syenite associated disseminated gold deposits in the abitibi greenstone belt canada a distinct group of gold deposits in the abitibi greenstone belt is spatially associated with quartz monzonite to syenite stocks and dikes the deposits occur mainly along major fault zones in association with preserved slivers of alluvial fluvial timiskaming type sedimentary rocks the deposits consist of disseminated sulfide replacement zones with variably developed stockworks of quartz carbonate k feldspar veinlets within zones of carbonate albite k feldspar and sericite alteration the syenitic intrusions are broadly contemporaneous with deposition of timiskaming sedimentary rocks and together with disseminated gold mineralization they have been overprinted by subsequent regional folding and related penetrative cleavage disseminated gold orebodies occur within composite syenitic stocks or along their margins along satellite dikes and sills and along faults and lithologic contacts away from intrusions orebodies in these different positions are interpreted to represent proximal to distal components of large magmatic hydrothermal systems centered on and possibly genetically related to composite syenitic stocks

magmato hydrothermal space a new metric for geochemical characterisation of metallic ore deposits abstract magmato hydrothermal space is a new mathematical construct where 24 ore and pathfinder elements are used to quantify ore element signatures quantification allows relationships between ore deposit samples to be mapped the broad scale view of magmato hydrothermal space reveals three important trends 1 zn pb sediment hosted mineralisation to igneous associated cu au mineralisation 2 cu au mineralisation to au only mineralisation and 3 ultramafic associated magmatic ni cu pge mineralisation through cu au mineralisation to granitoid associated mo w and sn mineralisation the view provided by magmato hydrothermal space reveals that there is a spectrum of ore element signatures that mirrors the spectrum of ore deposit classes described in the literature geochemical variations within individual ore deposit classes are examined for orogenic au vhms epithermal and sediment hosted cu samples sub groups within each of these classes are compared on element enrichment diagrams and described in the context of magmato hydrothermal space orogenic au samples are divided into two sub groups of as sb rich mineralisation and four sub groups of relatively as sb poor mineralisation the as sb poor sub groups include a te cu ag rich sub group that overlaps with the porphyry cu class and a te w bi mo rich class dominated by granitoid hosted deposits the vhms class ranges from a cu rich sub group that overlaps with porphyry cu and iocg classes through a cu zn sub group to two zn cu sub groups one of which overlaps with the shms class the epithermal class is divided into zn rich cu rich and base metal poor sub groups

inversion of magnetic and frequency domain electromagnetic data for investigating lithologies associated with gold mineralization in the canadian malartic area quebec canada canadian malartic is an archean low grade bulk tonnage native gold deposit the deposit is mostly located in altered clastic metasedimentary rocks mafic ultramafic dykes and monzodioritic porphyr

the timing of prograde metamorphism in the pontiac subprovince superior craton implications for archean geodynamics and gold mineralization abstract the pontiac subprovince is located in the superior province south of the abitibi subprovince the metasedimentary rocks of the pontiac group are characterized by a barrovian metamorphic gradient increasing from north to south from biotite through garnet to staurolite zone conditions the pontiac subprovince has been interpreted as an accretionary wedge or alternatively as an exotic terrane that was tectonically docked to the abitibi subprovince during archean subduction however few studies have attempted to characterize its pressure temperature time path to test this hypothesis and little is known about the timing relationship between regional metamorphism and the gold mineralization an e w lepidoblastic ductile micaceous foliation defines the regional fabric related to the second episode of deformation garnet and staurolite porphyroblasts are interpreted to be late to post kinematic to the regional fabric locally cordierite or andalusite porphyroblasts fully pseudomorphed by a polymineralic assemblage of muscovite feldspar and quartz are wrapped by the main foliation indicating that a potential low pressure high temperature metamorphism m1 preceded the main episode of deformation and barrovian metamorphism m2 pressure and temperature p t forward thermodynamic modelling on a water saturated pseudosection yielded peak conditions of 550 600 c and 5 6 kbar during a prograde clockwise p t path for m2 lu hf dating of garnet from three different locations within the staurolite zone yielded a weighted average age of 2657 5 4 4 ma 95 confidence level that is inferred to be representative of these conditions the age of garnet growth calls into question the previous tectonic interpretation of the abitibi and pontiac subprovinces and is coherent with the new rafted ribbon continent model of bedard 2018 because the canadian malartic gold mineralization is older or synchronous with the garnet growth episode in the staurolite zone south of the ore body this garnet age also provides an estimate of the minimum age of the mineralization event previously dated at 2664 11 ma with re os on molybdenite

from intrusion related to orogenic mineralization the wasamac deposit abitibi greenstone belt canada abstract the wasamac deposit is an example of archean greenstone hosted gold deposit located in the abitibi belt 15 km southwest of rouyn noranda the deposit is hosted by a second order ductile shear zone of the cadillac larder lake fault zone cllfz known as the francoeur wasa shear zone fwsz it regionally sits at the boundary between the orogenic gold district of noranda and the kirkland lake gold district dominated by intrusion related gold systems this specific location in between two different gold mineralization environments sets the wasamac deposit apart as a prime candidate for investigating hydrothermal processes along the cllfz within the wasamac deposit gold distribution is constrained to the altered mylonitized portion of the fwsz lode systems are absent hydrothermal alteration and associated disseminated mineralization occurs as a replacement of the blake river group metavolcanic units the hydrothermal signature displays two distinct alkaline alteration assemblages potassic and albitic each associated with specific gold characteristics 1 potassic alteration is characterized by the crystallization of microcline carbonates and quartz within this assemblage gold is associated with porous pyrite enriched in te ag au mo pb bi w deposited under oxidizing conditions such characteristics are widely described in the kirkland lake area and are found in examples of syenite related mineralization such as the beattie and malartic gold deposits 2 the albitic alteration assemblage composed of albite sericite and carbonates reflects more reduced hydrothermal conditions with mineralization characterized by free native gold this hydrothermal event is coeval with the brecciation of early gold rich pyrite reflecting a structural overprint that controlled late stage gold characteristics these alteration and structural features are common in orogenic gold deposits both worldwide and regionally particularly at the neighbouring kerr addison and francoeur deposits and in lode gold systems such as in the sigma lamaque deposit the gold mineralization at wasamac has similar characteristics to both intrusion related gold systems and structurally controlled orogenic gold deposits hydrothermal and structural crosscutting relationships at wasamac indicate that a structurally controlled hydrothermal event overprinted earlier potassic magmatic hydrothermal alteration this observation supports a multistage process of gold concentration during which new gold characteristics metal anomalies fluid conditions and alteration assemblages replaced earlier stages of gold enrichment in places completely obliterating previous signatures we propose that the wasamac deposit was originally related to an alkaline intrusion buried at depth beneath the francoeur wasa shear zone

possible intrusion related gold systems in the western lachlan orogen southeast australia several gold deposits occurring in the western lachlan orogen have geological geochemical and geochronological characteristics that distinguish them from typical vein hosted orogenic gold deposits of the central victorian gold province the latter are responsible for more than 90 percent of primary hard rock gold production from this region and are generally considered to represent the only economically significant type of gold deposit in the western lachlan orogen atypical gold occurrences at malmsbury myrtle creek mount piper and the wonga deposit in the stawell goldfield are characterized by a close spatial and temporal association with posttectonic felsic intrusions disseminated to stockwork style mineralization alteration dominated by sericitization sulfidation silicification carbonatization and tourmalinization and associated complex au mo w bi te cu the deposits have a number of features in common with intrusion related gold deposits elsewhere in phanerozoic orogenic belts although production from this type of gold mineralization in the western lachlan orogen has been small compared to orogenic gold deposits the possible existence of intrusion related gold deposits has potentially important implications for exploration in this region and also provides significant clues to the tectonic framework and paleozoic metallogeny of eastern australia

archean high mg monzodiorite syenite epidote skarn and biotite sericite gold lodes in the granny smith wallaby district australia u pb and re os chronometry of two intrusion related hydrothermal systems the granny smith 37 t au production and wallaby deposits 38 t out of a 180 t au resource are located northeast of kalgoorlie in 2 7 ga greenstones of the eastern goldfields province the youngest orogenic belt of the yilgarn craton western australia at granny smith a zoned monzodiorite granodiorite stock dated by a concordant titanite zircon u pb age of 2 665 3 ma cuts across east dipping thrust faults the stock is fractured but not displaced and sets a minimum age for large scale 1 km thrust faulting d2 regional folding d1 and dynamothermal metamorphism in the mining district the local gold pyrite mineralization controlled by fractured fault zones is younger than 2 665 3 ma in augite hornblende monzodiorite alteration progressed from a hematite stained alkali feldspar quartz calcite assemblage and quartz molybdenite pyrite veins to a late reduced sericite dolomite albite assemblage gold related monazite and xenotime define a u pb age of 2 660 5 ma and molybdenite from veins a re os isochron age of 2 661 6 ma indicating that mineralization took place shortly after the emplacement of the main stock perhaps coincident with the intrusion of late alkali granite dikes at wallaby a ne trending swarm of porphyry dikes comprising augite monzonite monzodiorite and minor kersantite intrudes folded and thrust faulted molasse the conglomerate and the dikes are overprinted by barren 1 600 m long replacement pipe which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite calcite pyrite skarn and syenite are cut by pink biotite calcite veins containing magnetite pyrite and subeconomic gold silver mineralization au ag 0 2 the veins are associated with red biotite sericite calcite albite alteration in adjacent monzonite dikes structural relations and the concordant titanite u pb age of the skarn constrain intrusion related mineralization to 2 662 3 ma the main stage gold pyrite ore au ag 10 forms hematite stained sericite dolomite albite lodes in stacked d2 reverse faults which offset skarn syenite and the biotite calcite veins by up to 25 m the molybdenite re os age 2 661 10 ma of the ore suggests a genetic link to intrusive activity but is in apparent conflict with a monazite xenotime u pb age 2 651 6 ma which differs from that of the skarn at the 95 confidence level the time relationships at both gold deposits are inconsistent with orogenic models invoking a principal role for metamorphic fluids released during the main phase of compression in the fold belt instead mineralization is related in space and time to late orogenic magnetite series high mg monzodiorite syenite intrusions of mantle origin characterized by mg mg fetotal 0 31 0 57 high cr 34 96 ppm ni 22 63 ppm ba 1 056 2 321 ppm sr 1 268 2 457 ppm th 15 36 ppm and rare earth elements total ree 343 523 ppm at wallaby shared ca k co2 metasomatism and th ree enrichment in allanite link au ag mineralization in biotite calcite veins to the formation of the giant epidote skarn implicating a th ree rich syenite pluton at depth as the source of the oxidized hydrothermal fluid at granny smith lead isotope data and the rb th u signature of early hematite bearing wall rock alteration point to fluid released by the source pluton of the differentiated alkali granite dikes

