boudinage and composite boudinage in superposed deformations and syntectonic migmatization abstract the banded gneisses of the jasidih deoghar area of east india behaved as a complex geological multilayer which evolved through the combined effects of deformation and leucosome emplacement the early foliation and banding were transposed and retransposed by two generations of isoclinal folds the intensity of foliation development the layer thickness ratios and the rheological contrasts within the gneisses changed both in space and in time under layer normal compression these complex multilayers gave rise to a variety of boudins and of their pegmatite filled separation zones the geometrical relations with successive generations of folds can distinguish the closely associated pre f 1 syn f 1 and syn f 2 boudins d 2 boudinage occurred at an advanced stage of f 2 folding so that boudinage induced subhorizontal extension was considerably less than the total subhorizontal extension during d 2 composite boudinage occurred during progressive syntectonic leucosome emplacement in the course of which a group of boudinaged layers with a profusion of coarse quartz feldspar leucosome became more competent than the adjoining rocks and underwent boudinage as a whole

tectonic implications and morphology of trapezoidal mica grains from the sutlej section of the higher himalayan shear zone indian himalaya abstractmicroscopic trapezoidal micas are reported from the sutlej section of the higher himalayan shear zone india and are attributed to an up dip top to southwest sense of brittle shear along c planes of preexisting ductile shear dipping northeast the longest margins of these trapezoids dip northeast and are oblique to either the c planes or their enveloping planes intragrain slips along cleavages aided their thrusting while the surrounding competent quartzofeldspathic minerals resisted it the cleavages of the trapezoids are parallel to their longest margins these cleavages the longest margins the overall asymmetry of trapezoid aggregates and the trails emanating from their corners are reliable indicators of brittle shear sense trails broken from the corners of developing trapezoids define both the p and the y shear planes subcircular stacks and triangular mineral grains are also possible variations of trapezoids some of the trapezoidal micas were products of ductile brittle deformation va

a study of zn and mo attenuation by waste rock mixing in neutral mine drainage using mixed material field barrels and humidity cells abstract we studied the attenuation of mo and zn in neutral ph drainage from waste rock at the antamina mine in peru we hypothesized that mo or zn contained in leachate produced in one waste rock type can be attenuated when the mo or zn containing leachate is allowed to contact a different waste rock type we tested the hypothesis using mixed material stacked field barrels and humidity cells connected in series where leachate from a mo or zn releasing waste rock type flows through a second waste rock material type results from both the humidity cells laboratory conditions and field barrels field conditions showed the same general attenuation patterns when drainage from mo releasing waste rock flowed through pb rich black marble waste rock mo was removed from solution molybdenum attenuation was not observed when the order of the waste rock materials was reversed such that drainage from pb rich waste rock flowed through mo releasing intrusive rock geochemical modeling mla and sem analyses supported the hypothesis that wulfenite precipitation was responsible for the observed attenuation of mo zinc is shown to be removed from leachate both by contact with mo releasing intrusive rock and by contact with calcite rich grey hornfels material results from geochemical modeling in phreeqc suggested that precipitation of zn carbonate or zn hydroxide minerals could not account for the degree of zn attenuation observed in this study scanning electron microscopy suggested that zn may have been incorporated into the crystal structure of phyllosilicate clay minerals

folding of boudinaged layers abstract the boudinage structure in the vaddo area in sweden developed during an early isoclinal folding during a second deformation which deformed the axial surfaces and the limbs of the isoclinal folds the shapes of boudins were variously modified the resulting structures include folding of the individual boudins into half waves a tile like piling up of straight or gently folded boudins and arrangement of straight boudins in a herring bone pattern similar structures have been produced experimentally in soft models containing boudins of different competencies the relative importance of the different physical parameters which contribute towards the development of the various structures is examined in particular the experiments showed that when the competence contrast between the boudin and the host material was rather small the shape of the boudins was modified by a second deformation into trapezoidal forms often with flame shaped projections at the edges from an analysis of the experimental and natural structures a set of criteria has been formulated which can be used to identify structures formed by superposed deformations and to give an approximate idea of the competence contrast between the boudin and the host rock during the second deformation

composition and evolution of fluids forming the baiyinnuo er zn pb skarn deposit northeastern china insights from laser ablation icp ms study of fluid inclusions the baiyinnuo er skarn deposit is one of the largest zn pb deposits in northeastern china with 32 74 million metric tons mt resources averaging 5 44 zn 2 02 pb and 31 36 g t ag the deposit formed in three stages the preore stage prograde skarn minerals with minor magnetite the synore stage sulfides and retrograde skarn minerals including calcite and minor quartz and the postore stage late veins composed of calcite quartz fluorite and chlorite cutting the above mineral assemblages in this study we analyzed the composition of single fluid inclusions using laser ablation inductively coupled plasma mass spectrometry la icp ms to 1 determine the composition of the fluids and the evolution through the stages 2 infer the fluid and metal sources and 3 explore the metal deposition mechanisms the preore fluids trapped in pyroxene have higher homogenization temperatures 432 504 c higher salinity 36 5 46 1 wt nacl equiv and higher concentrations of zn 0 9 wt pb 1 4 wt and other elements e g na k li as rb sr cs ba cl and br than synore mineralizing fluids 370 c 10 wt nacl equiv 450 ppm zn and 290 ppm pb the postore fluids show lower temperatures 250 c and a rather dilute composition 4 wt nacl equiv 33 ppm zn and 24 ppm pb geochemically the fluids of all paragenetic stages in baiyinnuo er have magmatic signatures based on the element mass ratios including elevated k na zn na and rb na ratios lower ca k ratios and combined cl br na k ratios which are distinctively different from basinal brines inclusion fluids in preore stage show little variation in composition between 510 and 430 c indicative of a closed cooling system in contrast the major components of the syn and postore fluids including cl na and k decrease and correlate with a drop of homogenization temperatures from 370 to 200 c indicating a dilution by mixing with groundwater the baiyinnuo er mineralizing fluids trapped in sphalerite have higher ca k mass ratios avg 0 78 than other proximal magmatic hydrothermal systems 0 06 0 52 but lower than that of the distal el mochito skarn avg 6 4 probably reflecting a gradually weakened magmatic signal away from the causative intrusions the metal contents in preore fluids are significantly higher than those in synore fluids but no mineralization occurred this confirms that the early fluids were although enriched in metals not responsible for ore precipitation most likely due to their high temperature and high salinities one important factor controlling zn pb mineralization was mixing with groundwater which resulted in temperature decrease and dilution that significantly reduced the metal solubility thereby promoting metal deposition another main driving force was the interaction with carbonate wall rock that buffered the acidity generated during the breakdown of zn and pb cl complexes and the precipitation of sulfides phase separation occurred in both the preore and the early part of the synore stages but no evidence indicated that it caused metal deposition the prograde minerals and retrograde minerals including ore minerals coexisting in the same samples could have been caused by two or more successive pulses of hydrothermal fluids released from residual melts of a progressively downward crystallizing magma each fluid produced a series of proximal high temperature prograde to distal low temperature assemblages with the lower temperature assemblages of later fluids overprinting the higher temperature assemblages at most locations

