magmatic anhydrite in plutonic rocks at the el teniente cu mo deposit chile and the role of sulfur and copper rich magmas in its formation anhydrite occurs along with biotite feldspars quartz fe oxides and sulfides in fine grained igneous rocks that form the small porphyry a stock at el teniente these minerals crystallized together in the space generated by the intrusion of this stock and they do not replace preexisting phases planar crystal boundaries between anhydrite and other phases as well as the fact that plagioclase and biotite are fresh and unaltered also suggest that anhydrite is an igneous phase and not the product of secondary hydrothermal alteration plagioclase is unusually na rich ranging from oligoclase in mafic varieties of these rocks with 20 percent biotite to albite in more felsic samples with 20 percent these unusual anhydrite bearing plutonic rocks which contain up to 3 wt percent s and 0 5 wt percent cu are isotopically similar to all other igneous rocks related to the deposit these rocks formed during a late miocene period of regional compressive deformation with no coeval volcanic activity in the area of the deposit which prevented devolitalization of the oxidized parent magma in the large productive magma chamber inferred to have underlain el teniente at 4 km below the paleosurface this allowed igneous fractionation involving the recharge of mantle derived mafic magmas into the base of the chamber as well as volatile transfer and concentration near its roof to produce the cu and s rich magmas that formed the anhydrite bearing intrusive rocks

geochronological and geochemical constraints on aolunhua porphyry mo cu deposit northeast china and its tectonic significance abstract the aolunhua porphyry mo cu deposit is located in the northern margin of the north china craton ncc and belongs to the northern part of the xilamulun metallogenic belt more than 90 of the mineralization occurs within the aolunhua monzogranite porphyry a small part is hosted within quartz veins that crosscut late permian strata the syenogranite occurring as dikes and cutting through the aolunhua monzogranite porphyry is radially distributed in the mining district zircon u pb ages show that the aolunhua monzogranite porphyry and the post ore syenogranite have concordant 206pb 238u ages of 138 7 1 2 ma and 131 4 2 8 ma respectively based on analyses of major trace elements and hf isotopes the aolunhua porphyry is characterized by high sr low y with high la yb and sr y ratios typical of adakitic granites whereas the post ore syenogranite has lower sr and higher y values showing apparently negative eu anomalies eu 0 26 to 0 31 the hf isotopic composition of the aolunhua porphyry ehf t 3 6 to 9 2 and the post ore syenogranite ehf t 3 6 to 8 7 indicates that both juvenile crustal sources and depleted mantle contributed to their origin the regional geological setting together with the discrepancy of geochemistry between the aolunhua porphyry and the post ore syenogranite probably indicates that they formed in different tectonic regimes the aolunhua porphyry is derived from partial melting of the thickened crust due to underplating of the basaltic magma under the transformation tectonic regime while the post ore syenogranite comes from the crustal root melting during the lithospheric delamination stage under the lithosphere thinning regime of northeast china

the fate of magmatic sulfides during intrusion or eruption bingham and tintic districts utah magmatic sulfides in 97 samples of volcanic and intrusive rocks from the tertiary bingham cu au mo and tintic ag pb zn cu au districts utah were examined to help better understand the fate of magmatic sulfides during intrusion and eruption our findings show that shallowly emplaced dikes and sills have erratic but locally high concentrations of sulfides volcanic rocks and large porphyry intrusions from these districts typically have at least two orders of magnitude fewer sulfides than the dikes sulfide concentrations vary dramatically across these dikes and sills for example in one sill in castro gulch bingham district sulfide abundance increases from 9 ppm by volume in the center to more than 2 000 ppm near the margin chalcophile metals show corresponding changes in abundance for example the whole rock copper content of the sill ranges from 23 ppm in the center to 35 ppm along the margins the textures of sulfide grains interpreted to reflect recrystallization resorption and degassing even in the most sulfide rich samples commonly have been modified suggesting that no sample preserves all of its original magmatic sulfide content immiscible liquids of monosulfide solid solution crystallized as pyrrhotite pyrrhotite and chalcopyrite or pyrite and chalcopyrite with declining temperature and pressure these locally recrystallized to pyrite and chalcopyrite or to pyrite and an fe oxide as they are oxidized the alteration and preservation textures change from subspherical sulfide blebs near the margins of dikes and sills to partially altered sulfides farther in to complete absence of sulfides in the vast majority of intrusions except where small sulfides are completely enclosed by phenocrysts sulfide concentrations appear to vary according to cooling rate and inferred pressure at the time of quenching or crystallization of the matrix most of the sulfides along the quenched margins of these dikes and sills are in the matrix slower cooling coupled with removal of magmatic volatiles including sulfurous gases e g h2s so2 allows the resorption or oxidation of magmatic sulfides to occur during final crystallization of a magma together these processes remove greater than 90 percent of the original endowment of magmatic sulfides this probably explains the low magmatic sulfide abundances of slowly cooled large porphyritic intrusions and most importantly allows metals and sulfur to participate in the formation of porphyry deposits the relative abundances of base metals lost from the center of the sill are similar to the relative abundances of the metals in the bingham deposit production and reserves suggesting that these processes also may have operated at a larger scale

