nonlinear forecasting analysis of inflation deflation patterns of an active caldera campi flegrei italy the ground level in pozzuoli italy at the center of the campi flegrei caldera was monitored by tide gauges between 1970 and 1976 and then continuously since 1982 tide gauges offer a long record of a variable that is believed to be related to the activity of an underlying shallow magma chamber previous work suggests that the dynamics of the campi flegrei system as reconstructed from the tide gauge record is chaotic and low dimensional according to this suggestion in spite of the complexity of the system at a time scale of days the ground motion is driven by a deterministic mechanism with few degrees of freedom however the interactions of the system may never be describable in full detail our new analysis of the tide gauge record from january 1987 to june 1989 using nonlinear forecasting confirms low dimensional chaos in the ground elevation record at campi flegrei and suggests that nonlinear forecasting could be a useful tool in volcanic surveillance

fluid chemistry structural setting and emplacement history of the rosario cu mo porphyry and cu ag au epithermal veins collahuasi district northern chile the rosario cu mo ag deposit is located in the collahuasi district of northern chile it comprises high grade cu ag au epithermal veins superimposed on the core of a porphyry cu mo orebody rosario has mining reserves of 1 094 million metric tons mt at 1 03 percent copper an additional 1 022 mt at 0 93 percent copper occurs in the district at the nearby ujina and quebrada blanca porphyry deposits the rosario reserve contains over 95 percent hypogene ore whereas supergene sulfide ores dominate at ujina and quebrada blanca mineralized veins are hosted within lower permian volcanic and sedimentary rocks lower triassic granodiorite and late eocene porphyritic quartz monzonite the rosario fault system a series of moderate southwest dipping faults has localized high grade cu ag au veins at cerro la grande similar high grade cu ag au veins are hosted in north northeast trending sinistral wrench faults normal movement in the rosario fault system is interpreted to have been synchronous with sinistral strike slip deformation at la grande hydrothermal alteration at rosario is characterized by a k feldspar core focused in the rosario porphyry that grades out to a secondary biotite albite magnetite assemblage paragenetic relationships indicate that magnetite was the earliest formed alteration product but has been replaced by biotite albite vein crosscutting relationships indicate that k feldspar formed during and after biotite albite alteration chalcopyrite and bornite were deposited in quartz veins associated with both k feldspar and biotite albite assemblages the early hydrothermal fluid was a hypersaline brine 40 45 wt nacl that coexisted with vapor between 400 degrees and 600 degrees c weakly mineralized illite chlorite intermediate argillic alteration of the early k and na silicate assemblages was caused by moderate temperature 250 degrees 350 degrees c moderate salinity brines 10 15 wt nacl molybdenite was precipitated in quartz veins that formed between the potassic and intermediate argillic alteration events these fluids were 350 degrees to 400 degrees c with salinities between 10 and 15 wt percent nacl porphyry style ore and alteration minerals were overprinted by structurally controlled quartz alunite pyrite pyrophyllite dickite and muscovite quartz phyllic alteration assemblages the quartz alunite pyrite alteration formed at 300 degrees to 400 degrees c from fluids with a salinity of 10 wt percent nacl the pyrophyllite dickite assemblage formed between 250 degrees and 320 degrees c from dilute 5 wt nacl fluids an upward flared zone of muscovite quartz pyrite altered rocks surrounds the fault controlled domain of advanced argillic alteration thick veins 0 5 2 m wide of fault hosted massive pyrite chalcopyrite and bornite precipitated brines with a salinity of 30 wt percent nacl at temperatures of 250 degrees to 300 degrees c pressure depth estimates indicate that at least 1 km of rock was eroded at rosario between formation of the k na silicate and advanced argillic assemblages this erosion was rapid occurring over a period of 1 8 m y the rosario porphyry intruded immediately after the incaic tectonic phase implying that it was emplaced as the domeyko cordillera underwent gravitational collapse expressed as normal faults in the upper crust gravitational sliding potentially accelerated exhumation and helped to promote telescoping of the high sulfidation environment onto the rosario porphyry the hydrothermal system responsible for porphyry cu mineralization at rosario was partially exhumed prior to the formation of high sulfidation ore and alteration assemblages this implies that emplacement of a second blind intrusion occurred somewhere beneath the rosario and cerro la grande high sulfidation vein systems and is supported by the fault geometry and zoning of precious metals and sulfosalts at the district scale

