characterization of granitoid and gneissic weathering profiles of the mucone river basin calabria southern italy the paper deals with the development of a multidisciplinary research on weathering profiles of granitoid and gneissic rocks related to tectonic and landscape evolution of the western sila grande massif calabria southern italy field scale observations and petrographical and mineralogical features are used to characterize in detail the weathering processes the weathering profiles of the granitoid cut slopes are generally simple showing a progressive weathering increase toward the top of the slopes whereas the weathering profiles of the gneissic cut slopes are generally complex with irregularities in the spatial distribution of weathered horizons the microfabric and petrographic analyses show that gneissic samples classes v vi of weathering grade are characterized by higher percentage of altered minerals and microfracture and void rather than granitoid samples classes v vi of weathering grade the main mineralogical changes concern the partial transformation of biotite and the partial destruction of feldspars mainly plagioclases associated with the neoformation of secondary minerals clay minerals and fe oxides and with a substitution of the original rock fabric neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage referred as physical changes coupled with chemical variations the final results of weathering process are a soil like material characterized by sand gravel grain size fraction for the granitoid rocks and by both silt clay and sand silt grain size fraction for the gneissic rocks this generally produces a greater value of the sgi sand generation index for granitoids and explains the great productivity in sandy deposits of this lithology

weathering and morphogenesis in a mediterranean climate calabria italy abstract deeply weathered plutonic rocks occur widely in the sila massif calabria southern italy three representative weathering profiles developed on the hilltops indicate that sand represents more than 50 by weight throughout most of the weathering profile and silt and clay size fractions are also well represented filling the interstices among corestones both sand and finer fractions of grus and soil horizons are thought to be derived from a combination of granular disintegration and chemical decomposition developed on relatively flat terrains of the sila massif these slopes are now experiencing transport limited morphodynamics under a montane modified mediterranean climate the depth of the weathered layers that have suffered little erosional truncation typically exceed 15 m and may reach 50 60 m or more major isolated or grouped exfoliation boulders are the most common minor landform feature developed on the sila massif granite boulders have developed as a result of spheroidal weathering and by removal of the sandy textured granite the schmidt hammer sh test on boulders and corestones suggests three distinctive degree of weathering from moderately to completely weathered rock and that biotite content is the major controlling factor of the granite mechanical behaviour understanding of the dynamics of this weathering system is crucial to the interpretation of the complex suite of variables that control landscape evolution of granitoid terrains

phenocryst crystallization during ascent of alkali basalt magma at rishiri volcano northern japan abstract phenocrysts in volcanic rocks are commonly used to deduce crystallization processes in magma chambers a fundamental assumption is that the phenocrysts crystallized in the magma chambers at isobaric and nearly equilibrium conditions on the basis of their large sizes however this assumption is not always true as demonstrated here for a porphyritic alkali basalt kutsugata lava from rishiri volcano northern japan all phenocryst phases in the kutsugata lava plagioclase olivine and augite have macroscopically homogeneous distribution of textures showing features characteristic of rapid growth throughout the crystals rarely a core region with distinct composition is present in all phenocryst phases phenocrysts excluding this core are occasionally in direct contact with each other forming crystal aggregates the equilibrium liquidus temperature of plagioclase the dominant phase 35 vol in the kutsugata lava can never exceed the estimated magmatic temperature unless the liquidus temperature increases significantly due to vesiculation of the magma during ascent this suggests that most phenocrysts in the kutsugata lava were formed by decompression of the magma during ascent in a conduit rather than by cooling during residence in a magma reservoir in the magma chamber before eruption probably located at depth of more than 7 km only cores of the phenocrysts were present and the magma was nearly aphyric 4 wt in the magma chamber and liquidus temperatures of phenocryst phases were significantly suppressed large undercooling caused by decompression and degassing of the magma was the driving force for significant crystallization during ascent because of the increase in liquidus temperature due to vapor exsolution low ascent rate of the kutsugata magma which is suggested by pahoehoe lava morphology and no association of pyroclastics gave sufficient time for crystallization furthermore the large degree of superheating of plagioclase in the magma chamber caused plagioclase crystallization with low population density and large crystal size which characterizes the porphyritic nature of the kutsugata lava alkali basalt is likely to satisfy these conditions and similar phenomena are suggested to occur in other volcanic systems

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

geochemical and isotopic zoning patterns of plagioclase megacrysts in gabbroic dykes from the gardar province south greenland implications for crystallisation processes in anorthositic magmas chemical and sr isotopic zoning patterns in plagioclase megacrysts from gabbroic dykes in the gardar province can be used to elucidate magma chamber and emplacement processes the megacrysts occur either as single crystals or assembled as anorthosite xenoliths the size of the megacrysts varies from 1 cm to 1 m they consist of a large core with variable zonation an58 39 and a relatively small 600 m normally zoned rim an62 27 the contact between core and rim is sharp and marked by a sharp increase in anorthite content which can reach 11 mol an this gap is interpreted as having formed during dyke emplacement due to a sudden pressure release some of the megacryst cores show a fairly constant composition whereas others exhibit an unusual wavy oscillatory zoning which has not been reported elsewhere to our knowledge the oscillatory zoning has wavelengths of up to 2 500 m and a maximum amplitude of 7 mol an it is interpreted as reflecting movements of the crystals in the magma reservoir the sr isotopic composition of one crystal shows a radiogenic inner core 87sr 86sr i 0 7044 and a less radiogenic outer core 87sr 86sr i 0 7039 0 7036 the lack of a significant change between outer core and rim 87sr 86sr i 0 7037 is consistent with formation of the more an rich rim due to pressure release variations in the core may be related to movements of the crystal and or magma mixing a trace element profile across a megacryst shows a small increase in sr and small decreases in ba and la contents of the recalculated melt composition across the core rim boundary whereas p ce nd and eu remain constant melt compositional changes upon emplacement are therefore considered to be of minor importance constant ratios of incompatible trace elements in the megacryst cores indicate a dominant influence of a lower crustal source on trace element budgets

zircon u pb dating and sr nd pb hf isotopes of the ore associated porphyry at the giant donggebi mo deposit eastern tianshan nw china abstract the giant donggebi porphyry mo deposit is located in the jueluotage metallogenic belt of eastern tianshan xinjiang northwest china mo mineralization mainly occurs as numerous veinlets in the altered sandstone wall rocks with the development of potassic phyllic argillic and propylitic alteration assemblages outward from a buried porphyritic granite stock zircon crystals from the buried porphyritic granite yield a weighted average 206 pb 238 u age of 236 2 2 ma mswd 1 2 1 n 17 slightly older than the molybdenite re os isotope ages of 231 234 ma suggesting that the donggebi porphyry mo deposit was formed in the triassic post collisional tectonism subsequent to termination of the paleo asia ocean the samples from porphyritic granite show high contents of sio 2 k 2 o and al 2 o 3 low contents of tio 2 mgo and cao and peraluminous high k calc alkaline to shoshonite affinity with obvious lree enrichment and negative eu anomalies they have high initial 87 sr 86 sr ratios of 0 70618 to 0 70821 e nd t values of 0 60 to 1 62 and t dm2 nd ages of 0 88 to 0 96 ga their 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t values are 17 122 18 577 15 493 15 574 and 37 887 38 006 respectively zircons from the porphyritic granite yield ehf t values of 1 58 to 4 82 and t dm2 hf ages of 0 96 1 36 ga these geochemical and isotopic data imply that the donggebi porphyritic granite originated mainly from partial melting of lower continental crust derived from a depleted mantle the donggebi mo deposit is unique based upon the crustal source for the causative porphyry the distal position of mineralization and the previously revealed co 2 rich ore forming fluids and thus belongs to the collisional or dabie type porphyry deposits as exemplified by the qiane chong and yaochong deposits in dabie shan the donggou deposit in qinling orogen china

minero petrographical features of weathering profiles in calabria southern italy abstract the paper reports interdisciplinary research of weathering profile stages on gneiss with regard to tectonic and landscape evolutions of the western sila grande massif southern italy the outcropping rocks consist of medium to coarse grained biotite garnet and sillimanite gneiss bgs g and medium to coarse grained biotite muscovite migmatitic gneiss m g the bgs g rocks are fractured and weathered with either massive or foliated texture whereas the m g rocks are intensely weathered and fractured with a massive texture and frequent pegmatite veins petrographical and mineralogical variations show that both gneissic rocks bgs g and m g samples underwent weathering processes characterized by a progressive chemical attack on the labile minerals with generation of neoformed minerals and substitution of the original rock fabric the weathering processes produced phyllosilicates and fe oxides neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage microfractures and morphological variations occur on the original rock and thereby affect the surrounding landscape processes the weathering profile mineralogy and rock textures viewed in the context of landscape evolution provide useful insights into the widespread slope movement phenomena in the sila grande massif gneiss

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

timescales of pre eruptive magmatic processes at vulcano aeolian islands italy during the last 1000 years abstract an integrated petrological and geochemical study on plagioclase crystals erupted at vulcano island aeolian islands southern italy over the past 1000 years allowed us to draw a detailed model of the internal structure of the volcanic system in which modes of magma interaction and timescales of storage at crustal depth are shown the integration of compositional textural and temporal record preserved in plagioclase crystals provides evidence for an articulated plumbing system constituted by several reservoirs connected at the crust mantle boundary here a basaltic shoshonitic magma resides and is thought to feed the shallow magma reservoir of both la fossa and vulcanello centers finally triggering eruptions throughout injections from depth textural and micro compositional data on plagioclase crystals suggest the presence of three main magma levels located between ca 17 and 2 km of depth beneath la fossa cone which were intermittently reactivated over the whole period of activity considered plagioclase textures and compositional zoning indicate that the shallow

mineralogy maketh mountains granitic landscapes shaped by dissolution abstract in tectonically quiet regions the shape of the landscape is controlled by the erosion resistance of the rocks erosion largely depends on the release of particles from the weathering rock which in turn requires a degree of dissolution of the more soluble grains the rate of dissolution of the common rock forming minerals allows the construction of a numerical rock weatherability scale rws based on the rock s modal mineralogical analysis applied regionally to three granitic landscape regions of the bega valley of southern new south wales the tate batholith and featherbed volcanics of north queensland and granitoids in the beaufort region of victoria the mean elevation of the larger plutons in each region correlates highly r 0 83 0 93 with their rws variation in composition within a pluton also shows there is a clear connection between changes in rws and relief within the pluton from these results it is apparent that the landscape of such granitic terrains is determined very largely by mineral dissolution rates with plagioclase composition and content being a major factor

comparing results from two continental geochemical surveys to world soil composition and deriving predicted empirical global soil pegs2 reference values analytical data for 10 major oxides al2o3 cao fe2o3 k2o mgo mno na2o p2o5 sio2 and tio2 16 total trace elements as ba ce co cr ga nb ni pb rb sr th v y zn and zr 14 aqua regia extracted elements ag as bi cd ce co cs cu fe la li mn mo and pb loss on ignition loi and ph from 3526 soil samples from two continets australia and europe are presented and compared to 1 the composition of the upper continetal crust 2 published word soil awerage values and 3 data from other continetal scale soil surveys it cab be demonstrated that average upper continetal crust values do not provide reliable estimates for natural concentrations of elements in soil for many elements there exist substantial differences between published world aoil averages and the median concentrations observed on two continets direct comparison with other continetal datasets is hampered by the fact that often mean instead of the statistically more robust median is reported using a database of the worldwide disstribution of lithological units it can be demonstrated that lithology is a poor predictor of soil chemistry climate related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis to overcome existing shortcomings of predicted global or world soil geochemical reference values we propose preliminary empirical global soil reference values based on analytical results of a representative number of soil samples from two continets pegs2