the dewulu reduced au cu skarn deposit in the xiahe hezuo district west qinling orogen china implications for an intrusion related gold system abstract the triassic west qinling orogen which formed by the continental collision between the south china block and north china craton following the subduction and closure of the paleo tethyan ocean hosts numerous gold deposits that have commonly considered as products of metamorphic dehydration during the oceanic subduction and subsequent continental collision however whether or not there are gold deposits that are genetically related to regional magmatism remains poorly understood here we present mineralogical compositional and geochronological data of the dewulu au cu skarn deposit in the xiahe hezuo district to understand the ore genesis and its genetic link to many coeval sediment hosted disseminated and magmatic hosted vein gold deposits in the same district which collectively reveal a possible intrusion related gold system the dewulu au cu skarn deposit in the eastern zone of the xiahe hezuo district is associated with the early triassic i type ilmenite series dewulu quartz diorite pluton that intrudes permian marine clastic and carbonate rocks ore related hydrothermal biotite separates yield a well defined 40ar 39ar plateau age of 239 9 1 4 ma 2 which agrees with a previous zircon u pb age 238 6 1 5 ma at 2 of the dewulu quartz diorite and thus demonstrates a temporal and likely genetic link between the two both prograde and retrograde skarn assemblages are well developed in the dewulu au cu deposit prograde garnet and pyroxene are compositionally dominated by grossularite and hedenbergite respectively indicating a reduced skarn system au cu mineralization is largely represented by the arsenopyrite loellingite chalcopyrite pyrrhotite bornite assemblage and is associated with retrograde skarns gold is mostly hosted in arsenopyrite loellingite and chalcopyrite and has close textural relations with native bismuth or bismuthides mineral stability relationships and fluid inclusion microthermometric data confirm that the prograde skarns formed at a low oxygen fugacity high temperature 630 c and a depth range of 2 9 to 6 5 km arsenopyrite and chlorite geothermometers indicate that the retrograde skarns and late quartz sulfide calcite assemblages formed at 550 to 345 c and

ore genesis and hydrothermal evolution of the kendenggao er copper molybdenum deposit western tianshan evidence from isotopes s pb h o and fluid inclusions abstract the boluokenu range is one of the most important metallogenic belts in northwest china and it contains numerous fe cu mo au etc deposits the kendenggao er cu mo deposit is located in the eastern segment of the boluokenu metallogenic belt within the western tianshan orogeny skarn and cu mo orebodies occur as lamellae or lenses along the contacts between different units of the upper carboniferous dongtujinhe formation and the aimujin granitic intrusions based on field investigations and petrographic observations three main metallogenic stages of skarn formation and ore deposition have been distinguished 1 the pre ore stage is characterized by the formation of garnet wollastonite and diopside and high temperature hypersaline hydrothermal fluids with oxygen isotopic compositions that are similar to those of magmatic fluids these fluids were most likely generated by the separation of brine from the silicate melt due to the immiscibility of primary magmatic fluids that occurred at a depth of approximately 1 km with inferred lithostatic pressure conditions of 300 bars 2 the main ore stage coincides with the replacement of garnet and diopside by vesuvianite epidote sulfides and quartz the hydrothermal fluids of this stage are represented by v type vapor rich fluid inclusions that coexist with l type liquid rich inclusions the oxygen isotope 18oh2o values of the main ore stages are in a narrow range of 7 5 9 9 which indicates that the mineralization related fluid is also of magmatic origin based on the fluid inclusion and stable isotopic data it can be concluded that the ore forming fluid evolved by the boiling of the magmatic fluids that likely occurred at a depth of 1 km and hydrostatic pressure of 100 bars and that this was the predominant mechanism for the large scale precipitation in the kendenggao er cu mo deposit 3 the post ore stage is characterized by the development of calcite quartz and chlorite the fluids during this stage are represented by the l type inclusions which mainly show low salinity and low homogenization temperatures these fluids yield the lowest 18oh2o values 2 8 to 3 7 the above data indicate that the post ore stage fluids originated from the mixing of residual main ore stage fluids with various proportions of external water low salinity low temperature no boiling occurred at this stage at the low temperatures the 34s values of the sulfides range from 4 3 to 1 9 and the 206pb 204pb 207pb 204pb and 208pb 204pb values of the sulfides range from 18 220 to 18 554 15 608 to 15 812 and 38 080 to 39 055 respectively the s and pb isotopic compositions indicate that the ore materials were mainly derived from magmas taken together these geologic geochemical and isotopic data confirm that kendenggao er is a typical skarn deposit

in situ major and trace elements of garnet and scheelite in the nuri cu w mo deposit south gangdese tibet implications for mineral genesis and ore forming fluid records abstract garnet and scheelite are common hydrothermal silicate mineral and metal mineral in skarn or porphyry skarn deposits and can aid in constraining the composition of ore forming fluid based on in situ major and trace element analyses of garnet and scheelite from the nuri cu w mo deposit we discuss the factors and mechanisms controlling the incorporation of rare earth elements rees into the garnet and scheelite and investigate the associated hydrothermal fluid characteristics the garnets from the nuri deposit belong to the grossular andradite grandite solid solution series and range in composition from adr64grs34 to adr91grs8 the ree patterns of garnet are enriched in light rare earth elements lrees and depleted in heavy rare earth elements hrees the rees characteristics indicates that the incorporation of rees into the nuri garnet was controlled by the surface adsorption and element substitution in the mineral structure based on the cathodoluminescence cl images of scheelite two growth stages early and late stages are identified these two stages of scheelite belong to the scheelite powellite series and are enriched in lrees and depleted in hrees however the early scheelite exhibits negative or no eu anomalies 0 34 0 95 whereas the late scheelite presents positive eu anomalies 1 25 2 89 the mo content in the early scheelite is positively correlated with the eu value while the mo content in the late scheelite is negatively correlated with eu these characteristics indicate that the redox state of the ore forming fluid gradually changed from the oxidized state to the reduced state the preferred ree3 substitution for ca2 in the nuri scheelite is 3ca2 2ree3 ca where ca is a ca site vacancy the ree features of the scheelite are mainly controlled by the ree nature of the ore forming fluid according to the characteristics of trace elements in garnet and scheelite we suggest that the ore forming fluid of the nuri deposit is a magmatic fluid mixed with a slightly acidic external fluid chloride complexes may be the main transport ligand of the rees and the oxygen fugacity of the ore forming fluid gradually decreased

vorticity determination distribution partitioning and the heterogeneity and non steadiness of natural deformations abstract an investigation on vorticity in general heterogeneous and non steady flows is presented the bulk vorticity of a flow is solely determined by the imposed boundary conditions and it exerts no constraints on local flow the distribution of bulk vorticity in different rheological domains and the partitioning of the distributed vorticity into shear induced vorticity and spin are both time dependent this indicates that heterogeneous flows are inevitably non steady in a quantitative example it is demonstrated that even though the imposed boundary movement is a constant simple shear local flow can be non steady spinning and non coaxial super simple shear flow with internal kinematic vorticity number greater than i occurs but the finite strain does not necessarily pulsate the geological implications of this investigation are discussed the significance of heterogeneity and non steadiness in natural deformations are emphasized it is concluded that vorticity distribution and partitioning is the link between different scale structures the internal kinematic vorticity number is not a criterion of finite strain oscillation

