corundum quartz bearing assemblage in the ihouhaouene area in ouzzal algeria granulite facies quartzites from the ihouhaouene region in the northern part of in ouzzal contain the assemblage corundum quartz magnetite together with hercynitic spinel quartz magnetite sillimanite quartz magnetite and almandine rich garnet quartz magnetite two types of corundum have been recognized the first is primary and is found with quartz and magnetite only the second type is found together with magnetite and chlorite rimming spinel as a fine grained corona the textures show that spinel rich magnetite probably exsolved primary corundum sillimanite spinel and garnet during the cooling history the secondary corundum formed later from the spinel already exsolved from magnetite the secondary corundum is certainly metastable with respect to quartz this may also apply for the primary corundum however given the high temperature setting of this rock it cannot be excluded that the stable contacts observed between primary corundum and quartz indicate equilibrium between the two phases taking into account the uncertainties in the thermodynamic data the stability of this assemblage would imply that this part of in ouzzal has recorded very high p t conditions above 1100 c at 12 kbar

garnet orthopyroxene bearing granulites from enderby land antarctica metamorphic pressure temperature time evolution of the archaean napier complex

an impact of subgrid scale ice ocean dynamics on sea ice cover a coupled sea ice ocean numerical model is used to study the impact of an ill resolved subgrid scale seaice ocean dynamical process on the areal coverage of the sea ice field the process of interest is the transmission of stress from the ocean into the sea ice cover and its subsequent interaction with the sea ice internal stress field an idealized experiment is performed to highlight the difference in evolution of the sea ice cover in the circumstance of a relatively coarse resolution grid versus that of a fine resolution one the experiment shows that the ubiquitous presence of instabilities in the near surface ocean flow field as seen on a fine resolution grid effectively leads to a sink of sea ice areal coverage that does not occur when such flow instabilities are absent as on a coarse resolution grid this result also implies that a fine resolution grid may have a more efficient atmosphere sea ice ocean thermodynamic exchange than a coarse one this sink of sea ice areal coverage arises because the sea ice undergoes sporadic irreversible plastic failure on a fine resolution grid that by contrast does not occur on a coarse resolution grid this demonstrates yet again that coarse resolution coupled climate models are not reaching fine enough resolution in the polar regions of the world ocean to claim that their numerical solutions have reached convergence

oxidized and reduced mineral assemblages in greenstone belt rocks of the st ives gold camp western australia vectors to high grade ore bodies in archaean gold deposits hydrothermal sulfide oxide gold mineral assemblages in gold deposits in the archaean st ives gold camp in western australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time reduced alteration assemblages pyrrhotite pyrite occur in deposits in the southwest of the camp e g argo junction deposits and moderately to strongly oxidized assemblages magnetite pyrite hematite pyrite occur in deposits in the central corridor in the northeast e g north orchin revenge deposits reduced mineral assemblages flank the central corridor of oxidized deposits and locally cut across it along e w trending faults oxidized mineral assemblages in the central corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1 000 m below present surface hydrothermal magnetite predates and is synchronous with early phases of gold associated albite carbonate pyrite biotite chlorite hydrothermal alteration later stage gold associated pyrite is in equilibrium with hematite the spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions the 34s values for pyrite for the st ives gold camp range between 8 4 and 5 1 with the negative values occurring in oxidized magnetite rich domains and slightly negative or positive values occurring in reduced pyrrhotitic domains preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the st ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite pyrite to relatively oxidized magnetite pyrite and hematite pyrite both in space and time gold deposition is inferred to have occurred where fluids of contrasting redox state mixed

tin metallogenesis associated with granitoids in the southwestern sanjiang tethyan domain nature deposit types and tectonic setting article i nfo tin mineralization in the southwestern sanjiang tethys sn metallogenic domain extends from the southeast asia tin belt in the south the eastern part of the domain does not contain significant sn deposits whereas the central part of the domain composed of the changning menglian sn belt and related to ca 239 178 ma s type granitoids generated by the collision between tengchong baoshan and simao blocks carries wide spread the hydrothermal vein type mineralization the western part of the domain composed of the tengchong baoshan sn metallogenic belt is related to both 136 113 ma and 89 52 ma s type granitoids the former granitoids resulted from the collision between western burma and tengchong baoshan blocks and generated skarn type tin deposits the younger groups correspond to the india asia continental collision and are associated with the xiaolonghe and lailishan greisen type sn deposits

textural control on gold distribution in as free pyrite from the dongping huangtuliang and hougou gold deposits north china craton hebei province china article i nfo pyrite from the dongping huangtuliang and hougou gold deposits hebei province china was investigated using a combination of ore microscopy including back scattered imaging and in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms a range of elements including au te ag pb bi cu co ni and as was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in as free pyrite thedatasetshowsexcellentcorrespondence betweenmeasuredhighgoldvaluesandthreekeytexturalcriteria i areasofclusteredtellurideinclusions especiallyindongping ii microshearingandfracturing brecciation dongping and huangtuliang and iii pyrite recrystallization huangtuliang invisible gold is only at trace levels in the hougou and gold bearing telluride minerals are not observed this is considered to result from larger scale remobilization of gold during advanced brecciation and recrystallization of pyrite pyrite grains containing clustered inclusions have by far the highest gold concentrations up to 1 wt with consistent values of thousands of ppm au interpretation of textures and la icp ms data infers that in these areas the distribution of telluride inclusions extends pervasively from micron to nanoscale i e as fields of nanoparticles local employment of coupled dissolution reprecipitation reaction between pyrite and fluids driving the k metasomatic alteration dated at 150 ma is invoked to explain such patterns syn deformational grain scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears the deformational event leads to gold enrichment in the huangtuliang pyrite where brittle fracturing brecciation has been followed by a resorption and recrystallization in the latter case foam textured pyrites again without as can contain up to hundreds of ppm gold theinterpreted sequenceof pyritepost depositional eventsis inaccordancewith the protracted magmaticevolution of the area starting with variscan alkaline intrusions 390 ma and reactivated during the yanshanian orogeny 150 ma thestudyshows i thatas freepyritecanreadilycontainsignificantamountsofinvisiblegold bothasnanoparticles

a pyroxene bearing meta ironstone and other pyroxene granulites from tonagh island enderby land antarctica further evidence for very high temperature 980 c archaean regional metamorphism in the napier complex a suite of granulites including a meta ironstone pyroxenites and spinel lherzolites from east tonagh island enderby land antarctica preserve exsolution recry stallization features consistent with a shared metamorphic evolution that involves marked cooling from initial metamorphic temperatures of nearly 1000 c reintegrated pre exsolution and pre reaction grain compositions in the meta ironstone indicate the former coexistence of metamorphic pigeonite wo12en38fs50 and ferroaugite wo35en31fs34 at temperatures in excess of 980 c for pressures of 7 kbar 0 7 gpa using pyroxene quadrilateral thermometry lindsley 1983 intra grain lamellae relationships indicate the exsolution of a second pigeonite wo12en35fs53 from the ferroaugite at temperatures in the range 930 970 c prior to the c 720 600 c exsolution of orthopyroxene and clinopyroxene 100 lamellae and later partial recrystallization at similar temperatures although pyroxenitic and iherzolitic granulites preserve a much less complete history reintegrated porphyroclast compositions in these yield temperature estimates which approach those inferred from the metaironstone pyroxene thermometry based on neoblast compositions suggests that recrystallization post dating a late low intensity deformation phase d3 occurred at temperatures greater than 600 c these results are consistent with the independent evidence obtained from studies of metapelitic and felsic rock types for very high temperature metamorphism throughout the napier complex followed by near isobaric cooling and later deformation under lower grade granulite facies conditions comparison with similar pyroxene data from fyfe hills sandiford powell 1986 demonstrates further the regional significance of these high temperatures and implies broadly isothermal metamorphic conditions over a large area 5000 km2 and thickness 6 9 km of lower crust at c 3070 ma