magma evolution recorded in plagioclase zoning in 1991 pinatubo eruption products plagioclase the most abundant phenocryst at mount pinatubo displays varying textures and compositions within the 1991 eruption products in june 7 14 dome forming andesite plagioclase phenocrysts show prominent rims with higher mgo 0 04 0 06 wt jo fe20j 0 6 0 8 wt o and k20 at given an than the interiors the compositions of the rims are identical to those of microlites which are abundant in the groundmass glass white dacitic pumice the most voluminous product of the june 15 eruption contains partly corroded plagioclase phenocrysts but no prominent rims and no microlites the interiors of phenocrysts from the dacitic pumice and the dome forming andesite are remarkably similar in terms of textures and compositions they show oscillatory zoning mostly an35 6o low mgo 0 02 wtojo and fe20j 0 10 0 30 wt jo and similar k20 at given an this similarity indicates that the two types of plagioclase phenocrysts formed in the same rhyolitic melt the oscillatory zoning likely formed by temperature fluctuations in the convecting magma and incorporation and degassing of external fluids a portion of the felsic magma 800 c mixed with a mafic melt 1000 1100 c to become an andesitic magma that extruded to form the june 7 14 dome all plagioclase phenocrysts in the andesite were derived from the felsic magma the mixing caused destabilization of phenocrysts forming sieve textures dusty zones and partial resorption extrusion of the mixed magma resulted in overgrowths on once resorbed phenocrysts and the nucleation of plagioclase microlites in the groundmass glass in the unmixed remaining portion of the felsic magma some plagioclase underwent partial resorption but did not develop overgrowths this lack of overgrowths and the absence of micro lites in the groundmass glass of the june 15 dacitic pumice indicate rapid magma ascent during the eruption and a short time span between the injection of a mafic melt and the cataclysmic eruption supporting the linkage between the two

unusual magma storage conditions at mt etna southern italy as evidenced by plagioclase megacryst bearing lavas implications for the plumbing system geometry and summit caldera collapse at mt etna volcano the emission of plagioclase megacryst bearing lavas known locally as cicirara has occurred rarely and generally in association with unusual volcanological phenomena in this work we interpret the magma chamber processes and the structural features of the plumbing system that led to the production of these peculiar volcanic rocks based on a detailed study of plagioclase megacrysts including their oscillatory zoning sieve textures and fluid inclusions patchy zoning suggests limited ascent in the deep levels of the plumbing system based on the plagioclase nucleation threshold and the volatile saturation depth at intermediate water undersaturated levels of the plumbing system ascent is faster as indicated by crystals with coarse sieve textures storage at shallow water saturated levels less than 6 km deep is associated with oscillatory zoning with very small changes in an slightly larger an variations coupled with different wavelengths provide evidence of convection of crystals across distinct zones of the chamber stripes of melt inclusions formed at steps of magma ascent and volatile loss whereas layers of fluid inclusions may be related to episodes of volatile flushing into the magma chamber in contrast strongly sieve textured envelopes with an increase and constant feo may be related to mixing with more volatile rich magmas of similar composition we interpret the repeated occurrence of cicirara lavas as evidence that the shallow portion of the plumbing system underwent a progressive coalescence of a complex network of dykes and sills in response to increasing rates of magma supply from depth major magma withdrawals from this larger reservoir may be linked to episodes of summit instability associated with major caldera collapses

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

soil formation on the wallagaraugh adamellite southeastern n s w australia abstract soil development on wallagaraugh adamellite has been studied within yambulla state forest southeastern australia twenty five soil profiles have been described and soil chemical and physical properties determined for selected horizons a geomorphological model is described for elucidating processes affecting soil development on this adamellite parent material three main geomorphic environments have been incorporated into this model residual surfaces found on interfluves and broad hillcrests transportational surfaces associated with ridges and hill slopes and depositional surfaces associated with foot slopes and valley floors residual surfaces have developed duplex primary profile forms yellow podzolics with structured b horizons of high clay content where exchangeable al dominates the exchange complex transportational surfaces have soils with shallow uniform to gradational profiles with minimal profile development and highest but most variable concentrations of the exchangeable ca k na and total p depositional surfaces are characterized by a thick accumulation of uniform coarse sandy colluvium alluvium where this surface is stable and well drained podzols have formed in contrast areas of impeded drainage on this depositional surface have humic gley profiles concentrations of total p exchangeable ca and mg are low throughout these aggraded soils the soil landscape units derived from the geomorphological model are discriminated by multivariate analysis using soil chemical and physical properties surface soil chemical properties are shown to be superior in discriminating soil landscape units to subsoil properties the mineralogy geochemistry and texture of the adamellite soil parent material are critical in determining the distinctive geomorphology which in turn affects the development of soils in this forest environment

the character and age structure of valley fills in upper wolumla creek catchment south coast new south wales australia extensive valley fills at the base of the escarpment in upper wolumla creek on the south coast of new south wales australia have formed from a combination of cut and fill processes the valley fills comprise series of alternating horizontally bedded sand and mud units reflecting reworking of detritus from deeply weathered granites of the bega batholith sand units are deposited as sand sheets or splays on floodplain surfaces or in floodouts that form atop intact valley fill surfaces downstream of discontinuous gullies alternatively sands are deposited from bedload and form bars or part of the valley floor within channel fills organic rich mud units are deposited from suspension in swamps or in seepage zones at the distal margin of floodouts within 5 km of the escarpment valley deposits grade downstream from sand sheet and splay deposition in floodouts to mud deposition in swamp and seepage zones radiocarbon dates indicate that virtually the entire valley fill of upper wolumla creek was excavated prior to 6000 years bp remnant terraces are evident at valley margins the valley subsequently filled between 6000 years bp and 1000 years bp producing valley fills around 12 m deep but no greater than 300 m wide reincision into the valley fill on a scale smaller than the present incision phase is indicated at around 1000 years bp following which the channel refilled portion plans dated from 1865 refer to the study area as wolumla big flat and show large areas of swampy terrain suggesting that the valley fill had re established by this time within a few decades of european settlement the valley fill incised once more upper wolumla creek now has a channel over 10 m deep and 100 m wide in places draining a catchment area of less than 20 km2 1998 john wiley sons ltd

soil erodibility and processes of water erosion on hillslope abstract the importance of the inherent resistance of soil to erosional processes or soil erodibility is generally recognized in hillslope and fluvial geomorphology but the full implications of the dynamic soil properties that affect erodibility are seldom considered in canada a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility this paper aims to place this work in an international framework of research on water erosion processes and to identify critical emerging research questions it focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales essential for event based soil erosion prediction results show that many components of erosional response such as partitioning between rill and interrill or surface and subsurface processes threshold hydraulic conditions for rill incision rill network configuration and hillslope sediment delivery are strongly affected by spatially variable and temporally dynamic soil properties this agrees with other recent studies but contrasts markedly with long held concepts of soil credibility as an essentially constant property for any soil type properties that determine erodibility such as soil aggregation and shear strength are strongly affected by climatic factors such as rainfall distribution and frost action and show systematic seasonal variation they can also change significantly over much shorter time scales with subtle variations in soil water conditions organic composition microbiological activity age hardening and the structural effect of applied stresses property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and therefore both short and long term hillslope erosional response similar property changes linked to climatic conditions may also significantly influence the stability and resilience of plant species and vegetation systems full understanding of such changes is essential if current event based soil erosion models such as wepp and eurosem are to attain their full potential predictive precision the complexity of the interacting processes involved may however ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics

fluid inclusion and stable isotope o h c constraints on the genesis of the pedra branca gold deposit troia massif borborema province ne brazil an example of hypozonal orogenic gold mineralization abstract at the archean paleoproterozoic troia massif ne brazil two major paleoproterozoic greenstone belts are documented algodoes and serra das pipocas they share similar lithostratigraphic characteristics with other 2 2 2 1 ga greenstone belts of the surrounding cratonic domains e g guiana shield and west africa craton gold mineralization in the serra das pipocas greenstone belt is associated with a regional ne trending shear zone in the mineralized area the pedra branca gold deposit the main gold mineralization is found in association with quartz veins calc silicate alteration e g diopside k feldspar amphibole titanite biotite pyrite albite magnetite carbonates and albitization pyrrhotite is commonly found as inclusions in pyrite and late magnetite replaces pyrite suggesting progressive oxidation of the ore forming fluid free milling gold commonly precipitates at the late stages of alteration in close association with magnetite and tellurides the main tellurides found are hessite altaite sylvanite calaverite and tellurobismuthite two fluid inclusion assemblages were identified from mineralized quartz veins assemblage 1 is characterized by pseudo secondary trails that show the coexistence of co2 rich and low salinity 0 8 wt nacl equiv co2 h2o nacl and h2o nacl inclusions suggesting formation during phase separation fluid immiscibility assemblage 2 is represented by late secondary low temperature th

ore genesis of the saridala gold deposit western tianshan nw china constraints from fluid inclusion s pb isotopes and 40ar 39ar dating abstract the saridala gold deposit is located in the western tianshan xinjiang nw china southwestern part of the central asian orogenic belt caob the deposit is mainly hosted in precambrian metamorphic rocks and early paleozoic granites and is structurally controlled by the shenglidaban ductile shear zone the gold orebodies consist of gold bearing quartz veins and altered mylonite the mineralization comprises three stages quartz pyrite veins early stage sulfide quartz veins middle stage and quartz carbonate veins veinlets late stage ore minerals and native gold were mainly formed in the middle stage four fluid inclusion types in quartz veins were identified pure co2 pc type co2 h2o c type aqueous w type and daughter mineral bearing s type inclusions hydrothermal fluids related to the mineralization are composed of co2 h2o nacl n2 fluids 115 307 mpa with th total values of 256 475 c peak at 320 380 c and salinities

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

structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in sanidine a cathodoluminescence and electron microprobe study microtextures and zoning patterns in sanidine phenocrysts from the phonolitic laacher see tephra germany were investigated in order to constrain processes occurring in the magma chamber before eruption the laacher see tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted layered magma chamber samples from various levels in the deposit were investigated we used a combination of textural studies optical microscopy and back scattered electron bse imaging electron microprobe emp analysis of major minor and trace elements ca na k al si ba sr fe and ti and element mapping the samples studied contain two feldspar phases and the ternary composition of the sanidine thus constrains the temperature of crystallization whereas its trace element content reflects the melt composition the large diversity in textures found in the sanidine crystals can be classified into three types composite c type pseudooscillatory po type and resorbed patchy r type trace elementpoor lamellar composite alkali feldspars c type are found in samples inferred to represent the top and the middle part of the magma chamber they grew as composite crystals from the melt at temperatures as low as 650 c in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall pseudooscillatory zoning with resorption surfaces po type is found in sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber repeated large an variations 1 4 mol reflect temperature variations of 100 300 ca ssociated with changes in water content variations of minor and trace elements ba sr and ti in sanidine decoupled from the pseudo oscillations of the major elements reflect chemical changes in the melt and are damped by chemicaldiffusioninthemelt bothmajorandminorelementvariations inpo typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic hotter melt this may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber however the additional role of magma recharge may be required to explain the large temperature variations resorbed patchy zoned crystals r type found mainly in samples corresponding to the middle part of the magma chamber reflect early growth in a differentiated boundary layer followed by resorption and overgrowthinthemainmagmabody manyofthelaacherseesanidine crystals did not crystallize for the most part in the melt in which they were erupted in the presence of preserved major and trace element zonation in the magma this observation indicates crystal dispersion within a layered magma chamber without large scale mixing and overturn

character and origin of deep arenaceous weathering mantles on the bega batholith southeastern australia summary arenaceous weathering mantles on the bega batholith southeastern australia are similar to those described from europe by millot as in europe they have been formed by hydrothermal alteration of the parent rock and later by chemical weathering of biotites and feldspars but comparisons with nearby torfields shows that their distribution is determined largely by mineralogical variations in the parent rock unlike the examples cited by millot in the bega mantles kaolinite is the dominant clay mineral nonetheless these mantles seem to be contemporary not relict features and apparently formed under a temperate climate

weathering or hydrothermal alteration summary altered granites are sometimes attributed to deep weathering and sometimes to hydrothermal alteration the nature of the evidence for the latter is discussed and found inadequate in many instances the alteration at bega australia and dartmoor england is considered to result from deep weathering

