did the massive magnetite lava flows of el laco chile form by magmatic or hydrothermal processes new constraints from magnetite composition by la icp ms the el laco magnetite deposits consist of more than 98 magnetite but show field textures remarkably similar to mafic lava flows therefore it has long been suggested that they represent a rare example of an effusive fe oxide liquid field and petrographic evidence however suggest that the magnetite deposits represent replacement of andesite flows and that the textures are pseudomorphs we determined the trace element content of magnetite by laser ablation inductively coupled plasma mass spectrometry la icp ms from various settings at el laco and compared them with magnetite from both igneous and hydrothermal environments this new technique allows us to place constraints on the conditions under which magnetite in these supposed magnetite lava flows formed the trace element content of magnetite from the massive magnetite samples is different to any known magmatic magnetite including primary magnetite phenocrysts from the unaltered andesite host rocks at el laco instead the el laco magnetite is most similar in composition to hydrothermal magnetite from high temperature environments 500 c such as iron oxide copper gold iocg and porphyry cu deposits the magnetite trace elements from massive magnetite are characterised by 1 depletion in elements considered relatively immobile in hydrothermal fluids e g ti al cr zr hf and sc 2 enrichment in elements that are highly incompatible with magmatic magnetite rare earth elements ree si ca na and p and normally present in very low abundance in magmatic magnetite 3 high ni cr ratios which are typical of magnetite from hydrothermal environments and 4 oscillatory zoning of si ca mg ree and most high field strength elements and zoning truncations indicating dissolution similar to that formed in hydrothermal fe skarn deposits in addition secondary magnetite in altered brecciated host rock forming disseminations and veins has the same composition as magnetite from the massive lenses euhedral magnetite lining both open spaced veins in the brecciated host rock and along the walls of large hollow chimneys in the massive magnetite lenses also displays oscillatory zoning and most likely formed by fluctuating composition and or physio chemical conditions of the fluid thus the chemical fingerprint of magnetite from the supposed el laco magnetite lava flows supports the hydrothermal model of metasomatic replacement of andesite lava flows by dissolution and precipitation of magnetite from high temperature fluids rather than a magmatic origin from an effusive fe oxide liquid

discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

rapid thermal rejuvenation of high crystallinity magma linked to porphyry copper deposit formation evidence from the koloula porphyry prospect solomon islands magmas containing the components needed to form porphyry copper deposits are relatively common within arcs yet mineralising events are uncommon within the long lived magmatic systems that host them understanding what causes the transition from barren to productive intrusions is critical to the development of conceptual deposit models we have constrained the tempo of pre and syn mineralisation magmatic events in relationship to the thermal evolution of the plutonic body that underlies one of the world s youngest exposed plutonic porphyry systems the inamumu zoned pluton koloula porphyry prospect solomon islands high precision id tims u pb dates of texturally and chemically characterised zircons indicate pluton emplacement over 50 crystals state past the point of rheological lock up we estimate that thermal rejuvenation of the deeper high crystallinity magma and generation of a mobile melt fraction may have occurred 10 kyr before its transport and emplacement within the porphyry environment the underlying pluton likely cooled and returned to high crystallinity states prior to subsequent remobilisation emplacement events titanium in zircon geothermometry and whole rock geochemistry suggest pre mineralisation intrusions were remobilised by mixing of a silicic magma with a high temperature less evolved melt in contrast syn mineralisation melts were most likely remobilised by the percolation of hot volatiles exsolved from contemporaneous less evolved intrusions cooling beneath the crystalline silicic magma the evidence for the rapid thermal rejuvenation and long term storage of highly crystalline silicic magmas is consistent with previous studies that indicate two components of exsolved volatiles contribute to ore forming fluids we conclude that the liberation of crystal rich porphyry copper deposit forming magmas and the addition of the chemical components required for ore formation are intrinsically linked to the volatiles released during the recharge of less evolved melt into a highly crystalline silicic magma

evidence of multiple halogen sources in scapolites from iron oxide copper gold iocg deposits and regional nacl metasomatic alteration norrbotten county sweden abstract scapolites from barren regional na cl metasomatic assemblages rm iron oxide copper gold deposits iocg scapolite altered metabasic rocks iocg m and from iocg proximal alteration na skarns iocg ps from norrbotten county in northern sweden have been analysed for halogen content and cl stable isotope composition the aim of the study was to constrain the source of halogens within alteration assemblages and to investigate the possible fractionation of cl isotopes between scapolite and the hydrothermal fluid scapolite separates were analysed for cl br and major oxide concentrations using electron probe micro analysis epma and micro x ray fluorescence xrfm spectrometry chlorine was extracted from the scapolite separates via pyrohydrolysis and then analysed for their stable cl isotope compositions by isotope ratio mass spectrometry irms all samples of scapolite investigated in this study are marialitic in composition one of the scapolites from the gruvberget deposit iocg ps had a cl br molar ratio of 2363 which is the highest amongst all scapolites reported in the literature to date cl br molar ratios lower than seawater 650 were identified in two iocg ps scapolite samples cl br 554 and 271 as well as in two iocg m scapolites cl br 393 and 565 three rm scapolites had cl br molar ratios very close to or slightly higher than seawater values 639 to 770 samples with cl br molar ratios less than seawater are inferred to have halogens derived from evaporative residual brines whereas samples with molar ratios higher than seawater may have halogens derived from fluids that have dissolved halite and or are from magmatic systems considering the wide variation of the cl br molar ratios in the iocg ps and iocg m scapolites compared to the restricted composition of the regional alteration rm it is proposed that the hydrothermal fluids interacted with several different protoliths to generate the iocg alteration rm alteration scapolites had 37 cl values from 0 1 to 0 3 two iocg m scapolites had values of 0 2 and iocg ps scapolites had 37 cl values from 0 1 to 1 0 using a previously published 37 cl value from fluid inclusion leachates 1 7 from the iocg m mineralisation at pahtohavare and the 37 cl value of co existing scapolite measured in this study 0 2 an empirical fluid scapolite fractionation factor was calculated to be 1 9 this large fractionation factor is not supported by previous predictions for monovalent chlorides and assuming equilibrium indicates that 37 cl was preferentially accommodated in the a site of the scapolite structure this indicates that either the stable cl isotope partitioning between the cacl 2 rich brine and the scapolite may differ from currently available estimates for nacl brines in equilibrium with silicate minerals or that the scapolite and brine are not in isotopic equilibrium overall the data in this study suggest that halogens in early scapolites were derived from residual brines and halite during metamorphism of evaporites linked to the rm alteration later in the history of the norrbotten district components of the rm alteration were recycled and mixed during magmatic and local metasomatic events to varying extents resulting in the brines associated with iocg alteration

