conflicting sm nd whole rock and u pb zircon ages for archean lavas from newton township abitibi belt ontario abstract archean komatiitic and tholeiitic lavas from newton township ontario have a sufficient range of sm nd ratios to define a well constrained line on the normal 143 nd 144 nd vs 147 sm 144 nd isochron plot the data give an isochron age of 2826 64ma and an initial e nd of 2 65 0 26 however u pb analysis of zircons from a dacitic volcaniclastic that underlies the komatiite tholeiite suite give an age of 2697 1 1ma there is strong evident that the zircon age is the eruption age suggesting that the older sm nd age is incorrect and probably results from mixing between isotopically distinct mantle sources at the time of eruption the sources had e nd values from about 4 2 to 1 6 indicating that the archean mantle in this area was markedly heterogeneous and not uniformly depleted

the steady state thermal structure of eroding orogenic belts and accretionary prisms an analytical expression derived in this paper for the steady state thermal structure of thrust belts and subduction systems shows that surface erosion rate basal accretion rate and upper plate heat production are extremely important in controlling the temperature and metamorphic history of orogenic belts and accretionary prisms especially where upper plate thickness h is large for example even at rapid erosion and accretion rates and with large upper plate heat productions temperatures near the toe of a thrust wedge e g at h 5 km are nearly the same as those that would be present in the absence of erosion accretion and upper plate heat production in thicker parts of the same wedge e g at h 30 km the combined effects of erosion accretion and upper plate heat production can be dramatic for sufficiently large magnitudes of upper plate heat production or sufficiently rapid erosion rates inverted negative geothermal gradients are produced in the lower part of the upper plate and the upper part of the lower plate although it is difficult to produce inverted geotherms where h 20 km the potential importance of erosion and accretion can be illustrated through two examples 1 beneath the himalayas increasing the upper plate radiogenic heat production from 0 to 2 5 mw m3 and increasing the rate of surface erosion from 0 to 1 mm yr raises the computed steady state temperatures on the main central thrust at h 30 km from 265 c to 600 c and produces a local temperature maximum of 635 c located 6 km above the fault and 2 within the upper plate of the peru trench increasing the rate of surface erosion and basal accretion from 0 to 2 4 mm yr or increasing the upper plate radiogenic heat production from 0 to 1 3 mw m3 increases the computed steady state surface heat flow at h 30 km from 10 to 33 mw m3 but only increases temperatures at the fault surface from 125 c to 170 c shear heating along thrust faults or subduction boundaries is not necessary to produce the high metamorphic temperatures or surface heat flows observed in these two examples and the generation of large amounts of heat by shear stresses on the faults more than a few tens of bars appears to be inconsistent with some of the observations made in these areas this study indicates that many of the major discrepancies between existing thermal models of overthrust belts and observed temperatures as inferred from field data can be attributed to neglect of horizontal and vertical advection of heat caused by surface erosion and by accretion of material from lower plate to upper plate across the fault surface

evidence for stratification of basic silicic and hybrid magmas in the newark island layered intrusion main labrador the newark island layered intrusion nili located in the nain anorthosite complex of labrador developed through a complex sequence of fractional crystallization periodic replenishment of both basic and silicic magmas and magma mixing it is subdivided into a lower layered series and an upper hybrid series three large transgressive trough structures cut these cumulate rocks at different levels each trough is lined by granitic rocks and filled mainly by chilled mafic pillows that grade inward to massive olivine gabbro each of these troughs originated as a large feeder dike of granitic magma into the nili chamber when it was floored by basic magma this resident basic magma collapsed downward into the granitic feeder and formed chilled pillows these pillows preserve the compositions of basic magma existing in the chamber at the time of granite replenishment pillows in the lowest trough show a wide compositional range and provide a direct record of compositional stratification of a magma chamber related to a layered intrusion

nd and sr isotope systematics for the kamiskotia montcalm area implications for the formation of late archean crust in the western abitibi subprovince canada geochemistry and nd isotopic compositions are used to characterize mantle and crustal sources and to provide constraints on petrogenetic models for tholeiitic calc alkalic and lamprophyric suites in the kamiskotia montcalm area the kamiskotia gabbroic complex kgc and cogenetic bimodal volcanic rocks have end t 2 2 to 2 6 consistent with a direct derivation from a long term light rare earth element lree depleted mantle the montcalm gabbroic complex has decreasing end t upsection from 2 8 to 1 0 consistent with contamination by long term lree enriched with respect to the long term lree depleted abitibi mantle crust during fractionation two calc alkalic lamprophyre samples characterized by large ion lithophile element lile and lree enrichment and high mgo ni and cr contents have end t of 2 5 and 2 8 indicating a derivation from a depleted mantle source that had undergone recent trace element enrichment a different lamprophyre suite is extremely lile and lree enriched and h