prolonged 100 ma ultrahigh temperature metamorphism in the napier complex east antarctica a petrochronological investigation of earth s hottest crust

continuum sea ice rheology determined from subcontinuum mechanics 1 a method is presented to calculate the continuum scale sea ice stress as an imposed continuum scale strain rate is varied the continuum scale stress is calculated as the area average of the stresses within the floes and leads in a region the continuum element the continuum scale stress depends upon the imposed strain rate the subcontinuum scale material rheology of sea ice the chosen configuration of sea ice floes and leads and a prescribed rule for determining the motion of the floes in response to the continuum scale strain rate we calculated plastic yield curves and flow rules associated with subcontinuum scale material sea ice rheologies with elliptic linear and modified coulombic elliptic plastic yield curves and with square diamond and irregular convex polygon shaped floes for the case of a tiling of square floes only for particular orientations of the leads have the principal axes of strain rate and calculated continuum scale sea ice stress aligned and these have been investigated analytically the ensemble average of calculated sea ice stress for square floes with uniform orientation with respect to the principal axes of strain rate yielded alignment of average stress and strain rate principal axes and an isotropic continuum scale sea ice rheology we present a lemon shaped yield curve with normal flow rule derived from ensemble averages of sea ice stress suitable for direct inclusion into the current generation of sea ice models this continuum scale sea ice rheology directly relates the size strength of the continuum scale yield curve to the material compressive strength

high pressure and ultrahigh temperature metamorphism at komateri northern madurai block southern india we report for the first time the evidence for prograde high pressure hp metamorphism preceding a peak ultrahigh temperature uht event in the northernmost part of the madurai block in southern india mg al rich grt ged rocks from komateri in karur district contain poikiloblastic garnet with numerous multi phase inclusions although most of the inclusion assemblages are composed of gedrite quartz and secondary biotite rare staurolite sapphirine and spinel quartz are also present the xmg mg fe mg of staurolite 0 45 0 49 is almost consistent with that reported previously from namakkal district in the palghat cauvery shear zone system xmg 0 51 0 52 north of the madurai block the hp event was followed by peak uht metamorphism at t 880 1040 c and p 9 8 12 5 kbar as indicated by thermobarometric computations in the grt ged rock and associated mafic granulite symplectic intergrowth of spinel xmg 0 50 0 59 zno 1 7 wt and quartz a diagnostic indicator of uht metamorphism probably formed by decompression at uht conditions the rocks subsequently underwent retrograde metamorphism at t 720 760 c and p 4 2 5 1 kbar the p t conditions and clockwise exhumation trajectory of the komateri rocks comparable to similar features recorded from the palghat cauvery shear zone system suggest that the madurai block and the palghat cauvery shear zone system underwent similar hp and uht metamorphic history probably related to the continent continent collision during the final stage of amalgamation of gondwana supercontinent

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

genesis and evolution of the leimengou porphyry mo deposit in west henan province east qinling dabie belt china constraints from hydrothermal alteration fluid inclusions and stable isotope data abstract the leimengou mo deposit is located in the east qinling dabie metallogenic mo belt located at the southern margin of the north china craton the deposit is hosted within the mesozoic leimengou granite porphyry pluton and at the contact between the granite and late archean gneisses in light of mineral assemblage and crosscutting relationships among veinlets the mineralization and alteration can be classified in four distinct stages 1 a mo barren pre mineralization stage of alteration characterized by massive k feldspar alteration of the granite porphyry 2 a k feldspar quartz vein stage that formed veinlets with minor molybdenite 3 a quartz sulfide veinlet stage which is the main stage of mineralization and 4 post mineralization quartz calcite vein stage stage 1 alteration is associated with fluid inclusions of low medium salinity 2 4 13 1 wt naclequiv that homogenized at medium to high temperatures 238 476 c stage 2 mineralization is associated with fluid inclusions that homogenized at 201 389 c and that have salinities of 2 0 13 6 wt naclequiv fluid inclusions that formed during stage 3 have homogenization temperatures of 205 370 c and corresponding salinities of 1 0 17 6 wt naclequiv to 31 4 40 6 wt naclequiv indicative of fluid immiscibility and mixing of hydrothermal fluids with meteoric water stage 4 h2o nacl fluids were trapped at lower temperatures 148 246 c and have salinities of 1 7 7 9 wt naclequiv stages 1 to 4 have calculated 18ofluid values of 3 6 4 3 2 7 2 8 0 6 2 3 and 3 2 to 3 8 respectively with dfluid values of 72 to 80 83 to 90 68 to 82 and 81 to 90 respectively these results are consistent with the fluid inclusion data outlined above and suggest that early fluids were exsolved from the granitic magma and underwent progressive mixing with meteoric water molybdenum was initially transported from the crystallizing magma in a hot alkaline and oxidized fluid while decreasing temperatures and ph water rock interaction and fluid immiscibility during fluid ascent resulted in its precipitation and deposition

a multithickness sea ice model accounting for sliding friction a multithickness sea ice model explicitly accounting for the ridging and sliding friction contributions to sea ice stress is developed both ridging and sliding contributions depend on the deformation type through functions adopted from the ukita and moritz kinematic model of floe interaction in contrast to most previous work the ice strength of a uniform ice sheet of constant ice thickness is taken to be proportional to the ice thickness raised to the 3 2 power as is revealed in discrete element simulations by hopkins the new multithickness sea ice model for sea ice stress has been implemented into the los alamos cice sea ice model code and is shown to improve agreement between model predictions and observed spatial distribution of sea ice thickness in the arctic

the luanchuan mo w pb zn ag magmatic hydrothermal system in the east qinling metallogenic belt china constrains on metallogenesis from c h o s pb isotope compositions and rb sr isochron ages abstract the luanchuan mo w pb zn ag polymetallic ore district is located in the east qinling metallogenic belt on the southern margin of the north china craton two ore fields nannihu and yuku are recognized in the district and three types of deposits are identified from the two ore fields as follows 1 the 6 proximal porphyry skarn type mo w deposits occurring at the inner contact zone of the granite porphyries 2 the 3 middle skarn hydrothermal type zn deposits and 3 the 8 distal hydrothermal type pb zn ag deposits at the periphery of the porphyry we present c h o isotope compositions of hydrothermal quartz and calcite s pb isotope compositions of sulfide minerals and sphalerite rb sr isochron ages from the 17 deposits the geochemical and geochronological data from the two ore fields all show systematic temporal and spatial variation and primarily lead to the following inferences 1 the temperatures and salinities of the ore forming fluids decreased during mineralization the ore forming fluids gradually evolved from magmatic water to mixed magmatic meteoric water 2 the metallogenic components were primarily derived from igneous rocks with increasing proportions of the materials from the ore bearing rocks 3 the mineralization ages of these deposits are close 147 136 ma which correspond to the emplacement of the granite intrusions 4 the three types of deposits and the ore related late mesozoic intrusives constitute a unified magmatic hydrothermal mineralization system finally we also suggest exploration strategies for the luanchuan ore district

a classification of gem corundum deposits aimed towards gem exploration abstract this classification of gem corundum ruby and sapphire deposits takes into consideration petrographic data and the mode of genesis of the deposits it is aimed at being practical and useful in the field particularly for prospecting purposes deposits are classified into primary and secondary deposits primary deposits include igneous and metamorphic deposits igneous gem corundum deposits are rare and include sapphire bearing syenites from kenya emphasis is put on metamorphic deposits that are subdivided into metamorphic s s metasomatic and anatectic deposits many gem corundum deposits result from metasomatic processes small scale metasomatism mostly involves desilication reactions between silico aluminous rocks pegmatites gneisses etc and silica poor rocks ultramafites meta carbonates and leads to the formation of limited size deposits large scale diffuse metasomatism is usually more difficult to characterize and therefore is not separated from isochemical metamorphism in this classification in metamorphic deposits gem corundum results from transformation of an al rich and or si poor protolith such deposits include ruby bearing mafic granulites ruby bearing meta limestones and ruby sapphire bearing gneisses and granulites an intermediate category includes anatectic deposits secondary deposits encompass sedimentary and volcanic xenoclastic occurrences in sedimentary deposits gem corundum occurs as clasts originating from other lithologies in volcanic deposits gem corundums are xenocrysts that have a range of origins the proposed classification outlines geological environments favorable to the crystallization and distribution of gem corundum thus facilitating prospecting and mining of this gemstone