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

p t x conditions of hydrothermal fluids and precipitation mechanism of stibnite gold mineralization at the wiluna lode gold deposits western australia conventional and infrared microthermometric constraints the wiluna lode gold deposits are located in the archean wiluna greenstone belt in the northern sector of the norseman wiluna belt in the yilgarn craton of western australia they are hosted in subgreenschist facies meta basalts and controlled by the wiluna strike slip fault system and associated shear veins and breccias the 13 individual lode gold deposits have produced around 115 t au from 1901 to 1946 and 1986 to today historically they also produced 38 3 t as and 3 5 t sb gold formed in two stages stage 1 gold pyrite arsenopyrite is finely disseminated in the wallrock and breccia fragments whereas stage 2 gold stibnite is located in massive shear veins and breccia matrix as fracture fill and in banded colloform textured veins stibnite gold orebodies only occur in some of the deposits e g moonlight and northern part of the west lode and also display a restricted vertical extent being preserved only in the uppermost 200 m of stibnite bearing lodes petrographic conventional and infrared microthermometric and laser raman analysis on stibnite bearing quartz veins and breccias reveal that the antimony and gold rich hydrothermal fluid was of mixed h2o nacl co2 ch4 type microthermometric measurements reveal maximum homogenization temperatures of 340 c average 290 25 c and a wide range of salinities between 0 2 and 23 eq wt nacl aqueous carbonic fluid inclusions contain variable xco2 ch4 0 03 to 0 82 with the carbonic phase containing a maximum xch4 of 0 21 combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low salinity medium xco2 ch4 homogeneous parent fluid at about 290 c and pressures between 700 and 1 700 bar fluid immiscibility was triggered by cyclic pressure release during fault zone movement the decompression adiabatic cooling of the hydrothermal fluids shifted the ore fluid to lower temperatures significantly reduced the degree of stibnite undersaturation and caused stibnite to precipitate the deposition of stibnite reduced the ore fluid h2s concentration thereby destabilized gold bisulfide complexes in solution and caused gold precipitation locally this mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite gold orebodies at wiluna

isotopic studies bearing on the tectonics of the west junggar region xinjiang china isotopic investigations from the hercynian age fold belt between the kazakhstan and siberian cratons in the west junggar region determine the timing of tectonic evolution and the petrogenesis of the granitic rocks of the region sphene from the leucogabbro phase of the tangbale ophiolite melange the oldest member of the ophiolite sequences in the fold belt yields an isotopic pb pb age of 523 2 7 2 ma zircon from a postcollision alkali granite yields slightly discordant isotopic u pb ages that indicate magma crystallization at 321 4 6 7 ma dating it in the lower carboniferous period radiometric dating thus documents a time span of circa 200 ma for igneous activity in the area petrogenetic studies were made to test whether precambrian crustal rocks might underlie the junggar sedimentary basin initial lead isotope ratios determined from potassium feldspars from five alkali granites show clear affinity with ratios from mid ocean ridge basalts in pb isotope correlation diagrams sm nd data from sphene and apatite from one of the granites yield an initial end t 6 1 the granite sources are depleted mantle rocks of oceanic affinity that show no involvement of recycled aged granitic crustal rocks

plagioclase zoning as an indicator of magma processes at bezymianny volcano kamchatka back scattered electron bse derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano kamchatka based on the 2000 2007 sequence of eruptive products the erupted magmas are two pyroxene andesites which last equilibrated at 915 c temperature 77 87 mpa pressure and a water content of 1 4 wt textural and compositional zoning of individual plagioclase phenocrysts typically includes a repeated core to rim sequence of oscillatory zoning an50 60 truncated by a dissolution surface followed by an abrupt increase in an content up to an85 which then gradually decreases rimward this zoning pattern is interpreted to be the result of frequent replenishments of the magma chamber which cause both thermal and chemical interaction between resident and recharge magmas the outermost 70 to 150 m wide zoning patterns of plagioclase phenocrysts are composed of dissolution surface with a subsequent increase in an and fe contents zoning patterns of the rims exhibit correlation among plagioclase phenocrysts within one eruption rims are interpreted as a result of crystallization of a batch of magma in the conduit after recharge event

epithermal deposits in north xinjiang nw china the north xinjiang region nw china is an important part of the central asia orogenic belt situated at the junction of siberia tarim and kazakhstan plates it is an area characterized by multiple stages of phanerozoic continental growth during which several porphyry and epithermal systems were formed the relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood in this paper we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in north xinjiang and classify them into high sulfidation and low sulfidation styles with the latter being predominant we have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail the deposit scale geology and geochemistry of epithermal systems in north xinjiang are essentially similar to those in other parts of the world all epithermal deposits in north xinjiang are hosted in volcanic rocks with ages ranging from devonian to triassic with the early carboniferous volcanic sequences being the most important followed by the permian and triassic the devonian early carboniferous host rocks belong to the calc alkaline series that developed in pre collisional arc back arc basin systems whereas the permian triassic host volcanic rocks of shoshonite series formed in post subduction regimes available isotopic ages of these epithermal systems cluster in two periods early carboniferous 320 ma and late carboniferous triassic 320 220 ma reflecting two metallogenic episodes that occurred during subduction related accretion and post subduction collision regimes respectively accordingly three groups of epithermal deposits in north xinjiang can be recognized as 1 pre collisional deposits without or with negligible collisional related modification 2 deposits formed in collision regime and 3 ore systems strongly overprinted by fluid flow in post subduction collision regime

junggar basin northwest china trapped late paleozoic ocean abstract the junggar basin originated during the late paleozoic as either a remnant lower to mid paleozoic ocean basin or a mid carboniferous back arc intra or inter arc basin bounded by emergent volcanic arcs south of the siberian craton the retreating junggar sea left behind a regressive sedimentary section comprising at least 3 4 km of marine volcaniclastics in the southern junggar area sandstones deposited in the junggar basin since the devonian are exclusively volcaniclastic demonstrating that precambrian basement rocks have never been exposed in the basin and supporting the hypothesis that the junggar is underlain by oceanic crustal materials the mid carboniferous junggar ocean may have been a remnant ocean basin of early to mid paleozoic age or alternatively may have been an extending intra or inter arc basin formed behind an emergent volcanic arc in the northern turpan region subsequent strike slip deformation and the general sparsity of geologic and geophysical data from the junggar area make it difficult to distinguish between these models late early permian through triassic sediments of the junggar basin are exclusively non marine deposited in a flexurally subsiding foreland basin during initial uplift of the ancestral tian shan mountains the sedimentary section deposited during the late permian early triassic appears to be inconsistent with a proposed rifting episode during this period

geology geochemistry and ore genesis of the wenyu gold deposit xiaoqinling gold field qinling orogen southern margin of north china craton abstract the wenyu giant gold deposit is hosted in the precambrian taihua supergroup metamorphic rocks within the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided into three stages quartz pyrite veins early quartz sulfide veins middle main and carbonate quartz veinlets late with gold being mainly introduced in main stage quartz formed in two earlier stages contains three compositional types of fluid inclusions i e pure co2 co2 h2o and nacl h2o but the late stage minerals only contain the nacl h2o inclusions the inclusions in quartz formed in the early main and late stages yield total homogenization temperatures of 262 417 c 236 407 c and 114 239 c respectively with salinities no higher than 13 wt nacl equiv trapping pressures estimated from co2 h2o inclusions are 139 399 mpa and 111 316 mpa in the early and main stages corresponding to mineralization depths of 14 km and 11 km respectively fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co2 rich to co2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18owater values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology fluid inclusion and c h o s pb isotope geochemistry we conclude that the wenyu gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

in situ surface shear strength as affected by soil characteristics and land use in calcareous soils of central iran abstract soil surface shear strength is an important input parameter in the process based soil erosion models but its direct measurement at the watershed scale is difficult time consuming and costly this study was conducted to predict in situ shear strength of the soil surface using multiple linear regression mlr the land use impact on the surface shear strength was examined as well a direct shear box was constructed to measure in situ shear strength cohesion c and angle of internal friction of the soil surface in the semirom region located in isfahan province central iran the shear device consisted of a circular shear box with 10 cm internal diameter and height of 1 cm an s shaped load cell for measuring horizontal shear stress and an electric motor for applying the shear stress the normal stress acting on the failure surface was adjusted by adding weights on the shear box soil surface shear strength was determined using the shear box at 100 locations under three land use systems of grassland irrigated farming and dryland farming soil particle size distribution clay silt sand and fine clay organic matter content om carbonate content bulk density and gravel content were determined as predictors of the surface shear strength normalized difference vegetation index ndvi was also calculated using satellite images the mlr was employed to predict the shear strength i e c and using two groups of input variables i easily available soil properties pedotransfer functions ptfs and ii easily available soil properties and ndvi soil spatial prediction functions sspfs a strong negative correlation r 0 72 p c and in the studied area positive correlation r 0 41 p c and fine clay content the c was negatively correlated r 0 31 p r 0 37 p r 0 47 p and gravel content indicating the roughness effect of coarse particles on frictional shear strength the results also showed that ndvi is an important factor indirectly explaining the variability of both c and in the studied soils the land use effect on the soil properties was investigated using the lsd 0 05 test the means of somehow follow the variation of gravel content among the land uses the highest means of clay and fine clay contents and c and the lowest means of sand and gravel contents and were observed in dryland farming the c has the same trend as did clay content irrigated farming with the highest mean of sand content and lowest mean of clay content had the lowest mean of c the c means were significantly different between irrigated farming and dryland farming prediction models of in situ shear strength derived using both soil properties and ndvi as predictors sspfs were more accurate than those derived using only soil properties ptfs

oscillatory zoning in meteoritic forsterite some isolated forsterite grains in allende c3v and alha 76004 ll3 show oscillatory zoning when viewed with cathodoluminescence concentration profiles for these grains show that the oscillations correspond to cyclic variations in al and ti and by inference with known correlations v and sc other elements including mg fe ca and cr show only monotonic changes across the oscillatory zoned area under reducing conditions assumed present during forsterite growth the varying elements should be trivalent or higher in charge whereas the mg fe ca cr group would be divalent substitution into the olivine structure is considered to be two trivalent elements dominated by ai for mg si which represents a small substitution of the spinel component into forsterite this same type of substitution is proposed for similar terrestrial oscillatory zoned olivines in which no fe or mg variation is found by analogy with terrestrial and lunar oscillatory zoned minerals crystallization of the forsterite from a liquid is probable currently no such source material is known although crystallization of porphyritic chondrules may produce grains of equivalent size with zoning although no oscillatory zoned forsterite has been observed in chondrules their recognition may be confirmation of the source of isolated forsterite grains alternatively the source of these forsterite grains has not yet been recognized

