan fold belt australia the metallogeny of i and s type granites granites crop out over 20 percent of the total exposed area of the lachlan fold belt and comprise subequal proportions of i and s types despite the volume of granite present economic mineralization is sporadic major sn mineralization is related to s and i type granites that are both reduced and have undergone extended feldspar dominated crystal fractionation mo showings are common but as for cu large deposits are absent scheelite skarn mineralization is represented by the major king island deposits however granite related w mineralization of a similar scale is not found elsewhere within the belt the i type granites of the belt represent the products of partial melting of older tonalitic granodioritic source rocks in the deep crust which were themselves ultimately derived through fusion of mantle materials m types this evolution is also mirrored in the nature of related mineralization which changes from cu dominated at the chemically primitive end of this series through to lithophile dominated in the more evolved i types most of the lachlan fold belt i types have not undergone significant crystal fractionation and are neither strongly oxidized nor reduced two prominent mineralized i type suites the boggy plain supersuite of the central lachlan fold belt and the grassy suite of king island are anomalously mineralized relative to other lachlan i types both are chemically distinct from other i types in the belt by being enriched in the incompatible elements and ni and cr mafic s types are universally restite rich and unmineralized s type magmas are in general more evolved chemically than 1 types are all relatively reduced and when highly fractionated are related to sn or w mineralization the ore element ratios sn w cu mo etc of granite related mineralization in the lachlan fold belt is a straightforward function of the relative oxidation state and degree of fractionation within the associated granite

origin of ree mineralization in the bastnas type fe ree cu mo bi au deposits bergslagen sweden the bastnas type deposits with mineral assemblages of fe oxides ca mg silicates rare earth element ree silicates ree fluorocarbonates and cu fe mo bi sulfides are associated with marble horizons in a strongly na k and or mg altered metavolcanic succession over a distance of at least 80 km in a sw ne trending zone in western bergslagen two subtypes occur 1 enriched relative to the other type in light ree lree and fe exemplified by the bastnas and rodbergsgruvan deposits and 2 enriched in heavy ree hree y mg ca and f represented by deposits in the norberg district bastnasite hosts primary fluid h2o co2 inclusions with salinities of 6 29 eq wt cacl2 and with total homogenization temperatures th tot of ca 300 400 c subtype 2 has late stage fluorite with fluid inclusions that show 1 16 eq wt nacl and th tot of ca 90 150 c molybdenite re os ages obtained from three deposits are 1 904 6 1 863 4 and 1 842 4 ma nd isotopic data from five different ree minerals yielded no defined isochron but a range in end 1 88 ga of 0 2 to 1 6 the oxygen isotope values 18osmow of dolomite and calcite from the associated ree mineralized skarn and recrystallized carbonate assemblages lie in the range 6 1 8 6 overlapping with those of the host marbles carbon isotope values 13cpdb show typical magmatic signatures of 6 7 to 4 4 while the host marbles group around ca 2 4 the sulfur isotope 34scdt values of associated sulfides range between 10 8 and 0 2 the combined evidence suggests ree mineralization beginning at 1 9 ga from mainly svecofennian juvenile magmatic 400 c fluids carrying si f cl s co2 and the ree in addition to other metals mineralization occurred through reactions with dolomitic layers in the supracrustal units coevally with regional metasomatic alteration associated with fluid circulation through an extensive active volcano plutonic complex

experimental study of soil microfabrics induced by isotropic stresses of wetting and drying this experimental study examines the relationship between texture and microfabric under isotropic stresses generated by wetting and drying this can be achieved by observing and measuring the reorganization of microfabrics plasmic fabrics and related distribution pattern rdp microfabrics are produced in the laboratory by mixing montmorillonite with various proportions of sand and silt and subjecting them to wetting and drying without confinement thin sections are cut to study their microfabrics results show broad and systematic variations in fabric with changes in texture fine matrix silt plus clay in physical continuity is developed in samples with low sand silt ratio and regardless of this ratio at high clay levels coarse porphyric and fine porphyric rdp are formed at low and high clay contents respectively plasmic fabrics are represented mainly by insepic and weakly developed mosepic and masepic fabrics in the matrix in the form of small plasma separations with random orientation and weak skelsepic plasma as embedded grain argillans on the other hand coarse matrix sand grains in physical continuity dominates the sandy samples which are associated with relatively thick and strongly birefringent free grain argillans giving well developed skelsepic fabric the rdp follows two major paths beginning with orthogranic very low clay content along the iunctic sequence at low clay silt ratio and along the chlamydic sequence at high ratio the regularities in fabric development are interpreted in the light of the dynamic properties and behaviour of the active clay fraction in a clay water system the pedogenetic implications of the results are explored and the term erdic fabric defined

micromorphology of a debris flow deposit evidence of basal shearing hydrofracturing liquefaction and rotational deformation during emplacement abstract micromorphological analysis has been applied to a very coarse debris flow deposit and associated sand dominated glaciofluvial sediments exposed in westend wood quarry carstairs central scotland the microstructures present folds faults plasmic fabrics within this diamicton and underlying predominantly sandy sediments are interpreted in terms of sedimentary processes active during emplacement of the debris flow these processes include the formation of a basal shear zone the deformation and mixing of fine grained sediments incorporated into the base of overriding debris flow features associated with liquefaction sediment remobilisation and water escape are also present and developed in response to increasing overburden pressure during debris flow emplacement these microstructures have also been recorded elsewhere within subglacial diamictons and an evaluation is made between microstructures in palaeo debris flow deposits and those found in modern debris flows

the role of granites in volcanic hosted massive sulphide ore forming systems an assessment of magmatic hydrothermal contributions assessment of geological geochemical and isotopic data indicates that a significant subgroup of volcanic hosted massive sulphide vhms deposits has a major or dominant magmatic hydrothermal source of ore fluids and metals this group which is typically characterised by high cu and au grades includes deposits such as those in the neoarchean doyon bousquet laronde and cambrian mount lyell districts these deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones in many of these deposits 34ssulphide is low with a major population below 3 34ssulphate differs from coexisting seawater and 34ssulphate sulphide 20 30 these characteristics are interpreted as the consequence of disproportionation of magmatic so2 as magmatic hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic hydrothermal contribution other characteristics that we consider diagnostic of significant magmatic hydrothermal input into vhms ore fluids include uniformly high 3 times modern seawater values salinities or very 18o enriched 18o 5 ore fluids we do not consider other criteria e g variable salinity moderately high 18ofluid 2 5 34ssulphide near 0 metal assemblages or a spatial association with porphyry cu or other clearly magmatic hydrothermal deposits that have been used previously to advocate significant magmatic hydrothermal contributions to be diagnostic as they can be produced by non magmatic processes known to occur in vhms mineral systems however in general a small magmatic hydrothermal contribution cannot be excluded in most vhms systems considered conclusive data that imply minimal magmatic hydrothermal contributions are only available in the paleoarchean panorama district where coeval seawater dominated and magmatic hydrothermal systems appear to have been physically separated this district which is characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages is typical of many vhms deposits around the world suggesting that for garden variety vhms deposits a significant magmatic hydrothermal contribution is not required other than deposits associated with advanced argillic alteration assemblages the only deposit for which we ascribe a major magmatic hydrothermal contribution is the devonian neves corvo deposit this deposit differs from other deposits in the iberian pyrite belt and around the world in being extremely sn rich with the sn closely associated with cu and in having formed from high 18o rich fluids 18ofluid 8 5 we consider these characteristics particularly the last as diagnostic of a significant magmatic hydrothermal contribution our analysis indicates that two subgroups of vhms deposits have a major magmatic hydrothermal contribution cu au rich deposits with aluminous alteration assemblages and reduced very sn rich deposits in which sn was introduced in a high temperature ore assemblage comparison with normal vhms deposits suggests that these subgroups of vhms deposits may form in specialised tectonic environments the cu au rich deposits appear to form adjacent to magmatic arcs an environment conducive to the generation of hydrous oxidised melts by melting metasomatised mantle in the wedge above the subducting slab this contrasts with the back arc setting of normal vhms deposits in which relatively dry granites in this contribution we use the term granite sensu latto formed by decompression melting drive seawater dominated hydrothermal circulation the tectonic setting of highly sn rich vhms deposits such as neves corvo is less clear however thick continental crust below the ore hosting basin may be critical as it is in other sn deposits

