late archean quetico accretionary complex superior province canada the 1200 km long quetico subprovince consists of monotonous metagraywacke with derived migmatite and granite in thrust and or transcurrent fault contact with the adjacent wabigoon and wawa metavolcanic subprovinces imbrication of sedimentary wedges derived from volcanic arcs to the north and south produced a 10 100 km wide stratigraphically north facing pile thermal relaxation in the 20 m y following accretion of the southern arc resulted in melting of the accretionary pile to produce peraluminous granite and associated low pressure metamorphism

surface wave focusing and acoustic communications in the surf zone the forward scattering of acoustic signals off of shoaling surface gravity waves in the surf zone results in a time varying channel impulse response that is characterized by intense rapidly fluctuating arrivals in some cases the acoustic focusing by the curvature of the wave crest results in the formation of caustics at or near a receiver location this focusing and the resulting caustics present challenges to the reliable operation of phase coherent underwater acoustic communications systems that must implicitly or explicitly track the fluctuations in the impulse response the propagation physics leading to focusing are studied with both experimental data and a propagation model using surface wave profiles measured during the collection of the experimental data the deterministic experimental and modeled data show good agreement and demonstrate the stages of the focusing event and the impact of the high intensity arrivals and rapid fluctuations on the ability of an algorithm to accurately estimate the impulse response the statistical characterization of experimental data shows that the focusing by surface gravity waves results in focused surface reflected arrivals whose intensity often exceeds that of the direct arrival and the focusing and caustic formation adversely impacts the performance of an impulse response estimation algorithm

determination of ocean surface wave shape from forward scattered sound forward scattered sound from the ocean surface is inverted for wave shape during three periods low wind mix of wind and swell and stormy derived wave profiles are spatially limited to a fresnel region at or near the nominal surface specular reflection point in some cases the surface wave profiles exhibit unrealistic temporal and spatial properties to remedy this the spatial gradient of inverted waves is constrained to a maximum slope of 0 88 under this global constraint only surface waves during low wind conditions result in a modeled surface multipath that accurately matches data the power spectral density of the inverted surface wave field saturates around a frequency of 8 hz while upward looking sonar saturates at 1 hz each shows a high frequency spectral slope of 4 that is in agreement with various empirical ocean wave spectra the improved high frequency resolution provided by the scattering inversion indicates that it is possible to remotely gain information about high frequency components of ocean waves the inability of the inversion algorithm to determine physically realistic surface waves in periods of high wind indicates that bubbles and out of plane scattering become important in those operating scenarios

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

chemostratigraphic division of the blake river group rouyn noranda area abitibi quebec the effusive rocks of the blake river group in the abitibi volcanic belt rouyn noranda region belong to a bimodal sequence in which andesites and rhyolites clearly dominate the identification of calc alkaline and tholeiitic affinities is made upon examination of the major trace and rare earth element ree content thus the andesites 58 normalized sio2 value without volatiles of the calc alkaline units have average k 4800 ppm ba 160 ppm and rb 13 ppm values that are greater than the average k 1800 ppm ba 130 ppm and rb 3 ppm values for andesites 57 sio2 that belong to associated tholeiitic units furthermore tholeiitic andesites have distinctive average values of ti 9600 ppm and y 40 ppm that are higher than the average values of ti 6700 ppm and y 25 ppm of calc alkaline andesites an effective discrimination between the calc alkaline and tholeiitic affinities is obtained using the zr y and ti zr ratios which are respectively less than 4 and greater than 70 in andes

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

simulations of acoustic tomography array performance with untracked or drifting sources and receivers ocean tomography as originally proposed required all sources and recievers to be tautly moored and acoustically tracked to separate travel time perturbations due to mooring motion from those due to ocean features it is possible to process the tomographic travel times to estimate both ocean sound speed perturbations and mooring offsets effecting a separation without external tracking a side effect of this processing is a check on the ray identification since the varying instrument positions can be used as a synthetic array for estimating ray angle simulations and examples with actual data were used to contrast mapping performance with and without mooring tracking for a variety of ray data sets in general the ocean maps degrade when the tracking data are withheld however when many high precision ray travel time measurements are available the degradation is small in these cases it would be possible to deploy free drifting instruments as part of a monitoring experiment