garnet forming reactions in mafic granulites from enderby land antarctica implications for geothermometry and geobarometry

mineral chemistry and metasomatic growth of aluminous enclaves in gedrite cordierite gneiss from southwestern new hampshire usa

impact of a new anisotropic rheology on simulations of arctic sea ice 1 a new rheology that explicitly accounts for the subcontinuum anisotropy of the sea ice cover is implemented into the los alamos sea ice model this is in contrast to all models of sea ice included in global circulation models that use an isotropic rheology the model contains one new prognostic variable the local structure tensor which quantifies the degree of anisotropy of the sea ice and two parameters that set the time scale of the evolution of this tensor the anisotropic rheology provides a subcontinuum description of the mechanical behavior of sea ice and accounts for a continuum scale stress with large shear to compression ratio and tensile stress component results over the arctic of a stand alone version of the model are presented and anisotropic model sensitivity runs are compared with a reference elasto visco plastic simulation under realistic forcing sea ice quickly becomes highly anisotropic over large length scales as is observed from satellite imagery the influence of the new rheology on the state and dynamics of the sea ice cover is discussed our reference anisotropic run reveals that the new rheology leads to a substantial change of the spatial distribution of ice thickness and ice drift relative to the reference standard visco plastic isotropic run with ice thickness regionally increased by more than 1 m and ice speed reduced by up to 50

evolution of high mg al granulites from sunkarametta eastern ghats india evidence for a lower crustal heating cooling trajectory a suite of high mg al granulites from sunkarametta eastern ghats belt india shows contrasting prograde assemblages of extremely aluminous orthopyroxene cordierite sapphirine and similarly aluminous orthopyroxene ti rich spinel in closely associated domains textural and compositional characteristics indicate that both were derived from prograde dehydration melting of biotite plagioclase quartz bearing protoliths the former assemblage was stabilized at relatively more magnesian bulk composition geothermobarometric data and petrogenetic grid considerations place peak metamorphic conditions at c 950 c and 9 kbar subsequent to peak metamorphism the rocks cooled to c 700 750 c with slight lowering of pressure and the retrograde reactions also involved melt solid interaction the inferred p t trajectory is one of heating cooling at lower crustal 25 30 km depths

ridging and strength in modeling the thickness distribution of arctic sea ice a theory describing evolution of the ice thickness distribution the probability density of ice thickness was proposed by thomdike et al 1975 and has been used in several sea ice models the advantage of this theory over the widely used two level formulation is that it treats ridging explicitly as a redistribution of ice thickness and ice strength as a function of energy losses incurred by ridge formation however the parameterization of these processes remains rather speculative and largely untested and so our purpose here is to explore these parameterizations using a numerical model based on this theory the model uses a 160 km resolution grid of the arctic and 7 years of observed atmospheric forcing data 1979 1985 monthly oceanic heat flux and current fields are obtained from a 40 km resolution coupled ice ocean model run separately with the same forcing by requiring the computed monthly mean ice drift to have the same magnitude as observed buoy drift we estimate the primary strength parameter the ratio of total to potential energy change during ridging this ratio depends on the value of other parameters however the standard case has a ratio of 17 which is within the range estimated by hopkins 1994 in simulations of individual ridging events the effects of ridge redistribution and shear ridging parameters are illustrated by a series of sensitivity studies and comparisons between observed and modeled ice thickness distributions and ridge statistics in addition these comparisons highlight the following shortcomings of the thickness distribution theory as it is presently implemented first the process of first year to multiyear ridge consolidation is ignored and second the observed preferential melt of thick ridged ice is not reproduced

a proposed new type of arsenian pyrite composition nanostructure and geological significance this report describes a new form of arsenian pyrite called as3 pyrite in which as substitutes for fe fe as s2 in contrast to the more common form of arsenian pyrite as1 pyrite in which as1 substitutes for s fe as s 2 as3 pyrite has been observed as colloformic overgrowths on as free pyrite in a hydrothermal gold deposit at yanacocha peru xps analyses of the as3 pyrite confirm that as is present largely as as3 empa analyses show that as3 pyrite incorporates up to 3 05 at of as and 0 53 at 0 1 at 0 27 at 0 22 at 0 08 at and 0 04 at of pb au cu zn ni and co respectively incorporation of as3 in the pyrite could be written like as3 y au 1 y 2 fe2 where au and vacancy help to maintain the excess charge hrtem observations reveal a sharp boundary between as free pyrite and the first overgrowth of as3 pyrite 20 40 nm thick and co linear lattice fringes indicating epitaxial growth of as3 pyrite on as free pyrite overgrowths of as3 pyrite onto as free pyrite can be divided into three groups on the basis of crystal size 8 20 nm 100 300 nm and 400 900 nm and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals the yanacocha deposit in which as3 pyrite was found formed under relatively oxidizing conditions in which the dominant form of dissolved as in the stability field of pyrite is as3 in contrast reducing conditions are typical of most environments that host as1 pyrite as3 pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments including high sulfidation epithermal deposits and shallow groundwater systems where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of as3 and toxic heavy metals in oxidizing natural systems

isotope geochemistry of the tieluping silver lead deposit henan china a case study of orogenic silver dominated deposits and related tectonic setting the tieluping silver deposit which is sited along ne trending faults within the high grade metamorphic basement of the xiong er terrane in the qinling orogenic belt is part of an important recently discovered mesozoic orogenic type ag pb belt ore formation includes three stages an early barren quartz pyrite stage e an intermediate polymetallic sulfide ore stage m and a late barren carbonate stage l carbon sulfur and lead isotope systematics indicate that the e stage fluids are deeply sourced the l stage fluids are shallow sourced meteoric water whereas the m stage fluids are a mix of deep sourced and shallow sourced fluids sulfur and lead isotope data show that the ore forming fluids must have originated from a source with elevated radiogenic lead and low 34s values that differs significantly from exposed geologic units in the xiong er terrane the lower crust and the mantle this supports the view that the carbonate shale chert sequences of the guandaokou and luanchuan groups south of the machaoying fault might be the favorable sources although little is known about their isotopic compositions a tectonic model that combines collisional orogeny metallogeny and hydrothermal fluid flow is proposed to explain the formation of the tieluping silver deposit during the mesozoic collision between the north china craton and south china block early mid triassic indosinian orogeny crustal slabs containing the carbonate shale chert sequences of the guandaokou and luanchuan groups locally rich in organic matter carbonaceous shale were thrust northwards beneath the xiong er terrane along the machaoying fault metamorphic devolatilisation of this underthrust slab probably provided the ore forming fluids to develop the ag pb ore belt which includes the tieluping silver deposit fluids and magmas were emplaced during extensional stages related to the jurassic cretaceous yanshanian orogeny