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

weathering of gneiss in calabria southern italy abstract the effects of weathering in a mediterranean climate on the mineralogy and microfabric of paleozoic gneiss of the sila massif calabria southern italy have been studied field observations show highly weathered rock forms a residual soil micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages having two distinct rock microfabrics in the first stage the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing and large portions of the rock remain unaltered the second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals this latter stage occurs along both compositional and microstructural discontinuities with etch pitting of feldspar and neoformation of clay minerals and ferruginous products replacing feldspar biotite and iron bearing garnet the determination of quantitative petrographic indices provides a measure of the various stages of weathering

fluid characteristics of granitoid hosted gold deposits in the birimian terrane of ghana a fluid inclusion microthermometric and raman spectroscopic study fluid inclusions in vein quartz from 10 granitoid hosted gold deposits and prospects in the birimian terrane of ghana as well as from the sansu mine ashanti shear zone type and quartz veins in the nonmineralized princess town granodiorite were studied by microthermometry and raman microspectrometry fluid inclusions from the granitoid hosted gold deposits are dominated by aqueous h2o co2 nacl type 1 and liquid co2 n2 ch4 type 2 with minor 10 aqueous h2o nacl type 3 type 1 inclusions show large variations in co2 phase volume proportions 10 90 at 25 c and have salinities commonly between 0 and 6 wt percent nacl equiv their bulk densities fall in a major range from 0 62 to 1 11 g cm3 type 2 inclusions show no visible h2o phase at room temperature and have bulk densities between 0 30 and 0 92 g cm3 type 3 inclusions containing 10 to 20 vol percent h2o vapor have salinities of 1 to 8 wt percent nacl equiv and bulk densities of 0 77 to 1 03 g cm3 in most cases the three types of fluid inclusions coexist as groups in individual quartz grains of the samples studied these fluid inclusions are interpreted to be trapped during phase separation of an originally homogeneous h2o co2 fluid with low salinity 6 wt nacl equiv and moderate to high density 0 65 0 95 g cm3 the type 1 fluid inclusions are suggested to be heterogeneous mixtures of the two end members of type 2 and 3 inclusions fluid immiscibility is documented by petrographic characteristics and microthermometric results of the three types of inclusions trapping temperatures and pressures estimated from microthermometry of type 3 inclusions equation of state and the p t x nature of the h2o co2 nacl system are mainly between 200 and 350 cand 1 and 3 kbars for the gold deposits by contrast fluid inclusions in the sansu mine at ashanti mostly comprise the liquid co2 n2 ch4 type 2 the inclusions are considered to represent postentrapment modifications of trapped fluids in addition fluid inclusions in barren vein quartz from the princess town granodiorite comprise the low salinity commonly 6 wt nacl equiv h2o nacl type 3 raman microspectrometry shows that gaseous compositions of fluid inclusions from both granitoid and shear zone hosted gold deposits are mainly composed of co2 80 95 mol with significant amounts of n2 2 20 mol and ch4 0 10 mol the distinct low salinity h2o co2 rich fluids from the granitoid hosted gold deposits are comparable in composition to those from the major ashanti and tarkwaian types of gold deposits in the birimian terrane of ghana these fluids are most likely to be metamorphic in origin and associated with the waning stages of the regional birimian orogeny gold deposition within the birimian granitoids was related to fluid phase separation and sulfidization of host rocks during hydrothermal alteration and mineralization the present study together with previous publications suggests that fluid inclusions are characterized by h2o co2 nacl and or co2 n2 ch4 types in mineralized areas whereas h2o nacl fluid compositions dominate in barren areas fluid inclusion characteristics may therefore be a useful tool for regional gold exploration in the birimian terrane of ghana

cathodoluminescence and trace element zoning in quartz phenocrysts and xenocrysts quartz phenocrysts and xenocrysts are a common component of volcanic rocks but rarely contribute to our understanding of magmatic or eruptive processes due to an apparent internal chemical and structural homogeneity scanning electron microscopy cathodoluminescence imaging sem cl and secondary ion mass spectroscopy ion microprobe analysis sims are used here to demonstrate that quartz crystals in volcanic rocks show hitherto unrecognised internal structural and chemical zoning two contrasting crystal morphologies have been studied porphyritic euhedral bipyramidal quartz crystals in dacite from bonne nuit bay jersey uk show fine scale growth zoning in sem cl zones are narrow 1 40 m wide planar parallel to crystal faces and overgrow more broadly zoned rounded cores these crystals are interpreted to have formed at small degrees of undercooling by diffusion controlled growth quiescent magma conditions are indicated by the preservation of an al rich diffusive boundary layer which has not been removed by melt shearing during convection in contrast rounded and embayed porphyritic quartz grains in a quartz dacite from the esperanza mine e1 salvador northern chile show broad internal sem cl zones with irregular boundaries some of which are truncated by grain margins indicating dissolution crystal rounding may occur by dissolution or melting due to thermal or thermal chemical disequilibrium with surrounding melt and embayments by gas bubble enhanced convective dissolution are consistent with the development of incipient ocelli textures strings of amphibole inclusions adjacent to quartz rims several episodes of rounding can be recognised in some xenocrysts ion microprobe sims analysis of quartz from both samples shows that a1 contents are higher in areas of bright cl emission previous studies of cl in quartz have suggested that several factors control luminescence although a1 substitution for si in sio4 tetrahedra may be partly responsible for sem cl zoning recorded in volcanic quartz additional mechanisms including the effect of growth rate on defect density probably also play a major role

pedogenic evolution on the arid bishop creek moraines eastern sierra nevada california abstract soil chronosequences on alpine moraine complexes have been used to help unravel the glacial histories of the eastern sierra nevada the moraine sequence along bishop creek includes well preserved moraines that have been previously dated using cosmogenic 36cl surface exposure ages the goal of this study was to interpret pedogenesis within a soil geomorphic context on these quantitatively dated moraines soil development surface clast cover and moraine morphology were studied on seven of the moraines ranging in age from 15 to 170 ka older moraines had gentler slopes broader crests and decreased surface rock cover soils showed weak development across the chronosequence of moraines pedogenesis involved slight increases in clay the formation of clay lamellae development of a vesicular horizon in a surface layer of aeolian dust and weathering of surface and subsurface granitic clasts soil reddening and structure development were minimal soil formation was likely inhibited by the arid to semi arid climate and intermittent wind and water erosion during the time span of the chronosequence

a ductile to brittle shear zone hosted cu mineralization geological geochronological geochemical and fluid inclusion studies of the lingyun cu deposit southern tianshan nw china abstract the lingyun cu deposit is located at the northern margin of the south tianshan accretionary complex nw china in the lingyun mine area the rocks are cut by a nw trending yanxingshan ductile to brittle shear zone all orebodies are hosted in crystal tuff the sulfide mineralization in the lingyun cu deposit can be divided into early e and late l paragenetic stages the e stage is characteristic of fault controlled sulfide assemblages chalcopyrite bornite chalcocite quartz veins in the foliation fabric of the crystal tuff with albite sericite epidote biotite assemblages in the l stage the assemblages of ankerite chalcopyrite bornite chalcocite are present in veinlets that cut the e stage assemblages the sulfide assemblages in the lingyun deposit are characterized by striations in the metamorphosed crystal tuff ribbon like silicate minerals in the crystal tuff share common deformation features with the sulfide assemblages the host rock of the lingyun cu deposit yields a concordia age of ca 405 ma indicating that the aerbishibulake formation formed during southward subduction of the south tianshan ocean beneath the tarim block moreover crystal tuff samples show well developed negative sr anomaly and positive rb th u nd and p anomalies which are common in arc related volcanic rocks the ca 297 ma re os isochron age yielded by sulfides is much younger than the host rock which implies that the lingyun cu deposit is a typical epigenetic deposit both similar ree fractionated patterns between sulfide ores and crystal tuff and the high initial 187 os 188 os ratio 18 54 0 67 indicate significant crustal materials input the 40 ar 39 ar plateau age of ca 292 ma from the ribbon like sericite in crystal tuff is coeval with the mineralization occurrence in the lingyun cu deposit by contrast diorite dikes that crosscut the crystal tuff formed at ca 221 ma which is much younger than the sulfide mineralization thus the mineralization in the lingyun deposit is likely to have been generated by shear zone activity rather than the intrusion of diorite dikes three types of fluid inclusions have been identified in the lingyun cu deposit aqueous w type mixed aqueous carbonic m type and pure carbonic c type inclusions these three types of fluid inclusions are all found in the e stage quartz whereas only the w type fluid inclusions have been observed in l stage ankerite fluid inclusions from the e stage commonly contain co 2 and h 2 o locally with n 2 with low salinity which are common in orogenic deposits by contrast l stage fluid inclusions show low co 2 concentrations and salinity indicating a significant inflow of meteoric water given the regional geology ore geology coeval ore forming and deformation and fluid inclusion features the lingyun cu deposit may be associated with the orogenic class of mineral systems

ore geology fluid inclusion and 40ar 39ar geochronology constraints on the genesis of the yingchengzi gold deposit southern heilongjiang province ne china abstract the yingchengzi gold deposit located at the eastern margin of the zhangguangcai range southern heilongjiang province ne china is the only high grade gold deposit in the region the deposit is hosted in mylonitized paleozoic granite and metavolcanic rocks and is structurally dominated by brittle ductile shear zones and faults the orebodies consist of gold bearing quartz veins and gold bearing altered mylonites the hydrothermal ore forming process can be divided into early middle and late stages characterized by quartz pyrite veins quartz gold polymetallic sulfide veins and quartz carbonate veins or veinlets respectively ore minerals and gold mainly occurred in the middle stage four types of fluid inclusions were identified in the vein minerals based on petrography and laser raman spectroscopy nacl h 2 o w type co 2 h 2 o c type pure co 2 pc type and less common calcite bearing s type inclusions the early stage minerals contain c type and rare pc type fluid inclusions which have homogenization temperatures of 262 400 c and low salinities of 2 20 8 51 wt nacl equiv only the middle stage minerals contain all four types of fluid inclusions with homogenization temperatures of 173 316 c and salinities of 2 20 12 42 wt nacl equiv the late stage quartz and calcite crystals contain only w type fluid inclusions which have homogenization temperatures of 104 207 c and salinities of 1 05 6 58 wt nacl equiv fluid boiling and the mixing caused the rapid precipitation of sulfides and gold these indicate that the ore forming fluid system evolved from co 2 rich metamorphogenic to co 2 poor due to the boiling and input of meteoric water the trapping pressures estimated from c type fluid inclusions are 98 245 mpa in the main ore forming stage giving a reasonable estimate that an alternating lithostatic hydrostatic fluid system controlled a fault valve activity at a depth of 9 10 km 40 ar 39 ar dating of hydrothermal sericite from gold bearing altered rock shows that gold mineralization occurred at 248 ma we assume that the yingchengzi gold deposit was formed in a late permian early triassic continental collision regime following closure of the paleo asian ocean the regional geology ore geology fluid inclusions mineralization age and tectonic setting infer that the yingchengzi gold deposit is a mesozonal orogenic gold system making it the first orogenic gold deposit discovered in the zhangguangcai range ne china

geology and fluid evolution of the wangfeng orogenic type gold deposit western tian shan china abstract the wangfeng gold deposit is located in western tian shan and the central section of the central asian orogenic belt caob the deposit is mainly hosted in precambrian metamorphic rocks and caledonian granites and is structurally controlled by the shenglidaban ductile shear zone the gold orebodies consist of gold bearing quartz veins and altered mylonite the mineralization can be divided into three stages quartz pyrite veins in the early stage sulfide quartz veins in the middle stage and quartz carbonate veins or veinlets in the late stage ore minerals and native gold mainly formed in the middle stage four types of fluid inclusions were identified based on petrography and laser raman spectroscopy co 2 h 2 o inclusions c type pure co 2 inclusions pc type nacl h 2 o inclusions w type and daughter mineral bearing inclusions s type the early stage quartz contains only primary co 2 h 2 o fluid inclusions with salinities of 1 62 to 8 03 wt nacl equivalent bulk densities of 0 73 to 0 89 g cm 3 and homogenization temperatures of 256 c 390 c vapor bubbles are composed of co 2 the middle stage quartz contains all four types of fluid inclusions of which the co 2 h 2 o and nacl h 2 o types yield homogenization temperatures of 210 c 340 c and 230 c 300 c respectively the co 2 h 2 o fluid inclusions have salinities of 0 83 to 9 59 wt nacl equivalent and bulk densities of 0 77 to 0 95 g cm 3 with vapor bubbles composed of co 2 ch 4 and n 2 fluid inclusions in the late stage quartz are nacl h 2 o solution with low salinities 0 35 3 87 wt nacl equivalent and low homogenization temperatures 122 c 214 c the coexistence of inclusions of these four types in middle stage quartz suggests that fluid boiling occurred in the middle stage mineralization trapping pressures estimated from co 2 h 2 o inclusions are 110 300 mpa and 90 250 mpa for the early and middle stages respectively suggesting that gold mineralization mainly occurred at depths of about 10 km in general the wangfeng gold deposit originated from a metamorphic fluid system characterized by low salinity low density and enrichment of co 2 depressurized fluid boiling caused gold precipitation given the regional geology ore geology fluid inclusion features and ore forming age the wangfeng gold deposit can be classified as a hypozonal orogenic gold deposit