sm nd and rb sr isotope systematics of an archean anorthosite and related rocks from the superior province of the canadian shield sm nd and rb sr isotopic data for the bad vermilion lake anorthosite complex bvl in the rainy lake area of the superior province of northwestern ontario show that direct ages of archean anorthosites can be obtained with these isotopic systems despite the effects of low grade metamorphism there is sufficient spread in sm nd between plagioclase megacrysts and coexisting mafic groundmass to allow the determination of reasonably precise internal sm nd isochrons anorthosite samples from bvl show an unusually large range in lil concentrations such that there is sufficient spread in rb sr for a whole rock isochron 2 69 0 10 ga isr 0 70079 8 this variability may have been caused by rb introduction during hydrothermal alteration and or low grade metamorphism the sm nd isochron for bvl 2747 58 ma end 2 0 1 4 includes data for anorthosite gabbro and metabasalt and is consistent with the consanguineity of these units in the rainy lake area the age is interpreted as the time of crystallization of the anorthosite complex and related mafic plutonics and volcanics visibly altered samples show evidence for disturbance of the sm nd and rb sr isotopic systems in one altered porphyritic dike plagioclase appears to have exchanged light ree with the relatively ree rich basaltic matrix this sample yields an internal sm nd age of 2 16 0 05 ga which may correspond to the time of local heating or represent a partial resetting from a still younger event initial isotopic ratios of nd and sr determined here add to the growing body of data indicating that the superior province is underlain by depleted mantle

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

trace element geochemistry of archean volcanic rocks and crystal growth in southwestern abitibi belt canada trace element geochemistry on 176 controlled samples in three adjoining abitibi 2 7 b y volcanic piles confirms the fundamental concept of archean volcanic cycles composed of lower tholeiitic and upper calc alkalic parts the volcanic piles each as much as 16 km thick are either unicyclic or multicyclic in the latter case the cycles display secular geochemical trends all the volcanic rocks studied are indicated to have come from mantle sources a fundamental feature of abitibi magma genesis is the simultaneous presence of both depleted and undepleted mantle sources abitibi tholeiitic basalts closely resemble modern mid ocean ridge basalts abitibi calc alkalic andesites and alkalic rocks are very similar to modern oceanic island arc andesites and to some modern volcanic arc high k rocks respectively the principal constraints to geodynamic processes are interpreted in terms of pulsating migrating mantle diapirism a type of hot spot tectonics mechanism involving a layered mantle responsible for the early tholeiitic depleted mantle source and later calc alkalic undepleted mantle source parts respectively of the volcanic cycles

fractional crystallization and magma mixing in the tigalak layered intrusion the nain anorthosite complex labrador the tigalak intrusion is a dominantly dioritic layered body about 80 km2 in area which ranges in composition from norite to granodiorite local areas of the layered rocks display upward fractionation from norite to ferrodiorite periodic reversals of mineral composition trends record the emplacement of less fractionated dioritic magma heterogeneous mixtures of dioritic and granodioritic rocks occur widely in mappable lenses and layers that alternate up section and along the strike with more uniformly layered rocks in these mixtures chilled dioritic pillows occur abundantly in a hybrid cumulate matrix of granodiorite to diorite composition cross cutting granodioritic dikes grade upward into stratigraphically bound lensoid masses of the hybrid cumulates it appears that the hybrid rocks formed as a result of the emplacement of the granodioritic magma through lower cumulates into the dioritic magma chamber and that the dioritic pillows represent chilled bodies of ferich dioritic magma that commingled with cooler granodioritic magma and settled to the floor of the tigalak magma chamber

archean metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 2 mobility of trace elements and petrogenetic constraints qualitative evaluation of altered mafic pillows from the rouyn noranda district of the abitibi metavolcanic belt reveals that for low grade metamorphism the high field strength elements hfs zr y ti and the rare earth elements ree are immobile however where alteration is extreme the ree elements are leached and redeposited by carbonate rich and k rich metasomatic fluids whilst zr y and zr ti remain unchanged rubidium ba and to a lesser extent sr are mobile at all levels of alteration however provided certain filters are applied the original geochemical values of the lavas for the alkaline elements the hfs elements and the ree can be defined the geochemical variations thus identified for the volcanic series of the rouyn noranda district are ascribed to a combination of contamination and fractional crystallization of a primitive tholeiitic magma