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

upb zircon age and geochemical constraints on tectonic evolution of the paleozoic accretionary orogenic system in the tongbai orogen central china abstract the tongbai orogen is located in a key tectonic position linking the qinling orogen to the west and the dabie sulu orogen to the east this orogen comprises a paleozoic accretionary orogenic system in the north and a permo triassic collisional orogenic system in the south hence it may serve as an ideal place to unravel the tectonic evolution from the initial oceanic subduction accretion to the final continental collision between the sino korean and yangtze cratons u pb zircon geochronology of metasedimentary and metaigneous rocks and geochemical characterization of metabasalts indicate a close genetic relationship between the individual tectonic units of the paleozoic accretionary orogenic system 1 the kuanping group as a neoproterozoic ordovician subduction accretion complex which received sediments from the qinling microcontinent 2 the erlangping group and huanggang diorite granodiorite complex as an ordovician silurian island arc evolving from backarc basin 3 the qinling group as a precambrian microcontinent converted into continental arc during the ordovician 4 the guishan complex as a mixture of the qinling continental arc and devonian forearc sediments and 5 the nanwan flysch as a devonian forearc sequence deposited on the newly accreted active margin of the sino korean craton consequently the northern and southern boundaries of the paleozoic accretionary orogenic system represent two sutures of the qinling microcontinent with the sino korean and yangtze cratons the new and previously published data reveal that the tectonic evolution of the tongbai orogen involved a series of events from ordovician early silurian ca 490 440 ma oceanic subduction and arc magmatism silurian early devonian ca 440 400 ma arc continent collision carboniferous ca 340 310 ma oceanic subduction and accretion late permian triassic ca 260 200 ma continental subduction and collision to cretaceous ca 140 90 ma extension and lateral eastward extrusion the entire accretionary orogenic processes until the final collision between the sino korean and yangtze cratons may have lasted more than 200 ma

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

carbon isotope anomaly in marbles associated with eclogites from the dabie mountains high 13c values up to 5 7 pdb were measured in marbles associated with ultrahigh pressure eclogites in the dabie mountains east china such a carbon isotope anomaly is interpreted to represent the carbon isotope composition of premetamorphic limestone i e the protolith of the marbles because there is no known process to enrich carbonate in 13c during regional metamorphism the high 13c also corresponds to high 18o of up to 22 9 smow suggesting that premetamorphic 13c values would be about 5 to 6 for their protolith limestones the carbon isotope anomaly in the protolith of the marbles implies a local change in the redox state of water during deposition of the limestones preservation of the unusually high positive 13c values in the marbles supports the previous conclusion that there was no significant isotopic exchange with the mantle during subduction of supracrustal rocks to mantle depths of greater than 100 km

evolution of aqueous carbonic fluids during contact metamorphism wall rock alteration and molybdenite deposition at trout lake british columbia the trout lake deposit is associated with a granodiorite tonalite stock that intruded greenschist facies calcareous and pelitic metasedimentary rocks it is typical of the fluorine deficient or granodiorite class of molybdenum deposits the stock is surrounded by a contact metamorphic aureole in which the mineral assemblages record evidence of fluid infiltration at the present erosional surface temperatures were below 400 degrees c and x sub co 2 in the calcareous rocks was 0 01 the confining pressure is estimated to have been 2 kbars contact metamorphism was followed successively by skarn and potassic alteration the latter developed as biotite halos around quartz albite veins in the metasedimentary rocks and as k feldspar halos around quartz veins in the intrusive rocks fluid inclusions in veins formed during potassic alteration are dominantly aqueous and have low to moderate salinities the ensuing quartz feldspar muscovite and muscovite ankerite alteration events were relatively pervasive aqueous carbonic fluid inclusions are commonly observed in quartz feldspar muscovite altered samples and are the dominant fluid inclusion type present in veins associated with muscovite ankerite alteration the aqueous fluid inclusions from all stages of alteration homogenize at temperatures between 170 degrees and 310 degrees c with a peak at 250 degrees c the aqueous carbonic fluid inclusions homogenize to the h 2 o phase between 240 degrees and 340 degrees c oxygen isotope compositions for muscovite quartz pairs yield temperatures of 370 degrees to 400 degrees c for quartz feldspar muscovite and muscovite ankerite alteration this indicates that the fluids were trapped at approximately 1 400 to 1 700 bars i e above the two phase region in the h 2 o co 2 nacl system calculated delta 18 o values for the fluid range from 8 0 to 8 4 per mil and taken in conjunction with pressure and temperature estimates suggest a magmatic and or modified ground water source phase relations of alteration minerals suggest that ph decreased during alteration mineralization is spatially and temporally associated with quartz feldspar muscovite alteration molybdenite is typically intergrown with muscovite that replaced alkali feldspar this textural relationship is interpreted to indicate that molybdenite deposited in response to decreases of temperature and or ph the common occurrence of these intergrowths in other fluorine deficient and enriched deposits suggests that the controls of mineralization for these deposits were similar to those at trout lake