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

metallogeny during continental outgrowth in the columbia supercontinent isotopic characterization of the zhaiwa mo cu system in the north china craton abstract the eastern qinling molybdenum belt eqmb in central china represents the largest mo province in the world located at the southern margin of the north china craton this mo province is largely associated with mesozoic granitoids here we report re os isochron age of 1761 33 ma 2 mswd 2 9 from molybdenite in the recently discovered zhaiwa porphyry mo cu system within the eqmb this age coincides with the peak eruption period 1 78 1 75 ga of the xiong er group volcanic rocks which unconformably overlie the taihua supergroup and are interpreted to have developed on a continental arc the re concentrations 1 to 43 ppm of the zhaiwa molybdenites are similar to those of typical porphyry cu mo au systems developed on continental arcs the 34 s values of the zhaiwa ores 2 7 7 3 average 5 2 suggest that the sulfur was mainly sourced from a magmatic system the sulfides from the ores yield sr i average of 0 70533 similar to that of the xiong er group 0 70547 albeit higher than that of the kuanping group 0 70334 and lower than the taihua supergroup 0 70763 suggesting a mixed source the average e nd 1 76 ga of the sulfides from the ores 0 9 falls between the averages of the taihua supergroup ca 6 8 and the kuanping group ca 7 4 the pb isotope ratios of the ores are similar to but slightly higher than those of the taihua supergroup reflecting preferential leaching of radiogenic pb from the taihua supergroup by magmatic fluids integrated data and interpretations constrain the zhaiwa mo cu deposit to be a porphyry mineral system developed within a ca 1 76 ga continental arc related to oceanic plate subduction beneath the southern margin of the north china craton a correlation between tectonic settings and metallogenic types clearly indicate that the xiong er group was formed in a volcanic arc confirming paleo mesoproterozoic continental outgrowth along the margins of the columbia supercontinent the isotopic characterization of the zhaiwa deposit provides new insights into the enigma of the widespread distribution of large and super large mo deposits of eqmb along the southern margin of the north china craton

re os and sr nd pb isotope constraints on source of fluids in the zhifang mo deposit qinling orogen china abstract the zhifang mo deposit is located in the northeastern qinling orogen along the southern margin of the north china craton the deposit represents a quartz vein system hosted in the mesoproterozoic xiong er group volcanic rocks we identify three hydrothermal stages early middle and late characterized by veinlets of quartz pyrite quartz molybdenite pyrite chalcopyrite galena sphalerite and quartz carbonate assemblages respectively five molybdenite samples from the zhifang deposit yield re os ages ranging from 241 2 1 6 ma to 247 4 2 5 ma with an isochron age of 246 0 5 2 ma 2 mswd 7 4 and a weighted mean age of 243 8 2 8 ma 2 mswd 5 5 the re os age shows that the mo mineralization occurred during the indosinian orogeny and suggests that the mineralization is unrelated to the yanshanian magmatism or the paleo mesoproterozoic volcanic hydrothermal event this study also reports a new sr nd pb isotope dataset from ore sulfides in an attempt to constrain the source of the ore forming fluids ten sulfide samples from middle stage of the zhifang mo deposit yield i sr t ratios of 0 710286 0 711943 with an average of 0 711004 e nd t values between 19 5 and 14 8 with an average of 16 7 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 126 17 535 15 374 15 466 and 37 485 37 848 with averages of 17 380 15 410 and 37 631 respectively one pyrite from the early stage yield i sr t of 0 722711 0 722855 with an average of 0 722783 which is higher than those of the middle stage sulfides and suggests equilibration with wallrocks the e nd t values are in the range of 17 3 to 16 6 with a mean at 17 0 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios are 17 386 15 405 and 37 622 respectively the ore sulfides show higher pb isotope ratios higher e nd t and lower i sr t values than the host rocks the results suggest that the ore forming fluids had lower i sr t and higher e nd t values than the ore sulfides and were possibly sourced from the dengfeng complex the southward subduction of the north china craton beneath the huaxiong block during the triassic was possibly responsible for the formation of the waifangshan orogenic mo system

theoretical phase relations involving cordierite and garnet revisited the influence of oxygen fugacity on the stability of sapphirine and spinel in the system mg fe al si o the theoreticalp t grid for stability relations of the phases cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and quartz qz of hensen 1971 has proved useful in the interpretation of metamorphic mineral assemblages formed at low oxygen fugacity both experimental data and evidence from natural rocks indicate that at high oxygen fugacity compatability relations change as a result of the enlargement of the stability field of spinel which causes a topological inversion and the stabilisation of the invariant points sa ga and cd this implies the stable existence of the univariant equilibria for f text o text 2 buffered conditions sp qz ga hy si o2 sa cd cd sp qz hy si o2 sa ga and sa sp qz hy si o2 ga cd and the divariant reaction sp qz hy si o2 sa ga cd these redox equilibria are restricted to conditions of high oxygen fugacity the proposed theoreticalp t grids for both low and high oxygen fugacity satisfactorily explain all experimental data and metamorphic mineral assemblages so far found in granulites

metastable growth of corundum adjacent to quartz in a spinel bearing quartzite from the archaean napier complex antarctica in a granulite facies spinel bearing quartzite corundum orthopyroxene and sapphirine and rarely cordierite and sillimanite form partial rims separating spinel from quartz textures indicate the reactions spinel quartz orthopyroxene corundum and spinel quartz orthopyroxene sapphirine thus corundum and sapphirine are produced by reactions involving quartz the low al content of the orthopyroxene 0 5 2 8 wt and low values for mg fe distribution coefficient for spinel sapphirine and spinel orthopyroxene reflect low temperature conditions during formation of the reaction products absence of zoning in spinel and a constant mg fe distribution coefficient for spinel sapphirine and spinel orthopyroxene over a compositional range indicate mg fe equilibration it is suggested that stable reactions such as spinel quartz cordierite or spinel quartz garnet sillimanite were over stepped and that metastable reactions give rise to the anomalous juxtaposition of corundum quartz

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

la icp ms trace element analysis of pyrite from the chang an gold deposit sanjiang region china implication for ore forming process abstract the chang an gold deposit yunnan province is one of five large gold deposits in the ailaoshan gold belt that is the most important ore belt of the sanjiang tethyan metallogenic domain geochemical study of pyrite in the deposit was conducted using laser ablation inductively coupled plasma mass spectroscopy three types of hydrothermal pyrite were identified in the ores and wall rocks i e the coarse euhedral crystals in syenite py1 the coarse grains disseminated in altered sandstones or sandstone ores py2 and the fine grained euhedral pyrite in sandstone ores py3 their trace elements exhibit different concentrations associations and rim core zoning implying different geneses and crystallization processes the cores of py1 were formed by magmatic fluids and have the lowest concentrations of au as cu and zn the cores of py2 were formed by metamorphic fluids and have relatively high au ag ni pb and cu concentrations the py3 grains and the growth rims of py1 and py2 show consistently high contents of au as pb and co suggesting that all of them were rapidly deposited from a mixing fluid system that was probably composed of fluids of metamorphic and magmatic origins this interpretation is supported by the observation that the high grade ores generally contain lots of py2 and py3 hence we consider that the deposit was formed during india asia collision slightly postdate the 33 35 ma tectono magmatism

modeling sea ice as a granular material including the dilatancy effect abstract a dynamic sea ice model based on granular material rheology is presented the sea ice model is coupled to both a mixed layer ocean model and a one layer thermodynamic atmospheric model which allows for an ice albedo feedback land is represented by a 6 m thick layer with a constant base temperature a 10 year integration including both thermodynamic and dynamic effects and incorporating prescribed climatological wind stress and ocean current data was performed in order for the model to reach a stable periodic seasonal cycle the commonly observed lead complexes along which sliding and opening of adjacent ice floes occur in the arctic sea ice cover are well reproduced in this simulation in particular shear lines extending from the western canadian archipelago toward the central arctic often observed in winter satellite images are present the ice edge is well positioned both in winter and summer using this thermodynamically coupled ocean ice atmosphere model the results also yield a sea ic