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

ages and geodynamic settings of xilamulun mo cu metallogenic belt in the northern part of the north china craton abstract the xilamulun belt along the northern part of the north china craton is located in eastern segment of the central asian orogenic belt and has great economic potential for mo cu mineralization more than ten medium to large ore deposits have been discovered in this region in the recent years the major types of mineralization type include porphyry chehugou mo cu kulitou mo cu xiaodonggou mo and jiguanshan mo quartz vein nianzigou mo xinjing mo epithermal hongshanzi mo u and alteration assemblage liulingou mo the timing of mineralization was previously thought to be yanshanian 208 290 ma however indosinian 260 208 ma ages for intrusions and mineralization have been recognized in recent years based on geochronologic data and regional geological evidence it is suggested that the mineralization in the xilamulun belt was formed during multiple events the mineralization processes are related to a post collisional extension stage 258 210 ma with the generation of the porphyry molybdenum copper deposit a tectonic stress transformation from ns to ew 185 150 ma that gave rise to vein or porphyry molybdenum deposit and a lithospheric thinning stage 140 110 ma with porphyry molybdenum deposit

hydroxide in pyroxene variations in the natural environment a suite of 51 pyroxenes from a wide range of geological environments was examined with infrared spectroscopy small amounts of oh occur in nearly all the samples suggesting that oh groups are a minor component of most pyroxenes the oh concentrations vary 0 002 0 12 wt oh as a function of geological setting with the greatest amounts occurring in mantle derived samples the intensities of certain oh absorption bands are somewhat correlated with pyroxene composition in particular with the presence of trivalent cations this suggests that crystal chemical or compositional factors also control the oh incorporation the oh incorporated in the pyroxene structure is easily distinguishable from oh owing to amphibole lamellae which usually occur in diopsides and often in orthopyroxenes oh in pyroxene is probably a function of the activity of hydrous components during crystallization but may also depend on postcrystallization changes in the geological environment

the role of magmatic sulfides and mafic alkaline magmas in the bingham and tintic mining districts utah this paper reports the existence of abundant magmatic sulfides in introduction latite lava vitrophyres and vent facies dikes from the bingham and the eruption of sulfur rich magmas from el chichon tintic districts in central utah these dikes and flows appear to luhr et al 1984 and mt pinatubo westrich gerlach be comagmatic with the ore related monzonite intrusions in addition 1992 in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the cu and ag present in the latites magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres sulfides and anhydrite however the occurrence of magpetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal resorption and oxidation s degassing of the globules may make many volcanic suites appear to be sulfide unsaturated the metal content available to a magmatic ore fluid minette and inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals what would their presence signify in magmatic fields associated with latite monzonite intrusions and hydrothermal systems that formed porphyry cu and mesothermal vein ore deposits of the tintic ag pb zn cu au and bingham deposits do they sequester a significant portion of the porphyry cu au mo districts utah the ages chemical and magmatic cu pb zn ag and au thereby restricting modal compositions and field relations of the mafic alkaline lavas metal availability of subsequent ore forming fluids suggest that such magmas mixed and fractionated at shallow crustal we have examined the volcanic rocks from the tintic levels to form the ore related latites and monzonites the unaltered and bingham mining districts fig 1 utah and found mafic alkaline lavas in these districts are some of the most cu rich that almost all of the volcanic units contain magmatic lavas in the great basin province sulfides some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic keith et al 1989 1991 waite 1996 the tintic district and east tintic sub district in utah have recorded over