subaqueous calderas in the archean abitibi greenstone belt an overview and new ideas abstract the 300 700 km abitibi greenstone belt in canada contains numerous world class archean volcanogenic massive sulfide vms deposits yet documentation of archean subaqueous calderas hosting such deposits is lacking the modern sunrise deposit in the myojin knoll caldera of the izu bonin arc shows that submarine calderas are first order sites for vms the hunter mine and normetal calderas as well as the blake river megacaldera complex are reviewed with respect to geometry regional geology physical volcanology dyke emplacement and hydrothermal carbonate alteration these subaqueous calderas are placed into the geodynamic context of the abitibi greenstone belt the abitibi belt displays a complex history of oceanic arc formation evolution collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes analogue models yielding new insights into the sequence of caldera forming events and their synvolcanic fault patterns are applied to explain archean examples underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events during subsidence two sets of faults propagate from the magma chamber margin 1 early reverse outward dipping faults and 2 normal inward dipping faults the largest massive sulfide deposits form preferentially at the caldera margin based on experimental studies and detailed facies mapping the hunter mine caldera is of the segmented piecemeal variety and the normetal caldera is akin to a piston structure the blake river megacaldera contains 1 the e w trending misema 2 the nw trending new senator and 3 the ne trending noranda calderas with the latter two being nested graben type calderas consistent with oblique archean subduction the poorly documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented the alteration study was evaluated at three levels microprobe analysis geochemical staining of drill core and whole rock analyses there were two principal stages of alteration related to vms formation an early silicification phase developed either at depth and or at the seawater interface whereby silicification was bedding parallel in fine grained volcaniclastic deposits near the water surface a pervasive and extensive semi conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently three distinct carbonate pairings were observed 1 proximal siderite sideroplesite fe ankerite next to the vms deposit 2 an intermediate ankerite fe dolomite zone and 3 a distal calcite dolomite zone the carbonate phase is associated with the mineralizing event transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap the silica carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented this alteration can be easily confused with primary carbonates and chemical precipitation deposits e g banded iron formation if detailed volcano sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient

gold mineralization at the syenite hosted beattie gold deposit duparquet neoarchean abitibi belt canada le gisement de beattie est situe dans la ceinture de roches vertes de l abitibi a proximite de la faille porcupine destor et est associe a une syenite porphyrique les corps mineralises ont une ressource totale inferee de 2 77moz contenu dans 56 2mt de minerai a 1 53g t d or dans le gisement de beattie deux styles de mineralisation sont presents a controle lithologique et a controle structural la mineralisation a controle lithologique est limitee exclusivement a la syenite alteree en carbonates de fer cette mineralisation represente du minerai a basse teneur mais fort tonnage dans lequel l or est porte par la pyrite arsenifere et l arsenopyrite l or est invisible il se presente sous la forme de solution solide dans le c ur poreux et riche en arsenic des pyrites la mineralisation a controle structural est presente uniquement dans des zones de cisaillement adjacentes et incluses dans la syenite le minerai est a haute teneur dans des zones de breches silicifiees a caractere hydraulique et tectonique dans des veines de quartz cherteux dans des veines polymetalliques intensement silicifiees et dans des dykes de syenite trachytique tres alteree l or y est visible sous forme d electrum dans les microfractures des pyrites brechifiees les deux styles de mineralisation et les alterations font partie d une evolution paragenetique commune dans un environnement magmatique hydrothermal des phases initiales oxydantes ont evolue en conditions reduites a la faveur de fluides magmatiques et externes riches en co2 ce changement d etat d oxydation a entraine la precipitation des sulfures et la cristallisation de l or invisible dans la pyrite arsenifere et l arsenopyrite une phase d alteration ulterieure dominee par des fluides hydrothermaux riches en silice a pour resultat la brechification des sulfures et leur redistribution dans des corridors siliceux ainsi que la remobilisation de l or dans les microfractures des pyrites brechifiees les compositions calculees de 18o et d sur les veines de quartz associees a cet evenement tardif sont respectivement 7 67 o et 66 o indiquant une dominance des fluides magmatiques avec une probable composante metamorphique cet evenement syn metamorphique transition d2 d3 est associe a un fort enrichissement en hg te mo ag sb as et se le style de cristallisation de l or dans le gisement de beattie est une consequence de la dominance des regimes en systemes ouverts tant au niveau de l incorporation dans le magma de l arsenic qui controle la precipitation de l or invisible que de la circulation tardive de fluides hydrothermaux riches en silice qui sont a l origine de la remobilisation de l or le gisement de beattie partage des affinites avec des gisements associes aux intrusions intrusion related gold deposit des gisements epithermaux a tendance neutre a intermediaire et des gisements de type mesothermaux mots cles de l auteur gisement d or porphyre archeen or invisible remobilisation de l or

physico chemical parameters of neoarchean syntectonic magmatism the example of the muscocho pluton abitibi subprovince abstract the muscocho pluton is one of a number of syntectonic neoarchean granodiorite intrusions formed during the main deformation phase in the abitibi subprovince that lead to stabilization of the superior craton such magma locally are associated with magmatic hydrothermal styles of mineralization interpreted by some works to reflect intrusion related gold systems irgs determining whether magmas can transport enough au to fertilize the upper crust during this tectonomagmatic interval requires insights into physico chemical parameters such as pressure temperature and oxygen fugacity o2 the o2 parameter is particularly important because it affects s speciation and s solubility which correlates with au solubility in magmas retrieving such parameters from the metamorphosed locally hydrothermally altered and generally deformed neoarchean rocks is particularly challenging as such this contribution uses fresh to altered granodiorites of the muscocho pluton a 16 km diameter granodiorite intrusion spatially associated with polymetallic mineralization to evaluate whether physico chemical parameters can be retrieved from ancient altered rocks based on amphibole apatite and zircon chemistry this study also has implications for the origins of the muscocho pluton which ascended slowly toward the upper crust as a single pulse of evolved magma and became emplaced at about 12 km depth the magma had an o2 above the ni nio solid oxygen buffer nno 1 which is not considered optimal for au transportation the magma also formed a deep intrusion unable to provide magmatic fluids to trigger an efficient hydrothermal system this study provides the basis for a systematic evaluation of the physico chemical conditions within which syntectonic magmas evolved in the upper crust knowledge of these physico chemical conditions are necessary to better constrain the irgs metallogenic model

fluid inclusion and stable isotope o h c constraints on the genesis of the pedra branca gold deposit troia massif borborema province ne brazil an example of hypozonal orogenic gold mineralization abstract at the archean paleoproterozoic troia massif ne brazil two major paleoproterozoic greenstone belts are documented algodoes and serra das pipocas they share similar lithostratigraphic characteristics with other 2 2 2 1 ga greenstone belts of the surrounding cratonic domains e g guiana shield and west africa craton gold mineralization in the serra das pipocas greenstone belt is associated with a regional ne trending shear zone in the mineralized area the pedra branca gold deposit the main gold mineralization is found in association with quartz veins calc silicate alteration e g diopside k feldspar amphibole titanite biotite pyrite albite magnetite carbonates and albitization pyrrhotite is commonly found as inclusions in pyrite and late magnetite replaces pyrite suggesting progressive oxidation of the ore forming fluid free milling gold commonly precipitates at the late stages of alteration in close association with magnetite and tellurides the main tellurides found are hessite altaite sylvanite calaverite and tellurobismuthite two fluid inclusion assemblages were identified from mineralized quartz veins assemblage 1 is characterized by pseudo secondary trails that show the coexistence of co2 rich and low salinity 0 8 wt nacl equiv co2 h2o nacl and h2o nacl inclusions suggesting formation during phase separation fluid immiscibility assemblage 2 is represented by late secondary low temperature th

structural setting of the young davidson syenite hosted gold deposit in the western cadillac larder lake deformation zone abitibi greenstone belt superior province ontario abstract within the southern abitibi greenstone belt of the superior province intrusion related in particular syenite hosted gold deposits represent a significant type that is poorly understood whether the gold mineralization is genetically linked to the syenite intrusions as in a magmatic model or structurally associated with the development of subsequent shear zones remains very controversial our new structural data show that the multiply deformed young davidson gold deposit and its surrounding matachewan area occur along the western extension of the cadillac larder lake deformation zone clldz a tectonically and economically important crustal scale deformation zone in the southern abitibi greenstone belt four generations d1 d4 of deformation are recognized the first part of the d1 deformation d1a records a ne sw oriented shortening and resulted in regional upright folding without penetrative foliation whereas the subsequent d1b generates regional penetrative foliations and top to ne reverse faults d2 occurs during a nw se oriented shortening and produces asymmetric folds oblique slip thrusts and dextral strike slip shear zones d3 semi brittle deformation refolds the d1 and d2 fabrics whereas the latest d4 sinistral fault records a paleoproterozoic brittle deformation the young davidson deposit is a lode gold deposit that at least in part was structurally controlled it is associated with the development of the clldz and hosted in a syenite four main generations of veins are identified in the syenite v1 veins are characterized by folded and boudinaged quartz ankerite veins v2 veins are represented by folded or en echelon quartz pyrite veinlets v3 veins are comprised of en echelon quartz carbonate veins with sulfide minerals and v4 veins consist of planar carbonate quartz veins and minor hematite petrological studies reveal that the major phase of gold mineralization is associated with the v2 veins and partially with the v3 veins gold mineralization and emplacement of the associated veins appear to have occurred during regional d1b ne sw oriented shortening and top to ne shearing and the syenite acted as a mechanical trap due to competency contrast to the wall rock

timing and characteristics of the archean subaqueous blake river megacaldera complex abitibi greenstone belt canada abstract the archean blake river group of the abitibi greenstone belt represents a megacaldera complex which evolved over 8 11 m y from approximately 2704 to 2696 ma the early misema caldera developed from a series of amalgamated shield volcano complexes identified by the remnants of mafic dyke and sill systems these remnants are found in the jevis clericy montsabrais renault clifford tannahill and colnet regions where summit calderas are delineated by circular ring dyke structures the secondary 330 trending new senator caldera formed within the envelope of the misema caldera and exhibits a box work graben type structure finally the felsic dominated 070 striking noranda caldera well known for its vms endowment represents the final collapse of the megacaldera complex deformation has overprinted the calderas but structural patterns can be used in order to reconstruct the pre existing volcanic architecture structures such as mafic ring dyke complexes and rhyolitic dome flow complexes have nucleated fold geometries and synvolcanic fractures were reactivated within zones of ductile deformation precise u pb geochronological analyses were conducted in selected areas with specific emphasis on the misema and new senator calderas felsic volcanism progressed throughout the evolution of the megacaldera complex and intermediate to felsic units have been dated to limit this evolution the misema caldera formed between 2704 and 2702 ma via the amalgamation of shield volcanoes that were probably active prior to 2704 ma the new senator caldera was generated between 2702 and 2700 ma during paroxysmal felsic volcanism followed by the collapse of the noranda caldera culminating between 2700 2696 ma the misema caldera was generated by a gravitational stress field consistent with the formation of ring and radial dyke architecture whereas the se trending new senator caldera is more compatible with a sw trending principal compression direction related to oblique convergence in the abitibi belt the noranda caldera is interpreted as a ne rift structure that formed in the final stages of megacaldera evolution