evidence for contrasting compositional spectra in comagmatic intrusive and extrusive rocks of the late archean blake river group abitibi quebec the flavrian pluton is a sill shaped intrusion in the blake river group brg volcanic rocks in the noranda region of the abitibi greenstone belt the pluton is dominated by trondhjemites and tonalites with minor peripheral quartz gabbro and hybrid phases the brg volcanic rocks consist of a bimodal suite of basalt andesite and rhyolite the flavrian trondhjemites are geochemically identical to the rhyolitic lavas of the brg sio2 72 la sm 3 4 la yb 3 6 zr y 3 9 y nb 3 1 and the flavrian gabbroic and dioritic rocks are identical to the brg basalts and andesites sio2 58 la sm 3 0 la yb 5 5 zr y 4 2 y nb 3 3 however the tonalitic rocks of the flavrian pluton have no extrusive equivalents in the brg the different compositional spectra of the extrusive and intrusive rocks are interpreted as being a result of a transition in magma chamber evolution from a zoned open system that was active during the evolution of the volcanic rocks to closed system plutonic crystallization

geochemical variations in middle ordovician volcanic rocks of the northern miramichi highlands and their tectonic significance a detailed geochemical study of middle ordovician volcanic rocks undertaken in the northern miramichi highlands of new brunswick shows that 10 basaltic suites can be distinguished these suites are assigned to the tetagouche and fournier groups the contact between these two groups is a major thrust zone marked for over 70 km by a prominent blueschist zone all the tetagouche group volcanic rocks have chemistries consistent with extrusion in a continental rift but most fournier group basalts in the miramichi highlands have chemistries suggestive of an oceanic back arc setting the chemical signatures stratigraphic variations and structural data indicate that the northern miramichi highlands preserve a section across a telescoped middle ordovician back arc basin that initially opened as a result of asthenospheric injection near the rear part of a lower ordovician ensialic arc

application of high field strength elements to discriminate tectonic settings in vms environments high field strength element ratios in felsic volcanic rocks reflect the tectonomagmatic evolution of a region th ta th hf ta hf th yb and ta yb ratios collectively help to define the tectonic environment of volcanism separating oceanic arcs active continental margins and within plate volcanic zones on the basis of the above empirical observations the tectonic environments of selected archean and post archean volcanogenic massive sulfide deposits were reexamined published data sets plotted on discriminant diagrams represent twelve volcanogenic massive sulfide vms deposits from two distinct tectonic environments the volcanic rocks of the kuroko deposits japan san nicolas mexico and bathurst new brunswick canada plot within the active continental margin field on all diagrams whereas volcanic rocks from archean deposits of the superior province canada kidd creek kamiskotia geco winston lake mattabi lyon lake noranda selbaie and south bay plot in the within plate volcanic zone field the discriminant diagrams demonstrate that although the chemical character of rhyolites has not changed significantly since the archean the range of geotectonic setting of vms deposits probably has it is suggested that archean deposits most likely formed in an ensimatic rift environment whereas post archean deposits formed in subduction related rift zones of arc environments subduction related rhyolites of vms deposits are variably enriched in th and the light rare earth elements with respect to ta nb and the heavy rare earth elements

zircon u pb ages from the wabigoon manitou lakes region wabigoon subprovince northwest ontario three distinct stratigraphic units have been recognized in the crow lake savant lake belt these are a basal unit consisting of high magnesium tholeiitic flows a middle unit consisting mostly of tholeiitic to calc alkaline pyroclastic rocks and flows and an upper unit of high iron tholeiitic flows a zircon u pb study has been carried out on seven rocks from the wabigoon manitou lakes region of this belt in the manitou lakes area a minimum age of 2755 ma on a porphyry pluton intruded into the wapageisi volcanics gives a minimum age for the high magnesium tholeiitic sequence a trondhjemite phase of the atikwa batholith near wabigoon lake that is dated at 2732 2 2 9 ma has the same age within experimental error as a rhyolite flow from the lower wabigoon volcanics in the same area that is dated at however a trondhjemite phase of the atikwa batholith at eagle lake that is dated at is distinctly younger than a dacite flow collected nearby from the lower wabigoon volcanics that is dated at both thes