the sedimentary record of drifting ice early wisconsin sunnybrook deposit in an ancestral ice dammed lake ontario canada abstract outcrops of pebbly mud diamict at scarborough in southern ontario canada the so called sunnybrook till are associated with the earliest incursion of the laurentide ice sheet lis into mid continent north america some 45 000 years ago the sunnybrook is a blanket like deposit containing deepwater ostracodes and occurs conformably within a thick 100 m succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake contextual evidence associated facies sedimentary structures deposit geometry and landforms indicates a low energy depositional setting in an ice dammed ancestral lake ontario in which scouring by floating ice masses was an important process u shaped iceberg cut scours with lateral berms up to 7 m deep occur on the upper surface of the sunnybrook and are underlain by sub scour structures that extend several meters below the scour base ice rafted concentrations of clasts clast layers grooved surfaces formed by floating ice glissading over a muddy lake floor soft sediment striations and melanges of sand and mud mixed by grounding ice keels ice keel turbates are present and are all well known from modern cold environments the wider significance of this depositional model is that the lis margin lay east of scarborough and did not overrun southern ontario this finding is in agreement with recent data from the erie basin of canada ohio and indiana where deposits formerly correlated with the sunnybrook and thus implying an extensive early wisconsin ice sheet are now regarded as illinoian a speculative hypothesis is proposed that relates deposition of the sunnybrook and two younger deposits of similar sedimentology to surge like instabilities of the southern lis margin

micromorphological criteria for discriminating subglacial and glacimarine sediments evidence from a contemporary tidewater glacier spitsbergen abstract sedimentological and micromorphological evidence is presented from four sites within st jonsfjorden western spitsbergen sedimentological and geomorphological evidence is used to distinguish sites comprising undisturbed glacimarine sediments from glacially over ridden glacimarine sediments and subglacial diamicts impregnated thin sections are used to define associations of micromorphological characteristics that allow diamicts formed under these different conditions to be discriminated in situ glacimarine deposits display winnowed textures dropstone structures and distinct vertical orientations of sand grains whilst subglacial conditions result in structures indicative of deformation under moderate to high stress regimes these criteria may help to determine the origin of ancient and quaternary diamicts of questionable subglacial or glacimarine origin

observing artificially induced strain implications for subglacial deformation by analysing a series of four successive thin sections from a ceramic clay that was subjected to uniaxial compression we were able to monitor the development of microstructures in a fine grained sediment the artificially induced microstructures such as unidirectional clay reorientations and linear and circular grain arrangements are identical to features that have been observed in thin sections of subglacially deformed tills and therefore may be used as representative analogues we argue that the structures reflecting slip planar shear displacements as well as rotational movements can be explained by assuming a coulomb plastic response to imposed shear we conclude that sediments subjected to subglacial deformation behave as coulomb materials at least during the final stages of the deformation the present study bridges the gap between field studies experimental studies and theoretical modelling the microscopic observations assist in visualising inferred subglacial processes and facilitate up and downscaling between diverse methodological approaches copyright 2003 john wiley sons ltd

geochemistry mineralogy and genesis of the ayazmant fe cu skarn deposit in ayvalik balikesir turkey abstract the ayazmant fe cu skarn deposit is located approximately 20 km se of ayvalik or 140 km n of izmir in western turkey the skarn occurs at the contact between metapelites and the metabasites of the early triassic kinik formation and the porphyritic hypabyssal intrusive rocks of the late oligocene kozak intrusive complex the major trace and rare earth element geochemical analysis of the igneous rocks indicate that they are i type subalkaline calc alkaline metaluminous i type products of a high level magma chamber generated in a continental arc setting the 40 ar 39 ar isochron age obtained from biotite of hornfels is 20 3 0 1 ma probably reflecting the age of metamorphic bimetasomatic alteration which commenced shortly after intrusion into impure carbonates three stages of skarn formation and ore development are recognized 1 early skarn stage stage i consisting mainly of garnet with grossular rich gr 75 79 cores and andradite rich gr 36 38 rims diopside di 94 97 scapolite and magnetite 2 sulfide rich skarn stage ii dominated by chalcopyrite with magnetite andraditic garnet ad 84 89 diopside di 65 75 and actinolite and 3 retrograde alteration stage iii dominated by actinolite epidote orthoclase phlogopite and chlorite in which sulfides are the main ore phases 40 ar 39 ar age data indicate that potassic alteration synchronous or postdating magnetite pyroxene amphibole skarn occurred at 20 0 0 1 ma the high pyroxene garnet ratio plus the presence of scapolite in calc silicate and associated ore paragenesis characterized by magnetite hematite chalcopyrite and bornite suggests that the bulk of the ayazmant skarns were formed under oxidized conditions oxygen isotope compositions of pyroxene magnetite and garnet of prograde skarn alteration indicate a magmatic fluid with 18 o values between 5 4 and 9 5 on the basis of oxygen isotope data from mineral pairs the early stage of prograde skarn formation is characterized by pyroxene di 94 97 magnetite assemblage formed at an upper temperature limit of 576 c the lower temperature limit for magnetite precipitation is estimated below 300 c on the basis of magnetite calcite pairs either as fracture fillings or massive ore in recrystallized limestone marble the sulfide assemblage is dominated by chalcopyrite with subordinate molybdenite pyrite cubanite bornite pyrrhotite galena sphalerite and idaite gold copper mineralization formed adjacent to andradite dominated skarn which occurs in close proximity to the intrusion contacts native gold and electrum are most abundant in sulfides as fine grained inclusions grain size with varying from 5 to 20 m sulfur isotope compositions obtained from pyrrhotite pyrite chalcopyrite sphalerite and galena form a narrow range between 4 8 and 1 6 suggesting the sulfur was probably mantle derived or leached from magmatic rocks geochemical data from ayazmant shows that cu is strongly associated with au bi te se cd zn pb ni and co the ayazmant mineralizing system possesses all the ingredients of a skarn system either cogenetic with or formed prior to a porphyry cu au mo system the results of this study indicate that the aegean region of turkey has considerable exploration potential for both porphyry related skarns and porphyry cu and au mineralization

be 10 ages from central east greenland constrain the extent of the greenland ice sheet during the last glacial maximum traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the east greenland continental margin during the last glacial maximum lgm ice to the shelf break south of scoresby sund and ice extending no further than to the inner shelf at and north of scoresby sund we report new 10be ages from erratic boulders perched at 250 m a s l on the kap brewster peninsula at the mouth of scoresby sund the average 10be ages calculated with an assumed maximum erosion rate of 1 cm ka and no erosion respectively 17 3 2 3 ka and 15 1 1 7 ka overlap with a period of increased sediment input to the scoresby sund fan 19 15 ka the results presented here suggest that ice reached at least 250 m a s l at the mouth of scoresby sund during the lgm and add to a growing body of evidence indicating that lgm ice extended onto the outer shelf in northeast greenland