the passa tres lode gold deposit parana state brazil an example of structurally controlled mineralisation formed during magmatic hydrothermal transition and hosted within granite abstract the passa tres granite is a nne ssw elongated shape intrusion located in the parana state southern brazil this intrusion was emplaced within metapelites of the mesoproterozoic votuverava group which are part of the n040 e trending lancinha shear zone gold mineralisation within the passa tres granite is held by meter scale quartz veins forming orebodies with variable massive banded sheared and or brecciated internal textures structural data indicate the existence of two orthogonal directions of structures n s and e w dipping 60 75 w and 45 70 s respectively mineralised veins contain in addition to the quartz of the gangue and in chronological order fluorite pyrite chalcopyrite gold aikinite molybdenite muscovite carbonate and baryte gold occurs as native grains within fractures that affect pyrite commonly associated with chalcopyrite and aikinite quartz veins are sometimes bordered by aplitic dykes additionally some of the veins exhibit a thin margin of k feldspar minerals that could represent the early stage of vein formation these observations the presence of unidirectional solidification textures ust along with abundant expression of pegmatite rich pockets within granite that crops out close to the surface allow the reconstruction of the granite architecture in terms of late magmatic evolution magmatic hydrothermal transition and position of the cupola n s and e w systems are interpreted to be contemporaneous and conjugate normal displacements are predominant and main mineralised veins are essentially located within extensional pull apart structures the structural model suggests that the normal faults were initiated along former low angle planes associated with aplite and or early quartz veins that subsequently controlled the opening of the pull apart structures that represent the economic orebodies zircon from the granite and muscovite grains from mineralised veins were dated by u pb and ar ar methods respectively zircons from the main facies medium grained gem and microgranite gef provided undistinguishable ages which were pooled to give an age of 611 9 3 6 ma a less abundant leucocratic facies white granite geb yielded a significantly younger age of 592 8 7 1 ma muscovites from quartz veins gave ar ar ages of 612 9 2 to 608 8 2 ma transitional vein with a k feldspar border 611 7 2 to 608 8 2 ma mineralised veins and 608 4 2 ma barren quartz vein thus the passa tres granite and its gold mineralisation appear to represent a unique example of an intrusion related gold system in which the mineralisation concentrates in the core of the magmatic intrusion in the form of meter scale veins strongly controlled by tectonics

an overview of timing and structural geometry of gold gold antimony and antimony mineralization in the jiangnan orogen southern china abstract the jiangnan orogen located between the yangtze and cathaysia blocks in southern china hosts significant gold and antimony resources long standing controversies over the number and precise timing of gold gold antimony and antimony mineralization event s and the genesis of these deposits limit the understanding and exploration of this giant gold and antimony system together with geological evidence a critical review of the published geochronological data of these deposits suggest that there were two gold events in the triassic 235 ma and early cretaceous 142 130 ma two gold antimony events in the early devonian 402 ma and late triassic middle jurassic 224 163 ma possibly equivalent to the two gold events and one antimony event in the early cretaceous 130 ma there are other possible gold events in the neoproterozoic or at an even older age and ordovician to early devonian which are constrained only by limited geological evidence and a few non robust isotopic ages the regional distribution of the gold gold antimony and antimony districts and deposits therein reveal a first order control on the mineralization by crustal scale faults which acted as ore forming fluid pathways connected to deep fluid and metal source areas second and third order faults that are situated along the jogs of the first order faults especially fault corridors defined by nne ne trending second order faults and third order nw to e w trending discontinuous oblique faults provided favorable locations for pre cretaceous gold antimony mineralization in addition ne trending open anticlines linked to deep crustal levels by first order faults host significant antimony and minor gold mineralization and the curvilinear fanjingshan detachment fault hosts some gold and antimony deposits locally at deposit to orebody scales pre ore barren quartz veins and magmatic dikes were the loci for mineralization in some gold antimony deposits the structural geometry of the pre cretaceous gold and gold antimony deposits suggests an early devonian orogenic gold antimony mineralization event during a transpressional tectonic regime related to coeval intracontinental orogeny between the yangtze and cathaysian blocks in contrast triassic orogenic gold and triassic middle jurassic orogenic gold antimony events are interpreted to relate to distal effects of the collision between the north and south china blocks the structurally contrasting major early cretaceous epizonal antimony mineralization event together with contemporaneous hydrothermal gold mineralization is interpreted to have been controlled by normal faults and pre ore open folds in an extensional tectonic regime related to the distal effects of rollback of the paleo pacific plate after 135 ma for future geoscience based exploration in the orogen documentation and interpretation of critical structural geometries of gold gold antimony and antimony deposits is a vital step towards successful target generation

re os molybdenite ages from the archean yellowknife greenstone belt comparison to u pb ages and evidence for metal introduction at 2675 ma the late archean yellowknife greenstone belt in the southwestern slave province hosts world class orogenic gold deposits with total production of 15 million ounces moz of gold the timing of gold mineralization is estimated to be ca 2600 ma based on the relative timing of d 2 structures and associated formation of deposit hosting shear zones the majority of studies on the deposits indicate that gold was emplaced by metamorphically driven hydrothermal fluids depositing gold in chemical and structural traps alternatively based on ore mineral compositions proximity to plutons and increased gold grades in the vicinity of quartz feldspar porphyry dikes it has been suggested that the gold deposits may also be related to the intrusions in this study we present two new re os molybdenite ages from two intermediate to felsic plutonic rocks and compare them with u pb zircon crystallization ages the duckfish aplite contains intergrown molybdenite and yields a re os model age of 2611 7 ma the same as a u pb zircon crystallization age of 2611 2 1 5 ma for the aplite and within assigned error of a previously reported 2608 3 ma u pb titanite age for the duckfish pluton the subvolcanic ryan lake pluton has synplutonic quartz veining with intergrown molybdenite that yields an re os model age of 2679 8 ma repeat analysis of 2675 7 within assigned error of the 2671 6 5 ma u pb zircon crystallization age of the pluton in both cases the re os and u pb chronometers survived later low to moderate temperature low pressure contact and regional metamorphism the ca 2675 ma ryan lake pluton and associated quartz feldspar porphyry dikes have gold contents significantly higher than the least altered ore hosting mafic volcanic rocks but the pluton is significantly older than the ca 2600 ma relative age of the gold deposits the age data and the fact that an early pluton carries elevated gold suggest that similar plutons and associated quartz feldspar porphyry dikes may have fertilized the greenstone belt prior to formation of the orogenic gold deposits we suggest that when ca 2600 ma metamorphically derived fluids interacted with these older rocks the gold budget in the hydrothermal fluid could have been increased as evidenced by increased gold grades near porphyries an intrusion related early introduction of gold into the yellowknife greenstone belt may have implications for other archean gold deposits where there is a spatial relationship between gold and early plutonic rocks

detecting magmatic derived fluids using pyrite chemistry example of the chibougamau area abitibi subprovince quebec abstract magmatic fluids are an important carrier of precious and base metals in many mineralized systems porphyry deposits intrusion related gold systems irgs volcanogenic massive sulfides vms recognizing magmatic inputs is essential for understanding metallogenic processes and for developing accurate exploration models and the importance of fluids exsolved from magmas remains a source of much debate for some contexts such as irgs and orogenic gold deposits this study aims to identify magmatic fluids in the chibougamau area northeastern corner of the neoarchean abitibi subprovince canada using pyrite chemistry this is achieved by comparing the chemistry of pyrites recovered from the cu au magmatic hydrothermal porphyry systems of the chibougamau area to background compositions i e the chemistry of pyrites from weakly mineralized rocks from the same area analyses of quantitative laser ablation inductively coupled plasma mass spectrometry la icp ms are processed in three distinct manners to better evaluate the trace elements controlled by silicates oxides sulfides and sulfosalt inclusions and the trace elements that are structurally bound to pyrite detailed investigation of the trace element content of pyrite indicates that most elements are controlled by silicate inclusions some reflect the composition of the host rock others correlate with the mineralizing style and only te and bi are discriminant of the porphyry systems of the chibougamau area tellurium is structurally bound to pyrite or forms telluride nanoparticles in the study area while the distribution of bi is controlled by galena and chalcopyrite inclusions and pyrite chemistry is interpreted using absolute te values and bi ratios bi pb and bi cu this study provides insight into the cu au magmatic hydrothermal systems of the chibougamau area it also has implications for the way pyrite chemistry can be used to probe for magmatic fluids in other mineralized contexts

the tectonic setting and evolution of the 2 7 ga kalgoorlie kurnalpi rift a world class archean gold province the yilgarn craton results from three major mantle input events at ca 3 0 2 9 2 8 and 2 7 ga that have interacted with 3 0 ga continental crust zircon geochronology and sm nd isotopic data subdivide the craton into an older yilgarn proto craton and the younger more primitive eastern goldfields superterrane egst formation of the kalgoorlie kurnalpi rift kkr within the egst was associated with the 2 7 ga event which exploited weakened crust at the eastern margin of the yilgarn proto craton where thick sequences of komatiite and basalt were erupted between ca 2710 and 2690 ma in the kalgoorlie terrane calc alkaline volcanism in the kurnalpi terrane began at ca 2730 ma and continued to ca 2690 ma overlapping rifting and plume related volcanism in the kalgoorlie terrane deposition of siliciclastic sedimentary rocks within basins at ca 2660 resulted from an intra orogenic extensional event and coincided with the transition from high ca to low ca granite magmatism and peak emplacement of intrusions with a metasomatised mantle source component most aspects of the kkr are satisfied by broadly coincident plume related magmatism in the kalgoorlie terrane and westward subduction to the east of the burtville terrane geochemical characteristics of 2730 2700 ma calc alkaline volcanism and 2685 2630 ma low sio2 and alkali rich intrusions support models for a continental margin subduction zone setting world class gold deposits formed in reactivated margins of the kkr which became flux zones for mantle derived magmas hydrothermal fluids and heat during 2675 2620 ma orogenesis the orogenic gold mineralisation can be subdivided into proximal intrusion related and distal source deposits