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

geochemistry and origin of archean felsic metavolcanic rocks central noranda area quebec canada felsic magma petrogenesis was studied by analyzing 24 stratigraphically controlled archean andesite to rhyolite lava flows of both tholeiitic and calc alkalic affinity from the upper noranda subgroup quebec using instrumental neutron activation and x ray fluorescence techniques the lavas have moderate values of la yb n 0 9 3 8 and low values of 100 th zr 1 according to calculations following batch partial melting and rayleigh fractional crystallization models both the calc alkalic and tholeiitic felsic volcanic rocks are probably products of shallow level fractional crystallization of mafic parental magmas formed respectively by lower 7 for calc alkalic and higher 14 for tholeiitic degrees of partial melting of a primitive mantle source contribution to the magma genesis from plausible crustal materials was negligible a back arc type diapirism is geochemically suggested for the tectonic model of origin of noranda felsic magmas in conformity with geological observations felsic volca

u pb dating of minerals in alteration halos of superior province massive sulfide deposits syngenesis versus metamorphism u pb geochronology of igneous zircon from rhyolitic host rocks to the archean kidd creek geco and winston lake massive sulfide deposits in the superior province of ontario shows that volcanism which accompanied mineralization occupied a narrow time span 2717 2 ma 2720 2 ma and 2723 2 ma respectively precise ages of hydrothermal monazite allanite and rutile from alteration zones surrounding the above deposits indicate that these minerals crystallized 40 70 million years after volcanism monazite from kidd creek mine is 2659 3 ma old in agreement with spatially associated 2664 25 ma old rutile monazite from a biotite schist at geoco mine gives a similar age of 2661 1 ma however monazite from a sericite schist which hosts the ore at geco mine is 2675 2 ma old abraded large monazite grains from three units in the winston lake deposit are coeval with biotite crystallization and record an age of 2677 2 ma approximately the same as monazite in the sericite schist at geco data points from allanite fractions from both the winston lake and geco deposits fall on a pb pb isochron that gives an age of 2672 5 ma rutile from winston lake gives a younger age of 2651 6 2 ma and may date retrograde alteration of biotite to chlorite the ca 2676 ma age of monazite from winston lake and in the sericite schist at geco mine probably dates a regional metamorphic event that affected most of the southern superior province the ca 2660 ma old monazite in the biotite schist at geco mine and in the chlorite sericite alteration at kidd creek may date later k metasomatism caused by metamorphically derived fluids that were focussed along old fault structures such fluids were also responsible for local sulfide remobilization monazite and rutile are spatially associated with chlorite and sericite alterations at kidd creek their young ages indicate that these originally syngenetic mineral assemblages may have been significantly affected by regional metamorphism formation of monazite at all three deposits studied was a result of significant ree remobilization during metamorphism the discrete character of syn metamorphic hydrothermal activity in different units of the same deposit as well as its synchroneity among different widely separated deposits requires a mechanism for episodic injection of heat and fluid into the crust on a regional scale these activities are broadly coeval with and probably related to plutonism within adjacent metasedimentary subprovinces and middle to lower crustal metamorphism in the superior province

secular variation in greenstone sequence development emphasizing superior province canada abstract evidence from the superior province of the canadian shield suggests the existence of several distinct lithostratigraphic associations in greenstone belts 1 quartz arenite and carbonate bearing sequences 2 mafic ultramafic volcanic sequences 3 mafic to felsic volcanic cycles and 4 timiskaming type sequences of fluviatile sediments and calc alkaline to alkaline volcanics recently recognized quartz arenite bearing sequences in the sachigo and wabigoon subprovinces are from base to top quartz arenite stromatolite bearing carbonate oxide facies iron formation and komatiite or tholeiite primary structures in the quartz arenites indicate shallow water deposition and represent mature sedimentation granitoid provenance of these sediments is postulated based upon petrography of coarse arenites and clasts of associated conglomerates the few dated superior province quartz arenite bearing sequences are 2 85 ga the shallow water origin of the primary structures and biota and the areal extent of the quartz arenite and carbonate sequences invite comparison with platform sediments at passive margins platform sequences unconformably overlie 3 ga granitoid rocks and older mafic volcanics where original lower contacts are preserved in two localities mafic volcanic sequences contain sheet flows iron formations and deep water argillites based on physical volcanology and sedimentology these sequences are compared to modern deep water mafic plain and hawaiian volcanism they generally underlie mafic to felsic volcanic cycles and overlie platform sequences mafic sequences are 2740 2700 ma in age mafic to felsic volcanic cycles consist of deep water tholeiitic flows overlain by shallow water to subaerial intermediate to felsic pyroclastics and flows the facies style of volcanism petrography and geochemistry of the mafic to felsic cycles most closely resemble the characteristics of crust in continental magmatic arc systems this type of lithostratigraphic association varies in age from 2775 to 2700 ma in the superior province with minor exceptions timiskaming type sequences consist of fluviatile conglomerate immature arenites and wackes with subaqueous to subaerial volcanics of variable chemistry longitudinal and lateral variation within fault bounded basins is extreme and the sequences have generally been affected by only late stages of deformation the combination of rock types facies distribution the fault bounded nature of the repositories and the locus of sedimentation along zones of transcurrent displacement suggest timiskaming sequences are best compared with modern pull apart basins superior province timiskaming sequences are within the superior province platform sequences are the earliest postorogenic lithostratigraphic unit in greenstone belts followed by mafic plain sequences arc volcanics and pull apart basins we suggest that platform sequences based upon limited evidence are preceded by an orogeny and that pull apart basins represent a subsequent orogeny the lithostratigraphic units above have distinct metallogenic associations 1 platform sequences based upon compilation of several shields may contain detrital au and u and oxide facies iron formations associated felsic volcanics contain no recognized volcanogenic cu zn deposits in the superior province the following metallogenic associations are noted 2 mafic plain sequences contain komatiite flow related ni deposits cu ni and platinum group deposits are associated with flows and coeval intrusions 3 arc volcanic sequences contain volcanogenic cu zn sulphide deposits and scarce deposits of porphyry type cu mo and 4 timiskaming sequences and related plutonism are related to lode au