highly fractionated late triassic i type granites and related molybdenum mineralization in the qinling orogenic belt geochemical and u pb hf and re os isotope constraints abstract we present new data on the highly fractionated late triassic i type liyuantang granite which is located in the middle segment of the south qinling subzone of central china and is associated with molybdenum mineralization zircon u pb dating indicates that the granite was emplaced at 210 1 1 9 ma with a single zircon containing an inherited core that yielded an age of 449 8 7 1 ma magmatic zircons from the granite have e hf t values of 4 0 to 1 5 whereas the inherited zircon core has a e hf t value of 5 3 calculated hf model ages of crust formation are indicative of substantial contributions from melting of proterozoic crust that ranges in age from 1501 to 1155 ma the granite contains high concentrations of si al na and k is enriched in rb th and u has elevated rb sr and ga al ratios and is depleted in ti fe mn mg ca and p with significantly negative eu anomalies eu 0 33 0 50 similar to other highly fractionated i type granites these data indicate that the magmas that formed the liyuantang pluton were produced during partial melting of proterozoic garnet absent quartz amphibolites the magmas then fractionated apatite feldspar ti bearing phases biotite and hornblende prior to emplacement re os isotope analysis of molybdenite from the study area yields a mineralization age of 200 9 6 2 ma suggesting that the liyuantang molybdenum deposit formed during a previously unrecognized mineralization event the present results together with previous data demonstrate that highly fractionated i type granites associated with the second pulse of magmatism in the south qinling subzone should be considered highly prospective for mineral exploration focusing on triassic early jurassic granitoids

late jurassic sn metallogeny in eastern guangdong se china coast evidence from geochronology geochemistry and sr nd hf s isotopes of the dadaoshan sn deposit abstract the newly discovered dadaoshan sn deposit is located in the eastern guangdong sn w province coastal se china the sn mineralization hosted in jurassic porphyritic granite and the lower jurassic jinji formation sedimentary wall rocks is considered to be granite related in this study the porphyritic granite was la icp ms zircon u pb dated to be 153 2 1 2 ma consistent with the syn mineralization molybdenite re os age of 152 6 1 8 ma the porphyritic granite samples are weakly peraluminous a cnk 1 0 1 1 and high k calc alkaline the rocks contain high sio2 72 9 75 6 wt moderate rb sr 5 9 and low ree 136 223 ppm they are enriched in f li rb and sn depleted in ba sr p zr th nb and y and have distinct negative eu anomalies eu 0 09 0 18 suggesting that the porphyritic granite is highly fractionated i type granite the calculated initial 87sr 86sr 0 711582 0 715173 relatively low nd t 9 48 to 8 54 tdm2 1638 1814 ma and the zircon ehf t 14 2 to 5 1 two stage model ages 1528 2103 ma all suggest that the granite was mainly crustal derived with little mantle input sulfur isotopic compositions for the sulfides arsenopyrite and chalcopyrite 34s 1 1 to 1 4 average 0 1 imply a dominantly magmatic sulfur source the calculated zircon ce4 ce3 and eun eun ratios of the dadaoshan granite range from 1 0 to 112 mean 31 7 and from 0 04 to 0 37 mean 0 14 respectively indicating a low oxygen fugacity for the magma the reducing and highly fractionated nature of the dadaoshan granitic magma may have played a key role in the sn mineralization it was previously argued that the jurassic sn w mineralization and its causative magmatism were largely confined in the south china interior e g the nanling range our new data suggest that the late jurassic sn w mineralization and its causative magmatism actually extended to the se china coastal area the dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle derived magmas in an extensional environment regional extension may have been related to the west directed flat slab subduction and delamination of the paleo pacific izanagi plate beneath the south china block another suite of early cretaceous sn w bearing granitic rocks in eastern guangdong may have mainly been crustal derived with minor mantle input and likely occurred under back arc extensional setting led by the paleo pacific subduction rollback

micromorphological aspects of glaciolacustrine sediments in northern patagonia argentina in this study the sedimentology micromorphology and structure of four deformation sites in end moraines or near end moraine settings are presented micromorphology has proven to be a powerful tool in the interpretation of the sediments the four sites are related to three of the four major glaciations known from this part of patagonia nahuel huapi anfiteatro and pichileufu all four sites are characterised by glaciolacustrine environments in which sedimentation occurred at least partly on and or against dead ice with the exception of one section in the san martin de los andes area where deformation occured by active ice push all major disturbances faults and folds are the result of dead ice collapse comparison with micromorphological observations on basal tills shows that the sediments all lack a clear subglacial imprint

iceberg deformation and erosion in soft sediments southeast norway abstract trenches in soft glaciomarine sediments have been excavated through two relict iceberg scours one upslope and the other horizontal and through one iceberg gravity crater the scours are 70 and 30 m wide respectively and are 1 m deep the grounding features were formed by current driven icebergs during flooding of previously emergent sea bottom 9200 yrs b p the clay beneath the scours and craters is deformed and small and larger scale folding small faults and thrusts joints fissures and collapsed lamination are found different scouring mechanisms apply for initial phases of upslope scouring and horizontal scouring at the start of upslope scouring the sediment mass is removed by thrusting and the depth of deformation within the subsoil is shallow in horizontal scouring two thirds of the scour depression is due to erosion and one third to deformation of the subsoil the deformation can in this case be detected down to four times the scour depth the current velocities are critical for survival of the plough ridges along the horizontal scour the plough ridges are missing because of current erosion during and after scouring

description and numerical model of pleistocene iceberg scours and ice keel turbated facies at toronto canada near toronto in southern ontario canada glaciolacustrine muds and shoreface sands of late pleistocene age early wisconsin glaciation 45 ka were deformed by icebergs ploughing the floor of an ancestral ice dammed lake ontario outcrop mapping and a ground penetrating radar survey identify ice scour structures up to 4 m deep up to 10 m wide and at least several hundred metres long with high standing lateral margins berms ploughing of lake floor sediment is also recorded by ice keel turbated facies in which storm deposited shoreface sands have been mechanically mixed with underlying muds palaeoenvironmental information for one prominent scour such as water depths estimates of the mass and draft of the ice mass and scouring forces can be determined using a simple finite element numerical model a mass of 0 04 million tonnes a keel draft of between 10 and 30 m and a scouring force of 5 103 kn is consistent with scouring by a small iceberg bergy bit or pressure ridged lake ice the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting estimates of ice mass dimensions agree with independent reconstructions of palaeobathymetry no greater than 20 m derived from storm deposited hummocky and swaley cross stratified facies that fill the scour data presented here aid the identification of ice scour structures and turbated sediment in the ancient record despite being a common process on modern high latitude shelves descriptions of ancient structures and facies are few

s type granites in the western superior province a marker of archean collision zones detailed field observations indicate that neoarchean s type granites were emplaced along and or proximal to some terrane tectonic boundary zones in the western superior province southeastern m

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

buried iceberg ploughmarks in the early quaternary sediments of the central north sea a two million year record of glacial influence from 3d seismic data abstract buried linear to curvilinear depressions interpreted as iceberg ploughmarks were identified through most of the 2 ma long and about 700 m thick early quaternary sedimentary record in two 3d seismic cubes from the central north sea basin 56 58 n 2 3 e the mean width of 402 features measured at 6 time slices in cube c08 was between 49 and 63 m and mean length was 2 5 to 3 7 km mapping the

storm influenced deltas and ice scouring in a late pleistocene glacial lake this paper identifies the sedimentary record of storms and bottom scouring ice masses that is preserved in upper pleistocene glaciolacustrine delta sediments deltaic sedimentation occurred on the margin of an enlarged ice dammed ancestral lake ontario with a surface elevation at least 80 m above the modern level beds of amalgamated hummocky and swaley cross strata separated by fairweather muds represent delta front storm deposits and overlie laminated prodelta clays the central and thickest part of a 5 km long outcrop exposes variably cross stratified sand in multiple channels inset within tabular sheets of rippled sand this complex represents a broad distributary channel system about 1 6 km wide and 20 m deep cut into delta front storm sequences a large scour and related deformation structures are attributed to bottom dragging ice masses possibly pressure ridged lake ice the depositional setting outlined in this paper emphasizes the importance of storm waves in large continental glacial lakes and provides a contrast with better known low energy conditions in small glacial lake basins