whole rock δ o and δ h footprint of the canadian malartic gold deposit pontiac sub province quebec canada the canadian malartic gold deposit was produced by a hydrothermal system that altered the host metasedimentary rocks of the pontiac group metavolcanic rocks of the piche group and associated porphyritic intrusions and mafic dykes the isotopic footprint in pontiac metasedimentary rocks is marked by an increase in 2h values from 91 near mineralization to background values of ca 59 whereas 18o values remain relatively constant near 10 the isotopic footprint in mafic dykes is marked by an increase in 2h values from 84 near mineralization to background values of ca 73 and a decrease in 18o values from 9 8 near mineralization to background values of ca 8 3 kriging of oxygen and hydrogen isotopic compositions around the canadian malartic deposit delineates the isotopic footprint of the deposit in greywackes the 59 2h isopleth encircles the mineralized domain and is elongated towards the northwest and southeast in mafic dykes the 73 2h isopleth encircles the mineralized domain as well as a large area to the south and southeast whereas the 8 3 18o isopleth encircles the center of the mineralized system and extends over an area towards the southeast host rock oxygen and hydrogen isotope compositions therefore define a cryptic alteration footprint up to 2 5 km outside of the canadian malartic deposit the isotopic composition of the metamorphic fluid in equilibrium with the average least altered greywacke at upper greenschist to amphibolite conditions of ca 550 c is approximately 18o 8 6 and 2h 19 this is close to the composition of the mineralizing fluid at the canadian malartic deposit reported by previous studies fluid rock oxygen and hydrogen isotope exchange modeling indicate that the isotopic footprint formed at relatively low fluid rock ratios up to 0 5 at temperatures near 350 400 c

syenitic group intrusions of the archean kurnalpi terrane yilgarn craton hosts to ancient alkali porphyry gold deposits abstract archean alkali rich syenitic group intrusions in the eastern goldfields superterrane yilgarn craton are chemically similar to intrusions associated with phanerozoic alkali porphyry systems high temperature potassic and ferruginous alteration associated with the yilgarn intrusions are also similar to those in phanerozoic counterparts but these are generally not well mineralized disseminated and fracture controlled gold mineralization associated with syenitic group intrusions is commonly hosted by mesothermal albite carbonate pyrite assemblages the origin of which is ambiguous this communication aims to stimulate discussion on the origin of gold in and around syenitic group intrusions and the apparent absence of significant gold or copper mineralization in associated high temperature alteration gold associated with syenitic group intrusions in the yilgarn craton has many similar characteristics to disseminated gold deposits associated with syenitic intrusions in the abitibi greenstone belt canada and may be present in other archean greenstone belts

expanding the size of multi parameter metasomatic footprints in gold exploration utilization of mafic dykes in the canadian malartic district quebec canada ore forming hydrothermal fluids react differently with different country rocks but few studies have applied this knowledge with the specific goal of expanding the size of hydrothermal footprints in mineral exploration to develop this concept 122 metamorphosed mafic dykes from the world class canadian malartic gold district 18 6 moz au were sampled and analyzed for mineralogy physical properties and lithogeochemistry partial and total digestion the mafic dykes intrude mainly metasedimentary rocks post date d1 deformation and cross cut early d2 quartz monzodiorite intrusions but they were deformed and altered during d2 deformation mineralization and metamorphism they can be subdivided into three groups group 1 dykes are least altered characterized by amphibole rich regional metamorphic assemblages and distributed throughout the pontiac subprovince group 2 and 3 dykes underwent ore related hydrothermal biotite calcite pyrite alteration and are associated with density and volume adjusted concentration gains of over 100 in au w te c s ag cs mo cu k rb se u pb ba f bi sn they define a metasomatic footprint up to 6 km away from the deposit toward the se and up to 2 km away from the deposit toward the sw fifty eight variables that define halos around the canadian malartic deposit have been identified and integrated using principal component analysis pc1 explains 30 of the variance separates least mobile elements from ore related elements and is interpreted to reflect the ore forming alteration process pc2 and pc3 represent igneous processes pc4 highlights the calcite pyrite and biotite alteration spatial variations of the modal abundances of amphibole biotite calcite and pyrite are the simplest expression of the metasomatic footprint and they can easily be documented during exploration at the camp scale

the geology and mineralogy of the loulo mining district mali west africa evidence for two distinct styles of orogenic gold mineralization loulo is a world class orogenic gold mining district in the birimian terrane of western mali orebodies are located along second or higher order shears associated with the senegal mali shear zone with gold mineralization largely linked to a transtensional event the mine camp is divided into two distinct styles of gold deposit on the basis of differing geologic characteristics one group is typified by the gara deposit whereas the other by the yalea deposit both deposit styles are hosted by similar rock types calcareous graywackes and calciticdolomitic marbles gara style orebodies occur as sulfide disseminations or ankerite rich shear vein stockworks hosted in folded tourmalinized sandstones and breccias mainly within 2 km of the senegal mali shear zone these deposits are characterized by intense multi stage albitization and tourmalinization pre syn and postmineralization gold lodes are fe rich dominated by nickeloan pyrite contain cu ni co minor and trace sulfides e g chalcopyrite gersdorffite pentlandite cobaltite millerite and show consistently high levels of p ree w bearing phases apatite monazite xenotime and scheelite base metal concentrations show a marked increase in marble host rocks with the formation of nickeloan pyrite cobaltite clausthalite ores in contrast yalea style deposits are associated with quartz ankerite vein lodes and disseminated sulfide stringer zones mineralization occurs along highly altered tourmaline absent brittle ductile shears up to 8 km away from the senegal mali shear zone wall rock alteration is characterized by addition of k 2 o cao co 2 h 2 o and sio 2 with mineral assemblages consisting of chlorite sericite carbonate quartz albite ore paragenesis is enriched in as mainly as multistage growth of arsenopyrite and arsenian pyrite base metal sulfides scheelite and ree phosphates are extremely rare the diversity in the ore paragenesis is controlled by a dynamic hydrothermal system that sourced fluids and metals from different reservoirs within the region the as rich yalea style deposits have characteristics typical of birimian gold mineralization in ghana and auriferous fluids are likely derived from the dewatering of sedimentary rocks during regional metamorphism on the other hand the polymetallic fe b rich gara style orebodies show atypical features for birimian gold mineralization instead field relations and the mineralogy and geochemistry of the gara style lodes indicate a strong hydrothermal influence from surrounding intrusive stocks with possible links between gold mineralization and iron oxide skarn development in the region the data collected at loulo highlight the diverse nature of orogenic gold deposits especially in west africa this style of ore deposit can form from a variety of fluid sources both metamorphic and magmatic

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

paleoproterozoic hydrothermal reactivation in a neoarchean orogenic lode gold deposit of the southern abitibi subprovince u pb monazite geochronological evidence from the young davidson mine ontario abstract an important but poorly constrained issue for neoarchean orogenic lode gold deposits of the southern abitibi subprovince is whether they were reactivated reworked or even enriched by younger hydrothermal fluids the young davidson mine is a lode gold deposit that at least in part was structurally controlled it experienced polyphase deformation and contains multiple generations of auriferous veins four stages of veining v 1 v 4 occurred after the emplacement of the host neoarchean syenite v 1 v 3 veins formed during neoarchean time and were responsible for the major phase of gold mineralization of the young davidson deposit crosscutting v 1 v 3 veins is a distinct group of v 4 planar to en echelon carbonate quartz hematite epidote veins which also cut both of the neoarchean syenite and paleoproterozoic matachewan diabase dyke hydrothermal monazite extracted from the v 4 veins gives a 235 u 207 pb age of 1730 5 ma this represents the first paleoproterozoic age reported from neoarchean gold deposits of the southern abitibi subprovince the hydrothermal activity was most likely related to the far field 1750 1700 ma killarnean or yavapai magmatism and metamorphism event that ultimately reactivated the pre existing neoarchean structures this paleoproterozoic activity provides a new perspective for understanding neoarchean lode gold deposits of the abitibi

structural setting for canadian malartic style of gold mineralization in the pontiac subprovince south of the cadillac larder lake deformation zone quebec canada abstract the structural setting of the pontiac subprovince in the vicinity of the world class canadian malartic gold deposit has been revisited by combining and reinterpreting airborne geophysical surveys together with a century of structural observations felsic intermediate intrusive bodies are a key component of this deposit defining the regional and local favorable structural setting for intrusive rock emplacement within the clastic meta sedimentary rocks of the pontiac group south of the cadillac larder lake deformation zone may further assist gold exploration in similar tectonic environment three structural domains are interpreted in the area based on the geometry of the bedding folds and structural fabrics related to the three major phases of deformation during these events four phases of magmatism and one metamorphic episode occurred the north domain which hosts the canadian malartic deposit is characterized by highly variable bedding orientations produced by the interference patterns of isoclinal f 1 folds overprinted by open to tight steeply dipping f 2 folds the bedding in this domain is cut by a penetrative s 2 biotite foliation which possibly built on rheological changes enhanced by metasomatism in the footprint of the canadian malartic deposit by contrast the central and south domains display homogeneous bedding orientations cross cut by a discrete s 2 biotite foliation and syn to late d 2 metamorphic porphyroblasts in all domains the l 2 stretching lineation consistently plunges at about 60 degrees toward the east d 3 is a minor deformation event in the pontiac subprovince which possibly correlates with late dextral transcurrent movement along the cadillac larder lake deformation zone intrusive bodies were emplaced throughout the first and second deformation events phase 1 monzonite quartz monzodiorite and granodiorite plutons ca 2683 2680 ma intruded into consolidated pontiac sedimentary rocks during d 1 phase 2 quartz monzodiorite bodies ca 2679 2676 ma predominantly formed in the north domain along f 1 fold axial surfaces prior to or at the onset of d 2 phase 3 basic dykes ca 2675 2673 ma cross cut earlier felsic intermediate intrusions across all domains and subsequently developed an s 2 metamorphic hornblende foliation phase 4 magmatism ca 2672 2662 ma is related to the decelles batholith s type granite and pegmatite which is interpreted to be contemporaneous with the peak of regional metamorphism the decelles batholith may project at depth underneath the canadian malartic deposit and could be associated with magmatic hydrothermal mineralizing fluids in the canadian malartic deposit gold mineralization at canadian malartic is spatially located on the contact of phase 2 quartz monzodiorite bodies the proximity to the cadillac larder lake deformation zone combined with the rheological contrast between steeply dipping clastic meta sedimentary rocks and quartz monzodiorite intrusions favored the protracted failure of the contacts between these two rock masses thus forming favorable conduits for hydrothermal fluids e g the sladen fault zone such specific rheological behavior is demonstrated by domains of structural complexity emphasized by the variance of the bedding dip these structurally complex zones systematically host gold mineralization in the canadian malartic district of the pontiac subprovince proximal to the cadillac larder lake deformation zone

thermal infrared spectroscopy on feldspars successes limitations and their implications for remote sensing abstract minerals of the feldspar group are the most common on earth feldspars are economically important in two ways either as industrial minerals or as a vector to ore for mineral deposits in order to use feldspars for classifying rock compositions or metasomatic conditions during rock alteration events there is a need for analytical methods to identify and classify feldspars traditionally feldspar composition and structure have been investigated using methods such as optical microscopy electron microprobe analysis empa cathodoluminescence and x ray diffraction xrd analysis in this paper infrared techniques 0 7 25 m are reviewed in detail and investigated in how far some of the traditional analytical methods can be replaced by infrared spectroscopy successes as well as limitations of infrared approaches are highlighted and existing work is scrutinized in terms of its applicability to remote sensing techniques even though numerous studies on mid infrared mir spectroscopy of feldspars exist their results often cannot be directly related to remote sensing applications examples are the effects of feldspar twinning exsolution textures and structural state on infrared spectra the applicability of the results to emission remote sensing requires further research it has been shown that linear unmixing of laboratory infrared spectra of rocks works fairly well detection limits for feldspar are around 5 and plagioclase composition can be determined within error margins of 4 anorthite component infrared spectroscopy can however not detect compositional zonation or different generations of feldspars infrared spectra represent the current average plagioclase and average alkali feldspar composition in the sample with several new airborne instruments under development it is opportune to focus upcoming research efforts on developing standardized processing techniques and spectral feldspar indices for thermal infrared imagery commercially interesting products include numbers of feldspars species plagioclase and alkali feldspar composition their structural state and relative or semi quantitative abundance in the rocks