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

the lightning creek sill complex cloncurry district northwest queensland a source of fluids for fe oxide cu au mineralization and sodic calcic alteration the lightning creek cu au prospect is hosted by a cogenetic suite of plutonic i type granitoids the dominant rock type is a porphyritic quartz monzodiorite that is intruded by more fractionated rocks including monzogranite and alkali feldspar granite a series of flat lying sills are interpreted to be late stage differentiates based on their timing mineralogy and chemistry in parts of the prospect there is pervasive sodic calcic alteration pyroxene after amphibole albite after k feldspar and oligoclase of the plutonic rocks this alteration predates sill emplacement and is unrelated to veining or fracturing of any kind the presence of small amounts of carbonate in the altered rocks suggests that the fluids were co2 bearing quartz and feldspar separates from these altered rocks have oxygen isotope compositions similar to those from fresh quartz monzodiorite suggesting that the fluids were hot and of magmatic composition sodium and ca were added and k fe cl and cu were stripped during what is interpreted as an autometasomatic event the sills display considerable textural and mineralogical complexity and evolved from equigranular quartzofeldspathic rocks aplites with magmatic chemistry to unusual fe rich rocks albite magnetite quartz that exhibit a range of bizarre spherulitic textures some of the albite and magnetite in the sills is secondary albite forms pseudomorphs after k feldspar na fe ca alteration along sill margins and within sills at the contacts between different textural zones halos of disseminated magnetite clinopyroxene fe ca na alteration are developed adjacent to early magnetite veins fluid inclusion studies indicate that these rocks crystallized at temperatures in excess of 500 c and at pressures in excess of 1 5 kbar the range of spherulitic textures is taken to indicate crystallization under hydrous conditions with the episodic release of a fluid phase this magmatic fluid phase was dominated by h2o co2 and chlorine and underwent phase separation into a co2 rich vapor and a hypersaline brine 33 55 wt nacl equiv the hypersaline fluid was enriched in fe 10 wt and cu 1 wt pixe analysis in addition to na k and ca where this fluid was retained within fe rich portions of the sills it caused ca fe na alteration pyroxene albite magnetite growth at the expense of quartz where the fluid was expelled from the sills it produced quartz magnetite clinopyroxene albite veins broadly coeval with the early magnetite veins although rich in cu these granitoid derived magmatic fluids did not generate significant cu au mineralization perhaps because of the high temperatures involved and or a lack of reduced sulfur in the fluids or host rock however the amount of iron present is estimated from the aeromagnetic anomaly to be in excess of 2 000 million tonnes mt a later generation of calcite chlorite pyrite chalcopyrite veins contain traces of cu au mineralization fluid inclusion and stable isotope work indicate that these veins probably crystallized from cooler 200 c more dilute 15 28 wt nacl equiv fluids perhaps generated by the admixture of a meteoric component the conclusions reached in this study have implications for understanding the genesis of fe oxide cu au deposits and related sodic calcic alteration the study indicates the potential for co2 rich granitoid magmas to evolve hypersaline fe and cu rich fluids capable of causing intense magnetite veining and cu au mineralization autometasomatic sodic calcic alteration of the granitoids may be an important precursor to mineralization contributing fe k cu and cl to the magmatic fluids

iron rich melts magmatic magnetite and superheated hydrothermal systems the el laco deposit chile we propose an integrated model that explains the magmatic and hydrothermal features of the unique el laco iron deposit that is located in a pliocene pleistocene volcano of the chilean andes sub volcanic crystallization of an iron rich melt as massive magnetite promoted the exsolution of a small volume of a hydrosaline melt and of large amounts of vapor that led to the formation of an alkali calcic hydrothermal assemblage replacing the host andesite this assemblage is capped and overprinted by a large zone of acid sulfate steam heated alteration forming as a whole a protracted shallow level magmatic hydrothermal system oxygen isotopic data for the massive magnetite 18o 4 3 5 0 and the alkali calcic altered rock diopside 18o 7 2 8 7 magnetite 18o 4 4 6 7 suggest that these rocks are genetically related to the host andesite 18o 7 4 9 6 the estimated temperature of the mineral assemblage 900 c may be the highest recorded in hydrothermal systems is attributed to exsolution of fluids from the crystallizing iron rich melts and is considered unlikely to reflect the convection of surficial fluids

deep seismic expression of a foreland basin taranaki basin new zealand a deep seismic reflection profile shot across the south taranaki basin new zealand indicates up to 10 km of crustal thickening beneath the taranaki boundary fault at the eastern margin of the basin the seismic data also show a broad flexure of the entire crust the locus of the flexure producing load appearing to be in the vicinity of the taranaki boundary fault such crustal thickening and flexure suggest a compressional foreland basin style of late cenozoic development rather than the rift graben origin previously assumed this change in interpretation for the south taranaki basin has implications for evaluating the thermal history of the basin and its possibilities for hydrocarbon prospects the study therefore demonstrates the value of deep seismic exploration of a hydrocarbon bearing basin in its early stage of exploration

tourmaline b isotopes fingerprint marine evaporites as the source of high salinity ore fluids in iron oxide copper gold deposits carajas mineral province brazil the carajas mineral province in northern brazil contains a variety of world class 100 mt ore iron oxide copper gold iocg deposits including the only archean examples of this deposit class e g the igarape bahia alemao and salobo deposits tourmaline of schorldravite composition a common gangue mineral in these deposits precipitated shortly prior to and after the ore assemblage a boron isotope study of texturally different tourmaline from three iocg deposits igarape bahia salobo and sossego using secondary ion mass spectrometry sims provides new evidence in the long standing debate of magmatic versus non magmatic sources for the high salinity up to 50 wt nacl equiv of ore fl uids in these deposits values of 11 b from 14 to 26 5 for the igarape bahia and salobo deposits confi rm marine evaporite derived brines in the ore fl uids whereas lower 11 b values for the igarape bahia deposit 5 8 to 8 8 suggest that these fl uids may have mixed with an isotopically different hydrothermal fl uid or one that had a mixed boron source more variable and isotopically lighter boron in tourmaline from the sossego deposit 8 to 11 is attributed to mixed sources including light boron leached from felsic intrusive and volcanic host rocks and heavy boron derived from marine evaporites the boron isotope data indicate that the characteristic high salinity of the ore fl uids in the carajas mineral province was acquired by the interaction of hydrothermal fl uids with marine evaporites for iocg deposits that contain tourmaline as a common gangue mineral boron isotopes offer a valuable tool to constrain the high salinity source problem which is a critical issue in metallogenesis of iocg deposits worldwide

