sulfur isotopic studies of the dunka road cu ni deposit duluth complex minnesota the dunka road deposit is one of a series of cu ni occurrences located within troctolitic rocks of the southern portion of the duluth complex minnesota sulfide minerals principally pyrrhotite chalcopyrite cubanite and minor pentlandite occur interstitially with silicate minerals and average about 2 volume percent in ore grade horizons areas of sulfide concentrations in excess of 1 to 2 percent occur erratically throughout the troctolitic sequence but are in general concentrated near the basal contact with rocks of the metasedimentary virginia formation the delta 34 s values of sulfides in the troctolites range from 0 2 to 15 8 per mil with an average value near 7 5 per mil pyrrhotite in the underlying virginia formation hornfels and pyrite from unmetamorphosed virginia formation are characterized by a similar range in delta 34 s values the high positive delta 34 s values and similarity to values found in the virginia formation strongly suggest that most of the sulfur in the dunka road deposit was derived from the breakdown of pyrite in the virginia formation the sulfur isotopic compositions of minerals in the troctolites show no consistent lateral or vertical trends and are in general characterized by a high degree of variability such fluctuations in delta 34 s values indicate that sulfur isotopic homogenization was not attained throughout the troctolitic sequence several mechanisms may have contributed to the variations in delta 34 s values found within the troctolites including mixing of sedimentary and igneous sulfur assimilation of sedimentary sulfur characterized by variable delta 34 s values fractionation caused by fluctuations in oxidation states during sulfur volatilization and assimilation and periodic introduction of isotopically distinct magma batches in light of the erratic sulfide mineral and delta 34 s distributions the predominant mechanism is thought to be the introduction of both isotopically and spatially variable country rock sulfur into crystallizing troctolitic magma

geomorphic effects of large debris flows on channel morphology at north fork mountain eastern west virginia usa extreme rainfall in june 1949 and november 1985 triggered numerous large debris flows on the steep slopes of north fork mountain eastern west virginia detailed mapping at four sites and field observations of several others indicate that the debris flows began in steep hillslope hollows propagated downslope through the channel system eroded channel sediment produced complex distributions of deposits in lower gradient channels and delivered sediment to floodwaters beyond the debris flow termini based on the distribution of deposits and eroded surfaces up to four zones were identified with each debris flow an upper failure zone a middle transport erosion zone a lower deposition zone and a sediment laden floodwater zone immediately downstream from the debris flow terminus geomorphic effects of the debris flows in these zones are spatially variable the initiation of debris flows in the failure zones and passage through the transport erosion zones are characterized by degradation 2300 to 17 000 m3 of sediment was eroded from these zones the total volume of channel erosion in the transport erosion zones was 1 3 to 1 5 times greater than the total volume of sediment that initially failed indicating that the debris flows were effective erosion agents as they travelled through the transport erosion zones the overall response in the deposition zones was aggradation however up to 43 per cent of the sediment delivered to these zones was eroded by floodwaters from joining tributaries immediately after debris flow deposition this sediment was incorporated into floodwaters downstream from the debris flow termini causing considerable erosion and deposition in these channels 1998 john wiley sons ltd

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

hydrocarbon generation and expulsion characteristics of eocene source rocks in the huilu area northern pearl river mouth basin south china sea implications for tight oil potential abstract in recent years new oil reservoirs have been discovered in the eocene tight sandstone of the huilu area northern part of the pearl river mouth basin south china sea indicating good prospects for tight oil exploration in the area exploration has shown that the huilu area contains two main sets of source rocks the eocene wenchang e2w and enping e2e formations to satisfy the requirements for further exploration in the huilu area particularly for tight oil in eocene sand reservoirs it is necessary to re examine and analyze the hydrocarbon generation and expulsion characteristics based on mass balance this study investigated the hydrocarbon generation and expulsion characteristics as well as the tight oil resource potential using geological and geochemical data and a modified conceptual model for generation and expulsion the results show that the threshold and peak expulsion of the e2w source rocks are at 0 6 vitrinite reflectance and 0 9 vitrinite reflectance respectively there were five hydrocarbon expulsion centers located in the western eastern and northern huizhou sag and the southern and northern lufeng sag the hydrocarbon yields attributed to e2w source rocks are 2 4 1011 tons and 1 6 1011 tons respectively with an expulsion efficiency of 65 the e2e source rock threshold and peak expulsion are at 0 65 vitrinite reflectance and 0 93 vitrinite reflectance respectively with hydrocarbon expulsion centers located in the centers of the huizhou and lufeng sags the yields attributed to e2e source rocks are 1 1 1011 tons and 0 2 1011 tons respectively with an expulsion efficiency of 20 using an accumulation coefficient of 7 13 the eocene tight reservoirs could contain approximately 1 3 1010 tons to 2 3 1010 tons with an average of 1 8 1010 tons of in place tight oil resources highest recoverable coefficient can reach 17 18 indicating that there is significant tight oil potential in the eocene strata of the huilu area

geochemical and fluid dynamic modeling of compositional variations in archean komatiite hosted nickel sulfide ores in western australia stratigraphic volcanological petrological and fluid dynamic studies suggest that archean komatiite associated nickel sulfide deposits in western australia formed by thermal erosion of unconsolidated sulfidic sediments beneath channelized lava flows geochemical and nd isotope data for the type area at kambalda suggest that mineralized lava channels are less contaminated than barren flanking segments of the flow owing to high discharge rates and continuous replenishment within the channel this interpretation has several implications for the mode of emplacement of sulfides their degree of equilibration with the host komatiite and the compositions of sulfide ores 1 the solubility of sulfur in komatiite is relatively low so most of the sulfide in eroded sediments will be melted and remain as a dense layer at the base of the flow or be incorporated into the turbulently flowing komatiite as immiscible sulfide droplets 2 sulfide ores will not necessarily be in equilibrium with overlying komatiites but will record equilibration with variably contaminated lavas during initial stages of emplacement and crystallization and 3 ore compositions will vary from channel to channel shoot to shoot depending on i the composition of the hybridized komatiite ii the fluid dynamics of the system and the effective magma sulfide ratio r factor and iii the sulfide silicate partition coefficients under the prevailing conditions of temperature and f sub o 2 f sub s 2 the size of immiscible droplets and the interface between two immiscible layers are affected by inertial forces during turbulent flow turbulence causes coalescence of small droplets and breakup of large droplets leading to an equilibrium droplet size if the average size of the droplets is small and or the flowage rate is high they may be carried in suspension in the flowing komatiite droplets have a large surface area to volume ratio and will be effective in scavenging chalcophile elements since they are carried by the turbulent motion of the flowing komatiite if the average size of the droplets is large or if the flowage rate is low they will settle and collect at the base of the komatiite komatiite and sulfide liquids may continue to flow but the sulfide layer will have a low surface area to volume ratio and will be ineffective in extracting chalcophile elements from the overlying komatiite layer thus the initial stages of emplacement when sulfides are initially melted and are most likely to be in suspension if at all control the effective r factor and therefore the tenor of the sulfide ores numerical modeling of the observed variations in ore compositions constrained by known komatiite compositions and experimentally or empirically determined distribution constants indicates that the observed range of ore compositions in western australian komatiite associated nickel sulfide deposits can be accounted for primarily by variations in the effective sulfide silicate ratio 500 r 100 although required variations in the partition coefficient for ni 200 d ni 100 suggest that f sub o 2 f sub s 2 may also have varied systematically assimilation of h 2 o fes rich sediments should increase f sub o 2 f sub s 2 because of the relative abundances of the two components in the magma and unconsolidated sediments if low tenor ores represent equilibration at lower r and higher f sub o 2 f sub s 2 and high tenor ores represent equilibration at higher r and lower f sub o 2 f sub s 2 as suggested by the modeling then d ni appears to decrease with increasing f sub o 2 f sub s 2 as suggested by doyle and naldrett 1987 the range of calculated r values is relatively low suggesting that low tenor sulfides were not entrained into the komatiite lava but remained as a segregated layer at the base of the flow and that high tenor sulfides were not transported long distances in suspension but settled rapidly to the base of the flow magma compositions vary only slightly from an inferred parental komatiite low tenor ores appear to have equilibrated with only slightly more evolved contaminated and fractionated lavas