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

origin of late mesozoic granitoids in the newly discovered zha shan porphyry cu district south qinling central china and implications for regional metallogeny abstract the newly discovered porphyry cu deposits in the south qinling belt sqb have not been well researched as compared with the large porphyry mo province in the southern north china block s ncb and the origin of granitoids associated with porphyry cu mineralization in the zha shan district sqb is poorly constrained here we present detailed zircon u pb geochronological whole rock elemental and sr nd isotopic data for important late mesozoic granitoid stocks associated with porphyry cu deposits in the zha shan district these data are used to constrain the age and the source of magmas that formed these granitoids and implication of regional metallogeny the new zircon la icpms u pb ages presented here indicate that the granitoids related to porphyry cu system at chigou beishagou shuangyuangou and yuanjiagou developed at 148 144 ma 144 ma 145 144 ma and 146 ma respectively these rocks are high k calc alkaline i type granitoids which are enriched in large ion lithophile elements e g th u and pb and light rare earth elements are depleted in nb ta and ti characterizing by wide variations in initial end t 3 8 to 9 5 and moderate radiogenic sr isotopes 87 sr 86 sr i 0 7046 to 0 7093 these features indicate that the magmas that formed the granitoids related to porphyry cu system in the zha shan district formed as a result of variable degrees of mixing between crustal and metasomatic lithospheric mantle the new zircon la icpms u pb ages in this study combined with previous published data suggest that regional scale late jurassic to early cretaceous granitoid stocks and associated porphyry cu and mo systems in both the s ncb and sqb formed almost contemporaneously with 147 139 ma porphyry mo deposits in the s ncb and 148 145 ma porphyry cu deposits in the sqb the cu related intrusions contained a greater contribution of lithospheric mantle component than the mo related intrusions in the east qinling orogeny

is the palea kavala bi te pb sb au district northeastern greece an intrusion related system abstract intrusion related gold systems are generally characterized by a au bi te sn w metal assemblage genetically linked to the emplacement of granitoids the palea kavala ore system greece consists of 150 minor fe mn pb zn ag fe mn au fe as au fe cu au and bi te au occurrences that occur primarily in quartz calcite sulfide veins hypogene mineralization or as supergene bodies in overlapping zones centered on the 21 22 ma granodioritic kavala pluton which intrudes metamorphic rocks of the paleozoic rhodope metamorphic core complex the pluton consists mostly of granodiorite with lesser amounts of diorite tonalite and monzodiorite which was emplaced along the regional e w trending kavala komotini fault the recently discovered 4 km long e w trending so called kavala vein is a sheeted quartz vein system of bi te pb sb au mineralization that crosscuts the kavala pluton and the schists and gneisses of the rhodope massif the kavala vein system is comprised of quartz with lesser amounts of k feldspar plagioclase and muscovite quartz sericite pyrite alteration is pervasive but minor kaolinite is also present pyrite 5 of vein volume contains inclusions of tetradymite some gold bearing bismuthinite and cosalite sulfur isotope values n 27 of pyrite from the kavala and chalkero veins as well as pyrite and galena from garizo hill fe mn pb vein range from 1 9 to 1 0 with one outlier of 4 6 and suggest a magmatic sulfur source homogenization temperatures th of type i two phase aqueous liquid vapor and type ii three phase h2o co2 rich fluid inclusions that homogenize into the liquid phase in quartz from the kavala and chalkero veins range from 216 0 to 420 0 c n 216 and 255 7 to 414 0 c n 112 respectively the th of type iii two phase aqueous liquid vapor which homogenize into the vapor phase ranges from 210 4 to 323 4 c n 28 the salinities of type i and type ii inclusions range from 15 9 to 22 6 wt nacl equiv and 5 5 to 11 2 wt nacl equiv respectively eutectic temperatures of 58 5 to 44 3 c for type i inclusions suggest the presence of appreciable cacl2 in addition to nacl clathrate melting temperatures for type ii inclusions of 56 7 c indicate that co2 is the major component of the gaseous phase however up to 6 ch4 is present in some inclusions the presence of a zoned metallogenetic district centered on bi te pb sb au mineralization within the kavala pluton the presence of both magnetite and ilmenite in the kavala pluton and the two high temperature high salinity immiscible carbonic and aqueous fluids associated with the kavala and chalkero veins are consistent with them being part of an intrusion related gold system that formed along the ilmenite magnetite buffer

late cretaceous granites from the giant dulong sn polymetallic ore district in yunnan province south china geochronology geochemistry mineral chemistry and nd hf isotopic compositions abstract as a world class tin tungsten province south china is well known for its extensive mesozoic granitic magmatism the dulong district located in the western cathaysia block of the south china tin tungsten province is characterized by widespread mesozoic granitoids and accompanying sn polymetallic ore deposit 30 mt of sn it is one of the most important polymetallic tin ore districts in china in this study three mineralization related granite types were identified in the dulong district including the dulong coarse grained granite dcg the dulong fine grained granite dfg and the dulong porphyritic granite dpg detailed studies are presented on zircon u pb ages major and trace elements mineral chemical and nd hf isotopic compositions of the tin bearing granites from the dulong district la icp ms u pb dating of zircon grains from these three granite bodies yields ages of 90 1 0 7 ma 89 7 0 8 ma and 86 0 0 5 ma respectively geochemically the granites are strongly peraluminous with high contents of alkalis enrichment in p li rb cs ta sn w and u depletion in ti mg co ni sr ba zr hf th and rare earth elements fractional crystallization of plagioclase and k feldspar was the principal process of magmatic differentiation that controlled rb sr ba and eu concentrations whereas rare earth elements were fractionated by accessory minerals such as apatite and monazite the geochemical data suggest that the rocks are highly fractionated s type granites the granites show bulk rock e nd t values in the range of 12 2 to 10 8 and zircon e hf t values from 15 5 to 2 5 with meso paleoproterozoic t dm c ages for both nd and hf isotopes geochemical and isotopic data suggest that these highly fractionated s type granites dcg dfg and dpg were originated from the same episode of partial melting of the protolith which have analogous components of metamorphosed pelitic rocks from the meso paleoproterozoic continental crust extreme fractional crystallization resulted in enrichment of tin in the evolved granitic magma and the reduced magmas fo 2 below nno would efficiently remove sn into a hydrothermal fluid and lead to deposition of sn rich mineral phases the association of dulong and gejiu magmatism in the western cathaysia block may be likely to mark the onset of back arc extension or intra arc rift in the region during late cretaceous the upwelling of asthenospheric mantle may have triggered partial melting of metasedimentary rocks in the overlying crust to generate the s type granitic magmas