diapycnal mixing in western boundary currents in a previous study pelegri and csanady 1991 we found upward entrainment and two way exchange between the upper thermocline and surface layers of the gulf stream here we use isopycnic coordinates to analyze the mechanism of diapycnal shear induced mixing in western boundary currents a hydrographic section across the gulf stream off the mid atlantic bight is used for a case study it shows that the upper thermocline layers of the gulf stream are characterized by relatively small 16 m averaged gradient richardson numbers ri analysis of the jacobian j z p with z the depth and p the potential density total vorticity and potential vorticity fields shows that this region has low jacobian values associated with high values of potential vorticity as required theoretically for the case of dominant diapycnal mixing the density tendency wp dp dt is calculated from the vertical gradient of the reynolds density flux the latter parameterized as density eddy diffusivity divided by the jacobian we use munk and anderson s 1948 expression for the eddy diffusivity coefficient modified to conform to data of ueda et al 1981 maintaining a ri 3 2 dependence for large ri from this we obtain an explicit expression for wp in terms of the ri and j distributions the distributions of wp its diapycnal gradient wp p and the diapycnal velocity wd jwp are then calculated regions of high diapycnal convergence large negative wp p values coincide with the location of anomalously low jacobians in agreement with the idea that diapycnal mixing is the consequence of anomalies produced during frontogenesis in some phase of the meanders we suggest that this process taking place intermittently in space and time is responsible for two way exchange in western boundary currents

thermohaline intrusions created isopycnically at oceanic fronts are inclined to isopycnals thermohaline intrusions have often been observed extending several kilometres from ocean fronts1 they have a central role in models of mixing2 3 however their origin has been the subject of controversy laboratory studies led to the idea that intrusions might be formed by double diffusion4 6 in which case they would slope across isopycnals surface of constant density that signature has been identified in ocean fine structure sections7 observations of the three dimensional structure of meandering fronts led to a different conjecture that intrusions might be formed isopycnically by the ageostrophic circulation within unstable meanders on the frontal jet1 8 in that conceptual model double diffusion does not initiate intrusions but may extend and dissipate those created by frontal circulation9 here we present first the observed structure of such an intrusion and then the results of a dynamical model simulating the isopycnic generation mechanism at an unstable meandering front we show that thermohaline intrusions formed isopycnically also slope across density surfaces so there is no need to invoke double diffusion to explain such structures

origin of thermohaline staircases hypotheses concerning the origin of thermohaline staircases in salt fingering regions are reviewed and assessed one such hypothesis that staircases arise from thermohaline intrusions is developed into a quantitative theory it is shown that growing intrusions evolve toward staircases when the background density ratio lies below a threshold value and nonlinear computations confirm that staircases are viable intrusion equilibria staircase properties such as step heights lateral density ratios and layer slopes lie closest to observed values when salt fingers are assumed not to contribute to shear stress and when turbulent mixing rates are smaller than usual thermocline values

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

evidence of enhanced double diffusive convection below the main stream of the kuroshio extension in this study a navis microrider microstructure float and an em apex float were deployed along the kuroshio extension front the observations deeper than 150 m reveal widespread interleaving thermohaline structures for at least 900 km along the front presumably generated through mesoscale stirring and near inertial oscillations in these interleaving structures microscale thermal dissipation rates are very high o 10 7 k2s 1 while turbulent kinetic energy dissipation rates are relatively low o 10 10 10 9 wkg 1 with effective thermal diffusivity k of o 10 3 m2s 1 consistent with the previous parameterizations for double diffusion and k is two orders of magnitude larger than the turbulent eddy diffusivity for density k the average observed dissipation ratio in salt finger and diffusive convection favorable conditions are 1 2 and 4 0 respectively and are larger than that for turbulence our results suggest that mesoscale subduction obduction and near inertial motions could catalyze double diffusive favorable conditions and thereby enhancing the diapycnal tracer fluxes below the kuroshio extension front

high pressure metamorphic rocks from tongbaishan central china u pb and 40ar 39ar age constraints on the provenance of protoliths and timing of metamorphism abstract the tongbaishan area is situated at the junction between the paleozoic north qinling orogen and the mesozoic south qinling dabie sulu orogen the area contains an important geological section for understanding the assembly of the sino korean and yangtze cratons two eclogite zones were recently recognized in this area the peak metamorphic conditions are estimated to be 530 610 c and 17 20 kbar for the northern eclogite zone and 460 560 c and 13 19 kbar for the southern eclogite zone shrimp u pb analyses on zircons of eclogite metagabbro and orthogneiss indicate that their protoliths were formed during the neoproterozoic and experienced high pressure hp recrystallization during the permian triassic period therefore the tongbaishan area belongs to the western extension of the dabieshan hp uhp terrane in addition u pb ages of detrital zircons from quartzite paragneiss and schist show three age populations of 2 49 ga 1 93 ga and 1 85 1 82 ga suggesting that extensive paleoproterozoic orogeny or tectonothermal events took place in the northern margin of the yangtze craton the shrimp dating and complementary 40ar 39ar dating of muscovite from quartzofeldspathic gneiss and quartzite reveal that the crustal rocks were subducted to great depths and underwent hp eclogite facies metamorphism at ca 255 ma slightly earlier than the timing of deep subduction of the uhp slice the hp rocks were later exhumed to mid to upper crustal levels and suffered from retrograde recrystallization at ca 238 ma the dating also discloses a still later phase of deformation and recrystallization at ca 215 ma the available age data throughout the tongbai dabie sulu orogen reflect diachronous exhumation from ca 238 ma for the hp slice to ca 213 ma for the uhp slice such a phenomenon could be explained by successive subduction and exhumation of the broken slices of the subducting yangtze slab