intra sill magmatic evolution in the cummings complex abitibi greenstone belt tholeiitic to calc alkaline magmatism recorded in an archaean subvolcanic conduit system abstract the stratigraphy of the abitibi greenstone belt in the chibougamau area southern superior province quebec is dominated by 2 cycles of mafic felsic metavolcanic and metasedimentary rocks constituting the roy group which is riddled by metagabbroic sills 25 the dore lake complex dlc 2728 ma is emplaced into the lower roy group the cummings complex sills 2717 ma were injected between the bruneau member and blondeau formations of the 2nd roy group cycle the sills of the cummings complex roberge ventures and bourbeau sills contain metaperidotite metapyroxenite metagabbro and metagranophyric facies the trace element contents of melts in equilibrium with these metacumulate rocks were calculated and are compared to roy group lavas to clarify the regional magmatic history many dlc model melts have fractionated trace element profiles with lile lree enrichment hree depletion and negative nb ta anomalies suggesting that the dlc formed largely from calc alkaline melts extracted from garnet bearing residues the dlc is coeval with and shows geochemical resemblances to waconichi formation tuffs the felsic cap of the 1st roy group cycle suggesting it could represent the waconichi s shallow magma chamber meta anorthosite rafts from the para autochtonous zone of the grenville province yield model melts closely resembling those of the dlc and are correlated on this basis most roy group sills yield model melts with trace element patterns typical of archaean tholeiites suggesting they fed the regionally dominant tholeiitic volcanic plain lavas of the roy group models for the cummings complex imply that it contained two types of magma model melts from the roberge sill have strongly fractionated calc alkaline like trace element patterns while those of the ventures and bourbeau sills are mostly flat n morb normalized tholeiitic like patterns that cannot be derived from the roberge sill melts by fractional crystallization the roberge sill must have a separate magmatic stem and represents the feeder system for a calc alkaline volcano possibly represented in part by blondeau formation rhyolites andesites and basalts if this is correct the roberge may be older than the ventures and bourbeau sills which would have fed the tholeiitic base of a third magmatic cycle since eroded

archean synvolcanic intrusions and volcanogenic massive sulfide at the genex mine kamiskotia area timmins ontario u pb geochronology and detailed field mapping has resulted in a new subdivision of the kamiskotia volcanic complex into lower and upper kamiskotia strata with a 3 5 m y volcanic hiatus between the two the hiatus is interpreted as an unconformity in common with newly recognized unconformities throughout the greenstone belt the genex and other volcanogenic massive sulfide vms deposits in the area occur within the upper kamiskotia strata volcanic facies mapping and reconstruction indicate that the genex vms deposit formed within a volcanic graben where synvolcanic mafic and intermediate sills and dikes with peperitic and locally pillowed contacts define a proximal volcanic vent area sulfide mineralization at genex occurs in three zones the first hosted in pillow breccia and hyaloclastite the second occurring at the contact between felsic tuff and an intermediate intrusion and the third hosted within the intermediate intrusion the mineralization represents subsea floor replacement sulfides localized within zones of higher primary permeability although the synvolcanic mafic intrusions are not directly related to the genex vms mineralization they are indicative of a high heat flow thermal regime the synvolcanic faults that controlled the emplacement of synvolcanic dikes also provided conduits for the hydrothermal fluids responsible for the mineralization and alteration at genex this high level mafic dike and sill complex was previously correlated with the upper zone of the kamiskotia gabbroic complex but is now interpreted to be younger and correlative with the upper kamiskotia volcanic complex new geochronological data also indicate that the kamiskotia gabbroic complex is older than the vms hosting upper kamiskotia strata and was emplaced into the lower kamiskotia volcanic complex this negates the possibility of a genetic relationship between the genex and other kamiskotia vms deposits within the kamiskotia gabbroic complex the small size of the synvolcanic intrusions indicates that they were also not the heat source for the genex hydrothermal alteration system however their spatial coincidence suggests that this part of the kamiskotia volcanic complex was the focus of long lived intrusive activity and high heat flow that defined a thermal corridor encompassing the vms deposits in the kamiskotia volcanic complex

rare earth elements in volcanic rocks associated with cu zn massive sulphide mineralization a preliminary report massive sulphide deposits are closely associated with felsic volcanism this association is believed to be genetic and it forms the cornerstone for most exploration programs but unfortunately not all felsic volcanic rocks contain ore it seems likely that ore bearing felsic volcanic rocks have a different genetic history from those that are barren and if this is so these differences should be reflected in their ree geochemistry a preliminary study of ree in archean felsic volcanic rocks has shown that those associated with ore have flat ree patterns with well developed eu anomalies whereas those from barren volcanic rocks have steep ree patterns with weak or absent eu anomalies the felsic volcanic rocks associated with ore can be subdivided into two types tholeiitic and calc alkaline kam kotia matagami and south bay are tholeiitic whereas sturgeon lake golden grove and kuroko are calc alkaline the well developed eu anomalies in the ore related felsic volcanic rocks indicate that the melt has und

neodymium isotopic evidence for galapagos hotspot spreading centre system evolution nd and sr isotope variations along the galapagos spreading centre support morgan s preferential subcrustal flow channel connecting the galapagos mantle plume with the northeastward migrating ridge axis decoupling of la sm and nd isotope variations near 91 w further suggests that basalts are derived from smaller degrees of melting and are deeper beneath this elevated part of the ridge

