contrasting arc and morb like assemblages in the paleoproterozoic flin flon belt manitoba and the role of intra arc extension in localizing volcanic hosted massive sulphide deposits the flin flon belt trans hudson orogen manitoba and saskatchewan is the largest paleoproterozoic volcanic hosted massive sulphide vms district in the world with 118 7 million tonnes mt of z

petrology and geochemistry of lavas from the sumisu and torishima backarc rifts thirteen dredge hauls from the active sumisu and torishima rift grabens west of the izu bonin arc at about 30 31 n 140 e recovered a suite of tholeiitic basalts to sodic rhyolites volcanism occurs along tensional faults within and bounding the rift grabens and along the transfer zones between adjoining rift segments the sumisu and torishima rift lavas differ significantly from the lavas of the adjacent arc volcanic centers in having loweral2o3 na2o ba zr v ti andba ce and higher abundances of the rare earth elements the rift lavas also have characteristics of backarc basin basalts in that they are enriched in al2o3 and depleted in total iron and tio2 relative to mid ocean ridge basalt characteristics which are consistent with a higher water content in the source thus the model of a progressive change in backarc basin basalt composition from arc like to mid ocean ridge like as a function of evolution of the basin as has been suggested from many backarc regions is not generally applicable the comparison of the sumisu and torishima rift lavas with mariana backarc basin lavas indicates that backarc basin basalts differ in composition from one basin to another the comparison of these backarc basin suites with mid ocean ridge suites from similar axial depths indicates that the overall control over the spectrum of backarc basin basalt compositions may be different extents of melting of the mantle the sumisu and torishima rift lavas formed by a slightly higher extent of melting than the mariana backarc basin basalts a phenomenon which is related to the depth of the ridge segments furthermore the data suggest a systematically higher extent of melting in the arc lavas than in the backarc lavas for both of these arc backarc systems consistent with a greater flux of water beneath the arc than beneath the backarc region

silicification and metal leaching in semiconformable alteration beneath the chisel lake massive sulfide deposit snow lake manitoba regionally extensive semiconformable zones of silicified fe mg metasomatized and epidotized dominantly mafic volcaniclastic strata and lava flows are exposed 1 to 2 km stratigraphically beneath the chisel lake zn cu massive sulfide deposit snow lake district manitoba the alteration zones occur within a lower proterozoic medium grade regional metamorphic terrane of felsic and mafic volcanics and marine sediments and lie between subvolcanic tonalite sills and the massive sulfide deposit semiconformable alteration occurs at two main stratigraphic positions the lower zone of silicification in pillowed and massive mafic lavas is inferred to have occurred close to the sea floor and probably was not related directly to formation of the chisel lake massive sulfide deposit the stratigraphically higher zone which may be spatially and temporally associated with massive sulfide deposition occurs in a approximately 300 m thick heterolithic mafic volcanic breccia and wacke unit this volcaniclastic hosted alteration is zoned laterally from dominantly silicification and epidotization to mainly fe mg metasomatized garnet chlorite or biotite or staurolite rocks nearer the chisel lake sulfide deposit a discordant footwall fe mg alteration zone directly beneath the sulfide deposit extends toward and may meet the semiconformable fe mg metasomatized zone silicification contributed to partial to complete replacement of volcanic clasts beds in the volcaniclastic unit rocks adjacent to some felsic dikes and pillow interiors by quartz and sodic plagioclase mass balance calculations for silicified rocks and equivalent least altered parts of volcaniclastic beds dikes and pillows indicate that sio 2 increased by up to 50 percent of its initial value and na 2 o by up to 30 percent up to 80 percent of the feo mgo cao and zn was removed during silicification elemental fluxes during fe mg metasomatism are generally opposite those characterizing silicification and are of comparable magnitude epidotization resulted in depletion of na total fe but increased the fe super 2 fe super 3 ratio mg mn k zn and ba and enrichment in ca and sr relative to least altered rocks almost constant interelement ratios of ti zr and al in altered and less altered rocks indicate that these elements were essentially immobile during metasomatism and subsequent medium grade regional metamorphisrm limited data suggest that the heavy ree were also immobile during silicification the subconcordant silicification in the mafic volcaniclastic unit is interpreted to have formed at subsea floor depths of 1 to 2 km where a felsic dike swarm and subvolcanic tonalite sills heated si rich evolved seawater above the temperature of the silica solubility maximum approximately 340 degrees 450 degrees c at pressures below 900 bars causing silica deposition and metal leaching a portion of the fe mg and possibly zn that was leached from the subconcordant silicified zone may have been transported laterally away from this environment thereby producing the semiconformable fe mg metasomatized zones cross stratal structures similar to the hydrothermally altered synvolcanic faults that are known to cut the semiconformable alteration may represent fluid flow paths from a subconcordant metal reservoir in the volcaniclastic unit to the sea floor where massive sulfides were deposited semiconformable pervasively silicified zones particularly those associated with fe mg metasomatized and or epidotized rocks are significantly larger exploration targets than areas of proximal alteration and indicate large scale hydrothermal mass transfer zonation of silicification to fe mg metasomatism laterally within the alteration may provide a vector toward the discordant fe mg enriched alteration zones that commonly underlie volcanic associated massive sulfide deposits

rapid extension in an eocene volcanic arc structure and paleogeography of an intra arc half graben in central idaho a study of extension volcanism and sedimentation in the middle eocene panther creek half graben in central idaho shows that it formed rapidly during an episode of voluminous volcanism the east southeast tilted panther creek half graben developed across the northeast edge of the largest cauldron complex of the challis volcanic field and along the northeast trending trans challis fault zone two normal fault systems bound the east side of the half graben one fault system strikes northeast parallel to the trans challis fault zone and the other strikes north to northwest the geometry of the basin fill deposits shows that movement on these two normal fault systems was synchronous and that both faults controlled the development of the panther creek half graben strikes of the synextension volcanic and sedimentary rocks are similar throughout the half graben whereas dips decrease incrementally upsection from as much as 60 to less than 10 previous k ar dates and a new 40 ar 39 ar plateau date from the youngest widespread tuff in the basin suggest that most of basin formation spanned 3 m y between about 47 7 ma and 44 5 ma as much as 6 5 km of volcanic and sedimentary rocks were deposited during that time although rates of extension and subsidence were very high intense volcanic activity continually filled the basin with ash flow tuffs outpacing subsidence and sedimentation until the end of basin development after the abrupt end of challis volcanism locally derived pebble to boulder conglomerate and massive reworked ash accumulated in the half graben these sedimentary rocks make up a small part of the basin fill in the panther creek half graben and were derived mainly from proterozoic metasedimentary rocks uplifted in the footwall of the basin the east southeast tilt of the sedimentary rocks their provenance and coarse grain size and the presence of a gravity slide block derived from tilted volcanic rocks in the hanging wall attest to continued tectonism during conglomerate deposition provenance data from the sedimentary rocks imply that the highland in the footwall of the panther creek half graben was never thickly blanketed by synextension volcanic rocks despite intense volcanic activity analysis of the panther creek half graben and other intra arc rift basins supports previous interpretations that relative rates of volcanism and subsidence control the proportion of volcanic rocks deposited in intra arc rifts

the rare earth element ree mineralisation potential of highly fractionated rhyolites a potential low grade bulk tonnage source of critical metals abstract the rare earth elements ree have become crucial for modern industry technology and medicine with the increase in demand for these elements over the past few years currently being met by relatively few well known mineral deposits this lack of a secure supply of the ree has led to increased research into potential alternative sources of these in demand elements the primary fractionation processes involved in the petrogenesis of highly fractionated high silica rhyolites can cause the magmas that form these units to become preferentially enriched in the ree especially in the more valuable heavy ree hree although this is dependent on the mineral assemblages fractionated by the system in question a factor that is in turn a function of the source and tectonic setting of a given magmatic event the mineralogy of the ree is also important with volatile exsolution and vapour phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the ree and other elements into concentrations and more importantly potentially acid leachable and therefore processable minerals that may be economically viable to extract this combined with the fact these rhyolites are often enriched in other critical and or economically important metals e g y nb ta be li f sn rb th and u means that these volcanic units should be considered as potential sources of these critical metals in addition the large volume nature of these rhyolites combined with the fact they frequently crop out at the earth s surface makes them ideally suited for more economical bulk open pit extraction this suggests that these high silica ree enriched rhyolites should be considered potential ree analogues of bulk tonnage low grade porphyry cu deposits warranting further investigation to determine whether these rhyolites are a viable new source of the ree especially the hree and are potential targets for future mineral exploration

a special issue on volcanogenic massive sulfide deposits of the trans hudson orogen preface paleoproterozoic volcanogenic massive sulfide vms deposits are hosted in greenstone belts that formed during assembly of earth s first supercontinent nuna at 2 1 to 1 7 ga these deposits account for a significant component of the world s vms tonnage and thus are an important global exploration target among these paleoproterozoic belts the 1 92 to 1 80 ga trans hudson orogen of canada is the largest and best endowed in laurentia with over 29 deposits totaling 320 mt of cu zn au ag pb ore study of its deposits districts and tectonostratigraphic evolution enables greater understanding of metallogenic and geodynamic processes during the paleoproterozoic we briefly overview the trans hudson orogen its vms deposits and their exploration history and illustrate that various distinct types of volcanogenic massive sulfide deposits form in predictive tectonostratigraphic sequences associated with both pre and postaccretion volcanism we present results from a four year program to investigate the deposits and evolution of the trans hudson orogen highlighting various approaches at district and belt scales to improve exploration models for other structurally complex and covered precambrian terranes