timing of the yuchiling giant porphyry mo system and implications for ore genesis the yuchiling mo deposit is a recently discovered giant porphyry system in the east qinling mo belt china its apparent causative intrusion i e the yuchiling granite porphyry is the youngest intrusion phase 4 of the heyu multiphase granite batholith which was emplaced between 143 and 135 ma new robust constraints on the formation of the yuchiling porphyry mo system are provided by combined zircon u pb biotite 40ar 39ar and molybdenite re os dating zircon grains from the mo mineralized granite porphyry yield weighted 206pb 238u age of 134 0 1 4 ma n 19 2 error mswd 0 30 magmatic biotite from the same sample yield a 40ar 39ar plateau age of 135 1 1 4 ma 2 error and an inverse isochron age of 135 6 2 0 ma n 7 2 error mswd 10 8 which are effectively coincident with the zircon u pb age within analytical error three pulses of mineralization can be deduced from the molybdenite re os ages namely 141 137 and 134 ma which agree well with the zircon u pb ages of granitic phases 1 2 and the yuchiling porphyry phase 4 respectively these well constrained temporal correlations indicate that mo mineralization was caused by pulses of granitic magmatism and that the ore forming magmatic hydrothermal activity responsible for the yuchiling porphyry mo system lasted about 8 ma the yuchiling mo deposit represents a unique style of porphyry mo system formed in a post collision setting and associated with f rich high k calc alkaline intrusions which differ from convergent margin associated porphyry mo deposits

stable isotope geochemistry of marbles from the coesite uhp terrains of dabieshan and sulu china abstract marbles from dabieshan and sulu china suffered ultra high pressure uhp metamorphism in the coesite eclogite facies at approximately 700 c and 30 kbars during triassic continental collision and subduction the marbles range in isotopic composition from 7 to 25 18 o vsmow and from 0 to 6 13 c vpdb high 13 c values are representative of unmodified protoliths and are similar to those of 13 c enriched sinian carbonate rocks from the yangtze craton high oxygen isotope ratios reflect pristine protoliths but the low values may have been caused by infiltration of low 18 o meteoric water during diagenesis and dolomitization by fracture controlled infiltration of water during subduction by metamorphic mineral reactions or by a combination of these processes no evidence of regional isotopic transport during uhp metamorphism has been found sampling on scales of 1 to 100 m shows marbles to be inhomogeneous in both carbon and oxygen isotopes only samples separated by less than 10 cm have equilibrated oxygen and carbon isotope compositions limited isotopic equilibration between adjacent rocks is consistent with the preservation of unaltered uhp minerals and indicates that the metamorphic fluid rock system was rock dominated during and following peak metamorphism a freely flowing pervasive fluid phase was not present during uhp metamorphism there is no evidence of isotopic exchange between marble and the upper mantle into which it was subducted correlation of geochemical similarities of uhp marbles with sinian limestones implies that the subducted edge of the yangtze craton extends at least as far north as the coesite eclogite facies rocks of dabieshan deposition of protolith carbonates may have taken place in a cold climate either preceding or following but not coincident with neoproterozoic glaciation

enhanced diapycnal mixing by salt fingers in the thermocline of the tropical atlantic diapycnal mixing plays a significant role in the ocean s circulation and uptake of heat and carbon dioxide but has not been quantified in salt finger driven thermohaline staircases we recently performed a tracer release experiment in the western tropical atlantic staircase at approximately 400 m depth the observed dispersion implies an effective diapycnal diffusivity for tracer and salt of 0 8 to 0 9 x 10 4 m2 s temperature microstructure data interpreted in terms of a vertical production dissipation balance yields a smaller effective diffusivity for heat of 0 45 0 2 x 10 4 m2 s consistent with salt fingers and well above the mixing ascribable to mechanical turbulence

paleoproterozoic positive δ13ccarb excursion in the northeastern sino korean craton evidence of the lomagundi event abstract the 2 33 2 06 ga positive 13 c carb excursion associated with environmental change and the breakup of the kenorland or superia supercontinent is called the lomagundi or jatulian event or great oxidation event and has been reported in many early precambrian cratons but not yet in the sino korean craton the guanmenshan formation of the liaohe group occurs in the northeastern part of the sino korean craton 13 c carb and 18 o values in 42 samples from this formation range from 3 5 5 9 v pdb and 15 4 24 8 v smow respectively showing a clear positive 13 c carb excursion that characterizes the lomagundi event thirty five of the 42 samples with less hydrothermal alteration have higher 13 c carb and 18 o carb values than the other 7 samples obviously affected by fluid flow confirming that it was fluid flow that reduced the 13 c carb and 18 o carb values this positive 13 c carb excursion places deposition of the guanmenshan formation within the age range of 2 33 2 06 ga