giant kiruna type deposits form by efficient flotation of magmatic magnetite suspensions kiruna type iron oxide apatite ioa deposits are an important source of fe ore and two radically different processes are being actively investigated for their origin one hypothesis invokes direct crystallization of immiscible fe rich melt that separated from a parent silicate magma while the other hypothesis invokes deposition of fe oxides from hydrothermal fluids of either magmatic or crustal origin here we present a new model based on fe and o stable isotopes and trace and major element geochemistry data of magnetite from the 350 mt fe los colorados ioa deposit in the chilean iron belt that merges these divergent processes into a single sequence of events that explains all characteristic features of these curious deposits we propose that concentration of magnetite takes place by the preferred wetting of magnetite followed by buoyant segregation of these earlyformed magmatic magnetite bubble pairs which become a rising magnetite suspension that deposits massive magnetite in regionalscale transcurrent faults our data demonstrate an unambiguous magmatic origin consistent with the namesake ioa analogue in the kiruna district sweden further our model explains the observed coexisting purely magmatic and hydrothermal magmatic features and allows a genetic connection between kiruna type ioa and iron oxide copper gold deposits contributing to a global understanding valuable to exploration efforts

using elemental and boron isotopic compositions of tourmaline to trace fluid evolutions of iocg systems the worldclass dahongshan fe cu deposit in sw china abstract the worldclass dahongshan iron oxide copper gold iocg deposit is hosted within the late paleoproterozoic dahongshan group in the kangdian region sw china the orebodies are spatially associated with sub volcanic intrusions and are structurally controlled extensive metamorphic overprinting during the neoproterozoic makes it difficult to determine the initial compositions of the ore fluids tourmaline however is a useful phase for this purpose because of its refractory nature and chemical diversity it occurs widely in the four stages of mineralization and alteration of the dahongshan deposit including pre mineralization sodic alteration stage i iron oxide mineralization stage ii sulfide mineralization stage iii and late quartz calcite veining stage iv the temporal association between tourmaline and hydrothermal alteration provides an excellent opportunity to investigate the fluid evolution tourmaline from all four stages belongs to the alkali group and ranges from dravite to schorl in composition in situ b isotope analyses of tourmaline conducted by la mc icpms yielded a total range of 11 b values from 14 7 to 5 9 and the values show significant variations among the different stages tourmaline of stage i albitization has 11 b values from 14 7 to 5 7 stage ii tourmaline from fe oxide ores shows 11 b values of 11 6 to 6 1 similar to those of stage i whereas stage iii tourmaline from cu sulfide ores displays significantly heavier isotopes with 11 b values from 4 4 to 0 6 tourmaline of stage iv represented by barren quartz calcite tourmaline veins in intensely altered wall rocks has positive 11 b values from 2 9 to 5 9 the observed variations of b isotopes cannot be produced by fractionation of the ore fluids alone mixing of b from at least two distinct sources a magmatic source and external sources with highly positive 11 b values are hence proposed on the basis of geological constraints and modal calculations the calculated oxygen isotope compositions of fluids in equilibrium with hydrothermal minerals that associated with tourmaline from stage ii stage iii and stage iv are 7 4 to 10 2 8 4 to 8 6 and 3 8 to 8 0 the decreasing trend of 18 o of fluids from stage ii to stage iv is consistent with the incursion of external basinal brines by fluid mixing our dataset thus demonstrates that ore fluids of dahongshan iocg system were initially of magmatic origin stages i and ii and were later progressively modified by mixing with external brines stages iii and iv

sulphur isotopic fractionation between sulphate and sulphide in hydrothermal ore deposits disequilibrium vs equilibrium processes correlative fractionation relationships of sulphur isotope data for coexisting sulphate and sulphide pairs from hydrothermal ore deposits on 38s versus 34s diagrams are deciphered theoretically taking into account dissolved h2s and so42 in hydrothermal fluids during precipitation of both sulphate and sulphide minerals a 4 species closed system is suggested for describing the conservation of mass among all sulphur bearing species on the diagrams the covariation in the 34s values of both sulphate and sulphide is ascribed to isotopic exchange between oxidized and reduced sulphur species during mineral precipitation the isotopic exchange could be a thermodynamic process due to simple cooling of high temperature fluids which results in an equilibrium fractionation or a kinetic process due to mixing of two sulphur reservoirs which leads to a disequilibrium fractionation the 34s value of total sulphur in a hydrothermal system could change due to the precipitation of minerals or due to the escape of h2s and or so42 sulphur isotope data for anhydrite and pyrite pairs from the luohe porphyrite iron deposit in the yangtze river valley is used to illustrate the mixing responsible for the disequilibrium fractionation

sulfide saturation and magma emplacement in the formation of the permian huangshandong ni cu sulfide deposit xinjiang northwestern china the eastern tianshan orogenic belt northwestern china hosts 120 mafic ultramafic intrusions and at least six of them host significant ni cu sulfide mineralization of which the permian huangshandong intrusion is the largest the mafic ultramafic rocks of the huangshandong intrusion comprise lherzolite gabbronorite gabbro and diorite individual orebodies are composed of pyrrhotite pentlandite and chalcopyrite as disseminated to net textured or massive to semimassive sulfide mineralization oxide bearing sulfide mineralization contains 1 to 5 magmatic magnetite that has ilmenite and spinel exsolution lamellae silicate rocks and sulfide mineralization have variable whole rock platinum group elements pge 0 38 362 ppb cu 42 97 000 ppm and ni 26 33 000 ppm concentrations the mineralization is broken out into two types termed oxide rich and oxide poor the oxide rich sulfide mineralization has high pge concentrations with low 187re 188os ratios 38 9 151 whereas oxide poor sulfide mineralization has low pge concentrations with high 187re 188os 159 781 both oxide rich and poor sulfide mineralization have highly variable os values 49 189 and 30 278 respectively oxide rich sulfide mineralization contains magnetite with variable amounts of mgo tio2 al2o3 feototal cr v zn and sn indicating that they crystallized from different stages during magma differentiation we propose that the host intrusion and associated sulfide mineralization were derived from high mg basaltic magmas from a mantle source that was previously modified by subducted oceanic slab oxide poor sulfide mineralization of the huangshandong intrusion formed from a magma that underwent 0 03 sulfide removal before emplacement and was thus pge depleted oxide rich sulfide mineralization formed from magma that had much lower amounts of sulfide 0 003 removed in the early stage before entering the huangshandong magma chamber an early sulfide saturation event was likely associated with fractionation of silicate minerals in a deep staging magma chamber the second sulfide saturation event that formed the sulfide mineralization was probably triggered by selective crustal contamination and fractionation in the high level chamber where mixing of magmas and accumulation of immiscible sulfide occurred