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

metal fluxes during magmatic degassing in the oceanic crust sulfide mineralisation at odp site 786b izu bonin forearc volcanogenic massive sulfide deposits are enriched in metals that are either derived from hydrothermal alteration of the basement rocks or supplied by exsolution of metal rich volatiles during magmatic differentiation the extent to which each process contributes to metal enrichment in these deposits varies between different tectonic settings ocean drilling program hole 786b recovered 800 m of upper oceanic crust from a supra subduction zone setting and includes a 30 m thick mineralised zone in situ s isotopic compositions of pyrite decrease from 5 9 2 9 in the upper mineralised zone down to 3 3 2 1 in the extensively altered central mineralisation zone potentially indicating strong magmatic fluid input in this area whole rock data and in situ trace element analyses in sulfide minerals show enrichment of ag as au bi mo s se sb and te in the mineralised zone evaluation of metal behaviour during magmatic differentiation and primary metal fertility of basement rocks suggests that degassing melt is the main source for the high au se and s enrichment observed in the mineralised zone magmatic volatile exsolution occurred late during the magmatic differentiation 2 wt mgo concomitant with oxide crystallisation and metal depletion in the melt comparison of ocean drilling program hole 786b with volcanogenic massive sulfide deposits hosted by boninitic volcanic successions such as in the semail ophiolite the newfoundland appalachians and the flin flon belt suggests that magmatic fluid exsolution could be a common mechanism for au enrichment in bimodal mafic volcanogenic massive sulfide deposits

3 d geologic modeling in the flin flon mining district trans hudson orogen canada evidence for polyphase imbrication of the flin flon 777 callinan volcanogenic massive sulfide ore system three dimensional geologic modeling by integrated analysis and interpretation of drill core 2 d and 3 d seismic mine survey and geologic map data provides new insights into the structural setting of the 85 5 million tonne mt flin flon callinan 777 volcanogenic massive sulfide vms ore system hosted in the paleoproterozoic flin flon belt of manitoba and saskatchewan canada the resultant camp scale 3 d geologic model was in addition to the densely drill intersected vms hosting mine horizon constrained by lithostratigraphic reference drill holes intersecting the footwall and hanging wall rock successions of the ore system which were established by relogging 52 drill holes and systematically reconciling the lithofacies classes in their log descriptions with the lithofacies units of the 1 10 000 scale flin flon mining district geologic map the lateral persistence and large stratigraphic range of these drill hole markers supported seismic interpretation and allowed tracing lithostratigraphic horizons and structures in areas with low drill hole density expanding 3 d subsurface insight from the local to the more regional structural setting of the ore system the overall 3 d modeled geometry and topological relationships between lithostratigraphic surfaces and multiple generations of thrust faults suggest that the flin flon mining district is underlain by an e dipping stack of w vergent thrust imbricates that formed during precollisional and collisional stages of the 1 9 to 1 8 ga trans hudson orogeny the imbricate stack was subsequently deformed by e trending ductile thrust faults that internally imbricated the flin flon arc assemblage and the molasse cover rocks of the missi group and brought up rocks of the former over the latter in a northerly direction the vms hosting millrock member has been stacked on at least four structural levels enhancing the vms potential in the footwall and hanging wall of the known ore deposits where both thrust systems intersect

geochemical and nd isotopic evolution of paleoproterozoic arc type granitoid magmatism in the flin flon belt trans hudson orogen canada granitoid magmatism spans three flin flon belt evolutionary stages i evolved arc 1920 ma plus early juvenile arc 1904 1880 ma plutonism during intraoceanic arc back arc formation ii early 1878 1860 ma and middle 1860 1844 ma successor arc plutonism following accretion and successor arc s development and iii late 1843 1826 ma successor arc plutonism accompanying successor basin formation and waning arc magmatism amphibole bearing mineralogy metaluminous compositions and igneous microgranitoid enclaves indicate derivation from infracrustal sources predominance of intermediate calc alkaline compositions and negative nb anomalies on normalized patterns over a 46 77 wt silica range indicate an arc setting basaltic end members indicate important contributions directly from the mantle e nd t values are predominately in the range 0 to 4 3 reflecting mixing between depleted mantle melts and an archean crustal component preserved in evolved arc plutons 3 9 to 6 temporal variations include the following i early juvenile arc plutons are low k high field strength element hfse depleted with relatively flat rare earth element ree patterns and negative eu anomalies indicative of low pressure partial melting fractionation in the mantle wedge with residual pyroxene and plagioclase ii early and middle successor arc plutonism is medium k with steep ree patterns and no eu anomalies indicative of input from melting of basaltic sources likely subducted back arc oceanic crust under high pressure conditions with residual garnet and or amphibole and no plagioclase iii late successor arc plutons are high k more hfse enriched with both variable ree pattern slopes and eu anomalies indicative of a significant petrogenetic role of recycling of preexisting juvenile arc accretionary complex crust

tectonic setting of the tetagouche group in northern new brunswick implications for plate tectonic models of the northern appalachians a regional compilation and reinterpretation of geochemical analyses of mafic igneous rocks from the ordovician tetagouche group in northern new brunswick indicates the presence of at least three mafic assemblages two groups of basalts and gabbros and one group of gabbros only the three groups can be separated on the basis of tio2 and trace element content group a basalts generally have mid ocean ridge basalt morb like compositions whereas group b basalts indicate a within plate setting wpb group c gabbros intrude into silicic volcanics that underlie the basalts but are rare or absent in the areas underlain by group a and b basalts the group c gabbros probably represent the earliest stages of mafic igneous activity and have morb like compositions or represent a transition between morb and arc basalts the association of group a and b basalts with abundant marine sediments such as thinly bedded turbidites and black and red shales and the fact that they erupted locally on top of continental crus

petrology of mariana trough and lau basin basalts the crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid ocean ridge basalts n morb but some subtle but distinctive differences exist these are largely due to differences in volatiles fe oxidation ratio abundances of large ion lithophile elements lil and some high field strength hfs elements isotope data for sr pb nd he and o are variable but broadly are morb like we present data contrasting mariana trough mtb and lau basin basalts lbb showing how they differ in certain trace element and isotopic signatures and compare both to n morb relative to n morb and lbb the mtb are enriched in alkalis alkaline earths light rare earth elements ree h2o and fe fe even for primitive samples while having morb type he 3 4 7 8 to 8 4 ra sr 87 86 mean 0 70293 and nd e 10 2 the lau basin is zoned with a central area having n morb characteristics for h2o lil ree nd e 8 1 to 9 0 and o but a depletion in hfs elements sr is more radiogenic mean 87 86 0 70347 and 3he 4he 3 4 7 2 to 11 0 ra is high relative to n morb the lau basin has a zone bordering the adjacent island arcs which is like mtb in both back arc basins relatively primitive unfractionated basalts with mg 100 mg fe 62 are found which resemble postulated primitive n morb calculated parental magmas obtained by adding xenocrystic olivine plot near or on 3 and 4 phase boundaries at 1 1 5 gpa for the ol di si system low p fractional crystallization and magma mixing explain most of the observed rock types possible explanations for differences between mtb and lbb include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere the long and complex history of mariana trough mantle sources led to a metasomatized mantle which gives rise to the distinctive mtb in contrast the lau basin is dominated by basalts derived from a source depleted in volatiles lil and hfs elements a previous melting history is implied mixing with a mantle component enriched in 87sr and 3he may be due to mantle counterflow driven by the subduction process

climatic and limnological changes associated with the younger dryas in atlantic canada pollen diatom and chironomid fossils from the sediments of a core from brier island bog lake nova scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in atlantic canada correlative with the european younger dryas ca 10 to 11 ka our paleolimnological data were then compared to similar types of data from splan pond new brunswick to determine if there were any significant differences between a coastal and a more inland site nonarboreal pollen was dominant throughout the brier island core and the interval 10 0 11 0 ka did not show the typical decline in picea and increases in tundra like vegetation characteristic of many sites in atlantic canada however the limnological indicators did undergo marked changes in taxon composition the chironomid assemblage was initially dominated by shallow water warm adapted chironomid taxa followed by abundant sergentia a cold stenotherm during 10 11 ka sergentia disappeared in the post younger dryas interval and the warm adapted genera resumed dominance chironomid inferred paleotemperature reconstructions revealed that at both brier island bog lake and splan pond summer surface water temperatures dropped abruptly to between 13 and 17 c during the 10 11 ka interval suggesting that a cooler climate was present in atlantic canada correlative with the european younger dryas diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations

shoshonitic magmas in nascent arcs new evidence from submarine volcanoes in the northern marianas volcanoes in the northern mariana arc between uracas lat 20 n and minami iwo jima 24 n are very active yet entirely submarine in contrast to the predominantly low k basaltic magmas of the central mariana arc the northern mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north the northern arc melts have enrichments in ba 800 ppm rb 70 ppm sr 1000 ppm ce 50 ppm and ce yb n 24 which increase to the north as far as iwo jima lavas from volcanoes north of iwo jima lack these enrichments and are indistinguishable from those of the central maranas the shoshonites are unusual in occurring along the magmatic front of a primitive intra oceanic arc we hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the mariana trough spreading center northward through the volcano arc shoshonites thus may characterize the initial stages of arc construction after an episode of back arc rifting and need not be restricted to the mature stages of arc evolution this situation contrasts with subduction zone initiation where first melts may be boninites or low k tholeiites these differing initial melts converge toward tholeiitic and calc alkaline compositions as arcs evolve