water weakening of clinopyroxenite in diffusion creep 1 we performed triaxial compressive creep tests to study water weakening of clinopyroxenite in the diffusion creep regime all tests were carried out on fine grained samples at confining pressures between 100 and 300 mpa at temperatures of 1321 to 1421 k for water saturated and 1398 to 1508 k for anhydrous conditions samples were prepared by hot pressing ground powder of sleaford bay clinopyroxenite water was added to the sample during the run by dehydration of a talc sleeve water saturated aggregates crept 30 times faster than aggregates under anhydrous conditions at a temperature of 1400 k and a pressure of 300 mpa the stress exponent in both cases was 1 and the activation energies under water saturated and anhydrous conditions were 340 30 and 760 20 kj mol respectively under water saturated conditions creep rate increased with increasing water fugacity to the power 1 4 0 2 with an activation volume for creep of 14 6 10 6 m3 mol comparison of the water weakening in aggregates of clinopyroxene olivine and anorthite deformed in the diffusion creep regime indicates that the creep strength of clinopyroxene has a stronger dependence on the water fugacity than do the creep strengths of olivine and anorthite in water rich environments clinopyroxene will be the weakest component in polycrystalline rocks composed of these phases

the adakite connection of the tuwu yandong copper porphyry belt eastern tianshan nw china trace element and sr nd pb isotope geochemistry the tuwu yandong porphyry copper belt lies in the eastern tianshan mountains eastern section of the central asian orogenic belt the copper mineralization is mainly hosted in plagiogranite porphyries intruded into early carboniferous volcanic rocks of the paleozoic dananhu island arc between the tarim and siberian plates the plagiogranite porphyries have contents of 65 73 wt sio2 14 17 wt al2o3 0 9 2 2 wt mgo 3 16 ppm y 0 4 1 40 ppm yb 347 920 ppm sr and positive eu anomalies the rocks also exhibit positive nd t values 5 0 to 9 4 and low initial 87sr 86sr values 0 70316 0 70378 such features are similar to those of adakites derived from partial melting of a subduction related oceanic slab the mineralization age is early carboniferous 350 320 ma which is close to that of the porphyries the close relationship between the cu mineralization and the porphyry is also indicated by their similar sr nd pb isotopic compositions we suggest that the copper porphyry magma system in the dananhu island arc was formed by direct melting of an obliquely subducting early carboniferous oceanic slab

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

geological features and origin of xiaodonggou porphyry molybdenum deposit in hexigten banner inner mongolia located in the easternmost part of the early paleozoic tectono magmatic belt within the ondur sum ongniud banner on the northern edge of the north china craton the newly discovered xiaodonggou deposit is a medium size porphyry molybdenum deposit occurring in central eastern inner mongolia during the mesozoic yanshanian orogeny intense tectonic and igneous activities resulted in large scale granitoid magmatism in xiaodonggou and its neighboring areas the xiaodonggou granitoid porphyry stock was emplaced in the volcano sedimentary sequence of the upper permian ranfangdi formation controlled by the ns trending fault zone with an outcrop area of 0 22 km2 it consists mainly of porphyritic biotite granite and fine grained biotite granite which have the same mineral assemblage rock forming minerals are mainly quartz microcline microperthite and plagioclase associated with minor biotite and sericite accessory minerals comprise magnetite apatite zircon sphene and allanite the porphyry stock is petrochemically characterized by relatively high sio2 k2o rb u and th and obviously low cao fe2o3 feo mgo sr ba nb ta and ree thus belonging to silicon high potassium rich rock of calc alkaline series molybdenum mineralization occurs exclusively within the xiaodonggou porphyritic granitoid stock as veins veinlets and disseminated blocks molybdenum ore consists of pyrite chalcopyrite molybdenite sphalerite pyrrhotite scheelite wolframite k feldspar quartz sericite chlorite and epidote as the most important economic molybdenum mineral molybdenite occurs in the forms of impregnation radioflakes thin films aggregated flakes and veinlets in veins re os isotopic data of six molybdenite separates define a correlation line corresponding to an age of 135 5 1 5 ma hydrothermal alterations in xiaodonggou roughly show zonation of k feldspathization greisenization silicification and propylitization from the porphyritic biotite granite stock outward of these alterations silicification and greisenization are well developed and have intimate relationship with molybdenum mineralization fluid inclusion studies yield homogeneous temperatures from 260 to 480 with the main ore forming stage ranging from 320 to 420 gaseous inclusions are frequently coexistent with multiphase inclusions containing such daughter minerals as halite sylvite molybdenite and k feldspar intense boiling of the ore forming fluid resulted in the deposition of a great volume of molybdenite under the circumstances of medium to high temperature relatively low f o2 and f s2 and weak acidity sulfur and oxygen isotopic data of the molybdenum ore indicate that the ore forming fluid was dominated by magmatic water at the early ore forming stage and characterized by mixed solution with magmatic water as the major source at the main ore forming stage in contrast the ore bearing fluid was mainly heated meteoric water therefore it is conceivable that sulfur and molybdenum were mostly derived from the magmatic source combined geochemical data field geological observations and petrological evidence indicate that the xiaodonggou deposit is a porphyry type hypothermal mesothermal molybdenum deposit formed by early cretaceous intraplate granitoid magmatism on the northern margin of the north china craton in addition the genetic model and mineral exploration criteria of the xiaodonggou deposit can also be used as useful tools in the comprehensive evaluation of concealed molybdenum deposits on the northern margin of north china craton