suspended sediment transport regime in a debris flow gully on vancouver island british columbia in debris flow prone channels normal fluvial sediment transport occurs nearly exclusively in suspended mode between episodic debris flow events observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types when flows exceeded a threshold of 270 l s 1 events yielded significant quantities of sediment and suspended sediment concentration increased with flow smaller events were strongly supply limited sediment concentration decreased as flow increased overall there is no consistent correlation between runoff and sediment yield within the season three subseasons were identified demarcated by periods of freezing weather within which a pattern of fine sediment replenishment and evacuation occurred finally a signature of fine sediment mobilization and exhaustion was observed within individual events fine sediment transport occurred in discrete pulses within storm periods most of the yield occurring within 5 to 15 of storm runoff duration so that it is unlikely that scheduled sampling programs would identify significant transport significant events are however generally forecastable on the basis of regional heavy rainfall warnings providing a basis for targeted observations radiative snowmelt events and rain on snow remain difficult to forecast since the projection of temperatures from the nearest regular weather station yields variable results copyright 2004 john wiley sons ltd

a laser ablation inductively coupled plasma mass spectrometry study of the distribution of chalcophile elements among sulfide phases in sedimentary and magmatic rocks of the duluth complex minnesota usa abstract nickel copper sulfide deposits occur in the basal unit of the partridge river intrusion duluth complex minnesota usa many lines of evidence suggest that these sulfides are formed after assimilation of the proterozoic s rich black shales known as the bedded pyrrhotite unit in addition to s black shales are enriched in te as bi sb and sn tabs and the basaltic magma of the intrusion is contaminated by the partial melt of the black shales the tabs are chalcophile and together with the platinum group elements ni and cu partitioned into the magmatic sulfide liquid that segregated from the duluth magma the tabs are important for the formation of platinum group minerals pgm thus their role during crystallization of the base metal sulfide minerals could affect the distribution of the pge however the concentrations of tabs in magmatic ni cu pge deposits and their distribution among base metal sulfide minerals are poorly documented in order to investigate whether the base metal sulfide minerals host tabs in magmatic ni cu pge deposits a petrographic and laser ablation inductively coupled plasma mass spectrometry la icp ms study has been carried out on base metal sulfide and silicate phases of the partridge river intrusion duluth complex petrographic observations showed that the proportions of the base metal sulfide minerals vary with rock type the sulfide assemblage of the least metamorphosed bedded pyrrhotite unit from outside the contact metamorphic aureole consists of pyrite with minor pyrrhotite plus chalcopyrite 95 with small amount of chalcopyrite our la icp ms study shows that sulfides of the bedded pyrrhotite unit are rich in tabs consistent with these s rich black shales being the source of tabs that contaminated the mafic magma most of the tabs are associated with sulfides and platinum group minerals in the rocks of the bedded pyrrhotite unit from the contact aureole the bedded pyrrhotite unit xenoliths and the mafic rocks of the duluth complex in addition to these phases the laser maps show that silicate phases i e orthopyroxene and plagioclase contain sn and pb respectively in contrast in the least metamorphosed samples of the bedded pyrrhotite unit from outside the contact aureole although the pyrite contains some tabs mass balance calculations indicates that most the tabs are contained in other phases in these rocks galena hosts significant amounts of te bi sb sn and ag and few very small grains of sb rich phases were also observed the host phases for as were not established but possibly organic compounds may have contributed

hydrothermal alteration in the babbitt cu ni deposit duluth complex mineralogy and hydrogen isotope systematics hydrothermal alteration at the babbitt cu ni deposit of the duluth complex is widespread but highly variable in terms of intensity alteration styles range from the filling of microfractures in plagioclase and olivine or minor alteration along grain margins to more intense alteration in the form of macroscopic fracture fillings or massive replacement of primary minerals with or without well developed fractures chlorite occurs as a macroscopic fracture filling within microveinlets in plagioclase and as an alteration of pyroxene biotite and rarely olivine along grain margins or fractures mats of chlorite are intergrown with amphibole epidote calcite and prehnite as part of massive replacement of calcic plagioclase greenalite is found in areas of intense alteration particularly in the vicinity of sulfide mineralization iron rich serpentine occurs along fractures in olivine or as a more massive replacement of olivine in picritic units serpentine composition is related to that of the parent olivine as well as to the degree of serpentinization in addition to its involvement in plagioclase alteration calcic amphibole hornblende actinolite is found as a partial replacement of primocryst and interstitial clinopyroxene ca poor amphibole occurs as an alteration product of orthopyroxene the presence of the assemblage chlorite prehnite actinolite epidote suggests that alteration continued to temperatures less than 400 degrees c the delta d values and h 2 o contents of igneous rocks at babbitt range from 56 to 138 per mil and 0 49 and 4 60 wt percent respectively biotite separates are characterized by delta d values of 67 to 86 per mil and delta 18 o values of 4 2 to 6 1 per mil a range considered normal for biotite in mafic igneous rocks because most of the low temperature reactions between fluids and minerals in the cooling igneous system involved hydration h 2 o content is an approximate indicator of the extent of low temperature alteration rocks with h 2 o contents in excess of approximately 1 5 percent are characterized by delta d values greater than 87 per mil except for a sample of highly serpentinized picrite which has a delta d value of 120 per mil modeling of the isotopic composition of a fluid exsolved from interstitial melt indicates that for samples with minor alteration and h 2 o contents less than approximately 1 wt percent secondary mineral assemblages were probably produced as a d depleted magmatic vapor reacted with primary minerals along cooling fractures and grain margins areas of more intense alteration may have formed from localized accumulations of d enriched vapor released from underlying interstitial melt alternatively intensely altered zones may have formed due to the introduction of relatively d enriched fluid derived from devolatilization of metasedimentary xenoliths and footwall the latter interpretation is consistent with previously reported isotopic ripley and taib 1989 and fluid inclusion pasteris 1989 data both oxygen and hydrogen isotope compositions of one serpentinized picrite suggest that a low 18 o low d fluid of probable meteoric origin has been involved in the serpentinization of olivine rich units an insufficient number of samples have been analyzed to determine if a direct positive correlation exists between platinum group element pge content and degree of alteration in the babbitt deposit however the presence of discrete platinum group minerals in intensely altered zones suggests that most pt and pd remobilization occurred via transport by a d enriched fluid a positive correlation between whole rock delta d values and pd content for samples that contain less than 300 ppb pd suggests that magmatic fluids as well as high delta d fluids derived from metasedimentary country rocks may have been involved in local pt pd redistribution

breathing new life into postmortem analysis identification of key failure modes for conventional petroleum segments offshore new zealand abstract technically rigorous systematic and consistent postmortem analysis of dry holes is necessary to improve future exploration performance here we identify the key failure modes for three segments in conventional petroleum prospects using a previously developed decision tree the failed segments were tested by wells whio 1 and kanuka 1 in the taranaki basin offshore new zealand using comprehensive geological geophysical and geochemical data from the wells we determined that the segments failed due to lack of petroleum migration segment m2a in well whio 1 and segment mt messenger in well kanuka 1 and due to unfavorable timing of petroleum migration segment mangahewa in well whio 1 these failure modes are broadly aligned with those determined by the operators of these wells however the use of decision tree results in more consistent and less vague definitions of failure modes

the role of fluids in the formation of platinum group minerals duluth complex minnesota mineralogic textural and chemical evidence several new occurrences of platinum group minerals pgm including sperrylite ptas 2 taimyrite pd cu 3 sn froodite pdbi 2 michenerite pdbite and moncheite pt bi 2 te 3 are recorded from drill core samples of the basal troctolites of the duluth complex the first documentation of a vanadium chromium hercynite v 2 o 3 ranging from 5 14 5 23 wt in graphite rich samples of the mineralized zone of the duluth complex is also reported the pgm are associated predominantly with serpentinized olivine and secondary magnetite or with altered calcic plagioclase approximately an 75 prehnite actinolite hornblende and chlorite the pd bismutho tellurides are associated with parkerite ni 3 bi 2 s 2 tellurobismuthite bi 2 te 3 bismuthinite bi 2 s 3 hessite ag 2 te native gold and clausthalite pb s se with low temperature sulfides like valleriite 2 fe cu s 3 mg fe oh 2 violarite feni 2 s 4 heazlewoodite ni 3 s 2 and in some instances graphite these associations especially the occurrence of the pgm in altered silicates suggest that the pgm reported in this study were transported and deposited during a late magmatic hydrothermal event which could be related to the introduction of volatiles from the metasedimentary virginia formation and the biwabik iron formation the high cl contents of the serpentine biotite apatite and graphite as well as the high an contents of the plagioclase in contact with the sulfides and pgm further suggest that chloride complexing was a possible mechanism for the transport and deposition of the pgm during the hydrothermal event the occurrence of high vanadium chromium hercynite is also consistent with this interpretation