shrimp zircon u pb geochronology geochemistry and h o si s pb isotope systematics of the kanggur gold deposit in eastern tianshan nw china implication for ore genesis abstract the kanggur gold deposit is located in the southern margin of the central asia orogenic belt and in the western segment of the kanggur huangshan ductile shear belt in eastern tianshan northwestern china the orebodies of this deposit are hosted in the lower carboniferous volcanic rocks of the aqishan formation and mainly consist of andesite dacite and pyroclastic rocks the shrimp zircon u pb age data of the andesite indicate that the volcanism in the kanggur area might have occurred at ca 339 ma in the early carboniferous and that the mineralization age of the kanggur gold deposit was later than the age of volcanic rocks in the area geochemically the andesite rocks of the aqishan formation belong to low tholeiite and calc alkaline series and display relative depletions in high field strength elements hfses i e nb ta and ti the 18 o w and d w values vary from 9 1 to 3 8 and 66 0 to 33 9 respectively indicating that the ore forming fluids were mixtures of metamorphic and meteoric waters the 30 si values of 13 quartz samples range from 0 3 to 0 1 with an average of 0 15 and the 34 s values of 18 sulphide samples range from 0 9 to 2 2 with an average of 0 54 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of 10 sulphide samples range from 18 166 to 18 880 15 553 to 15 635 and 38 050 to 38 813 respectively showing similarities to orogenic pb these values are consistent with those of the andesite from the kanggur area suggesting a common lead source all of the silicon sulphur and lead isotopic systems indicate that the ore forming fluids and materials were mainly derived from the aqishan formation and that the host volcanic rocks of the aqishan formation probably played a significant role in the kanggur gold mineralization integrating the data obtained from studies on geology geochronology petro geochemistry and h o si s pb isotope systematics we suggest that the kanggur gold deposit is an orogenic type deposit formed in eastern tianshan orogenic belt during the permian post collisional tectonism

three years 2011 2013 of eruptive activity at mt etna working modes and timescales of the modern volcano plumbing system from micro analytical studies of crystals abstract tracking magma dynamics at active volcanoes by using the compositional and textural records of minerals is becoming an important aspect of modern volcanology to solve key issues such as temporal relationships between magma recharge and eruption duration of magma storage and final ascent upward to the surface these issues are relevant at mt etna where the style of volcanic activity during the last years showed drastic variations in duration and intensity the paroxysmal activity between 2011 and 2013 at the volcano summit has given the opportunity to investigate the chemical physical processes driving the activity and to fix their spatial temporal relationships into the plumbing system an extensive compositional dataset of plagioclase and olivine crystals from lavas emitted between the 2011 and 2013 at mt etna has been used to constrain modes and timescales of magma storage and transfer to the surface plagioclase crystals display either near equilibrium or disequilibrium textures at the core and rim that indicate complex histories of magma crystallization under variable chemical and physical conditions crystals with different textures have been characterized for major an minor fe and mg and trace elements sr ba textural relationships at the plagioclase cores support the idea that crystals undergo variable decompression rates in the deep parts of the plumbing system fe and mg zoning vs anorthite in correspondence of plagioclase sieve textures at the rim suggest that processes of gas flushing have a dominant role in triggering paroxysmal eruptions determining a sudden intensification of the eruptive activity up to the fountaining phase the sr ba ratio in oscillatory zoned plagioclase revealed the dominant presence into the plumbing system of high sr magma volumes coexisting with low sr magma batches that preserve a geochemical signature similar to that of magmas feeding the pre 1971 activity through sr diffusion modeling in plagioclase the maximum time of magma storage during the considered eruptive period has been evaluated timescales of crystal residence in the plumbing system are short five years to three decades suggesting limited magma storage and faster transfer dynamics to the surface chemical zoning of olivine crystals highlights processes of multi step magma transfer and residence at different levels of the plumbing system the upward migration of magmas occurred primarily through multiple episodes of injection and mixing between five compositionally distinct magmatic environments m i whose p t o 2 characteristics and concentrations in dissolved volatiles were constrained by thermodynamic modeling on the basis of the forsterite contents found at the olivine cores from a deepest reservoir located at depth of 600 mpa the most primitive magma m00 fo 84 moved along dominant pathways intercepting the m0 fo 80 82 at 390 mpa and or m1a fo 78 250 mpa m1b fo 75 140 mpa and finally the shallow m2 fo 70 73 40 mpa storage zones for some eruptive episodes olivine zoning highlights a preferential route of transfer connecting the m00 and m2 storage zones that facilitated the fast migration of primitive magma at shallow depth fe mg diffusion modeling on olivine normal and reverse zoning defines the timescales of magma transfer and storage across these magmatic environments which vary from 1 to 18 months whereas intrusion and mixing by more basic magma into the shallowest reservoir occurred always within 5 months before the eruption relevance of this study mainly relies on the quantification of volcanic processes at depth that may have considerable consequences in development of unusual high energy eruptions at basaltic volcanoes generally acknowledged for their weak to mild explosive activity

genesis of the dadonggou pb zn deposit in kelan basin altay nw china constraints from zircon u pb and biotite 40ar 39ar geochronological data abstract the genesis of polymetallic deposits in southern altay nw china has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic type mineralization the dadonggou pb zn deposit occurs as nw trending veins in the devonian kangbutiebao formation volcanic sedimentary sequence in the kelan basin southern altay a set of integrated zircon u pb and biotite 40ar 39ar geochronological data were applied to constrain the forming ages of the ores and their country rocks three samples of host volcanic rocks yielded weighted mean 206pb 238u ages of 397 1 4 5 ma 391 7 3 6 ma and 391 1 4 2 ma respectively indicating that the kangbutiebao formation was deposited in a devonian back arc basin two biotite samples separated from the pb zn containing quartz veins yielded 40ar 39ar plateau ages of 205 9 2 1 ma and 204 3 2 2 ma respectively which represent the age of the pb zn mineralization that is attributed to the closure of the kelan back arc basin and the late triassic orogeny combining the available geological and geochronological data this contribution outlines the successive evolution from the development of a devonian back arc basin to the late triassic post subduction orogeny and proposes that the dadonggou pb zn deposit is an epigenetic orogenic type deposit placed in the late triassic orogeny

lithological effects in soil formation and soil slips on weathering limited slopes underlain by granitic bedrocks in japan abstract soil slips occur every few years due to heavy rains on biotite granite gb and hornblende biotite granite ghb slopes in the taga mountains ibaraki prefecture japan the occurrence density of soil slips per unit area is 2 7 times greater in the gb slopes than that in ghb slopes we examined the chemical mineral physical and mechanical properties of two soil profiles on soil slip scars in these slopes to study the effect of bedrock mineral composition on the density of soil slips for a given size of mineral grain the amount of biotite which is susceptible to chemical weathering in granitic bedrocks strongly influenced the density of soil slips in the gb slope the soil layer becomes thinner because of the smaller proportion of biotite in the bedrock this restricts the downward movement of soil water into the material below the slip plane during heavy rainfall the water surface then rises toward the slope surface above the slip plane this promotes soil slips increasing the density of soil slip scars in contrast in the ghb slope with more biotite in the bedrock the soil layer becomes thicker so that soil water moves easily into the material beneath the slip plane this limits the rise of water surface toward the slope surface above the slip plane even during heavy rainfalls there are consequently fewer soil slips and density of soil slip scars

trace element geochemistry of magnetite implications for ore genesis of the talate skarn pb zn fe deposit altay nw china abstract the talate skarn pb zn fe deposit is hosted in the kangbutiebao formation of the abagong polymetallic belt altay nw china the talate magnetite comprises the magmatic hydrothermal hydrothermal disseminated and massive magnetite types and formed during the early skarn and quartz magnetite stage the magmatic hydrothermal disseminated magnetite is nb ta ti depleted whereas the hydrothermal disseminated magnetite associated with skarn alteration is geochemically similar to the ca skarn with slight ta mg ni depletions the massive magnetite ores have similar ni concentrations with the ca skarn but contain minor depletions in sn sc ta nb mg and co probably attributed to magma host rock interactions the talate hydrothermal disseminated magnetite contains lower sn than magnetite from typical skarn deposits and likely resulted from cassiterite crystallization as it is found co precipitated with disseminated magnetite both magmatic hydrothermal and hydrothermal disseminated magnetite are characterized by narrow ti concentration range and variable co ni ratios which likely reflect rapid cooling rate and significant fluid rock interaction during multiple successive stages of skarn alteration as the co has a higher solubility over the ni in the ore forming fluid whereas the talate massive magnetite contains wider ti concentration range and in some cases with 120 triple junctions the co ni ratios mostly

insights into the genesis of orogenic gold deposits from the zhengchong gold field northeastern hunan province china abstract the zhengchong gold deposit is located in the central jiangnan orogen belt where gold ore occurs mainly as quartz veins altered slates and minor breccias hosted by shear zones in the lengjiaxi group based on its vein crosscutting relationships mineral assemblages and paragenetic sequences mineralization in this deposit is divided into four stages stage 1 quartz q1 pyrite stage stage 2 quartz q2 pyrite arsenopyrite stage stage 3 quartz q3 pyrite polymetallic sulfide mineral stage and stage 4 quartz q4 carbonate stage two types of fluid inclusions have been recognized in the quartz grains co2 bearing fluid inclusions c type and aqueous fluid inclusions w type fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312 406 c and 4 65 9 21 wt naclequiv stage 1 252 324 c and 2 20 8 10 wt naclequiv stage 2 193 296 c and 2 24 14 04 wt naclequiv stage 3 and 127 209 c and 2 57 6 59 wt naclequiv stage 4 the co occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during stages 2 and 3 of mineralization possibly as a result of episodic pressure decreases linked to fault valve activity laser raman spectroscopic analysis results reveal that small quantities of ch4 and n2 are present in the stage 2 3 fluid inclusions fluid inclusion data and microthermometric results show that the ore fluids were low salinity and co2 rich yielding both co2 inclusions c type and aqueous inclusions w type the trapping pressures estimated from the c type inclusions are 80 180 mpa for stages 2 and 3 yielding gold mineralization depths of 7 8 km the mineralizing fluids had calculated 18oh2o values ranging from 3 7 to 8 2 and d values from 75 2 to 61 8 indicating derivation mainly from metamorphic fluids the sulfide minerals yield 34s values of 8 9 to 0 1 and 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 83 18 12 15 67 15 76 and 38 03 38 62 respectively which differ significantly from the isotopic composition of the granodiorite 34s 2 4 to 1 0 206pb 204pb 18 57 19 28 207pb 204pb 15 69 15 76 208pb 204pb 38 97 40 34 however the s pb isotopic compositions of the sulfide minerals are similar to those of slates of the lengjiaxi group in the study area the zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity low density and co2 enrichment with limited admixture of magmatic fluids based on similarities to other orogenic gold deposits we infer that the zhengchong orebody represents an orogenic gold deposit formed during the late ordovician jiangnan orogeny caused by collision of the yangtze and cathaysia blocks