mapping the 3d lithofacies architecture of a vms ore system on a curvilinear faulted grid a case study from the flin flon mining camp canada abstract the 3d lithofacies architecture of the thrust imbricated paleoproterozoic 85 5 mt flin flon volcanogenic massive sulfide vms ore system trans hudson orogen canada has been mapped in 3d using a numerical grid modeling methodology this methodology is based on the structural knowledge universal approach skua modeling work flow developed for modeling hydrocarbon reservoirs one of the major advantages of applying this methodology to mineral exploration is that it allows exploiting knowledge on the structural setting of the ore deposit without the need to determine all kinematic constraints that would be required for a full 3d balanced restoration the work flow proceeds by modeling the volume of the thrust repeated mine horizon on a curvilinear faulted grid that is conformable to the enveloping geological structure and that includes discontinuities to model fault offsets it then uses a coordinate transformation to partly remove the influence of geological structure on euclidean distance based geostatistical estimations it subsequently applies the inverse of this coordinate transformation to represent the interpolated or simulated lithofacies distribution in the finite deformed state randomized validation experiments show that the geostatistical analysis resulted in an estimated overall 74 accuracy of the predicted lithofacies classes over the grid the lithofacies grid models provide insight into the post depositional deformation history of the ore system and the rifted volcanic arc setting in which the flin flon massive sulfide ore was deposited the lithofacies grid models also serve as stratified containers for generating lithochemical property models that can be used for spatially characterizing ore forming processes such as hydrothermal alteration and ore metal zoning

mode of seafloor spreading in the northern mariana trough abstract a geophysical study was conducted to clarify the mode of seafloor spreading in the northern mariana trough north of 20 n magnetic anomaly data and single channel seismic reflection profiles were taken along ship s tracks typically with a 2 4 mile spacing the transition from back arc rifting to true seafloor spreading occurs at a structural boundary which has ne sw strike at about 22 n south of this boundary clear magnetic lineations occur and axial rift valleys on the spreading ridges are visible on the seismic profiles our identification of the magnetic lineations shows that the accretion of oceanic crust started at about 3 5 ma with a spreading half rate of 2 cm yr the average spreading rate during the brunhes chron is of the order of 1 cm yr the rate increases northward and is accompanied by a decrease in the relative depths of the axial rift valleys a ridge axis discontinuity is found at about 21 n two spreading axes overlap each other about 50 km along strike and are offset about 30 km we interpret this discontinuity as an on going ridge jump from the western axis to the eastern one the southern end of the western axis is cut by a transform fault but the eastern axis is now propagating northwards arc volcanoes comprising the present volcanic front occur on the eastern flank of the spreading ridges suggesting basinward migration of the volcanic arc the spreading center of the mariana trough is located not at the center but on the eastern or the volcanic arc side of the trough in general offset is caused by the arcward ridge jump and the basinward migration of the volcanic arc asymmetric rifting before the beginning of the accretion of oceanic crust would be another reason for the offset a row of rift grabens along the eastern margin of the trough north of 22 n where the extension of island arc crust is concentrated continues to the spreading ridge south of 22 n the arcward offset of spreading ridges is also found in the lau basin suggesting that it is a common feature of the evolution of back arc basins

geochemistry of metamorphosed volcanic rocks in the neoarchean qingyuan greenstone belt north china craton implications for geodynamic evolution and vms mineralization abstract the qingyuan greenstone belt qgb situated in the northeastern section of the north china craton ncc is considered to be the unique metallogenic province in china that hosts both banded iron formations bifs and volcanogenic massive sulfide vms deposits traditionally the qgb is divided into the hunbei and hunnan terranes separated by the hunhe fault and grouped into the lower shipengzi middle hongtoushan and upper nantianmen formations which have undergone amphibolite to granulite facies metamorphism exposed supracrustal rocks are composed of plagioclase amphibolite and biotite plagioclase gneiss with minor amounts of bif marble and schist in this study detailed field and petrographic observations lithogeochemical u pb geochronological as well as whole rock sm nd isotope analyses were conducted on the metamorphosed mafic and felsic volcanic rocks i e plagioclase amphibolite and biotite plagioclase gneiss respectively in the qgb in order to discuss implications for tectonic evolution and comitant vms mineralization the supracrustal rocks of both hunbei and hunnan regions were formed synchronously from 2 57 to 2 53 ga and then had undergone 2 52 2 48 ga regional metamorphism specifically the lower section of the shipengzi formation is composed dominantly of transitional tholeiitic basalts with negative nb anomalies suggesting that they were likely generated by partial melting of a mantle source that was previously altered by variable amounts of slab derived fluids or melts in contrast the lithologic assemblages grade upward into interlayered bimodal volcanic rocks i e n morb type tholeiitic basalts and fi to fii type dacites of transitional to calc alkalic affinities representing a change in tectonic regime related to subduction from compression to extension among them all the basalts are characterized by consistently positive initial nd compositions end t 2 7 to 3 4 further indicate a depleted mantle source whereas those dacites possess negative to positive initial nd values end t 4 6 to 3 0 suggesting they were formed by partial melting of depleted mafic source likely lower mafic crust and accompanied with variable addition of old crustal material significantly vms deposits are genetically linked to this extensional event and closely associated with the fii type dacites that were generated by higher melting degree at high temperature conditions and shallow crustal level likely 10 15 km in all geochemical features e g negative nb anomalies and end value together with contamination from continental crusts for tholeiitic mafic rocks and inherited zircons from these volcanic rocks imply a continental arc setting where the qgb was evolved

trace element geochemistry of ore associated and barren felsic metavolcanic rocks in the superior province canada reply archaean felsic metavolcanic rocks in the superior province of the canadian shield may be divided into three major groups on the basis of trace element abundances and ratios 1 fi felsic metavolcanic rocks are dacites and rhyodacites characterized by steep ree patterns with weakly negative to moderately positive eu anomalies high zr y low abundances of high field strength elements e g hree y zr hf and high abundances of sr examples occur in the bowman subgroup and skead group in the abitibi belt in the kakagi lake lake of the woods shoal lake and sturgeon lake areas of the wabigoon belt and in the confederation lake area of the uchi belt none of these horizons as known hosts base metal sulphide deposits 2 fii felsic metavolcanic rocks are rhyodacites and rhyolites characterized by gently sloping ree patterns with variable eu anomalies moderate zr y and intermediate abundances of hfs elements and sr examples occur in the misema subgroup of the abitibi belt in the wabigoon lake a

allerod younger dryas coleoptera from western cape breton island nova scotia canada studies of coleoptera remains from two late glacial sites on cape breton island nova scotia canada present a picture of the paleoenvironment and paleoclimate during the allerod younger dryas transition in the maritimes region they provide evidence for the younger dryas event in northeastern north america between 11 300 and 10 800 bp the beetle assemblages at the campbell site are typical of faunas of the modern middle to northern boreal forest the west mabou site contains beetle fossils younger than 10 900 bp possibly as young as 10 500 bp extending into the time period of the younger dryas dated from 10 800 to 10 000 bp in the maritimes a cold climate indicator recognizable in the beetle fauna olophrum boreale occurs in relative abundance and provides an interesting comparison with sites in europe where the same northern boreo montane species is evident at the beginning of the younger dryas

age and origin of the jan lake complex a glimpse at the buried archean craton of the trans hudson orogen the largely buried sask craton is a continental fragment or microcontinent that collided with and underthrust the paleoproterozoic flin flon glennie protocontinent along the pelican decollement zone at 1840 1830 ma rocks of the sask craton are exposed in three tectonic windows those of the pelican window have been named the jan lake complex and comprise 2960 ma arc derived leucocratic orthogneisses migmatitic paragneisses and a tholeiitic within plate igneous suite comprising 2488 ma dioritic to gabbroic rocks and 2450 ma enderbitic and charnockitic rocks including the sahli granite ages of ca 2450 ma are also common from the other two tectonic windows to the sask craton suggesting that emplacement of the igneous suite was widespread and perhaps part of the coeval matachewan igneous event the absence of rocks in the 2960 and ca 2450 ma age ranges on both the adjacent superior and rae hearne cratonic margins makes it improbable that the sask craton was derived by simple fragmentation without large scale tectonic transport the overthrust paleoproterozoic rocks represent a high grade northwestern extension of the flin flon volcanic belt and include 1856 ma leucotonalite and 1843 ma quartz monzodiorite an 1830 ma suite of homogeneous calc alkaline enderbitic rocks which intrude burntwood semipelitic migmatites throughout the kisseynew domain has also been emplaced in mylonites of the pelican decollement zone zircon and monazite ages in the 1812 1803 ma range record a high grade metamorphic event that resulted from collision between the sask craton and flin flon glennie complex