genesis morphology and mineralogy of planosols developed from different parent materials in southern brazil abstract the genesis of planosols is a complex process since it can involve multiple cycles of soil formation deposition of allochthonous materials and also past climate changes furthermore this subject is still poorly studied in the humid tropics thus hindering a proper appraisal of the potentials and limitations of planosols the objective of this research was to study pedogenetic processes and properties of planosols formed from different parent materials in southern brazil four soils were sampled p1 hypereutric luvic albic planosol developed on lagoon plain sediments p2 orthoeutric luvic albic planosol on holocene alluvial deposits p3 hypereutric luvic albic planosol on granite and p4 orthoeutric luvic albic planosol on gneiss all planosols presented sandy horizons a and e with low ph

contribution of mafic melt to porphyry copper mineralization evidence from mount pinatubo philippines and bingham canyon utah usa mount pinatubo in the philippines known for its cataclysmic eruption in 1991 hosts several porphyry copper deposits and active geothermal systems an underlying mafic melt supplied much of the sulphur for the dacitic magma and its injection into the dacitic magma chamber triggered the eruption the eruption caused purging of the sulphur rich fluid from the dacite to the atmosphere and extensive fracturing similar events took place at bingham canyon utah site of the largest copper and gold deposit in north america at 38 ma the bingham canyon mineralization took place beneath an active stratovolcano and pyroclastic flows contemporaneous with the mineralization show evidence for magma mingling ascent of mafic melt supplied sulphur and chalcophile elements to the felsic magma which consolidated to form the bingham stock and its underlying magma chamber injections of the mafic melt caused periodic eruptions of felsic magma to form the stratovolcano and deposition of sulphide minerals in highly fractured rocks in and around the stock

contrasting oxygen diffusion in nepheline diopside and other silicates and their relevance to isotopic systematics in meteorites oxygen self diffusion coefficients have been determined in natural nepheline na3 na k al4si4o16 and synthetic diopside camg sio3 2 at one atmosphere by monitoring the rate of 18o exchange between co2 gas and minerals of pre determined grain size 10 12 5 and 15 m radius oxygen self diffusion in nepheline between 1000 and 1300 c fits a linear arrhenius relation of the form d 5 9 10 9 exp 25 0 2 5 103calrt and for diopside between 1150 and 1350 c d 6 3 exp 96 7 5 8 103calrt the activation energy for oxygen diffusion in nepheline is similar to that of melilite 31 9 0 1 kcal mol but the oxygen diffusivity is lower by two orders of magnitude the diffusion of oxygen in diopside is similar to that of nepheline at 1375 c however the activation energy is almost four times higher this contrast suggests a difference in the crystal chemical and structural controls of the minerals both nepheline and melilite are characterized by strongly distorted alkali sites within their frameworks which could account for their relatively low activation energies and high diffusivities more importantly nepheline and melilite have sheet like structures and high anionic porosities which may provide ready migration paths for oxygen the concentration of open space between the silicate sheets in melilite may explain the greater diffusivity of oxygen in melilite than in nepheline diopside forsterite anorthite spinel are characterized by high activation energies 80 to 100 kcal and are refractory with very stable bonds and low anion porosities furthermore these minerals are much denser and closer packed than nepheline or melilite making it difficult for oxygen to migrate within the crystalline structure and have access to the cation oxygen bonds oxygen diffusion studies constrain interpretations of post solidus oxygen exchange among minerals and may be used to explain the stable isotope systematics observed in ca al rich inclusions of carbonaceous chondrites the slow exchange and diffusion of oxygen in diopside suggests that the isotopic composition of clinopyroxenes in ca al rich inclusions of carbonaceous chondrites has not changed appreciably since their incorporation into the meteorite however minerals such as nepheline and melilite which readily exchange oxygen record the isotopic composition of the last nebular gas to which they were exposed