mineralogy and geochemistry of the clay fraction of till in northern finland abstract the mineralogy and geochemistry of the clay fraction of till in different moraine types and in different bedrock areas in northern finland have been studied moraine types include ground moraine rogen moraine pulju moraine sevetti moraine and kianta moraine the bedrock is composed of granite granite gneiss and mafic volcanite x ray diffraction differential thermal and thermogravimetric analyses transmission electron microscopy x ray fluorescence and atomic absorption spectrometry were used as analytical methods quartz feldspars and amphibole are the primary rock forming minerals occurring in nearly all the samples of each study area the clay minerals proper include kaolinite vermiculite swelling lattice vermiculite chlorite illite and mixed layer minerals kaolinite occurs most abundantly only in till in the kittilaarea where a preglacial weathering crust has been the source rock poorly crystalline or amorphous fe oxides also abound in till at kittila sodium ca and si have been depleted and al mg fe k ti p and trace elements have been enriched in the clay fraction compared with the fine fraction the contents of si k and na are higher in the granitic areas and the contents of cu co ni and zn are higher in the mafic volcanite areas preglacial weathering has led to the depletion of si mg ca k and na and to the enrichment of al fe ti p and trace elements in the clay fraction of till in the kittilaarea high base metal values in the inari area suggest the possibility of sulphide mineralizations there and high as values in the kittilaarea indicate au potential there the most important factors controlling the mineralogical and geochemical composition of the clay fraction of the tills in northern finland are the composition of the bedrock and the possible occurrence of an old weathering crust the final grain size composition of the tills and consequently the quantitative proportions of the different minerals are often related to the last glacial quarrying and sorting processes therefore the mineralogical composition of the tills is to a certain extent bound also to the respective moraine types

timing of magmatism and deformation in the kamiskotia kidd creek area western abitibi subprovince canada abstract the kamiskotia kidd creek area comprises well preserved granitoid greenstone belt lithologies of the western most abitibi subprovince similar in composition and structural style to other late archean granitoid greenstone terranes e g kalgoorlie norseman western australia belingwe zimbabwe slave province canada it contains the kidd creek volcanogenic massive sulfide deposit and lesser deposits of the kamiskotia district and lode gold deposits associated with the destor porcupine fault zone near the prolific porcupine gold district the magmatic and tectonic history for the area is provided through detailed structural mapping and high precision u pb geochronology field observations support the following sequence of magmatic and structural events in the kamiskotia area 1 formation of older mafic and intermediate volcanic rocks followed by the emplacement of the kamiskotia gabbroic complex kgc and cogenetic massive sulfide bearing bimodal volcanic rocks kv also accompanied by coeval intrusion of granitoid a into the crystallizing kgc 2 regional bulk rotation about a sub horizontal axis of this stratigraphy to form a ne facing monocline 3 emplacement of three large granitoid intrusions imparting their respective contact strain aureoles on the stratigraphy 4 regional sub horizontal bulk north south shortening that formed a non penetrative east west flattening fabric with an element of 5 late dextral transpression that formed high strain zones related to western destor porcupine fault zone dpfz within less competent volcanic units and 6 emplacement of alkalic dikes associated with the late stages of transpressive deformation u pb ages help substantiate this chronology and aid in the correlation of kamiskotia lithologies across the southern abitibi subprovince zircon ages for the kgc and a kamiskotia rhyolite are 2707 2 ma and 2705 2 ma respectively these ages are coeval with the reid rhyolite with a zircon age of 2706 2 ma but are significantly younger than the kidd creek rhyolite and the prosser rhyolite with zircon ages of 2717 2 ma data refined by the addition of an abraded concordant analysis and 2716 6 3 ma respectively two of the granitoid intrusions have zircon ages of 2696 1 5 and 2694 4 ma the older granitoid intrusion has a titanite population with a 207 pb 206 pb minimum age of 2692 5 ma which may represent a protracted cooling history or a metamorphic event after the setting of the zircon u pb system two zircon fractions from the younger granitoid intrusion exhibit inheritance with 207 pb 206 pb minimum ages up to 2926 ma indicating the presence of significantly older crust in this region timing of north south compression and late transpression may be constrained by a u pb garnet titanite age on a late to post tectonic alkalic dike at 2687 3 ma