geology and geochronology of magnetite apatite deposits in the ning wu volcanic basin eastern china the ning wu volcanic basin is an important part of the middle lower yangtze river valley metallogenic belt in eastern china where magnetite apatite deposits are common these magnetite apatite deposits can be classified into two types the first type includes the washan taocun heshangqiao and dongshan deposits which are hosted in diorite porphyry and adjacent volcanic rocks the second type includes gushan baixiangshan and hemushan deposits developed at the contact between gabbro diorite and sedimentary rocks we used 40ar 39ar dating on phlogopite and u pb la icp ms dating of zircon in ore related diorite porphyry and gabbro diorite to determine the timing of iron mineralization in the basin the ages of the magnetite apatite deposits such as washan taocun heshangqiao gushan baixiangshan hemushan deposits are from 130 ma to 131 ma thus the magnetite apatite deposits in the ning wu volcanic basin all formed at about 130 ma later than the skarn and porphyry cu au deposits in the adjacent fault uplift areas such as edongnan jiu rui anqing guichi and tongling clusters that are between 146 ma and 135 ma based on available petrological and geochemical data the magnetite apatite deposits in the ning wu volcanic basin are interpreted to have formed under regional lithospheric extension and thinning and ore forming elements were derived from basaltic melts sourced from enriched lithospheric mantle and the crust

in situ elemental and isotopic analysis of fluorapatite from the taocun magnetite apatite deposit eastern china constraints on fluid metasomatism metasomatic alteration of fluorapatite has been reported in several iron oxide apatite ioa deposits but its effect on elemental and isotopic variations has not been well understood in this study we present integrated elemental u pb sr and o isotopic microanalytical data on fresh and altered domains in fluorapatite from the taocun ioa deposit eastern china to evaluate the timing and nature of the metasomatism and its effects on the ore forming event orebodies of the taocun deposit are spatially associated with a subvolcanic intermediate intrusion which displays zonal alteration patterns with albite in the center and increasing actinolite chlorite epidote and carbonate toward the margin both disseminated and vein type ores are present in the taocun deposit and fluorapatite commonly occurs with magnetite and actinolite in most ores fluorapatite grains from the both types of ores have been variably metasomatized through a coupled dissolution reprecipitation mechanism many trace elements including na cl s si mg sr u th and rees y were variably leached from the fluorapatite grains during this process and the sr and o isotopic signatures of the grains were also modified the altered fluorapatite grains domains have in situ 87 sr 86 sr ratios 0 70829 0 70971 slightly higher than those of the fresh fluorapatite 0 70777 0 70868 and 18 o values 3 0 to 3 4 variably lower than the primary domains 5 3 to 7 5 the sr and o isotopes of the primary fluorapatite are consistent with or slightly higher than those of the ore hosting intrusion implying that the early stage ore forming fluids were magmatic in origin but underwent weak interaction with the country rocks u pb dating of the fresh and altered domains of the fluorapatite yielded indistinguishable ages of 131 ma which are the same as the age of the ore hosting intrusion in combination with fluid inclusion data we propose that the metasomatism of fluorapatite was induced by hydrothermal fluids at a late stage of the ore forming event the shifts to higher 87 sr 86 sr ratios and lower 18 o values in the altered fluorapatite indicate that the alteration was induced by fluids with more radioactive sr and lighter o isotope signatures the metasomatic fluids were likely dominated by meteoric waters that were mixed with the earlier magmatic fluids and interacted with sedimentary rocks our study highlights that elemental and isotopic compositions of fluorapatite can be significantly modified by hydrothermal fluids during ore forming events thus instead of traditional bulk rock analysis in situ microanalysis is important to provide accurate constraints on the magmatic and or hydrothermal evolution of complex ore forming systems

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

evidence for hydrothermal alteration and source regions for the kiruna iron oxide apatite ore northern sweden from zircon hf and o isotopes zircon grains from the kiruna iron oxide apatite ioa ore bodies in northern sweden are distinct in their hafnium and oxygen isotopic ratios compared to zircon grains from adjacent metavolcanic host rocks and related intrusions here we combine these two isotopic systems on previously dated zircon grains to improve our understanding of these ore deposits with a long debated origin contrasting theories for the formation of the kiruna iron ores suggest either 1 emplacement through immiscible silicate iron oxide melts or 2 transportation and deposition of iron by hydrothermal fluids zircon from the metavolcanic host rocks and intrusions have oxygen isotopic ratios 18 o 3 that lie below typical magmatic compositions which is evidence that roof rocks altered by meteoric water were digested into the magma in contrast the ores show an influence of a fluid that is higher in 18 o 7 based on these findings we propose the involvement of episodic magmatic hydrothermal fluids in the ore genesis of the kiruna iron ore deposits 1 the first episode related to a deep seated magmatism and to regional scale metasomatic alteration and 2 a later fluid event related to shallow intrusions and responsible for the ore formation distinct differences in the hf isotopic ratios for host rocks and intrusions e hfi 6 to 10 archean crust and ore e hfi 5 to 3 depleted mantle further allow us to screen possible fluid sources for their involvement in the ore process

early proterozoic cu au and fe ore deposits associated with regional nacl metasomatism in northern fennoscandia scapolite is widely distributed in 1 9 2 5 ga volcano sedimentary rocks and 1 77 2 2 ga igneous rocks over several hundred square kilometres in northern fennoscandia comprising northern sweden no

trace element signature of pyrite from the los colorados iron oxide apatite ioa deposit chile a missing link between andean ioa and iron oxide copper gold systems although studies have proposed that iron oxide apatite ioa deposits may represent the deeper roots of some andean iron oxide copper gold iocg systems their genetic links remain obscure and controversial a key question when considering an integrated genetic model is whether a magmatic hydrothermal fluid that precipitates massive magnetite will continue transporting significant amounts of dissolved fe cu and au after ioa precipitation here we provide new geochemical data for accessory pyrite from the los colorados ioa deposit in the chilean iron belt that confirm the role of this sulfide as a relevant repository for economic metals in ioa deposits pyrite occurs at los colorados as disseminated grains and as veinlets associated with magnetite and actinolite that postdate the main igneous magnetite stage electron probe microanalysis epma data for pyrite show anomalously high co and ni concentrations up 3 9 and 1 5 wt respectively and relatively high as contents 100s of ppm to a maximum of 2 000 ppm when combined with results from secondary ion mass spectrometry sims spot analyses pyrite data show significant amounts of cu that range from sub ppm values 100 ppb up to 1 000s of ppm plus nonnegligible concentrations of zn pb cd sb se and te up to 100 ppm the highest contents of cu measured wt level most likely record the presence of cu bearing submicron sized mineral inclusions contents of au and ag are up to 1 and 10 ppm respectively with maximum concentrations that can rise up to 800 ppm au and 300 ppm ag due to the presence of submicron sized inclusions the high co ni ratios of pyrite from los colorados are consistent with a magmatic hydrothermal origin associated with a greater mafic affinity compared to pyrite from porphyry cu deposits furthermore the geochemical signature of los colorados pyrite shares important similarities of composition and microtexture with the few published data for pyrite from iocg deposits e g ernest henry australia and manto verde chile these findings combined with recent geochemical and isotopic studies that support an igneous origin for the dike shaped magnetite orebodies at los colorados point to a magmatic source of mafic to intermediate composition for the contained metals and support the hypothesis that ioa systems can source fe cu au rich fluids based on experimental studies these ioa derived fluids may continue transporting significant amounts of metals to form iocg mineralization at shallower levels in the crust