the magmatic hydrothermal transition evidence from quartz phenocryst textures and endoskarn abundance in cu zn skarns at the empire mine idaho usa information about the magmatic to hydrothermal transition is preserved in late stage features of quartz phenocrysts and endoskarn alteration in some cu zn skarn deposits such as the empire mine in idaho important features include 1 quartz phenocrysts with strong resorption textures such as vermicular zones of igneous groundmass cutting primary quartz cathodoluminescence banding 2 anomalous amounts of endoskarn more than 50 of mineralized rock 3 high f activities as evidenced by fluorite as an accessory mineral in igneous rocks in alteration assemblages and in fluid inclusions and by high f in hydroxyl sites in igneous biotite and amphibole and 4 direct association of zn which normally is deposited distally at low temperature with cu in proximal locations and in endoskarn these features are explained by the following model 1 f lowers the solidus temperature of the magma thus changing the timing temperature and duration of hydrothermal fluid exsolution 2 upon magmatic vapor saturation the f rich hydrothermal fluids form bubbles that adhere to quartz phenocrysts and chemically corrode tunnel into the quartz forming vermicular resorption textures 3 f rich hydrothermal fluids also promote the formation of endoskarn silicic rocks are attacked by f rich fluids in the same sense that carbonate wall rocks are dissolved by weakly to moderately acidic hydrothermal fluids 4 low fluid exsolution temperature facilitated by high f activity promotes high zn cu ratios in proximal locations due to the solubility of zn relative to cu at lower temperatures this model may be applicable at other localities such as the world class cu zn skarn antamina mine as well as some tin and rapakivi granites

genesis and magmatic hydrothermal evolution of the yangla skarn cu deposit southwest china the yangla skarn cu deposit 150 mt at 1 03 cu is located in the central segment of the jinshajiang metallogenic belt within the sanjiang three rivers region southwest china skarn orebodies are mainly developed between different units of devonian carbonate and quartz sandstone rocks with stratiform like shapes or within the contact zone between granitoids and marbles re os dating of molybdenite intergrowth with chalcopyrite yielded a well constrained 187re 187os isochron age of 232 0 1 5 ma with a weighted average age of 231 8 1 3 ma both coeval with the related intrusions 233 1 1 4 and 231 0 1 6 ma at 2 by zircon u pb dating from our previously published work field and textural relationships indicate three hydrothermal stages characterized by assemblages of prograde skarn pre ore stage retrograde skarn and cu fe mo bi sulfides main ore stage and pb zn sulfides associated with calcite and quartz late ore stage as well as one supergene stage marked by secondary cu mineralization malachite and azurite skarns contain garnets with andraditic compositions ad96 gr2 3py0 1 and clinopyroxene two series hd6di94 and hd86di13jo1 with low mn fe ratios 0 1 typical of cu skarn deposits worldwide three stages of fluid evolution were observed by a detailed fluid inclusion study 1 early fluids were trapped under two phase conditions as evidenced by the coexistence of brine homogenization temperatures 560 600 c average salinity 49 4 1 7 wt nacl equiv n 33 and vapor rich inclusions in pre ore stage andradite and diopside trapped at 600 bars or a depth of approximately 2 km assuming lithostatic pressure conditions 2 main ore stage fluid inclusions in quartz were also trapped under two phase conditions boiling as identified by the coexistence of vapor and liquid rich fluid inclusions liquid rich inclusions homogenized between 312 and 389 c average 350 24 7 c n 20 with salinities of 2 4 to 5 6 wt nacl equiv average 4 2 0 9 wt nacl equiv n 13 and a depth of 2 km 200 bars hydrostatic pressure conditions 3 late ore stage fluids are represented by inclusions in calcite characterized by homogenization temperatures ranging from 220 to 290 c average 249 27 c n 14 and salinities between 2 1 and 8 0 wt nacl equiv average 4 6 1 5 wt nacl equiv n 11 sulfur isotope compositions of sulfide minerals pyrite chalcopyrite pyrrhotite and molybdenite from the main and late ore stage have a narrow range of 34s values from 1 9 to 2 6 consistent with a magmatic origin calcite in the late ore stage has 13c values ranging from 3 2 to 5 9 and 18o from 7 2 to 18 0 distinct from the host rock marble compositions 13c 1 2 4 3 18o 10 8 23 9 when corrected for temperature 250 c estimated from fluid inclusion analysis in calcites these calcite data correspond to ore fluid 13cfluid values of 2 0 to 4 6 and 18ofluid values of 0 5 to 11 2 clustering at 10 which are consistent with a magmatic origin lead isotope compositions of sulfides 206pb 204pb 18 273 18 369 207pb 204pb 15 627 15 677 and 208pb 204pb 38 445 39 611 are similar to those of the granitic intrusions and sedimentary wall rocks but distinct from those of basalts 206pb 204pb 18 282 19 133 207pb 204pb 15 564 15 665 and 208pb 204pb 38 367 38 942 in the mining area taken together these geologic geochemical and isotopic data confirm that yangla is a typical cu skarn deposit

southern hemisphere forcing of pliocene δ18o and the evolution of indo asian monsoons monsoon phase relationships consistent with direct orbital forcing across the entire indo asian region including marine and terrestrial proxies from the chinese loess plateau the south china sea and the arabian sea strong pliocene summer and winter monsoons were in phase with one another strengthened at obliquity minima and precession minima the summer monsoon was also strengthened at precession maxima yielding a semiprecession spectral signal strong pliocene monsoons at orbital extremes indicate a direct response to fast physics processes including sensible heating and cooling of the asian landmass and for the summer monsoon the export of latent heat from the southern indian ocean as northern hemisphere ice volume grew into the pleistocene the timing of strong winter and summer monsoons drifted apart becoming influenced by the combined effects of fast physics and slow physics ice volume variables the phase of strong winter monsoons shifted toward ice maxima and the phase of strong summer monsoons shifted toward ice minima

development of east asian summer monsoon environments in the late miocene radiolarian evidence from site 1143 of odp leg 184 abundant radiolarians are preserved in the relatively complete upper miocene section of odp site 1143 three radiolarian zones rn6 rn7 and rn8 are recognized on the basis of diartus petterssoni total range in rn6 6 7 ma variations in the abundance of radiolarians especially pyloniid forms radiolarian flux and species diversity are good proxies of upwelling which similar to today s was likely driven by summer monsoons these radiolarian paleomonsoon proxies indicate that the east asian summer monsoon first initiated close to the middle late miocene boundary at similar to 12 11 ma and reached a maximum strength at similar to 8 24 ma therefore the initiation of the east asian summer monsoon was likely earlier than the first indian monsoon which appeared similar to 8 myr ago c 2003 elsevier b v all rights reserved