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

fluid inclusion and h o c isotope geochemistry of the yaochong porphyry mo deposit in dabie shan china a case study of porphyry systems in continental collision orogens the yaochong porphyry mo deposit in xinxian county henan province china is located in the hong an terrane that is the western part of the dabie orogen the dabie orogen is part of a 1 500 km long triassic continental collision belt between the north china block and the south china block four types of vein are present paragenetically from early to late they are as follows stage 1 quartz k feldspar pyrite magnetite vein stage 2 quartz k feldspar molybdenite pyrite vein stage 3 quartz polymetallic sulfides k feldspar vein and stage 4 quartz carbonate fluorite vein four compositional types of fluid inclusion pure co2 co2 bearing aqueous and solid bearing are present in quartz from the first three stages only low salinity aqueous fluid inclusions occur in quartz from the last stage all the estimated salinities are 13 1 wt nacl eq and no halite crystals were identified homogenization temperatures for the fluid inclusions from stages 1 to 4 are in the ranges of 262 501 202 380 168 345 and 128 286 c respectively and estimated depths decrease from 6 9 to 8 9 km through 6 2 7 2 to 4 7 km quartz separates from the veins yielded a 18o value of 7 7 11 2 corresponding to 18oh2o values of 1 3 to 6 9 using temperature estimates from fluid inclusion data dh2o values of fluid inclusion vary from 80 to 55 and 13cco2 from 2 3 to 2 7 suggesting that the ore fluids evolved from magmatic to meteoric sources we conclude that the ore forming fluid system at yaochong was initially high temperature high salinity and co2 rich and then progressively evolved to co2 poor lower salinity and lower temperature by mixing with meteoric water which results in ore precipitation

fluid evolution of the yuchiling porphyry mo deposit east qinling china the yuchiling mo deposit east qinling china belongs to a typical porphyry mo system associated with high k calc alkaline intrusions the pure co2 pc co2 bearing c aqueous h2o naci w and

early cretaceous granitoids and their implications for the collapse of the dabie orogen eastern china shrimp zircon u pb dating and geochemistry abstract two stages of early cretaceous post orogenic granitoids are recognized in the dabie orogen eastern china which recorded processes of extensional collapse of the orogen the early stage granitoids 132 ma are foliated hornblende quartz monzonites and porphyritic monzogranites they are of high k calc alkaline series and metaluminous to weakly peraluminous with high k 2 o and low mgo contents mg values 32 0 46 0 they contain high sr low y and heavy rare earth elements hree and have high sr y and la yb n ratios without clear negative eu sr and ti anomalies the early stage deformed granitoids have adakitic geochemical compositions and are equilibrated with residues rich in garnet and poor in anorthite rich plagioclase and thus indicate the existence of an over thickened 50 km crustal root beneath the orogen at 132 ma the later stage granitoids 128 ma are undeformed fine grained monzogranites fine grained k feldspar granites and coarse grained k feldspar granite porphyry they belong to a peraluminous and high k calc alkaline to shoshonite series and display a flat hree pattern and have strong negative eu sr and ti anomalies with low sr y and la yb n ratios the late stage granitoids are equilibrated with residues rich in anorthite rich plagioclase hornblende ilmenite titanite and poor in garnet indicating that the crust of the dabie orogen became thinner

spatial and temporal patterns of small scale mixing in drake passage temperature and salinity profiles obtained with expendable ctd probes throughout drake passage between february 2002 and july 2005 are analyzed to estimate turbulent diapycnal eddy diffusivities to a depth of 1000 m diffusivity values are inferred from density temperature inversions and internal wave vertical strain both methods reveal the same pattern of spatial variability across drake passage diffusivity estimates from inversions exceed those from vertical strain by a factor of 3 over most of drake passage the polar front pf separates two dynamically different regions strong thermohaline intrusions characterize profiles obtained north of the pf south of the pf stratification is determined largely by salinity and temperature is typically unstably stratified between 100 and 600 m depth in the upper 400 m turbulent diapycnal diffusivities are o 10 3 m2 s 1 north of the pf but decrease to o 10 4 m2 s 1 or smaller south of the pf below 400 m diffusivities typically exceed 10 4 m 2 s 1 diffusivities decay weakly with depth north of the pf whereas diffusivities increase with depth and peak near the local temperature maximum south of the pf the meridional pattern in near surface mixing corresponds to local maxima and minima of both wind stress and wind stress variance near surface diffusivities are also found to be larger during winter months north of the pf wind driven near inertial waves strong mesoscale eddy activity and double diffusive convection are suggested as possible factors contributing to observed mixing patterns

life and demise of intrathermocline mesoscale vortices abstractthis study is focused on finescale dissipation mechanisms of intra thermocline mesoscale vortices exemplified by meddies large anticyclonic salt lenses of mediterranean origin commonly observed in the lower north atlantic thermocline high resolution numerical experiments are diagnosed to quantify the rates of temperature t and salinity s dispersion in salt lenses and to determine the relative contribution of various mixing processes in the decay of their thermohaline signatures we find in agreement with observations that meddies dissipate on the characteristic timescale of several years and that their ultimate disintegration can be attributed to thermohaline interleaving driven by double diffusive mixing mechanically generated turbulence on the other hand tends to suppress the interleaving and therefore has an adverse net effect on eddy dispersion it is found that the dispersion properties of static lenses characterized by density compensated t s patterns and their rapidly rotating