timing of gold mineralization at red lake northwestern ontario canada new constraints from u pb geochronology at the goldcorp high grade zone red lake mine and the madsen mine the goldcorp high grade zone at the red lake mine has reserves proven and probable established at 1 775 million tons mt at an average grade of 80 6 g t au new u pb geochronologic data combined with detailed mapping and crosscutting relationships provide timing constraints and new insights into the formation of the exceptionally rich goldcorp high grade zone the results show that the main stage of the high grade mineralization in the high grade zone formed before 2712 ma and that a second stage of gold mineralization much smaller in terms of total gold content but spectacular in terms of grade formed after 2702 ma this second stage is attributed to gold remobilization caused by the enhanced thermal gradient and deformation associated with the emplacement of the cat island pluton 2699 ma approximately 7 km east of the deposit or by the ca 2 63 to 2 66 ga postorogenic regional thermal event indicated by hornblende muscovite and biotite ar ar cooling ages from the uchi subprovince it is proposed that the main stage of high grade mineralization formed between ca 2723 to 2712 ma possibly synchronous with emplacement of the dome and mckenzie island stocks the abino granodiorite and hammell lake batholith as well as with penetrative d2 main stage regional deformation lamprophyre dikes spatially associated with the deposit postdate main stage mineralization by at least 10 m y a postore granodiorite dike from the madsen mine the second largest deposit in the district was dated at 2698 1 ma this age is similar to a postalteration and late deformation diorite dike at the creek zone showing near the former starratt olsen mine which was dated at 2696 2 ma the crosscutting relationships confirm that the main stage of mineralization at the madsen mine is pre 2698 ma a folded and metamorphosed polymictic conglomerate located stratigraphically above the campbell red lake deposit and deposited after ca 2747 but before 2712 ma is correlated with the newly recognized huston assemblage crosscutting and overprinting relationships between the conglomerate and the alteration indicate protracted multistage aluminous and iron carbonate quartz veining and or alteration event s before and after deposition of the conglomerate the age of the conglomerate confirms that the campbell red lake deposit is proximal to a folded regional unconformity consistent with the empirical relationship between large gold deposits and unconformities elsewhere in archean greenstone belts this paleosurface represents a key first order exploration target and it is proposed that areas of high potential for gold exploration in red lake occur in the balmer assemblage rocks within 500 m to 1 km of the unconformity

tellurium magmatic fluids and orogenic gold an early magmatic fluid pulse at cononish gold deposit scotland significant tellurium enrichment occurs in many orogenic gold deposits but the factors causing this are little understood some authors suggest this demands a magmatic input whereas others suggest it need not fractionation of te from se and s could offer insight into source pathway processes of auriferous fluids the metasedimentary hosted cononish vein gold deposit scotland is unusually te rich compared to many orogenic gold deposits with te au 2 4 whereas most orogenic deposits have te au 1 here ag in au ag alloy increases from 10 to 90 wt through the paragenesis correlating with decreasing hessite ag2te abundance this suggests the au ag alloy composition was controlled by the fluid te activity and that this decreased through time this is coupled to an increase in pyrite 34s from 2 0 to 11 4 through the paragenesis thus the deposit formed from a primary fluid with a low 34s and high te au ag that evolved to a high 34s low te pb cu bearing fluid the high 34s of the later fluid suggests it can only be sourced from specific nearby metamorphosed sedex horizons the early fluid that deposited most of the gold could be sourced from other metasedimentary units in the stratigraphy or be magmatic in origin we argue that two observations taken together suggest it is most likely that this fluid was magmatic the age of the mineralisation is identical to the last stage of crystallization of nearby granite batholiths and the fluid has a s isotope signature consistent with a magmatic source gold deposits in orogenic belts are almost certainly polygenetic and this study demonstrates evidence for te rich orogenic deposits having a significant magmatic component

evidence of upgrading of gold tenor in an orogenic quartz carbonate vein system by late magmatic hydrothermal fluids at the madrid deposit hope bay greenstone belt nunavut canada abstract evidence of secondary gold enrichment due to the addition of new gold into an earlier orogenic quartz carbonate vein deposit by magmatic hydrothermal fluids is strongly suggested for the madrid deposit hosted in the hope bay greenstone belt in nunavut canada the conclusion is based on an extensive in situ microanalytical protocol sem confocal raman microspectroscopy microthermometry decrepitate mound analysis la icp ms cathodoluminescence sims not previously applied to gold systems this approach was used to characterize the mineralogy and fluid inclusion systematics associated with the upgrading event mineralization comprised of only ag bearing gold electrum 89 8 at au avg n 8 is present throughout all investigated laminated and brecciated orogenic quartz veins however in high grade vein intersections where gold grades are locally elevated up to 122 g t assemblages containing tennantite tetrahedrite chalcopyrite electrum 80 7 at au avg n 15 ag pb au tellurides occur that are texturally late stage relative to electrum only mineralization subdomains of quartz coeval with this later assemblage are optically and texturally distinct from earlier orogenic quartz this late mineral assemblage is absent in all low grade vein intersections 1 g t au avg examined where only electrum is identified quartz hosted fluid inclusions h2o nacl co2 of intermediate salinity 16 7 1 2 wt nacl equiv n 93 were identified only in the high grade vein samples and are present along healed planes associated with tennantite tetrahedrite chalcopyrite electrum ag pb au telluride assemblages in situ sims 18o analyses of quartz combined with temperature constraints from mineral equilibria show that early orogenic vein quartz and late quartz subdomains associated with gold upgrading precipitated from fluids with similar 18oh2o values of 4 5 12 4 n 10 and 5 5 to 11 8 n 13 respectively isotopic data suggests that meteoric water was a negligible component in fluids responsible for gold precipitation microthermometry and raman spectroscopy show that upgrading fluids were distinct in composition compared to the earlier metamorphic fluids h2o nacl co2 ch4 n2 4 6 1 6 wt nacl equiv n 33 and later canadian shield basement brines h2o nacl 22 4 1 2 wt nacl equiv n 12 which have also been identified in the fluid inclusion record at madrid laser ablation icp ms analyses indicate the gold upgrading fluids are enriched in as sb zn pb and lile cs ba rb sr these data are consistent with late fluids derived from an evolved magmatic hydrothermal system trace element mapping of pyrite coupled with principle component analysis of the data confirms a strong correlation between au and ag te sb bi w as in upgraded veins whereas only au and as strongly correlate in low grade veins the study suggests that gold upgrading either involving newly introduced gold or remobilization of existing gold can be linked to the incursion of a late magmatic hydrothermal fluid that post dated formation of the main orogenic type auriferous quartz vein system the geological setting and mineral chemical features suggest an intrusion related i e porphyry or intermediate sulfidation epithermal mineralization style for the later event this work provides another example of the importance of compositionally distinct cumulative hydrothermal events in the development of high grade gold deposits in orogenic settings

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

dating the late cenozoic glacial sequence pieman river basin western tasmania australia abstract the pieman river basin western tasmania displays one of the most complete middle to early pleistocene glacial sequences from a southern hemisphere mid latitude site most of the glacial deposits exceed the 14 c limit although mapping of the depositional units using morphostratigraphic post depositional weathering criteria and magnetostratigraphy shows that the sediments of the boco and bobadil glaciation were deposited during the brunhes normal chron 275 kyr late last margaret glaciation advances in the pieman basin are much more restricted in extent and display evidence for multiple stillstand readvance phases during the decay of the system with most of the ice having disappeared by 14 kyr bp

metallogeny of the syenite related dongping gold deposit in the northern part of the north china craton a review and synthesis abstract the dongping gold deposit is located at the northern margin of the north china craton in hebei province china it is the largest alkaline pluton related au deposit in china the ore deposit is hosted in the 400 386 ma la icpms and shrimp zircon u pb method shuiquangou syenite intrusion which cuts archean aged metamorphic rocks the ore bodies consist of a set of en echelon lenses and veins controlled by shear zones the ores can be divided into auriferous quartz vein stockwork and disseminated ores two stages of gold mineralization can be distinguished the first stage mineralization consists of high grade 10 g t grayish quartz veins enveloped by stockwork and disseminated ores whereas the second stage mineralization occurs as low grade studies of fluid inclusions in quartz indicate that the ore forming fluids have low salinity 0 7 8 1 nacl equivalent in the h2o co2 nacl system and have homogenization temperatures varying from 310 to 350 c the ore forming fluids have 18o values varying from 1 7 to 6 9 with an average of 2 9 and d values from 108 to 66 5 with an average of 85 indicating a magmatic origin with some involvement of meteoric fluid the ore forming fluids have initial 87sr 86sr385ma ratios of 0 705 0 706 and 3he 4he ratios of 0 3 to 5 2 ra ra being the atmospheric ratio of 1 0 indicative of a mantle contribution of the fluids the ores have bulk 34s values varying from 1 to 2 similar to those of the host syenites 34s 1 8 3 and the archean metamorphic rocks 34s 0 04 to 4 4 lead isotope analyses of sulfides stock and disseminated ores quartz veins fresh host syenites and the archean metamorphic rocks have a linear correlation of 208pb 206pb and 207pb 206pb indicating a genetic link between the gold mineralization and the syenites hydrothermal zircons from the high grade ores of the first stage can be distinguished from magmatic zircons based on internal textures on cathodoluminescence images and rare earth element patterns these zircons have been dated at 389 1 0 to 385 5 7 ma whereas those from the second stage low grade auriferous quartz vein were dated at 140 ma la icpms and sim u pb methods we propose a model for the formation of the dongping gold deposit involving a late magmatic hydrothermal process related to a devonian mantle sourced syenites with a late jurassic early cretaceous hydrothermal overprint