in situ trace element and sulfur isotope analysis of pyrite in a paleoproterozoic gold placer deposit pardo and clement townships ontario canada extensive pyrite bearing auriferous cobble and boulder conglomerates are present in the basal 30 in of the mississagi formation in pardo and clement townships ontario canada the sedimentology of the conglomerates combined with regional geology indicates limited fluvial transport in a gravel bed braided river with local hyperconcentrated flows with material derived from a highly restricted catchment area postdepositional overprinting of the conglomerates is related to the penokean orogeny at 1 85 to 1 5 ga and alkali metasomatism at similar to 1 7 ga several pyrite varieties including detrital and postdepositional recrystallized and altered grains are present in the conglomerates detailed in situ laser ablation inductively coupled plasma mass spectrometry la icpms analysis of pyrite revealed that the gold in the deposit is intimately associated to large detrital pyrite grains as invisible au with lesser amounts of free gold postdepositional pyrite and pyrite overgrowths have very low au content elements such as pb bi sb te ag and hg together with au were mobilized during hydrothermal alteration and dissolution of detrital pyrite grains small scale transport and reprecipitation formed part of the postdepositional pyrite and free gold in immediate contact with postdepositional grains in contrast ni co and as were not mobilized external fluid infiltration is negligible and is indicated only by minor compositionally distinct late sulfide veinlets crosscutting the conglomerates sulfur isotope analysis of detrital pyrite yields generally positive delta 34 s values 0 97 9 26 0 the delta 34 s sulfur isotope composition of pyrite overgrowths and postdepositional grains overlaps the isotopic range of the detrital grains suggesting a near closed s system during postd epositional processes however the detrital pyrite tends to have slightly negative delta 33 s while the postdepositional and overgrowth pyrite are either neutral or slightly positive the s isotope composition of the detrital pyrite is compatible with an origin of s as dissolved sulfate in an ocean under a low oxygen atmosphere the potential source of the au bearing detrital pyrite appears to have been an as yet undiscovered archean deposit located within 1 to 8 kin of the placer deposit

a corundum and sapphirine paragenesis from the limpopo mobile belt southern africa an assemblage consisting of corundum sapphirine spinel cordierite garnet biotite and bronzite is described from the messina area of the limpopo mobile belt and consideration given to its petrogenesis various geothermometers and geobarometers have been applied in an attempt to determine the temperatures and pressures of metamorphism a former coexistence of garnet and corundum is suggested to have developed during the earliest high pressure phase of the metamorphism where temperatures exceeded 800 c and pressures as high as 10kbar may have been experienced subsequently continuous retrograding reactions from medium pressure granulite facies at about 800 c and 8kbar towards amphibolite facies generated spinel cordierite sapphirine and possibly also bronzite the most notable reaction was probably of the form garnet corundum cordierite sapphirine spinel

sequence of late jurassic early cretaceous magmatic hydrothermal events in the xiong ershan region central china an overview with new zircon u pb geochronology data on quartz porphyries recent investigations have revealed several large au and mo deposits in the xiong ershan region central china most quartz porphyries associated with the mineralization occur as dikes and apophyses or as rubbles cemented in mineralized breccia pipes three types of quartz porphyries were sampled from the leimengou mo deposit the qiyugou au deposit and the niutougou au deposit la icp ms zircon u pb analysis was performed in zircons from two quartz porphyries the results yielded ages of 125 4 0 77 ma for leimengou mo deposit and 150 1 1 1 ma for qiyugou au deposit the magma source of leimengou quartz porphyry is similar to that of the mineralized cementing material in breccia pipes of the qiyugou au deposit whereas the magma source of qiyugou quartz porphyry is the same as that of quartz porphyries in niutougou au deposit based on the new u pb isotopic ages of granitic plutons reported in this study together with the age data in the literature we identify distinct magmatic pulses in the xiong ershan region at ca 160 150 143 133 125 and 115 ma during the late jurassic early cretaceous the ages of au and mo mineralization coincide with the thermal events at about 115 125 133 and 143 ma are considered to be co eval with granitic magmatism no mineralization ages of 150 and 160 ma thermal events have been previously reported our study demonstrates late jurassic early cretaceous multiple magmatic pulses and mineralization in the xiong ershan region

mineralogy and textural relationships among sulphosalts and related minerals in the bleikvassli zn pb cu deposit nordland norway several distinct assemblages of pb sb pb as cu pb sb and cu fe zn sn sulphosalts are identified in sulphide samples from bleikvassli mine norway detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types tetrahedrite typically containing 10 16 wt ag rare freibergite containing 25 30 wt ag has also been identified in two samples stannite cu2 fe zn sns4 and meneghinite cupb13sb7s24 are widely distributed as trace constituents throughout massive pyritic and galena rich ores native antimony and pyrargyrite occur in trace amounts in all ore types as the breakdown products of earlier sulphosalts several distinct types of wall rock mineralisation are present at bleikvassli of considerable mineralogical interest are the coarse grained sulphide mobilisates within the wall rock which contain a distinct and characteristic suite of pb as sulphosalts tennantite jordanite pb14as6s23 seligmannite cupbass3 dufrenoysite pb2as2s5 bournonite cupbsbs3 is the only sb bearing sulphosalt recognised in significant amounts within the mobilisates meneghinite and tetrahedrite being conspicuously absent these mobilisates display considerable au enrichment electrum can be confirmed intimately associated with jordanite and tennantite appreciable sb up to 3 wt is contained within galena in the mobilisates in contrast to galena from massive ores which contains only negligible sb contents of ag and bi in galena vary considerably in all ore types but confirm earlier suggestions that galena is a major ag carrier at bleikvassli boulangerite pb5sb4s11 jamesonite fepb4sb6s14 and gudmundite fesbs occur in trace amounts sn sulphosalts are represented by kesterite cu2 zn fe sns4 but commonly zoned with respect to zn fe ratio in the mobilisates rather than by stannite a rare type of mobilisate also in the wall rock in which chalcocite and bornite are the main minerals contains native ag stromeyerite agcus mckinstryite ag cu 2 s ag free tetrahedrite an unnamed cu ag fe sulphide cu3ag2fes4 and native bi myrmekitically intergrown with chalcocite although a comprehensive genetic model for the wall rock mineralisation at bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes a multi stage model of remobilisation during regional metamorphism is considered to best explain the observations an interplay of different solid and liquid state remobilisation mechanisms in various combinations is required to account for the macro and microscopic observations remobilisation probably began during the earlier stages of metamorphism with crystallisation and further remobilisation taking place during the entire metamorphic cycle giving rise to the extensive chemical and mineralogical diversity observed today preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late metamorphic crystallisation and subsequent cooling

trace element characteristics of different pyrite types in mesoarchaean to palaeoproterozoic placer deposits a comparative in situ la icp ms trace element study on pyrite from three different variably auriferous archaean to palaeoproterozoic palaeoplacer deposits in the ouro fino syncline quadrilatero ferrifero brazil the elliot lake area north of lake huron se canada and several deposits within the witwatersrand basin south africa revealed systematic differences between morphologically different pyrite types and between the various palaeoplacer deposits especially the ni and au concentrations as well as co ni and mo ni ratios were found to be systematically different in detrital compact detrital porous and post sedimentary hydrothermal pyrite grains from different source areas high co ni ratios and low au concentrations are typical of post sedimentary pyrite which is hydrothermal in origin in contrast relatively low co ni ratios and high au contents characterise detrital porous banded and concentric pyrite grains au 1 ppm which are syn sedimentary in origin in the elliot lake area and the witwatersrand basin detrital compact rounded pyrite is characterised by high co ni ratios which is in agreement with derivation from a hydrothermal source low au concentrations in this pyrite type support the contention of the gold and the pyrite in these deposits coming from different source rocks in contrast derivation from an originally diagenetic pyrite is suggested for the detrital compact pyrite in the ouro fino syncline because of low to intermediate co ni ratios high au contents may indicate a genetic relationship between pyrite and gold there systematic differences exist between the three areas with respect to au ni co mo and cu distributions in detrital pyrite which reflects differences in the provenance a predominantly mafic ultramafic source is indicated for the ouro fino a felsic source for the elliot lake and a mixed felsic mafic provenance for the witwatersrand pyrite populations independently of pyrite type the higher au endowment of the studied witwatersrand and ouro fino conglomerates are also reflected by an overall higher au concentration in the respective pyrite grains compared to the relatively au poor samples from elliot lake in general a strong positive correlation between au and pb levels in the various pyrite grains is noted analogous to pb which is well known for not being easily accommodated in the pyrite crystal lattice but occurring as discrete pbs phases au is considered to be present mainly in the form of discrete au phases in minute pores and interstices of the pyrite grains rather than within the pyrite lattice