the differentiation of the skaergaard intrusion mcbirney and naslund have missed the two central points that we reiterate for clarity first the composition of the cotectic cumulate extract for the lzc best estimated from the average composition of adcumulate rocks had a substantially lower silica content than any conceivable basaltic liquid so silica enrichment is unavoidable this is true of all the dyke compositions reported by brooks and nielsen even the anomalous rock e with sio2 46 second it is the normal behaviour of tholeiite basaltic magma to produce increasingly iron rich cumulate extracts with little change in silica until feti oxide precipitation occurs when silica enrichment and compositional divergence begins such divergence between equivalent cumulate plutonic and fractionated volcanic rocks hads been widely documented skaergaard magmas do have some uncommon features however similar assemblages exist in volcanic rocks as in the andesitic to rhyolitic glasses of the loch ba ring dyke mull sparks 1988 it is also a basic principle that elements enriched in cumulate rocks often become depleted in the corresponding liquids iron enrichment in the skaergaard cumulates is complementary to iron depletion in liquids

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

geochemical constraints on the petrogenesis of the kamiskotia gabbroic complex and related basalts western abitibi subprovince ontario canada barrie c t gorton m p naldrett a j and hart t r 1991 geochemical constraints on the petrogenesis of the kamiskotia gabbroic complex and related basalts western abitibi subprovince ontario canada precambrian res 50 173 199 the kamiskotia gabbroic complex kgc is a large 170 km 2 late archean synvolcanic intrusion located in the western abitibi subprovince canada it is divided into four stratigraphic units a lower zone lz comprised of adcumulus and mesocumulus peridotites troctolites and gabbro norites mg number 86 73 a middle zone mz comprised of mesocumulus gabbro norites mg number 74 60 mesocumulus and orthocumulus gabbro norites and ferroan gabbro norites of the upper zone uz mg number 64 37 which are overlain and partly along strike with granophyric rocks of intermediate to felsic composition the cumulates are characterized by fiat ree patterns with lan ybr 0 4 2 6 and range from 0 6 2 chondrites for olivine bearing lz adcumulates to 10 25 chondrites for upper uz meso to orthocumulates europium anomalies are strongly positive for the lz and and diminish upsection to the upper uz which has slight negative eu anomalies chilled rocks are found in mixed magma and contact chill outcrops and have a mg number of 54 58 lan ybn 0 8 1 2 and slight negative eu anomalies phase relationships and mass balance calculations using the ree indicate that lz cumulates may be derived from the average chill composition similarly upper uz cumulates may be derived from evolved basalts which overlie the kgc assimilation fractional crystallization modeling indicates that the evolved basalts may be derived from the average chill composition by 70 80 fractionation at low pressures or lower degrees of fractionation accompanied by recharge of the average chill composition into the system the basalt compositions do not reflect significant assimilation of nearby felsic rocks or average archean crust during fractionation primitive kgc liquids are estimated by adding an average olivine bearing adcumulate composition to the kgc chill composition in equal proportions to obtain a liquid with an mg number of 70 the ree content of such a liquid is consistent with a derivation by 34 partial melting of a chemically primitive mantle neodymium isotope ratios for kgc cumulates mineral separates and overlying volcanic rocks plot on a 2710 ma isochron with nd t 2 5 0 8 in close agreement with u pb zircon ages for the kgc and kamiskotia felsic volcanic rocks at 2707 2 ma and 2705 2 ma respectively the initial value is identical to the isotopically depleted morb iike abitibi mantle signature at 2 7 ga and provides supporting evidence for fractionation dominated supracrustal processes with no detectable assimilation of an isotopically enriched crustal component kamiskotia mafic magmatism is similar to more recent rift related systems represented by the skaergaard intrusion east greenland and differentiated tholeiitic volcanic fields in eastern iceland and along the galapagos spreading center

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

u pb garnet and titanite age for the bristol township lamprophyre suite western abitibi subprovince canada a u pb age of 2687 3 ma has been determined for a garnetite dike using melanite garnet and titanite mineral separates this is the first primary igneous u pb age reported using garnet the garne

origin of archean anorthosites evidence from the bad vermilion lake anorthosite complex ontario the bad vermilion lake anorthosite complex 2 700 m y is exposed over an area of about 100 km2 near rainy lake ontario as is typical of other archean anorthosites it is composed of coarse 1 30 cm across equidimensional euhedral to subhedral calcic an80 plagioclase in a finer grained mafic matrix the amount of mafic matrix in individual samples ranges from none to about 70 by volume the complex has been variably metamorphosed to greenschist facies zoisite chlorite and hornblende are abundant but primary plagioclase is preserved in many places