short wavelength infrared swir spectroscopy of phyllosilicate minerals from the tonglushan cu au fe deposit eastern china new exploration indicators for concealed skarn orebodies abstract the middle lower yangtze river metallogenic belt mlyrb is one of the most important cu au fe mo skarn porphyry metallogenic belts in eastern china after several decades of mining the shallow level mineral resources have been gradually exhausted which call for new exploration tools for concealed orebodies the tonglushan cu au fe skarn deposit 86 3 mt 1 66 cu 0 94 g t au and 39 4 fe is located in the western mlyrb skarn alteration mineralization are mainly hosted in the contact zone between cretaceous 141 ma quartz monzodiorite and its porphyry and the lower triassic carbonate rocks based on the mineral assemblages and their macro microscopic textural relationships the tonglushan cu au fe mineralization alteration can be divided into five stages pre ore s1 skarn potassic alteration fe ore s2 retrograde alteration and fe oxides cu au ore s3 quartz sulfides carbonate alteration s4 and supergene alteration s5 apart from the major skarn and retrograde alteration and carbonate minerals abundant fine grained phyllosilicate minerals including chlorite white mica illite muscovite and phengite smectite montmorillonite and saponite and kandite kaolinite dickite and halloysite group minerals have been identified at tonglushan by swir spectrometry integrating petrographic observations and swir spectral analysis four alteration zones with distinct phyllosilicate assemblages have been distinguished from the intrusion outward i ore barren quartz monzodiorite and its porphyry montmorillonite illite chlorite ii endoskarn close to the skarn hydrothermal mineralization center montmorillonite illite chlorite kaolinite dickite iii skarn hydrothermal mineralization center saponite chlorite and iv the external contact zone in dolomitic marble montmorillonite chlorite kaolinite dickite for the tonglushan altered rock samples swir spectrometry has identified wavelength shifts in the fe oh al oh and sub al oh absorption features of chlorite white mica montmorillonite and kandite respectively chlorite fe oh absorption occurs at longer wavelengths 2 250 nm white mica montmorillonite al oh absorption occurs at unusually long 2 212 nm and short 2 170 nm in strongly altered skarn proximal samples moreover the presence of kaolinite dickite saponite actinolite phlogopite and or chlorite quartz sulfides veins in these samples can be used as new vectors to explore deep level mineralization centers at tonglushan the distribution of various kinds of phyllosilicate alteration minerals at tonglushan especially the white mica and kandites with higher crystallinity in the deep contact zones indicates that the neutral to acidic hydrothermal fluids may have been generated with the precipitation of fe oxides and sulfides this study also highlights the potential of swir spectroscopy of phyllosilicate minerals for exploring concealed skarn orebodies in the mlyrb

tracking fluid sources for skarn formation using scapolite geochemistry an example from the jinshandian iron skarn deposit eastern china scapolite occurs as the major halogen bearing phase at all paragenetic stages of skarn formation and mineralization in the jinshandian iron skarn deposit eastern china here we integrate geochemical characteristics of scapolite with in situ b and sr isotopes of associated tourmaline and fluorapatite respectively to trace the sources and evolution of the fluids responsible for mineralization in this deposit pre ore stage i scapolite has molar cl br ratios ranging from 920 to 2200 which together with the boron isotope composition of pre ore stage i tourmaline are consistent with formation from magmatic fluids from the jinshandian intrusion in contrast scapolite in syn and post ore stages ii and iii has significantly higher cl br ratios 2900 6200 that are outside the range of magmatic fluids but are consistent with involvement of fluids derived from the halite bearing evaporite horizons that lie within regionally extensive sedimentary country rocks the influx of sedimentary derived fluids is also consistent with 87sr 86sr of syn ore stages ii fluorapatite 0 7098 0 7109 which are significantly higher than those of the skarn related quartz diorite intrusions 0 7058 0 7061 but approach the isotopic compositions of the middle triassic evaporites and other continental sedimentary country rocks these data indicate that evaporite sourced fluids were involved in iron ore formation at the jinshandian deposit and may be important for the formations of other iron ore deposits our findings also show that scapolite halogen geochemistry in combination with other fluid tracers such as b and sr isotopes can be extremely useful for identifying the origins and evolution of fluids in magmatic hydrothermal systems

ore genesis and hydrothermal evolution of the baiyinnuo er zinc lead skarn deposit northeast china evidence from isotopes s pb and fluid inclusions the baiyinnuo er zinc lead deposit 32 74 mt at 5 44 zn 2 02 pb and 31 36 g t ag located in the south segment of the great xing an range is the largest zn pb deposit in northern china skarn and orebodies mainly occur between the different units of the huanggangliang formation or within the contact zone between the intrusions and permian marble several phases of igneous rocks exposed within the mining areas and among them the yanshanian plutonic rocks which intruded into limestone of the early permian huanggangliang formation are interpreted to be the source of ore since their pb isotope compositions 206pb 204pb 18 25 18 35 207pb 204pb 15 50 15 56 and 208pb 204pb 38 14 38 32 are highly consistent with the sulfides including sphalerite galena and chalcopyrite 206pb 204pb 18 23 18 37 207pb 204pb 15 47 15 62 and 208pb 204pb 37 93 38 44 sulfur isotope values of the sulfides give a narrow 34s interval of 6 1 to 4 6 mean 5 4 n 15 suggesting the ore forming fluid is of magmatic origin three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observation which are the preore stage garnet clinpyroxene wollastonite magnetite sulfides the synore stage sulfides epidote quartz calcite garnet and the postore stage calcite chlorite quartz fluorite several fluid evolution episodes can be inferred from microthermometric results at the baiyinnuo er zn pb deposit 1 immiscibility preore stage coexistence of halite bearing brine inclusions s1 type 44 wt nacl equiv and vapor rich fluid inclusions v type sharing the same homogenization temperatures 470 c confirms that fluid unmixing occurred under lithostatic pressures of 400 bars 1 5 km and the brine is considered to account for most prograde skarn minerals e g clinopyroxene 2 overpressure trapping preore stage brine inclusions homogenized by halite dissolution s2 type postdated the immiscible assemblages this type of inclusions is characterized by high but variable minimum trapping pressures 150 3 000 bars relative to s1 type inclusions and can be explained as a result of entrapment under overpressuring condition 3 boiling the presence of both vapor and liquid inclusions i e v and l type in the same assemblages within synore stage quartz calcite and sphalerite indicates the occurrence of fluid boiling 350 c at hydrostatic pressures of 150 bars and depth of 1 5 km which resulted in large scale mineralization in the baiyinnuo er zn pb deposit 4 mixing with external fluids fluid inclusions scattered within postore stage calcite or secondary trails in synore stage minerals show low homogenization temperatures 260 c and both decreasing for l type and increasing for cacl2 bearing inclusions i e lc type trends for salinities as homogenization temperatures decrease implying addition of both meteoric water low temperature low salinity and basinal brines low temperature ca rich respectively systematic fluid inclusion studies also indicate that the mineralization related fluid is of magmatic origin prograde minerals formed during the preore stage fluid immiscibility while sulfides deposition occurred during the synore stage fluid boiling mixing with external fluids began as the hydrothermal system cooled to 300 c when the main metal precipitation process had ended

high resolution elemental records from the south china sea and their paleoproductivity implications 1 the biogenic related elements ca sr ba p cd scavenged al and ti were analyzed by inductively coupled plasma mass spectrometry icp ms and inductively coupled plasma atomic emission spectrometry icp aes for core ns93 5 from the west slope of the south china sea terrestrial input as estimated from the accumulation of ti was higher during glacials than during interglacials carbonate accumulation rates are inversely related to those of terrestrial input suggesting higher production of calcareous phytoplankton during interglacials the accumulation patterns of authigenic sr ba p and cd match that of carbonate further indicating higher calcareous phytoplankton production during interglacials scavenged al and excess sio2 which is related to biogenic opal exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input this indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production as calcareous phytoplankton is the dominant component of the biogenic sediments in the south china sea particularly during interglacials previous inference of higher productivity in the south china sea during glacials based on only the biogenic opal proxy needs to be reconsidered