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

debris in icebergs and rates of glaci marine sedimentation observations from spitsbergen and a simple model debris distribution and content in spitsbergen icebergs varies but basal debris rich layers often 1 m thick are the most important sources of iceberg rafted material angular iceberg rafted clasts in the glaci marine record imply the presence of nunataks or valley walls rather than unbroken ice sheet surfaces indicating paleo ice mass configuration calculated iceberg melt rates imply that most iceberg rafted debris is released within spitsbergen fjords sedimentation from icebergs is calculated as 1 mm a 1 for inner mollerfjorden and 8 mm a 1 for inner kongsfjorden an order of magnitude lower than total sediment inputs turbid subglacial meltwater is a more important debris source a simple model is proposed to calculate the flux of basal debris in icebergs and iceberg sedimentation rates

origin of the granites and related sn and pb zn polymetallic ore deposits in the pengshan district jiangxi province south china constraints from geochronology geochemistry mineral chemistry and sr nd hf pb s isotopes the pengshan sn and pb zn polymetallic deposits are located in the south margin of the jiujiang ruichang jiurui district of the middle lower yangtze river metallogenic belt in south china four large deposits include huangjinwa zengjialong jianfengpo and zhangshiba the former three are sn dominant deposits which occur as stratiform orebodies in the contact zones of the pengshan granites and within the country rock strata whereas zhangshiba consists of stratiform pb zn orebodies within the precambrian metasedimentary strata in this study we present results on zircon u pb ages major and trace elements and mineral chemistry as well as sr nd hf isotope data of the granites pb and s isotopes of both the sn dominant and pb zn dominant deposits and u pb dating of cassiterite from the pengshan district shrimp and la icp ms zircon u pb dating shows that the pengshan granites were emplaced in the early cretaceous 129 128 ma which is in good agreement with the u pb dating 130 128 ma of cassiterite from the jianfengpo sn deposit the pengshan granites consist mainly of weakly peraluminous highly fractionated i type affinity granitic rocks detailed elemental and isotopic data suggest that the granites formed by partial melting of mesoproterozoic metamorphic basement materials with minor input of mantle derived melts the mineral chemistry of biotite demonstrates that the pengshan granitic magma had a low oxygen fugacity thereby precluding the tin dominantly partitioning into the rock forming silicate minerals and favoring accumulation in the exsolved residual liquid during magma crystallization stages sulfur isotopes show a relatively heavy sulfur isotopic composition from 5 8 to 17 6 and no difference for sulfur isotopes between the sn deposits 5 8 13 4 huangjinwa zengjialong jianfengpo and the pb zn deposit mostly 7 1 13 0 except for one 17 6 zhangshiba the sulfur isotope data of pyrite from the host sedimentary rocks show relatively higher 34s values of 22 7 28 7 lead isotopes indicate that the granites have higher 206pb 204pb 207pb 204pb and 208pb 204pb ratios than the host precambrian metasedimentary rocks and the sulfide minerals from the orebodies fall in between them again there is no difference for pb isotopes between the sn deposits huangjinwa zengjialong jianfengpo and the zhangshiba pb zn deposit the coincidence in s and pb isotope compositions for sn and pb zn deposits suggests that similar sources for these mineralization possibly derived from a mixed source of the granitic magmas and the precambrian metasedimentary rocks these data therefore favor of a magmatic hydrothermal origin for both the sn and pb zn polymetallic mineralization in the pengshan district

micromorphology of diamicton affected by iceberg keel scouring scoresby sund east greenland this research was primarily funded by the university of brighton s rising stars initiative and the school of environment and technology research investment fund with supplementary funds awarded by the quaternary research association the funding sources had no involvement in study design in collection analysis and interpretation of data in the writing of the article and in the decision to submit the article for publication

u pb and re os isotopic systematics and zircon ce4 ce3 ratios in the shiyaogou mo deposit in eastern qinling central china insights into the oxidation state of granitoids and mo au mineralization article i nfo the newly discovered shiyaogou molybdenum deposit is located in the eastern qinling metallogenic belt in central china the deposit contains at least 152 000 t of mo metal and bears typical porphyry type features in terms of its concentric alteration zonation quartz vein hosted mo mineralization veining sequence and the spatial association with concealed granite porphyries re os isotope analyses of molybdenite from the de posit yield an ore forming age of 132 3 2 8 ma la icp ms u pb zircon dating of ore related porphyries yields crystallization ages from 135 ma to 132 ma indicating a temporal link between granitic magmatism and mo mineralization a population of captured magmatic zircons indicates another pulse of magmatism at 143 ma a barren granite intrusion near the deposit gives a zircon u pb age of 148 1 1 1 ma these magmatic activities were concurrent with the emplacement of the nearby heyu granitic batholith a largely ore barren intrusive complex formed from 148 ma to 127 ma zircon ce 4 ce 3 ratios of ore related por phyries are obviously higher than those of contemporaneous barren granitoids implying an affinity between mo mineralization and highly oxidized magmas moreover zircons from these granitoids overall have de creasing ce 4 ce 3 ratios from 148 ma to 132 ma reflecting decreasing oxygen fugacities during magma evolution available geological radiometric and stable isotopic evidence suggests that the decrease of magma oxygen fugacity was probably associated with an increase of mantle contribution to granitic magmatism and metallogenesis which probably gave rise to successive mineralization of mo and au in the eastern qinling the intense magmatic metallogenic events in the eastern qinling during late jurassic to early cretaceous times are interpreted as a response to the large scale lithosphere thinning and subsequent asthenosphere upwelling beneath the eastern part of the north china craton

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

the 3d microscopic signature of strain within glacial sediments revealed using x ray computed microtomography abstract x ray computed microtomography ct a non destructive analytical technique was used to create volumetric three dimensional 3d models representing the internal composition and structure of undisturbed pro and subglacial soft sediment sample plugs for the purposes of identifying and analysing kinematic indicators the technique is introduced and a methodology is presented addressing specific issues relating to the investigation of unlithified polymineralic sediments six samples were selected based on their proximity to type brittle and ductile deformation structures or because of their perceived suitability for successful application of the technique analysis of a proglacial ideal specimen permitted the 3d geometry of a suite of micro faults and folds to be investigated and the strain history of the sample reconstructed the poor contrast achieved in scanning a diamicton of glaciomarine origin is attributable to overconsolidation under normal loading the sediment demonstrated to have undergone subsequent subglacial deformation another overconsolidated diamicton contains an extensive small scale the subglacial sample evidence indicates that complex polyphase brittle ductile deformation histories are common in such diamictic soft sediments and that the local micro scale environment composition structure shear forces and effective pressure controls rheology the sediment void ratio is a key indicator of strain three of the samples are tentatively placed at different points on the strain cycle for subglacially deforming soft sediment based on their void ratio characteristics and distribution it has been demonstrated that ct offers significant potential for elucidating glacial soft sediment kinematics the ability of the technique to both test a variety of hypotheses pertaining to mechanisms operating within the subglacial environment and evaluate efforts to replicate those processes under controlled laboratory conditions is therefore discussed along with solutions to the problems encountered within this project ct also permits the seamless linking of analytical techniques applied at the hand specimen mm micromorphological m mm scanning electron microscopy and x ray diffraction fluorescence nm m scales and the archiving duplication and dissemination of sample volumetric 3d data