fluid inclusion study of the nannihu giant porphyry mo w deposit henan province china implications for the nature of porphyry ore fluid systems formed in a continental collision setting abstract the nannihu mo w deposit located in the henan province of china is a giant porphyry deposit formed in the qinling orogen during the jurassic continental collision between the north china and yangtze cratons mo w mineralization is associated with the nannihu porphyritic monzogranite occurring as numerous stockwork veinlets in the altered wallrocks and the causative porphyry both the porphyry stock and wallrocks underwent intense hydrothermal alteration ranging outwardly from potassic to phyllic alteration and to carbonation zones with increasing distance from the intrusion the hydrothermal ore forming process can be divided into four stages characterized by veinlets from early to late 1 quartz potassic feldspar molybdenite pyrite 2 quartz molybdenite veins containing minor pyrite and chalcopyrite 3 quartz polymetal sulfide and 4 quartz carbonate fluorite most of the ores are formed during stages 2 and 3 four types of fluid inclusions fis are distinguished in this study based on petrographic and microthermometric criteria i e pure co 2 nacl h 2 o co 2 h 2 o and daughter mineral bearing fluid inclusions all of the four types of fis can be observed in the hydrothermal quartz formed in stages 1 2 and 3 while the stage 4 minerals contain only nacl h 2 o fluid inclusions fluid inclusions of stage 1 are mainly homogenized between 350 and 460 c with salinities ranging from 5 7 to 17 9 wt nacl equiv the stage 2 fis yield homogeneous temperatures of 300 380 c and salinities of 3 5 16 9 wt nacl equiv fis of stage 3 are homogenized between 250 and 370 c with salinities of 1 8 14 3 and 28 6 39 1 wt nacl equiv fis of stage 4 are homogenized at temperatures of 115 to 265 c yielding salinities of 0 5 to 1 2 wt nacl equiv daughter minerals such as halite chalcopyrite and some unknown minerals are frequently present in stage 3 fis which probably represent a reducing and oversaturated fluid system resulting from fluid boiling the daughter mineral bearing fis coexist with vapor and liquid rich nacl h 2 o fis that have contrasting salinities these fis are homogenized in divergent ways at similar temperatures suggesting that fluid boiling took place in stages 2 and 3 the estimated pressures range from 70 to 270 mpa in stage 1 through 30 150 mpa in stage 2 to 30 85 mpa in stage 3 corresponding to a depth of no less than 3 km in other words the ore forming fluids are characterized by high temperature high salinity high f o 2 and high co 2 content and fluid boiling resulted in co 2 release f o 2 decrease and ore mineral precipitation we suggest that the co 2 rich fluid is a distinctive feature of porphyry systems developed in continental collision setting in transitional compressional to extensional regime contrasting to the co 2 poor nacl h 2 o fluids observed in volcanic arcs

on the parameterization of diapycnal fluxes due to double diffusive intrusions abstract an attempt is made to parameterized the large scale average diapycnal cross isopycnal mixing that presumably occurs in the thermohaline fronts that develop when large scale epipycnal along isopycnal gradients of t and s are stirred along isopycnals by mesoscale eddies it is assumed that double diffusive intrusions develop at the fronts and that their thickness is given by the formula of ruddick and turner 1979 this combined with a crude estimate of the frontal width and a very over simplified model of the eddy field leads to a formula for the average diapycnal diffusivity for salt or some neutral tracer and suggests that the mechanism is important in weakly stratified water with a large epipycnal gradient of salinity the diapycnal eddy diffusivities for temperature is negative for a stably stratified temperature field however the opposite signs of the diapycnal diffusivities for salt and heat are unlikely to lead to observable consequences on account of the dominance in duxes acros

