gold speciation and transport in geological fluids insights from experiments and physical chemical modelling this contribution provides an overview of available experimental thermodynamic and molecular data on au aqueous speciation solubility and partitioning in major types of geological fluids in the earth s crust from low temperature aqueous solution to supercritical hydrothermal magmatic fluids vapours and silicate melts critical revisions of these data allow generation of a set of thermodynamic properties of the auoh aucl 2 auhs and au hs 2 complexes dominant in aqueous hydrothermal solutions however other complexes involving different sulphur forms chloride and alkali metals may operate in high temperature sulphur rich fluids vapours and melts the large affinity of au for reduced sulphur is responsible for au enrichment in s rich vapours and sulphide melts which are important gold sources for hydrothermal deposits thermo dynamic speciation and partitioning data and their comparison with au and s contents in natural fluid inclusions from magmatic hydrothermal gold deposits provide new constraints on the major physical chemical parameters temperature pressure salinity acidity redox and ubiquitous fluid components sulphur carbon dioxide arsenic affecting au concentration transport precipitation and fractionation from other metals in the crust the availability and speciation of sulphur and their changes with the fluid and melt evolution are the key factors controlling gold behaviour in most geological situations

the timing of gold mineralization across the eastern yilgarn craton using u pb geochronology of hydrothermal phosphate minerals the highly mineralized eastern goldfields of the eastern yilgarn craton is an amalgamation of dominantly neoarchaean granitoid greenstone terranes and domains that record a history of early rifting followed by westward directed collision with initial arc formation collision and clastic basin formation and final accretion to the western yilgarn proto craton between 2 66 and 2 60 billion years ago the gold deposits that define this region as a world class gold province are the product of orogenic processes that operated during accretion late in the tectonic history after initial compressional deformation d1 d2 and the majority of granitoid magmatism minor gold was also deposited throughout the entire tectonic history in magmatic hydrothermal related systems however such mineralization mostly 0 3 g t gold is nowhere economic unless it overprints or is overprinted by much higher grade orogenic gold lodes robust shrimp u pb geochronology of gold related hydrothermal xenotime and monazite supports structural studies that gold mineralization occurred during late transpressional events d3 d4 shortly before cratonization however westward migration of collision and accretion produced a complementary diachroneity in the timing of gold mineralization of 5 to 20 m y between c 2 65 ma in the east including laverton district kurnalpi terrane to c 2 63 ma in the west including kalgoorlie terrane across the eastern part of the craton the robust geochronology refutes previous suggestions that significant gold mineralization events extended from de to d4 in the evolution of the orogen and that the kalgoorlie gold deposits formed over a period of 45 m y the crustal continuum model is applicable within terranes where orogenic gold depositional events were penecontemporaneous but must be modified to account for diachroneity of orogenic events and gold mineralization across the eastern goldfields

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

fluid evolution of the late archaean ramepuro gold deposit in the ilomantsi greenstone belt in eastern finland the late archaean ca 2 7 ga ilomantsi greenstone belt hosts a large number of small mesozonal gold occurrences the ramepuro deposit is spatially related to a feldspar porphyry dyke which has intruded the contact between metagreywackes and intermediate metavolcanic rocks it consists of gold bearing quartz tourmaline sulphide veins located mainly within an intensively altered and sheared zone about 20 30 m in width two types of fluid inclusions were distinguished in the quartz veins 1 h2o ch4 9 equiv wt nacl and 2 h2o co2 12 equiv wt nacl the two compositionally different fluid inclusion types occur in separate veins the compositions of decrepitate residues indicate that the type 1 fluid inclusions consist predominantly of na s ca cl and in lesser proportions of k and fe the residues of the type 2 fluid inclusions are dominated by na ca cl and minor k for the type 1 and type 2 fluid inclusions microthermometric experiments indicate average homogenisation temperatures of 310 350 and 220 250 c respectively both types of fluid inclusions contain 1 3 anisotropic solids ca mg carbonate nahcolite tourmaline sulphide daughter minerals occur only in the type 1 fluid inclusions this fluid type is also often associated with short trails of sulphide inclusions which suggest mobilisation and redistribution of ore constituents some type 1 fluid inclusions display distinct morphological features implosion textures related to post trapping re equilibration the presence of the fluid inclusion re equilibration textures in some auriferous quartz veins and their absence in other gold bearing quartz veins suggest an age difference between them this conclusion is also supported by the compositionally different fluid regimes associated with the different quartz veins indicating a change from reducing ch4 to a more oxidising co2 fluid environment the fluid inclusion evidence suggests two separate gold mineralisation events one related to late archaean regional metamorphism the other to palaeoproterozoic thrusting and metamorphism

modern and paleofluid pathways revealed by cu isotope compositions in surface waters and ores of the pebble porphyry cu au mo deposit alaska copper isotope ratios measured in minerals and shallow groundwater and surface waters provide insight into high temperature mineralization and active weathering processes at the pebble porphyry cu au mo deposit alaska the west zone of the deposit contains hypogene mineralization with a supergene overprint and a thin oxide leached capping whereas the contiguous east zone contains only hypogene mineralization sulfide rich rock powders and mineral separates have 65cu values that range from 0 78 to 2 28 hypogene west 0 02 to 1 55 hypogene east 3 49 to 1 88 oxide west and 5 04 to 1 27 supergene west the results from hypogene samples show that there is a systematic increase in 65cu values from deeper to shallower portions of the deposit furthermore the 65cu values correlate with silicate alteration assemblages mostly positive values correspond to quartz illite pyrite sericite and quartz pyrophyllite alteration zones which formed at relatively lower temperatures whereas negative values characterize the higher temperature potassic and sodic potassic domains this empirical evidence could indicate that fractionation of cu isotopes during hypogene alteration is controlled by ph and or temperature variations shallow surface waters proximal to the deposit and which likely interacted with underlying concealed mineralization have heavy 65cu values which contrast with lighter values in waters distal from the deposit patterns measured in the copper isotope ratios of both solids and surface waters demonstrate the potential use of copper isotope distribution as a vectoring tool in mineral exploration and aid in understanding the sources of copper in the surface and near surface environments