the role of black shales as a source of sulfur and semimetals in magmatic nickel copper deposits example from the partridge river intrusion duluth complex minnesota usa the basal unit of the duluth complex minnesota usa contains ni cu sulfide deposits the s in these is thought to be derived from a sulfide rich black shale unit known as the bedded pyrrhotite unit a stratigraphic unit within the virginia formation host rocks however the mechanism of s transfer has not been clearly established in order to understand how this transfer occurs we have undertaken petrography and whole rock geochemistry of the rocks from the contact aureole and the basal unit in the contact aureole the bedded pyrrhotite unit consists of a very fine grained graphitic shales with thin beds of sulfides consisting of pyrrhotite with minor chalcopyrite 1 the basal unit contains numerous bedded pyrrhotite unit xenoliths surrounded by norites the bedded pyrrhotite unit xenoliths are partially melted and the sulfide beds are disrupted leucosomes are present and these contain blebs of sulfides consisting of pyrrhotite pentlandite cubanite and chalcopyrite in the mafic rocks surrounding the xenoliths small patches of sulfide bearing leucosome are found in addition to being rich in s the bedded pyrrhotite unit is rich in as 38 ppm sb 4 1 ppm and bi 0 6 ppm and te 0 4 ppm and has high 34s values the 34s as s bi s and sb s decrease with distance from the xenoliths similarly the ni s cu s se s and platinum group elements s ratios are higher in the mafic rocks and increase with distance from the xenoliths our model proposes that droplets of sulfide melt derived from the bedded pyrrhotite unit xenoliths were entrained in the anatectic silicate melt of the xenoliths and transferred to the mafic magma the sulfide droplets equilibrated with the mafic magma those close to the xenoliths did not have the opportunity to react with a large quantity of magma and hence their composition is similar to the sulfides of the bedded pyrrhotite unit i e rich in semimetals and poor in ni cu and pge farther away from the xenoliths the sulfide droplets could have reacted with more magma and the composition of these sulfides approach that of sulfides derived mainly from mafic magma

selenium and sulfur concentrations in country rocks from the duluth complex minnesota usa implications for formation of the cu ni pge sulfides various studies suggest that the formation of a magmatic ni cu platinum group element pge sulfide deposit requires addition of s from the country rocks into the magma many sulfide deposits have s se ratios higher than primary magmas which is attributed to the preferential addition of s from the country rocks however this has not been clearly demonstrated because most studies do not determine se in the country rocks partly because although se concentration in igneous rocks can be assessed by most routine analytical techniques their detection limits are too low for measuring with precision the level of se in sedimentary rocks we have determined se abundances using thiol cotton fiber tcf combined with instrumental neutron activation analysis inaa s and delta super 34 s on the magmatic sulfides of the duluth complex and on the host rock sediments of the virginia formation our data show that the pelitic and metapelitic rocks of the virginia formation are characterized by low s se ratios approximately 3 000 close to the mantle values whereas the s rich layer known as the bedded pyrrhotite unit has high s se ratios approximately 20 000 consequently most of the virginia formation sediments and xenoliths are unsuitable as a source of s because they have s se ratios and delta super 34 s values lower than those of the mineralized rocks 10 000 only the bedded pyrrhotite unit which is present at the contact with the intrusion and as partly digested xenoliths within the intrusion has s se ratios and delta super 34 s values higher than those of the magmatic sulfides and could thus be the source of the s furthermore the presence of sulfides in the norites around the xenoliths suggests that the s was released from the xenolith during melting of the xenolith detailed sampling from the xenoliths into the norite shows that the s se ratio and delta super 34 s decrease with distance from the xenolith our results favor a mechanism of crustal s contamination by in situ assimilation of bedded pyrrhotite unit xenoliths

platinum group elements in the uitkomst complex south africa the mafic ultramafic uitkomst complex of south africa is a tubular intrusion that is believed to be coeval and cogenetic with the 2054 ma bushveld complex it consists of a thin 3 5 m basal gabbronoritic phase that is overlain by ca 450 m of ultramafic rocks and 250 m of gabbroic and dioritic rocks the basal 300 m of the intrusion hosts disseminated ni cu platinum group element pge sulfides 100 mt at ca 0 55 ni 0 17 cu in addition several lenses of massive sulfides 2 9 mt at 2 04 ni 1 13 cu and 6 ppm total pge are situated in the immediate floor of the intrusion we determined the pge concentrations in 86 samples from the uitkomst complex the rocks containing disseminated sulfides have up to 3 ppm total pge and the massive sulfides have up to 7 ppm total pge sulfide segregation was triggered by assimilation of external sulfur from the country rocks adjacent to the intrusion the most important contaminant was probably dolomite of the malmani subgroup that includes sulfidic shale interlayers the composition of the magmatic sulfides can be modeled by applying an r factor mass ratio of silicate melt to sulfide melt of between 800 and 1 000 the sulfides in the ultramafic rocks show little tendency of metal depletion with height and thus appear to have segregated from successive surges of fertile magma this suggests that the basal portion of the uitkomst complex crystallized in an open magmatic system e g a magma conduit the gabbroic and dioritic rocks in the upper portion of the complex are relatively pge depleted cu pd mostly higher than in primitive mantle suggesting that they crystallized from the residual magmas to the ultramafic rocks in a closed magmatic system some of the ultramafic rocks in the central portion of the complex are s poor mostly 700 ppb s but contain relatively high amounts 30 250 ppb of total pge these rocks have unusually low pd ir 0 6 ca 10 cu zr typically 0 5 and high pt pd up to 19 suggesting that either pd cu and s were remobilized or that the magma was undersaturated in sulfide liquid at the time the rocks formed and that platinum group minerals pgm crystallized the present study suggests that sill like bodies of bushveld affinity that intruded dolomitic rocks may generally have an enhanced potential to host massive magmatic ni cu pge sulfides

integrate instead of ignoring base rate neglect as a common fallacy of petroleum explorers when petroleum explorers estimate geological probability of success pos and success case volumes for their prospects they commonly suffer from various biases and fallacies that result in poor assessments using a data set of 25 exploration wells drilled by lundin petroleum on the norwegian continental shelf ncs during the 5 yr period from 2011 to 2015 i demonstrate the base rate neglect fallacy in petroleum exploration lundin explorers consistently and significantly underestimated the geological pos and overestimated the success case volumes relative to the available base rate information on historical exploration success rates and sizes of previously discovered fields in the ncs area these findings are consistent with previous studies of exploration track records of the industry and individual companies explorers erroneously tend to ignore the base rates likely because they do not see them as relevant to the evaluation of their specific prospects as a result exploration portfolios generally fail to deliver on promise however base rate neglect fallacy can be mitigated and eliminated explorers should make an effort to learn the base rates relevant to their prospects and integrate them with prospect evaluations and managers should ensure that modeled portfolio outcomes are consistent with relevant base rates

platinum group element geochemistry of cu ni mineralization in the basal zone of the babbitt deposit duluth complex minnesota the babbitt cu ni sulfide deposit located in the duluth complex of minnesota contains associated low grade platinum group element pge mineralization interelement correlations show that for both massive and disseminated ore zones rh ru os re and ir are positively correlated to s abundance and suggest that they have behaved as immobile elements however pt pd and au are strongly decoupled from the rh ru os re ir group and show no significant correlation with s cu or ni a pge enriched zone up to 3 000 ppb pt and 1 100 ppb pd is located laterally adjacent to the highest grade cu ni ore the pge enriched zone is characterized by abundant bornite lower sulfide delta 34 s values 1 4 to 8 9ppm than those from other sulfide bearing zones at babbitt and oxide assemblages that include cr bearing hercynite and magnetite rich spinels as well as ilmenite sperrylite ptas 2 is the only discrete pge mineral identified in the babbitt deposit synchrotron x ray fluorescence microprobe analyses indicate that some rocks with a high bulk pge content are characterized by ppm quantities 16 132 of pd in cubanite chalcopyrite maucherite and mackinawire although cl contents of biotite and apatite from mineralized units range from 0 10 to 0 71 and 0 87 to 1 43 wt percent respectively no direct relationship between pge enrichment and cl content of volatile rich phases has been observed geochemical data suggest that both magmatic and hydrothermal processes have been important in the localization of pge at the babbitt deposit the distribution of rh ru os re and ir reflects magmatic concentration processes whereas pt pd and au have been locally mobilized and redistributed during hydrothermal alteration