the gold content of volcanogenic massive sulfide deposits volcanogenic massive sulfide deposits contain variable amounts of gold both in terms of average grade and total gold content with some vms deposits hosting world class gold mines with more than 100 t au previous studies have identified gold rich vms as having an average gold grade expressed in g t exceeding the total abundance of base metals expressed in wt however statistically meaningful criteria for the identification of truly anomalous deposits have not been established this paper presents a more extensive analysis of gold grades and tonnages of 513 vms deposits worldwide revealing a number of important features in the distribution of the data a large proportion of deposits are characterized by a relatively low gold grade 2 g t with a gradual decrease in frequency towards maximum gold grades defining a log normal distribution in the analysis presented in this paper the geometric mean and geometric standard deviation appear to be the simplest metric for identifying subclasses of vms deposits based on gold grade especially when comparing deposits within individual belts and districts the geometric mean gold grade of 513 vms deposits worldwide is 0 76 g t the geometric standard deviation is 2 70 g t au in this analysis deposits with more than 3 46 g t au geometric mean plus one geometric standard deviation are considered auriferous the geometric mean gold content is 4 7 t au with a geometric standard deviation of 26 3 t au deposits containing 31 t au or more geometric mean plus one geometric standard deviation are also considered to be anomalous in terms of gold content irrespective of the gold grade deposits with more than 3 46 g t au and 31 t au are considered gold rich vms a large proportion of the total gold hosted in vms worldwide is found in a relatively small number of such deposits the identification of these truly anomalous systems helps shed light on the geological parameters that control unusual enrichment of gold in vms at the district scale the gold rich deposits occupy a stratigraphic position and volcanic setting that commonly differs from other deposits of the district possibly due to a step change in the geodynamic and magmatic evolution of local volcanic complexes the gold rich vms are commonly associated with transitional to calc alkaline intermediate to felsic volcanic rocks which may reflect a particularly fertile geodynamic setting and or timing e g early arc rifting or rifting front at the deposit scale uncommon alteration assemblages e g advanced argillic aluminous strongly siliceous or potassium feldspar alteration and trace element signatures may be recognized e g au ag as sb bi hg te suggesting a direct magmatic input in some systems

paleoproterozoic 1 90 1 86 ga arc volcanism in the flin flon belt trans hudson orogen canada geochemical and isotopic nd sr data are reported on paleoproterozoic 1904 1864 ma maficintermediate 1870 ma collision and subsequent intra arc deformation

late glacial allerod younger dryas buried organic deposits nova scotia canada a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract numerous deposits of organic shallow pond sediments and wetland peat accumulations buried by minerogenic sediments have been discovered throughout nova scotia they are interpreted as representing a late glacial climatic oscillation correlative with the allerod younger dryas event of europe and the north atlantic ocean the organic deposits began forming during the warm or warming interval following deglaciation and often record a transition to colder conditions the climatic reversion recorded in many deposits began about 10 8 ka bp and continued or sustained cooling culminated in the burial of the organic deposits by minerogenic sediments indicative of solifluction and mass wasting processes some deposits provide strong evidence for regeneration or rejuvenation of local glaciers as the organic deposits are not as susceptible as lake sediments to contamination by old carbon they provide a more reliable chronological framework for deglaciation and late glacial vegetational history palynological evidence shows that pioneer herb tundra communities colonized some areas shortly after 13 ka bp willow and birch shrubs followed soon after spruce woodlands had migrated into the region prior to 10 8 ka bp but had not yet reached the northeast mainland and cape breton island cooling after 10 8 ka bp decimated tree populations and favoured a return to shrub and herb communities the record in the buried deposits was then truncated by deposition of minerogenic sediments and lake sediment sequences from deeper basins with continuous sedimentation are required to complete the record

intraoceanic tectonics and the development of continental crust 1 92 1 84 ga evolution of the flin flon belt canada the flin flon belt is a complex amisk collage of distinct tectono stratigraphic assemblages that was brought together at a relatively early stage in the tectonic evolution of the paleoproterozoic trans hudson orogen four main tectono stratigraphic assemblage types are recognized isotopically juvenile oceanic arc 1 90 1 88 ga ocean floor ca 1 90 ga oceanic plateau ocean island and isotopically evolved arc 1 92 1 90 ga oceanic arc assemblages include tholeiitic calc alkaline and lesser shoshonitic volcanic and volcaniclastic rocks as well as turbidites and arc rift volcanic rocks the tectono stratigraphic assemblages were juxtaposed in an accretionary complex amisk collage at ca 1 88 1 87 ga probably as a result of arc arc collision collisions accretionary collage structures are largely obliterated by subsequent deformation and metamorphic events but can be inferred where cut by calc alkaline plutons related to a 1 866 1 838 ga arc coeval subaerial volcanism is recorded in ca 1 87 1 85 ga calc alkaline to shoshonitic volcaniclastic sequences unroofing of the accretionary collage development of a paleosol and deposition of continental alluvial fluvial sedimentary rocks occurred ca 1 85 1 84 ga coeval with the waning stages of post accretion arc magmatism stabilization of the flin flon belt by 1 85 1 84 ga as part of a philippines or japan like microcontinent is attributed to both tectonic and magmatic thickening of the lithosphere

the setting style and role of magmatism in the formation of volcanogenic massive sulfide deposits throughout earth s history all volcanogenic massive sulfide vms hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry petrochemical assemblages indicative of formation at anomalously high temperatures within extensional geodynamic environments in mafic dominated juvenile ophiolitic vms environments there is a preferential association with mafic rocks with boninite and low ti tholeiite mid ocean ridge basalt morb and or back arc basin basalt affinities representing forearc rifting or back arc initiation mid ocean ridges or back arc basin spreading or back arc basins respectively felsic rocks in juvenile oceanic arc environments in archean terrains are high field strength element hfse and rare earth element ree enriched in post archean juvenile oceanic arc terrains felsic rocks are commonly hfse and ree depleted and have boninite like to tholeiitic signatures in vms environments that are associated with continental crust i e continental arc and back arc and dominated by felsic volcanic and or sedimentary rocks evolved environments felsic rocks are the dominant hosts to mineralization and are generally hfse and ree enriched with calc alkalic a type and or peralkalic affinities representing continental arc rifts continental back arcs and continental back arcs to continental rifts respectively coeval mafic rocks in evolved environments have alkalic within plate ocean island basalt like and morb signatures that represent arc to back arc rift versus back arc spreading respectively the high temperature magmatic activity in vms environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments e g mid ocean ridges back arc basins and intra arc rifts underplated basaltic magma provides the heat required to drive hydrothermal circulation extensional geodynamic activity also provides accommodation space at the base of the lithosphere that allows for the underplated basalt to drive hydrothermal circulation and induce crustal melting the latter leading to the formation of vms associated rhyolites in felsic dominated and bimodal vms environments rifts also provide extensional faults and the permeability and porosity required for recharge and discharge of vms related hydrothermal fluids rifts are also critical in creating environments conducive to preservation of vms mineralization either through shielding massive sulfides from seafloor weathering and mass wasting or by creating environments conducive to the precipitation of subseafloor replacement style mineralization in sedimented rifts subvolcanic intrusions are also products of the elevated heat flow regime common to vms forming environments shallow level intrusive complexes i e within 1 3 km of the seafloor may not be the main drivers of vms related hydrothermal circulation but are likely the manifestation of deeper seated mantle derived heat i e 3 10 km depth that drives hydrothermal circulation these shallower intrusive complexes are commonly long lived i e millions of years and reflect a sustained thermally anomalous geodynamic environment such a thermally anomalous environment has the potential to drive significant hydrothermal circulation and therefore multi phase long lived subvolcanic intrusive complexes are excellent indicators of a potentially fertile vms environment the absence of intrusive complexes however does not indicate an area of low potential as they may have been moved or removed due to post vms tectonic activity in some cases shallow level intrusive systems contribute metals to the vms hydrothermal system

wisconsinan late glacial environmental change in nova scotia a regional synthesis a synthesis of the interpreted vegetational and climatic history of nova scotia during the wisconsinan late glacial period 14 9 ka bp is presented and described in 500 year intervals the concomitant regional deglaciation history of the region is also described a synthesis chart is provided which includes a qualitative curve of temperature reconstructions for the late glacial period

early thrusting and folding in the snow lake camp manitoba tectonic implications and effects on volcanogenic massive sulfide deposits the chisel sequence occurs within the snow lake arc assemblage sla of the paleoproterozoic trans hudson orogen it is host to six economic volcanogenic massive sulfide vms deposits that formed within a single time stratigraphic ore interval the sla was previously interpreted to share the same deformation history as the ca 1 86 1 84 ga burntwood group turbidites of the kisseynew basin to the north however early isoclinal folds identified in the arc assemblage cannot be correlated with structures in the turbidites and therefore developed prior to burntwood group deposition this indicates that the sla underwent a significant deformation event prior to 1 86 ga likely due to intraoceanic accretion or pre 1 86 ga accretion to the amisk collage during closure of the ancestral manikewan ocean evidence for this early folding event is recorded in the chisel sequence deposits where it has influenced the geometry of the deposits and the location of the ore interval the deposits are isoclinally folded by t