source of ore forming fluids of the yangshan gold field western qinling orogen china evidence from microthermometry noble gas isotopes and in situ sulfur isotopes of au carrying pyrite abstract the yangshan gold ore belt contains a series of sediment hosted disseminated gold deposits in the southern subzone of the western qinling orogen the ore deposits formed in the middle devonian carbonaceous clastic carbonate sequences that underwent strong deformation and low greenschist facies regional metamorphism the shapes and distribution of the ore bodies are strictly confined by the e w trending anchanghe guanyinba thrust fault zone pyrite and arsenopyrite are the major au carrying minerals microthermometric results show that the ore forming fluids are co2 rich aqueous solutions the homogenization temperatures range from 221 to 303 5 c and salinities range from 2 0 to 7 2 wt nacl equiv these characteristics are consistent with orogenic gold deposit noble gas isotopic measurement shows that 3he 4he ratios of pyrite and quartz grains inherited from the mineralized carbonaceous phyllite ranging from 0 033 to 0 081 ra implying that the origins of ore fluids are restricted within the crustal regime the 40ar 36ar ratios range from 434 to 863 indicating 34 to 68 crust derived radiogenic 40ar in the ore fluids based on the backscattered electron bse maps of pyrite three generations i e core mantle rim are distinguished pre ore pyrite including framboidal pyrites and the cores of zoned pyrites both in the phyllite and plagiogranite dikes ore stage pyrites including the middle zones of the three zoned pyrites in the granitic dikes and the outer zones of the zoned pyrites in the phyllite post ore pyrites i e the outermost rims of the zoned pyrites in the dikes the arsenopyrite in the phyllite has similar texture to the pyrite and is regarded as the peak of the mineralization due to its highest au concentrations high spatial resolution nanosims multi elemental maps of the pyrites reveal that i gold is distributed heterogeneously as lattice bounded au in the zoned pyrites with higher au as in the middle zones and lower au as in the inner and outermost zones no nano particles of native gold was identified in pyrite ii gold mineralization occurred in a single event instead of multistage ore formation iii gold precipitation event is followed by an overgrown zone with low au and as concentrations in situ sulfur isotopes of au bearing pyrite identified two types of sulfur sources one is framboidal pyrite and the barren core of pyrite in the carbonaceous phyllite which have very negative 34s values combining au concentrations with the corresponding 34s values in the pyrites reveals that the zones with high au have lower 34s values and vice versa this coupling relation between au and s isotope has been also identified in other orogenic and carlin type gold deposits the oxidation of ore fluid is taken as the key for gold precipitation during formation of orogenic gold deposit however the oxidation of ore fluids accompanied by the escape of reduced gas e g h2s should result in high au coupled with high 34s therefore we propose that the yangshan gold deposit forms through partitioning aqueous vapor with high au as and lower 34s from a deep magma chamber under the ore field which leads to overgrowth of the pre existing pyrites based on the geological features texture of pyrite and sulfur isotopic characteristics we suggested that the yangshan gold deposits have the characteristics between carlin type and orogenic gold deposits they are the product of the western qinling orogeny during the late triassic

lithogeochemical and stratigraphic controls on gold mineralization within the metavolcanic rocks of the hoyle pond mine timmins ontario the hoyle pond gold deposit is hosted in complexly deformed mafic ultramafic volcanic rocks of the hersey lake and central formations tisdale assemblage in the porcupine gold camp located approximately 15 km northeast of timmins in the abitibi greenstone belt the deposit is hosted within a homoclinal sequence of south facing stacked volcanic flows of high mg tholeiitic basalt basaltic komatiite and komatiite flows and interbedded high mg tholeiitic basalt and fe rich tholeiitic basalts the bulk of the gold mineralization was emplaced at lithologic contacts along late shear zones associated with isoclinal folding and thrusting the mineralization is characterized by micron to centimeter sized flakes of free gold or veinlets in quartz carbonate dolomite and ferroan dolomite shear and extension vein arrays at the mine scale a broad carbonate alteration is evident two alteration zones surrounding the veins were mapped at the meter scale an inner sericite alteration zone composed of sericite muscovite fuchsite cr muscovite quartz arsenopyrite pyrite ferroan dolomite dolomite and graphite plus tourmaline and an outer zone of albite alteration consisting of albite quartz ferroan dolomite and dolomite geochemical analyses of 355 samples show that the ree zr al2o3 tio2 and y were largely immobile during alteration and mineralization co2 k2o na2o cr2o3 rb as b sio2 and cao and locally fe2o3 feo and mgo were mobile during alteration and mineralization the chromium enrichment is not primary and is interpreted to have been caused by remobilization from ultramafic rocks during mineralization in addition an intense graphite alteration originally derived from organic matter probably from sedimentary rocks and now associated with mineralization is present in zones that were porous and permeable at the time of mineralization in common with other mesozonal orogenic gold deposits gold was likely transported as a thio complex the cr enrichment in the wall rock indicates that cr was mobile most likely as cr6 because species such as cr6 are transported under oxidizing conditions and carbon and au hs species are transported under reduced conditions we suggest that more than one fluid was involved in the mineralization and or alteration mixing between reducing and oxidizing fluids is thought to have reduced cr6 to cr3 oxidized the organic matter to form graphite oxidized sulfur to form sulfides and precipitated au this is consistent with the observed para genesis reducing fluids rich in boron arsenic carbon and au may have been generated from sedimentary rocks porcupine assemblage at depth and expelled during orogenesis into syndeformation structures within overlying volcanic rocks where they mixed with oxidizing fluids containing cr k2o sio2 na2o and cao

new u pb geochronology from timiskaming type assemblages in the shebandowan and vermilion greenstone belts wawa subprovince superior craton implications for the neoarchean development of the southwestern superior province abstract timiskaming type assemblages in the wawa abitibi terrane of the superior craton and other archean cratons worldwide are important because of their spatial and temporal association with world class orogenic gold mineralization especially in the kirkland lake area of ontario these mainly locally derived sedimentary assemblages are deposited in transpressional pull apart basins that developed during the final stages of terrane accretion and are commonly associated with calc alkalic to alkalic volcanic and plutonic rocks the shebandowan and vermilion greenstone belts sgb vgb in the wawa subprovince have significantly less economic base and precious metal mineralization than the greenstone belts of the abitibi subprovince and the timing of deformation and magmatism in the sgb and vgb is less well constrained this study presents new u pb geochronology from the sgb and vgb that demonstrating that the sedimentary and volcanic rocks of the lake vermilion formation in the vgb are coeval with similar rocks in the sgb and their interpreted depositional environment are consistent with these units being timiskaming type assemblages analyses of magmatic zircons in a dacitic tuff breccia from the gafvert lake sequence the volcanic member of the lake vermilion formation provided a high precision u pb age of 2689 7 0 8 ma using thermal ionization mass spectrometry detrital zircon geochronology using la icp ms confirms that the source of the detritus in the lake vermilion formation was locally derived from the gafvert lake metavolcanic lithofacies a similar temporal pattern was observed in many of the timiskaming type sedimentary rocks that were sampled in the sgb the locally derived alluvial fluvial to shallow marine depositional environment in long narrow basins with rapid lateral facies changes described in the sgb and vgb are consistent with deposition in structurally controlled pull apart basins however one sample from the sgb had detrital zircons with ages that were more akin to the age range found to the north in the wabigoon subprovince which is suggestive of trans terrane transport of detritus in a foreland type basin geochemically the timiskaming type volcanic rocks in the vgb and sgb are less enriched in incompatible elements and are comparatively less alkalic than the volcanic rocks in the timiskaming assemblage of kirkland lake this may indicate that the structures that formed the basins within the sgb and vgb in the wawa were not as deeply penetrating as those in the abitibi which may explain the paucity of economic gold mineralization associated with the former the timiskaming type deposits of the northern wawa abitibi terrane are 20 ma older than the timiskaming assemblage in the abitibi subprovince and co depositional with the flysch like deposits of the porcupine assemblage in the southern part of that terrane

hydrothermal alteration mineralogy and geochemistry of the archean world class canadian malartic disseminated stockwork gold deposit southern abitibi greenstone belt quebec canada

geochemical and mineralogical diagnosis on gold ores a case study from the cadillac larder lake fault zone abitibi canada abstract numerous orogenic gold deposits have been discovered within the archean abitibi greenstone belt of canada these include the francoeur wasamac astoria zulapa goldex lamaque lac herbin and beaufor deposits all of which are located within the cadillac larder lake fault zone cllfz these gold deposits are hosted by various lithologies and vary in terms of style of mineralization sulfide abundance and hydrothermal alteration these variations mean that exploration for new deposits has been difficult in this area using common exploration criteria this study presents the results of a principal component analysis pca based approach combining geochemical and mineralogical data to quickly identify different types of gold mineralization within the cllfz including assessing the use of this approach in mineral exploration the first principal components in both classification methods used during this study pce1 and pcm1 representing element geochemical and mineralogical classification respectively can efficiently discriminate between mineralization and barren altered rocks the second principal components pce2 and pcm2 can be used to constrain the host rocks altered vs barren and style of mineralization disseminated vs vein hosted respectively finally pce3 and pcm3 give more detailed information on the nature of the mineralization in an area possible reflecting variations in the composition of ore forming fluids all of the above indicates that the two pce and pcm classification methods are complementary which means that using approaches that combine these methods will provide a comprehensive understanding of the nature of studied samples and or deposits information extracted from the results of the pca undertaken during this study may be beneficial for mineral exploration in unknown districts such as glaciated areas where traditional geological fieldwork is challenging this study also defines element and mineral mineralization indices based on pce1 and pcm1 which enables evaluation of the extent and style of gold mineralization in an area this study indicates that pca based automated mineralogical and geochemical classification methods could be highly useful in exploration for gold deposits

granulite hosted gold tectonic setting and lithogeochemistry of the tropicana deposit western australia the tropicana gold deposit 7 9 moz is hosted by the neoarchean amphibolite to granulite grade tropicana gneiss these rocks form part of the plumridge terrane a tectonic unit that separates the in situ eastern margin of the yilgarn craton from proterozoic elements of the albany fraser orogen western australia the gneissic host package to the orebody originally constituted a suite of medium to high k calc alkaline and adakitic basaltic to rhyolitic lavas emplaced in a relatively thick crustal continental margin arc amphibolitized mafic intrusions have back arc basin basalt like compositions consistent with their having formed during extension and incipient rifting of the arc gold mineralization occurs mainly within a sheet like syenitic gneiss that ranges compositionally from basaltic andesite to rhyolite and derived through metasomatism of compositionally equivalent lavas within an interpreted shear zone coarse perthite textures in microcline ruffle exsolution in brown biotite and occasional pyrite inclusions away from fractures in microcline porphyroblasts indicate that this shear zone predated peak metamorphism relative to the unmineralized host gneisses the mineralized syenitic gneisses show significant enrichments in s and the ore elements mo te tl ag au w and occasionally bi and sb but not as cu or zn in the k group elements and also in p light rare earth elements lree th u zr and hf depletions in most major elements si ti fe mg and ca as well as v cr ni and co are considered to reflect dissolution of relatively low volume mafic phases hornblende augite fe ti oxides and plagioclase in the protoliths some of the distinctive enrichments p lree zr hf are linked to volume loss in excess of 50 associated with dissolution of silica and concentration of insoluble apatite and zircon in the mineralized unit but the ore elements and strongly enriched similar to x10 th and u were added from the hydrothermal fluids involved exhumation of the tropicana gneiss into the upper crust was accompanied by fluid ingress and retrogression this produced mm to cm scale wavy biotite pyrite shears solution seams and disseminations throughout the syenitic gneiss which were further retrogressed to sericite chlorite assemblages in places both of which host most of the gold in the deposit thus although the present deportment of gold is unambiguously associated with the postpeak metamorphic greenschist grade retrogression at ca 2520 ma there is compelling evidence that the paucity of quartz and carbonate veining atypical element enrichments and sheet like nature of the tropicana deposit in part reflect metasomatism associated with a prepeak metamorphic relatively deep shear zone at present we have no direct evidence for the timing of introduction of gold and a protracted history of gold precipitation redistribution and enrichment is implied