genesis of the 1 76 ga zhaiwa mo cu and its link with the xiong er volcanics in the north china craton implications for accretionary growth along the margin of the columbia supercontinent abstract the east qinling molybdenum belt hosting numerous mesozoic magmatic hydrothermal mo deposits is one of the largest molybdenum provinces in the world the recently discovered zhaiwa mo cu deposit luoning county henan province occurs within the xiong er terrane of the east qinling orogenic belt the mo cu mineralization is associated with widespread stockworks or veinlets occurring within altered amphibolite here we investigate the characteristics of the ore mineralization through systematic fluid inclusion petrography microthermometry and laser raman spectroscopy the typical inclusions in the veins and stockworks are aqueous daughter mineral bearing and a subordinate co2 rich type the homogenization temperatures of the aqueous inclusions in quartz molybdenite veins are up to 370 c which together with some daughter mineral bearing inclusions homogenized by dissolution of halite at 500 c indicates that the ore forming fluids were derived from a hypothermal fluid system the daughter mineral bearing inclusions assign high salinities for the ore forming fluids correlating the ore deposit to a magmatic hydrothermal system we also present h o isotope systematics which support this interpretation the recently reported re os molybdenite age of 1 76 0 03 ga from this deposit is coeval to the xiong er group andesite dominated volcanic sequence 1 8 1 45 ga based on which we propose that the zhaiwa deposit represents the upper domain of a porphyry system developed within a subduction related setting with accretion to the southern margin of the north china craton our study provides new constraints on the outgrowth of the columbia supercontinent during paleoproterozoic

no mass independent sulfur isotope fractionation in auriferous fluids supports a magmatic origin for archean gold deposits the source of the auriferous fluids that formed archean greenstone gold deposits remains controversial metamorphic fluids fluids derived from felsic magmas mantle fluids and meteoric water have all been suggested we report the results of ion microprobe sensitive high resolution ion microprobe stable isotopes multiple sulfur isotope analyses 32 s 33 s 34 s conducted to constrain the source of sulfur in four archean gold deposits the analyses are of pyrite samples that are genetically related to the gold mineralization from the bellerophon victory and wallaby deposits in the eastern goldfield superterrane of the yilgarn craton western australia together with sulfide from black shale from the golden mile deposit and st ives gold camp ore associated pyrite from the beattie gold deposit of the abitibi greenstone belt of the superior craton in canada was measured to test whether the results obtained from the yilgarn craton apply to other archean gold deposits sulfur analyses from sulfide from shale show mass independent fractionation mif with 33 s as high as 1 8 whereas those from the 4 archean gold deposits are dominated by mass dependent fractionation with only a minor contribution of mif sulfur in this respect archean gold deposits contrast with archean nis deposits which are dominated by mif sulfur the absence of mif in the pyrite from the four archean gold deposits analyzed in this study is consistent with the auriferous fluid originating from a felsic magma or mantle source but inconsistent with the metamorphic and meteoritic fluid hypotheses

p t grids for silica undersaturated granulites in the systems mas n 4 and fmas n 3 tools for the derivation of p t paths of metamorphism abstract considering the minerals cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and corundum co in the system feo mgo al2o3 sio2 fmas the stable invariant points are co ga cd and sa constraints imposed by experimental data for the system mas indicate that under low ph2o conditions the invariant points occur at high temperature 900 c and intermediate pressure 7 10 kbar this temperature is higher than that commonly advocated for granulite facies metamorphism in granulites fe mg exchange geothermometers may yield temperatures of 100 150 c below peak metamorphic conditions and evidence for peak temperatures is best preserved by relict high temperature assemblages and by al rich cores in orthopyroxene application of the fmas grid to some well documented granulite occurrences introduces important constraints on their p t histories rocks of different bulk compositions occurring in close proximity in the field may record distinct segments of their p t paths this applies particularly to rocks with evidence for reaction in the form of coronas symplectites and zoned minerals consideration of curved reaction boundaries and xms isopleths may explain apparently contradictory results for the stability of cordierite obtained from low temperature experiments and thermochemical calculations on the one hand and hightemperature experimental data on the other

formation of sea ice bridges in narrow straits in response to wind and water stresses ice bridges are rigid structures composed of sea ice that form seasonally in the many straits and channels of the canadian arctic archipelago driven primarily by atmospheric stresses these ice bridges are formed when sufficiently thick ice jams during the course of its flow between land masses resulting in a region of stationary compacted ice that is separated from a region of flowing open water a polynya by a static arch using a continuum description of sea ice that is widely used in climate modeling we present an asymptotic theory of the process of formation of such bridges in slender channels when the motion of the ice is driven by external wind and water stresses we show that for an arbitrary channel shape ice bridges can only form within a range of ice properties that is determined by the channel geometry and the external stress we then compare the results of our theory with direct numerical simulations and observational evidence finally we provide simple analytical expressions for the mean velocity of the ice flow as a function of the channel shape the properties of the ice and the wind and water stresses along the channel

isotope systematics and fluid inclusion studies of the qiyugou breccia pipe hosted gold deposit qinling orogen henan province china implications for ore genesis abstract the qiyugou gold deposits henan province are hosted in breccia pipes within the xiong er terrane qinling orogen on the southern margin of the north china craton in these deposits three paragenetic assemblages have been recognized an early k feldspar epidote quartz pyrite a middle quartz polymetallic sulfide and a late quartz carbonate adularia in this paper we review and interpret fluid inclusion and stable and radiogenic isotopic data of host rocks and ores fluid inclusions in quartz and calcite include water rich co 2 rich and daughter crystal bearing the co 2 rich and daughter mineral bearing fluid inclusions are common in the early stage quartz and absent in the late stage quartz and calcite which only contain water rich fluid inclusions accordingly the early stage ore fluids are magmatic in origin and characterized by high temperature 350 c high salinity 30 wt nacl equiv and are co 2 rich fluid boiling in the middle ore stage resulted in co 2 release decreasing oxygen fugacity and rapid precipitation of ore materials the late stage fluids have low temperature low salinity are co 2 poor and lack daughter minerals these fluids are probably sourced from meteoric water h o c isotope systematics confirm that the ore fluid system evolved from magmatic to meteoric the carbon and lead isotope ratios indicate that the meso neoproterozoic sequence south of the xiong er terrane was the likely source of the ore forming materials the qiyugou breccia pipes and their associated gold ores were emplaced during an extensional regime following a transition from collision to rifting tectonics linked to collision and subduction of the yangtze plate beneath the north china craton geochronological studies show that mesozoic magmatism in the region occurred between the triassic and cretaceous the triassic to jurassic magmas were mostly derived from partial melting of ancient crust whereas the cretaceous magmas show juvenile signatures indicating mantle derived components processes of fragmentation of lithospheric roots crustal and lithospheric thinning extension and rifting were probably associated with the subducting pacific izanagi plate these crust mantle geodynamic processes were responsible for the development of anorogenic granitic melts that interacted with the meso neoproterozoic volatile rich sedimentary successions producing a flow of gas rich hydrothermal fluids that resulted in the emplacement of the qiyugou auriferous breccia pipes we conclude that the qiyugou gold deposits are intrusion related explosive breccia pipe type that evolved from hypothermal through mesothermal to epithermal

pyrite as a record of hydrothermal fluid evolution in a porphyry copper system a sims empa trace element study porphyry copper deposits are currently the world s largest source of copper and molybdenum and are also among the largest reservoirs of gold in the upper crust despite the fact that pyrite is a ubiquitous mineral phase in these deposits and secondary cu enrichment processes are commonly controlled by the abundance of this sulfide the major and trace element chemistry of pyrite from porphyry systems remains unconstrained in this study we report the first comprehensive trace element database of pyrite from the dexing deposit china s largest porphyry cu deposit by combining high spatial resolution and x ray mapping capabilities of electron microprobe analysis empa with low detection limits and depth profiling capabilities of secondary ion mass spectrometry sims in a suite of samples from the dexing deposit we show that the concentrations of precious metals e g au ag metalloids e g as sb se te and heavy metals e g cu co ni zn hg in pyrite from porphyry systems are more significant than previously thought among the elements analyzed cu as au and ni are the most abundant with concentrations that vary from sub ppm levels to a few wt i e 6 wt cu 3 wt as 0 25 wt au and 0 2 wt ni detailed wavelength dispersive spectrometry wds x ray maps and sims depth vs isotope concentration profiles reveal that pyrite from the dexing deposit is characterized by complex chemical zoning where the studied elements occur in different mineralogical forms while as occurs as a structurally bound element in pyrite cu and au can occur as both solid solution and micro to nano sized particles of chalcopyrite and native au or au tellurides respectively indicating that pyrite can control metal speciation and partitioning during porphyry cu mineralization the well developed oscillatory zoning detected in pyrite where cu rich as depleted growth zones alternate with cu depleted as rich layers indicates that cu is geochemically decoupled from as suggesting that this selective partitioning of metals into pyrite is most likely the result of changes in hydrothermal fluid composition