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

an overview of the role of weathering in the production of quartz silt abstract quartz silt is a widespread detrital sediment with large aeolian loess and alluvial silt deposits forming important components of many contemporary landscapes despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments e g glacial grinding fluvial comminution aeolian abrasion frost weathering salt weathering insolation weathering and deep weathering the glacial aeolian hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a quaternary phenomenon as a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre quaternary environments in particular earth scientists may have considerably underestimated the role of weathering in global silt generation as there are now many references to the existence of a patchy but widespread distribution of pre quaternary weathering profiles across the glacial and periglacial landscapes of the northern hemisphere e g north america british isles north and central europe landscapes within which many of the classical loess deposits are located these observations suggest that weathering profiles may have covered large tracts of the northern hemisphere land surface prior to the quaternary glaciations this in turn may have important implications for quartz silt generation as 1 experimental studies indicate that many weathering processes are capable of generating significant quantities of silt sized debris and 2 particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt sized material or quartz grains that are weakened by weathering derived microfractures thus weathering profiles may represent mines of actual and potential quartz silt available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial fluvial and aeolian erosion

mechanisms of granite alteration into grus karkonosze granite sw poland abstract granitic gruses are usually considered as a product of deep weathering but the influence of hydrothermal fluids was also noticed in this work a wide range of mineralogical and chemical methods performed on 43 samples from three representative outcrops and a reference site is used to determine the influence of hydrothermal and weathering fluids on the development of granitic gruses from the coarse grained karkonosze granite four types of altered granites have been distinguished including compact and friable granite typical grus and localized heavy altered zones mineralogical observations such as complete albitization of plagioclase and crystallization of secondary quartz revealed an important role of hydrothermal alteration at the early stage of grusification the origin of smectite and alteration of biotite into muscovite are likely to be connected with circulation of hydrothermal fluids too grusification sensu stricto was primarily caused by vermiculitization of biotite which resulted in volumetric expansion and the development of transmineral microcracks with non accordant pore surfaces thus it requires hydrothermal alteration to be relatively minor confined to postmagmatic changes since more advanced alteration of biotite into muscovite rather than vermiculite arrests further development of microcracks and leads to the development of friable granite

isotope and fluid inclusion geochemistry and genesis of the qiangma gold deposit xiaoqinling gold field qinling orogen china abstract the qiangma gold deposit is hosted in the 1 9 ga taihua supergroup metamorphic rocks in the xiaoqinling terrane qinling orogen on the southern margin of the north china craton the mineralization can be divided as follows quartz pyrite veins early quartz polymetallic sulfide veinlets middle and carbonate quartz veinlets late stages with gold being mainly introduced in the middle stage three types of fluid inclusions were identified based on petrography and laser raman spectroscopy i e pure carbonic carbonic aqueous co 2 h 2 o and aqueous inclusions the early stage quartz contains pure carbonic and co 2 h 2 o inclusions with salinities up to 12 7 wt nacl equiv bulk densities of 0 67 to 0 86 g cm 3 and homogenization temperatures of 280 365 c the early stage is related to h 2 o co 2 n 2 ch 4 fluids with isotopic signatures consistent with a metamorphic origin 18 o water 3 1 to 5 2 d 37 to 73 the middle stage quartz contains all three types of fluid inclusions of which the co 2 h 2 o and aqueous inclusions yield homogenization temperatures of 249 346 c and 230 345 c respectively the co 2 h 2 o inclusions have salinities up to 10 9 wt nacl equiv and bulk densities of 0 70 to 0 98 g cm 3 with vapor bubbles composed of co 2 and n 2 the isotopic ratios 18 o water 2 2 to 3 6 d 47 to 79 suggest that the middle stage fluids were mixed by metamorphic and meteoric fluids in the late stage quartz only the aqueous inclusions are observed which have low salinities 0 9 9 9 wt nacl equiv and low homogenization temperatures 145 223 c the isotopic composition 18 o water 1 9 to 0 5 d 55 to 66 indicates the late stage fluids were mainly meteoric water trapping pressures estimated from co 2 h 2 o inclusions are 100 285 mpa for the middle stage suggesting that gold mineralization mainly occurred at depths of 10 km fluid boiling and mixing caused rapid precipitation of sulfides and native au through boiling and inflow of meteoric water the ore forming fluid system evolved from co 2 rich to co 2 poor in composition and from metamorphic to meteoric as indicated by decreasing 18 o water values from early to late the carbon sulfur and lead isotope compositions suggest the hostrocks within the taihua supergroup to be a significant source of ore metals integrating the data obtained from the studies including regional geology ore geology and fluid inclusion and c h o s pb isotope geochemistry we conclude that the qiangma gold deposit was an orogenic type system formed in the tectonic transition from compression to extension during the jurassic early cretaceous continental collision between the north china and yangtze cratons

an unusual occurrence of probable pleistocene corestone within a cretaceous dioritic enclave peninsular ranges california abstract we here document an unusual occurrence of probable pleistocene corestone within an 5 m by 5 m dioritic enclave contained within a cretaceous tonalitic pluton santa margarita ecological reserve sw california the enclave lies within 3 5 km of the seismically active 1 5 2 ma elsinore fault zone and may have been subjected to 70 90 ground shaking events since 22 000 18 000 years ago the studied corestone is elliptical with major axis measuring 55 cm and minor axis 26 cm in length it is surrounded by a discontinuous 7 cm thick rind that breaks apart under slightly greater finger pressure than does the surrounding saprolite in order to assess changes in the physical and chemical properties of the corestone rind and saprolite we collected along an 66 5 cm long traverse 4 samples from the corestone 1 from the rind and 5 from the saprolite for bulk and grain density porosity and major and trace element analyses textural and clay mineral data along with the redistribution of elemental mass indicate that the weathering of biotite and to much lesser degrees apatite and the an rich cores of plagioclase played critical roles in the production of saprolite especially in a narrow 20 cm wide zone adjacent to the rind of the corestone within this zone bulk densities reach their minimum values while porosities and positive volume strains reach their maximums in addition the maximum loss of k fe mn and ca mass occurred just inside this region and is paralleled by the highest cia values and highest additions of si and rb mass in contrast the masses of na and sr are progressively increased and decreased respectively along the entire sampling traverse while the loss of mg ti and p mass is episodic with the greatest losses occurring within the narrow zone adjacent to the rind and at the end of the traverse the above observations indicate that the conversion of biotite to expandable mixed layered clay minerals aided by the alteration of the an rich cores of plagioclase produced sufficient stress on grain boundaries that a weakening or loss of intercrystalline cohesion occurred however unlike the well documented isovolumetric development of saprolite in other areas at the study site saprolitization was accompanied by a volume expansion we speculate that repeated ground shaking in response to earthquakes generated in the nearby elsinore fault zone may be responsible for this difference important byproducts of ground shaking would include additional weakening or loss of intercrystalline cohesion and the production and enhancement of new and older fluid pathways respectively the fact that the most intensely altered material at the study site lies adjacent to the boundary between the rind and saprolite suggests that this interface acted to guide fluid flow around the corestone and rind and into the adjacent saprolite where elemental mass was redistributed down various paths leading to the underlying water table most of the leached elemental mass was removed from the area of the sampling traverse but small increases in si rb and na mass suggest redistribution of these elements from elevated areas outside the area sampled during this study the result of the above complex set of processes is a variably porous and chemically altered saprolitic enclave that is still undergoing modification as it adjusts to the vicissitudes of the paralithic environment and continuing ground shaking during earthquakes generated along the elsinore fault

the geochemistry of young volcanism throughout western panama and southeastern costa rica an overview oblique aseismic subduction below western panama and southeastern costa rica has produced recent arc related volcanism the aseismicity is probably related to the subduction of relatively hot oceanic lithosphere the volcanism throughout this region over the past 2 ma has been quite distinct consisting of felsic magmas andesites to rhyolites but mainly dacites with geochemical signatures suggesting a metamorphosed basaltic source it is believed that the subduction of young oceanic crust sets up conditions under which the slab melts rather than the overlying mantle wedge rocks with slab melt geochemistries and associated with young subducted crust have been termed adakites elsewhere the young adakite melts are sometimes associated with a few rare young high nb basalts but there is no obvious genetic link between them through differentiation high nb basalts may also be derived from the partial melting of the subducted oceanic crust high nb basalt migmatites have been found with pegmatites of adakite compositions in the exposed subduction terrain of the catalina schist california alternatively the high nb basalts may be partial melts of phlogopite rich mantle that has previously reacted with adakite magmas eruption of adakites and high nb basalts was preceded by a 2 3 ma period of relative quiescence prior to this there was a 7 ma period of calc alkaline volcanism typical of the present day magmatism associated with a distinct benioff zone found throughout the central american arc the abrupt transition in volcanism with time from an early calc alkaline sequence to a later adakite high nb basalt sequence may record a change in the tectonic setting of western panama and southeastern costa rica over the past 12 ma

formation of the baiyun gold deposit liaodong gold province ne china constraints from zircon u pb age fluid inclusion and c h o pb he isotopes abstract the baiyun gold deposit is located in the liaodong peninsula in ne china the gold orebodies are hosted in the paleoproterozoic liaohe group metamorphic rocks the alteration mineralization can be divided into three stages i quartz pyrite k feldspar veins ii quartz polymetallic sulfide veins iii quartz carbonate veins new la icp ms zircon u pb dating suggests all the ore related porphyries including monzonite porphyry 224 2 1 3 ma quartz porphyry 221 4 1 2 ma and diorite porphyry 221 8 1 2 ma were emplaced in the late triassic four types of fluid inclusions fis are identified in the ore related quartz i e liquid rich two phase vapor rich two phase co2 bearing and pure co2 fis the ore forming fluids were likely characterized by medium temperature low salinity low density co2 rich and belong to the h2o nacl co2 n2 c4h6 system we propose that fluid phase separation likely caused rapid precipitation of the ore minerals the c h o pb isotope data indicate that the ore forming fluids may have had multiple sources including magmatic metamorphic and meteoric fluids the ore forming materials may have mainly derived from metamorphic rocks of the proterozoic gaixian formation and minor from the triassic intermediate felsic rocks the he ar isotope data indicate that the ore forming fluids were mainly crust derived we conclude that the baiyun gold deposit is an orogenic type system formed during the late triassic north china yangtze continent continent collision

a fluid inclusion study of au bearing quartz vein systems in the central and north deborah deposits of the bendigo gold field central victoria australia the central and north deborah gold deposits with a production of about 7 tons au are located in one of 15 domes in the bendigo gold field central victoria australia an important mesothermal lode gold province the gold bearing quartz vein systems are hosted predominantly by reverse faults in lower ordovician turbidites which underwent lower greenschist facies metamorphism in the central and north deborah mines there are six stages of quartz veins that developed in the following sequence 1 laminated veins with a metal association of au as sb pb zn ni 2 spurs au 3 massive barren veins main dilation stage 4 brecciated veins with au as 5 quartz ankerite veinlets and 6 late pure quartz or calcite veinlets of the three mineralized vein stages 1 2 and 4 only the first one predated or was coeval with the main deformation event whereas stages 2 and 4 postdated the main deformation the vein structures indicate that vein development was controlled by repeated fluctuations of fluid pressure inducing hydraulic fracturing fluid inclusions in vein quartz contain c o h fluids of variable compositions three main types of fluid inclusions are recognized at room temperature type i two phase primary ch4 v h2o l fluid inclusions type ii two or three phase primary pseudosecondary co2 v or l ch4 v or l h2o l fluid inclusions including iia ch4 co2 h2o and iib co2 h2o fluid inclusions and type iii h2o v h2o l fluid inclusions type iii fluid inclusions are further divided into three groups iiia primary pseudosecondary vapor rich iiib primary pseudosecondary liquid rich and iiic secondary liquid rich data from fluid inclusion distribution microthermometry and raman spectroscopy indicate that fluids associated with au mineralized quartz veins stages 1 2 and 4 have moderate salinity ranging from 0 to 12 wt percent nacl equiv modeled salinities around 7 8 wt nacl equiv these veins formatted at temperatures from 325 to 375 c and pressures of 200 to 300 mpa with emplacement depths of about 8 to 12 km fluids associated with barren quartz veins stages 3 5 and 6 have a low salinity of about 0 to 3 wt percent nacl equiv modeled salinities about 2 3 wt nacl equiv and lower temperatures there is evidence of fluid immiscibility in all vein stages and mixing between fluids of the same souce but differing fo2 may also have influenced gold deposition cox et al 1995 hydrothermal ore forming fluids responsible for gold mineralization are in the ch2 co2 h2o nacl system whereas those of massive barren veins stage 3 and veinlets stages 5 and 6 are in the co2 h2o nacl and h2o nacl systems respectively the carbonic phases of type i and ii fluid inclusions range from pure ch4 through mixed ch4 and co2 to pure co2 gold ore forming fluids were weakly acidic with f o2 estimated to have been 10 25 to 10 37 bars and generally above the co2 ch4 and below the so2 h2s buffer boundaries throughout gold mineralization the relatively reduced mineralizing fluids are similar to those of other turbidite hosted lode gold deposits and counterparts in volcanic plutonic terranes