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

sediment distribution and sea floor morphology of storbanken implications for the glacial history of the northern barents sea acoustical sparker 3 5 khz and side scan sonar and sedimentological data from a local study on storbanken in the northern barents sea support the concept of a late weichselian ice sheet covering most of the barents sea during a major halt in the retreat of the ice sheet locally thicker 38 m accumulations of ice proximal glaciomarine sediments were deposited after which rapid retreat took place sea floor morphology indicates that the retreat across storbanken most likely took place without surging or climatically controlled oscillations intense iceberg ploughing characterizes the sea floor down to water depths of 210 220 m most of this is relict but occasional gouges in the shallowest regions may have had a more recent origin the apparent lower limit of ploughing interpreted in terms of relative sea level indicates a rather moderate isostatic depression this probably resulted from a thin ice sheet fed from several ice source areas depth of the plough marks is largely dependent on thicknes

iceberg rafting and scouring in the early permian shoalhaven group of new south wales australia evidence of heinrich like events abstract this paper describes multiple layers of ice rafted debris and an ice scour structure in early permian marine strata within the shoalhaven group of the sydney basin new south wales australia strata were deposited on a high latitude glacially influenced continental margin during the final stages of late palaeozoic glaciation between 277 and 260 ma poorly sorted ice rafted debris forming layers up to 1 25 m thick is common within inner to outer shelf and continental slope facies of the shoalhaven group more than 120 layers can be identified these are argued to record the enhanced delivery of debris by icebergs drifting north from marine based antarctic ice margins deformation structures in associated sediments are interpreted as iceberg scours and ice keel turbates associated glendonites record early diagenesis of organic rich sediment and bottom water temperatures close to freezing a speculative hypothesis relates layers of ice rafted debris within the shoalhaven group to multiple episodes of accelerated calving at the margins of a marine based early permian ice sheet in east antarctica these events may be analogous to late pleistocene heinrich events when huge armadas of icebergs were released from the marine based laurentide ice sheet and triggered abrupt changes in ocean circulation and climate similar forcing may have characterized the early permian ice ocean system regardless of the climatic significance of ice rafted layers this is the first time such facies have been documented in the pre pleistocene literature to date few ice scour structures and no ice keel turbates have been reported

genetic environment of w skarn and pb zn vein mineralization associated with the imog granite in the taebaeksan mineralized district south korea abstract w skarn and pb zn vein mineralization were developed in the imog and seojin deposits in association with the imog granite that intruded the cambro ordovician carbonate rocks in the taebaeksan mineralized district south korea garnet pyroxene ratios in the skarn of both deposits decreased as away from the granite in the imog deposit garnet compositions vary from andradite to grossular series with increasing distance from the igneous contact however andradite is dominant in the seojin deposit in both the deposits diopside series remained dominant with a slight increase in johannsenite composition in late stage the skarn ore minerals mainly comprise scheelite and pyrrhotite whereas the vein ores comprise galena sphalerite and arsenopyrite in sphalerite a decrease in the cds contents and an increase in the mns contents from w skarn to pb zn vein ore can be attributed to leaching from sedimentary rocks and high mobility in magmatic hydrothermal fluids respectively the 34sh2s values of sulfide minerals were 3 3 4 9 for w skarn and 4 1 6 7 for pb zn vein ore in the imog deposit mostly belonging to magmatic origin but a slight increase is observed in the vein stage due to the interaction with carbonate host rock the isotopic depletion of 18o and 13c values from host rock to skarn and pb zn vein can be mostly attributed to the infiltration of external fluids involving magmatic components the effects of organic carbon in the host rock and input of meteoric water resulted in distinctly low 13c and 18o values in the skarn and vein samples respectively the sulfur isotope geothermometer and mineral stability in combination with fluid inclusion data constrained the upper limit of skarn formation to 520 c and 3 kbar and a temperature range of 0 5 kbar for w and pb zn mineralization in the imog deposit but pressure would be higher in the seojin deposit the skarn was formed by the intrusion of oxidized magma and scheelite mineralization occurred with decreasing oxygen fugacity the pb zn vein ores were precipitated with decreasing sulfur fugacity and increasing ph under the influence of meteoric water and carbonate host rock

holocene glacimarine sedimentation inner scoresby sund east greenland the influence of fast flowing ice sheet outlet glaciers abstract holocene glacimarine sedimentation associated with fast flowing outlet glaciers draining the greenland ice sheet is investigated using sedimentary and acoustic data from inner scoresby sund east greenland sedimentation in inner scoresby sund is dominated by three processes which are influenced by differences in proximity to fast flowing outlet glaciers extent of glacier ice cover and fjord bathymetry 1 sediment gravity flow principally in the form of turbidity currents and debris flows 2 suspension sedimentation from turbid meltwater plumes and 3 iceberg rafting these processes result in texturally and sedimentologically heterogeneous lithofacies proportionally fine grained muds laminated stratified and massive facies dominate cores recovered from inner scoresby sund accounting for 80 of the total whereas diamict facies account for only 15 abundant fine grained muds demonstrate that meltwater flux and sedimentation is significant in this high arctic glacimarine environment in settings proximal to fast flowing outlet glaciers with increasing distance from these glacier termini muds are replaced progressively by iceberg rafted coarse grained sediment the dominance of this iceberg rafted sediment in outer scoresby sund reflects both its more distal location from fast flowing glacier termini and the high calving flux associated with these ice masses laminated muds deposited by turbidity currents and suspension settling from overflow plumes in inner scoresby sund are similar to lithofacies produced in temperate and subpolar glacimarine systems this implies a similarity in sedimentation processes and resulting facies across a wide spectrum of climatically glaciologically fast flowing and non fast flowing ice masses and oceanographically variable glacimarine settings recognition of laminated fine grained facies in the geological record therefore does not necessarily indicate a temperate palaeo glacial setting however the predominance of iceberg rafted diamict facies in ice distal sedimentary records suggests the former presence of relatively cold environmental conditions in which iceberg sedimentation played a dominant role

till fabric patterns and significance particle response to subglacial stress abstract the analysis of particle arrangements within glacial sediments fabric has long been considered to reflect the behaviour of the ice that transported and deposited or deformed the sediment particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier as such fabric analysis has been used to try and understand the complex relationship between glacier and ice sheet dynamics and the geological evidence of former glaciation developments have focused on the use of stereonet patterns and statistical measures vector and eigenvector analysis of clast fabric to infer the process of sediment deposition deformation and consequent ice flow directions and dynamics however as this study identifies fundamental processes of particle orientation march jeffery and taylor rotation mechanisms would suggest more complex explanations than have been previously reported this study reports the results of a detailed field and laboratory investigation of macro scale clast and microfabrics from a till sequence in central scotland the results suggest a systematic behaviour of different particle size fractions which may be interpreted in terms of the strain response of sediment three fabric patterns are identified that illustrate consistent progressively shifting and more complex particle behaviour it is suggested these orientation patterns indicate the degree to which subglacial sediment has undergone strain and the nature of the deforming bed erosional or accretionary it is concluded that this approach may yield fundamental information about the strain conditions underlying different ice masses providing critical data linking glaciological modelling with the sedimentary evidence of glaciation

tourmaline rich features in the heemskirk and pieman heads granites from western tasmania australia characteristics origins and implications for tin mineralization distinctive magmatic hydrothermal tourmaline rich features have developed in the heemskirk and pieman heads granites from western tasmania australia they are categorized as tourmaline rich patches orbicules cavities and veins based on their distinctive morphologies sizes mineral assemblages and contact relationships with host granites these textural features occur in discrete layers in the roof zone of granitic sills within the heemskirk and pieman heads granites tourmaline patches commonly occur below a tourmaline orbicule rich granitic sill tourmaline filled cavities have typically developed above the tourmaline quartz orbicules in the upper layer of the white phase of the heemskirk granite tourmaline quartz veins penetrate all exposed levels of the granites locally cutting tourmaline orbicules and cavities the tourmalines are mostly schorl fe rich and foitite with an average end member component of schorl 45 dravite 6 tsilaisite 1 uvite 0 fe uvite 3 foitite 31 mg foitite 4 olenite 10 element substitutions of the tourmalines are controlled by femg 1 al y x square r2 na 1 and minor alo al y r2 oh 1 where r2 fe2 mg2 mn2 exchange vectors several trace elements in tourmaline have consistent chemical evolutions grouped from tourmaline patches through orbicules and cavities to veins there is a progressive decrease of most transition and large ion lithophile elements and a gradual increase of most high field strength elements these compositional variations in the different tourmaline rich features probably relate to element partitioning occurring in these phases due to volatile exsolution and fluxing of aqueous boron rich fluids that separated from the granitic melts during the emplacement of s type magmas into the shallow crust 4 to 5 5 km tourmalines from the heemskirk granite are enriched in fe na li be sn ta nb zr hf th and rare earth elements relative to the tourmalines from the pieman heads granite but depleted in mg mn sc v co ni pb sr and most transition elements these results imply that bulk compositions of the host granites exert a major control on the chemical variations of tourmalines the trace element compositions of tourmalines from the sn mineralized heemskirk granite are different from those of the barren pieman heads granite trace element ratios e g zn nb co nb sr ta and co la and sn concentrations in tourmaline can distinguish the productive heemskirk granite from the barren pieman heads granite