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

geological and isotopic evidence for magmatic hydrothermal origin of the ag pb zn deposits in the lengshuikeng district east central china the lengshuikeng ore district in east central china has an ore reserve of 43 mt with an average grade of 204 53 g t ag and 4 63 pb zn based on contrasting geological characteristics the mineralization in the lengshuikeng ore district can be divided into porphyry hosted and stratabound types the porphyry hosted mineralization is distributed in and around the lengshuikeng granite porphyry and shows a distinct alteration zoning including minor chloritization and sericitization in the proximal zone sericitization silicification and carbonatization in the peripheral zone and sericitization and carbonatization in the distal zone the stratabound mineralization occurs in volcano sedimentary rocks at 100 400 m depth without obvious zoning of alterations and ore minerals porphyry hosted and stratabound mineralization are both characterized by early stage pyrite chalcopyrite sphalerite middle stage acanthite native silver galena sphalerite and late stage pyrite quartz calcite the 34s values of pyrite sphalerite and galena in the ores range from 3 8 to 6 9 with an average of 2 0 the c o isotope values of siderite calcite and dolomite range from 7 2 to 1 5 with an average of 4 4 v pdb and from 10 9 to 19 5 with an average of 14 8 v smow respectively hydrogen oxygen and carbon isotopes indicate that the hydrothermal fluids were derived mainly from meteoric water with addition of minor amounts of magmatic water geochronology employing la icp ms analyses of zircons from a quartz syenite porphyry yielded a weighted mean 206pb 238u age of 136 3 0 8 ma considered as the emplacement age of the porphyry rb sr dating of sphalerite from the main ore stage yielded an age of 126 9 7 1 ma marking the time of mineralization the lengshuikeng mineralization classifies as an epithermal ag pb zn deposit

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

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

dependence of sea ice yield curve shape on ice thickness in this note the authors discuss the contribution that frictional sliding of ice floes or floe aggregates past each other and pressure ridging make to the plastic yield curve of sea ice using results from a previous study that explicitly modeled the amount of sliding and ridging that occurs for a given global strain rate it is noted that the relative contribution of sliding and ridging to ice stress depends upon ice thickness the implication is that the shape and size of the plastic yield curve is dependent upon ice thickness the yield curve shape dependence is in addition to plastic hardening weakening that relates the size of the yield curve to ice thickness in most sea ice dynamics models the yield curve shape is taken to be independent of ice thickness the authors show that the change of the yield curve due to a change in the ice thickness can be taken into account by a weighted sum of two thickness independent rheologies describing ridging and sliding effects separately it would be straightforward to implement the thickness dependent yield curve shape described here into sea ice models used for global or regional ice prediction

the metamorphic evolution of granulites at fyfe hills implications for archaean crustal thickness in enderby land antarctica granulites at fyfe hills in enderby land antarctica crystallized at temperatures in excess of 850 c and possibly as high as 1000 c and at pressures of 8 10kbar during the mid to late archaean a number of features including repeated retrograde metamorphism at 5 5 8kbar retrograde reaction textures and rimward zoning in pressure sensitive systems suggest that following peak metamorphism the granulites stabilized at a depth of 18 26 km after stabilization the granulites cooled near isobarically to temperatures of 600 700 c assuming a total crustal thickness of 35 40 km during this late archaean interval of isobaric cooling the peak metamorphic crustal thickness is estimated at 35 56 km this estimate is significantly less than the 60 70 km obtained by summing the depths of the present levels of exposure 26 34 km and the thickness of the crust presently beneath fyfe hills approxi mately 35km and is therefore consistent with independent evidence for extensive post archaean thickening of the enderby land crust

evaluation of arctic sea ice thickness simulated by arctic ocean model intercomparison project models six aomip model simulations are compared with estimates of sea ice thickness derived from pan arctic satellite freeboard measurements 2004 2008 airborne electromagnetic measurements 2001 2009 ice draft data from moored instruments in fram strait the greenland sea and the beaufort sea 1992 2008 and from submarines 1975 2000 drill hole data from the arctic basin laptev and east siberian marginal seas 1982 1986 and coastal stations 1998 2009 despite an assessment of six models that differ in numerical methods resolution domain forcing and boundary conditions the models generally overestimate the thickness of measured ice thinner than 2 m and underestimate the thickness of ice measured thicker than about 2 m in the regions of flat immobile land fast ice shallow siberian seas with depths less than 25 30 m the models generally overestimate both the total observed sea ice thickness and rates of september and october ice growth from observations by more than four times and more than one standard deviation respectively the models do not reproduce conditions of fast ice formation and growth instead the modeled fast ice is replaced with pack ice which drifts generates ridges of increasing ice thickness in addition to thermodynamic ice growth considering all observational data sets the better correlations and smaller differences from observations are from the ecco2 and uw models

temporal evolution of granitic magmas in the luanchuan metallogenic belt east qinling orogen central china implications for mo metallogenesis abstract the luanchuan metallogenic belt located within the eastern part of the qinling orogen central china hosts a number of world class mo deposits that are closely related to small late mesozoic granitic plutons zircon u pb dating of distinct plutons in the luanchuan metallogenic belt has yielded ages of 153 1 154 2 152 2 and 148 1 ma molybdenite re os isotopic compositions of yuku ore district in the southern part of luanchuan metallogenic belt has yielded an isochron age of 146 1 ma which is consistent with the large scale mineralization ages in the northern part of the luanchuan metallogenic belt a combination of previous studies and new geochronological and isotopic data show a concordant temporal and genetic link between granitic magmatism and mo mineralization in the luanchuan metallogenic belt suggesting that this mineralization episode formed the most extensive mo mineralization belt in the east qinling orogen zircon grains from mo related granitic plutons show similar trace element distributions high precision multi collector inductively coupled plasma mass spectrometry mc icp ms pb isotope analysis of k feldspar megacrysts from mineralization related granites suggest that they were derived from the lower crust similarly the pb isotopic compositions of pyrite coprecipitated with molybdenite also suggest that the metals were derived form the lower crust with probably minor mantle contribution a continuum mineralization model that describes the sourcing of mo from an evolving granitic magma over successive differentiation events possibly in separate but connected magma chambers could explain the remarkable mo enrichment in the luanchuan metallogenic belt the volatile and mo bearing granitic magmas ascended as diapirs from the deep crust and were emplaced as dikes in the upper crust lithological differences between these mo bearing granites may relate to different stages in the evolution of individual magmas finally ore forming fluids were exsolved from the granitic melts in shallow crustal magma chambers resulting in the formation of the mo deposits of the luanchuan metallogenic belt this model may account for the widespread late mesozoic mo deposits of eastern china