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

crystallization processes of quartz in a granitic magma cathodoluminescence zonation pattern controlled by temperature and titanium diffusivity abstract quartz from a granitic pluton is found to have formed through sequential growth events under different mechanisms and crystallization temperatures which can provide new insights into magmatic processes of granitic magmas that were eventually consolidified into plutons the events were identified using 1 the description of crystal shape and occurrence 2 the study of the internal structure with cathodoluminescence cl and 3 derivation of the crystallization temperatures based on titaniq thermometry the magmatic quartz crystals from the toki granite central japan are characterized as having the following internal structures oscillatory zonation no oscillatory zonation with luminescence gradation gradational zonation and heterogeneous cl the quartz crystals with oscillatory zonation were formed in the temperature range of about 800 c to below 700 c which is referred to as oscillatory zoning temperature ozt conditions the cl zonation pattern was controlled by the temperature conditions and titanium diffusivity in the melt magma the crystallization process of quartz within the toki granite reveals the cooling processes of the granitic pluton the lithofacies with a high frequency of oscillatory zoned quartz underwent slower cooling under the ozt conditions than those in other lithofacies

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

noise and oscillatory zoning of minerals oscillatory mineral zonation is usually associated with crystal growth in an open system either a hydrothermal system or a melt after a period of magma mixing or degassing such systems may be driven sufficiently far from thermodynamic equilibrium to produce autonomous patterns by geochemical self organization the resulting zonation patterns will be the result of coupling between the generally nonlinear crystal growth dynamics and the boundary conditions imposed by externally controlled fluctuations we examine the effects of noisy boundary conditions on four different crystal growth models these are models for plagioclase growth in magmatic systems l heureux and fowler 1996 for carbonates in sedimentary systems wang and merino 1992 for garnets in hydrothermal systems jamtveit 1991 and for silicate growth from a melt wang and wu 1995 the plagioclase model is sensitive to noise even to low amplitude noise implying that an observed zonation pattern will be significantly affected by processes other than local growth and transport processes for the garnet model fluctuations in the external environment may cause synchronization so that different crystals develop similar zonation patterns even if the formation of zonation patterns is a consequence of nonlinear local dynamics this implies that similarity in intracrystalline zonation does not necessarily imply that the zonation pattern was produced by changes in the external environmental conditions the formation of a zonation pattern may be a consequence of local nonlinearities in the growth process but the pattern details may be strongly affected by subtle changes in the external environment copyright 2000 elsevier science ltd

evolution of ore forming fluids in the sawayaerdun gold deposit in the southwestern chinese tianshan metallogenic belt northwest china the sawayaerdun gold deposit was discovered in the early 1990s and is the largest orogenic gold deposit in the chinese tianshan gold mineralization occurs in quartz veins which are hosted in carbonaceous metasediments and controlled by faults and fractures three major hydrothermal events can be identified at sawayaerdun an early barren quartz vein stage middle stage quartz veins with pyrite and gold mineralization and late carbonate quartz veins fluid inclusion studies of quartz pyrite and carbonate formed during the major hydrothermal stagesshow distinct changes in fluid temperature composition and redox conditions occurred during fluid evolution three types of fluid inclusions have been identified at sawayaerdun h2o nacl l v h2o nacl co2 l v and co2 l v fluids trapped in early barren quartz have high temperatures 280 420 c low salinities 3 wt nacl equiv high cl and are co2 rich middle stage quartz contains fluids with lower temperatures 210 310 c and variable salinities 0 8 17 5 wt nacl equiv they are commonly s rich co2 containing and relatively reduced compared with early stage fluids in contrast hydrothermal pyrite hosted in middle stage quartz veins trapped fluids formed over a narrower temperature range 220 270 c more oxidized high co2 ch4 ratio and have higher ca k and mg than fluids in quartz late stage carbonate is dominated by fluids with low temperatures 200 c and low contents of cl s and k fluid immiscibility probably commenced at the onset of mineralization along with middle stage quartz formation resulting in the generation of coexisting fluid inclusions with distinguishable vapor liquid ratios and salinities the compositional difference between fluids trapped in pyrite and quartz indicate fluid mixing may have occurred during the mineralization stage the oxidized fluids probably a mixture of meteoric water and fluids generated during water host rock interaction emerged into the ore forming system to generate extensive metals precipitation the fluid immiscibility and fluid mixing are most likely caused by pressure decrease during late paleozoic uplift and erosion in the chinese southern tianshan area comparison of fluids between four major mineralization zones at sawayaerdun indicate that zone ii is similar to the most important zone iv and the order of similarity is probably zone ii xi i which could be applied to the future mineral exploration in this area

geology and genesis of the xiaguan ag pb zn orefield in qinling orogen henan province china fluid inclusion and isotope constraints abstract the xiaguan ag pb zn orefield neixiang county henan province hosting the yindonggou zhouzhuang yinhulugou and laozhuang fault controlled lode deposits is situated in the erlangping terrane eastern qinling orogen the quartz sulfide vein mineralization is dominated by main alteration styles of silicic sericite carbonate chlorite and sulfide alteration major ag bearing minerals are freibergite argentite and native ag the deposits were formed by a co2 rich mesothermal ca 250 320 c low density and low salinity the 18oh2o values change from the early e stage 7 8 10 8 through middle m stage 6 0 9 4 to late l stage 1 5 3 3 with d values changing from e stage 95 to 46 through m stage 82 to 70 to l stage 95 to 82 13cco2 values of the ore fluids in the e and m stage quartz vary between 0 1 and 0 9 average 0 3 13cco2 values of l stage fis are 0 2 0 1 in quartz and 6 8 to 3 5 in calcite the h o c isotopic data indicate that the initial ore fluids were sourced from the underthrusted qinling group marine carbonates and were then interacted with the ore hosting erlangping group metasedimentary rocks inflow of circulated meteoric water may have dominated the l stage fluid evolution sulfur 34s 1 9 8 1 and lead isotopic compositions 206pb 204pb 18 202 18 446 207pb 204pb 15 567 15 773 and 208pb 204pb 38 491 39 089 of sulfides suggest that the ore forming materials were mainly sourced from the ore hosting metasedimentary strata the stepped heating sericite 40ar 39ar detection suggests that the mineralization occurred in the middle jurassic to early cretaceous ca 187 124 ma considering the regional tectonic evolution of the erlangping terrane we propose that the xiaguan ag pb zn orefield was formed in a continent continent collisional tectonic regime in accordance with the tectonic model for continental collision metallogeny and fluid flow cmf

mineralogical and textural controls on the weathering of granitoid rocks summary the results obtained in several recent studies provide convincing evidence that potassium rich granitoid rocks are relatively more resistant to weathering than their less potassic counterparts this reflects the fact that microcline and orthoclase are more stable in most weathering environments than calcic plagioclase and biotite relatively slight differences in bulk rock chemical composition can lead to differential rates of weathering in areas of inhomogeneous granitoid terrain thereby leading to the development of topographic features such as inselbergs a second major control on the rate of weathering is rock permeability this is largely a function of degree of microfracturing and jointing in most circumstances grain size and other textural differences probably exert a minor influence on rates of chemical weathering although laboratory tests have shown they may profoundly affect physical strength parameters

the tianger bingdaban shear zone hosted gold deposit west tianshan nw china petrographic and geochemical characteristics abstract the wangfeng tianger saridala ore district consists of over 20 orebodies with total proven gold reserves exceeding 15 tonnes the district is located on the ew striking tianger bingdaban shear zone in west tianshan mountains northwest china the lensoid orebodies are distributed along the shear zone in a region about 25 km in length and 1 km in width enhanced fluid flow and fracturing controlled location and orientation of mineralized zones during deformation along narrow shear bands oriented oblique to the overall shear zone margins fabrics in fractures and strain shadow overgrowths generally plunge steeply parallel to the lineation in the surrounding cataclasite matrix consisting of new grains of quartz and minor amounts of micas native gold occurs in mylonitized granites or mylonitized sulfide mica quartz veins gold grade is closely related with the occurrence of sulfide quartz veins pyrite and pyrrhotite in gold bearing sulfide quartz veins contain inclusions of native gold chondrite normalized rare earth element ree distribution patterns for pyrite from the orebodies show light ree enrichments and negative eu anomalies relationships between gold contents and th u zr hf and la yb n values for pyrites imply that gold rich pyrites are different from gold poor pyrites thus indicate that the pyrites in the orebodies have a different origin compared with those in wall rocks a rb sr isochron for the mylonitized au bearing quartz veins indicates an age of 224 14 ma with an initial 87 sr 86 sr ratio of 0 7294 0 0089 mswd 1 1 this age is conformed by 40 ar 39 ar dating on muscovites 220 9 to 222 5 ma which is interpreted as the age of ore formation in the tianger deposit high initial 87 sr 86 sr ratios 0 7294 high 34 s values 11 2 to 16 5 low 18 o h2o values 1 67 to 3 07 and low d values 84 to 104 indicate that the ore forming fluid was unrelated to any magmatic process

grus weathering mantles problems of interpretation abstract grus is an ill defined product of deep weathering of coarse grained rocks whose relationships to other weathering changes remain unclear this paper attempts to address this issue by reviewing a number of examples of coarse saprolites from a variety of climatic and topographic settings grus is the category of weathering mantle that possesses the following characteristics sand gravel 75 100 silt clay

feo rich porphyritic pyroxene chondrules in unequilibrated ordinary chondrites abstract a suite of feo rich type ii porphyritic olivine pyroxene pop chondrules has been studied in detail data for ten chondrules from semarkona ll3 0 are emphasized and one chondrule from chainpur ll3 4 and two from parnallee ll3 6 are included as further examples of certain properties the chondrules contain phenocrysts of pyroxene and olivine in varying proportions and have fe fe mg 10 mol in the silicate minerals four pyroxene minerals are present clinoenstatite orthorhombic enstatite pigeonite and augite pyroxene phenocrysts may consist of all four minerals with progressive overgrowths in order of increasing wo content enstatite may occur independently of clinoenstatite but ca rich pyroxenes pigeonite and augite always nucleate on low ca pyroxene phenocrysts pyroxene and olivine phenocrysts may be independent of each other or may be intergrown and commonly show hopper morphologies indicative of rapid growth pyroxenes and olivines are commonly strongly zoned as a result of fractional crystallization of the chondrules in addition low ca pyroxene may contain ghost regions of slightly more feo and minor element rich material in the cores of grains these regions are partially resorbed and appear to be derived from previous crystallization of essentially the same chondrule oscillatory zoning is observed in enstatite in two chondrules and is believed to be the result of disquilibrium kinetic effects relict grains including a forsterite relict and a partially reduced feo rich relict in the same chondrule and clinoenstatite cores of pyroxene phenocrysts in another chondrule are evidence for recycling and mixing of chondrule material all of the chondrules are highly disequilibrium assemblages they appear to have cooled from essentially molten droplets with little volatile loss or recondensation occurring during the heating event peak temperatures were probably close to liquidus temperatures 1500 1700 c and cooling rates were probably of the order of hundreds of degrees per hour this description will serve as a basis for future interpretation of the effects of metamorphism on porphyritic pyroxene rich chondrules

partial least squares regression for linking aggregate pore characteristics to the detachment of undisturbed soil by simulating concentrated flow in ultisols subtropical china soil pores are known as an effective medium for water air and chemical movement however quantifying pore structures and their relationship to the detachment of undisturbed soil by concentrated flow is not fully understood the objectives of this study were to quantify 3d aggregate microstructures using synchrotron based high resolution x ray micro computed tomography sr mu ct under wetting and drying cycles and to investigate the effects of pore characteristics on the detachment of undisturbed soil by simulating concentrated flow the detachment rates d r of undisturbed topsoil samples which were subjected to a pretreatment of zero to eleven wetting and drying cycles were measured in a 3 8 m long 0 2 m wide hydraulic flume under unitary flow shear stresses tau 14 49 pa 3 5 mm aggregates were collected from the pretreatment soils which were subjected to zero five and eleven wetting and drying cycles and were scanned at a 3 7 mu m voxel resolution for reconstructing three dimensional microtomography images the relationships among pore characteristics and d r were analyzed using partial least squares regression plsr the results indicated that d r and the aggregate microstructure changed significantly after the wetting and drying cycles dr was closely associated with the pore characteristics the pore characteristics such as a 100 mu m porosity total porosity fraction of regular pores 30 75 mu m porosity fraction of elongated pores and fraction of irregular pores were identified as the primary parameters that control the d r the pore characteristics and clay content could account for as much as 68 2 of the variation in d r d r was significantly and positively related to a 100 mu m porosity total porosity and fraction of elongated pores thus soil fragmentation depended on microcracks that formed during the wetting and drying cycles and on the geometrical characteristics of the pores or cracks the results from this study provide a quantitative evaluation of the relationships between pore characteristics and the detachment of undisturbed soil by simulated concentrated flow a further understanding of the effect of topsoil microstructure on water erosion and quantitative information for assessing and modeling erosion processes was obtained c 2015 elsevier b v all rights reserved