laser microprobe sulphur isotope analysis of arsenopyrite experimental calibration and application to the boliden au cu as massive sulphide deposit abstract metamorphic remobilization of arsenopyrite rich ores is a globally important process which can lead to significant concentrations of gold in order to understand this and related processes relations of sulphur isotopes can give a number of important clues to resolve such relations in detail we have successfully calibrated and applied a laser combustion system for in situ analysis of sulphur isotopic compositions of arsenopyrite experimental calibration of the laser fractionation factor 0 4 was obtained by using compositionally and isotopically homogeneous natural samples from ore deposits at boliden sweden and freiberg germany subsequent to detailed microscopic study the s isotope ratios of these samples were measured by conventional and laser combustion techniques the present application to different types of arsenopyrite in the palaeoproterozoic metamorphosed vhms ores of the boliden au cu as deposit skellefte district northern sweden shows that the sulphur isotope composition of arsenopyrite is essentially unmodified during medium grade metamorphic recrystallization and remobilization here massive arsenopyrite ore is crosscut by later veins that carry a complex quartz sulphosalt sulphide assemblage the latter ore type is markedly au rich compared to the host ore and thus of significant economic interest we find that both ore types exhibit very similar sulphur isotope compositions ca 2 to 3 v cdt which is similar to most massive sulphide deposits in the skellefte district thus the crosscutting au rich vein ore has inherited the sulphur isotope composition from sulphur liberated by metamorphic reactions affecting the massive ore and most likely also inherited the au through this mechanism the latter finding clearly has important implications both for the general discussion on and the prospecting for similar high grade au ores in this world class mining region

structure of the alula fartak fracture zone gulf of aden the alula fartak transform fault is associated with a broad steep sided valley running nne ssw across the mouth of the gulf of aden a discussion of the tectonics of the fracture zone is based principally on gloria side scan sonar and gravity data the transform valley is 180 km long and 25 km across has 3 5 km of relief and is bounded by transverse ridges the northern two thirds is highly asymmetrical in cross section the eastern wall dips 38 and appears to be a single scarp exposing a section of oceanic crust 3100 m thick the western wall is much less steep and accommodates several normal faults oriented at about 15 to its general trend a very fine long sonar target running along part of the valley delineates the main active strike slip fault the sonar data also reveal many fine faultlike targets between the main walls running approximately at right angles to the trend of the valley which may be anti riedel shears a 50 km long 7 5 km wide and 1 5 km high median ridge runs along the southern third of the transform valley gravity data show that the valley is underlain by a significant mass deficiency thought to be a large serpentinite intrusion the median ridge is suggested to be the surface manifestation of a large serpentinite diapir the ridges flanking the transform valley are above a level compatible with isostatic equilibrium and are interpreted as flexural features raised in response to the upward loads imposed on the lithosphere by the fracture zone valley and its underlying mass deficiency very shallow crust is located close to the ridge transform intersections this is considered to result from static flexure induced by the negative load of the transform valley superimposed on dynamic compensation of the spreading center valley evidence of a c 3 5 m y b p change in spreading direction suggests the transform has experienced a recent component of opening accounting for several aspects of its structure

physical chemical properties and metal budget of au transporting hydrothermal fluids in orogenic deposits we use a set of analytical techniques for fluid inclusion analysis to determine the bulk properties of the ore fluids from five orogenic gold deposits the most common ore fluid is a low salinity 0 4 6 5 wt nacl twoto three phase aqueous carbonic fluid its th total range is 200 400 8c and total homogenization occurs by bubble or liquid disappearance a less common aqueous fluid of similar bulk salinity and t h total is also documented microchemical data show that the ore fluid in the five deposits is chemically uniform and made of na subordinate k and b and minor to trace amounts of cu as li sr rb ba cs sb and au range 0 5 5 mg g thermodynamic modelling carried out for one of the studied deposits indicates that the ore fluid was in equilibrium with vein minerals at the time of gold deposition and that its vapour phase was distinctly enriched in au b as and sb the proposed mechanism of gold precipitation is a combination of fluid decompression and boiling combining these results with 3d geometrical reconstructions of one of the studied deposits sigma we estimate that a minimum ore fluid volume of c 0 1 1 0 km is sufficient to generate a world class orogenic deposit orogenic deposits provide about a third of the global gold production goldfarb et al 2001 frimmel 2008 these deposits are formed within active continental margins in orogenic belts where major tectonic boundaries juxtapose metamorphosed volcanic plutonic and sedimentary terranes the ore bodies consist of au mineralized vein networks filled with quartz carbonates and other silicates that in places crosscut the stacked terranes of the continental margins the veins are dilated portions of vertically extensive brittle ductile to ductile fracture networks that form due to the advection of aqueous hydrothermal fluids within the continental crust ridley et al 1996 groves et al 2003 these ore fluids are generated in still undefined source regions deep in the crust and transported to shallower levels 3 15 km depth through the vein networks along which they deposit gold a number of studies kerrich et al 2000 ridley diamond 2000 groves et al 2003 showed that although these networks do not occur systematically in all orogens they have a set of important geological features in common which include 1 formation during accretionary orogenic events 2 occurrence relatively close to regional tectonic lineaments especially along lower order splays of these structures 3 spatial association with granitoid intrusions 4 occurrence within some metamorphic belts with gold precipitation being synto postmetamorphic in age 5 relatively low sulphide abundance within the veins 6 carbonate sericitealbite sulphide hydrothermal alteration of host rocks postdating metamorphism 7 poorly developed mineral and metal zoning within the ore bodies and 8 genesis from low to moderate salinity ore fluids over a large temperature range 250 700 8c but mostly within 300 350 8c these common traits occur systematically in deposits from different terrains having distinct ages suggesting that a common geological process and au transporting fluid are responsible for their formation here we present a database of fluid inclusion properties from five typical orogenic deposits which show most of the geological characteristics listed above the database was constructed with the aim of determining as accurately as possible the properties of the au transporting fluid in this geological environment in particular laser ablation inductively coupled plasma mass spectrometry la icp ms of single fluid inclusions paragenetically coeval with vein gold provides the concentration of a suite of metals including au in this fluid this dataset when combined with 3d geometrical reconstructions of one of these deposits offers new constraints on the volume of the ore from garofalo p s ridley j r eds gold transporting hydrothermal fluids in the earth s crust geological society london special publications 402 http dx doi org 10 1144 sp402 8 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics by guest on april 3 2014 http sp lyellcollection org downloaded from