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

fluid regime and ore formation in the tungsten yttrium deposits of kyzyltau mongolian altai evidence for fluid variability in tungsten tin ore systems abstract the kyzyltau ore field is located in the northern part of the mongolian altai mountains w y be mo mineralization occurs in veins and stockworks in granites felsic volcanics basaltic flows and conglomerates the main ore minerals in the veins are wolframite fluorite beryl and minor molybdenite inclusions in hydrothermal quartz fluorite and beryl from veins as well as in magmatic quartz in vein hosting granites of the ulaan uul buraat uul and tsunkheg deposits were investigated using microthermometry and laser raman spectroscopy pseudosecondary primary inclusions in the kyzyltau ore veins are predominantly liquid rich aqueous inclusions containing variable amounts of co 2 as the main gas component and showing n 2 ch 4 ratios 1 secondary inclusions contain no or only trace concentrations of gases as indicated by clathrate melting the t h values of pseudosecondary primary inclusions in veins are between 180 and 433 c fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz ii and green fluorite ii in the ulaan uul and buraat uul ore veins phase separation pressures of 100 350 bars were estimated fluorite i from the kyzyltau ore field shows a strong enrichment of hree and a strong negative eu anomaly common for rare metal bearing ore systems fluorite ii from buraat uul and tsunkheg is characterized by a change in the incorporation of rare earth elements ree with decreasing hree contents and a decreasing eu anomaly the ree distribution patterns in fluorite ii from ulaan uul remained unchanged compared with fluorite i despite a strong increase in the total ree content a review of the literature shows that from high temperature fe rich k dominated brines cassiterite ores can precipitate in quartz veins together with fe chlorite and fe tourmaline bolivian type if phase separation of a gas rich low salinity and fe rich fluid occurs cassiterite wolframite ores may be deposited cornwall devon type the deposits of kyzyltau are characterized by low fe alteration assemblages a predominance of sodium over potassium high contents of ree and y and a lack of extended tin mineralization despite the tin potential of the ore systems fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of li f rich sub volcanic intrusions we interpret the ph of the mineralizing fluid to be the main factor controlling wolframite precipitation in the kyzyltau ore field fluid wall rock interactions a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid co 2 bearing fluid into a ph range where tungstates were precipitated it can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten according to this inference tin mineralization may be found in a more favourable setting in the vicinity of the kyzyltau deposits

ore geology fluid inclusions and four stage hydrothermal mineralization of the shangfanggou giant mo fe deposit in eastern qinling central china article i nfo the eastern qinling central china containing more than 20 mesozoic porphyry skarn systems is the most important mo province in the world the shangfanggou giant mo deposit luanchuan county henan province is a porphyry skarn system hosted in a lithologic association comprising carbonaceous sandstone shale carbon ate and chert within the neoproterozoic luanchuan group mo ores are mainly altered porphyry skarn and hornfels with minor altered gabbro the mineralization process includes four stages potassic alteration of the porphyry and skarnization of dolomite marble in stage 1 stockworks of quartz molybdenite sulfide stage 2 pyrite quartz sulfides stage 3 and carbonate quartz fluorite stage 4 respectively mo mineralization was generally associated with strong silicification and or phyllic alteration the fluid inclusions in minerals include three compositional types i e co2 bearing c type aqueous w type and daughter mineral bearing s type minerals formed in stages 1 to 3 contain all the three types of fis but the stage 4 minerals only contain the w type fis oxides and cu phosphate are recognized as daughter minerals in s type inclusions in minerals of stage 1 whereas the daughter sulfide and reducing gases such as co ch4 h 2 sa nd c2h6 can be observed in quartz of stages 2 and 3 suggesting that the ore forming fluids were initially oxidizing and then evolved to reducing boiling fluid inclusion assemblages can be observed in minerals formed in stage 2 or earlier but not in stage 3 or later fluid boiling caused co2 escape oxygen fugacity decrease and rapid precip itation of ore minerals and was a key factor causing mo mineralization at shangfanggou data and interpreta tions presented in this contribution show that the fluids forming the shangfanggou mo deposit evolved from co2 rich high salinity hypothermal to co2 poor low salinity epithermal low t the mo mineralization at theshangfanggoudepositmainlyoccurredatdepthof6 6 7 0 km deeperthanthemajorityofporphyrysystems in volcanic arcs which resulted from a co2 rich magma fluid system originating from partial melting of thick ened lower crust the shangfanggou mineral system developed during 158 134 ma when the yangtze north china continental collision began to evolve from compression to extension magmatic hydrothermal deposits developed in a continental collision regime are generally formed by co2 rich high salinity fluids

nonlinear equilibration of thermohaline intrusions abstract the nonlinear behavior of thermohaline intrusions on a wide front is investigated using a one dimensional numerical model the model is used to follow the evolution of a field of intrusions from infinitesimal amplitude to a large amplitude state characterized by inversions in temperature and salinity it is thus possible to extend the analytical studies of toole and georgi and others to large amplitude allowing for the effects of amplitude dependent diffusivities and for the appearance of stably stratified diffusively stratified and statically unstable regions in the water column as the intrusions grow the model runs are initialized with infinitesimal disturbances that grow exponentially in time until inversions in temperature and salinity occur after inversions appear the intrusions evolve toward an equilibrium state in which friction balances buoyancy forces for both finger and diffusive sense basic state stratifications these equilibrium states are characterized by statically unstabl