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

influence of declining mean annual rainfall on the behavior and yield of sediment and particulate organic carbon from tropical watersheds abstract the capacity to forecast climate and land use driven changes to runoff soil erosion and sediment transport in the tropics is hindered by a lack of long term data sets and model study systems to address these issues we utilized three watersheds characterized by similar shape geology soils vegetation cover and land use arranged across a 900 mm gradient in mean annual rainfall mar using this space for time design we quantified suspended sediment ss and particulate organic carbon poc export over 18 months to examine how large scale climate trends mar affect sediment supply and delivery patterns hysteresis in tropical watersheds average daily ss yield ranged from 0 128 to 0 618 t km 2 while average daily poc ranged from 0 002 to 0 018 t km 2 for the largest storm events we found that sediment delivery exhibited similar clockwise hysteresis patterns among the watersheds with no significant differences in the similarity function between watershed pairs indicating that 1 in stream and near stream sediment sources drive sediment flux and 2 the shape and timing of hysteresis is not affected by mar with declining mar the ratio of runoff to baseflow and inter storm length between pulse events both increased despite increases in daily rainfall and the number of days with large rainfall events increasing with mar there was a decline in daily ss yield possibly due to the exhaustion of sediment supply by frequent runoff events in high mar watersheds by contrast mean daily poc yield increased with increasing mar possibly as a result of increased soil organic matter decomposition greater biomass or increased carbon availability in higher mar watersheds we compared results to modeled values using the load estimator loadest fortran model confirming the negative relationship between mar and sediment yield however because of its dependency on mean daily flow loadest tended to under predict sediment yield a result of its poor ability to capture the high variability in tropical streamflow taken together results indicate that declines in mar can have contrasting effects on hydrological processes in tropical watersheds with consequences for instream ecology downstream water users and nearshore habitat

geodynamic settings of mineral deposit systems mineral deposits represent extraordinary metal concentrations that form by magmatic magmatic hydrothermal or hydrothermal processes in geodynamic environments typified by anomalously high thermal and or mechanical energy near plate boundaries as they require the conjunction of specific environmental conditions to form particular mineral deposit types tend to occupy specific geodynamic niches the temporal distributions of mineral deposit types reflect both formational and preservational processes in the archaean and palaeoproterozoic these were linked because of preservation in continental crust connected to thick buoyant subcontinental lithospheric mantle sclm but were decoupled by the neoproterozoic and phanerozoic as a result of evolution to thinner increasingly dense sclm the transition marks a change from mantle plume influenced plate tectonics to modern style plate tectonics with broadly coincident environmental changes and a major impact on the nature and abundance of preserved mineral deposit types as mineral deposits represent an integral part of tectonic process they are essential indicators of that process and geodynamic settings and should be incorporated into any holistic tectonic terrane analysis their distribution also provides a particularly critical test on ancient continental reconstructions derived from palaeomagnetic data conversely such reconstructions provide a first order targeting tool for the conceptual exploration required to discover new mineral provinces and deposits under cover

weathering erosion and sediment composition in a high gradient river calabria italy source rock lithology and immediate modifying processes such as chemical weathering and mechanical erosion are primary controls on fluvial sediment supply sand composition and chemical index of alteration cia of parent rocks soil and fluvial sand of the savuto river watershed calabria italy were used to evaluate the modifications of source rocks through different sections of the basin characterized by different geomorphic processes in a sub humid mediterranean climate the headwaters with gentle topography produce a coarse grained sediment load derived from deeply weathered gneiss having sand of quartzofeldspathic composition compositionally very different from in situ degraded bedrock maximum estimated cia values suggest that source rock has been affected significantly by weathering and it testifies to a climatic threshold on the destruction of the bedrock the mid course has steeper slopes and a deeply incised valley bedrock consists of mica schist and phyllite with a very thin regolith which provides large cobble to very coarse sand sediments to the main channel slope instability with an areal incidence of over 40 per cent largely supplies detritus to the main channel sand sized detritus of soil and fluvial sand is lithic estimated cia value testifies to a significant weathering of the bedrock too even if in this part of the drainage basin steeper slopes allow erosion to exceed chemical weathering the lower course has a braided pattern and sediment load is coarse to medium fine grained the river cuts across palaeozoic crystalline rocks and miocene siliciclastic deposits sand sized detritus contributed from these rocks and homogenized by transport processes has been found in the quartzolithic distal samples field and laboratory evidence indicates that landscape development was the result of extensive weathering during the last postglacial temperature maximum in the headwaters and of mass failure and fluvial erosional processes in the mid and low course copyright 2000 john wiley sons ltd

dating the xiaobaishitou skarn w mo deposit eastern tianshan nw china constraints from zircon u pb muscovite 40ar 39ar and molybdenite re os system abstract the xiaobaishitou deposit 36 264 tonnes 0 78 wt wo3 in the eastern tianshan orogenic belt is a medium sized skarn deposit characterized by w mo ore bodies that developed along contacts between triassic biotite granite and mesoproterozoic carbonaceous rocks scheelite and molybdenite are the dominant metallic minerals in this deposit and mostly precipitated during the retrograde stage and or quartz sulfide stage respectively laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms zircon u pb dating of the mineralization related biotite granites from underground openings and outcrops yields ages of 247 9 1 7 ma 1 n 22 mswd 0 69 and 252 2 3 0 ma 1 n 12 mswd 1 60 implying they were emplaced in the early triassic a muscovite 40ar 39ar weighted plateau age of 247 6 2 3 ma 2 mswd 2 03 and molybdenite re os model ages ranging from 235 8 5 7 ma to 249 6 3 6 ma weighted mean age 251 1 1 6 ma 2 mswd 0 70 are interpreted as the time of the hydrothermal activity mineralization the excellent agreement among the u pb 40ar 39ar and re os chronometers confirms that the xiaobaishitou deposit formed in the early triassic the re contents of the molybdenites range from 18 477 to 130 447 ng g suggesting that the ore forming materials were derived from continental crust together with the involvement of abundant mantle components as one of the representative triassic deposit in eastern tianshan the xiaobaishitou provides important chronological evidence for metallogenic regularity in the eastern tianshan and the central asian orogenic belt the new ages reported here confirm that the xiaobaishitou deposit represents one of the magmatic hydrothermal mineralization events that occurred in the eastern tianshan orogenic belt in lithospheric extension during the triassic it is suggested that mantle material played a role in producing the triassic mineralization and associated magmatism

structural and geochemical controls on the development of turbidite hosted gold quartz vein deposits wattle gully mine central victoria australia gold quartz vein deposits in the wattle gully mine arefault related structures developed in a low grade metamorphosed ordovician quartz rich flysch sequence the major mineralization is associated with a high angle reverse fault wattle gully fault that has a maximum displacement of 40 m over 10 6 metric tons t of vein quartz averaging 10 5 g t au occur within a dilatant jog in this structure fold geometry has controlled fault geometry and resulted in the localization of the jog segment where the wattle gully fault traverses an east dipping fold limb to link two more steeply dipping bedding parallel fault sediments on adjacent west dipping fold limbs gold mineralization is also associated with several minor east clipping reverse faults and a bedding parallel fault whose development is related to flexural slip during fold tightening mineralization occurs within fault fill veins and extension veins adjacent to faults the geometry and internal structures of veins indicate that vein growth has been controlled by repeated fluctuations in fluid pressure and shear stress associated with fault valve behavior vein mineralogy is dominated by quartz with minor carbonates chlorite white mica albite and apatite arsenopyrite and pyrite are the major sulfide phases but sphalerite galena chalcopyrite and pyrrhotite are also present the highest au grades tend to be localised in vein systems that are in proximity to carbonaceous slates wall rock alteration is minor and restricted mainly to narrow zones adjacent to major vein systems sulfur isotope fractionation between galena and sphalerite indicates mineralization occurred at temperatures around 300 degrees c the delta 34 s compositions of pyrite and arsenopyrite are nearly uniform throughout the mine 1 5 2 8 but are generally not in equilibrium with the delta 34 s values of associated base metal sulfides 0 7 5 3 the delta 18 o values for vein quartz vary between 15 6 and 18 0 per mil and correspond to delta 18 o values

genesis of two different types of gold mineralization in the linglong gold field china constrains from geology fluid inclusions and stable isotope abstract the dongfeng and linglong gold deposits are located in the northwest jiaodong peninsula north china craton the deposits are mainly hosted in the mesozoic granitoids and structurally controlled by the zhaoyuan pingdu fault zone gold mineralization at dongfeng occurs as disseminated ores and sulfide stockworks typically enveloped by broad alteration selvages in contrast mineralization at linglong is characterized by massive auriferous quartz veins with narrow alteration halos three stages of mineralization were identified in both deposits with the early stage represented by quartz pyrite the middle stage by gold quartz pyrite or gold quartz base metal sulfides and the late stage by quartz carbonate pyrite respectively four types of fluid inclusions were distinguished based on petrography microthermometry and laser raman spectroscopy including 1 pure co2 fluid inclusions type i 2 h2o co2 nacl fluid inclusions type ii 3 h2o nacl fluid inclusions type iii and 4 daughter mineral bearing or multiphase fluid inclusions type iv in the dongfeng gold deposit the early and middle stage quartz mainly contains primary type ii fluid inclusions that completely homogenized at temperatures of 276 341 c with salinities of 2 8 11 7 wt nacl equivalent and temperatures of 248 310 c with salinities of 3 3 10 8 wt nacl equivalent respectively a few primary type i fluid inclusions could be observed in the early stage quartz in contrast the late stage quartz contains only the type iii fluid inclusions with homogenization temperatures of 117 219 c and salinities of 0 5 8 5 wt nacl equivalent the estimated pressures for the middle stage fluids are 226 338 mpa suggesting that gold mineralization mainly occurred at paleodepths of deeper than 8 4 12 5 km the mineralization resulted from extensive water rock interaction between the h2o co2 nacl fluids and wallrocks in the first order fault in the linglong gold deposit the early stage quartz mainly contains primary type ii fluid inclusions and a few type i fluid inclusions of which type ii fluid inclusions have salinities of 3 3 7 5 wt nacl equivalent and homogenization temperatures of 271 374 c the middle stage quartz mainly contains all four types of fluid inclusions among which the type ii fluid inclusions yield homogenization temperatures of 251 287 c and salinities of 5 5 10 3 wt nacl equivalent while the type iii fluid inclusions have homogenization temperatures of 244 291 c and salinities of 4 1 13 3 wt nacl equivalent fluid inclusions in the late stage quartz are type iii fluid inclusions with low salinities of 0 3 8 2 wt nacl equivalent and low homogenization temperatures of 103 215 c the trapping pressure estimated for the middle stage fluids is 228 326 mpa suggesting that the gold mineralization mainly occurred at paleodepths of about 8 4 12 1 km precipitation of gold is possibly a consequence of phase separation or boiling of the h2o co2 nacl fluids in response to pressure and temperature fluctuations in the open space of the secondary faults the 34s values of pyrite are similar for the dongfeng and linglong deposits and show a range of 5 8 to 7 0 and 5 9 to 7 4 respectively oxygen and hydrogen stable isotopic analyses for quartz yielded the following results 18o 3 8 to 6 4 and d 90 5 to 82 7 for the dongfeng deposit and 18o 0 0 to 8 9 and d 77 4 to 63 7 for the linglong deposit stable isotope data show that the ore forming fluids of the two gold deposits are of magmatic origin with gradual incorporation of shallower meteoric water during after mineralization