fluid inclusion characteristics of auriferous quartz veins in archean and paleoproterozoic greenstone belts of eastern and southern finland fluid inclusions in auriferous quartz veins in five deposits in the archean 2 9 2 7 ga and paleoproterozoic 2 0 1 75 ga greenstone belts of eastern and southwestern finland have been characterized on the basis of their composition reconstructed isochores and decrepitation behavior the dominant fluids associated with gold mineralization are h2o co2 ch4 halite archean and h2o co2 ch4 or h2o ch4 paleoproterozoic in composition phase ratios were generally uniform h2o co2 in the archean but were variable in the paleoproterozoic in the archean au sulfide quartz veins the mineralizing fluids contain less ch4 30 mol and have higher salinities up to 39 wt nacl equiv than the corresponding fluids in the paleoproterozoic au sulfide quartz veins up to 38 mol ch4 and below 13 wt nacl equiv additionally the estimated pressure temperature conditions for gold mineralization differ markedly between the two domains mineralization occurred in a pressure temperature range of 300 to 500 c at 2 to 3 5 kbars in the archean domain and 200 to 300 c at 1 to 2 kbars in the paleoproterozoic domain decrepigrams for the archean and paleoproterozoic auriferous quartz veins show different characteristics and permit classification of the different fluid inclusion populations on a regional scale

copper isotopic zonation in the northparkes porphyry cu au deposit se australia abstract significant systematic cu isotopic variations have been found in the northparkes porphyry cu au deposit nsw australia which is an orthomagmatic porphyry cu deposit copper isotope ratios have been measured in sulfide minerals chalcopyrite and bornite by both solution and laser ablation multi collector inductively coupled plasma mass spectrometry mc icp ms the results from both methods show a variation in 65cu of hypogene sulfide minerals of greater than 1 relative to nist976 significantly the results from four drill holes through two separate ore bodies show strikingly similar patterns of cu isotope variation the patterns are characterized by a sharp down hole decrease from up to 0 8 0 29 0 56 1 n 20 in the low grade peripheral alteration zones phyllic propylitic alteration zone to a low of 0 4 0 25 0 36 1 n 30 at the margins of the most mineralized zones cu grade 1 wt in the high grade cores of the systems the compositions are more consistent at around 0 2 0 19 0 14 1 n 40 the cu isotopic zonation may be explained by isotope fractionation of cu between vapor solution and sulfides at high temperature during boiling and sulfide precipitation processes sulfur isotopes also show an isotopically light shell at the margins of the high grade ore zones but these are displaced from the low 65cu shells such that there is no correlation between the cu and s isotope signatures fe isotope data do not show any discernable variation along the drill core this work demonstrates that cu isotopes show a large response to high temperature porphyry mineralizing processes and that they may act as a vector to buried mineralization

uniformity in sulfur isotope composition in the orogenic gold deposits from the dharwar craton southern india the sulfur isotope composition of sulfides mainly pyrite and arsenopyrite from gold deposits prospects of the dharwar craton such as hutti hira buddini uti kolar chigargunta ajjanahalli and jonnagiri has a narrow range 34s 1 1 to 7 1 such craton scale uniformity of the above gold camps is noteworthy in spite of the wide diversity in host rock compositions and their metamorphic conditions and suggests a magmatic or average crustal source of sulfur for all deposits studied in addition our study points towards gold precipitation from reduced ore fluids with near homogeneous sulfur isotope compositions

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

hydrothermal transport and depositional processes in archean lode gold systems a review abstract compelling evidence now exists for the formation of archean lode gold deposits over a substantial range in metamorphic conditions and crustal depth the commonality of ore fluid isotopic and geochemical characteristics the extreme fluid rock ratios within actual ore zones and the observed depth continuity within individual orebodies all suggest that these deposits formed within vertically extensive crustal scale hydrothermal systems calculations based on new thermodynamic data and estimated ore fluid conditions suggest that gold would have been transported as au hs 2 over most of this range gold transport in the ore fluids that formed some diopside and diopside k feldspar class deposits t 550 c would have been as aucl2 whereas the au hs complex may have been significant in some of the lower temperature 270 c less alkaline ore fluids the high solubility of gold in lode gold ore fluids at amphibolite facies conditions 10 s to 1000 s ppb suggests that fluids may have been undersaturated in gold within their source regions promoting the ore fluid s capacity to retain gold in solution over the large transport distances involved ore depositional mechanisms were also likely to vary between crustal levels fluid rock interactions and wallrock sulphidation in particular appear to be the most important type of precipitation mechanism however with decreasing depth of formation the scope of other depositional mechanisms notably phase separation and fluid mixing becomes greater