hydrometeorological triggers of periglacial debris flows in the zermatt valley switzerland since 1864 1 the triggering of debris flows depends on a critical combination of available unconsolidated material and water supply in periglacial environments debris flows are generally triggered by liquefaction of loose material in a channel or by progressive erosion during a large release of water here we link an unusually dense and highly resolved database on periglacial debris flows with meteorological records dating back to ad 1864 to reconstruct 150 yr of rainstorms that triggered debris flows at high elevation sites source area elevations ranging from 2000 to 4545 m a s l in the swiss alps analysis is based on a tree ring derived frequency series of debris flows from eight torrents as well as on daily records from three meteorological stations and runoff data from four river gauging stations results show that the debris flow season at these high altitude sites now is much longer may to october than it used to be in the late nineteenth century when activity was limited to june september debris flows early in the season are generally triggered by lower rainstorm totals 20 mm day than those occurring later in the season because early season snowmelt adds considerable amounts of water to the system and therefore facilitates debris flow formation debris flows in may june july and august are triggered primarily by short duration high intensity rainstorms local thunderstorms whereas late season september october debris flows are commonly related to longer lasting advective rainstorms

sulfur and oxygen isotope studies of melt country rock interaction babbitt cu ni deposit duluth complex minnesota the babbitt cu ni deposit formerly known as minnamax occurs within troctolitic and gabbroic rocks of the precambrian duluth complex both massive and disseminated mineralizations are found in the deposit pyrrhotite cubanite chalcopyrite and minor pentlandite mineralization occurs near the basal contact with pelitic metasedimentary rocks of the virginia formation or higher in the igneous sequence associated with abundant country rock xenoliths cloud zones sulfur and oxygen isotope studies have been carried out to evaluate the importance of melt country rock interaction in localizing sulfide mineralization the delta 34 s values of pyrrhotite plus pyrite from the virginia formation located outside the contact aureole range from 5 6 to 13 7 per mil pyrrhotite from footwall virginia formation hornfels or inclusions in the basal zone exhibits delta 34 s values ranging from 1 5 to 6 2 per mil whereas delta 34 s values of pyrrhotite from xenoliths in cloud zones range from 2 6 to 21 4 per mil isotopic values of basal zone cu ni sulfides range from 6 0 to 13 0 per mil with a mode at 8 to 9 per mil two features highlight basal zone delta 34 s values first delta 34 s values of sulfide mineralization are higher than those of pyrrhotite in immediately adjacent virginia formation hornfels second higher grade ore areas 1 cu show 34 s enrichment with delta 34 s values in the range of 9 to 13 per mil sulfides in cloud zones show a wide range in delta 34 s values from 0 7 to 19 7 per mil sulfur isotope data suggest that most of the sulfur found in the deposit has been derived from sedimentary country rocks however an in situ process of sulfur derivation is not indicated sulfur in basal mineralized zones must have been derived at depth within an auxiliary magma chamber or during magma ascent and emplacement isotopic homogenization was not achieved during the sulfide forming process as evidenced by the spatial variability of delta 34 s values oxygen isotope values of both mildly metamorphosed virginia formation and footwall hornfels range from 8 2 to 14 0 per mil inclusions of virginia formation show pronounced isotopic effects due to interaction with melt xenolith margins may have values as low as 7 to 8 per mil and are depleted in 18 o with respect to xenolith interiors the delta 18 o values of igneous rocks from the babbitt deposit range from 3 9 to 12 2 per mil zones of 18 o depletion are rare and suggest that exchange with a low 18 o fluid phase was spatially restricted anomalous delta 18 o values in excess of 7 to 7 5 per mil are common throughout the deposit but are limited to within 3 m of virginia formation xenoliths a model of diffusion controlled 18 exchange between igneous material and xenoliths best describes the delta 18 o distribution devolatilization and desilicification of the xenoliths occurred early in their history when physical mixing in the host magma was possible addition of high 18 o material from these processes into a large volume of melt affected delta 18 o distributions only slightly continued exchange of oxygen after major cation transfer produced the observed delta 18 o profiles in the case of basal zone cu ni mineralization at babbitt isotopic evidence indicates that sulfide saturation was not caused by in situ addition of sulfur silica or oxygen sulfide saturation is thought to have been achieved at depth triggered by assimilation of large quantities of sulfide liberated through devolatilization reactions occurring in country rocks

marine influence helps preserve the oil potential of coaly source rocks eocene mangahewa formation taranaki basin new zealand abstract many cretaceous cenozoic coaly source rocks in australasian and southeast asian basins were deposited in coastal plain environments yet the effect of early diagenetic marine influence on their oil potential is not well understood an integrated organic geochemical and petrographic study of humic coals from the eocene mangahewa formation taranaki basin new zealand was undertaken with coals predominantly from raised mire petrofacies with subordinate proportions from planar mires the total s content of 0 63 4 4 dry ash free indicated very slight to strong degrees of marine influence other than minor addition of inferred mangrove derived suberinite and associated liptodetrinite the degree of marine influence had no obvious effect on maceral or plant tissue abundance however hydrogen index hi values were up to ca 150 109 mg hc g toc higher and total c 6 oil potential up to ca 140 43 mg g toc higher among the more strongly marine influenced coals correlation of organic s with solvent extract parameters pristane phytane c 27 c 29 diasteranes steranes c 29 steranes hopanes c 35 c 35 c 34 homohopanes and oleanane index suggested that inundation of brackish water into the early diagenetic peat forming environment enhanced the bio resistance of higher plant and other lipids through sulfurization thereby helping to preserve more of the inherent h content and total oil potential of the original peat biomass conversely marine influence had only a minor effect on the capacity of mangahewa coals to generate paraffinic oil total n c 6 and non volatile n c 15 paraffinic oil potentials were instead controlled primarily by the abundance of leaf derived cutinite and associated liptodetrinite this in turn was dependent on the type of peat mire facies with planar mire facies having better potential for preservation of leaf litter than raised mire facies because of their generally higher groundwater level marine influence is nonetheless beneficial for paraffinic oil charge from coaly source rock sequences in that the associated higher his enhance the efficiency and quantum of paraffinic oil expulsion through increased saturation of the coal pore system

ni cu au and platinum group element contents of sulphides associated with intraplate magmatism a synthesis the tectonic setting of intraplate magmas typically a plume intersecting a rift is ideal for the development of ni cu platinum group element bearing sulphides the plume transports metal rich magmas close to the mantle crust boundary the interaction of the rift and plume permits rapid transport of the magma into the crust thus ensuring that no sulphides are lost from the magma en route to the crust the rift may contain sediments which could provide the sulphur necessary to bring about sulphide saturation in the magmas the plume provides large volumes of mafic magma thus any sulphides that form can collect metals from a large volume of magma and consequently the sulphides will be metal rich the large volume of magma provides sufficient heat to release large quantities of s from the crust thus providing sufficient s to form a large sulphide deposit the composition of the sulphides varies on a number of scales i there is a variation between geographic areas in which sulphides from the noril