basalts of the north fiji basin the generation of back arc basin magmas by mixing of depleted and enriched mantle sources active spreading ridges in the north fiji basin range from well developed stable ridges where largescale mantle upwelling is in progress to proto ridges where spreading is incipient south of 17 s where the central ridge of the north fiji basin has a bathymetric profile normally expected of a fast spreading steadystate mid ocean ridge basalts are evolved n type morbs north of 17 s where the central ridge is propagating northward into old north fiji basin crust and spreading is in the initial stages two types of basalt have been recovered n type morbs from this northern arm of the central ridge are believed to be samples of older north fiji basin crust basalts with transitional alkalic chemistry up to 0 5 ne in the norm and characterized by strong relative enrichments in rb ba k nb la ce sr p zr and ti are believed to be associated with incipient rifting among the latter group are compositions that are intermediate between transitional alkalic types and morbs and these are geochemically similar to the back arc basin babb magma type defined by sinton and fryer 1987 from a study of mariana back arc basin basalts dredges along the south pandora ridge a transform zone characterized by short spreading segments are dominated by basalts that are enriched in large ion lithophile and high field strength minor and trace elements and compositions range from types resembling ocean island tholeiites to transitional alkalic varieties basalts from rotuma are regarded as alkalic end members of the south pandora ridge magmatic spectrum in areas of the north fiji basin where relatively fast spreading must be accompanied by largescale asthenospheric upwelling depleted n type morbs dominate whereas in areas of slow mantle upwelling or where some other tectonic effect e g a transform fault causes a transient thermal disturbance within the lithosphere or upper asthenosphere enriched alkalic magmas either dominate or make a significant and noticeable contribution to the overall chemical characteristics of basalts being erupted the morbs have a depleted asthenospheric source and the alkalic component is believed to derive from an enriched lithospheric or shallow asthenospheric source the babb magma type may simply be part of the spectrum of mixed magmas that can occur in the transitional tectonic settings represented by the early development of most back arc basins

stratigraphic and tectonic setting of early proterozoic volcanogenic massive sulfide deposits flin flon manitoba volcanogenic massive sulfide deposits in the flin flon metavolcanic belt occur in an early proterozoic island arc setting that includes arc tholelite back arc ocean floor and shoshonitic assemblages near the town of flin flon manitoba these volcanic assemblages are structurally juxtaposed in a tectonic collage nearly all of the volcanogenie massive sulfide deposits at flin flon are associated with the arc tholeiite assemblage and occur in complex stratigraphic sequences which represent volcanic constructs and associated intravolcanic basins within the former magmatic arc back arc or ocean floor basalts in the flin flon belt host only a few small cu rich massive sulfide deposits and consequently have a lower exploration potential than the arc tholeiite assemblage within the arc tholeiite assemblage volcanogenie massive sulfide deposits occur in association with felsic volcanic units at major stratigraphic and compositional breaks in the volcanic sequence the breaks can be recognized by contrasting major element trace element and isotopic characteristics of the underlying and overlying mafic rocks most volcanogenie massive sulfide deposits are underlain by coarse mafic intermediate or felsic volcaniclastic rocks the best documented examples including the flin flon cuprus and white lake deposits discussed in this paper are clearly localized in basinal structures that vary widely in size the flin flon deposit 62 4 mt occurs in a proximal volcanic environment it lies on the upper flank of a shallow subaqueous basalt volcano possibly in a fault bounded depression the massive sulfides are emplaced within a rhyolite flow complex and are underlain by a disconformable chloritic hydrothermal alteration zone developed in footwall basalt breccia the massive sulfides were overlain by a thick 3 km subaqueous basalt basaltic andesite succession compositionally unrelated to basalts in the stratigraphic footwall the cuprus and white lake deposits total 1 3 mt occur in a 5 5 km thick sequence dominated by more than 3 km of basaltic andesitc interpreted as a subaqueous shield volcano this volcano contains a collapse caldera within which an intracaldera subaqueous rhyolite flow and coeval felsic and intermediate basin filling volcaniclastic rocks were deposited massive sulfides accumulated in subbasins within the caldera hosted by a thin unit of graphitic mudstone and chert overlying formations are laterally extensive unlike the wedgeshaped caldera filling deposits and were deposited in a large deep water basin these rocks are chemically and isotopically unrelated to formations underlying the massive sulfide deposit

evolution of the snow lake portion of the palaeoproterozoic flin flon and kisseynew belts trans hudson orogen manitoba canada abstract understanding growth of early precambrian crust requires knowledge of the evolution of granite greenstone and metasedimentary belts two of the fundamental building blocks of early precambrian cratons u pb geochronologic data from the snow lake area which straddles the flin flon granite greenstone and kisseynew metasedimentary belts of the trans hudson orogen documents a 60 70 ma period of palaeoproterozoic crust formation from inception of these belts in ocean basins through their eventual structural telescoping during ocean basin consumption and collision with bounding archaean cratons earliest volcanic and plutonic rocks of the flin flon granite greenstone terrane at snow lake formed 1 89 ga mainly in a juvenile oceanic arc tectonic setting sedimentary rocks of the kisseynew belt previously thought to be contemporaneous with snow lake area arc volcanism are up to 30 50 ma younger 1 86 1 84 ga and postdate deformation associated with 1 88 1 87 ga arc arc collisions and 1 87 1 84 ga calc alkaline plutonism that affected much of the western flin flon belt deformation at snow lake occurred during two widely spaced episodes both of which effect the post 1 86 1 84 ga turbidite sequence and thus postdate 1 88 1 87 ga intraoceanic accretion in the western flin flon belt the older deformational episode involved isoclinal folding formed during 1 84 ga convergence of the kisseynew and flin flon belts and thrusting of kisseynew sedimentary lithologies southwards onto the flin flon volcanic rocks the younger deformational episode occurred 15 25 ma later and involved further folding and southwest thrusting accompanied by a 1 81 ga high grade thermal metamorphic episode centred in the kisseynew belt only minor increase of crustal material in the form of late intrusions were added following this episode

oblique rainfall and contemporary geomorphological dynamics serra da estrela portugal coarse sand accumulations are polygenic microforms that attain a width of several metres a height up to 30 40 cm a gradient of 8 12 and a slope length up to 1 m these accumulations are frequent in the gruss covered plateaus of the granite mountains of central and northern portugal but they have been described in other mountain areas i e cairngorms scotland though these microforms are frequent features studies on them are rare they have been attributed to complex genesis controlled primarily by aeolian processes but also by wash and cryogenic dynamics results presented here add new insights into the origin of the sand accumulations and emphasize the importance of rainsplash saltation induced by oblique rainfall as the main transportation mechanism the study was conducted in the serra da estrela a granite mountain in central portugal 1993 m above sea level and is supported by a detailed mapping of the orientation of the accumulations monitoring of the surface material and analysis of meteorological data the results are particularly significant since they indicate that the coarse sand accumulations are very active features that show a clear climatic and ecological signal copyright 2004 john wiley sons ltd

u pb geochronology of late neoarchean tonalites in the flin flon belt trans hudson orogen surprise at surface the flin flon volcanic belt of the trans hudson orogen in northern manitoba comprises magmatic rocks 1 88 1 90 ga generated in an intra oceanic arc and identified as one of the best examples of juvenile paleoproterozoic crust in the flin flon athapapuskow lake area the belt consists of a series of fault bounded blocks each having distinct stratigraphic and magmatic affinities juxtaposed to form an accretionary collage two tonalitic bodies within the northeast arm shear zone a major deformation corridor separating two of the most important blocks in the area have been dated by the u pb zircon method at and these results indicate the presence of fragments of late neoarchean crust within the flin flon belt possibly related to ca 2 5 ga granitic bodies found in terranes beyond the western limit of the belt the presence of ca 2 5 ga tonalites within the flin flon belt herein reported for the first time has major implications for basement involvement in the early tectonic evolution of the f

evolution of the paleoproterozoic snow lake arc assemblage and geodynamic setting for associated volcanic hosted massive sulphide deposits flin flon belt manitoba canada the majority of volcanogenic massive sulphide vms deposits at the east end of the paleoproterozoic flin flon greenstone belt occur in the 1 89 ga snow lake arc assemblage vms deposits in this

allerod younger dryas lake temperatures from midge fossils in atlantic canada remains of freshwater midges are abundant in lake sediments and their species distributions are closely related to the surface water temperature of lakes their distributions thus provide a powerful tool for paleoclimatology the distribution of species in a core from splan pond in atlantic canada indicates that there were abrupt transitions in late glacial temperatures between warm and cold states the transitions are correlative with the well known warm allerod and cold younger dryas events in europe these data thus confirm the inference from palynological data that these events affected regions on both sides of the atlantic

the facies architecture of a paleoproterozoic basaltic andesite synvolcanic intrusion flin flon manitoba canada the paleoproterozic 1920 unit occurs at the base of the hidden formation overlying greater than 90 million tons of volcanogenic massive sulfide deposits at flin flon manitoba canada the 1920 unit is a laterally discontinuous fe ti p rich basaltic andesite fe2o3 12 wt tio2 1 1 wt and p2o5 0 30 wt consisting of massive pillowed and in situ brecciated basaltic andesite the 1920 unit is characterised by facies textures and structures similar to those associated with subaqueous basaltic lavas however the presence of blocky and fluidal peperite along the upper contact and lens shaped inclusions of tuff within and along its basal contact as well as the discordancy of the upper contact suggest that the predominantly massive basaltic andesite was emplaced as a high level synvolcanic sill into wet unconsolidated volcaniclastic deposits the presence of a breccia containing clasts of the 1920 unit within the package of volcaniclastic rocks overlying the 1920 unit and a pillowed facies within the 1920 unit suggest that locally the 1920 unit breached the seafloor an abundance of synvolcanic dikes within the footwall to the 1920 unit including the presence of a basaltic andesite dike that merges into the 1920 unit indicates the possible location of the feeder for the 1920 unit in the northwestern portion of the area