geochronological and petrogeochemical constraints on the skarn deposits in tongshanling ore district southern hunan province implications for jurassic cu and w metallogenic events in south china abstract southern hunan province south china is located in the central part of the qin hang metallogenic belt and is characterized by abundant cu pb zn and w sn polymetallic ore deposits the cu pb zn deposits are associated with jurassic granodiorite porphyries whereas the w sn deposits occur within jurassic granite porphyries here we present geochronologic and geochemical data for the tongshanling cu mo pb zn deposit and the weijia w deposit in the district of tongshanling southern hunan zircon u pb dating and molybdenite re os geochronology indicate that the emplacement of the tongshanling granodiorite porphyry and the associated cu mineralization occurred at 162 160 ma slightly earlier than the formation of the xianglinpu granite porphyry and associated w mineralization at 159 158 ma the tongshanling granodiorite is high k calc alkaline weakly peraluminous and weakly fractionated with zircon e hf t values of 15 1 to 5 6 in contrast the xianglinpu granite is alkaline peraluminous and highly fractionated with e hf t values of 9 5 to 0 9 our data indicate that the tongshanling granodiorite is relatively oxidized and was formed by the partial melting of paleoproterozoic crustal material with inputs of mafic magma which was derived from a subduction modified lithospheric mantle in contrast the xianglinpu granite porphyry is relatively reduced and was formed by direct interaction between the crust and asthenospheric mantle the difference in magma generation and tectonics is considered to have resulted in the different types of mineralization associated with these two intrusive bodies

sedimentology of late glacial clays in lacustrine basins central ireland abstract distal bottom sediments of a large ice marginal interdomal lake that covered most of the central part midlands of ireland during the last deglaciation were poorly known recent work centred on two raised bog covered basins confirmed relatively thick distal glaciolacustrine sediments undisturbed samples taken in 100 mm cores enabled thin sectioning and micromorphological analysis to be carried out the upper part of the fine sediment mostly clay which is apparently homogenous at the macroscopic level is shown to have been bedded or laminated and subsequently homogenised by load casting with depth bedding or lamination becomes more common until the whole deposit is very finely and rhythmically laminated turbidites a consequence of density underflows together with coarse sediment rain out and dropstones confirm a likely ice marginal environment the finer sediment towards the top of the sequence reflects increasing distality synsedimentary folding and faulting load casting and water escape structures point to rapidly accumulating sediment in an unstable sedimentary environment the lack of bioturbation is not surprising and apparent minor traces towards the base of the rhythmites seems most likely to relate to synsedimentary faulting

the role of the southward wind shift in both the seasonal synchronization and duration of enso events near the end of the calendar year when el nino events typically reach their peak amplitude there is a southward shift of the zonal wind anomalies which were centred around the equator prior to the event peak previous studies have shown that enso s anomalous wind stresses including this southward shift can be reconstructed with the two leading eofs of wind stresses over the tropical pacific here a hybrid coupled model is developed featuring a statistical atmosphere that utilises these first two eofs along with a linear shallow water model ocean and a stochastic westerly wind burst model this hybrid coupled model is then used to assess the role of this meridional wind movement on both the seasonal synchronization as well as the duration of the events it is found that the addition of the southward wind shift in the model leads to a christmas peak in variance similar to the observed timing although with weaker amplitude we also find that the added meridional wind movement enhances the termination of el nino events making the events shorter while this movement does not appear to play an important role on the duration of la nina events thus our results strongly suggest that the meridional movement of enso zonal wind anomalies is at least partly responsible for seasonal synchronization of enso events and the duration asymmetry between the warm el nino and cool la nina phases

microscopic evidence of subglacial deformation abstract subglacial deformation is by now a well established process however recognition of this process in pleistocene tills is not always clear studies of thin sections of pleistocene tills show that there are a variety of microscopic features caused by deformation this paper gives a review of microscopic evidence for subglacial deformation and starts with a case where deformation could be established macroscopically then traces the microscopic features through planar and rotational movements which are described and separated accordingly attention is also given to features caused by crushing of grains and sediment dewatering these studies indicate that almost all basal tills show evidence of subglacial deformation rather than sedimentary derivation this implies that if we want to understand subglacial processes such tills should be described in tectonic rather than sedimentary terminology

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

in situ raman spectroscopic investigation of the hydrothermal speciation of tungsten implications for the ore forming process abstract knowledge on hydrothermal tungsten w species is vital towards a better understanding of tungsten transport and mineralization mechanisms in this study in situ raman spectra of a 0 005 0 1 mol kg m k2wo4 solution containing co2 hcl and nahco3 were collected at 50 400 c and 20 60 mpa the spectra for the symmetric stretching vibration mode of the w o bond v1 w o were analyzed to investigate the hydrothermal tungstate species results showed that carbonate bicarbonate do not associate with tungstate to form carbonic tungstate species nevertheless the presence of co2 can increase the fluid acidity which favors the formation of polymeric tungstate species at o modes of these species are centered at 930 cm 1 and 950 cm 1 based on the above observations we simulated the mineralization process in the context of fluid rock interactions using tungstate and alkali tungstate ion pairs as the only aqueous w species the thermodynamic simulations showed that a the timing of mineralization mainly depends on the w concentration in the initial mineralizing fluid and the availability of ca2 fe2 and mn2 with higher w concentrations generally favoring higher temperature mineralization b highly w enriched fluid is not essential for w mineralization while extremely low contents of fe mn and ca in the magma are useful to maintain the mobility of aqueous w until favorable host rocks are encountered and c a hydrogen reservoir effect was identified for dissolved co2 the presence of co2 can promote the extraction of fe ii from the pelitic host rocks thereby facilitating a high grade vein type w mineralization at o modes are centered at 965 995 cm 1 are important hydrothermal w species along with monomeric tungstates therefore polymeric tungstate species should be considered in future thermodynamic modeling of w transport and mineralization at

a new microstructural mapping methodology for the identification analysis and interpretation of polyphase deformation within subglacial sediments although integrated clast macro and microfabric studies have been used to provide evidence of palaeo ice flow directions to discriminate between diamictons deposited in differing sedimentary environments and to model the response of tills to subglacial deformation such studies have typically only examined the bulk fabric developed within the diamicton largely ignoring the potential for several phases of fabric development within these typically polydeformed deposits we present a new graphical method for the identification description and analysis of clast microfabrics in polydeformed tills this method utilises high resolution digital scans of orientated thin sections imported into a standard computer graphics package to measure the orientation of long axes of detrital skeleton grains included within the till these data are then used to identify the main clast microfabrics present within the till allowing the delineation of clast microfabric domains in which elongate grains share a similar preferred orientation this process leads to the identification characterisation and most importantly the interrelationships between the various generations of microfabrics the relationships between these clast microfabrics and other microstructures e g plasmic fabrics turbate structures shears folds faults etc can also be examined providing a detailed microfabric microstructural map of the thin section clast long axis orientation data collected for different parts of a thin section are plotted on a series of rose diagrams allowing the variation in clast microfabric orientation to be displayed graphically a new set of terminology for the description of clast microfabrics in tills which is based upon the system used by metamorphic petrologists is also presented three case studies of the fabrics present within subglacial sediments of pleistocene age as well as the present are used as examples of how to apply this methodology