petrogenesis of pelitic xenoliths at the babbitt cuni deposit duluth complex minnesota u s a abstract the babbitt deposit consists of disseminated cu fe ni sulfides found within mafic rocks of the duluth complex generally near contacts with underlying metasedimentary rock types host rocks for the deposit include troctolites olivine gabbros gabbronorites norites and occasionally country rock hornfels xenoliths of country rocks are abundant in the deposit and suggest a relationship between sulfide mineralization and country rock contamination country rocks in the babbitt area include those of the middle precambrian biwabik iron formation and both calcareous and non calcareous pelites of the virginia formation xenoliths contain the assemblage cordierite plagioclase biotite orthopyroxene and are thought to have been derived from virginia formation protoliths comparison of protoliths and xenoliths using composition volume element ratio and mass balance techniques suggests that xenoliths have been strongly depleted in volatiles alkalis and si footwall rocks show only a depletion in volatiles neither fluid phase transport nor diffusion through an intergranular fluid can account for the mass of material transferred extensive partial melting of xenoliths with residual enrichment of feo mgo and al2o3 is the most viable transfer process the lack of sio2 concentration gradients around xenoliths and anomalous igneous rock compositions suggest that desilicification occurred at a time when physical mixing of extracted partial melt and host magma was possible and prior to final emplacement sulfide saturation may have been initiated due to si assimilation with an auxiliary magma chamber however the composition of ores in the babbitt deposit is consistent with saturation being achieved by addition of sediment derived volatile sulfur independent of major element assimilation

the inception and growth of leucosomes microstructure at the start of melt segregation in migmatites the beginning stages of melt segregation and the formation of leucosomes are rarely preserved in migmatites most arrays of leucosomes record a more advanced stage where flow dominates over segregation however the early stages in the formation of leucosomes and the segregation of melt are preserved in a partially melted meta argillite from the metatexite zone 800 c of the contact aureole around the duluth complex minnesota the rock contains 2 4 modal leucosome in a matrix consisting of 40 5 in situ neosome and 57 1 cordierite plagioclase framework the domainal microstructure in the matrix is a pre anatectic feature resulting from the bulk composition terminal chlorite reactions produced a large volume of cordierite which with plagioclase formed a framework that enclosed patches of biotite quartz plagioclase k feldspar upon melting these fertile domains became patches of in situ neosome plagioclase in the neosome is less sodic than in the leucosome hence segregation of melt occurred during crystallization not melting segregation was delayed because the cordierite plagioclase framework was strong enough to resist dilatation and compaction until after crystallization started the leucosomes are small i e they are microleucosomes and display a systematic progression in morphology as length and aspect ratio increase from 1 to 19 mm and from 2 5 to 30 respectively small equant micropores form first and in places these coalesce into small 1 mm aspect ratio 2 5 isolated blunt ended elliptical microleucosomes in the next stage micropores develop ahead of and at 45 to the left and right of the blunt tip of a microleucosome one of these develops into an elliptical leucosome and an en echelon array of either a left or right stepping elliptical microleucosome forms each elliptical microleucosome in the en echelon arrays is separated by a bridge of matrix next microleucosomes of greater length 4 mm and aspect ratio 5 form when the bridges of cordierite plagioclase matrix rupture and the elliptical microleucosomes link together to form a zigzag shaped microleucosome finally still longer microleucosomes with greater aspect ratios 30 are formed by the joining of zigzag arrays such a progression is characteristic of the way ductile fractures grow the segregation of melt was driven by the pressure gradient between the dilatant fracture and an adjacent in situ neosome which drew melt to the growing fracture thereby creating a microleucosome the microleucosomes are filled arrays of ductile fractures melt was contiguous only between microleucosomes and adjacent patches of in situ neosome the length scale of segregation was 5 mm the size of a typical patch of in situ neosome and restricted by the surrounding impermeable cordierite plagioclase framework the melt in the microleucosome was the most fractionated and the last to crystallize all microleucosomes contain entrained minerals as a consequence of their mechanism of growth rupture of the bridges resulted in the entrainment of pre anatectic phases however microleucosomes that cross patches of in situ neosome are also contaminated with peritectic phases that were transported with the melt

pgm facies variations for cu pge deposits in the coldwell alkaline complex ontario canada abstract accurate characterization of the platinum group mineral pgm assemblages for cu ni pge deposits are typically constrained by sample size and the difficulty of finding statistically significant numbers of grains which is expected given the low concentrations of platinum group elements 75 m can account for large fractions of total mass despite these limitations an accurate survey of pgm from different deposit types would have significant value towards developing deposit models and respective exploration strategies in this study we present results for a comprehensive evaluation of pgm at four copper pge occurrences hosted within separate but co genetic gabbro or troctolite intrusions in the coldwell alkaline complex and confirm that accurate surveys are possible with sufficient sample material and efficient pgm concentration methods the pgm concentration methods used include 1 hydroseparation of sieved size fractions of pulverized material and 2 panning of grain separates produced by electric pulse disaggregation of drill core specimens a favourable comparison of the results has verified the reliability of each method and added confidence that the pgm assemblages identified at three of the four locations are fully characterized precious metal mineral pmm assemblages are determined for the main zone and w horizon at the marathon deposit and the main zones at each of the geordie lake deposit and area 41 occurrence a total of 10 824 pmm grains pge and au ag and 68 mineral species including 16 unknown minerals were identified of which 768 grains and 31 species occur at the main zone 523 grains and 41 species at area 41 9485 grains and 43 species at w horizon and 56 grains and 12 species at geordie lake the pmm are grouped as follows pd ge pge s as pt fe alloy pd cu pb au pd ni s pd pt sn pt as pd as pd pt sb as pd pt bi te and au ag all of the deposits were found to contain similar proportions of pd pt sb as pd pt bi te and au ag minerals but the w horizon and area 41 are distinguished from the marathon main zone and geordie lake deposits by the presence of minerals in the pge s as pt fe alloy pd cu pb au and pd ge groups taken together the pmm assemblages for deposits in the coldwell exhibit a strong correlation to pge enrichment relative to the range for mantle cu pd values 1000 10 000 and there is no relationship between the abundances of pd pt bi te and pd pt sb as minerals that are commonly associated with hydrous phases and the intensity of hydrothermal alteration thus minerals found only at the w horizon and area 41 where significant pge upgrading has occurred including pt fe alloys rustenburgite marathonite palladogermanide unknown rh ni fe sulfide au pd cu alloy braggite coldwellite laurite zvyagintsevite laflammeite and unknown phases pd 5 as 2 pd 3 as pd 3 as pb bi might be considered as index minerals for pge enriched types of mineralization in the coldwell

nickel copper occurrences in the belleterre angliers belt of the pontiac subprovince and the use of cu pd ratios in interpreting platinum group element distributions within the belleterre angliers greenstone belt of the pontiac subprovince there are a number of ni cu sulfide occurrences associated with synvolcanic gabbros the stratigraphy and geochemistry of the belt suggest that it is a rifted island arc and that the gabbros which contain the ni cu sulfides were derived from the mantle plume that rifted the island arc the conditions under which the sulfides formed may be modeled either by recalculating the sulfide compositions to 100 percent sulfide or by using the cu pd ratios both approaches suggest that most of the sulfide occurrences formed from an enriched morb magma with r factors of 200 to 1 000 one of the occurrences la force is depleted in platinum group elements pge relative to cu and this depletion may be the result of the removal of sulfides from the magma prior to emplacement at this stratigraphic level the advantage of using the cu pd ratio rather than recalculating to 100 percent sulfide is that it is not necessary to have s analyses to model the conditions of formation of the sulfides further the cu pd ratio may be used as a prospecting tool rocks with ratios greater than mantle values formed from magmas depleted in pd possibly due to removal of sulfide from the magma this implies the potential for a pge bearing sulfide deposit at stratigraphically lower levels such an approach has been applied to pge targets in the eastern abitibi subprovince samples from four ni cu occurrences with cu pd ratios close to mantle ratios have the potential to produce pge as a by product samples from seven ni cu sulfide occurrences and the layered intrusions lac dore bell river and cummings complex have cu pd ratios much greater than mantle ratios indicating that these intrusions and sulfides are not good targets for pge at this stratigraphic level although there may be pge rich sulfides present at depth

normalized measures of exploration performance in terms of basin sediment volumes the normalized measures of exploration performance defined in this paper are the exploratory drilling density in feet per cubic mile of sediments and the hydrocarbon discovery density in boe per cubic mile these density measures provide a convenient means for summarizing the status of exploration in the sedimentary provinces of the lower 48 states of the united states revealing that the smaller hydrocarbon rich provinces have been explored much more intensely than the larger ones the most important application of the drilling and hydrocarbon discovery densities is in defining normalized discovery functions that is the relationships between the normalized measures of cumulative exploratory drilling and discoveries normalized rather than absolute discovery functions are necessary for proper comparison of the results of exploration in regions or depth zones of differing sizes the normalized drilling and discovery measures are also useful for developing meaningful statistics of exploration performance