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

tourmaline boron and strontium isotope systematics reveal magmatic fluid pulses and external fluid influx in a giant iron oxide apatite ioa deposit abstract tourmaline is a common boron bearing mineral in hydrothermal system and has been widely used as a mineral probe to reconstruct geological processes because of its broad range in composition and resistance to metasomatic alteration the origin of kiruna type iron oxide apatite ioa deposits commonly linked to andesitic subvolcanic or volcanic rocks is highly controversial constraints on the evolution of these mineralizing systems are needed to advance understanding of the ore forming process in this study we apply in situ elemental and combined b sr isotopic analyses of tourmaline to elucidate the nature and evolution of the subsurface hydrothermal system associated with ioa mineralization in the giant taocun deposit eastern china taocun is hosted at the top of a diorite intrusion and exhibits three stages of hydrothermal alteration that contain tourmaline pre ore na alteration tur i syn ore magnetite formation and associated ca fe alteration tur ii and post ore ca mg alteration with sulfide veins tur iii compositional data for each stage of tourmaline plot along the oxy dravite povondraite join which is indicative of precipitation from relatively oxidizing fluids ranges of sr isotopic compositions in tur i 0 7065 0 7078 and tur ii 0 7068 0 7076 are identical to those of the igneous host rocks indicating precipitation from magmatic hydrothermal fluids the range of b isotopic compositions in tur i 11b values of 6 3 to 1 2 is also consistent with a magmatic source higher 11b values 2 4 to 5 4 obtained from tur ii are mainly ascribed to rayleigh fractionation in the magmatic hydrothermal system as tourmaline precipitated post ore tur iii has a wide range of mostly lower b isotopic compositions 8 5 to 0 8 that record another pulse of magmatic fluid input this interpretation is supported by the enrichment of na li be w sn v and ti in tur iii relative to tur i and ii however the higher sr isotope composition 0 7076 0 7086 of tur iii and available o isotope composition 7 to 3 5 of fluids of this stage record the infiltration of meteoric ground water from adjacent sedimentary country rocks the results suggest that the taocun ioa deposit formed in a magmatic hydrothermal system characterized by two or more pulses of magmatic fluid discharge from subvolcanic diorite intrusions followed by the influx of external ground water as the system waned this study highlights the utility of tourmaline as a robust geochemical and isotopic monitor of ore forming processes in such systems

boron sr o and h isotope geochemistry of groundwaters from mt etna sicily hydrologic implications combined b o h and sr isotopic studies of groundwaters from mt etna provide new constraints on their origin and the consequences of fluid rock interaction within this hydrologic system variations in d 18 o 29 7 to 27 2 and d d 262 to 223 mainly lie along the regional meteoric water line and suggest that most waters originated as local precipitation however small shifts in d 18 o and variable 87 sr 86 sr 0 70355 to 0 70879 and d 11 b 25 2 to 125 8 indicate that subsequent interactions occurred between the fluids and local rocks high b cl ratios in all samples seemingly preclude direct involvement of seawater in the hydrologic system despite the proximity to the coast and in some samples elevated 87 sr 86 sr and d 11 b two general end member water types are recognized on the basis of their chemistry these apparently are produced by interactions of local meteoric waters with the dominant reservoir rocks either basaltic lavas of etna or the underlying sediments respectively high d 11 b in the sediment hosted end member points to a significant marine carbonate contribution subsequent mixing between these or similar end members produced a range of intermediate composition groundwaters certain anomalous water compositions require the presence locally of a distinct component with high b and moderate d 11 b ca 110 but relatively low 87 sr 86 sr an anthropogenic source for this component is plausible one unusual sample has b and sr isotopic compositions similar to the other volcanic rock hosted waters but anomalously high cl content that likely reflects local magmatic outgassing near this sampling locality in general this study indicates that groundwater b and sr isotopic compositions are rock dominated these data provide useful constraints on the origin and evolution of groundwaters copyright 2000 elsevier science ltd

tourmaline as a recorder of magmatic hydrothermal evolution an in situ major and trace element analysis of tourmaline from the qitianling batholith south china four types of tourmaline in the qitianling granitic batholith south china were identified in this study euhedral disseminated tourmaline dt type in the early stage of granite consolidation typical interstitial nodular tourmaline nt type formed late in the crystallization history radial tourmaline veinlet rt type and vein tourmaline vt type of hydrothermal origin we performed major and trace element analysis by in situ electron microprobe and laser ablation inductively coupled plasma mass spectrometry on these four tourmaline types compositionally these tourmalines fall into the alkali group and schorl dravite solid solution series there is clear correlation between trace and major elements in vt type tourmalines likely related to co variations of these elements in the hydrothermal fluid from which the tourmaline precipitated tourmaline from granites displays low ree abundances and negative lree trends positive eu anomalies and hree below or close to their detection limits the dt type tourmalines show a positive eu anomaly which is probably due to a preferential incorporation of eu2 over eu3 ree depletion in nt type tourmalines may reflect co crystallization of ree rich minerals the positive eu anomaly in nt type tourmalines is due to late stage release of eu2 caused by tourmaline replacement of early feldspar vein tourmalines rt and vt type display similar slopes from la to nd without an eu anomaly the chondrite normalized ree patterns in tourmalines from veins display a concave upward shaped mree depleted pattern with minimum values at ho increasing steadily to lu and may reflect the ree characteristics of the precipitated medium hree enrichment in hydrothermal fluid can be attributed to the formation of ree fluoride complexes during the internal fluid evolution

trace element systematics of tourmaline in pegmatitic and hydrothermal systems from the variscan schwarzwald germany the importance of major element composition sector zoning and fluid or melt composition article an extensive data set on the compositional variation of tourmaline from granitic pegmatites from migmatitic gneisses and from various types of hydrothermal veins from the schwarzwald germany is provided the investigated tourmalines are members of the alkali and x vacant groups representing mostly dravite schorl solid solutions with some analyses belonging to the foitite mg foitite series oxygen isotope data on quartz tourmaline pairs indicate formation temperatures between 550 and 350 c for most of the quartz tourmaline veins most of the tourmalines show strong sector zonation fractionating certain major e g na mg minor e g ti ca and trace elements e g sr pb ree among the different crystallographic sectors of the crystals we conclude that comparison of tourmaline compositions for petrogenetic interpretations must be based on the concentrations in the neutral a sector in order to eliminate the effects of intra crystalline fractionation most trace element contents vary over several orders of magnitude with median concentrations generally be tween 0 1 and 10 g g the highest concentrations are found for zn v sr sc sn and li median concentrations of several tens to hundreds of g g whereas very low median concentrations b0 1 g g were found for u th bi tl and cs the concentration of several trace elements e g sr ree co correlates with the major element composition of the tourmaline which implies potential crystal chemical effects on their incorporation conse quently the general assumption that tourmaline is a passive monitor for the chemical compositions of the melts or fluids from which it crystallizes has to be questioned nevertheless our study demonstrates that the trace element composition of tourmaline allows to distinguish between geochemically distinct fluid sources and the trace element composition of tourmaline may therefore be used to unravel the chemical complexity of granite related hydrothermal systems