evidence for voluminous bimodal pyroclastic volcanism during rifting of a paleoproterozoic arc at snow lake manitoba the thrust bounded mcleod road birch lake mb sequence occurs within the paleoproterozoic snow lake arc sla assemblage of the flin flon belt stratigraphic correlation of volcanic strata of the mb sequence with strata of the thrust bounded chisel sequence indicates that distinctive submarine eruption fed pyroclastic flow deposits are more extensive and voluminous than previously recognized 10 km3 these voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the sla the felsic pyroclastic deposits define the remnants of a basin or of nested basins that formed during arc rifting and subsidence and their eruption immediately preceded formation of the chisel sequence volcanogenic massive sulfide vms deposits although the chisel sequence ore interval is recognized in the mb sequence the lack of vms related alteration indicates that vms hydrothermal activity was restricted to the chisel portion of the

volcanic reconstruction of paleoproterozoic arc volcanoes the hidden and louis formations flin flon manitoba canadathis is a companion paper to dewolfe y m gibson h l and piercey s j 2009 petrogenesis of the 1 9 ga mafic hanging wall sequence to the flin flon callinan and triple 7 massive sulphide deposits flin flon manitoba canada canadian journal of earth sciences 46 this issue the hanging wall to the flin flon callinan and triple 7 volcanogenic massive sulphide deposits of the flin flon district is composed of the hidden and louis formations the contact between these formations is marked by mafic tuff that represents a hiatus in effusive volcanism the formations form a composite volcanic edifice that was erupted and grew within a large volcanic tectonic subsidence structure hosting the deposits that developed within a rifted arc environment the formations are evidence of resurgent effusive volcanism and subsidence following a hiatus in volcanism marked by ore formation since they consist of dominantly basaltic flows sills and volcaniclastic rocks with subordinate basaltic andesite and rhyodacitic flows and volcaniclastic rocks the hidden formation is interpreted to represent a small shield volcano and the louis formation a separate shield volcano that developed on its flank both the hidden and louis volcanic edifices were constructed by continuous low volume eruptions of pillow lava a gradual change from a dominantly extensional environment during the formation of the footwall flin flon formation to a progressively more dominant convergent environment during the emplacement of the hanging wall suggests that the hidden and louis formations are unlikely to host significant volcanogenic massive sulphide type mineralization however synvolcanic structures in the formations define structural corridors that project downwards into the footwall where they encompass massive sulphide mineralization indicating their control on ore formation longevity and reactivation as magma and fluid pathways during the growth of the hidden and louis volcanoes

hanging wall vectoring for buried volcanogenic massive sulfide deposits paleoproterozoic flin flon mining camp manitoba canada the paleoproterozoic flin flon mining district is one of the world s most prolific volcanogenic massive sulfide vms camps and includes a single stratigraphic interval that hosts the 85 5 million tonne mt flin flon 777 and callinan zn cu au deposits rapid seafloor burial of the vms hydrothermal system by a thick succession of pillowed basalt resulted in the hanging wall strata being affected to varying degrees by the still upward migrating fluids this hanging wall alteration hydrothermal fingerprint allows delineation of the regionally metamorphosed paleohydrothermal system and its characterization has the potential to lead to discovery of buried stacked or structurally displaced mineralization evidence for the presence of continued seafloor hydrothermal activity above the flin flon callinan vms horizon is observed in the pillowed flows interlayered hyaloclastite rich flow tops and also within finely bedded interflow volcaniclastic sediment a 30 to 60 metalliferous exhalative component was detected through geochemical and mineral analysis in interpillow volcaniclastic rocks chert and epidosite in the hanging wall sequence the regional distribution of fe and mg rich chlorite epidote clinozoisite biotite annite actinolite hornblende ferrotschermakite and stilpnomelane and albite oligoclase modifies metamorphic isograds and defines discrete vertical fluid pathways controlled by synvolcanic growth faults and associated sill dike swarms silica enriched hanging wall alteration zones are proximal to fe ti basalt sills and occur as discrete hanging wall zones parallel to the plunge of the 62 mt flin flon deposit anomalous concentrations of hg sb ag pb te as au and bi form within these hanging wall halo alteration zones indicating migration of the more volatile metals present in the underlying vms deposits synvolcanic depressions dike swarms and hydrothermal metamorphic fluid corridors are detectable through trace element anomalies trace mineral chemistry and 18o isotope geochemistry oxygen isotope analysis of the flin flon 777 callinan vms hanging wall strata defines a number of high o18 anomalies extending 1 200 m above that indicate that 300 c subseafloor hydrothermal activity continued after burial of the massive sulfide deposits coupled with the geochemical and mineral chemical anomalies this is indicative of the presence of continued relatively low temperature hydrothermal fluid leakage from a robust seafloor hydrothermal event that generated the vms deposits a combination of techniques including mineral chemistry isotope and trace element data is demonstrated to be successful in identifying and delineating zones of hanging wall hydrothermal alteration in greenschist to amphibolite grade metamorphic rocks of the flin flon mining camp use of these coupled with mapping to define periods of quiescence as marked by horizons of sedimentary rocks in the hanging wall basalts of the hidden formation has the potential to lead to discovery of deeply buried deposits on the flin flon horizon or deposits at higher stratigraphic levels our findings indicate that the basaltic hanging wall on the flin flon 777 callinan hydrothermal system was an efficient cap on the system with vestiges of continued hydrothermal fluid flow detected in the interpillow and interflow components these volumetrically minor components are critical sampling media and are pertinent to global exploration for detection of vms mineralization buried beneath thick mafic volcanic sequences

subaqueous strombolian eruptions and eruption fed pyroclastic deposits in a paleoproterozoic rifted arc hidden formation flin flon canada abstract the hidden formation of the paleoproterozoic flin flon arc assemblage comprises the stratigraphic hanging wall to the volcanogenic massive sulfide vms deposits at flin flon manitoba canada it represents a basaltic volcanic edifice erupted within a large subsidence structure developed in a rifted arc environment it is predominately pillow lavas with subordinated amounts volcaniclastic rocks rocks that stratigraphically overly the schist and mandy vms deposits 5 km southeast of the main flin flon deposits have been correlated through litho and chemo stratigraphy with the hidden formation they display evidence of pyroclastic volcanism and concomitant subsidence pillow lavas and hyaloclastite are unequivocal evidence of subaqueous eruption the hidden formation in the schist mandy area comprises mafic tuff mafic megabreccia basalt lava fluidal clast breccia and plagioclase crystal rich volcaniclastic lithofacies intruded by synvolcanic dikes and sills the megabreccia lithofacies is characterized by angular basalt clasts 1 20 m in a matrix of finer basalt clasts and is interpreted to have been deposited by mass flows due to slumping of the caldera wall a within flow vertical transition in the lavas from massive to pillowed flows suggests a slowing of emplacement velocity decrease in temperature and an increase in the viscosity during eruption based on the monolithic nature of the fluidal clast breccias and the fluidal shapes of clasts with delicate tails and intact glassy margins they are interpreted to be the result of strombolian eruptions an increase in the ingestion of water in the vent s lead to a change from magmatic to phreatomagmatic fragmentation planar and cross laminations graded beds and the abundance of broken plagioclase crystals in combination with scoria and lithic clasts suggest the mafic tuff and plagioclase crystal rich volcaniclastic lithofacies were deposited by subaqueous eruption fed density currents derived from a phreatomagmatic eruption detailed mapping of the volcanic lithofacies in the schist mandy area has facilitated the identification of synvolcanic faults defining inner caldera margins and volcanic vents these structures when traced downwards through stratigraphy define structural corridors corresponding with the schist and mandy vms deposits indicating they represent long lived structures that also acted as magmas and fluid pathways

chronology of crustal growth and recycling in the paleoproterozoic amisk collage flin flon belt trans hudson orogen canada u pb zircon ages have been compiled for magmatic and sedimentary rocks from the low metamorphic grade portion of the flin flon greenstone belt now recognized as a paleoproterozoic tectonic collage

geochemistry of lau basin volcanic rocks influence of ridge segmentation and arc proximity side scan sonar imaging of the central lau basin sw pacific has revealed a central lau spreading centre clsc propagating southwards at the expense of an eastern lau spreading centre elsc with a small intermediate lau spreading centre ilsc forming a relay between the two volcanic rocks sampled along these spreading centres and from two adjacent seamounts are glassy to fine grained pillow lavas and sheet flows of basalts ferrobasalts and andesites the evolved rocks are mostly confined to the propagating tip of the clsc and can be explained by a high rate of cooling relative to magma supply as invoked for magma genesis at propagating ridges elsewhere compared with equivalent rocks from the eastern pacific the most evolved members of the clsc suite require similarly high degrees 90 of fractional crystallization from their basaltic parents fractional crystallisation cannot however account for the compositional differences between clsc and elsc lavas whereas the composition of the clsc lavas lies just within the compositional spectrum of typical n morb the elsc lavas are distinctly enriched in alkali and alkaline earth elements reach oxide and apatite saturation at lower fe ti and p concentrations and generally show greater vesicularity despite slightly greater depths of eruption all indicative of a water rich subduction component they also have lower contents of ni sc na and fe and higher contents of si at a given mgo concentration that indicate a more depleted and more hydrous mantle beneath the elsc compared with the clsc these results provide further evidence that beneath the central lau basin the source composition changes progressively from morb type to island arc tholeiite type as the subduction zone is approached both eastwards from the clsc to elsc and southwards along the elsc to the valu fa ridge they also indicate that the composition of the subduction component may vary systematically away from the arc with th lree ba rb and h as h2o all present close to the arc only ba rb and h2o present at intermediate distances and just h2o perceptible at the furthest distances

kisseynew metasedimentary gneiss belt trans hudson orogen canada back arc origin and collisional inversion the kisseynew metasedimentary gneiss belt initially developed in a back arc setting the ages of detrital zircons and crosscutting plutons constrain turbidite sedimentation to 1 855 1 841 ga postdating early deformation and metamorphism associated with arc arc and arc continent collisions affecting much of the trans hudson orogen these turbidites are interpreted to have been deposited in a back arc basin behind a retreating subduction boundary the kisseynew domain and its southern flank are marked by 1 84 1 83 ga magmatic rocks that may be related to subduction of back arc basin oceanic crust collapse of the kisseynew basin by ductile fold and thrust deformation began during 1 84 1 83 ga magmatism and continued through peak metamorphism at ca 1 820 1 805 ga from authors