sulfide globules in mid ocean ridge basalts morb and the effect of oxygen abundance in feso liquids on the ability of those liquids to partition metals from morb and komatiite magmas the coexistence of sulfide liquids or more accurately fe s o liquids with silicate liquids in a variety of magma systems is well known as is the ability of immiscible fe s o liquids to segregate ni cu and platinum group metals into orebodies evidence for association of fe s o liquids with magmas that form mid ocean ridge basalts morb comes from sulfide globules in basalt glass from siqueiros fracture zone east pacific rise three fracture zones in the indian ocean lau basin and 23 previously published oceanic localities approximately 40 of the sulfur originally present in magma at siqueiros fracture zone exsolves as a sulfide liquid during fractional crystallization virtually all of the cu and 20 of the ni originally in the magma is extracted by the sulfide liquid significant variations in the ability of fe s o liquids to partition ni cu exist among morb and other mafic magmas such as komatiites and layered mafic intrusions nernst partition coefficients sulfide to silicate melt dsl are 2 3 times higher for ni in morb than in komatiite and 5 times higher for cu reasons for this variation are not entirely clear but a possible contributing factor is that fe s o liquids in morb appear to have a higher oxygen content than those in komatiites that fe s o liquids associated with morb magma are oxygen rich is suggested by low observed values at siqueiros fracture zone for the ni fe exchange coefficient kd3 1 21 4 56 kd3 feni olivine feni sulfide it has been previously shown that natural magmatic fe s o liquids are rich in o2 o s o is apparently always greater than 0 49 and that kd3 is inversely correlated with o s o kd3 values below 12 would result from fe s o liquids with o s o 0 49 kd3 value of 20 would be impossible values from 12 to 20 would be unlikely because they would require an fe s o liquid poor in o2 this argument for low kd3 in magmas is strengthened by the low kd3 values of morb whose globules are inarguably of magmatic origin kd3 in komatiites is higher than in morb indicating a lower oxygen fugacity in komatiite magma and varies from 5 to 20 with values of 20 coming from highly metamorphosed komatiites fleet and macrae argued on the basis of experimental results that kd3 values of 20 could not have resulted from magmatic processes but might have come from metamorphism under oxygen deficient conditions

improved statistical method for assessment of undiscovered petroleum resources a statistically significant straight line correlation exists between logarithms of oil or gas field sizes and order of discovery in some of australia s petroleum provinces the correlation is predicted by the hypotheses 1 that the probability of discovery of each field is proportional to size raised to a constant power lambda lgr and 2 that fields are discovered without replacement from a population with a lognormal size distribution a computer program has been developed that uses extrapolations of the straight line to predict the number and size of future discoveries the program takes into account a dependent relationship among lambda and the average slope and intercept of the fitted lines and the average standard deviation of the residuals that is indicated by the hypotheses the new field wildcat drilling required is estimated using predicted success rates

dendrogeomorphic approaches for identifying the probable occurrence of debris flows and related torrential processes in steep headwater catchments the hrubý jesenik mountains czech republic abstract culminating parts of mid mountain ranges in central europe are interwoven by a network of high gradient streams these parts together with the surrounding slopes form a coupling system in which hazardous geomorphic processes such as landslides debris flows or flash floods can occur in the case of the hrub jesenik mountains eastern sudetes czech republic we present an evaluation of the debris flows and related torrential processes in the high gradient streams of the selected catchment based on dendrogeomorphic methods in addition to the classical dendrogeomorphic approaches we refined the procedure of identifying certain and probable events using new weighted indexes for event reconstruction additionally because of the steep narrow channels without a characteristic accumulation cone a new spatial approach is defined based on the spacing of disturbed trees for each event random distribution or clustering and location of disturbed trees in an individual section of the valley floor using kernel density analysis for each event and calculating the particular grids in arcgis software we are able to describe the spatial reach and probable nature of an event debris flow or hyperconcentrated flow dendrogeomorphic analysis of 397 sampled trees predominantly coniferous trees revealed 24 torrential events 15 certain nine probable since 1928 with peaks in 1991 1997 and 2010 according to index values in addition the spatial distribution of disturbed trees grouped in clusters in these years indicates debris flow events in the upper parts of the catchment it seems that new dendrogeomorphic approaches should be valuable in remote steep headwater catchments where several types of processes affect the valley floors

subduction platform subsidence and foreland thrust loading the late tertiary development of taranaki basin new zealand borehole seismic and gravity data are used to investigate deformation of continental lithosphere at a miocene collisional zone deformation is manifested in the three following principal forms a long wavelength 500 km platform subsidence ascribed to mantle convection flexural deformation on a scale of 100 200 km due to crustal thrusting at the eastern boundary of the taranaki basin and a ductile thickening evident on the deep seismic section of taranaki basin that occurs on a scale of 10 km evidence for flexural deformation principally comes from the deep seismic section that shows a 150 km wavelength bending of the moho down toward the major zone of thrusting within the taranaki fault zone paleowater depths however provide evidence for an initial early miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading instead we propose that this broad platform subsidence was driven by loading from a deep source probably subduction induced flow in the mantle by 22 19 ma 1 2 km of water existed over most of the area now occupied by south taranaki basin by 19 17 ma the water depth in the zone east of the taranaki basin the taranaki fault zone had been replaced by rock due to submarine thrusting and crustal thickening this build up of submarine topography in the taranaki fault zone constitutes part of the load 25 8 mpa that created and maintains south taranaki basin gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading equivalent to 15 7 mpa over a 50 km wide zone this intracrustal load is explained as being due to thick skinned thrusting bringing denser lower crustal rocks nearer to the surface in the thrust zone the complete load on the taranaki foreland is therefore in three parts the submarine topographic load the intracrustal load and the loading of infilling sediments

re os sm nd and pb isotopic constraints on mantle and crustal contributions to magmatic sulfide mineralization in the duluth complex abstract previous petrologic and stable isotopic studies of sulfide mineralization in the duluth complex have led to the premise that sulfide genesis is strongly linked to the interaction between mantle derived magmas and sedimentary country rocks in a rift zone environment in order to more fully evaluate the nature of this interaction and to gain an insight into the possible importance of externally derived metals in the ore forming process pb sm nd and re os isotopic studies of the babbitt cu ni deposit were initiated rock types examined include low sulfide troctolite that show very little petrologic evidence for contamination disseminated sulfide bearing troctolitic to gabbroic rocks that occur close to the basal contact with country rocks and contain metasedimentary xenoliths and massive sulfide lead isotopic values of whole rocks plagioclase mineral separates and massive sulfides show only subtle differences and are compatible with 3 to 5 contamination of a mantle derived melt with a proterozoic crustal contaminant e nd 1 1 ga values of the troctolite and gabbro samples are chondritic and only the massive sulfides show strong evidence for contamination based on sm nd isotopic values massive sulfides tend to be more sensitive indicators of contamination in the sm nd system because of late stage incorporation of a light rare earth element rich fluid into a ca po 4 apatite component of the immiscible sulfide liquid os 1 1 ga values are also strongly anomalous and range from 500 to 1200 in disseminated sulfide bearing troctolites and massive sulfides these values are also consistent with from 1 to 3 contamination by c rich and strongly radiogenic proterozoic sedimentary rocks elemental and isotopic mass balance calculations suggest that up to 50 of the pb and at least 35 of the os in the sulfide mineralization have been derived from external sources a corollary is that other metals may also be in part derived from external sources which would aid in explaining the compositional diversity of the sulfide mineralization selective assimilation of country rocks by mantle derived magmas may occur in crustal staging chambers during ascent to shallower levels or in situ as a result of devolatilization reactions and partial melting

petrochemical studies of the dunka road cu ni deposit duluth complex minnesota troctolitic sequence divided into three major units oxygen isotope values confirm the chemical studies and indicate that major element assimilation is restricted to within approximately 10 m of country rock inclusions pyrrhotite crystallization followed by separation of a cu rich sulfide melt blending and partial crystallization of chemically similar magma and enrichment of cu in the final residual liquid modified journal abstract

deciphering magmatic and metasomatic processes recorded by fluid inclusions and apatite within the cu ni pge sulfide mineralized bathtub intrusion of the duluth complex ne minnesota usa