a critical assessment of neoarchean plume only geodynamics evidence from the superior province abstract criticisms of archean plate tectonic models rarely offer detailed descriptions of alternative paradigms the catalytic delamination driven model for the coupled genesis of archean crust and sub continental lithospheric mantle described by bedard 2006 is an exception in that a relatively comprehensive but essentially 2 d model is described although this novel model is frequently cited as an example of the diversity in geodynamic thought for the archean it is rarely assessed with reference to events in a specific craton such as the superior province or a particular greenstone belt such as the abitibi when this type of assessment is undertaken it becomes clear that the apparent simplicity of the model one of its supposed virtues constitutes a critical weakness although bedard 2006 developed the catalytic model to overcome the perceived melt productivity deficit of archean plate tectonic models the catalytic process at the heart of the model is likely to be inefficient and provides insignificant improvements to crustal generation rates associated with subduction and non catalytic plume tectonics the model implies a near global craton in the mesoarchean to neoarchean but fails to address that fate of this craton during and after crustal rigidification seismic reflectors observed beneath archean cratons are characterized as failed delamination features but their global abundance suggests that syn to post tectonic ttg suites could not have been generated as a result of crustal restite delamination the brief descriptions of suggested mechanisms for the generation of minor rock types such as sanukitoids mask the complexity inherent in the overall model when considered in terms of the evolution of the superior province as a whole it is evident that many of these suggestions are not only implausible they are inconsistent with the timing and distribution of geological criteria used to mark the onset of crustal rigidification

the timmins porcupine gold camp ontario anatomy of an archean greenstone belt and ontogeny of gold mineralization new structural and geochronological data and interpretations from the timmins porcupine gold camp abitibi subprovince more precisely define the stratigraphy and the generation timing and effects of deformation tisdale basalts and porcupine volcaniclastic and turbiditic sedimentary rocks assemblage rocks exhibit three major foliations s2 s3 s4 plus a late constrictional fabric of which s3 and s4 are also present in younger timiskaming assemblage sedimentary rocks pre timiskaming folding has long been recognized in tisdale assemblage rocks but no foliation had previously been attributed to such an event d1 regional uplift and extension produced a low angle unconformity between the tisdale and porcupine assemblages with partial excision of upper tisdale stratigraphy and perhaps of the blake river assemblage d2 involved imbrication of a set of south over north thrust sheets rooted in the porcupine destor deformation zone d3 en echelon folds along the northern flank of the porcupine destor deformation zone are a result of left lateral strike slip along this zone the timiskaming basin lying along the curvilinear trace of the porcupine destor deformation zone formed as a d3 transtensional half graben and the dome fault formed its faulted margin s4 foliation formed during subsequent right lateral strike slip movement and folding of s3 foliation intense d5 constrictional strain deformed earlier lineations as the previously dilatational jog that hosts timiskaming assemblage rocks acted as a compressional jog during right lateral movement along the porcupine destor deformation zone these d2 to d5 phases represent an overall thrusting strike slip transpressional regime there were several phases of gold mineralization in the timmins porcupine gold camp clasts of ankerite veins occur in timiskaming assemblage conglomerate at the dome mine and d3 foliation and folds crosscut early ankerite veining and alteration and some quartz veining thus low grade mineralization and possibly the quartz fuchsite veins predate timiskaming sedimentation however the bulk of gold postdates timiskaming sedimentation quartz carbonate tourmaline gold veins hollinger mcintyre hoyle pond dome aunor delnite mines formed within timiskaming assemblage and tisdale assemblage rocks these gold deposits developed largely as oblique slip and extensional vein arrays formed during north south shortening and local strike slip faulting younger deposits pamour are associated with d4 dip slip faulting and were weakly deformed during late d4 thus the largest known archean lode gold camp formed throughout protracted orogenesis consisting of a broadly transpressional regime with unusually well developed early thrusting

the use of lithogeochemistry in delineating hydrothermal fluid pathways and vectoring towards gold mineralization in the malartic district quebec abstract the world class oxidized intrusion related canadian malartic gold deposit with reserves estimated at 5 56 moz au grading 1 10 g t au and a total geological endowment of 16 3 moz au is one of the largest gold deposits in the archean superior province of canada the gold mineralization is hosted predominantly by pontiac group metasedimentary rocks piche group metavolcanic rocks and quartz monzodiorite to granodiorite porphyritic intrusions the ore takes the form of a low grade envelope of disseminated pyrite 0 35 to 1 g t au grading inwards into higher grade 1 g t au stockwork and breccia zones hydrothermal alteration in the metasedimentary rocks is zonally distributed around the fluid pathways proximal alteration is characterized by a microcline albite quartz replacement type assemblage with lesser phlogopite calcite fe dolomite pyrite and rutile the distal alteration assemblage comprises biotite microcline albite phengite quartz calcite pyrite and rutile in this study we assess the magnitude and distribution of fluid rock interaction in the metasedimentary rocks of the malartic district the metaturbidites are separated into four lithotypes based on grain size to reduce the effects of primary depositional processes on mass change calculations despite the variability in protolith composition the metasedimentary rocks define a geochemically consistent cogenetic sequence the results of the mass transfer calculations indicate progressive gains in co2 s k2o and loi as well as au te w ag as be sb bi mo and pb from background to distal and proximal alteration zones relative to the least altered samples molar element ratio analysis alkali aluminum indicates an increase in alkali metasomatism k and na adjacent to the main hydrothermal fluid pathways which is manifested by the progressive stabilization of microcline and albite at the expense of oligoclase biotite and white mica ore associated pathfinder elements delineate broad enrichment patterns around the deposit and are used to understand hydrothermal fluid circulation in the malartic district a statistical approach based on a comparison of the mass change results with the background composition provides robust constraints on the magnitude and extent of the lithogeochemical haloes generally the alteration forms envelopes that extend along the s2 fabric with the largest lithogeochemical anomalies e g au w te and ag reaching up to 10 km in length and 2 km in width the results of this study demonstrate that whole rock lithogeochemistry can provide a valuable tool with which to define vectors toward gold mineralization in a regional exploration context

nature of ore forming fluid and formation conditions of bif hosted gold mineralization in the archean amalia greenstone belt south africa constraints from fluid inclusion and stable isotope studies abstract orogenic gold mineralization in the amalia greenstone belt is hosted by oxide facies banded iron formation bif hydrothermal alteration of the bif layers is characterized by chloritization carbonatization hematization and pyritization and quartz carbonate veins that cut across the layers the alteration mineral assemblages consist of ankerite ferroan dolomite minerals siderite chlorite hematite pyrite and subordinate amounts of arsenopyrite and chalcopyrite information on the physico chemical properties of the ore forming fluids and ambient conditions that promoted gold mineralization at amalia were deduced from sulfur oxygen and carbon isotopic ratios and fluid inclusions from quartz carbonate samples associated with the gold mineralization microthermometric and laser raman analyses indicated that the ore forming fluid was composed of low salinity h 2 o co 2 composition 3 wt nacl equiv the combination of microthermometric data and arsenopyrite pyrite geothermometry suggest that quartz carbonate vein formation gold mineralization and associated alteration of the proximal bif wall rock occurred at temperature pressure conditions of 300 30 c and 2 kbar thermodynamic calculations at 300 c suggest an increase in f o 2 10 32 10 30 bars and corresponding decrease in total sulfur concentration 0 002 0 001 m that overlapped the pyrite hematite magnetite boundary during gold mineralization although hematite in the alteration assemblage indicate oxidizing conditions at the deposit site the calculated low f o 2 values are consistent with previously determined high fe fe mg ratios 0 7 in associated chlorite absence of sulfates and restricted positive 34 s values in associated pyrite based on the fluid composition metal association and physico chemical conditions reported in the current study it is confirmed that gold in the amalia fluid was transported as reduced bisulfide complexes e g au hs 2 at amalia gold deposition was most likely a combined effect of increase in f o 2 corresponding to the magnetite hematite buffer and reduction in total sulfur contents due to sulfide precipitation during progressive fluid rock interaction the epigenetic features coupled with the isotopic compositions of the ore forming fluid 34 s s 1 8 to 2 3 18 o h2o 6 6 to 7 9 and 13 c c 6 0 to 7 7 at 300 330 c are consistent with an externally deep sourced fluid of igneous signature or and prograde metamorphism of mantle derived rocks

examining the controls on gold deposit distribution in the swayze greenstone belt ontario canada using multi scale methods of spatial data analysis abstract understanding the spatial controls on mineral deposits is crucial in mineral exploration targeting this paper uses a combination of spatial data analysis techniques such as the distance distribution method fry nearest neighbor index ripley s k function multi distance fractal and kernel density analysis to better define controls on the distribution of gold deposits in the swayze greenstone belt ontario canada according to results obtained with the distance distribution method d2 structures were critical in controlling the spatial distribution of the gold mineralization with 97 of the gold deposits occurring within 7 km of these structures and 65 within 4 km fry analysis confirmed this spatial relationship with a close agreement between the orientations of the d2 structures and gold deposit alignment the outcome of ripley s k function cluster analysis suggests that gold deposits occur within 4 km distances of other gold deposits these findings are consistent with the results from the fractal analysis showing that gold deposit distribution is bifractal and that different geological features occurred at local 8 km scales we conclude that higher order d2 structures and lower order faults connected to the d2 structures acted as pathways to focus gold bearing hydrothermal fluids thus leading to the observed concentration and distribution of gold deposits at the regional to local scales