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

tertiary arc rifting in northern luzon philippines the north luzon terrane nlt comprising the section of luzon north of the philippine fault is one of the largest arc terranes in the philippine archipelago numerous features suggest that the nlt is a late oligocene to early miocene analogue for the processes in the modern intra arc rift zone at the northern end of the mariana trough first the nlt has bifurcating magmatic arcs sharing similar magmatic histories these include the northern sierra madre nsm and cordillera central cc magmatic arcs which are separated by the cagayan basin but which are linked in the caraballo range to the south the rock record indicates that the nsm cc and caraballo ranges were active arcs in late eocene to late oligocene time second seismic reflection and well data indicate that the cagayan basin formed by extensional faulting in late oligocene to early miocene time third alkalic arc magmatism recognized to be a precursor of intra arc rifting in modern settings occurred at the juncture of the nsm and cc arcs in late oligocene to early miocene time fourth oceanic crust represented by the itogon ophiolite formed at the southwestern end of the cagayan basin in late oligocene to early miocene time major and trace element chemistry show that the itogon sheeted dikes have tholeiitic arc and backarc basin basalt affinities the rock record and geophysical offshore data suggest that the nlt was developing in an island arc system above the subducting west philippine plate in late eocene time rifting occurred in the island arc from late oligocene to early miocene time but did not mature into backarc spreading most likely because of the collision of the benham rise a basaltic rise in the west philippine basin with the nlt the arc rifting in the nlt may be another manifestation of the extensional tectonism that affected most of southeast asia in late oligocene to early miocene time during which the south china and southeast sulu basins formed subsequent to arc rifting the history of the nlt has been linked to the subduction of the south china plate along the manila trench the structural history of the cagayan basin and magmatic history of the southern cc suggest that the subduction in the manila trench at the latitude of the nlt began about 15 ma

geochemistry of 1 9 ga morb and oib like basalts from the amisk collage flin flon belt canada evidence for an intra oceanic origin subaqueously erupted basalts that occur in kilometre scale allochthons within the 1 9 ga flin flon belt canada appear to have been generated at oceanic ridges and possibly oceanic plateaus remote from archean cratons the ocean floor basalts fall into two categories 1 n type resembling n morbs and mariana type back arc basin basalts depleted to flat ree patterns high zrnb variable thnb and initial nd 3 3 to 5 4 2 e type resembling transitional and plume morbs slightly enriched ree patterns lower zrnb initial nd 3 1 to 4 5 in the largest and best studied allochthon the elbow athapapuskow assemblage mixing between depleted n morb and enriched oib sources or melts coupled with variable addition of a subduction lile component can explain the chemical variations in the basalts zircon u pb dates of 1904 ma for a syn volcanic diabase sill and 1901 6 5 ma for a gabbro peridotite cumulate complex demonstrate that crystallization of the ocean floor basalts overlapped with in part eruption of the tectonically juxtaposed 1 90 1 88 ga arc volcanic rocks the elbow athapapuskow allochthon is interpreted as back arc basin crust that developed simultaneously with flin flon arc magmatism subaerially erupted basalts that chemically resemble tholeiitic oibs 8 14 mgo relative hree depletion initial nd 2 2 to 3 4 occur in tectonic contact with the elbow athapapuskow assemblage the oibs may have been generated by deeper garnet residue melting of enriched mantle tapped during extension in the elbow athapapuskow back arc basin and were possibly erupted onto a remnant arc deeper mantle melting is also indicated by the presence of the lree enriched oceanic plateau like basalts of the sandy bay assemblage the back arc 01b and plateau volcanic assemblages were jux taposed against ca 1 9 ga arc assemblages in a philippines like intraoceanic accretionary complex by 1 87 ga

early geochemical evolution of an oceanic island arc and backarc fiji and the south fiji basin the initial 25 to 35 ma of oceanic arc volcanism in fiji the early arc stage was dominated by eruption of lree depleted low k tholeiitic basalts and andesites the oldest volcanics include the highest hfse group morb like in composition plus high mg basalts and basic andesites with flat ree patterns as low as 4x chondritic concentrations these erupted either within the volcanic arc during its first 5 ma or in an adjacent backarc during its first ma of formation subsequent volcanics of the early arc stage apparently erupted onto early backarc basin crust most are intermediate between earlier extremes in hfse contents but at least one volcano produced strongly lree depleted island arc tholeiites in contrast medium k tholeiitic and calc alkaline andesites erupted during the mature arc stage parental basalts were enriched in lree but depleted in hree relative to earlier basalts due to a change in source composition counterflowing morb source asthenosphere within the mantle wedge dominated vol

petrogenesis of the 1 9 ga mafic hanging wall sequence to the flin flon callinan and triple 7 massive sulphide deposits flin flon manitoba canada a detailed study of the geochemical and isotopic characteristics of the volcanic rocks of the hidden and louis formations which make up the hanging wall to the volcanogenic massive sulphide deposits at flin flon manitoba was carried out on a stratigraphically controlled set of samples the stratigraphy consists of the lowermost dominantly basaltic hidden formation and the overlying dominantly basaltic louis formation of importance petrogenetically is the 1920 unit a basaltic andesite with nb thmn 0 54 0 62 end 1 9ga 3 6 5 9 ehf 1 9ga 8 5 9 6 and 204pb 206pb 23 9 the basaltic flows that dominate the hidden formation have nb thmn 0 16 0 29 end 1 9ga 1 7 4 4 ehf 1 9ga 7 0 11 8 and 204pb 206pb 16 9 18 6 the carlisle lake basaltic andesite top of hidden formation is characterized by nb thmn 0 16 0 14 and 204pb 206pb 21 4 the rhyodacitic tower member bottom of louis formation has nb thmn 0 23 end1 9ga 4 6 ehf1 9ga 9 3 and 204pb 206pb 22 2 the

a special issue on archean magmatism volcanism and ore deposits part 2 volcanogenic massive sulfide deposits preface this is the second of a two part special issue of economic geology devoted to archean ore deposits the first part of the special issue vol 107 no 5 contains six papers that discuss craton to deposit scale controls on komatiite associated ni cu pge deposits barnes and fiorentini 2012 collins et al 2012 fiorentini et al 2012 heggie et al 2012a b taranovic et al 2012 and six papers that discuss the diversity and key aspects of greenstone hosted au deposits cote mantha et al 2012 garde et al 2012 leclerc et al 2012 mercier langevin et al 2012b schneider et al 2012 sherlock et al 2012 a general introduction to the special issue and an overview of some implications for exploration for greenstone hosted au and komatiite associated ni cu pge deposits in ancient belts is given in mercier langevin et al 2012a the ten papers in this second part of the special issue discuss specific aspects of archean volcanogenic massive sulfide vms deposits the archean which represents more than one third of earth s history was a prolific period for the formation of vms deposits franklin et al 2005 most of these deposits formed within a comparatively narrow time interval between 2740 and 2690 ma in the neoarchean approximately 8 of the global vms tonnage production reserves and geologic resources is contained within deposits of archean age fig 1a given the low degree of preservation of archean crust compared to phanerozoic crust e g veizer 1988 the abundance of archean vms deposits is remarkable proterozoic vms deposits account for approximately 20 of the global vms tonnage whereas the phanerozoic deposits contain 72 of the global tonnage the latter is due in large part to giant vms deposits of the iberian pyrite belt in spain and portugal the urals in russia the rudny

extensional habitats of rhyolite hosted massive sulfide deposits generation of rhyolite hosted massive sulfide deposits is restricted to extensional habitats these include interarc and back arc volcano tectonic rifts related to orthogonal or oblique subduction and rifts induced by either transform faulting or intraplate activity modern analogs of some of these habitats could contain recent massive sulfide deposits