stable isotope geochemistry of the archean val d or canada orogenic gold vein field a systematic study of the auriferous quartz veins of the val d or vein field abitibi quebec canada demonstrates that the c o s isotope composition of silicate carbonate borate oxide tungstate and sulphide minerals have a range in composition comparable to that previously determined for the whole superior province the oxygen isotope composition of quartz from early quartz carbonate auriferous veins ranges from 9 4 to 14 4 whereas later quartz tourmaline carbonate veins have 18oquartz values ranging from 9 2 to 13 8 quartz carbonate veins have carbonate 18o 6 9 12 5 13c 6 2 1 9 and pyrite 34s 1 2 and 1 9 isotope compositions comparable to those of quartz tourmaline carbonate veins 18o 7 9 11 7 13c 8 0 2 4 34s 0 6 6 0 18oquartz values in quartz tourmaline carbonate veins have a variance comparable to analytical uncertainty at the scale of one locality irrespective of the type of structure the texture of the quartz or its position along strike across strike or down dip a vein in contrast the oxygen isotope composition of quartz in quartz tourmaline carbonate veins displays a regional distribution with higher 18o values in the south central part of the vein field near the cadillac tectonic zone and which 18o values decrease regularly towards the north another zone of high 18o values in the northeast corner of the region and along the trace of the senneville fault is separated by a valley of lower 18o values from the higher values near the cadillac tectonic zone oxygen isotope isopleths cut across lithological contacts and tectonic structures this regional pattern in quartz tourmaline carbonate veins is interpreted to be a product of reaction with country rocks and mixing between 1 a deep seated hydrothermal fluid of metamorphic origin with minimum 18o 8 5 13c 0 6 and 34s 0 4 and 2 a supracrustal fluid most likely archean seawater with a long history of water rock exchange and with maximum 18o 3 9 13 c 5 6 and 34s 5 0

geochronological constraints on pre syn and postmineralization events at the world class cleo gold deposit eastern goldfields province western australia recent geological and geochronological studies have led to a reevaluation of whether or not the majority of the lode gold deposits of the yilgarn craton formed nearly synchronously during an archean craton wide hydrothermal event as previously proposed the majority of reliable data indicate that gold mineralization took place at ca 2640 to 2625 ma however recent work in the far north of the eastern goldfields province provides structural evidence for instances of earlier gold mineralization and geochronological data for interpreted postore rocks that are considerably older than 2640 ma the documentation of xenotime and monazite in association with ore minerals at the cleo deposit provides a valuable means of determining the absolute age of gold mineralization at the cleo deposit high grade western lodes veins crosscut the sunrise shear zone at a high angle with only centimeter scale offset given that the stratigraphic sequence indicates at least several hundred meters offset across the shear zone the minimal offset of the western lodes veins indicates that gold mineralization was late in the history of movement in the shear zone the absolute ages of pre syn and postmineralization elements in the mine stratigraphic succession have been determined using a variety of geochronological techniques fuchsite micas formed in the sunrise shear zone yield an 40ar 39ar isochron age of 2667 19 ma rhyodacite porphyry dikes postdate the formation of the shear zone but predate the main phase of gold mineralization dike intrusion is constrained to 2674 3 ma by shrimp ii u pb analysis of zircons from these dikes rhenium os analysis of molybdenite from quartz chalcopyrite molybdenite veins that crosscut the porphyry dikes gives an age of formation at 2663 11 ma consistent with their relationship to the porphyry dikes both the dikes and these veins are crosscut by gold bearing western lodes veins mutually crosscutting relationships with ore minerals indicate that microscopic xenotime and monazite grains were deposited during ore formation in the western lodes ore zones shrimp ii u pb analyses of xenotime and monazite grains indicate that western lodes mineralization took place at 2654 8 ma at least 9 m y after the intrusion of the porphyry dikes 95 confidence evidence for substantial temporal separation between intrusive activity and gold mineralization is recorded by other researchers for other deposits associated with granitic intrusions in the leonora laverton area phlogopitic micas from a lamprophyre that crosscuts the whole succession including the sunrise shear zone yield an ar ar plateau age of 2080 4 ma this study constrains the timing of multiple events at cleo including the main phase of gold mineralization during a relatively short span of time however in the context of the larger debate about the existence of a dominant 2640 to 2625 ma period of gold mineralization and the extent of a proposed widespread pre 2660 ma mineralization event in the yilgarn craton the data from cleo are equivocal the 2654 8 ma age for mineralization being significantly older than 2640 ma but not significantly pre 2660 ma even if the maximum possible age is accepted