quantitative analysis of trace oh in garnet and pyroxenes to calibrate infrared ir spectroscopy for quantitative analysis of trace structural oh in specific minerals we have determined concentrations of h in pure separates of mantle derived pyrope garnet 56 6 ppm h 2o by weight augite 268 8 ppm h 2o and enstatite 217 11 ppm h 2o by manometry after heating the samples and extracting h 2 gas under vacuum ir spectroscopy confirmed the presence of intrinsic oh in these samples prior to extraction and indicated between 86 and 100 removal of h during the extraction procedure the integral specific absorption coefficients of 1 39 0 14 l 7 09 0 32 and 15 6 0 94 ppm h 2o cm 2 for pyrope augite and enstatite respectively allow precise spectroscopic determination of the oh content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million uncertainties in accuracy depend on mineral composition and characteristics of the oh absorption spectrum and are estimated to range between 10 and 50

water weakening of clinopyroxene in the dislocation creep regime we performed a series of triaxial compressive creep experiments at two different water fugacities to investigate the effect of water on the creep strength of a natural clinopyroxenite samples were deformed under water saturated conditions at temperatures between 1373 and 1473 k confining pressures of 150 and 300 mpa and differential stresses from 34 to 261 mpa strain rates were in the range 10 7 to 10 5 s 1 water fugacity was controlled at either 140 or 280 mpa the creep results yield a stress exponent of 2 7 0 3 and an activation energy of 670 40 kj mol compared to dry clinopyroxene wet samples creep over 100 times faster at a given temperature confining pressure water fugacity and differential stress the creep rate of clinopyroxene is proportional to the water fugacity to the 3 0 0 6 power with an activation volume of 0 m 3 mol one possible water weakening mechanism is an enhancement of the rate of dislocation climb associated with increases in the concentration of jogs and the diffusivity of silicon ions compared to other major minerals in earth s lower crust specifically olivine and plagioclase the water weakening effect is most significant for clinopyroxene under hydrous conditions the strengths of clinopyroxene and anorthite are comparable over the investigated stress range and both phases are weaker than olivine since the mineral assemblages in earth s lower continental crust are often dominated by plagioclase and pyroxene in places where a wet flow law applies the mechanical behavior of clinopyroxene will have a substantial effect on creep strength

regional metallogeny of mo bearing deposits in northeastern china with new re os dates of porphyry mo deposits in the northern xilamulun district with many new discoveries of giant mo deposits in the past decade northeastern china has become the largest molybdenum mineralization region in china the xilamulun district is in the southern part of northeastern china and contains 25 mo deposits and prospects dominantly of porphyry type these deposits are mostly along the e striking xilamulun fault re os dating of hydrothermal molybdenite from four deposits in the northern xilamulun district revealed mineralization ages of 137 to 129 ma 129 4 3 4 ma for aolunhua 135 3 2 6 ma for shabutai 136 4 0 8 ma for haisugou and 136 1 6 6 ma for banlashan in general agreement with the crystallization ages of their host granitoids the compilation of existing data on mo bearing deposits in northeastern china including the new data of this study shows that mesozoic mo deposits in this region have a wide range of ages from 250 to 90 ma we propose that they are linked to three tectonic magmatic events 1 triassic mo deposits 250 220 ma are mainly distributed along the e trending xilamulun fault and are related to postcollisional crustal extension following the final closure of the paleo asian ocean 2 jurassic mo mineralization 200 140 ma displays a clear younging trend from southeast to northwest coincides with the regional magmatism trend and is interpreted to be related to the northwestward flat slab subduction of the paleo pacific plate beneath the eurasian continent that started in the early jurassic ca 200 ma 3 cretaceous mo mineralization 140 90 ma shows a reversed migration trend from northwest to southeast and can be explained by the coastward migration of slab rollback related to lower crust delamination asthenospheric upwelling and lithospheric thinning in eastern china the spatial temporal distribution of mesozoic mo mineralization is important for regional metallogeny and exploration recently numerous epithermal au cu mo deposits have been recognized in the southeast margin of northeastern china according to this study we predict that hidden porphyry skarn systems could be located beneath these epithermal deposits