structural and stratigraphic controls on magmatic volcanogenic and shear zone hosted mineralization in the chapais chibougamau mining camp northeastern abitibi canada the structure and stratigraphy of the chapais chibougamau mining camp in the archean abitibi greenstone belt of the superior craton quebec canada is reevaluated from new aeromagnetic data geochronology and field studies to provide a framework for syngenetic and epigenetic mineralization mineralization in the chapais chibougamau area is synvolcanic volcanogenic massive sulfide vms synmagmatic fe ti v ni cu au ag cu zn pb veins chibougamau type cu au veins and shear zone hosted including opemiska cu au veins subtype vms deposits occur within felsic volcanic rocks of tholeiitic affinity and mafic to felsic volcanic rocks of transitional to calc alkaline affinity at the top of three volcanic cycles of the roy group vms deposits and early polymetallic veins au ag cu zn pb are associated with nnw to nne striking synvolcanic faults fe ti v deposits occur within the layered zone of the lac dore complex especially where it thickens in areas of interpreted synmagmatic faults subeconomic magmatic ni cu deposits occur at the contacts of mafic ultramafic or tonalitic intrusions chibougamau type cu au veins formed through magmatic hydrothermal processes they are cut by dikes that predate regional d2 deformation but are located within and are deformed by nw and ne trending d2 shear zones shear zone hosted au deposits are developed preferentially within regional e w trending deformation corridors and along nne striking sinistral shear zones while opemiska type cu au veins occur within regional overturned anticlines in mafic sills of the cummings complex u pb dating of detrital zircons provides maximum depositional ages for metasedimentary rocks of the blondeau formation of the roy group and the stella formation of the opemisca group which unconformably overlies the roy group the blondeau formation is 2721 3 ma which is coeval to the age of the windfall member in the urban barry belt both show similar exploration potential as they host early polymetallic au ag cu zn pb veins the stella formation is 2704 2 ma and is unaffected by first generation folds thus providing a time constraint for the earliest folding event d1 this new age also indicates that sedimentation in the chapais chibougamau area occurred earlier than for the timiskaming type assemblages in the southern abitibi greenstone belt but the structural setting and presence of alkaline intrusions suggests similar potential for syenite associated au deposits in the stella formation

hydrothermal alteration and ore forming fluids associated with gold tellurium mineralization in the dongping gold deposit china abstract the dongping gold deposit hosted in syenites is one of the largest hydrothermal gold deposits in china and composed of ore veins in the upper parts and altered zones in the lower parts of the ore bodies pervasive potassic alteration and silicification overprint the wall rocks of the ore deposit the alteration minerals include orthoclase microcline perthite quartz sericite epidote calcite hematite and pyrite with the quartz pyrite and hematite assemblages closely associated with gold mineralization the phases of hydrothermal alteration include i potassic alteration ii potassic alteration silicification iii silicification epidotization hematitization iv silicification sericitization pyritization and v carbonation mass balance calculations in potassic altered and silicified rocks reveal the gain of k2o na2o sio2 hfses and transition elements tes and the loss of rees most major elements were affected by intense mineral reactions and the ree patterns of the ore are consistent with those of the syenites gold silver and tellurium show positive correlation and close association with silicification fluid inclusion homogenization temperatures in quartz veins range from 154 c to 382 c peak at 275 c 325 c with salinities of 4 9 wt nacl equiv at temperatures of 325 c the fluid is estimated to have ph 3 70 5 86 log fo2 32 4 to 28 1 with au and te transported as au hs 2 and te22 complexes the ore forming fluids evolved from high ph and fo2 at moderate temperatures into moderate low ph low fo2 and low temperature conditions the fineness of the precipitated native gold and the contents of the oxide minerals e g magnetite and hematite decreased followed by precipitation of au and ag bearing tellurides the hydrothermal system was derived from an alkaline magma and the deposit is defined as an alkaline rock hosted hydrothermal gold deposit

deformation history of the kunavaram complex eastern ghats belt india implications for alkaline magmatism along the indo antarctica suture abstract the kunavaram alkaline complex is a ne sw trending elongate body located along a major lineament the sileru shear zone ssz that is regarded as a proterozoic suture related to indo antarctica collision the complex is hosted within migmatitic quartzofeldspathic gneisses mafic granulites retrogressed to amphibolites and quartzites the structural evolution of the country rocks and the alkaline complex are similar the first phase of deformation d1 produces a pervasive segregation banding s1 in all rock units within and outside the complex a second deformation phase d2 isoclinally folded s1 along subvertical axial planes with shallow plunging axes f2 isoclinal folds are ubiquitous in the country rocks and the eastern extremity of the complex in the interior of the alkaline body d2 strain decreases and s1 is commonly subhorizontal while amphibolite to granulite facies conditions prevailed during deformation post d2 annealing textures testify to persisting high grade conditions in the west a nne ssw trending dextral shear zone with strike slip sense d3 truncates the complex within this shear zone quartzofeldspathic country rocks are plastically deformed while hornblende k feldspar assemblages of the complex are retrogressed to biotite and plagioclase warping related to d3 shears also resulted in fold interference patterns on the subhorizontal s1 foliation in low d2 strain domains based on its steep dip north easterly trend and non coaxial nature with dextral strike slip sense the d3 shear zone can be correlated with the ssz since this shear zone i e the ssz is not associated with primary igneous fabrics and resulted in solid state deformation of the complex it cannot be considered as a conduit for alkaline magmatism but is probably responsible for the post tectonic disposition of the pluton

signatures of multiple mineralization processes in the archean orogenic gold deposit of the pampalo mine hattu schist belt eastern finland the hattu schist belt is an emerging gold producing ore district in the western part of the archean karelian province of the fennoscandian shield the belt consists of 2 76 to 2 70 ga tonalite granodiorite and leucogranite intruded into a mafic felsic epiclastic volcanic sequence of an only slightly older age complex and successive folding shearing and hydrothermal processes affected these rocks prior to the lower amphibolites facies peak metamorphism 550 50 c 3 5 kbar at ca 2 70 ga orogenic gold deposits are hosted by the highly strained zones that developed during the archean deformation of the belt however previous k ar and rb sr geochronological studies indicated that a second tectonothermal overprint affected the hattu schist belt between 1 7 and 1 8 ga during the svecofennian orogeny results of our field mineralogical textural and pb isotope studies suggest that ore deposition at pampalo was initiated by hydrothermal processes at the time of the emplacement of feldspar porphyry and tonalite intrusions and dikes at around 2 72 ga albitization and quartz tourmaline biotite muscovite veining characterize this hydrothermal activity the major stage of gold ore deposition can be confined to the subsequent development of high strain zones in an intermediate felsic tuffaceous unit mafic schist characterized by biotite carbonate pyrite alteration ar ar studies revealed the complete resetting of the ar ar system in muscovite and biotite due to the svecofennian orogeny with closure of the isotopic system at 1 81 ga results of pb isotope studies of hydrothermal k feldspar galena and altaite by laser ablation inductively coupled plasma mass spectrometry indicate that k feldspar alteration and remobilization of metals also took place during the svecofennian reactivation of high strain zones the petrographic manifestation of this process is the replacement of albite by hydrothermal k feldspar fluid inclusion data from hydrothermal k feldspar suggest that carbonic aqueous low salinity fluids interacted with the archean ore at 350 to 400 c and 1 8 to 2 4 kbar during the svecofennian overprint results of mass transfer calculations indicate that potassium gain correlates with increase of gold concentrations in the mafic schist and feldspar porphyry units therefore the svecofennian overprint locally also enhanced the grade of gold mineralization mostly along competency differences of the mafic schist and feldspar porphyry blocks dikes later percolation of relatively low temperature 300 c saline basin fluids in some fractures of the crystalline basement also left their pb isotope and fluid inclusion signatures on the mineralization while further modifying the composition of the ore occurrences of hydrothermal proto ores as well as fluid flow events along structures reactivated by overprinting orogenic processes are not exceptional features in archean orogenic gold provinces this study shows that the combination of in situ pb isotope studies of u poor alteration minerals and pb rich ore minerals together with evaluation of relationships between gold enrichment and hydrothermal alteration and fluid inclusion studies can be very useful in determining the significance and conditions of overprinting processes as well as their potential implications for genetic and exploration models

geologic and structural setting of gold mineralization in the kirkland lake larder lake gold belt ontario the kirkland lake larder lake gold belt includes the giant kirkland lake and world class kerr addison chesterville gold deposits along with several smaller deposits and occurrences it corresponds to an east trending band of timiskaming clastic and volcanic rocks that unconformably overlie older volcanic assemblages in the southern abitibi greenstone belt of the archean superior province the gold belt is bounded to the south by the larder lake cadillac deformation zone which roughly follows the contact between the younger timiskaming rocks and the older volcanic units three generations of fabrics formed during post timiskaming regional deformation d2 d3 and d4 of the belt north south shortening during d2 produced a penetrative generally east striking steeply dipping s2 foliation and an east plunging l2 stretching lineation s2 is most intense within the syn d2 larder lake cadillac deformation zone and its northeast trending splay the upper canada deformation zone the d2 structures are overprinted by a north trending crenulation cleavage s3 which formed during east west d3 shortening across the belt a northeast trending regional s4 foliation associated with z shaped f4 folds and overprinting both s2 and s3 formed during northwest southeast d4 shortening gold mineralization is localized along the larder lake cadillac deformation zone anoki and mcbean deposits the upper canada deformation zone upper canada deposit and the brittle kirkland lake fault and 04 break kirkland lake deposit the upper canada mcbean and anoki deposits formed during d2 and along with kerr addison chesterville omega and cheminis deposits are probably related to a regionally extensive hydrothermal system associated with the larder lake cadillac deformation zone the sulfide poor gold and telluride bearing quartz veins of the kirkland lake deposit are interpreted to have been emplaced during d4 synchronous with reverse dextral movement along the ore controlling brittle kirkland lake fault the kirkland lake mineralization has a distinct metal signature te au mo pb ag high au ag low as and probably represents a separate hydrothermal system linked to a deep magmatic alkalic fluid source and unrelated to mineralization along the syn d2 deformation zones

granitoid associated orogenic intrusion related and porphyry style metal deposits in the archean yilgarn craton western australia abstract the yilgarn craton hosts three types of archean granitoid associated metallogenic systems orogenic gold intrusion related and porphyry systems these systems may occur in the same terrane and share many broad characteristics including spatial coincidence with granitoids gangue silicate mineralogy metal associations and local structural controls features of archean orogenic gold systems spatially associated with granitoids include i a broad range of granitoid host compositions ii gold mineralization is mostly late with respect to yilgarn wide granitoid emplacement peak metamorphism and deformation iii orebodies are structurally controlled and iv gold deposition occurs over a large range of temperatures pressures and crustal depths 2 to 15 km from a co 2 rich low to moderate salinity reduced ore fluid that was derived from a metamorphic and or distal magmatic fluid source these systems do not display deposit scale vertical or lateral zonation of metals away from granitoid contacts host granitoid age composition or oxidation state are not important in controlling gold mineralization processes whereas structural setting and fluid flux are paramount archean intrusion related au mo w and mo au systems in the yilgarn craton are commonly small 2 bearing moderate to high salinity fluid during ore deposition archean porphyry cu mo au cu mo and cu au systems are spatially and temporally associated with volumetrically small pervasively altered felsic plutons and dikes surrounded by altered and mineralized supracrustal countryrock lateral zonation of metals away from porphyry centers commonly includes a decrease in cu au and ag au ratios with distance from the source pluton microthermometry studies on fluid inclusions in gold bearing veins suggest that early ore fluids were high temperature and high salinity and that mineralization occurred at 2 o 3 feo are demonstrated in phanerozoic terranes but are presently ill defined in the yilgarn craton crustal depth estimation is important in defining areas likely to have preserve shallow forming archean porphyry systems