the diversity of b isotope variations in tourmaline from rare element pegmatites in the borborema province of brazil abstract tourmaline chemical and b isotope compositions have been determined from 4 rare element pegmatites and 1 barren pegmatite in the borborema pegmatite province of ne brazil and also from a leucogranite considered to be parental to the pegmatites the rare element pegmatites are of the lct lithium cesium tantalum class and they display a classic zoning structure with tourmaline present in all units but the quartz core tourmaline major element composition varies systematically from schorl dravite in the border and wall zones to varicolored elbaite in the inner zones consistent with increasing differentiation of a pegmatite magma previous studies supposed a continuous variation in li contents from schorl dravite to elbaite but the sims data instead show a major gap between 0 07 wt and 0 72 wt li 2 o followed by a continuous variation to the maximum value of 1 8 wt the barren pegmatite and leucogranite contain schorl dravite only the full range of 11 b values in tourmaline from the borborema pegmatites is from 20 2 to 1 6 n 62 which comes close to the total known diversity of pegmatite tourmalines worldwide and is much broader than the range of the associated leucogranite 15 1 to 13 4 n 3 however more than 80 of the pegmatite tourmalines define a main range between 17 and 9 11 b the average value of the latter 13 5 s d 2 3 n 50 is identical within error with the leucogranite supporting suggestions of a genetic relationship the b isotope compositions of barren and mineralized pegmatites overlap within the main range we find no correlation between chemical composition and b isotope ratios famous for the borboreman province are gem quality crystals of blue paraiba type elbaite the 11 b values of blue tourmaline from the capoeira pegmatite also fall within the main range 16 4 to 11 9 n 5 four of the 5 pegmatites studied are heterogeneous in 11 b with typical variations of 6 however there are no consistent trends in these examples from outer to inner units or from core to rim of zoned crystals that would fit any one scenario of melt evolution instead the factors controlling b isotope evolution e g crystallization fluid exsolution or mixing with external b reservoirs appear to vary locally and can be specific to the individual pegmatite or internal zone within it for example the carrascao pegmatite shows a shift from higher to lower 11 b values in tourmaline from the outer to inner zone 14 9 to 9 1 vs 20 2 to 13 9 resp and there is a parallel trend of lighter rims in zoned elbaite from the inner intemediate zone these trends are consistent with 11 b removal by tourmaline crystallization and or fluid exsolution an opposite trend in isotopic variation was found in zoned tourmaline from the wall zone of the boqueirao pegmatite whose core compositions are in the main range 15 1 to 14 9 and whose rims are much heavier 5 5 to 1 7 similarly high 11 b values about 10 beyond the main range were found in wall zone tourmaline in the barren fazenda turmalina pegmatite 6 0 to 1 6 the patchy distribution of heavy b isotopic compositions found only in outer zones of pegmatites and the strong isotopic contrast with the main range suggest the possibility of mixing with heavy b from the country rocks a potential source being layers of marble and calc silicate rocks

late archean granitoid hosted lode gold deposits yilgarn craton western australia deposit characteristics crustal architecture and implications for ore genesis granitoid hosted lode gold deposits constitute a sub group of late archean lode gold deposits in the yilgarn craton of western australia they share a number of common characteristics including 1 a strong structural control on a variety of scales 2 in most instances the presence of mineralisation in adjacent supracrustal sequence 3 wallrock alteration and vein assemblages consistent with the addition of sio2 k2o co2 s na2o but dependent on the p t conditions of the host environment and ore fluid 4 a metal association comprising au ag as bi te w mo and low concentrations of cu pb and zn and 5 deposition from a low moderate salinity near neutral h2o co2 ch4 fluid over a temperature and pressure range from 250 to 600 c and 1 to 4 kbar which corresponds to a range of crustal environments from lower greenschist to upper amphibolite facies these characteristics suggest that the granitoid hosted lode gold deposits represent a coherent genetic group that is equivalent to the more abundant greenstone hosted lode gold deposits of the craton in combination lode gold deposits irrespective of their host rocks and host terrane formed over a range of crustal levels and developed late in the tectonic sequence of the craton granitoids which host lode gold mineralisation are older than the inferred age of mineralisation by at least 10 million years and in combination with thermodynamic and isotope studies indicate that the host granitoids are not the dominant source of the ore fluid however the host granitoids do provide a structural and to a lesser extent chemical trap for gold bearing fluids in combination trace element and isotope studies of greenstone and granitoid hosted deposits suggest that the ore fluid originated from a deep mid to lower crustal source and at least interacted with granitic rocks at some stage the ore fluid composition is quite constant over the range of crustal levels from deep to shallow implying that the extent of modification by interaction with fluid conduit rocks is variable but not substantial

hydrothermal gold mineralization at the hira buddini gold mine india constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline we determined the boron isotope and chemical compositions of tourmaline from the hira buddini gold deposit within the archean hutti maski greenstone belt in southern india to investigate the evolution of the hydrothermal system and to constrain its fluid sources tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization the hira buddini tourmaline belongs to the dravite schorl series with variations in al fe fe mg ca ti and cr contents that can be related to their host lithology the total range of 11b values determined is extreme from 13 3 to 9 0 but 95 of the values are between 4 and 9 the boron isotope compositions of metabasalt hosted tourmaline show a bimodal distribution with peak 11b values at about 2 and 6 the wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources which entered the hydrothermal system separately and were subsequently mixed the estimated 11b values of the hydrothermal fluids based on the peak tourmaline compositions and a mineralization temperature of 550 c are around 1 and 10 the isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies whereas the 11b rich fluid is attributed to degassing of i type granitic magmas that intruded the greenstone sequence providing heat and fluids to the hydrothermal system