hydrothermal evolution and ore genesis of the beiya giant au polymetallic deposit western yunnan china evidence from fluid inclusions and h o s pb isotopes abstract the beiya porphyry skarn gold polymetallic deposit is one of the largest gold deposits in china and also contains significant amounts of silver and base metals the estimated reserve at the end of 2015 was 130 million metric tonnes mt of ores grading 2 42 g t au 0 48 wt cu 25 5 wt fe 38 85 g t ag 1 24 wt pb and 0 53 wt zn the deposit is located in the jinshajiang ailaoshan porphyry skarn cu mo au metallogenic belt in western yunnan province southwest china skarn alteration and mineralization are spatially and temporally associated with eocene monzogranite porphyries which were emplaced into triassic carbonates field evidence and petrographic observations indicate there are four stages of hydrothermal activity i e prograde stage i iron oxide stage ii sulfide stage iii and carbonate stage stage iv stage i is characterized by the formation of garnet and pyroxene by high temperature 398 560 c hypersaline 48 81 67 24 wt nacl equiv hydrothermal fluids with h o isotopic compositions that are similar to typical magmatic fluids these fluids were most likely generated by the separation of brine from a silicate melt in stage ii garnet and pyroxene was replaced by epidote amphibole chlorite quartz and magnetite associated hydrothermal fluids are preserved in coexisting l type and v type fluid inclusions and are characterized by anomalously low d values approximately 80 and lower 18 o than stage i fluids the decrease in ore fluid 18 o h2o values with time coincided with marked decreases in fluid salinity and temperature based on the fluid inclusion and stable isotopic data we suggest that the ore fluid evolved by boiling of the magmatic brine stage iii is characterized by the development of pyrite chalcopyrite galena and sphalerite fluids inclusions associated with stage iii display and continuous range of salinities with the majority being low salinity inclusions 1 28 3 54 wt nacl equiv these fluids yield lower 18 o h2o values 0 85 to 5 52 and moderate d values 78 6 to 88 6 altogether these data indicate that stage iii fluids originated from the mixing of residual stage ii fluids with meteoric water the sulfur isotope 34 s values of stage iii sulfides cover a narrow range of 4 2 to 1 2 mean 1 1 and boiling also occurred at low temperatures 165 347 c during stage iii in stage iv only l type fluid inclusions are present which yielded the lowest homogenization temperatures 157 272 c and the lowest salinities 1 06 12 20 wt nacl equiv the h o isotope data indicate that the ore forming fluids were dominated by magmatic water in stage i and stage ii and that the magmatic water gradually mixed with circulating meteoric water during stage iii and stage iv this conclusion is further supported by the isotopic composition of lead of the ores which is similar to that of the monzogranite porphyries but differs significantly from permian basalts and triassic wall rocks

garnets in porphyry skarn systems a la icp ms fluid inclusion and stable isotope study of garnets from the hongniu hongshan copper deposit zhongdian area nw yunnan province china abstract the late cretaceous hongniu hongshan porphyry skarn copper deposit is located in the zhongdian area of northwestern yunnan province china garnets from the deposit have compositions that range from adr14grs86 to almost pure andradite adr98grs2 and display two different styles of zoning the garnets are predominantly of magmatic hydrothermal origin as is evidenced by their 18ofluid 5 4 6 9 and low dfluid 142 to 100 values both of which likely result from late stage magmatic open system degassing three generations of garnet have been identified in this deposit 1 al rich garnets grt i adr22 57grs78 43 are anisotropic have sector dodecahedral twinning are slightly enriched in light rare earth elements lrees compared with the heavy rare earth elements hrees have negative or negligible eu anomalies and contain high concentrations of f fluid inclusions within these al rich garnets generally have salinities of 12 39 wt nacl eq and have liquid vapor homogenization temperatures th of 272 331 c the grt i are most likely associated with low to medium salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low w r water rock ratios these garnets formed as a result of the high f activity of the system which increased the solubility of al within the magmato hydrothermal fluids in the system 2 fe rich garnets adr75 98grs25 2 have trapezohedral faces and are both anisotropic with oscillatory zoning and isotropic these second generation fe rich garnets grt ii have high ree concentrations are lree enriched and hree depleted and generally have positive but variable eu anomalies all of the fe rich garnets contain high salinity fluid inclusions with multiple daughter minerals with salinities of 33 80 wt nacl eq some of them show higher temperatures of halite dissolution 465 591 c than liquid vapor homogenization temperatures 319 473 c and several fe rich garnets contain inclusion groups indicative of boiling the grt ii are associated with high temperature hypersaline fluids that were segregated from magma at a depth of at least 5 6 km and reacted with carbonates at depths shallower than 2 0 km 3 al rich garnet veins adr14 60grs86 40 contain allotriomorphic crystals have lower hfse high field strength element and ree concentrations than the other garnets and have hree enriched and lree depleted patterns with small eu anomalies that are typical of the majority of garnets the grt iii most likely formed from residual metasomatic fluids

coeval boudinage and folding of oblique single layers under coaxial plane strain layer rotation around the principal stretching axis x abstract we carried out scaled analogue modelling to show the influence of varying layer obliquity on the geometry of single layer folds and boudins which developed simultaneously under coaxial plane strain the initial angle z i between the competent layer and the shortening axis z was gradually changed by turning the layer around the principal stretching axis x although oblique layer rotation was similar fast like that of a corresponding passive plane each layer was crossing different strain fields shortening reduced shortening elongation resulting in coeval boudinage and f1 folding the latter with fold axes parallel to x a rise in z i led to increase of boudinage and decrease of f1 folding the amplitude of f1 folds increased with viscosity ratio between layer and matrix but was hardly affected by z i the arc and wavelength of f1 folds on the other hand increased if z i 45 in cases of low viscosity ratio between layer and matrix boudins were affected by f2 folds with axes subperpendicular to the layer both f1 and f2 folds show increasing interlimb angles at rising z i the structures of the present study are largely not cylindrical and require investigation in three dimensions they are frequent in high pressure low temperature metamorphic rocks of subduction zone settings and in salt walls

development of concave face boudin in chhotanagpur granite gneiss complex of jasidih deoghar area eastern india insight from finite element modeling abstract with the help of 2d finite element modeling the present study analyses the role of syntectonic migmatisation on the development of concave face boudins within amphibolite dykes in chhotanagpur granite gneiss complex of jasidih deoghar area eastern india amphibolitic bands embedded in quartzofeldspathic gneiss show concave face boudins with varied face geometries resulted due to rheological changes during syntectonic migmatisation detailed study reveals that due to couple effect of h 2 o infiltration and potassium k metasomatism associated with the invasion of pegmatitic fluid pyroxene converted to amphibole and later to biotite at the marginal part of the amphibolitic bands and especially near the separation zone of boudin in this study three types of models are prepared to simulate three different patterns of syntectonic rheological changes that can best explain the features observed in the field type i is a symmetric rim model representing equal amount of rheological changes in all directions of a rectangular boudin object other two are asymmetric rim models type ii and type iii with different amount of rheological changes along length and width of the boudin block the analysis also takes into account the effects of rate of syntectonic rheological changes d the study reveals that the pattern and rate of rheological changes have strong influences on the development of concave face boudin type i model produces barrel shaped fish mouth boudin with extremely sharp corners whereas type iii model produces more lensoid shape with relatively tighter fish mouth for all types of model u shaped concave face boudin develops at lower rate of rheological changes and the face geometry gradually transforms to v shape with increasing the rate the progressive change of face curvature fc exterior curvature ec and aspect ratio ar depends on the timing of rheological inversion during progressive deformation