chemical and boron isotopic composition of hydrothermal tourmaline from the panasqueira w sn cu deposit portugal abstract tourmaline is a locally abundant hydrothermal mineral in the wallrocks surrounding the w sn cu mineralized veins in the panasqueira deposit portugal and a minor phase within the veins themselves tourmaline chemical and boron isotope compositions have been determined from three settings 1 pervasive fine grained tourmalinization zones in wallrocks within 10 cm of the veins 2 coarser tourmaline in wallrock hosted fault zones and 3 needle shaped tourmaline from late stage vugs in the quartz veins all tourmalines from panasqueira have ferromagnesian compositions with significant octahedral aluminum contents and variable x site vacancies tourmaline compositions show significant chemical variations at the grain and sample scale but are homogeneous on the deposit scale tourmaline is typically optically and chemically zoned showing significant increases in fe and f and decrease in mg ca and al from core to rim moreover as a general trend al increases and mg decreases with proximity to the vein contact the observed chemical variation seems to have been controlled mainly by the vectors femg 1 x alna 1 r2 1 x al oh na 1 r2 1f 1 r2 oh f al 1o 1 and x al2o na 1 r2 2 oh f 1 the total range in tourmaline 11b values from the panasqueira w sn cu deposit is from 3 7 to 12 7 including tourmaline from the three settings the calculated b isotope composition of the hydrothermal fluid based on the average tourmaline composition of 9 and an estimated alteration temperature in the wallrocks based on ti in quartz thermometry of 500 c is 7 1 this isotopic composition is permissive of a boron source from local metasediments or an s type granite but the high boron concentration in the wallrocks with 50 vol tourmaline along with the typical element association of panasqueira w sn f nb ta rb makes a granitic source more likely late stage tourmaline needles in vugs within the mineralized veins show the same patterns and ranges in both chemical and boron isotope composition suggesting that exsolved magmatic fluids were injected in at least two pulses the variations in chemical and boron isotopic compositions of tourmaline combined with estimates from ti in quartz thermometry suggest that hydrothermal ore formation is associated with fluid cooling and geochemical fluid rock interactions

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

chemical and stable isotopic compositions of proterozoic metamorphosed evaporites and associated tourmalines from the houxianyu borate deposit eastern liaoning china an integrated major element trace and rare earth element and stable isotope b si o and s study has been carried out on the houxianyu borate deposit eastern liaoning china the present day mineralogy of the deposit is closely similar to that of magnesian skarn deposits and the borates are underlain by granite however the geochemical and isotopic evidence does not favour a skarn type origin in particular the boron isotopic compositions of the borate minerals and associated tourmalines preclude their origin from fluids derived from the granite rather the data are compatible with the borate deposit being a metamorphosed evaporite the mineralogy and chemistry of the deposit are most compatible with a non marineorigin although the high 34s and 11b values suggest that there may have been some marine components to the evaporitic brines overall the premetamorphic origin of the houxianyu borate deposit is similar to that of the tertiary non marine evaporite borate deposits of western turkey there are also similarities with other proterozoic early rifting environments e g the upper proterozoic damaran orogen of south africa that have implications for the structural evolution and mineral potential of the region

tourmaline at diagenetic to low grade metamorphic conditions its petrologic applicability article i nfo tourmaline developed under low temperature conditions b 300 c typically has distinctive morphological and chemical characteristics that reveal significant information about the environments in which they crys tallize under diagenetic conditions tourmaline can develop as overgrowths on detrital tourmaline cores or as new authigenic crystals tourmaline as monopolar crystal overgrowths is found in sandstones shales conglomerates dolostones and limestones nucleating exclusively at the positive end of the c axis cpole on the detrital grain a feature related to the mineral s polar nature these overgrowths tend to have compo sitions dominated by x site vacant tourmaline species e g foitite and can be linked to growth in aqueous environments low in na with other chemical characteristics related to the host rocks as temperature in creases tourmaline overgrowths develop at both the cpole andc pole but continue to exhibit a signif icant degree of morphological and chemical asymmetries these differences at either pole diminish as a function of increasing temperature such that it can be used as an intramineral geothermometer authigenic tourmalines without detrital tourmaline nuclei are found in many sedimentary or weakly meta morphosed metasedimentary rocks as well as fluid dominated geothermal systems here tourmalines are commonly foititic but have mg fe contents influenced by the host rock composition low temperature tour malines developed in hypersaline environments e g salt domes have distinct chemical characteristics high na fe 3 and w o and follow a trend between oxy dravite and povondraite o p trend this composi tional trend can be used as a guide to indicate tourmaline development within low temperature hypersaline environments and appears to be diagnostic of an oxidizing environment with high na in the fluid and high sa linity with the resulting reduction of the activity of h2o the o p trend is retained in some meta evaporite de posits that are relatively high grade and is found in tourmaline from some types of economically important metal deposits although tourmalines in low temperature environments are largely overlooked they have po tential to be a useful indicator of the chemical and thermal environments in a regime largely absent of such indicators

the distribution and timing of molybdenite mineralization at the el teniente cu mo porphyry deposit chile this journal is published under the terms of green open access authors may post a copy of the accepted i e post peer review version of their paper https doi org 10 2113 econgeo 110 2 387 in a repository of their choice or to their personal website after the relevant embargo period has passed the embargo period will be 12 months from formal online publication