boron isotopic composition of tourmaline prismatine and grandidierite from granulite facies paragneisses in the larsemann hills prydz bay east antarctica evidence for a non marine evaporite source a unique assemblage of b rich rocks 2 wt b containing the borosilicate minerals tourmaline tur prismatine prs and grandidierite gdd is exposed in the ca 1000 ma brattstrand paragneiss in the larsemann hills east antarctica the b isotope composition of these three minerals in 21 paragneisses and 6 anatectic pegmatites were measured in situ using secondary ion mass spectrometry 11b ranges from 2 8 to 14 4 in tourmaline from 9 6 to 17 8 in prismatine and from 2 8 to 8 7 in grandidierite weighted uncertainties mostly 1 2 per sample in most cases average 11b increases in a given sample prs tur gdd whether the observed b isotope distribution has attained equilibrium were assessed using two criteria microstructural equilibrium and regular distribution of mg and fe in samples for which the two criteria are met we assume the measured distribution of isotopes 11ba b 11ba 11bb represents equilibrium 11btur prs 5 0 1 4 5 of 12 pairs 11btur gdd 3 3 0 8 3 of 5 pairs and 11bgdd prs 7 2 1 3 2 of 2 pairs consistent with the preference of 10b for tetrahedral sites prismatine and 11b for trigonal sites tourmaline grandidierite ab initio computations of b isotope fractionation factors 11btur prs 6 4 1 3 11btur gdd 1 8 1 1 and 11bgdd prs 8 2 1 1 provide confirmation of the measured fractionations the computed relaxed ionic structure of grandidierite gave a shorter 1 368 a b o bond length than in case of dravite 1 385 a which explains the measured enrichment of grandidierite in 11b relative to tourmaline the precursor of the b rich rock least changed by metamorphism tourmaline metaquartzite 11b tur 8 6 to 5 9 is interpreted to be a product of pre metamorphic hydrothermal b metasomatism boron sources consistent with this 11b range include oceanic crust clastic sediments volcanic rocks and non marine evaporite borate but not marine evaporite however dominance of metasediments in the brattstrand paragneiss major and trace element compositions of the b rich rocks and presence of abundant b are consistent with non marine evaporite being the most important source of b for the b rich lithologies of the larsemann hills a possible scenario for precursors of these rocks is a succession of clastic sediments in part tuffaceous intercalated with b rich evaporite deposits in a continental rift basin in which circulating hydrothermal fluids leached b from the evaporite and precipitated it as tourmaline in the associated clastic rocks to form the precursors to the tourmaline metaquartzites

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

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

chemical and boron isotopic compositions of tourmaline from the archean big bell and mount gibson gold deposits murchison province yilgarn craton western australia abstract tourmaline is a commonly found gangue mineral in archean greenstone belt lode gold deposits worldwide in this paper we report major trace and rare earth element ree and boron isotopic compositions of tourmaline from two major amphibolite grade archean gold deposits big bell and mount gibson murchison province yilgarn craton western australia in an attempt to better understand the hydrothermal gold formation processes that were also responsible for tourmalinization tourmalines in these two major deposits all belong to the dravite schorl series and tend to be mg rich where closely associated with gold and sulfide ores the ore related tourmalines also contain high concentrations of ore metals such as au ag pb and cu in the big bell deposit tourmalines occur along the foliation in lode schists and show low fe fe mg ratios of 0 11 0 30 tio 2 contents of 0 15 0 73 wt and negligible mno 11 b values of 17 7 to 15 0 in the mount gibson deposit the tourmalines closely associated with the sulfide ores are the most mg rich with low fe fe mg ratios of 0 19 0 22 while tourmalines from garnet bearing biotite muscovite schists that overly the lode gold orebody are more fe rich fe fe mg 0 30 0 63 tourmalines from an amphibolite schist are mg rich with fe fe mg ratios 0 27 0 34 that lie between the above two groups of tourmalines the compositional trend from fe rich tourmalines in the sulfide poor schists to mg rich in the sulfide ores at mount gibson is similar to that observed in massive sulfide ore deposits worldwide alternatively the mg rich nature of the sulfide related tourmalines may be due to metamorphic reactions that are accompanied by fe incorporation into sulfides leaving coexisting silicates more mg rich the ree geochemistry of the tourmalines from the mount gibson ore zone schists displays strong hree enrichments and positive eu anomalies with eu eu ratios up to 2 4 which are similar to tourmalines associated with massive sulfide deposits the ore related tourmalines disseminated in the host schists show 11 b values of 18 6 to 17 0 whereas one coarse grained tourmaline vein has a lower 11 b value of 21 9 to 21 4 these data support hypotheses which suggest that the schists that host the gold mineralization are the metamorphosed equivalents of a base metal rich hydrothermally altered seafloor horizon that is typical of vms style mineralization with the boron possibly derived from leaching of footwall sedimentary and volcanic rocks during hydrothermal circulation

no mass independent sulfur isotope fractionation in auriferous fluids supports a magmatic origin for archean gold deposits the source of the auriferous fluids that formed archean greenstone gold deposits remains controversial metamorphic fluids fluids derived from felsic magmas mantle fluids and meteoric water have all been suggested we report the results of ion microprobe sensitive high resolution ion microprobe stable isotopes multiple sulfur isotope analyses 32 s 33 s 34 s conducted to constrain the source of sulfur in four archean gold deposits the analyses are of pyrite samples that are genetically related to the gold mineralization from the bellerophon victory and wallaby deposits in the eastern goldfield superterrane of the yilgarn craton western australia together with sulfide from black shale from the golden mile deposit and st ives gold camp ore associated pyrite from the beattie gold deposit of the abitibi greenstone belt of the superior craton in canada was measured to test whether the results obtained from the yilgarn craton apply to other archean gold deposits sulfur analyses from sulfide from shale show mass independent fractionation mif with 33 s as high as 1 8 whereas those from the 4 archean gold deposits are dominated by mass dependent fractionation with only a minor contribution of mif sulfur in this respect archean gold deposits contrast with archean nis deposits which are dominated by mif sulfur the absence of mif in the pyrite from the four archean gold deposits analyzed in this study is consistent with the auriferous fluid originating from a felsic magma or mantle source but inconsistent with the metamorphic and meteoritic fluid hypotheses