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

garnet and scheelite as indicators of multi stage tungsten mineralization in the huangshaping deposit southern hunan province china abstract the huangshaping w mo pb zn deposit in southern hunan province south china contains multiple generations of garnet and scheelite in skarn and sulfide carbonate altered rocks optical characteristics and chondrite normalized rare earth element reen patterns obtained by in situ laser ablation inductively coupled plasma mass spectrometry analysis were used to distinguish different generations of garnet and scheelite these data show a clear correspondence of garnet reen patterns to major element zonation with hrees e g gd lu being depleted overall coarse grained garnets in the huangshaping deposit have extreme hree depletions and significant lree e g la eu enrichment particularly for ce pr and nd this indicates that rees in these garnets are the result of coupled substitutions ca2 viii 1 ree3 viii 1 and fe2 iv 1 al3 iv 1 medium grained garnets have reen patterns showing significant lree enrichment and depleted hrees with high sn contents this suggests that substitution of rees in these garnets occurs as ca2 viii 1 ree3 viii 1 sn4 iv 1 al3 iv 1 the fact that medium grained garnets have high sn contents indicates mineralizing fluids were oxidizing which is consistent with significant positive eu anomalies however hump shaped reen patterns for garnet rims suggest substitution by ca2 viii 2 na viii 1 ree3 viii 1 where nd tb are preferentially incorporated into the garnet lattice over other rees group 1a scheelite has black cores in cathodoluminescence images and reen patterns showing extreme lree enrichment and hree depletion group 1b scheelite has cores with fine oscillatory zoning and enriched lrees with depleted hrees similar to the reen patterns of group 2a scheelite that occur as rims with bright cl surrounding both group 1a and 1b scheelite the substitution mechanism for rees in these three types of scheelite is ca2 viii 3 viii 1 ree3 viii 2 with being a ca site vacancy the influence of ree speciation in the hydrothermal fluid dominates the reen patterns of these types of scheelite however for group 2b bright rims of scheelite rees are incorporated as ca2 viii 2 na viii 1 ree3 viii 1 similar to the garnet rims finally scheelite mo contents and eu values that decrease from group 1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids ratios of y ho and mo contents that decrease from group 1a and 1b to group 2a and 2b scheelites are similar to those in porphyry related skarn w mo and quartz vein au w deposits respectively our studies also suggest that all these scheelites in this deposit formed from magmatic fluids at the huangshaping deposit medium grained garnets associated with group 1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism as indicated by their complementary y ho ratios paragentically younger scheelite particularly group 2b may have formed from dilute magmatic fluids that underwent large scale hydrothermal circulation the characteristics of group 1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic huangshaping deposit

magmatic hydrothermal evolution of the anjerd cu skarn deposit nw iran perspectives on mineral chemistry fluid inclusions and stable isotopes abstract the anjerd cu skarn deposit is located 40 km north of ahar nw iran which comprises three different stages of skarn type mineralization and metasomatic alteration including i prograde ii early retrograde and iii late retrograde prograde stage is identified by garnet as andradite grossularite and diopsidic pyroxene crystallization whereas retrograde stage overprinted the prograde skarn and is predominantly composed of tremolite actinolite quartz epidote and chlorite metasomatic alteration started with generation and evolution of the mineralizing fluids in the shayvar batholith followed by the fluids ascending into fractures of the skarn in the metamorphic zone subsequently retrograde alteration continued to the end of the skarnification process based on mineral chemistry studies garnet is dominated by andradite 27 78 mol and grossularite 20 67 mol compositions and pyroxenes by diopside 65 98 mol and hedenbergite 2 34 mol compositions based on detailed petrography studies three types of fluid inclusions were recognized including two phase liquid rich lv vapor rich vl and three phase lvs inclusions the characteristic of the mineralizing fluids during the skarn evolution was changed significantly from early retrograde stage with i high temperature up to 460 c and high salinity up to 39 wt nacl equiv through late retrograde stage with ii moderate to high temperature 334 to 446 c and low salinity 0 3 to 0 8 wt nacl equiv iii low to moderate temperature 158 to 362 c and moderate salinity 1 7 to 12 3 wt nacl equiv suggesting that high temperature and moderately saline fluids are indicative of a magmatic source within the minerals belonging to the prograde skarn while the fluids with lower temperature and low to moderate salinity indicating a meteoric source for the retrograde skarn assemblage the 18o values for prograde garnet and magnetite vary from 0 to 8 2 whereas 18o and d values for retrograde calc silicates in equilibrium with fluid including epidote range from 6 7 to 9 2 and 10 2 to 31 4 and for chlorite range from 1 9 to 2 7 and 37 5 to 48 1 respectively pointing out that mixing of magmatic fluids with meteoric water in the retrograde alteration moreover the 34s values of pyrite and chalcopyrite 3 6 and 4 9 suggesting a magmatic source for sulfur which was largely responsible for the mineralization in the anjerd deposit

phase equilibria of a be u and f enriched vitrophyre from spor mountain utah abstract the equilibrium melting relations of a vitrophyre representative of topaz rhyolites have been experimentally determined in order to constrain the pre eruption temperature and h2o content of topaz rhyolite magmas the vitrophyre sample is strongly enriched in f and incompatible elements and consists of approximately 70 unaltered volcanic glass and 30 crystals of biotite quartz sanidine plagioclase magmatic fluorite and a variety of accessory phases biotite stability is strongly dependent on temperature pressure and ah2o in the melt and is apparently independent of the variations in o2 over the range investigated in this study the thermal stability of biotite increases relative to that of quartz sanidine and plagioclase in water saturated melts as pressure increases from 1 2 to 2 kbar fluorite is stable to temperatures below but within 50 to 75 c of the biotite stability curve and topaz is present in the products of runs at and near the solidus for all fluid conditions investigated the 1 2 wt f in the vitrophyre results in very low solidus temperatures of 525 c for all fluid conditions studied comparison of the experimentally determined crystallization sequence of the vitrophyre with the observed crystallization sequence of the vitrophyre and of the overlying topaz rhyolites indicates that the phenocrysts in the vitrophyre and in the topaz rhyolites crystallized at a pressure 1 kb that the magma contained at least 4 wt water during initial crystallization of biotite and that the magma contained a pre eruption water content of 5 wt