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

the role of evaporites in the formation of magnetite apatite deposits along the middle and lower yangtze river china evidence from la icp ms analysis of fluid inclusions abstract numerous magnetite apatite deposits occur in the ningwu and luzong sedimentary basins along the middle and lower yangtze river china these deposits are located in the contact zone of gabbro dioritic porphyries with surrounding volcanic or sedimentary rocks and are characterized by massive vein and disseminated magnetite apatite anhydrite mineralization associated with voluminous sodic calcic alteration petrologic and microthermometric studies on multiphase inclusions in pre to syn mineralization pyroxene and garnet from the deposits at meishan ningwu basin luohe and nihe both in luzong basin demonstrate that they represent extremely saline brines 90 wt nacl equiv that were trapped at temperatures of about 780 c laser ablation icp ms analyses and raman spectroscopic studies on the natural fluid inclusions and synthetic fluid inclusions manufactured at similar p t conditions reveal that the brines are composed mainly of na 13 24 wt k 7 11 wt ca 7 wt fe 2 wt cl 19 47 wt and variable amounts of so 4 3 39 wt their cl br na k and na b ratios are markedly different from those of seawater evaporation brines and lie between those of magmatic fluids and sedimentary halite suggesting a significant contribution from halite bearing evaporites high s b and ca na ratios in the fluid inclusions and heavy sulfur isotopic signatures of syn to post mineralization anhydrite 34 s anh 15 2 to 16 9 and pyrite 34 s py 4 6 to 12 1 further suggest a significant contribution from sedimentary anhydrite these interpretations are in line with the presence of evaporite sequences in the lower parts of the sedimentary basins the combined evidence thus suggests that the magnetite apatite deposits along the middle and lower yangtze river formed by fluids that exsolved from magmas that assimilated substantial amounts of triassic evaporites during their ascent due to their fe oxide dominated mineralogy their association with large scale sodic calcic alteration and their spatial and temporal associations with subvolcanic intrusions we interpret them as a special type of iocg deposits that is characterized by unusually high contents of na ca cl and so 4 in the ore forming fluids evaporite assimilation apparently led to the production of large amounts of high salinity brine and thus to an enhanced capacity to extract iron from the gabbro dioritic intrusions and to concentrate it in the form of ore bodies hence we believe that evaporite bearing sedimentary basins are more prospective for magnetite apatite deposits than evaporite free basins

chemical and boron isotope variations in tourmalines from an s type granite and its source rocks the erongo granite and tourmalinites in the damara belt namibia tourmaline is widespread in metapelites and pegmatites from the neoproterozoic damara belt which form the basement and potential source rocks of the cretaceous erongo granite this study traces the b isotope variations in tourmalines from the basement from the erongo granite and from its hydrothermal stage tourmalines from the basement are alkali deficient schorl dravites with b isotope ratios typical for continental crust 11b average 8 4 1 4 n 11 one sample at 13 n 2 virtually all tourmaline in the erongo granite occurs in distinctive tourmaline quartz orbicules this main stage tourmaline is alkali deficient schorl 20 30 x site vacancy fe fe mg 0 8 1 with uniform b isotope compositions 11b 8 7 1 5 n 49 that are indistinguishable from the basement average suggesting that boron was derived from anatexis of the local basement rocks with no significant shift in isotopic composition secondary hydrothermal tourmaline in the granite has a bimodal b isotope distribution with one peak at about 9 like the main stage tourmaline and a second at 2 we propose that the tourmaline rich orbicules formed late in the crystallization history from an immiscible na b fe rich hydrous melt the massive precipitation of orbicular tourmaline nearly exhausted the melt in boron and the shift of 11b to 2 in secondary tourmaline can be explained by rayleigh fractionation after about 90 b depletion in the residual fluid

boron isotope systematics of tourmaline formation in the sullivan pb zn ag deposit british columbia canada abstract we report here the results of 54 boron isotope analyses of tourmaline associated with the giant sullivan pb zn ag deposit in southeastern british columbia canada the 11 b values range from 11 1 to 2 9 which is almost as great as the range found worldwide in tourmalines from 33 massive sulfide deposits and tourmalinites in dominantly clastic metasedimentary terranes the major control on the overall 11 b values of the sullivan tourmalinites is the boron source potential controls over the large range of the data also include 1 differences in formation temperatures of the tourmalinites 2 different stages of tourmaline formation 3 variations in the proportions of dissolved boron incorporated into the tourmaline rayleigh fractionation 4 seawater entrainment and 5 post depositional metamorphism the boron isotope data at sullivan are consistent with boron derivation from leaching of footwall clastic sediments however the great abundance of tourmaline in the sullivan deposit suggests that the local clastic sediments were not the sole source of boron and we argue that non marine evaporites buried deep below the orebody are the most viable source of this additional boron it is likely that some of the variation in tourmaline 11 b values reflect mixing of boron from these two sources comparison of the potential effects of these controls with geologic and other geochemical evidence suggests that major causes for the wide range of 11 b values measured at sullivan are seawater entrainment and rayleigh fractionation although in places post depositional alteration and thermal metamorphism were important in determining 11 b values of some of the recrystallized tourmalinites

geology alteration age and origin of iron oxide apatite deposits in upper eocene quartz monzonite zanjan district nw iran iron oxide apatite deposits are present in upper eocene pyroxene quartz monzonitic rocks of the zanjan district northwestern iran mineralization occurred in five stages 1 deposition of disseminated magnetite and apatite in the host rock 2 mineralization of massive and banded magnetite ores in veins and stockwork associated with minor brecciation and calcic alteration of host rocks 3 deposition of sulfide ores together with potassic alteration 4 formation of quartz and carbonate veins and sericite chlorite epidote silica carbonate and tourmaline alteration and 5 supergene alteration and weathering u pb dating of monazite inclusions in the apatite indicates an age of 39 99 0 24 ma which is nearly coeval with the time of emplacement of the host quartz monzonite supporting the genetic connection fluid inclusions in the apatite have homogenization temperatures of about 300 c and oxygen isotopic compositions of the magnetite support precipitation from magmatic fluids late stage quartz resulted from the introduction of a cooler less saline and isotopically depleted fluid the iron oxide apatite deposits in the tarom area of the zanjan district are typical of a magmatic hydrothermal origin and are similar to the kiruna type deposits with respect to mineral assemblages fabric and structure of the iron ores occurrence of the ore bodies and wall rock alteration

isotopic and elemental partitioning of boron between hydrous fluid and silicate melt the fractionation of b and its isotopes between aqueous fluid and silicate melt has been studied from 550 to 1100 c and 100 500 mpa fluid melt partition coefficients are 1 for rhyolite melt this shows that b is not always strongly extracted from melts into hydrous fluids boron isotopic fractionation is large compared with the carbon and oxygen stable isotopic systems especially at high t and is most simply explained by differences in coordination trigonal vs tetrahedral among coexisting phases combined with earlier measurements on illite water 300 350 c b isotopic fractionation defines a temperature dependent trend from 300 to 1100 c because of the large magnitude and apparent low sensitivity to bulk composition b isotopic fractionation can be readily applied to studies of diagenesis hydrothermal alteration of planetary bodies subduction zone processing and arc magma generation and magma chamber evolution