boron sulphur and copper isotope systematics in the orogenic gold deposits of the archaean hattu schist belt eastern finland abstract the hattu schist belt is located in the western part of the archaean karelian domain of the fennoscandian shield the orogenic gold deposits with au bi te geochemical signatures are hosted by ne sw n s and nw se oriented shear zones that deform 2 76 2 73 ga volcanic and sedimentary sequences as well as 2 75 2 72 ga tonalite granodiorite intrusions and diverse felsic porphyry dykes mo w mineralization is also present in some tonalite intrusions both separate from and associated with au mineralization somewhat younger unmineralized leucogranite intrusions 2 70 ga also intrude the belt lower amphibolite facies peak metamorphism at 3 5 kbar pressures and at 500 600 c temperatures affected the belt at around 2 70 ga and post date hydrothermal alteration and ore formation in this study we investigated the potential influence of magmatic hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope b s cu studies of tourmaline and sulphide minerals by application of in situ sims and la icp ms analytical techniques crystal chemistry of tourmaline from a mo w mineralization hosted by a tonalite intrusion in the hattu schist belt is characterized by fe3 al3 substitution indicating relatively oxidizing conditions of hydrothermal processes the range of 11b data for this kind of tourmaline is from 17 2 to 12 2 the hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry e g dravite povondraite compositional trend with fe3 al3 substitution and 11b values between 19 0 and 9 6 the uvite foitite compositional trend and 11b values between 24 1 and 13 6 characterize metasomatic hydrothermal tourmaline from the metasediment hosted gold deposits composition of hydrothermal vein filling and disseminated tourmaline from the gold bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment hosted tourmaline rock forming magmatic tourmaline from leucogranite has 11b values between 14 5 and 10 8 and the major element composition is similar to that of the metasediment hosted tourmaline the range of 34svcdt values measured in pyrite chalcopyrite and pyrrhotite is from 9 1 to 8 5 which falls within the typical range of sulphur isotope data for archaean orogenic gold deposits in the hattu schist belt positive 34svcdt values characterize metasediment hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite the 34svcdt values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite purely negative values were only recorded from the pyrite dominated gold mineralization within metavolcanic units therefore the shift of 34svcdt values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids the range of measured 65cunbs978 values from chalcopyrite is from 1 11 to 1 19 positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks positive and negative 65cunbs978 values occur in the ores hosted by metavolcanic rocks there is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains evaluation of sulphur and boron isotope data together and comparisons with other archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the hattu schist belt variations in major element and boron isotope compositions in tourmaline as well as in the 34svcdt values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes the results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes

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

the geochemical cycle of boron constraints from boron isotope partitioning experiments between mica and fluid abstract the fractionation of boron isotopes between synthetic boromuscovite and fluid was experimentally determined at 3 0 gpa 500 c and 3 0 gpa 700 c for near neutral fluids 11b mica fluid 11b mica 11b fluid is 10 9 1 3 at 500 c and 6 5 0 4 at 700 c this supports earlier assumptions that the main fractionation effect is due to the change from trigonal coordination of boron in neutral fluids to tetrahedrally coordinated boron in micas clays and melts the t dependence of this effect is approximated by the equation 11b mica clay melt neutral fluid 10 69 1000 t k 3 88 r2 0 992 valid from 25 c for fluid clay up to about 1000 c for fluid silicate melt experiments at 0 4 gpa that used strongly basic fluids produced significantly lower fractionations with 11b mica fluid of 7 4 1 0 at 400 c and 4 8 1 0 at 500 c showing the reduced fractionation effect when large amounts of boron in basic fluids are tetrahedrally coordinated field studies have shown that boron concentrations and 11b 10b ratios in volcanic arcs systematically decrease across the arc with increasing distance from the trench thus reflecting the thermal structure of the subducting slab our experiments show that the boron isotopic signature in volcanic arcs probably results from continuous dehydration of micas along a distinct p t range continuous slab dehydration and boron transport via fluid into the mantle wedge is responsible for the boron isotopic signature in volcanic arcs

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

copper isotope ratios in magmatic and hydrothermal ore forming environments multi collector inductively coupled plasma mass spectrometry now provides for precise and accurate measurements of cu isotope ratios copper minerals prepared by direct dissolution with and without chromatographic purification yield identical cu isotope ratios within analytic precision of about 0 04x 1r cu isotope ratios have been measured for copper minerals from worldwide magmatic and hydrothermal copper deposits and for several weathered deposits natural variations in d65cu values relative to nbs976 range over 9x chalcopyrite samples from mafic intrusions lie within a narrow range of about 1 5x and most cluster tightly between 0 10xand 0 20x this range lies within the broader black smoker chalcopyrite and iron meteorite ranges and possibly represents a bulk mantle cu isotope ratio most values for hydrothermal native copper from the michigan native copper district also show a narrow range just larger than 0 1xand suggest a common homogeneous source for cu in this large hydrothermal system later copper sulfide and arsenide minerals from this district range to values more than 2x lower than native copper ratios for chalcopyrite and bornite from moderate to high temperature porphyry skarn and replacement deposits as a group and within individual deposits exhibit a broad range of values variations of nearly 1xare observed over distances on the order of 1 m in some cases these variations may result from multiple mineralization events or copper remobilization during retrograde or later hydrothermal activity fractionations between chalcopyrite and bornite where they occur in the same sample or in related samples cluster near 0 4x suggesting equilibrium cu isotope fractionation between them at moderate temperatures in addition weathering of hydrothermal copper minerals produces a wide range of values in secondary copper phases in the supergene environment cuprite typically has higher values than associated native copper therefore redox states appear to exert a significant control over fractionation at low temperatures significant questions remain to be answered before the source of copper in hydrothermal environments can be fully addressed source reservoir cu ratios need to be determined and chemical and physical factors that control cu isotope fractionation must be quantitatively defined d 2003 elsevier b v all rights reserved