geochemistry of volcanic rocks associated with cu zn and ni cu deposits in the abitibi subprovince volcanogenic massive sulfide vhms deposits in the abitibi subprovince are preferentially associated with volcanic successions containing 150 m thicknesses of felsic volcanic rocks approximately 50 by area of volcanic terranes and are found within volcanic sequences of at least three distinct affinities group i which is host to greater than half of the volcanogenic massive sulfide deposits by tonnage and which comprises only approximately 10 percent by area of volcanic terranes is composed of bimodal tholeiitic basalt basaltic andesite and high silica rhyolite the basaltic andesites and high silica rhyolites are characterized by high high field strength element and heavy rare earth element ree contents low light to heavy ree ratios most with la n yb n 0 8 3 and strong negative eu anomalies the kamiskotia matagami and chibougamau lower cycle volcanogenic massive sulfide areas all of which are also underlain by large synvolcanic gabbroic complexes are associated with group i volcanic sequences the kidd creek potter normetal and horne deposits are also included in this category group ii which is host to one third of the volcanogenic massive sulfide deposits by tonnage and which is also approximately 10 percent by area of volcanic terranes is composed of bimodal transitional tholeiitic to calc alkalic andesitc and rhyolite characterized by intermediate high field strength element contents and slightly higher ree ratios la n yb n 1 4 noranda camp excluding the horne deposit and val d or camp group iii is host to only one known deposit the selbaie mine which is unusual in that much of its mineralization cuts stratigraphy the selbaie mine sequence contains calc alkalic andesite rhyolite with relatively low high field strength element and ree contents and higher ree ratios la n yb n 3 9 the vast majority of volcanogenic massive sulfide bearing mafic and felsic volcanic rocks in the abitibi subprovince have la n yb n 5 barren volcanic sequences are group iv calc alkalic basaltic andesite to rhyodacite with low high field strength element and relatively high ree ratios la n yb n 8 20 represented by the upper skead group the quebec hunter mine group and the upper cycle chibougamau rocks and group v mafic to felsic alkalic volcanic rocks with high ree ratios la n yb n 12 62 represented by the timiskaming opemisca and ridout series rocks group i is most similar to thickened oceanic rift suites e g galapagos spreading center iceland east rift group ii is similar to suites in rifled island arcs e g hokuroku district japan and group iii is comparable to continental arc suites e g southern volcanic zone central chile groups iv and v are comparable to arc related suites derived from metasomatized mantle with variable amounts of crustal contamination e g setouchi area japan roman province italy known ni cu deposits in volcanic sequences are hosted exclusively in komatiitic flows and hypabyssal sills represented by chill compositions with high mgo contents 20 35 wt anhydrous very low incompatible element contents and depleted signatures la n sm n 0 5 0 8 zr y 2 5 alexo marbridge and shaw dome deposits in comparison to most barren komatiites in the abitibi subprovince their depleted trace element signatures indicate minimal crustal assimilation which would appear contrary to the widely held view that crustal contamination e g addition of silica sulfur oxygen of a mantle derived melt is necessary for sulfur saturation and magmatic sulfide segregation this problem may be reconciled by considering the dynamics of komatiite flows lesher and arndt 1990 where contaminated present address 23 euclid avenue ottawa ontario canada kis 2w2 komatiite liquid segregated and deposited sulfide and was subsequently swept downstream and replenished by uncontaminated magma over the deposit as the flow ebbed and cooled when considered together with geologic features such as evidence for thermal erosion in the footwall langmuir deposits and the presence of sulfidic footwall rocks shaw dome deposits the distinctive depleted geochemical signature of mineralized komatiites is useful in exploration for ni cu deposits

zircon thermometry of high temperature rhyolites near volcanic associated massive sulfide deposits abitibi subprovince canada high temperature high silica rhyolites are commonly found near cu zn volcanic associated massive sulfide vms deposits in the archean abitibi subprovince they are characterized by anhydrous phenocrysts feldspar quartz in concentrations of generally 73 sio 2 high incompatible element contents rb sr 1 zr y

stratigraphy and u pb zircon geochronology of kidd creek implications for the formation of giant volcanogenic massive sulphide deposits and the tectonic history of the abitibi greenstone belt within the context of a structural stratigraphic analysis of the giant kidd creek cu zn ag deposit precise u pb zircon ages have been obtained for five critical rock units associated with the deposit massive flow banded footwall rhyolite is dated at 2714 3 1 2 ma slightly younger than a previously published age of 2717 2 ma on nearby rhyolite breccia extrusive rhyolite in the immediate hanging wall to the main ore lenses is dated at 2711 5 1 2 ma leaving an interval of one to several million years for the formation of the deposit we consider the demonstrated longevity of the kidd creek hydrothermal system as a major control on its giant size age constraints together with the size of the deposit suggest a time averaged rate of base metal sulphide deposition of about 10 100 t year peak rates were likely one to possibly two orders of magnitude above time averaged rates hence 100 1000 t year or higher detrital zircon ages on greywackes in the structural footwall to the deposit support structu

the flin flon paleosol revisited a ca 1 85 ga paleosol developed on seafloor altered mafic rocks is preserved beneath continental sandstones and conglomerates of the missi group near flin flon manitoba previous work has focused

late glacial allerod younger dryas coleoptera from central cape breton island nova scotia canada coleoptera from three late glacial sites on cape breton island nova scotia canada provide proxy climate data from 12 600 to 10400 bp samples older than about 11 800 bp contain tundra to tree line species between 11 800 and about 10 800 bp beetle assemblages become typical of the modern boreal forest beetles younger than 10 800 bp responded to climatic deterioration during the younger dryas although coleopteran evidence for the younger dryas is not as strong as that presented by palynological and stratigraphic studies the appearance of olophrum boreale and other species found today in the northern boreal forest and on tundra or coastal tundra corresponds with the decline of shrub birch and the rise in willow and alder pollen beetles responded just as likely to changes in vegetation and ground cover as to changes in temperature the extent to which coleoptera were affected may lie somewhere between a moderated continental response seen in the great lakes region in north america and more extreme changes recorded in europe this response is consistent with shifts in the north atlantic oceanic polar front in the ruddiman and mcintyre model resumc les colkoptkres trouvks dans trois sites glaciaires tardifs de l ile du cap breton ouvelle cosse canada

volcanic reconstruction of the paleoproterozoic stroud breccia understanding the transition from a primitive to mature arc and its impact on vms ore formation snow lake manitoba canada abstract the stroud breccia is a 400 m thick package of dominantly felsic volcaniclastic rocks within the paleoproterozoic snow lake arc assemblage it stratigraphically overlies the ore interval for the anderson stall and rod volcanogenic massive sulfide vms deposits at snow lake manitoba canada and occupies the stratigraphic interval between the underlying primitive arc anderson sequence and the overlying mature arc chisel sequence the stroud breccia is interpreted to be a product of subaqueous pyroclastic and effusive dominantly rhyolitic volcanism and concomitant subsidence it consists of felsic tuff to lapilli tuff crystal rich felsic tuff felsic lapillistone felsic tuff breccia mafic tuff to lapilli tuff heterolithic tuff breccia to breccia and rhyolite the finer felsic volcaniclastic units are characterised by angular or broken quartz crystals angular lithic rhyolite lapilli and pumice fine ash broken crystals and pumice suggest they were deposited by eruption fed density currents associated with a phreatomagmatic eruption the coarser felsic volcaniclastic units are characterized by blocks of strongly quartz feldspar porphyritic rhyolite and pumice and are interpreted to have been deposited during the reworking of pyroclastic debris flow deposits on the seafloor during mass wasting events at fault scarps planar and cross laminations graded beds and bomb sag structures suggest the mafic tuff to lapilli tuff unit was deposited by a combination of subaqueous eruption fed density currents and eruption driven ballistically emplaced ejecta likely through subaqueous tephra jetting lithofacies analyses and geochemistry has allowed comparison between the felsic volcanic rocks of the stroud breccia and those that host the anderson stall and rod vms deposits detailed mapping has led to the identification of synvolcanic faults defining basins and volcanic vents that indicate that the process of incipient rifting of the anderson sequence primitive arc continued during emplacement of the stroud breccia these structures also define magma and fluid pathways critical in controlling the formation of the anderson vms deposits meaning they represent deep seated and long lived structures that can be used as vectors to mineralization at depth

significance of pre 1860 ma granitoid magmatism for crustal evolution and exploration targeting in the flin flon assemblage trans hudson orogen canada granitoid plutonism a significant contributor to orogenic evolution is a commonly overlooked vector in exploration targeting using the flin flon glennie complex of the trans hudson orogen as a template we show that the geochemistry of granitoid rocks can be a useful parameter in differentiating prospective and nonprospective areas for volcanic hosted massive sulfide vhms deposits the flin flon glennie complex includes 1910 to 1860 ma plutonic rocks that can be subdivided into three suites 1 juvenile arc related rocks of ferroan and magnesian subtypes 2 contaminated arc related rocks and 3 successor arc related rocks of both low and high sr y ratio petrogenesis of ferroan juvenile and low sr y successor arc plutons indicates they formed in regions of thinner crust and hence would have been associated with higher heat flow and arc rifting conditions that favor vhms endowment regions of the orogen with both ferroan and low sr y plutonic subtypes were long lived zones of thin crust and preserve vhms mineralization related to both juvenile and successor arc magmatism in contrast volcanic belts dominated by contaminated arc or high sr y successor arc plutons formed on thicker substrates with contaminated arc rocks built on archean paleoproterozoic pericratonic slivers and high sr y successor arc rocks associated with submarine to subaerial arc systems these regions of thicker crust demonstrably lack vhms deposits and were also the locus for late unroofing our results suggest that pluton geochemistry regionally correlates with mineral occurrence and could represent a useful regional exploration tool in buried or poorly exposed parts of the flin flon glennie complex and other paleoproterozoic orogens