direct evolution of brine from a crystallizing silicic melt at the questa new mexico molybdenum deposit molybdenum mineralization in the southwest orebody at the questa deposit is associated with crystallization of aplite porphyry explosive brecciation and exsolution of magmatic hydrothermal fluids quartz k feldspar fluorophlogopite and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall rock clasts forming a magmatic hydrothermal breccia ore fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum two fluid inclusion populations associated with molybdenite mineralization were identified the largest population commonly contains liquid vapor halite sylvite and one or more opaque daughter crystals these inclusions homogenize between 200 degrees and 500 degrees c and have a prominent mode at 360 degrees to 400 degrees c salinities vary from 31 to 57 wt percent nacl equiv low first ice melting temperatures suggest that additional fluid components possibly calcium or magnesium chlorides may be present approximately 80 percent of these inclusions homogenize by halite dissolution phase equilibria constraints require that these inclusions trapped fluids in the vapor absent field the remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures significantly the saline fluid did not coexist with a low density aqueous fluid a second population of inclusions contains fluids with salinities of 2 7 to 25 0 wt percent nacl equiv and homogenizes by vapor bubble disappearance vapor bubble expansion or critical behavior textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near critical conditions pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids saline fluids were trapped as the system sealed following a major brecciation event these high salinity fluids were produced as the melt under pressure that increased from hydrostatic to lithostatic partitioned increasing amounts of chlorine into the exsolving aqueous fluid renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid lower salinity fluids exsolved at near critical conditions and were trapped by inclusions that homogenize to liquid to vapor or by critical behavior the lack of cogenetic liquid and vapor rich fluid inclusions and phase equilibria constraints indicate that high salinity fluids or 57 wt nacl equiv were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility

fluid inclusion study of the wunugetu cu mo deposit inner mongolia china hydrothermal alteration and mineralization at the wunugetu porphyry cu mo deposit china include four stages i e the early stage characterized by quartz k feldspar and minor mineralization followed by a molybdenum mineralization stage associated with potassic alteration copper mineralization associated with sericitization and the last pb zn mineralization stage associated with carbonation hydrothermal quartz contains three types of fluid inclusions namely aqueous w type daughter mineral bearing s type and co2 rich c type inclusion with the latter two types absent in the late stage fluid inclusions in the early stage display homogenization temperatures above 510 c with salinities up to 75 8 wt nacl equivalent the presence of s type inclusions containing anhydrite and hematite daughter minerals and c type inclusions indicates an oxidizing co2 bearing environment fluid inclusions in the mo and cu mineralization stages yield homogenization temperatures of 342 508 c and 241 336 c and salinities of 8 6 49 4 and 6 3 35 7 wt nacl equivalent respectively the presence of chalcopyrite instead of hematite and anhydrite daughter minerals in s type inclusions indicates a decreasing of oxygen fugacity in the late stage fluid inclusions yield homogenization temperatures of 115 234 c and salinities lower than 12 4 wt nacl equivalent it is concluded that the early stage fluids were co2 bearing magmatic in origin and characterized by high temperature high salinity and high oxygen fugacity phase separation occurred during the mo and cu mineralization stages resulting in co2 release oxygen fugacity decrease and rapid precipitation of sulfides the late stage fluids were meteoric in origin and characterized by low temperature low salinity and co2 poor

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

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

mechanics of thermohaline interleaving beyond the empirical flux laws the article of record as published may be found at http dx doi org 10 1017 s0022112011000061

oceanic thermohaline intrusions observations intrusions are commonly observed in the upper deep and coastal oceans and are closely linked to lateral fluxes of heat salt and momentum this is a review of observations of intrusions and the results of comparisons of properties such as scale slopes microstructure activity and fluxes with theoretical models a summary of estimates of lateral heat fluxes indicates a wide range of lateral diffusivities we conclude by noting that our present knowledge is insufficient to predict the structure length scales and lateral fluxes of thermohaline intrusions with confidence and list a number of unresolved questions suggestions are made for compilation of existing data into a database for exploratory analysis and testing of theoretical hypotheses an outline is given of a potential collaborative field experiment using ctd fluorescent dye and microstructure observations

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

water mass analysis with three conservative variables with one conservative tracer in addition to salinity and potential temperature it is possible to determine the relative strengths of lateral and vertical mixing processes this is achieved by first eliminating vertical advection through neutral surfaces and then forming a linear combination of the three conservative tracers so that the epineutral gradient i e the lateral gradient along the neutral surface of the new variable is zero thereby eliminating lateral advection the resulting expression for the ratio of the vertical and lateral diffusivities involves the curvatures of property property diagrams formed both from vertical casts and from data measured on a neutral surface the method requires that the epineutral gradients of potential temperature salinity and the third conservative tracer are parallel this condition is often met in the common situation where water parcels are the result of mixing between just two parent water masses

inferring in situ stress changes by statistical analysis of microseismic event characteristics two commonly estimated fractal dimensions called b and d values represent statistical characteristics in the distribution of magnitude sizes b and spatial hypocenter locations d of microseismic events respectively we establish that the values of these two dimensions are related to specific stress regimes through the case study of a heavy oil field drained using cyclic steam stimulation we infer that the measured temporal variation in fractal dimension b is most likely due to significant changes in the local stress regime over a seven month period ranging from extensional faulting fractures opening via a strike slip regime to finally compressive faulting fractures closing the fracture dimension d indicates predominantly planar to spherical hypocenter spatial distributions in the first and last stages but changes to a more linear to planar spatial pattern in the intermediate strike slip regime when the vertical stress is anticipated to be in between the maximum and minimum horizontal stre

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization