u pb evidence for abitibi gold mineralization postdating greenstone magmatism and metamorphism two widely held theories for the origin of archaean lode gold deposits the magmatic1 and metamorphic replacement2 models predict that gold emplacement should have occurred near the end of late syn kinematic greenstone magmatism here we report that at the camflo mine in the abitibi subprovince of canada u pb ages for rutile and titanite in auriferous alteration 2 625 7 myr are much younger than the age of the host quartz syenite 2 680 4 myr and ages for regional magmatism 2 670 myr 3 and metamorphism 2 680 myr 4 mineral associations and pb pb systematics indicate that the hydrothermal minerals record crystallization ages that are probably coeval with the gold mineralization these ages and others from the abitibi subprovince4 6 rule out a direct connection between gold and magmatism or metamorphism associated with regional folding of the greenstone belt they are broadly contemporaneous with metamorphism at deep crustal levels7 and may record late devolatilization of the lower crust

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 role of granitic intrusions in the evolution of the abitibi belt canada abstract the abitibi greenstone belt canada constitutes a segment of a broad volcanic arc that experienced three distinct periods of volcanic activity peaking at 2730 2725 2718 2714 and 2705 2700 ma during all three volcanic episodes which were generated by subduction related processes mantle plume derived komatiitic volcanic rocks were also added to the composite abitibi arc plume activity resulted in local regional extension and restricted later volcanism within the belt north south shortening produced thrusts and folds followed by se trending dextral strike slip faults between 2700 and 2692 ma the principal belt wide deformation subsequent e w dextral strike slip faulting limited to the major faults continued to 2690 2680 ma destor porcupine fault and even to 2680 2670 ma cadillac larder fault extensional structures resulting from the thickened crust developed around 2660 ma granitic intrusions are associated with all the volcanic episodes and phases of deformation and have been used to constrain the age of many of these events their role in stabilizing and adding to the volcanic crust is perhaps less well appreciated large synvolcanic tonalite dominated intrusions of the tonalite trondhjemite granodiorite ttg suite are associated with the three major periods of volcanic activity of the abitibi greenstone belt and are genetically related to the volcanism these synvolcanic intrusions occur both as high level flat cauldron subsidence complexes and as batholithic masses at the base of the oceanic crust tonalite gneiss dated from 2714 to 2703 ma occurring in structural culminations is considered to be arc underplated material the gneiss crystallized at depth and in contrast to the other tonalites does not appear to have intruded volcanic rocks the gneisses also record the earliest compressional deformation numerous intrusions of island arc affinity both the ttg and monzodiorite mzd suites form stocks and small plutons emplaced during the late phases of major deformation these are more numerous than voluminous and most of the tonalite end members of the suites probably intruded deeper within the sequence retarded by the now thickened crust large tonalite intrusions dominate the uplifted deeper sections adjacent to the abitibi belt in the kapuskasing uplift and grenville parautochthon and presumably make up much of the deep crust of the abitibi belt imaged in lithoprobe seismic profiles small stocks and dyke complexes characterize the late localized strike slip deformational phase these intrusions are porphyritic syenites and related rocks including some alkaline compositions garnetiferous granites of crustal derivation were emplaced in the final period of extensional activity around 2660 ma thus plutonic rocks are a volumetrically major overall component of the abitibi belt and were implicated in every phase of its development from early volcanic arc magmatic activity through the various stages of deformation to final stabilization as continental crust

numerical model to determine the composition of h2o nacl cacl2 fluid inclusions based on microthermometric and microanalytical data natural fluids approximated by the h2o nacl cacl2 system are common in a wide range of geologic environments including sedimentary basins associated with hydrocarbon occurrences and mvt deposits submarine hydrothermal systems and other metamorphic magmatic and hydrothermal environments we present a comprehensive numerical model and microsoft excel based computer program to determine the compositions of fluid inclusions in the h2o nacl cacl2 system based on microthermometric and microanalytical data the model consists of six polynomial correlation equations that describe liquid salinity as a function of nacl cacl2 ratio and melting temperature on each of the ice hydrohalite halite antarcticite cacl2 4h2o and cacl2 2h2o vapor saturated liquidus surfaces the cotectic and peritectic boundaries are determined from the intersections of the liquidus surfaces the model is implicitly internally consistent and topologically correct the model expands upon the compositional range of applicability and the data types that can be used for compositional determination it reproduces experimental data for all compositions that lie within the h2o nacl cacl2 4h2o compositional triangle in the h2o nacl cacl2 system and yields accurate reproductions of the h2o nacl and h2o cacl2 binaries furthermore in comparison to previously published models the one presented here eliminates systematic errors wavy isotherms and cotectic and peritectic curves with local bumps

100 ma timing paradox of archean gold abitibi greenstone belt canada new evidence from u pb and pb pb evaporation ages of hydrothermal zircons abundant hydrothermal zircon occurs within quartz tourma line veins at four gold deposits in the val d or district of the archean abitibi greenstone belt canada host rocks to the gold bearing veins are characterized by pronounced metasomatic enrichment of zr hf y and rare earth elements hydrothermal zircons contain inclusions of quartz tourmaline scheelite pyrite and gold in hydrothermal zircons and quartz primary low salinity h2 co2 fluid inclusions coexist with co2 rich inclusions indicating co2 unmixing and gold precipitation at 260 to 380 c and 2 kbar the zircons have 207pb 206pb evaporation ages of 2683 20 to 2703 4 ma close to a concordant u pb age of 2693 2 ma both commensurate with previous shrimp ages for the zircons the same vein systems have u pb ages on rutile and titanite sm nd dates on scheelite and 40ar 39ar ages on muscovite that scatter between 2630 to 2579 ma these ages gave rise to a late gold model in the archean superior province vein gold deposits are related in space and time to terrane boundary structures which mark the diachronous accretion of allochthonous tectonostratigraphic terranes from south to north from 2720 to 2680 ma consequently the vein zircon ages of 2690 to 2680 ma at val d or represent the primary mineralizing event consistent with its late kinematic timing throughout the superior province and with late archean supercontinent assembly globally whereas the young scattered ages record the time of secondary fluid events associated with reactivation of the structures resetting some isotopic systems below their conventional blocking temperature

a gravity survey across the bourlamaque massif southeastern abitibi greenstone belt quebec canada the relationship between the geometry of tonalite plutons and associated gold mineralization abstract gravity data collected over the bourlamaque massif near val d or quebec are used to obtain a three dimensional image of this pluton the interpretation is based on density measurements of samples of the pluton and its envelope the small gravity anomaly less than 5 mgal over the massif indicates that the pluton is a thin body 1 km pronounced differences between the southern and the northern segments of the gravity profiles suggest that the northern lobe of the pluton is thicker than the southern lobe geometrically the pluton resembles a dyke cutting across the stratigraphic layers at a 80 angle it was apparently emplaced in an extensional environment before being deformed in the kenorean orogeny the location of the lode type gold deposits near the pluton is determined by its shape and the competency contrast at the lower intrusive contact

upb zircon and rutile chronology of archean greenstone formation and gold mineralization in the val d or region quebec abstract u pb geochronology provides an absolute time framework for the evolution of the sigma gold deposit and surrounding rocks at val d or southern abitibi subprovince the bourlamaque batholith the largest pluton in the area gives a 2699 8 1 0 ma u pb zircon age this pluton cuts the val d or formation which hosts the mineralization a u pb zircon age of 2704 9 1 1 ma on a felsic volcanic rock the colombiere rhyolite 13 km east of the mine dates that formation the gold bearing quartz vein system at sigma is hosted by andesites and two generations of porphyry intrusions all metamorphosed to the greenschist facies the oldest porphyry porphyritic diorite shows the same deformation as the volcanic rocks and has a 2703 7 2 5 ma u pb zircon age the porphyritic diorite and volcanic rocks are cut by feldspar porphyry dykes which post date regional folding and have a 2694 0 2 2 ma u pb zircon age regional greenschist metamorphism has been dated directly with a u pb date of 2684 7 ma on rutile in the colombiere rhyolite the mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals hydrothermal rutile from an alteration halo around the veins in andesite has a 2599 9 ma u pb age textural evidence clearly indicates that the wall rock alteration and vein filling are contemporaneous and hence the vein system and gold mineralization appear to have developed at least 80 m y after the formation and metamorphism of host greenstones

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part i geologic relations and formation of the vein system the sigma deposit consists of an archean gold bearing vein system in metavolcanic rocks intruded by an irregular body of porphyritic diorite both affected by regional deformation and in turn cut by younger undeformed feldspar porphyry dikes the veins cut all rock types and are composed chiefly of quartz and tourmaline with minor amounts of carbonates pyrite chlorite scheelite and free gold they were emplaced during or after a greenschist facies metamorphism postdating the intrusion of feldspar porphyry dikes the veins were not significantly affected by any subsequent metamorphism or tectonism two principal types of veins occur in the mine subvertical veins and subhorizontal veins they are contemporaneous and cogenetic subvertical veins occur within steeply dipping east west trending ductile shear zones along which reverse subvertical displacements have taken place the veins occupy openings created by overriding of undulations and irregularities of foliation and slip planes during progressive shearing movements within the shears subhorizontal veins occupy extensional fractures which developed between ductile shear zones preferentially in the more competent host rocks these veins were formed by one or several episodes of open space filling geologic relations indicate that the mineralized veins were emplaced progressively in a dynamic tectonic environment during and shortly after the formation of ductile shear zones a structural analysis has shown that the ductile shear zones and the two vein types can be related to a single strain ellipsoid of the following orientation the z axis trending north south and horizontal the y axis plunging 10 degrees west and the x axis plunging 80 degrees east the deformation responsible for the generation of ductile shear zones and emplacement of the veins is ascribed to a late north south trending compression postdating regional deformation

mechanics of formation of the gold bearing quartz fuchsite vein at the dome mine timmins area ontario the highest grade orebody in the dome mine is a steeply dipping 500 m long 550 m high and 3 5 m wide banded quartz fuchsite vein qfv accompanied by subsidiary veins in the adjacent wall rock t

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

modification of fluid inclusions in quartz by deviatoric stress i experimentally induced changes in inclusion shapes and microstructures fluid inclusions in quartz are known to modify their shapes and microstructures textures during weak plastic deformation however such changes have not been experimentally demonstrated and criteria are not available to relate them to paleostress conditions to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure strains of up to 1 cause the inclusions to develop irregular shapes and to generate microcracks in crystallographic planes oriented subperpendicular to the major compression axis 1 the uniform alignment of the microcracks imparts a planar fabric to the samples the microcracks heal and form swarms of tiny satellite inclusions these new inclusions lose h2o by diffusion thereby triggering plastic deformation of the surrounding quartz via h2o weakening consequently the quartz samples deform plastically only in domains originally rich in inclusions this study shows that fluid inclusions deformed by deviatoric stresses may indeed record information on paleostress orientations and that they play a key role in facilitating crystal plastic deformation of quartz

synthetic fluid inclusions viii vapor saturated halite solubility in part of the system nacl cacl2 h2o with application to fluid inclusions from oceanic hydrothermal systems abstract halite solubility along part of the vapor saturated liquidus in the system nacl cacl 2 h 2 o has been determined using the synthetic fluid inclusion technique data allow the construction of liquidus isotherms for temperatures up to 500 c and bulk compositions containing 60 wt total salt and as much as 25 wt cacl 2 combined with previous data for the binary system nacl h 2 o and for the ternary system nacl cacl 2 h 2 o in the low salinity low temperature region a preliminary ternary phase diagram can be constructed that remains incomplete only in the cacl 2 rich region results are applied to the interpretation of saline fluid inclusions from quartz veins in oceanic metagabbros and can be applied to many other natural inclusions containing aqueous solutions with nacl and cacl 2 the dominant solutes microthermometric measurements at equilibrium of the melting temperature of ice tm ice and of the dissolution temperature of halite tm halite are sufficient to determine the bulk composition of the nacl cacl 2 h 2 o fluid

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

accretion of archean oceanic plateau fragments in the abitibi greenstone belt canada the arc arc collision model is often applied to the evolution of archean greenstone belts this model predicts concordant stratigraphic relations among the various lithologies evolving generally from komatiitic tholeiitic affinities toward calc alkalic affinities new geological data from the malartic composite block of the abitibi greenstone belt indicate that this volcanic pile rather than representing a conformable sequence is composed of four distinct mafic lithotectonic domains that are overlain by a calc alkalic sequence the mafic domains are thought to be examples of accreted archean oceanic plateau material that were deformed during their collage state the younger calc alkalic sequence represents extension related volcanism that erupted through the ac creted and deformed plateau material possibly as a consequence of ridge subduction in a regime of oblique convergence the relations described here may represent a common feature of archean terranes

internal structure of the cadillac tectonic zone southeast of val d or abitibi greenstone belt quebec the kirkland lake larder lake cadillac break is a major fault zone of the abitibi greenstone belt well known for its spatially associated gold camps a detailed structural analysis of this fault zone in the val d or area has shown the presence of a 200 750 m wide zone of high strain defined here as the cadillac tectonic zone ctz which includes the narrower schist zone generally regarded as the cadillac break the boundaries of the ctz which coincide with major lithologic contacts strike approximately east west and dip 80 to the north the internal structure of the ctz is best analysed in terms of two increments of the same progressive deformation the d1 strain increment is characterized by an east west striking subvertical s1 foliation at low angle in strike to the bound aries of the ctz and containing subvertical elongation lineation primary lithological contacts have been transposed into s1 and folded by f1a folds f1b intrafolial folds of s1 ranging from noncylindrical subhorizontal f

the influence of dikes on auriferous shear zone development within granitoid intrusions the bourlamaque pluton val d or district abitibi greenstone belt shear zone related gold quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes which may have a profound influence on the localization orientation and kinematics of auriferous shear zones the bourlamaque pluton of the val d or district contains several economic auriferous shear zones most of which follow and overprint diorite dikes mineralization in all deposits consists of quartz tourmaline pyrite veins in reverse oblique orientation with a significant range of strike dip and slip direction the geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion the stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly directed compression recorded by similar shear zones outside the pluton this indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes which

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

archaean hydrothermal zircon in the abitibi greenstone belt constraints on the timing of gold mineralisation abstract hydrothermal zircons have been found in archaean mesothermal au veins and altered wallrock selvages at val d or in the abitibi greenstone belt of canada the zircons are paragenetically associated with vein quartz tourmaline mica carbonate scheelite pyrite and gold zirconium mobility and the consequent occurrence of hydrothermal zircon may be associated with the intense tourmalinisation characteristic of archaean gold deposits in this district the shrimp ion microprobe has been used to analyse hydrothermal zircons from four separate mines spatially associated with the bourlamaque batholith and has yielded ages constraining formation of the au bearing vein systems to within 20 ma of emplacement of the pluton the ion microprobe data reveal multiple stages of hydrothermal zircon growth in the vein systems contemporaneous with the regional metamorphic peak and late kinematic activity along regional structures younger including proterozoic ages previously obtained for the veins using other minerals and isotopic schemes must reflect either alteration or renewed mineral growth during much later reactivation of fluids along the same structures up to 400 ma after initial formation of the veins

hydrothermal zircon and baddeleyite in val d or archean mesothermal gold deposits characteristics compositions and fluid inclusion properties with implications fortiming of primary gold mineralization zircon and baddeleyite occur within quartz tourmaline veins at four gold deposits in the val d or district of the archean abitibi southern volcanic zone host rocks have experienced intense metasomatic enrichment of zr hf y and rare earth elements the zircons contain primary inclusions of quartz tourmaline pyrite albite k mica scheelite and gold and gold occurs in primary fluid inclusions in zircons magmatic zircons in host rocks do not have this suite of inclusions consequently a wall rock inheritance model for the vein zircons is implausible compositionally the zircons feature pronounced interzone and intergrain variations of hf y yb th and u and sporadic anomalous ce contents of 1100 ppm distinct from magmatic counterparts two principal types of primary fluid inclusion occur in the vein zircons type 1 h2o co2 inclusions have low salinities variable quantities of co2 and homogenization temperatures of 260 380 c and type 2 co2 rich inclusions contain minor h2o and ch4 the vei

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

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

how accurately can we date the duration of magmatic hydrothermal events in porphyry systems an invited paper determining the absolute duration of magmatic hydrothermal events leading to the formation of porphyry systems i e including porphyry copper skarn and epithermal deposits is one of the key questions in ore geology this is so because the duration of magmatic hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy the problem of determining the absolute duration of magmatic hydrothermal events in porphyry systems has been addressed through thermal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydrothermal systems with known metal concentrations and fluid fluxes both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo annum ka isotopic dating in contrast is the only possible way to determine the life span of magmatic hydrothermal events in fossil porphyry systems analytical and methodological developments during the last decade in the fields of the most robust isotopic systems commonly used for absolute dating u pb 40ar 39ar re os allow us to date minerals with internal precisions 0 2 2 for a 10 ma old mineral this corresponds to a 20 ka uncertainty which is marginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo annum scale however many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events which extend the overall life of the porphyry systems to a few 0 x and up to 2 ma in some cases internal precisions of the above mentioned dating methods allow us in theory to comfortably discriminate events at the 0 x scale and the combination of u pb 40ar 39ar and reos geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic hydrothermal events in porphyry systems in this review we discuss some fundamental problems that are systematically overlooked in most geochronological studies trying to bracket the life span of porphyry systems we show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry systems will be estimated we also provide basic guidelines to follow when trying to resolve the duration of magmatic hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

the tectonic evolution of the abitibi greenstone belt of canada based on structural geochemical sedimentological and geochronological studies we have formulated a model for the evolution of the late archaean abitibi greenstone belt of the superior province of canada the southern volcanic zone svz of the belt is dominated by komatiitic to tholeiitic volcanic plateaux and large bimodal mafic felsic volcanic centres these volcanic rocks were erupted between approximately 2710 ma and 2700 ma in a series of rift basins formed as a result of wrench fault tectonics the svz superimposes an older volcanic terrane which is characterized in the northern volcanic zone nvz of the abitibi belt and is approximately 2720 ma or older the nvz comprises basaltic to andesitic and dacitic subaqueous massive volcanics which are cored by comagmatic sill complexes and layered mafic anorthositic plutonic complexes these volcanics are overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma the tectonic model envisages the svz to have formed in a series of rift basins which dissected an earlier formed volcanic arc the nvz analogous rift environments have been postulated for the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs the difference between rift related submergent volcanism in the svz and emergent volcanism in the nvz resulted in the contrasting metallogenic styles the former being characterized by syngenetic massive sulphide deposits whilst the latter was dominated by epigenetic porphyry type cu au deposits

sm nd dating of scheelite and tourmaline implications for the genesis of archean gold deposits val d or canada sm nd analyses of 19 scheelite samples from auriferous quartz carbonate tourmaline scheelite gold veins from three mines in the val d or gold camp in the abitibi greenstone belt in western quebec the sigma pascalis north and siscoe extension mines yield a linear array on an isochron diagram with a mean square weighted deviation mswd of 3 6 corresponding to an age of 2596 or 33 ma and epsilon sub nd 1 2 5 eight scheelite samples from the pascalis north mine alone define an excellent linear array with an mswd 0 31 an age of 2593 or 18 ma and epsilon sub nd 1 2 7 these ages are interpreted to represent the age of quartz carbonate tourmaline scheelite vein hosted gold mineralization in the three mines sampled sm nd analyses of tourmaline suggest that this mineral may also be useful for sm nd dating of hydrothermal mineralization the sm nd scheelite age of ca 2600 ma is in good agreement with u pb ages obtained from mineralization related rutile and titanite in the val d or area these results indicate that the quartz carbonate tourmaline scheelite vein hosted gold mineralization was emplaced approximately 70 m y later than the youngest observed premineralization magmatic activity and approximately 60 m y later than peak regional metamorphism in the val d or area these ages do not support hypotheses for deposit formation which involve fluids derived from spatially related intrusive rocks or metamorphism although they do not preclude an earlier stage of introduction of gold into the val d or area the scheelite sm nd age and depleted mantlelike epsilon sub nd 1 and the mineralogy and alteration of the quartz carbonate tourmaline veins are consistent with the derivation of the mineralizing fluids from a relatively homogeneous external source and introduction into the upper crust as part of a single large hydrothermal system the formation of the val d or gold deposits also appears to be broadly synchronous with the growth of zircon in high grade metamorphic rocks of the lower crust underlying the greenstone belt material suggesting that these may be related processes

oblique archean subduction accretion and exhumation of an oceanic arc during dextral transpression southern volcanic zone abitibi subprovince canada abstract the archean abitibi subprovince divided into northern nvz and southern svz volcanic zones is characterized by the crustal scale destor porcupine manneville fault zone dpmfz which links the svz and nvz and the cadillac larder lake fault zone cllfz which separates the abitibi and pontiac subprovinces the dpmfz and cllfz represent major deformation zones that record over 60 million years of archean deformation the dextral transpressional phase in the nvz which represents incipient svz deformation occurred between 2700 and 2692 ma and is characterized by southeast se trending dextral faults e g macamic fault synorogenic flysch sedimentation is focussed at the interface between the svz nvz and pontiac abitibi subprovinces the se trending parfouru fault linking the two major trench fault systems is interpreted as a reactivated leaky transform fault and is associated with synorogenic flysch sedimentation the early monzodioritic suite of the preissac lacorne batholith was related to dpmfz thrusting ca 2692 2690 ma the change from early thrusting to transcurrent motion is recorded in the duparquet strike slip basin which formed between 2690 and 2680 ma along the dpmfz and the granada pull apart basin which evolved between 2680 and 2670 ma along the cllfz the timing of these basins indicates a diachronous evolution renewed thrusting affected the granada basin but not the northern duparquet strike slip basin so that a southward migrating deformation front is inferred late exhumation resulted in extension along both fault zones and was responsible for the juxtaposition of medium and low grade metamorphic rocks the monzogranitic suite of the lamotte pluton which occurred between 2660 and 2642 ma is linked to exhumation final dextral transpression post dating exhumation produced shearing and folding the svz of the abitibi subprovince shows the salient attributes of modern oblique orogenic collisions with alternating phases of thrusting and strike slip movement along crustal scale faults during dextral transpression

modification of fluid inclusions in quartz by deviatoric stress ii experimentally induced changes in inclusion volume and composition fluid inclusions in quartz are known to modify their densities during shear deformation modifications of chemical composition are also suspected however such changes have not been experimentally demonstrated their mechanisms remain unexplained and no criteria are available to assess whether deformed inclusions preserve information on paleofluid properties to address these issues quartz crystals containing natural co2 h2o nacl fluid inclusions have been experimentally subjected to compressive deviatoric stresses of 90 250 mpa at 700 c and 600 mpa confining pressure the resulting microcracking of the inclusions leads to expansion by up to 20 producing low fluid densities that bear no relation to physical conditions outside the sample nevertheless the chemical composition of the precursor inclusions is preserved with time the microcracks heal and form swarms of tiny satellite inclusions with a wide range of densities the highest reflecting the value of the maximum principle stress 1 these new inclusions lose h2o via diffusion thereby passively increasing their salt and gas contents and triggering plastic deformation of the surrounding quartz via h2o weakening using microstructural criteria to identify the characteristic types of modified inclusions both the pre deformation fluid composition and syn deformation maximum stress on the host mineral can be derived from microthermometric analysis and thermodynamic modelling

thermochronology of the camflo gold deposit malartic quebec implications for magmatic underplating and the formation of gold bearing quartz veins the dominant ore host at camflo is a small monzonite pluton cut by main stage gold bearing quartz veins containing hydrothermal titanite and k feldspar main stage veins are spatially and temporally related to brittle ductile faults emplaced into most faults are younger transitional stage quartz pyrite lodes with sericite rutile alteration halos titanite in main stage gold quartz veins is replaced by rutile calcite quartz where overprinted by transitional stage sericitic alteration a u pb zircon age from the camflo monzonite indicates that the stock was emplaced at 2685 or 10 ma a u pb age of 2621 or 4 ma for hydrothermal titanite and a pb pb isochron age of 2621 or 7 ma defined by seven titanite and two k feldspar samples indicate that the gold quartz veins formed approximately 60 m y later which precludes a direct genetic link between these two events rutile analyses plot below the titanite feldspar pb pb isochron and so support field and petrographic evidence suggesting rutile did not precipitate from the same fluid that formed the titanite and k feldspar incremental heating and total fusion 40 ar 39 ar ages of hydrothermal micas related to gold quartz veins and quartz pyrite lodes are 70 to 170 m y younger than the hydrothermal u pb ages in addition 40 ar 39 ar ages of micas on the 1650 level are approximately 10 to 15 m y older than like micas on the 3475 level the younger 40 ar 39 ar ages are interpreted as cooling and not recrystallization or reset ages 40 ar 39 ar ages indicate cooling rates of approximately 1 degrees c m y for 2600 to 2550 ma rutile vein muscovite approximately 0 6 degrees c m y for 2550 to 2511 ma vein muscovite wall rock muscovite and approximately 0 3 degrees c m y for 2507 to 2452 ma large biotite small biotite an apparent uplift rate of approximately 0 04 km m y for 2520 to 2478 ma is calculated by comparing biotite and white mica ages from the 1650 and 3475 levels the u pb and 40 ar 39 ar thermochronology is consistent with an accretionary tectonic setting for camflo during the terminal stages of tectonic construction of the superior province a critical feature of this setting is large volumes of mantle derived basalt underplating the lower crust during peak granulite formation at approximately 2648 to 2640 ma co 2 rich fluids liberated by solidification of ponded mafic magma after peak granulite formation interacted with other fluids magmas and rock either at their source or during migration in shear zones to upper crustal levels where they deposited significant quantities of gold at camflo at approximately 2621 ma slow cooling and slow apparent uplift at camflo ensued for 150 m y after magmatic under plating resulting in the young 40 ar 39 ar cooling ages recorded by hydrothermal minerals this model is consistent with ages for granulite facies metamorphism in the kapuskasing structural zone postpeak metamorphic ages for co 2 h 2 o fluid inclusions in regional granulite terranes and geochronological data from other gold deposits and may have widespread implications for the formation of gold deposits in the southern superior province

dating of archean auriferous quartz vein deposits in the abitibi greenstone belt canada 40 ar 39 ar evidence for a 70 to 100 m y time gap between plutonism metamorphism and mineralization the sigma mine at val d9or quebec in the abitibi belt is typical of vein type gold deposits in archcan greenstone belts although the relative timing of gold mineralization with respect to magmatism metamorphism deformation and hydrothermal events in the mine is well documented precise isotopic age constraints have until recently been lacking this paper presents the results of a 40 ar 39 ar dating study of the sigma mine and of the davidson tisdale deposit in the abitibi belt in the sigma mine dates on metamorphic amphibole indicate that the regional metamorphism which predates the vein formation occurred at ca 2 68 ga muscovite from the gold bearing quartz veins yields a plateau date of 2579 or 9 ma 2sigma whereas biotite from the veins shows disturbed saddle shaped age spectra the mild disturbance of the biotite is attributed to later diabase dike emplacement and a 40 ar 39 ar date on a dike indicates that this event is younger than 2 3 ga thermal effects of the grenville orogeny 1 2 1 0 ga may also be present a muscovite separate from a gold bearing quartz vein at the davidson tisdale deposit yields a 2607 or 10 ma 2sigma plateau date although the amphibole and muscovite dates at the sigma mine bracket the gold mineralization event at between ca 2 68 and 2 58 ga a number of tectonothermal histories are possible for this time interval it is concluded based on all evidence that the muscovite plateau dates are the time of vein and gold formation which thus occurred in the sigma mine ca 100 m y and in the davidson tisdale deposit ca 70 m y after syn to post tectonic magmatism and regional metamorphism

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

benthic foraminiferal distribution at middle valley juan de fuca ridge a northeast pacific hydrothermal venting site fourteen benthic foraminiferal bearing surface samples collected from the area of active venting aav in middle valley at a depth of 2430 m at the northern end of juan de fuca ridge northeast pacific ocean yielded 156 identifiable taxa sample sites were selected near active or recently active vents where temperatures up to 274 c have been measured the sea floor beyond hydrothermal mounds is characterized by unaltered soft hemipelagic mud and is dominated by a calcareous foraminiferal assemblage which includes numerous allochthonous species derived from the shelf via turbidite flows into the valley within the aav agglutinated foraminifera dominate with proximity to hydrothermal vent activity species of the family hormosinidae subfamily reophacinae dominate in the hydrothermal habitat because of their success at colonization attached agglutinated foraminifera densely colonize the indurated sediment in close proximity to vent sites however like the macrofauna observed near hydrothermal vents foraminifera do not venture into the extreme habitats where temperatures are greater than 20 c where clam beds are found in association with active hydrogen sulphide venting benthic foraminifera occur rarely these beds occur in loose pyritic mud that is toxic to all but species e g the clam culyp ena that co exist symbiotically with sulphur oxidizing bacteria the sparse distribution of calcareous benthic foraminifera in the vent areas is caused by enhanced carbonate dissolution at ph values of 5 2 low foraminiferal abundance and species diversity at the immediate site of active venting is attributed to rapid changes in physical and chemical conditions caused by circulating hydrothermal vent waters

formation of archean batholith hosted gold veins at the lac herbin deposit val d or district canada mineralogical and fluid inclusion constraints the lac herbin deposit consists of a network of mineralized parallel steep reverse faults within the synvolcanic bourlamaque granodiorite batholith at val d or in the archean abitibi greenstone belt there are two related quartz tourmaline carbonate fault fill vein sets in the faults which consist of subvertical fault fill veins associated with subhorizontal veins the paragenetic sequence is characterized by a main vein filling ore stage including quartz tourmaline carbonate and pyrite hosted gold chalcopyrite tellurides pyrrhotite and cubanite inclusions most of the gold is located in fractures in deformed pyrite and quartz in equilibrium with chalcopyrite and carbonates with local pyrrhotite sphalerite galena cobaltite pyrite or tellurides petrography and microthermometry on quartz from the main vein filling ore stage reveal the presence of three unrelated fluid inclusion types 1 gold bearing aqueous carbonic inclusions arranged in three dimensional intragranular clusters in quartz crystals responsible for the main vein filling stage 2 barren high temperature aqueous moderately saline inclusions observed in healed fractures postdating the aqueous carbonic inclusions and considered as a remobilizing agent of earlier precipitated gold in late fractures and 3 barren low temperature aqueous high saline inclusions in healed fractures similar to the crustal brines reported throughout the canadian shield and considered to be unrelated to the gold mineralization at the lac herbin deposit the aqueous carbonic inclusions are interpreted to have formed first and to represent the gold bearing fluid which were generated contemporaneous with regional greenschist facies metamorphism in contrast the high temperature aqueous fluid dissolved gold from the main vein filling ore stage transported and reprecipitated it in late fractures during a subsequent local thermal event

genesis of the auriferous c quartz tourmaline vein of the siscoe mine val d or district abitibi subprovince canada structural mineralogical and fluid inclusion constraints the c quartz tourmaline vein of the siscoe deposit is a classic example of a high grade archean gold lode and averages 45 g t au locally attaining 221 g t au this vein cuts all dikes the main regional foliation s2 and several auriferous quartz carbonate veins and is interpreted to be a shear vein which formed during the development of a late to post d2 reverse fault the vein is composed of alternating tourmaline and quartz rich layers with minor amounts of rutile scheelite apatite chlorite muscovite carbonate mainly calcite pyrite chalcopyrite tetradymite and native gold vein filling occurred during the development of a reverse fault through a process involving repeated episodes of opening mineral deposition and plastic and brittle deformation the vein geometry was controlled by local rheologic heterogeneities or by a west northwest east southeast compressive event the wall rock alteration is characterized by the occurrence of tourmaline pyrite and calcite the timing of gold deposition and the gold fineness in the c quartz tourmaline vein differ from those of the wall rock in the vein native gold 4 7 7 3 wt ag was the latest phase to deposit and commonly occurs in fractures that cut across the quartz and tourmaline layers whereas in the wall rock gold 7 9 13 2 wt ag started to precipitate just before or synchronously with pyrite consequently the textural and mineral chemical evidence suggests that the fluids in the vein and wall rock were not in equilibrium with each other during gold deposition and that the mechanisms of precious metal precipitation were different in the two environments in the wall rock gold started to precipitate synchronously with sulfides due to reaction of hydrothermal fluids with magmatic ilmenite this reaction caused the destabilization of gold bisulfide complexes and prompted gold deposition however sulfides are very rare in the c quartz tourmaline vein and gold deposited after the main episode of vein filling suggesting that its precipitation was not controlled by pyrite deposition the occurrence of aqueous carbonic ac fluid inclusions in healed fractures that radiate from gold grains suggests that these fluids were associated with the ore forming process two types of aqueous carbonic fluid inclusions were identified h2o nacl co2 bearing salinities between 4 and 7 wt nacl equiv and h2o nacl co2 ch4 bearing salinities varying between 7 and 9 wt nacl equiv both types homogenize at t 190 c based on structural textural and fluid inclusion evidence we propose that gold deposition in the c quartz tourmaline vein took place after the main episode of vein filling as a result of continued fracturing and mixing of these two fluids

evolution of the south central segment of the archean abitibi belt quebec part ii tectonic evolution and geomechanical model in this paper we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the archean abitibi and bellecombe belts volcanism in the abitibi belt created a very thick anisotropic plate composed of competent volcanic rocks and broken by the duparquet destor break the depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole the cadillac break a normal fault separated the abitibi and bellecombe belts the latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic mafic flows north south compression of the volcanic terrain during the kenoran orogeny produced a set of flexure folds f1 that curve around the consolidated cores of central volcanic complexes generally in an easterly direction synclinoria nucleated at the dee

exsolution in hornblende and its consequences for 40ar39ar age spectra and closure temperature abstract step heating studies of hornblende and biotite which coexist in an amphibolite near north walpole vermont reveal dramatically different 40 ar 39 ar age spectra the biotite mg 59 is characterized by a plateau over 98 percent 39ar release at 343 5 ma in strong contrast to the amphibole which exhibits both a complex age spectrum and a k ar age significantly younger than the biotite the amphibole release pattern contains three complete age cycles which range between extremes of 199 ma and 408 ma interestingly the k ca ratio calculated from reactor produced isotopes also varies with ar release but follows a trend which is antipathetic to the 40 ar 39 ar age pattern detailed microstructural examination including transmission electron microscopy tem reveals a complex exsolution structure that is consistent with both the complexity of the release pattern as well as the low degree of radiogenic 40ar 40ar retentivity in the amphibole this result underscores the variability of closure temperature tc for 40ar in metamorphic amphiboles and should warn against accepting a single universal value of tc

formation of the auriferous and barren north dipper veins in the sigma mine val d or canada constraints from structural mineralogical fluid inclusion and isotopic data the sigma lamaque mine 100 metric tons t of gold is an example of an archean greenstone belt gold deposit formed by processes related to multistage hydrothermal fluid circulation the earliest recognized vein systems are steeply to moderately dipping fault fill veins within shear zones and contemporaneous subhorizontal veins which were overprinted by the late north dipper vein system the latter strikes east west dips moderately to the north and exhibits complex internal geometry with features similar to fault fill and extensional veins and therefore is interpreted as extensional shear veins this late vein system was considered one of the major sources of gold in the shallow underground and open pit ore reserve estimations these late north dipper veins were studied in detail in the sigma pit where they contain ore grade gold and are hosted by the calc alkaline tuffs of the val d or formation and in the north zone where they are barren and hosted by the tholeiitic volcanic rocks of the jacola formation in the sigma pit these veins have apparent thicknesses of 0 8 to 3 m and very irregular contacts with the vein walls they comprise irregular zones of milky quartz filling disrupted blocks of layered quartz and tourmaline and slabs of foliated pyrite rich wall rock layers with tourmaline and quartz crystals oriented perpendicular to the vein walls are observed close to the vein walls the veins contain minor amounts of calcite pyrite rutile and traces of chlorite muscovite pyrrhotite chalcopyrite galena bismuth tellurides and gold locally the sulfide content can attain 10 modal percent of the vein mineralogy in the veins native gold with 6 wt ag occurs rarely associated with the main vein filling minerals commonly as inclusions in pyrite main vein filling stage and most commonly filling fractures in pyrite tourmaline and quartz where it is alloyed with 8 to 17 wt percent ag and is associated with calcite and bi tellurides late auriferous stage the proximal wall rock alteration related to the auriferous north dipper veins overprints the metamorphic assemblage and is characterized by abundant fine grained plagioclase calcite quartz and minor chlorite tourmaline and pyrite in the tuffs and more abundant muscovite in the intrusive feldspar porphyry in the wall rock gold with 6 to 28 wt percent ag is found locally filling fractures in pyrite where it is associated with a late generation of calcite the barren north dipper vein also comprises mainly quartz and tourmaline but lacks calcite and gold has a very low content of sulfides aqueous carbonic fluid inclusions with salinities less than 8 wt percent nacl equiv and homogenization temperatures between 228 and 440 c and carbonic fluid inclusions with less than 0 2 mol percent ch 4 coexisting in the same healed fractures are common in the auriferous north dipper veins but very rare in the barren vein where aqueous fluid inclusions have lower temperatures dominantly 125 225 c crush leaching and laser ablation time of flight inductively coupled mass spectrometry la tof icpms of fluids in the inclusions indicate elevated concentrations of ni cu sb pb and ag in the fluids in the auriferous veins compared to the aqueous fluids in the barren veins this suggests different sources for the metals in the fluids associated with the gold possibly including both igneous and sedimentary rocks calculated oxygen isotope equilibration temperatures for quartz tourmaline pairs from the auriferous main vein filling stage are 323 to 370 c this is within the range documented in fluid inclusions related to the late auriferous stage indicating that the temperature of the auriferous hydrothermal fluids did not change appreciably during the evolution of the system calculated 18 o h 2 o values for the mineralizing fluids are 9 5 per mil consistent with either low water rock ratio systems associated with high grade metamorphism or a magmatic origin for the fluids gold included in pyrite may have precipitated during the main vein filling stage due to the decrease of h 2 sconcentration in the hydrothermal fluid following the deposition of sulfides however gold in fractures in the main vein filling minerals precipitated later due probably to dilution of the auriferous aqueous carbonic fluids by mixing with aqueous fluids the absence of ore grade gold in the barren north zone vein is probably due to the lack of circulation of auriferous aqueous carbonic fluids in the north zone located distal to the first order larder lake cadillac fault which may have served as the main regional conduit for the auriferous aqueous carbonic fluids

morphology origin and infrared microthermometry of fluid inclusions in pyrite from the radka epithermal copper deposit srednogorie zone bulgaria pyrite samples from the radka epithermal replacement type volcanic rock hosted copper deposit bulgaria have been studied using near infrared ir microscopy two generations of pyrite based on their textures composition and behaviour in ir light can be distinguished electron microprobe analyses x ray elemental mapping and fourier transform infrared spectroscopy were used to study the relationship between crystal zoning trace element contents and ir transmittance of pyrite the observed crystal zoning is related to variable arsenic contents in massive fine grained and colloform pyrite from the early pyrite quartz assemblage and cobalt contents in pyrite crystals from the late quartz pyrite vein assemblage there is a negative correlation between trace element content and ir transmittance of pyrite the ir transparency of pyrite is thus a sensitive indicator of changes in trace element concentrations fluid inclusions have only been found in the second pyrite generation scanning electron microscopy observations on open fluid inclusion cavities permitted the crystallographic features of vacuoles to be determined a characteristic feature of primary fluid inclusions in pyrite is a negative crystal habit shaped mainly by 100 111 and 210 this complicated polyhedral morphology is the reason for the observed opacity of some isometric primary inclusions secondary fluid inclusion morphology depends on the nature of the surface of the healed fracture recognition of the primary or secondary origin of fluid inclusions is enhanced by using crystallographically oriented sections microthermometric measurements of primary inclusions indicate that the second pyrite generation was deposited at maximum p t conditions of 400 c and 430 bar and from a fluid of low bulk salinity 3 5 4 6 wt possibly kcl dominant there are large ranges for homogenisation temperatures in secondary inclusions because of necking down processes decrepitation features of some of pyrite hosted inclusions and of all inclusions in associated quartz indicate reheating of the veins to 500 550 c the late cobalt rich quartz pyrite vein assemblage in the radka deposit may be the shallow manifestation of deeper and genetically related porphyry copper mineralisation this is a common observation of many intermediate to high sulfidation epithermal replacement type ore bodies in this ore district and possibly the cretaceous banat srednogorie metallogenic belt in general

characteristics and chronology of fracture fluid infiltration in the archean eye dashwa lakes pluton superior province evidence from h c o isotopes and fluid inclusions the archean eye dashwa lakes pluton 2672 24 ma has domains of mineralogically fresh isotropic granite domains that have undergone bulk hydrothermal alteration and at least eleven sets of sequential fracture arrays each with distinctive mineral assemblages fresh granite is characterized by whole rock 18o 8 1 to 8 6 and primary magmatic quartz feldspar 1 3 quartz biotite 5 2 to 5 4 and quartz magnetite 9 8 fractionations magmatic fluids had a calculated isotopic composition of 18o 7 9 0 5 and d 80 5 these isotropic volumes of the granite have not experienced significant incursion of external thermal waters pegmatites quartz molybdenite veins and phlogopite muscovite coated fractures are sporadically distributed in the granite and were precipitated from high temperature magmatic fluids where 18o 8 0 to 10 3 and d 80 5

hydrothermal fluid evolution within the cadillac tectonic zone abitibi greenstone belt canada relationship to auriferous fluids in adjacent second and third order shear zones the cadillac tectonic zone in the abitibi greenstone belt canada is spatially associated with world class gold deposits that are hosted in second and third order faults five types of hydrothermal quartz veins with distinct structural timing are distinguished in the cadillac tectonic zone in the val d or camp and are related to d 2 steep reverse faulting and d 3 oblique transcurrent movement fluid inclusions in gold bearing and barren hydrothermal quartz veins in the transcrustal cadillac tectonic zone record the progressive evolution of the hydrothermal fluids within the cadillac tectonic zone oldest h 2 o co 2 ch 4 nacl fluid inclusions which predate gold mineralization are superseded by gold associated dominantly carbonic co 2 ch 4 h 2 o nacl fluid inclusions on the basis of variable phase ratios and similar total homogenization temperatures in contemporaneous fluid inclusions trails the oldest h 2 o co 2 ch 4 nacl fluids are interpreted to have undergone phase separation the ch 4 content increases from the older x ch 4 0 03 0 24 to the younger x ch 4 0 15 0 71 fluid inclusions and the salinity is low to moderate in the older fluid inclusions mean 1 7 2 6 2 wt nacl equiv and increases in the younger fluid inclusions mean 1 16 2 6 0 wt nacl equiv trails of late stage co 2 ch 4 n 2 h 2 o and ch 4 c 2 h 6 c 3 h 8 fluid inclusions crosscut earlier carbonic aqueous fluid inclusion trails in all veins the texturally latest fluid inclusions occur in trails that crosscut earlier fluid inclusion trails and quartz deformation bands and are composed of h 2 o nacl cacl 2 postentrapment modifications are considered unlikely for most fluid inclusions in the cadillac tectonic zone the hydrothermal fluids in the cadillac tectonic zone were compared with those in second and third order fault zones in the world class sigma deposit to evaluate whether the two fluid systems are of similar derivation carbonic aqueous fluids that deposited quartz in veins and some gold in the cadillac tectonic zone are distinct from those that are hosted in structures of similar timing at sigma cadillac fluids have higher co 2 content and marginally higher salinity 0 6 15 3 wt nacl equiv and 1 10 wt nacl equiv in the cadillac tectonic zone and at sigma respectively but contain similar amounts of ch 4 the high salinity aqueous inclusions at sigma which are interpreted to represent the unmixed h 2 o rich end member of a combined co 2 ch 4 h 2 o nacl fluid are absent in the cadillac tectonic zone veins of d 3 timing which contain a high ch 4 component in the cadillac tectonic zone to 70 mole have not been documented at sigma the magnitude of the hydrothermal quartz vein field and the homogeneity of quartz vein mineralogy and textures in the val d or camp strongly suggest that the fluids that precipitated auriferous quartz veins in second and third order shear zones were not locally derived it is suggested that ore bearing fluids ascended along the cadillac tectonic zone and infiltrated the second and third order fault network an unknown amount of metamorphic h 2 o from the greenstone belt probably mixed with these fluids differences in the fluid composition in the cadillac tectonic zone and those in second and third order shear zones are explained by phase separation with preferential vapor loss into the upper portions of the cadillac tectonic zone and by in situ phase separation without vapor loss during ore deposition at sigma methane enrichment in the late fluids in the cadillac tectonic zone was most likely controlled by an increased fluid interaction with reduced carbon in sedimentary rocks but increasing mantle outgassing and cooling of an f o 2 buffered ascending fluid may also have contributed to the ch 4 budget the youngest aqueous brines in the cadillac tectonic zone are similar to fluids in late fracture fillings and to canadian shield basement brines

pb isotope compositions of pyrite from the c quartz tourmaline vein of the siscoe gold deposit val d or quebec constraints on the origin and age of the gold mineralization the siscoe mine was one of the richest in the val d or mining camp producing 27 5 tonnes t of gold and 9 5 t of silver from 1929 to 1949 the c quartz tourmaline vein at the siscoe mine which is the youngest auriferous vein on the property is an excellent example of a high grade archean lode gold deposit it contains an average of 45 g t au and locally up to 221 g t au this vein cuts all dikes the main regional foliation s2 and several auriferous quartz carbonate veins and is interpreted to be a shear structure that formed during the development of a late to post d2 reverse fault the vein comprises mainly alternating tourmaline and quartz rich layers and gold occurs commonly in late fractures cutting the vein the visible wall rock alteration is characterized by the occurrence of tourmaline pyrite and calcite in this study we report the pb isotope compositions of hydrothermal pyrite separates taken from the c quartz tourmaline vein and its wall rock pyrite is abundant in the wall rock where it occurs as grains with inclusions of chalcopyrite gold tetradymite pyrrhotite rutile silicates and carbonates in the vein it forms euhedra generally devoid of inclusions locally the euhedra are fractured and the fractures are filled with native gold calcite and tetradymite textural relationships suggest that pyrite precipitated synchronously with and or after gold in the wall rock but predated gold in the vein pyrite separates from the vein and its wall rock yielded similar 206pb 204pb 207pb 204pb and 208pb 204pb ratios 13 63 13 83 14 58 14 62 and 33 42 33 76 respectively which are more radiogenic than those reported for volcanic supracrustal and syntectonic plutonic rocks of the southern abitibi subprovince but are very similar to those of the late to posttectonic s type granites in the pontiac subprovince and lacorne block this suggests that the pb originated from a reservoir similar to that of the magmas which produced these granites or alternatively that it was leached from the latter the pb ratios yield a model age of 2 57 0 07 ga which is interpreted to date the cooling of the hydrothermal system that introduced and or remobilized gold into the c quartz tourmaline vein these results when considered in the context of the evolution of the southern abitibi indicate that widespread hydrothermal circulation occurred between 2 64 and 2 55 ga after the collision of the pontiac and abitibi subprovinces and was caused by dewatering and s type magmatism in the thickened unstable continental crust this long lived hydrothermal system promoted remobilization of gold from earlier veins and possibly introduction of gold from deeper zones enhancing gold resources in the siscoe deposit

single zircon age constraints on the tectonic juxtaposition of the archean abitibi greenstone belt and pontiac subprovince quebec canada abstract zircons from metasediments and granitoids in the high grade lacorne block within the low grade archean abitibi greenstone belt have been dated by the single zircon pb evaporation technique yielding 207pb 206pb minimum ages detrital zircons in the mature clastic metasediments of the lacorne block display a range of ages from 2691 8 ma to 3042 6 ma the younger zircon ages 2691 8 2695 4 2715 16 and 2719 4 ma thus impose an upper limit for deposition and indicate that the high grade lacorne block is not basement to the abitibi supracrustal sequence 2747 2680 ma existence of abundant 69 older detrital zircons 2750 ma suggests in turn that the abitibi supracrustal rocks are not the source of the lacorne sediments two generations of granitoids occur in the lacorne block an early monzodiorite monzonite granodiorite syenite series mmgs 2671 4 to 2675 24 ma and a younger s type garnet muscovite granite series gmg 2630 20 to 2655 8 ma this contrasts with granitoid magmatism in the abitibi greenstone belt which ended at 2675 ma the pontiac subprovince to the south of the abitibi greenstone belt shares all of the above features of the lacorne block including detrital zircon ages as well as the composition and timing of granitoid magmatism this is interpreted to indicate that the lacorne block was originally part of the same tectonic terrane as the pontiac subprovince after development of the mmgs magmatism 21670 2680 ma the pontiac subprovince locally underthrust the abitibi greenstone belt and crustal thickening promoted partial melting of underthrust pontiac metasediments to form the 2644 13 ma s type granites later differential uplift exposed the lacorne block as a high grade tectonic window in the abitibi greenstone belt

ore forming fluids in archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec canada archean gold bearing quartz veins at the sigma mine occur in deformed metavolcanics intruded by two generations of preore porphyries the veins were emplaced during a late compressional tectonic event and they consist primarily of quartz tourmaline carbonates pyrite and scheelite vein minerals have been deformed and are also cut by abundant healed fractures outlined by fluid inclusions in the veins gold typically occurs in late fractures and in recrystallized quartz microthermometric sem eda leachate analysis and gas chromatographic techniques were used to study fluid inclusions in quartz most fluid inclusions at sigma occur in late fractures and are secondary the fluid inclusions are commonly found in fractures parallel to or less commonly within gold bearing fractures and are genetically related to the gold three types of fluid inclusions are identified 1 high salinity na ca cl aqueous inclusions 25 34 wt salt with small amounts of co 2 some containing halite calcite and nahcolite as daughter minerals 2 co 2 rich inclusions containing small amounts of h 2 o and ch 4 and 3 low salinity h 2 o co 2 inclusions 10 equiv wt nacl with co 2 contents which are variable but commonly in the range of 15 to 30 mole percent co 2 leachate analyses show that in addition to na and ca the aqueous fluids contain minor amounts of k fe mg and li homogenization temperatures of h 2 o co 2 inclusions with constant phase ratios range from 285 degrees to 395 degrees c those of aqueous inclusions range from 60 degrees to 295 degrees c the aqueous and co 2 rich inclusions are interpreted to have trapped two coexisting fluids resulting from the unmixing of a homogeneous h 2 o co 2 parent fluid itself occasionally trapped in late fractures the ore bearing fluid is interpreted to be a low salinity 10 equiv wt nacl fluid containing 15 to 30 mole percent co 2 at minimum temperatures in the range of 285 degrees to 395 degrees c the relatively low homogenization temperatures of aqueous inclusions are interpreted to be the result of co 2 effervescence from a co 2 saturated aqueous fluid due to pressure fluctuations at the time of entrapment it is also proposed that the onset of gold deposition is related to the onset of fluid unmixing

timing of gold mineralization in the val d or district southern abitibi belt evidence for two distinct mineralizing events gold bearing quartz vein deposits in the val d or area of the southern abitibi greenstone belt are classified in two categories based on structural and chronologic relationships young deposits 2690 ma feature commonly deformed orebodies that are cut by dikes of various composition such deposits occur at the siscoe kiena orion and norlartic mines the norlartic main orebody is crosscut by a tonalite dike which has been dated by u pb at 2692 or 2 ma in agreement with structural data these observations show that gold mineralization in the val d or area occurs in at least two different settings and was emplaced at different times

fluid chemistry and evolution of hydrothermal fluids in an archaean transcrustal fault zone network the case of the cadillac tectonic zone abitibi greenstone belt canada detailed fluid geochemistry studies on hydrothermal quartz veins from the rouyn noranda and val d or areas along the transcrustal cadillac tectonic zone ctz indicate that unmineralized with respect to gold sections of the ctz contained a distinct co2 dominated h2s poor hydrothermal fluid in contrast both gold mineralized sections of the ctz e g at orenada 2 and associated higher order shear zones have a h2o co2 c h 4 nacl hydrothermal fluid their co2 h2s ratios indicate h2s rich compositions the br cl compositions in fluid inclusions trapped in these veins indicate that hydrothermal fluids have been equilibrated with the crust oxygen isotope ratios from hydrothermal quartz veins in the ctz are consistently 2 more enriched than those of associated higher order shear zones which are inter preted to be a function of greater fluid rock ratios in the ctz and lower fluid rock ratios and more efficient equilibration of the hydrothermal fluid with the wall rock in higher order shear zones an implication from this study is that the lower metal endowment of the transcrustal ctz when compared with the higher metal endowment in higher order shear zones ratio of about 1 1000 may be the result of the lack of significant amounts of h 2o h2 sr ich fluids in most of the ctz in contrast gold mineralization in the higher order shear zones appear to be controlled by the high h 2s activity of the aqueous fluids because gold was likely transported in a bisulfide complex and was deposited during sulfidation reac tions in the wall rock and phase separation in the quartz veins

40ar 39ar age constraints on the thermal history of the archean abitibi greenstone belt and the pontiac subprovince implications for terrane collision differential uplift and overprinting of gold deposits 40ar 39ar mineral age spectra of granitic and metamorphic rocks in conjunction with existing conventional zircon geochronology indicate that at least two major late archean thermal events affected tectonic blocks of the abitibi southern volcanic zone svz and the juxtaposed pontiac subprovince the earlier thermal activity 2690 2670 ma was accompanied by the intrusion of voluminous syntectonic plutons and caused low pressure greenschist facies metamorphism in the svz and intermediate pressure metamorphism in the pontiac subprovince the second thermal event 2660 2630 ma was coeval with the emplacement of syncollisional s type garnet muscovite granites in the pontiac subprovince and the higher grade lacorne block of the abitibi svz and reset the k ar systems in preexisting rocks magmatic amphibole from the syntectonic round lake batholith 2695 ma u pb zircon age of the abitibi svz has a slightly disturbed ar release spectrum with an upper plateau age of 2669 6 ma signifying that the low gra

a special issue on archean magmatism volcanism and ore deposits part 1 komatiite associated ni cu pge sulfide and greenstone hosted au deposits preface the archean which represents more than a third of earth s history contains some of the largest and richest ore deposits of the world numerous cratons of variable size and age have been mapped fig 1 and others are still being discovered or delineated largely due to the widespread use of high precision u pb geochronology one of the specific characteristics of archean cratons is the coexistence and juxtaposition of different and major styles of base and precious metals deposits formed at different times and crustal levels poulsen et al 2000 groves et al 2005a robert et al 2005 fig 1 global geographic distribution of archean cratons map modified from chorlton 2007 and kjarsgaard 2007 possible archean crust in central anatolia turkey from paquette and le pennec 2012 it has long been recognized that archean cratons are extremely well endowed in metals e g meyer 1981 de wit and thiart 2005 especially in komatiite associated ni cu pge greenstone hosted au and volcanogenic massive sulfide vms deposits most of these deposits were formed in periods of supercontinent s or supercraton s formation e g 2800 2500 ma kenorland williams et al 1991 aspler and chiarenzelli 1998 2600 2200 ma sclavia bleeker 2003 although some of these deposit types greenstone hosted au and vms were formed episodically at various epochs in earth s history cf goldfarb et al 2010 archean examples appear to be more common and in many cases larger and or richer although common in the archean the deposits are not uniformly distributed among the cratons highlighting the fact that the metal endowment of specific assemblages reflects both secular variations and craton to district scale controls for example the yilgarn craton is very well endowed in komatiite associated ni deposits in contrast to the superior craton which contains more significant vms deposits however the study of archean deposits