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

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

the jiguanshan porphyry mo deposit in the xilamulun metallogenic belt northern margin of the north china craton u pb geochronology isotope systematics geochemistry and fluid inclusion studies implications for a genetic model abstract the jiguanshan porphyry mo deposit is located in the southern part of xilamulun metallogenic belt at the northern margin of the north china craton ncc in the jiguanshan mining district two stages of granitoids intrusions have been recognized a pre ore granite porphyry with stockworks and veins of mo mineralization and a granite porphyry with disseminated mo mineralization zircon u pb data and hf isotope analyses show that the dissemination mineralized granite porphyry yielded a weighted mean 206pb 238u age of 156 0 1 3 ma with a crustal ehf t values from 5 6 to 0 2 and that the main group of magmatic zircons from the pre ore granite porphyry have a weighted mean 206pb 238u age of 167 7 1 7 ma with ehf t values from 3 2 to 1 0 combined with groundmass ar ar age data of the granite porphyry and molybdenite re os age it is suggested that the mo mineralization of jiguanshan deposit was formed in the late jurassic 153 155 ma during tectonic and magmatic events that affected northeast china the mo mineralization was a little bit later than the host granite porphyry besides disseminated in the host granite porphyry mo mineralization also presents in middle jurassic pre ore granite porphyry jurassic fine grained diabase triassic quartz porphyry and in rhyolitic volcanic rocks as well as syenite of devonian age the jiguanshan mining district was affected by the tectonic events associated with the paleo asian ocean closure and later by far field tectonism related to subduction of the paleo pacific plate izanagi in the jurassic cretaceous the tectonic and thermal events linked with the latter are commonly referred to as yanshanian tectono thermal event and consists of a series of geodynamic magmatic and ore forming processes which in the mining district area included the intrusion of the pre ore granite porphyry the host granite porphyry mo mineralization and fine grained diabase major and trace element analyses show that the host granite porphyry is characterized by high silica abundances sio2 77 16 to 77 51 high rb sr ratios 13 57 to 14 83 high oxidation fe2o3 feo 34 25 to 62 00 and high alkalies na2o k2o 8 21 to 8 38 petrographic and microthermometry studies of the fluid inclusions from mo mineralized veins characterized by plenty of daughter mineral bearing inclusions showed that the predominant homogenization temperatures range from 250 to 440 c combined with laser raman analysis of the fluid inclusions it is indicated that mo mineralization is related to a high temperature hypersaline and high oxygen fugacity h2o nacl fluid system with high f contents based on geology geochronology isotope systematics geochemistry and fluid inclusion studies as well as regional geology we propose for the first time a genetic model for the jiguanshan porphyry mo deposit during the jurassic geodynamic evolution of northeast china high silicic high oxidized and alkaline rich granitic magma probably derived from partial melting of the lower crust episodically intruded along faults into the country rocks this fluid system fractionating from the highly differentiated granitic magma and bearing mo with minor cu metals migrated upwards and interacted with the older wall rocks and associated fractures in which the ore minerals precipitated resulting in the development of what we refer to as the jiguanshan type porphyry mo deposit

the mesozoic caosiyao giant porphyry mo deposit in inner mongolia north china and paleo pacific subduction related magmatism in the northern north china craton abstract the caosiyao giant porphyry mo deposit is located in the wulanchabu area of inner mongolia within the northern north china craton ncc it contains more than 2385 mt of ore with an average grade of 0 075 mo in the caosiyao mining district mo mineralization occurs mainly in a mesozoic granite porphyry as disseminations and stockworks with some mo distributed in archean metamorphic rocks and diabase as stockworks and veins the host granite porphyry is composed of two different phases that can be distinguished based on mineral assemblages and textures one phase contains large and abundant phenocrysts coarse grained while the other phase is characterized by fewer and smaller phenocrysts medium grained zircon u pb hf analyses of the former phase yielded a concordant 206pb 238u age of 149 8 2 4 ma with a 206pb 238u weighted mean age of 149 9 2 4 ma and ehf t values ranging from 12 2 to 18 3 while the latter phase gave a concordant 206pb 238u age of 149 0 2 2 ma with a 206pb 238u weighted mean age of 149 0 2 1 ma and ehf t values ranging from 13 1 to 17 7 five samples of disseminated molybdenite have a 187re 187os isochron age of 149 5 5 3 ma with a weighted average age of 149 0 1 8 ma whereas six veinlet type molybdenite samples have a well constrained 187re 187os isochron age of 146 9 3 1 ma and a weighted average age of 146 5 0 8 ma thus it is suggested that the mo mineralization of the caosiyao deposit occurred during the late jurassic ca 147 149 ma almost coeval with the emplacement of the host granite porphyry ca 149 150 ma the host granite porphyry is characterized by high silica sio2 71 52 74 10 wt relatively high levels of oxidation fe2o3 feo 0 32 0 94 wt and high alkali element concentrations na2o k2o 8 21 8 76 wt the host granite porphyry also shows enrichments in u and k and depletion in ba sr p eu and ti suggesting strong fractional crystallization of plagioclase biotite and accessory minerals these observations together with high sio2 contents and a high differentiation index di 89 04 92 44 indicate a strong differentiation of the granite magma based on geological geochronological isotope systematics and geochemical studies we propose for the first time a genetic model for the caosiyao porphyry mo deposit under a regional extensional setting caused by far field tectonics related to the paleo pacific subduction during the late jurassic a series of geodynamic magmatic and ore forming processes took place including formation of multi directional and multi phase faults emplacement of the granitic host rocks and mo mineralization highly silicic highly oxidized and alkali rich granitic magma derived from partial melting of old lower crust intruded into the country rocks this highly differentiated granitic magma and the exsolved ore forming fluids enriched in mo migrated upward and interacted with the wall rocks eventually ore minerals precipitated in fractures resulting in the extensive deposition of molybdenite