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

evaporitic source model for igneous related fe oxide ree cu au u mineralization we propose that many igneous related fe oxide rich ree cu au u bearing deposits form by hydrothermal processes involving evaporitic ligand sources either coeval salars or older evaporites these deposits are abundant in both phanerozoic and proterozoic extensional continental and continent margin settings they commonly form in global arid zones but they also occur where magmatism is superimposed upon older evaporites magmatic compositions exert only second order control mainly on alteration mineralogy and on element abundances hot s poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments siderophile lithophile and hydrothermal alteration sodic locally alkaline found in these systems this model contrasts with immiscible oxide melt and magmatic hydrothermal origins commonly proposed for these deposits although all three mechanisms can occur 31 refs 3 figs 1 tab

boron isotopic variations in fumarolic condensates and thermal waters from vulcano island italy implications for evolution of volcanic fluids abstract temporal variation in the isotopic composition of boron has been monitored in fumarolic condensates collected over an extended time period 1970 1996 from la fossa crater volcano island we also report comparative boron isotopic data for representative vulcano lavas and for shallow hydrologic samples seawater wells thermal springs from the north flank of la fossa combined with concurrent chemical and isotopic 18o d data for the fumaroles these results indicate that the fumarolic fluids record mixing relations between three distinct fluid end members 1 a dominantly magmatic fluid em1 2 a mixture of modified seawater with magmatic fluid em2 and 3 an aqueous fluid produced from seawater by extensive wall rock reaction evaporation and boiling af differences between the latter two end members are most clearly accentuated on the basis of the boron isotopic data long term compositional variations for crater fumaroles were dominated by em1 af mixing between 1979 88 with progressive decrease in em1 contribution with time and by em2 af mixing between 1988 96 the exact spatial distribution of these fluid reservoirs remains unclear but all must have been present throughout the monitoring period to account for the observed variations moreover the combined b o h data seem to preclude important contributions from shallow meteoric reservoirs marked short term variations in 11b closely coincide with episodes of local seismicity which presumably triggered reorganization of hydrothermal circulation patterns gradual variations over periods up to 3 4 years are associated with relatively low seismicity during which fluid circulation was likely influenced by effects of mineral precipitation on permeability of the hydrologic system

allogenic controls on the fluvial architecture and fossil preservation of the upper triassic ischigualasto formation nw argentina abstract the upper triassic ischigualasto formation in nw argentina was deposited in a fluvial system during the synrift filling of the extensional ischigualasto villa union basin the expansive exposures of the fluvial architecture and paleosols provide a framework to reconstruct the paleoenvironmental evolution of this basin during the upper triassic using continental sequence stratigraphy the ischigualasto formation deposition can be divided into seven sequential sedimentary stages the 1 bypass stage 2 confined low accommodation stage 3 confined high accommodation stage 4 unstable accommodation stage 5 unconfined high accommodation stage 6 unconfined low accommodation stage and finally 7 unconfined high accommodation stage the sedimentary evolution of the ischigualasto formation was driven by different allogenic controls such as rises and falls in lake levels local tectonism subsidence volcanism and climate which also produced modifications of the equilibrium profile of the fluvial systems all of these factors result in different accommodations in central and flank areas of the basin which led to different architectural configurations of channels and floodplains allogenic processes affected not only the sequence stratigraphy of the basin but also the vertebrate and plant taphocenosis therefore the sequence stratigraphy can be used not only as a predictive tool related to fossil occurrence but also to understand the taphonomic history of the basin at each temporal interval

subduction like fluids in the genesis of mt etna magmas evidence from boron isotopes and fluid mobile elements abstract new whole rock b sr nd isotope ratios and 87sr 86sr on clinopyroxenes have been collected to study the enrichment of fluid mobile elements fmes observed in mt etna volcanics etna volcano one of the most active in the world is located in an extremely complex tectonic context at the boundary between colliding african and european plates the analytical work focuses on current 1974 1998 and historic 1851 1971 eruptive activity including some key prehistoric lavas in order to interpret the secular shift of its geochemical signature to more alkaline compositions boron is used as a tool to unravel the role of fluids in the genesis of magmas revealing far reaching consequences beyond the case study of mt etna small variations are observed in 11b 3 5 to 8 0 87sr 86sr 0 70323 0 70370 and 143nd 144nd 0 51293 0 51287 moreover temporal evolution to higher 11b and 87sr 86sr and to lower 143nd 144nd is observed in the current activity defining a regular trend sr isotopic equilibrium between whole rock and clinopyroxene pairs indicates the successive introduction of three distinct magma types into the etna plumbing system over time these are characterized by differing degrees of fme enrichment in addition certain lavas exhibit evidence for country rock assimilation magma fluid interaction or magma mixing in the shallow feeding system at times these processes apparently lowered magmatic 11b and or induced sr isotopic disequilibrium between whole rock and clinopyroxene the regular increase of 11b values is correlated with nb fme and 87sr 86sr ratios these correlations are consistent with simple mixing between the mantle source and aqueous fluids derived from nearby ionian slab the best fit of mt etna data is obtained using an enriched morb mantle source and a fluid phase with 11b of about 2 and 87sr 86sr of 0 708 we argue that the slab window generated by differential roll back of subducting ionian lithosphere with respect to sicily allows the upwelling of asthenosphere from below the subduction system and provides a suitable path of rise for subduction related fluids the increasing geochemical signature of fluid mobile elements enrichment to mt etna lavas is considered a consequence of the progressive opening of slab window through time

late magmatic immiscibility during batholith formation assessment of b isotopes and trace elements in tourmaline from the land s end granite sw england quartz tourmaline orbicules are unevenly distributed in the roof segment of the land s end granite sw england this study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes trace elements and boron isotope fractionation can be tracked in tourmaline and create a timeline for crystallization tourmaline from the granite matrix has higher v cr and mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline overgrowths of blue tourmaline occurring together with quartz showing hydrothermal cathodoluminescence textures crystallized from an aqueous fluid during the very last crystallization and are significantly higher in sr and sn and isotopically heavier tourmaline associated with sn mineralization is also high in sr and sn but has boron isotopic compositions close to that of the magmatic tourmaline and is not formed by the same fluids responsible for the blue overgrowths the ore forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite but exsolved deeper in the magma chamber and at a later stage than orbicule formation tourmaline from massive quartz tourmaline rocks is concentrically zoned with major and trace element compositions indicating crystallization from a similar melt as for the orbicules but shows a more evolved signature

boron isotope fractionation during supercritical phase separation abstract boron isotopic fractionation between vapor and brine phases separated under supercritical conditions has been experimentally examined using a na ca k cl fluid experiments were conducted at 425 440 and 450 c phase separation was controlled by adjusting pressure fractionation between the coexisting phases was less than 0 5 in contrast fractionation between trigonal and tetrahedral b at these temperatures has been predicted to be approximately 8 the lack of fractionation suggests that the trigonal tetrahedral speciation of b is similar in the two phases although this result may not be general for other fluid compositions it is relevant to ridge crest hydrothermal solutions and indicates that the boron isotopic compositions of these solutions reflect the proportions of b from seawater and crustal sources and not phase separation