genesis of the weibao banded skarn pb zn deposit qimantagh xinjiang insights from skarn mineralogy and muscovite 40ar 39ar dating abstract the weibao pb zn deposit is located in the qimantagh area xinjiang nw china at weibao stratiform pb zn ore bodies are hosted by the skarn altered mesoproterozoic langyashan formation both of the skarn rocks and pb zn ores are banded the skarn bands are normally 0 5 to 5 cm wide and comprise alternating garnet and pyroxene zones systematic mineralogical studies indicate that the weibao banded skarn was formed by infiltrative metasomatism of magmatic fluids in a disequilibriated geochemical system rather than by the bimetasomatism between marble and si al units or the metamorphism of calc silicate rich submarine exhalative beds this infiltrative metasomatic process can be further divided into four stages namely the prograde skarn retrograde skarn sulfide and carbonate stage three garnet types garnet i ii and iii and two pyroxene types pyroxene i and ii have been identified at weibao garnet i has commonly fe rich core and al rich rim ad 34 gr 65 to ad 96 gr 3 while garnet ii has a wider composition range ad 23 gr 73 to ad 97 gr 2 average ad 59 gr 41 garnet iii is compositionally more homogeneous and mn rich ad 17 sp 3 gr 80 to ad 55 sp 6 gr 39 average ad 47 sp 4 gr 49 pyroxene i is diopside rich hd 20 jo 1 di 79 to hd 36 jo 2 di 62 average hd 29 jo 1 di 70 while pyroxene ii has lower diopside component hd 34 jo 3 di 63 to hd 55 jo 13 di 32 average hd 48 jo 5 di 47 garnet i and pyroxene i may have formed by a small volume of high temperature and volatile rich fluids exsolved from the magmas at its initial crystallization stage further fractionation generated abundant magmatic fluids that reacted with the impure carbonates through infiltrative metasomatism forming garnet ii and pyroxene ii in the banded skarn garnet iii occurs as garnet sphalerite galena calcite veinlets crosscutting the early stage pyroxene and garnet zones and may have been a product of late hydrothermal superimposition sulfide stage is the main ore forming stage at weibao sulfide minerals in this stage precipitated mainly through replacing anhydrous e g pyroxene and hydrous e g amphibole minerals or as interstitials among early formed minerals a minor amount of the sulfides also occurs as sulfide veins the sulfide precipitation may have been controlled chiefly by physicochemical changes of ore forming fluids and the characteristics of early formed skarn minerals specifically hydrothermal replacement of skarn minerals has provided the space for sulfide to precipitate and thus controlled their distribution and further shaped the mineralization into a banded structure 40 ar 39 ar dating of the syn mineralization muscovite yielded a late triassic age ca 226 ma which was coeval to the massive post collisional intermediate felsic granitoids emplacement in the qimantagh area magmatic fluids evolved from these intermediate felsic granitoids have induced the regional scale magmatic hydrothermal mineralization including that at weibao

ore genesis of the duotoushan fe cu deposit eastern tianshan nw china constraints from ore geology mineral geochemistry fluid inclusion and stable isotopes abstract the duotoushan fe cu deposit is located in the western segment of the aqishan yamansu metallogenic belt in eastern tianshan xinjiang china magnetite orebodies are mainly developed in the upper carboniferous volcano sedimentary rocks and are mostly stratabound pyrite re os dating has yielded an isochron age of 312 24 ma mswd 1 5 five hydrothermal and one supergene alteration mineralization stages have been recognized from the spatial distribution of alteration zoning mineral assemblages and textural relationships the earliest alteration of albite ab84 98or2 16 amphibole was related to the nearby albitization granite porphyry prograde alteration was developed on the footwall of the intermediate mafic volcanic rocks and formed a garnet ad60 95gr5 40 clinopyroxene hd0di93jo7 to hd10di83jo7 assemblage alteration associated with magnetite can be further divided into three sub stages consisting of magnetite amphibole titanite stage iii a magnetite amphibole epidote stage iii b and epidote magnetite quartz amphibole titanite pyrite stage iii c mineral assemblages the secondary amphibole is dominantly actinolite pyrite with minor chlorite chalcopyrite veins cut the magnetite ore followed by later quartz calcite hematite veinlets based on fluid inclusions fis and stable isotopes studies the pre ore stage stage ii was formed at high temperature 500 c and originated from magmatic hydrothermal fluids 18 o h 2 o 7 1 d h 2 o 85 two garnet samples have similar 18 o h 2 o values 5 6 and 6 4 but considerably lower d h 2 o values 134 and 139 indicating the overprinting by late meteoric water iron ore and hydrous minerals assemblages and the associated fluids had overprinted the early anhydrous minerals early magnetite mineralization stage stage iii a shows clear magmatic water input as constrained from the 18 o h 2 o 6 9 to 7 8 and d h 2 o 85 to 72 values later magnetite stage was magmatic hydrothermal fluid dominated but with mixing of heavy d h 2 o as indicated by stable isotope compositions 18 o h 2 o 6 1 to 7 8 d h 2 o 47 to 32 sulfur isotope values of the stage iv pyrite give a 34s interval of 8 8 to 12 1 suggesting significant addition of external basin fluid seawater or evaporite sulfur source to magmatic fluid the low temperatures 83 213 c average 135 c generally medium high but variable salinities 9 9 27 2 wt nacl equiv average 21 3 wt and ca mg rich components of stage v fluids show clear features of involvement of basinal brines seawater and minor meteoric water in the late hydrothermal stages we infer that the temperature drop of the hydrothermal fluids may have been the main cause of massive magnetite precipitation at the duotoushan deposit whereas increasing ph values decreasing temperature and fluid mixing maybe responsible for cu precipitation ore deposit geology mineral geochemistry and fluid evolution confirm that the duotoushan fe cu deposit is different from typical skarns and may represent a distinct group of fe cu deposits formed during the aqishan yamansu back intra arc basin inversion which show many similarities with the central andean iocg deposits

the empire cu zn mine idaho exploration implications of unusual skarn features related to high fluorine activity the empire cu zn skarn deposit is unusual because of the proximal position of zn mineralization abundance of endoskarn and the extremely vermicular texture of quartz phenocrysts in the related intrusive rocks cu zn skarn occurs at the contact between upper mississippian white knob limestone and the granite porphyry phase of the mackay stock which consists from early to late of quartz monzodiorite granophyre granite porphyry porphyritic granite and many dikes the late phases have high f and also extremely vermicular quartz phenocrysts endoskarn is more abundant than exoskarn the earliest alteration of the intrusive rocks consists of disseminated diopsidic pyroxene di64hd36 to di88hd12 actinolite and titanite this assemblage was cut by early scapolite me18 to me35 mostly me18 26 and or green pyroxene di14hd80 to di20hd77 veinlets with or without wollastonite halos these early veins were then cut by main stage endoskarn veins that typically have a garnet minor pyroxene inner zone a wollastonite and or pyroxene ca rich plagioclase an56 to an89 envelope and a halo containing disseminated fine grained alteration minerals of the same assemblage as the envelope some veins contain only the envelope assemblage and are interpreted to represent the alteration front the inner zone locally contains vesuvianite where many veins intersect endoskarn is massive pyroxene is zoned around fluid conduits the distal pyroxene is fe rich hedenbergitic whereas the proximal pyroxene is fe poor diopsidic the garnet changes in the opposite way being fe poor al rich grossularitic in locations distal to the fluid conduits and fe rich andraditic in proximal locations in contrast in the exoskarn all pyroxene is diopsidic and garnet is andraditic weak retrograde alteration composed of quartz calcite chlorite with minor fluorite talc and epidote overprinted both endoskarn and exoskarn magnetite precipitated after garnet pyroxene in both endoskarn and exoskarn sphalerite precipitated together with chalcopyrite in proximal locations and is associated with retrograde alteration other ore minerals include minor molybdenite bornite pyrite galena arsenopyrite native au as well as supergene minerals such as chrysocolla malachite azurite native cu and limonite fluid xenoliths from pyroxene in early endoskarn veinlets homogenize at 600 c massive endoskarn and exoskarn replacing limestone inclusions in granite porphyry formed at 500 to 700 c whereas the highest temperature inclusions 700 c occur in narrow garnet minor pyroxene veins fluid inclusions in exoskarn replacing wall rock have homogenization temperatures of 500 to 650 c retrograde alteration and cu zn mineralization occurred at 250 to 300 c fluid inclusions in prograde minerals contain daughter minerals whereas fluid inclusions in retrograde minerals do not indicating a decrease in salinity with time late stage fluids have low eutectic temperatures indicating the possible presence of kcl nacl fecl2 cacl2 mgcl2 k2co3 and or na2co3 formation of the unusually abundant endoskarn the proximal position of zn mineralization and the extremely vermicular texture of quartz phenocrysts are all believed to have been promoted by the high f content of the magmatic fluid these features may serve as exploration indicators of associated high f mineralization such as buried porphyry mo deposits