boron isotope and light element sector zoning in tourmaline implications for the formation of b isotopic signatures hourglass sector zoning in metamorphic tourmaline is known to effectively fractionate the major and trace elements between different sectors producing three distinct compositions at the growth surface here we show that the light elements li be h and b as well as the 11 b signature are also affected by sector zoning the sector enrichment in elements is controlled by a dual process of initial preference due to growth surface charge and morphology followed by consecutive charge balance controlled enrichment the light elements especially b and h appear to act as charge balance cations in this mechanism with a preferred b 3 for si 4 and o 2 for oh substitution in the c sector a lighter 11 b signature d c c 1 8f0 6x accompanies this increase in b iv in the c sector in line with the lighter signatures for b iv compared to b iii in minerals however it exceeds this theoretical fractionation by a factor of 10 although we have not identified a definite process that is responsible for this fractionation it may be related to local variations in host medium along the growth surface resulting from preferred uptake of elements these observations show that 11 b signatures in tourmaline are not an independent measure of its host environment but also a function of mineral composition and the 3 dimensional zoning variations herein 2007 elsevier b v all rights reserved

boron isotope composition of tourmalinite and vein tourmalines associated with gold mineralization serra do itaberaba group central ribeira belt se brazil abstract important concentrations of tourmaline occur as gold bearing stratiform tourmalinites and in mineralized quartz tourmaline veins at the tapera grande and quartzito gold prospects in the mesoproterozoic serra do itaberaba group central ribeira belt sao paulo state se brazil the main rock types in both prospects constitute the volcanic sedimentary morro da pedra preta formation which formed in a submarine back arc setting at tapera grande the volcanic sedimentary sequence is composed of metabasic and metavolcaniclastic rocks graphitic and sulfur rich metapelites banded iron formation metandesite metarhyolite calc silicates tourmalinites and metahydrothermalites derived from mafic and felsic rocks the mesoproterozoic rocks at quartzito prospect are lithologically similar but they have been affected by neoproterozoic faulting and shearing and by the emplacement of granitic rocks resulting in the formation of tourmaline rich quartz carbonate veins with gold and base metal mineralization we conducted a chemical and b isotope study of tourmalines in order to better understand the origin of the stratiform tourmalinites in the morro da pedra preta formation and their relationship with gold mineralization the overall range of 11b values obtained for the tourmalinite and vein tourmalines is between 15 and 5 with the tourmalinites falling at the low end of this range 15 to 8 such values are typical for continental crust and inconsistent with a primary marine boron signature as expected from the submarine exhalative model for the gold prospects we conclude from this that tourmaline formed or recrystallized from crustal fluids related to the amphibolite grade metamorphism which affected the serra do itaberaba group and that gold deposition occurred syn to post peak metamorphism by phase immiscibility as attested by fluid inclusions in tapera grande tourmalinite tourmaline and quartz the vein hosted tourmalines at quartzito have isotopically variable boron signatures with heavier 11b values of 5 to 8 for acicular green tourmalines and lighter values 15 to 7 for light blue ti free tourmaline from quartz carbonate veins we attribute the heavier boron to fluids derived from the volcano sedimentary rocks of marine affinity whereas the lighter boron was contributed by crustal fluids related to the granitoids or metasediments in the continental crust

erratum to variations of sulphur isotope signatures in sulphides from the metamorphosed ming cu au volcanogenic massive sulphide deposit newfoundland appalachians canada the ming deposit is an early ordovician bimodal mafic cu au volcanogenic massive sulphide vms deposit in the newfoundland appalachians that was metamorphosed to upper greenschist lower amphibolite facies conditions and deformed in the silurian and devonian the ming deposit consists of several spatially proximal ore bodies of which the 1806 zone 1807 zone ming south up plunge and down plunge and the lower footwall zone are the focus of this paper the ore bodies have similar stratigraphic sequences the ore bodies can be divided into 1 a silicified horizon that caps the massive sulphides 2 semi massive to massive sulphides and 3 sulphide mineralization in a rhyodacitic footwall sulphide mineralization in a rhyodacitic footwall includes a sulphide stringers immediately below the semi massive to massive sulphides and b chalcopyrite pyrrhotite pyrite stringers distally from semi massive to massive sulphides in the lower footwall zone pyrite chalcopyrite pyrrhotite arsenopyrite and galena were analysed by in situ secondary ion mass spectrometry sims for sulphur isotope compositions the isotopic signatures of pyrite chalcopyrite pyrrhotite and arsenopyrite fall within a limited range of 2 8 to 12 0 for semi massive to massive sulphides and sulphide mineralization in the footwall the silicified horizon capping the semi massive to massive sulphides has higher 34s 5 8 19 6 especially for pyrrhotite mean 17 2 2 2 n 8 the sulphur isotope composition of galena is more heterogeneous especially within semi massive to massive sulphides and sulphide stringers ranging from 0 8 to 17 3 mean 6 1 4 3 n 35 and 7 6 to 17 1 mean 13 7 5 3 n 3 respectively geothermometric calculations give insufficient formation and metamorphism temperatures for neighbouring mineral pairs because sulphides were not in isotopic equilibrium while deposited in early ordovician or re equilibrated during silurian devonian metamorphism respectively therefore original isotopic compositions of sulphides at the ming deposit have been preserved modelling of the source of sulphur shows that 1 reduced seawater sulphate and 2 sulphur leached from igneous wall rock and or derived from magmatic fluids are the main sources of sulphur in the ming deposit the influence of igneous sulphur igneous wall rock magmatic fluids increases with temperature and is an important sulphur source for the semi massive to massive sulphides and footwall mineralization in addition to a contribution from thermochemical sulphate reduction tsr of seawater it is difficult to distinguish between sulphur leached from igneous rocks and magmatic fluid related sulphur and it is possible that both sources contributed to the ores at the ming deposit in addition to igneous sulphur the heavy isotopes of the silicified horizon are consistent with the sulphur in this horizon being derived only from thermochemical sulphate reduction of early ordovician seawater sulphate

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event