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part ii vein paragenesis and hydrothermal alteration the sigma deposit consists of an archean gold bearing vein system in deformed volcanic rocks intruded by two generations of porphyries the veins cut all rock types and wall rock alteration is superposed on greenschist facies metamorphic assemblages there are two related vein sets subvertical veins in ductile shears and subhorizontal veins in extensional fractures between shear zones this paper reports on the paragenesis of extensional veins and related hydrothermal alteration tension veins are composed chiefly of quartz and tourmaline and subordinate amounts of carbonates chlorite pyrite pyrrhotite scheelite and free gold the veins formed by one or more episodes of open space filling the paragenetic sequence consists essentially of successive deposition of carbonate scheelite tourmaline pyrite pyrrhotite carbonate chlorite and quartz most of the gold and tellurides was introduced into fractures and along grain boundaries of recrystallized vein minerals during a postfilling episode of deformation veins are surrounded by zoned alteration envelopes consisting of an outer zone of cryptic alteration characterized by a chlorite carbonate white mica assemblage and an inner zone of visible alteration characterized by a carbonate white mica outer subzone and a carbonate albite inner subzone alteration zones represent reaction fronts advancing into the wall rocks and resulted from progressive interaction of wall rocks with a single hydrothermal fluid the chlorite carbonate white mica zone is characterized by replacement of epidote by calcite and white mica accompanied by fixation of co 2 and k and by release of small amounts of si in carbonate white mica and carbonate albite subzones of visible alteration chlorite biotite and white mica were replaced by calcite albite and quartz variable amounts of gold tourmaline pyrite pyrrhotite and ilmenite were also introduced visible alteration zones are characterized by additions of ca co 2 na b s p and au and by important losses of mg fe al and h 2 o mass balance calculations show that ca na si co 2 s and b in vein minerals were contributed from the hydrothermal fluid whereas fe mg and al were derived from the walls the development of alteration envelopes began with the infiltration of hydrothermal fluids into open extensional fractures and it ceased before complete filling of the veins when continuous mineral coatings formed along vein walls deposition of carbonate accompanied development of cryptic alteration including initial co 2 additions to the wall rocks subsequent deposition of tourmaline pyrite and pyrrhotite carbonate chlorite accompanied the progressive development of visible alteration which encroached on cryptically altered rocks visible alteration is characterized by additions of ca and co 2 to the wall rocks and by release of mg fe and al later bulk quartz deposition which filled the vein openings generally took place after complete development of the alteration envelopes except for this late quartz deposition of vein minerals is attributed to chemical changes in the fluid resulting from progressive wall rock alteration bulk quartz deposition is attributed to progressive cooling of the hydrothermal fluid

evolution of the south central part of the archean abitibi belt quebec part i stratigraphy and paleogeographic model the region comprises parts of the southern zone of the abitibi greenstone belt and of the bellecombe gneiss belt and the belleterre angliers greenstone belt the stratigraphic sequence of the abitibi belt consists of 1 a lower ultramafic division 2 a middle tholeiitic division and 3 an upper diverse division these divisions lap onto an older volcanic sequence to the north and west in the bellecombe belt sediments overlie the lower ultramafic division these sediments coarsen toward the abitibi belt and toward the stratigraphic top the volcanic rocks of the belleterre angliers belt overlie the sediments of the bellecombe belt five paleogeographic phases have been recognized during phase i a deep marine ultramafic lava plain covered the south part of the abitibi belt and the bellecombe belt faulting took place at the duparquet destor break during phase ii tholeiitic basalts formed a deep marine lava plain in the west of the abitibi belt whereas flows erupted mainly from central volcanic c

the relationship between particle characteristics and frictional strength in basal fault breccias implications for fault rock evolution and rockslide susceptibility abstract microstructural analysis of fault rock breccias along the basal shear zone bsz of potential rock slope failures in norway demonstrates that particle size distribution curves show a spectrum from particle to matrix supported we demonstrate that variation in residual shear strength from 450 to 700 kpa is directly related to particle size and shape characteristics we also show that these characteristics are dependent on the fault rock evolution and breakdown mechanism and demonstrate this with simulated examples particle supported fault rocks have higher residual strength than matrix supported samples as the amount of fine material increases the residual shear strength of the fault material decreases particle aspect ratio is variable suggesting different comminution mechanisms and fault zone evolution as particle size decreases below 10 20 m particle aspect ratio approaches 1 1 suggesting that as the fault rock evolves the particles become rounder as aspect ratio increases fault strength decreases we contend that the susceptibility of potential rock slope failures is fundamentally linked to and depends partly on the microscopic properties of the underlying fault rocks and is linked to their comminution history

evolution of the southern abitibi greenstone belt based on u pb geochronology autochthonous volcanic construction followed by plutonism regional deformation and sedimentation abstract new mapping and u pb zircon geochronological results in the southern abitibi greenstone belt sagb support an autochthonous regional stratigraphy comprised of nine supracrustal assemblages rather than the collage of allochthonous terranes proposed in recent publications based on lithological and geochronological criteria these supracrustal assemblages also encompass the swayze shining tree and montcalm greenstone belts indicating that despite separation by large granitic intrusions they are in fact part of one extensive greenstone belt in conjunction with the mapping the geochronological results support coherent upward facing stratigraphic sections with about 20 of the samples containing inherited zircons with ages similar to those found in underlying assemblages the seven oldest assemblages represent semi continuous volcanism from 2750 to 2697 ma the volcanism is compositionally diverse ranging from komatiite and tholeiitic basalt to calc alkaline mafic to felsic lavas intimate intermingling of the different magma clans occurs throughout much of the stratigraphic section regional fault control on the distribution of the volcanic assemblages provides evidence for early dip slip movement associated with volcanic extension dating back to at least 2725 ma the two youngest assemblages are dominantly sedimentary and were unconformably deposited on the volcanic assemblages in close proximity to regional faults the earlier sedimentary assemblage consists of turbidites and minor iron formation deposited from 2696 to 2692 ma and the youngest one of subaerial conglomerates fluvial sandstones and alkalic to shoshonitic volcanic rocks ranging in age from 2687 to 2675 ma the sedimentary assemblages are broadly contemporaneous with the emplacement of syntectonic granitic plutons regional folding and reactivated movement on the regional faults probably related to accretion of the abitibi to the superior province craton autochthonous repetition of different geodynamic environments over the 50 million years of volcanic activity with five dominantly tholeiitic komatiitic assemblages and two dominantly calc alkaline assemblages as well as the extensive intermingling of these different magma clans in a number of the assemblages appears to be unique to the archean it suggests complex large scale and long lived interaction between mantle plumes and subduction zone magmas the nd isotope data indicate a derivation of the diverse volcanic magmas from homogeneously depleted sources with end 2 5 0 5 demonstrating a lack of contamination by ancient enriched components

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define