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

early history of the midcontinent rift inferred from geochemistry and sedimentology of the mesoproterozoic osler group northwestern ontario the mesoproterozoic 1108 1105 ma osler group a3k m thick succession of basaltic flows and sedimentary units on the north shore of lake superior is among the oldest expressions of the midcontinent rift basal sediments of the simpson island formation new name deposited by braided fluvial systems record westward transport of debris eroded from local archean and proterozoic rock units strata deposited by this fluvial system are intercalated with and overlain by ocean island basalt oib like basalts which become increasingly contaminated up section end 1100ma 0 3 to 5 3 the light rare earth element lree enriched la smn 1 5 3 9 and heavy ree hree fractionated gd ybn 1 5 3 7 subaerial flows are divisible into two units that correlate with other sections of the osler group to the east but simple correlations with more distant sequences are difficult the volcanic rock dominated portion of the succession is overlain by a thin 25 m thick conglomerate sandstone assemblage representing southeast progradation of an alluvial fan in a semi arid climatic setting clast lithologies and geochemistry indicate no extra rift detritus was delivered from the hinterland of the fan various lines of evidence in both volcanic and sedimentary rocks support a scenario where early pre 1108 ma subsidence along a north south axis from the western arm of the rift to the nipigon embayment was replaced by subsidence along the east west rift axis between 1108 and 1105 ma resume le groupe d osler mesoproterozoique 1108 1105 ma une succession de coulees basaltiques et d unites sedimentaires d une epaisseur de 3 km sur la rive nord du lac superieur est l une des plus anciennes expressions du rift mi continental les sediments a la base de la formation simpson island nouveau nom deposes par un systeme fluvial anastomose enregistrent le transport vers l ouest de debris erodes des unites rocheuses locales archeennes et proterozoiques des basaltes de points chauds recouvrent et sont intercales avec les strates deposees par ce systeme fluvial ces basaltes sont de plus en plus contamines en remontant la section end 1100ma 0 3 to 5 3 les ecoule ments sub aeriens de terres rares legeres enrichies la smn 1 5 3 9 et de terres rares lourdes enrichies fractionnees gd ybn 1 5 3 7 peuvent etre divises en deux unites qui correspondent a d autres sections du groupe d osler vers lst mais de simples correlations avec des sequences plus eloignees sont difficiles la portion de la succession dominee par des roches volcaniques est recouverte d un mince 25 m assemblage conglomerat gres qui represente la prograda tion vers le sud est d un delta alluvionnaire dans un environnement climatique semi aride la lithologie des clastes et la geochimie indiquent qu aucun detritus hors du rift ne provient de l arriere pays du delta diverses preuves a la fois dans les roches sedimentaires et les roches volcaniques soutiennent un scenario selon lequel une subsidence precoce avant 1108 ma le long d un axe nord sud a partir du bras ouest du rift vers la baie nipigon a ete remplacee par de la subsidence le long de l axe est ouest du rift entre 1108 et 1105 ma

petrology of the st stephen intrusion and the genesis of related nickel copper sulfide deposits the st stephen intrusion is a tholeiitic mafic ultramafic intrusion of devonian age occurring in the gander terrane of the appalachian orogen the intrusion is dominated by olivine plagioclase cumulates olivine cumulates and plagioclase cumulates olivine ranges in composition from fo 61 to fo 85 and plagioclase from an 43 to an 89 variations in the compositions of clinopyroxene and orthopyroxene are within wo sub 42 47 en sub 37 50 fs sub 6 18 and wo sub 3 3 en sub 50 71 fs sub 26 47 respectively the cr cr al and mg mg fe super 2 ratios of chromites range from 0 25 to 0 75 and 0 01 to 0 65 respectively this appears to have resulted from the changes in the composition of the melt from which chromites were crystallized and reaction of the early formed cumulus chromites with the intercumulus melt the observed crystallization sequence olivine chromite olivine plagioclase olivine plagioclase clinopyroxene plagioclase clinopyroxene orthopyroxene olivine plagioclase orthopyroxene clinopyroxene plagioclase clinopyroxene appears to have resulted from simple fractional crystallization of a common tholeiitic parent magma the composition of the parent magma seems to have an affinity to the mid ocean ridge basalts the intrusion contains numerous zones of significant ni cu sulfide mineralization the principal sulfide minerals are those typical of magmatic assemblages pyrrhotite pentlandite and chalcopyrite ni and cu concentrations reach 2 40 and 3 90 percent respectively platinum group element concentrations are generally low with maximum abundances in massive sulfides for example not exceeding 62 ppb attainment of sulfur saturation in the st stephen magma during the early stages of the differentiation corresponds to the appearance of plagioclase on the liquidus following crystallization of about 10 percent of the olivine the nickel depleted nature of olivines at this interval can be explained by fractional crystallization of olivine and sulfide in the proportion of 50 1 an earlier segregation of sulfide from the parental magma seems to be responsible for the very low levels of platinum group elements in the interstitial sulfides associated with the olivine cumulates preferential assimilation of the sulfide rich portions of the country rock metasediments and attainment of sulfide silicate equilibrium on a local scale are believed to have played important roles in the formation of large pyrrhotite rich sulfide bodies

landslide inventory in a rugged forested watershed a comparison between air photo and field survey data abstract landslide inventories are routinely compiled by means of aerial photo interpretation api when examining photo pairs the forest canopy notably in old growth forest hides a population of not visible landslides in the present study we attempt to estimate how important is the contribution of landslides not detectable from aerial photographs to the global mass of sediment production from mass failures on forested terrain of the capilano basin coastal british columbia api was coupled with intensive fieldwork for identification and measurement of all landslides a 30 year framework was adopted we show that not visible landslides can represent up to 85 of the total number of failures and account for 30 of the volume of debris mobilised such percentages display high sub basin variability with rates of sediment production varying by one order of magnitude between two sub basins of the study area this is explained qualitatively by gis based analysis of slope frequency distributions drainage density and spatial distribution of surficial materials such observations find further support in the definitions of transport limited and supply limited basins as a practical consideration to land managers we envisage that supplementary fieldwork for landslide identification is mandatory in transport limited systems only fieldwork has demonstrated that gully related failures have a greater importance than one could expect from api

the influence of country rock assimilation and silicate to sulfide ratios r factor on the genesis of the dunka road cu ni platinum group element deposit duluth complex minnesota the dunka road deposit is one of several cu ni platinum group element pge sulfide occurrences found along the northwestern margin of the duluth complex where the host troctolitic rocks are in contact with metasedimentary rocks of the animikie group magma contamination through assimilation of sulfidic argillaceous country rocks is generally recognized as having played a key role in the genesis of the mineralization three main types of disseminated sulfide mineralization have been identified within the dunka road deposit i norite hosted sulfides ii troctolite hosted sulfides and iii pge rich sulfide horizons the norite hosted sulfides are found either adjacent to country rock xenoliths or near the basal contact the troctolite hosted sulfides form the bulk of the deposit and occur throughout the lower 250 m of the intrusion the pge rich sulfide horizons are typically localized directly beneath ultramafic layers the composition of the different types of sulfide occurrences is modelled using cuipd ratios it is shown that each type results from the interplay of two main parameters namely the degree of magma contamination and the silicate magma to sulfide melt ratio r factor the norite hosted sulfides formed at low r factors and high degrees of contamination as expressed by their pge depleted nature low seis ratios and elevated content in pyrrhotite and arsenide minerals the troctolite hosted sulfides formed at moderate r factors and small degrees of contamination as shown by their moderate pge content and mantle like seis ratios finally the pge rich sulfide horizons are modelled using elevated r factors from an uncontaminated parental magma which is substantiated by their elevated noble metal content and seis ratios and low pyrrhotite to precious metal sulfide ratio le gite de dunka road est un parmi plusieurs gites de sulfures de cu ni elements du groupe du platine egp trouves le long de la bordure nord ouest du complexe de duluth ou les roches hotes troctolitiques sont en contact avec les roches metasedimentaires du groupe d animikie il est generalement reconnu que la contamination du magma par l assimilation de roches argileuses sulfurees encaissantes a joue un role capital dans la genese de la mineralisation trois types principaux de mineralisation de sulfures dissemines ont ete identifies dans le gite de dunka road i sulfures dans la norite hote ii sulfures dans la troctolite hote et iii horizons de sulfures enrichis en egp les sulfures dans la norite hote apparaissent soit dans les zones adjacentes aux xenolites encaissants ou pres du contact basal les sulfures dans la troctolite hote forment le plus gros du gisement et ils apparaissent dans les 250m inferieurs de l intrusion la localisation typique des horizons de sulfures enrichis en egp se trouve directement sous les couches ultramafiques les rapports cu pd ont ete utilises pour elaborer un modele de la composition des differents types de mineralisation de sulfures il est demontre que chaque type resulte de l interaction de deux parametres dominants a savoir le degre de contamination du magma et le rapport du magma silicate au liquide sulfure facteur r les sulfures dans la norite hote ont ete formes sous des conditions de faibles facteurs r et de fortes contaminations comme en temoignent la teneur appauvrie en egp les faibles rapports se s et les concentrations elevees de la pyrrhotite et des mineraux arsenieux les sulfures dans la troctolite hote ont ete formes sous des conditions de facteurs r moderes et de faibles contaminations comme le revelent leur teneur modere en egp et les rapports se s analogues a ceux du manteau finalement les horizons de sulfures enrichis en egp sont modelises en utilisant des facteurs r eleves et un magma parental non contamine ce qui est appuye par leur forte teneur en elements nobles et les rapports se s eleves et par le rapport faible de la pyrrhotite sur les sulfures de metaux precieux