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

3d microstructural architecture of deformed glacigenic sediments associated with large scale glacitectonism jasmund peninsula ne rugen germany the wissower bach syncline on the jasmund peninsula ne germany has been examined to understand the complicated glacitectonic environment in the southern baltic sea region comprising folds and thrust faults from the weichselian pleniglacial soft sediment thin sections from a sw dipping thrust fault at the south western limb of the syncline between cretaceous chalk hangingwall and pleistocene deposits footwall were analysed using micromorphology and microstructural mapping within the diamicton bounding the fault three different clast microfabrics were distinguished an older but dominant s1 fabric a second s2 foliation orientated perpendicular to s1 and a younger subvertical s3 fabric these fabrics developed during large scale folding and thrusting subsequent fabric rotation adjacent to the thrust fault accompanied by dewatering of the diamicton and extension the extension implies late stage reactivation and gravitational relaxation at the south western limb of the syncline as the ice retreated the combination of a 3d microstructural model and the macroscale information has led to the development of a detailed model for the evolution of the wissower bach syncline during glacitectonism and the localized reactivation of the associated thrusts in response to ice retreat moreover this methodology provides a robust dataset on which to interpret the structural evolution of glacitectonic complexes

micromorphology of ice keel scour in pebbly sandy mud and fine grained sands scarborough bluffs ontario canada the keels of icebergs and ice pressure ridges plough through unconsolidated sea lake sediments gouging out long grooves known as ice keel scour marks although the surface and more recently subsurface morphology of scours are well documented little is known of the effect of grain size on the detectability style and intensity of sub scour deformation this investigation macroscopically and microscopically two dimensional thin sections examines suspected ice keel scour in i glaciolacustrine pebbly sandy mud and ii fine grained sands at scarborough bluffs ontario canada in this investigation there is an almost identical suite of deformation structures individual structures and overprinted structural patterns to those identified in icebergscoured clays from former glacial lake agassiz manitoba canada this confirms that deformation in the pebbly sandy mud and fine grained sands at scarborough bluffs is likely to be indicative of ice keel scour discrete differences in the detectability style and intensity of deformation between the scarborough bluffs and glacial lake agassiz sediments are probably a function of grain size in response to ice keel scour this research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes this information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes it also demonstrates the potential value of micromorphology where for example the study of cores is necessary

thin section production of diamicts problems and solutions abstract thin section production of diamict samples presents many problems primarily as a result of incomplete impregnation this problem is investigated in diamicts of known glacial glaciomarine and subaerial origin the inherent sedimentological characteristics rather than particular mode of deposition appears to influence resin impregnation of diamicts a technique of surface impregnation is presented to overcome this problem when samples fail to impregnate fully during initial preparation and is incorporated into current techniques within a flowchart in the majority of cases this technique results in successful production of a useful thin section

age and granite association of skarn w mineralization at niutangjie district south china block abstract numerous w sn deposits are developed in the south china block with the majority related to the yanshanian jurassic to cretaceous granites a smaller number of deposits have been found associated with kwangsian middle paleozoic granites the largest of which is the niutangjie skarn w deposit the niutangjie deposit is spatially associated with two suites of granites the unmineralized yuechengling biotite and two mica granites have zircon u pb ages of 427 1 2 9 ma and 427 5 3 5 ma respectively whereas the mineralized niutangjie muscovite granite yields a younger age of 421 0 1 5 ma u pb dating of cassiterite coexisting with scheelite from the niutangjie muscovite granite indicates a mineralization age of 420 8 8 0 ma consistent with the age of the host rock the unmineralized yuechengling biotite granites have a cnk ratios of 0 97 1 16 and show characteristics of both i type and s type granites in contrast the mineralized niutangjie muscovite granites are s type granites with a cnk ratios of 1 12 1 72 and have higher sio2 contents and rb sr ratios and lower nb ta zr hf and k rb ratios than the unmineralized yuechengling biotite granites geochemical differences together with zircon hf isotopic compositions indicate that the relatively fractionated mineralized niutangjie muscovite granites were generated by partial melting of proterozoic meta sediments whereas the unmineralized yuechengling biotite granites were derived from partial melting of proterozoic meta sediments with subordinate meta igneous rocks the unmineralized yuechengling two mica granites have similar geochemical characteristics to the mineralized niutangjie muscovite granites but their relatively small volumes and lack of exploration may explain why the yuechengling two mica granites have not so far been found to be mineralized similarly the larger volume and more highly fractionated nature of the mesozoic yanshanian mineralized granites may explain the greater abundance of w sn mineralization associated with these rocks compared to the paleozoic kwangsian granites

microstructures in subglacial and proglacial sediments understanding faults folds and fabrics and the influence of water on the style of deformation abstract macroscopic field and micromorphological studies have been carried out on subglacially and proglacially deformed glacigenic sequences at a number of sites throughout scotland uk examination of microstructures folds faults hydrofractures plasmic fabrics aided understanding of the deformation histories preserved in the sediments but a similar range of structures were developed in both subglacial and proglacial settings discrimination between subglacial and proglacial deformation was only possible when micromorphological data was used in conjunction with larger scale field observations variations in lithology and water content were controlling factors influencing the style and apparent intensity of deformation recorded changes in pore water content and pressure during deformation can lead to liquefaction and hydrofracturing with early formed structures locally controlling the pattern of water escape liquefaction can also lead to homogenisation of the sediments and the destruction of earlier deformation structures even at relatively low strains beds or zones of liquefied sand and silt may form highly lubricated detachments within the sediment pile resulting in a marked reduction in the amount of shear transmitted to underlying units a multidisciplinary approach involving sedimentological geomorphological stratigraphical and structural field observations combined with micromorphological analysis is recommended to confidently unravel the glacitectonic history and depositional environment of most deformed glacigenic sedimentary sequences

granitoid associated orogenic intrusion related and porphyry style metal deposits in the archean yilgarn craton western australia abstract the yilgarn craton hosts three types of archean granitoid associated metallogenic systems orogenic gold intrusion related and porphyry systems these systems may occur in the same terrane and share many broad characteristics including spatial coincidence with granitoids gangue silicate mineralogy metal associations and local structural controls features of archean orogenic gold systems spatially associated with granitoids include i a broad range of granitoid host compositions ii gold mineralization is mostly late with respect to yilgarn wide granitoid emplacement peak metamorphism and deformation iii orebodies are structurally controlled and iv gold deposition occurs over a large range of temperatures pressures and crustal depths 2 to 15 km from a co 2 rich low to moderate salinity reduced ore fluid that was derived from a metamorphic and or distal magmatic fluid source these systems do not display deposit scale vertical or lateral zonation of metals away from granitoid contacts host granitoid age composition or oxidation state are not important in controlling gold mineralization processes whereas structural setting and fluid flux are paramount archean intrusion related au mo w and mo au systems in the yilgarn craton are commonly small 2 bearing moderate to high salinity fluid during ore deposition archean porphyry cu mo au cu mo and cu au systems are spatially and temporally associated with volumetrically small pervasively altered felsic plutons and dikes surrounded by altered and mineralized supracrustal countryrock lateral zonation of metals away from porphyry centers commonly includes a decrease in cu au and ag au ratios with distance from the source pluton microthermometry studies on fluid inclusions in gold bearing veins suggest that early ore fluids were high temperature and high salinity and that mineralization occurred at 2 o 3 feo are demonstrated in phanerozoic terranes but are presently ill defined in the yilgarn craton crustal depth estimation is important in defining areas likely to have preserve shallow forming archean porphyry systems