la icp ms trace element analysis of pyrite from the xiaoqinling gold district china implications for ore genesis abstract the xiaoqinling district the second largest gold producing district in china is located on the southern margin of the north china craton it consists of three ore belts namely the northern ore belt the middle ore belt and the southern ore belt pyrite from the dahu gold deposit in the northern ore belt and wenyu and yinxin gold deposits in the southern ore belt were investigated using a combination of ore microscopy and in situ laser ablation inductively coupled plasma mass spectrometry la icp ms a range of trace elements was analyzed including au te ag pb bi cu co ni zn mo hg as and si the results show that there are no systematic differences between the trace element compositions of pyrite in the three deposits from different ore belts in general au concentrations in pyrite are low from 2 rich ore fluids spatial association with large scale compressional structures of the qinling orogen 18 o and d data suggestive of mixing between metamorphic and meteoric waters 34 s and pb isotopic data that point to a mixed crustal mantle source all point to typical orogenic type gold deposits high ni concentrations up to 8425 ppm of pyrite possibly linked to deep seated mafic ultramafic metamorphic rocks provide further evidence on the orogenic gold deposit affinity but against the model of a granitic derivation of the mineralizing fluid as previously suggested by some workers generally low au concentration in pyrite is also consistent with those from worldwide orogenic gold deposits therefore the gold mineralization in the xiaoqinling district is described as orogenic type and is probably related to indosinian collision between the north china craton and the yangtze craton

a corundum quartz assemblage from the eastern ghats granulite belt india evidence for high p t metamorphism corundum quartz bearing assemblages occur in small lenses in granulite facies metapelites in rayagada north central part of the eastern ghats granulite belt india corundum porphyroblasts and quartz coexist with porphyroblastic almandine rich garnet hercynite spinel ilmenite and magnetite corundum and quartz are separated by sillimanite or a composite corona consisting of sillimanite and garnet whereas corundum shows sharp grain boundaries with spinel ilmenite and magnetite porphyroblastic corundum contains prismatic sillimanite inclusions in which irregularly shaped quartz is enclosed two distinct reactions are inferred from the textural features corundum quartz sillimanite and spinel quartz garnet sillimanite from the petrographical features we infer that corundum quartz garnet spinel was the peak metamorphic assemblage although large uncertainties exist regarding the positions of the respective reactions in p t space from several published experimental results and theoretical calculations a peak metamorphic condition of 12 kbar and 1100 c is estimated as the lower stability limit of the corundum quartz assemblage decompression from the peak p t condition to c 9 kbar 950 c is inferred

minor and trace elements in bornite and associated cu fe sulfides a la icp ms studybornite mineral chemistry abstract in situ laser ablation inductively coupled mass spectroscopy la icp ms has been used to provide a baseline dataset on the minor element contents in hypogene bornite and accompanying cu sulfides from 12 deposits with emphasis on syn metamorphic cu vein systems in norway and skarn porphyry and epithermal systems in se europe bornite contains significant concentrations of both ag and bi especially in the vein and skarn deposits studied and has the potential to be a major ag carrier in such ores concentrations of up to 1 wt of both elements are documented measured concentrations appear to be independent of whether discrete ag and or bi minerals are present within the analyzed sulfide where bornite and chalcocite or mixtures of cu sulfides coexist ag is preferentially partitioned into chalcocite over co existing bornite and bi is partitioned into the bornite bornite is a relatively poor host for au which mimics ag by being typically richer in coexisting chalcocite most anomalous au concentrations in bornite can be readily tracked to micron and submicron scale inclusions but bornite and chalcocite containing up to 3 and 28 ppm au in solid solution can be documented selenium and te concentrations in bornite may be as high as several thousand ppm and correlate with the abundance of selenides and tellurides within the sample selenium distributions show some promise as a vector in exploration offering the possibility to track a fluid source bornite and chalcocite are poor hosts for a range of other elements such as co ni ga and ge etc which have been reported to be commonly substituted within sulfides hypogene bornite and chalcocite may have significantly different trace element geochemical signatures from secondary supergene bornite

gold deposits in the xiaoqinling xiong ershan region qinling mountains central china the gold rich xiaoqinling xiong ershan region in eastern shaanxi and western henan provinces central china lies about 30 50 km inland of the southern margin of the north china craton more than 100 gold deposits and occurrences are concentrated in the xiaoqinling west xiaoshan middle and xiong ershan east areas late archean gneiss of the taihua group and middle proterozoic metavolcanic rocks of the xiong er group are the main host rocks for the deposits mesozoic granitoids ca 178 104 ma are present in most gold districts but deposits are typically hosted in the precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones deposits in the xiaoqinling and xiaoshan areas are best classified as orogenic gold deposits with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks alteration assemblages are dominated by quartz sericite pyrite and carbonate minerals the ore forming fluids were low salinity co2 rich and characterized by isotopically heavy 18o four deposits dongchuang wenyu yangzhaiyu and dahu in the xiaoqinling area each contain resources of about 1 moz au some of the gold deposits in the xiong ershan area represent more shallowly emplaced tellurium enriched orogenic systems which include resources of approximately 1 1 5 moz au at shanggong and beiling or tantou others are epithermal deposits e g qiyugou and dianfang that are hosted in volcanic breccia pipes isotopic dates for all gold deposits although often contradictory generally cluster between 172 99 ma and are coeval with emplacement of the post kinematic granitoids the gold deposits formed during a period of relaxation of far field compressional stresses clearly subsequent to the extensive paleozoic early mesozoic accretion of arc terranes and the yangtze craton onto the southern margin of the north china craton hydrothermal and magmatic events occurred locally where extension related precambrian basement uplifting took place along the craton margin fluids for the orogenic gold deposits in the xiaoqinling xiaoshan and xiong ershan areas may have been released from evolving magmas or resulted from prograde metamorphic reactions within the uplift zones alternatively for the epithermal gold deposits at shallower levels in the xiong ershan area gold transporting fluids were mainly exsolved from coeval magmas although meteoric water was also involved in these hydrothermal systems

in situ trace element and sulfur isotope of pyrite constrain ore genesis in the shapoling molybdenum deposit east qinling orogen china abstract the early cretaceous ca 128 ma shapoling vein type molybdenum mo mineralization associated with the huashan intrusion is a newly discovered deposit in the xiong ershan district east qinling china where pyrite is a ubiquitous mineral phase here we present results from an integrated study on the texture in situ trace element chemistry from laser ablation inductively coupled plasma mass spectrometry la icp ms and sulfur isotopic composition using secondary ion mass spectrometry sims with a view to understand the geochemical variation genesis of mo mineralization and ore forming process the distinct textural patterns as revealed by petrographic observations suggest three types of pyrites py1 is composed of coarse grained euhedral pyrite in the wall rock and early barren quartz vein at stage i py2 is represented by subhedral anhedral grains coexisting with molybdenite in quartz veins at stage ii and py3 forms irregular interstitial grains in the quartz k feldspar molybdenite dominated veins at stage iii the mo enrichment mainly occurred in py3 with co ni ratios 1 and 34s values mainly

on modeling the anisotropic failure and flow of flawed sea ice the failure and flow of sea ice on scales small and large is characterized by the propagation of oriented leads and cracks in this paper a theory for the dynamical treatment of anisotropic oriented flaws in sea ice is developed and used to examine the interaction of these oriented flaws under idealized stress forcing the essential idea of the theory is to take one or more oriented weak leads imbedded in thick ice a constitutive law for both the thin and thick ice is taken to be similar to laboratory observations which are consistent with mohr coulomb like failure application of normal continuum mechanics boundary conditions leads to anisotropic flow and failure characteristics of this anisotropic composite under both near and far field forcing the local failure characteristics show that there is a preferred orientation for failure with the intersection between leads increasing as confinement increases for spatially separated interacting flaws the theory predicts a preference for the weakening of flaws in a narrow range of angles of 10 20 relative to the principal far field stress imbedding isolated flaws leads to simulated damage directions consistent with local failure characteristics in the case where the ice is considered to have available flaws in all directions fracture propagation is found to proceed by picking out oriented flaws alternating in direction along large scale damage strikes with individual flaw alignments of 20 relative to far field principal stresses the mechanisms responsible for these results and how this anisotropic sea ice rheology might be implemented in current dynamic thermodynamic sea ice models are discussed