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

geochronology and fluid inclusion study of the shabutai porphyry mo deposit inner mongolia abstract the shabutai molybdenum deposit is a newly discovered deposit located in the northern part of the xilamulun metallogenic belt molybdenum mineralization is distributed in granite porphyry and its exocontact zone is in the shape of quartz veins the la icp ms zircon u pb age of ore bearing granite porphyry is 140 1 0 7 ma with a msdw of 0 078 the granite belongs to the high k calc alkaline series characterized by relatively high lree low hree depletion of ti ba and nb and a negative eu anomaly mineralization evolution is divided into three stages early middle and late the stages are characterized by potassium feldspar veins quartz potassium feldspar veins and quartz veins in the early stage quartz molybdenite veins in the middle stage and quartz carbonate veins in the late stage ore minerals were mainly precipitated in the middle stage pure vapor pv vapor rich v liquid rich l and daughter mineral bearing s fluid inclusions were observed in the hydrothermal quartz homogeneous temperatures of fluid inclusions in the early stage ranged from 240 c to 420 c with salinities ranging from 4 0 to 57 2 wt nacl eqv the fluid inclusions contained hematite daughter minerals indicating high oxygen fugacity conditions in the early stage the temperatures of the fluid inclusions at the middle stage ranged predominantly from 200 to 300 c with a salinity range of 0 5 48 5 wt nacl eqv the inclusions also showed high k ion content characteristics both in the early and middle stage fluid a drop in potassium concentration caused by potassic alteration created a favorable condition for mo precipitation the temperature range of the late stage fluid inclusions was 160 307 c with salinities below 10 7 wt nacl eqv according to laser raman microprobe data co 2 occurred only in a few gas fluid inclusions while most gases were h 2 o microthermometric analysis results suggested that fluid boiling was the main factor triggering molybdenite precipitate and forming the shabutai molybdenum deposit

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

geochronology and geochemistry constraints of the early cretaceous taibudai porphyry cu deposit northeast china and its tectonic significance abstract the southern great xing an range sgxr located in the southeastern part of inner mongolia china shows intense mesozoic tectono magmatic activity and hosts economically important polymetallic cu pb zn sn fe ag au mo mineralization here we present new zircon u pb ages whole rock geochemical data nd sr hf isotopic data and re os ages for the taibudai deposit in the sgxr the taibudai granitoids show high sio2 70 62 72 13 wt and alkali na2o k2o 7 04 8 60 wt concentrations low mgo 0 89 1 37 wt and al2o3 14 wt asi ratios

hydroxyl in clinopyroxene from the deep subducted crust evidence for h2o transport into the mantle clinopyroxenes in eclogites from the deep subducted crust in the kokchetav kazakhstan ultrahigh pressure metamorphic terrane were found by infrared spectroscopy to contain up to 3020 ppm oh these rocks were recrystallized at pressures over 60 kbar and temperatures over 1000 c where no hydrous minerals are stable infrared spectra of the clinopyroxenes show three hydroxyl absorption bands in the regions 3440 3460 cm 1 3500 3530 cm 1 and 3600 3625 cm 1 the hydroxyl absorbance increases with recrystallization pressure of the eclogites and with vacancy concentration in the pyroxene structure ca eskola component clinopyroxenes represent about 40 50 vol of eclogites such that the bulk eclogites contain approximately 1300 ppm hydroxyl at depths greater than 150 km thus subducted oceanic crust can transport trace amounts of h2o into the upper mantle even in the absence of nominally hydrous minerals