an oxygen hydrogen sulfur and carbon isotope study of carbonate replacement skarn tin deposits of the dachang tin field china the dachang tin field located in guangxi province of southern china is one of the largest in the world it comprises the changpo bali and longtaoshan carbonate replacement tin deposits and the lamo cu zn skarn deposit these deposits are hosted by devonian carbonate rich sedimentary rocks which have been metamorphosed to calc silicate skarn and marble near the contact of the longxianggei granite calculated delta 18 o sub h 2 o values of the hydrothermal fluids in equilibrium with quartz cassiterite and calcite are 10 6 and 11 6 9 1 to 10 2 and 7 5 to 9 8 per mil respectively measured delta d values of fluid inclusion waters in cassiterite and calcite are 115 and 120 and 73 to 93 per mil respectively the decrease in the calculated delta 18 o sub h 2 o values from 11 6 to 7 5 per mil is attributed to increase in the co 2 content of the hydrothermal fluids the low delta d values of fluid inclusion waters in cassiterite may be the result of decreasing ch 4 co 2 as the originally magmatic fluid migrated from reducing conditions in carbonaceous black shale to oxidizing conditions in pure limestone oxygen and hydrogen isotope data indicate that the hydrothermal fluid was derived from the longxianggei granite variations in delta 13 c and delta 18 o values of calcite in orebodies altered limestone and marble are due to continuous isotopic exchange reaction between magmatic fluid and carbonate rocks at variable water to rock ratios between 300 degrees to 600 degrees c sulfur isotope data indicate that host rocks controlled the variations in sulfur isotope compositions of sulfide minerals in different deposits of the tin field with significant contribution of sulfur from magmatic fluids

kinematics of constant arc length folding for different fold shapes abstract basic mathematical functions are applied for the two dimensional geometrical and kinematical analysis of different fold shapes relationships between different fold parameters are established and related to the bulk shortening taking place during folding under upper crustal conditions the bulk shortening taking place during constant arc length folding is mathematically related to the bulk shortening during homogenous pure shear using a particular aspect ratio which is for folding the ratio of amplitude to half wavelength and for pure shear the ratio of vertical to horizontal length of the deformed initially square body the evolution of the fold aspect ratio with bulk shortening is similar for a wide range of fold shapes and indicates that the fold aspect ratio allows a good estimate of the bulk shortening the change of the geometry of individual layers across a multilayer sequence in disharmonic folding indicates a specific kinematics of multilayer folding referred to here as wrap folding which does not require significant flexural slip nor flexural flow the kinematic analysis indicates that there is a critical value for constant arc length folding between shortening values of 30 40 depending on the fold geometry for shortening values smaller than the critical value limb rotation and fold amplitude growth are dominating for shortening larger than this value faulting boudinage and foliation development are likely the dominating deformation process during continued shortening the kinematical analysis of constant arc length folding can be used for estimating the bulk shortening taking place during multilayer folding which is an important component of the deformation of crustal rocks during the early history of shortening the bulk shortening is estimated for a natural multilayer detachment fold and the shortening estimates based on the kinematic analysis are compared and supported by numerical finite element simulations of multilayer detachment folding in power law materials

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

stable isotope and fluid inclusion constraints on the source and evolution of ore fluids in the hongniu hongshan cu skarn deposit yunnan province china the hongniu hongshan cu skarn deposit 77 8 mt at 1 8 cu is located in the central part of the zhongdian porphyry and skarn cu belt in southwestern china skarn and orebodies occur mainly between the different units of the upper triassic qugasi formation or within altered limestone adjacent to late cretaceous intrusions 78 76 ma three main paragenetic stages of skarn formation and ore deposition have been recognized on the basis of petrographic observations 1 pre ore stage hornfels with diopside di87 72hd12 7 small scale endoskarn with reddish grossular adr22 57gr78 43 diopside di83 92hd7 15 vesuvianite and abundant exoskarn with red brown andradite adr75 98gr2 22 sahlite di28 41hd58 71 and wollastonite 2 syn ore stage retrograde minerals sulfides pyrite chalcopyrite pyrrhotite molybdenite galena and sphalerite quartz and calcite and 3 post ore stage calcite veins sulfur isotope values of sulfides are relatively high with an average 34s 4 9 n 40 suggesting that the ore forming fluid was magmatic and that the sulfides precipitated from a relatively reducing ore fluid the coexistence of silicate melt and primary fluid inclusions in quartz phenocrysts of the mineralization related quartz monzonite porphyry indicates the simultaneous entrapment of fluid and melt and records the process of the aqueous fluid exsolving from the crystallizing melt the initial single phase fluid has a salinity of 8 8 to 12 7 wt nacl equiv and homogenization temperatures of 566 to 650 c corresponding to pressures of 680 to 940 bar and lithostatic depth of 2 5 to 3 5 km the primary fluid inclusions in the pre ore stage garnet and pyroxene composed of coeval vapor rich v type and halite bearing s i and s ii types containing sylvite inclusions 32 79 total wt salts share similar homogenization temperatures 450 550 c indicative of the occurrence of fluid unmixing under lithostatic pressures of 550 to 780 bar 2 0 km depth primary fluid inclusions trapped in syn ore quartz calcite and epidote show the common development of s type inclusions 37 3 wt nacl equiv with coexisting v type liquid rich l type and co2 bearing c i type inclusions all of which have homogenization temperatures of 300 to 400 c and trapping pressures of 100 to 400 bar 1 5 km depth brine inclusions homogenized by halite dissolution after vapor disappearance in both the pre and syn ore stages are interpreted to have been trapped under overpressured conditions 1 520 bar oxygen isotope analyses were conducted on garnet wollastonite epidote quartz and calcite the pre ore stage garnet and wollastonite have 18ofluid values of 5 6 to 8 1 whereas the syn ore stage epidote quartz and calcite have more variable 18ofluid values in the range of 3 9 to 17 5 the 18ofluid values of the post ore stage vein calcite 15 2 21 3 are much higher than both the pre and syn ore stages the vapor phase of inclusions contains h2s ch4 and c2h6 in the syn ore stages all these observations reveal that 1 the formation of the cu skarn deposit was dominated by a magmatic hydrothermal system 2 multiple fluid pulses contributed to the formation of the pre and syn ore stage skarn minerals and sulfides and 3 the increase in ph due to the neutralization of the acidic fluid could be the main factor controlling the large scale ore deposition in hongniu hongshan

climatically linked oscillations in arabian sea denitrification over the past 1 m y implications for the marine n cycle water column and core top 15n data show that arabian sea denitrification produces large nitrogen isotopic enrichments that are regionally recorded with fidelity in the sediments these results facilitate interpretation of a 1 m y 15n record for ocean drilling program site 722b on the owen ridge in terms of climatically linked oscillations in denitrification at the major orbital periods as at present denitrification was greatest during interglacial periods and apparently was not active during most glacial intervals cross spectral analysis of 15n with foraminiferal 18o global climate sea level index and lithogenic grain size monsoon strength index suggests forcings by changes in hydrography and productivity acting through the extent and intensity of the oxygen minimum zone the data suggest that denitrification may be an internal forcing mechanism for climate change during major glacial interglacial transitions through influence on marine n inventory and atmospheric co2 however compensation or amplification may occur from other sinks sediment denitrification or sources nitrogen fixation