an unusual sink for rare elements the rhyolite basalt contact of the archean winston lake volcanogenic massive sulfide deposit superior province canada

rare earth element mobility in alteration pipes below massive cuzn sulfide deposits abstract a convincing demonstration of trace element mobility should satisfy two criteria 1 the range of trace element concentrations in the rock before and after alteration must be known with confidence and 2 the absolute abundances and the ratios of the mobile trace elements should vary between altered and unaltered rocks these criteria have been applied to the host felsic volcanics and alteration pipes associated with several canadian massive cu zn sulfide deposits although there is no evidence of rare earth element ree mobility in the pervasive low grade alteration envelopes adjacent to the deposits the light and middle ree lree and mree plus y have been systematically mobilized relative to the heavy ree hree and other trace elements in the alteration pipes beneath the ore zones there is evidence of minor lree and mree depletion in the most altered rocks at the south bay mine uchi lake and of significant lree depletion in the alteration pipe beneath the mattabi mine sturgeon lake however the strongest mobility is found at the kidd creek mine where the lree were leached from the rocks in the footwall stringer zone and redeposited in a metasomatic chlorite zone directly beneath the massive ore horizon and the mree and y were preferentially lost from the system producing distinctive chondrite normalized ree patterns with tb yb n ratios less than unity eu2 was found to be more mobile than the trivalent ree especially at kidd creek where there is a marked increase in the magnitude of the eu anomaly in the most altered samples high field strength elements such as u th hf and zr have not decoupled and apparently remained relatively immobile during all but the most intense alteration i e kidd creek preliminary data suggest that the degree of ree mobility increases with the size of the deposit thus ree mobility is a potentially useful method of distinguishing between small and large massive sulfide deposits at an early stage in exploration however this hypothesis requires further testing

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

the selbaie zn cu ag deposits quebec canada an example of evolution from subaqueous to subaerial volcanism and mineralization in an archean caldera environment the selbaie deposits of western quebec are hosted in calc alkalic pyroclastic rocks of the abitibi subprovince rocks range upward from subaqueous debris flows through pumiceous tuff to densely welded ignimbrite they form an intracaldera sequence over 1 200 m thick which records evolution from subaqueous to subaerial deposition mineralization occurred within this sequence on the southwest flank of the brouillan tonalite a central intrusion and possibly a resurgent dome and includes regionally extensive and temporally early exhalite local massive sulfide and later epithermal veins these veins were emplaced by open space filling along synvolcanic structures and make up the bulk of the economic resource mineralization and alteration show similarities to both massive sulfide and epithermal deposits cu zn increases with depth but also increases laterally toward veins and toward the intrusion ag cu in veins is higher in the upper levels of the system whole rock mass balance calculations indicate enrichment in si fe mg and mn with proximity to mineralization and depletion in ca k and na na metasomatism common in host rocks to archean massive sulfide deposits is absent in subaerially emplaced tuff at selbaie and k feldspar is preserved selbaie is unusual 1 as an archean example of a subaerial caldera that evolved from subaqueous to subaerial volcanism 2 in representing economically important archean epithermal mineralization and 3 in demonstrating the link between subaqueous volcanogenic massive sulfide deposits and subaerial volcanogenic epithermal veins it is perhaps unique in preserving so well all three of these aspects in a single mineralized system the rarity of similar mineralized subaerial volcanic settings in the abitibi subprovince reflects its primitive crustal development but may also be due to incomplete preservation of subaerial environments