controls on different mineralization styles of the dongbulage mo and taibudai cu mo porphyry deposits in the great xing an range ne china abstract the dongbulage porphyry mo dominant and taibudai cu mo deposits are located in the central southern great xing an range inner mongolia northeastern china and are associated with granite porphyry and monzogranite intrusions respectively re os isotope data for five molybdenite samples from the dongbulage mo deposit give a weighted mean model age of 164 3 1 2 ma which is in accordance with a zircon u pb age of 164 5 1 7 ma for the host granite porphyry indicating that the deposit formed at the end of the middle jurassic the zircon u pb age of the taibudai ore bearing monzogranite is 137 9 1 7 ma indicating that the deposit formed in the early cretaceous whole rock geochemical data indicate that the dongbulage granite porphyry and the taibudai monzogranite are high k calc alkaline and have ree patterned light rare earth elements lrees enriched and heavy rare earth elements hrees depleted both plutons show ba nb and ti depletions on normalized trace element diagrams and the dongbulage granite porphyry shows strongly negative eu anomalies which are absent in the taibudai intrusion the geochemical differences between the two intrusions suggest that the dongbulage granite porphyry is the result of more advanced fractional crystallization which led to the formation of a mo dominant deposit whereas the lesser degree of crystal fractionation in the taibudai monzogranitic magma resulted in the formation of a cu deposit the relatively listric shaped ree patterns of taibudai rocks suggest more hydrous parental magmas than that of dongbulage rocks therefore fractional crystallization and magma water content exert a significant control on the styles of mineralization mo versus cu dominant in the central southern great xing an range

geology and geochronology of the xilamulun molybdenum metallogenic belt in eastern inner mongolia china the xilamulun molybdenum metallogenic belt located in eastern inner mongolia china has great economic potential as a major producer of molybdenum four major types of mo deposits have been recognized in the xilamulun molybdenum metallogenic belt porphyry quartz vein volcanic hosted and greisen these mesozoic mo deposits are closely related to si and k rich intrusives and are usually hosted by granite plutons or located at the endo or exo contact zones of the granite porphyry shrimp zircon u pb dating gives the emplacement ages of the intrusions related to mo mineralization as 245 1 4 4 152 4 1 6 and 139 1 2 3 ma re os analysis of five molybdenite samples from the chehugou porphyry mo deposit yields an isochron age of 245 5 ma 2 indicating that the mineralization age of the porphyry mo deposit is about 245 ma re os analyses of six molybdenite samples from the nianzigou quartz vein type mo deposit yield an isochron age of 154 3 3 6 ma 2 constraining the mineralization age of the quartz vein mo deposit to 154 ma our results suggest that the mo mineralization in the xilamulun belt formed during at least three stages i e the triassic late jurassic and early cretaceous and is coeval with the granitic magmatism the corresponding geodynamic background covers the syncollision between the north china and siberian plates during the early to middle triassic a compression setting related to the subduction of the paleo pacific plate during the jurassic and lithospheric thinning during the early cretaceous in eastern china

geodynamic settings and tectonic model of skarn gold deposits in china an overview seventy skarn type gold deposits including 1 super large 19 large and 24 medium sized are known from different geotectonic units of china they contain a total resource of approximately 1000 t of gold 625 t in south china and account for 20 of china s gold reserves these skarn deposits are sited in collisional orogenic belts fault controlled magmatic belts and reactivated cratonic margins all of the chinese skarn gold provinces were affected by phanerozoic collisional orogenesis the timing of the metallogenic events and the spatial temporal distribution of the chinese skarn gold deposits indicates that they were formed during ore forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen and not to subduction systems as is commonly advocated for porphyry copper systems around the pacific rim

gabbro derived granulites from the northern apennines italy evidence for lower crustal emplacement of tholeiitic liquids in post variscan times apennines and the western alps the protoliths of the fe tithe mafic granulites from the northern apennines commonly contain oxide bearing mafic granulites can be related to the least evolved significant amounts of either olivine or fe ti oxide phases on the rocks through fractional crystallization and assimilation of crustal basis of mineralogy and whole rock major and trace element material the felsic granulites probably represent anatectic and compositions their protoliths are recognized as cumulus rocks derived migmatitic rocks resulting from multi stage melting of lower crustal from variably evolved tholeiitic liquids clinopyroxenes from the basement rocks olivine bearing rocks show peculiar trace element compositions e g low amounts of cr zr and lanthanides coupled with relatively high sr concentrations that record a process of granulite facies trace element redistribution controlled by a reaction between olivine and

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

experimental determination of ree partition coefficients between amphibole and basaltic to andesitic liquids at high pressure abstract amphibole liquid partition coefficients for the ree damph liqree obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy ree five new experimentally determined sets of dree la sm eu2 ho lu and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole over a range of temperature pressure and oxygen fugacity the partition coefficients increase significantly with decreasing temperature and increase slightly with increasing oxygen fugacity pressure does not appear to have a major effect although one data set suggests increased pressure lowers damph liqree in a basaltic composition