the contribution of geomorphological mapping to sediment transfer evaluation in small alpine catchments the assessment of sediment transfer processes is necessary to understand the hydro geomorphological functioning of small alpine watersheds prone to channelised debris flows because their occurrence often depends on the amount of debris available in the gully systems therefore sediment budgets should be studied through the identification of erosion transport and deposition processes sediment transfer processes were investigated in a small catchment by field measurements and more specifically through the application of a process based geomorphological mapping method the proposed methodology is based on data directly derived from gis analysis using high resolution dem field measurements and aerial photograph interpretations it has been conceived to estimate sediment transfer dynamics taking into account the role of different sediment stores in the torrential system the proposed geomorphological mapping methodology is quite innovative in comparison with most legend systems that are not adequate for mapping comprehensively active and complex geomorphological systems such as debris flow catchments maps representing the various sediment storages and their relationships can be used for hydro geomorphological hazard mitigation

re os isotopic systematics of the voisey s bay ni cu co magmatic ore system labrador canada abstract re and os concentrations and os isotopic compositions have been obtained for massive matrix and disseminated sulphide ores from three environments within the voisey s bay intrusion the ovoid eastern deeps and discovery hill zone in order to assess the role of crustal contamination in the genesis of this large cu ni co deposit these samples have high re concentrations 148 to 288 ppb in 100 sulphide for their common os concentrations 4 8 to 24 ppb in 100 sulphide yielding high re os ratios 12 to 33 these data confirm that the magma parental to the voisey s bay ore system was broadly basaltic in major element chemistry rather than picritic consistent with the low ni cu ratio of the ores 1 5 re os isotopic data exhibit a limited spread in 187 re 188 os 57 to 157 and define an imprecise 1323 135 ma model 3 isochron likely the result of small r factor variations within the ore system the re os isochron age is within error of 1334 ma u pb ages obtained for baddeleyite from the ore bearing troctolites demonstrating that whole rock re os isotopic systematics have remained closed since crystallisation the initial os isotopic composition of the isochron os 1040 200 implies significant magma interactions with radiogenic os that most likely resides in the nain churchill province crust these data are therefore consistent with the parental magma achieving sulphide saturation as a result of contamination by radiogenic crustal components with further addition of base and precious metals as a function of r factor analyses of sulphide separates from the proterozoic tasiuyak churchill and archaean nain gneisses confirm that both units contained significant os 8 6 ppb and 0 38 ppb respectively that was very radiogenic at 1334 ma os 1908 and 5202 respectively yielding crustal residence tchur model ages of 2200 to 2400 ma however these model ages may have been affected by re and or os mobility during the 1 85 ga torngat and 1 1 ga grenville orogeny re os isotopic modelling suggests that a reasonable fit to the ore data may be obtained via bulk crustal contamination of magmas parental to the nain plutonic suite nps with either tasiuyak 2 contamination or nain 16 contamination gneiss followed by an r factor process 200 to 1000 which improved the tenor of the sulphide liquid during transport in active magma conduits or after deposition in an active replenished voisey s bay intrusion magma chamber however the dominance of plagioclase rich high al2o3 magmas in the mafic members of the nps troctolites and anorthosites may indicate that other deeper forms of lithospheric interaction potentially involving mafic lower crust may be crucial to understanding this style of magmatic sulphide ore system

reconnaissance sediment budgets for lynn valley british columbia holocene and contemporary time scales volumes of erosional and depositional landforms were estimated by reconnaissance methods in a steep forested drainage basin in the coast mountains british columbia to examine what insight might be gained into the sediment budget in the absence of direct measurements of sediment transfer processes sediment transfers in postglacial and contemporary time were inferred on hillslopes from hillslopes to stream channels and within stream channels data were collected by aerial photographic analysis and field observation postglacial sediment sources are major gullies created by debris slides and flows failures in glaciolacustrine terraces and stream channel degradation depositional landforms consist of talus slopes and colluvial and alluvial fans contemporary sediment sources include debris slides and flows in established gullies and minor processes on hillslopes debris slide and debris flow volumes were calculated and other processes were estimated from regional values erosion rate averaged over postglacial time is 276 t km 2 a 1 0 15 mm a 1 surface lowering with gullies and stream channel degradation contributing 170 and 82 t km 2 a 1 respectively a terminal alluvial fan provides an independent check of the results in contemporary time erosion rates are calculated to be 350 t km 2 a 1 with debris flows and slides contributing nearly all of this sediment the contemporary rate is probably perturbed by recent land use history mass movement processes appear to be the dominant mechanism of sediment transfer and contributions from pleistocene valley deposits have declined significantly during holocene time resume les volumes de terrain erodes et deposes ont ete estimes par des methodes de reconnaissance dans un bassin de drainage boise a pentes abruptes des montagnes cotieres de la colombie britannique afin d etudier quelles connaissances sur le budget sedimentaire pourraient etre acquises en l absence de mesures directes du processus de transfert de sediments les transferts de sediments a l epoque post glaciaire et contemporaine ont ete inferes sur les flancs des cotes des flancs des cotes vers les chenaux des rivieres et dans les chenaux des rivieres les donnees proviennent de l analyse de photographies aeriennes et d observations sur le terrain les sources de sediments post glaciaires sont des ravines creees par des glissements et des coulees de debris des effondrements de terrasses glacio lacustres et la degradation de chenaux les formes de terrain creees par deposition comprennent des tabliers d eboulis et des deltas colluviaux et alluvionnaires les sources contemporaines de sediments comprennent des glissements et des coulees de debris dans des ravines etablies et des processus mineurs sur des pentes les volumes des glissements et des coulees de debris ont ete calcules et d autres processus ont ete evalues a partir de valeurs regionales la moyenne du taux d erosion pour la periode post glaciaire est de 276 tonnes km 2 a 1 abaissement de la surface de 0 15 mm a les ravines et la degradation des chenaux des ruisseaux contribuant respectivement 170 et 82 tonnes km 2 a 1 un delta alluvionnaire terminal permet une verification independante des resultats a l epoque contemporaine les taux d erosion sont calcules comme etant 350 tonnes km 2 a 1 et les glissements et des coulees de debris y contribueraient pour la presque totalite le taux contemporain est probablement perturbe par l utilisation recente du terrain les processus de mouvements de masse semblent etre le mecanisme dominant de transfert de sediments et les contributions provenant des depositions dans les vallees au pleistocene ont diminue de facon significative durant l holocene traduit par la redaction campbell and church 713

lithologic control of debris torrent occurrence a field based investigation into the frequency and magnitude of debris torrent systems reveals that lithology controls the spatial and temporal occurrence of debris torrents in the tsitika watershed vancouver island british columbia we identified 125 debris torrent systems in the watershed for half these basins we used dendrochronology historical air photographs and field surveys to estimate debris torrent frequency and magnitude for a 30 year period we find that the volcaniclastic half of the watershed contains more than twice as many debris torrent systems in which debris torrents occur over seven times more frequently and the deposits have a higher rate of delivery of sediment to the mainstem river than the intrusive half lithologic differences in weathering rates weathering product grain size and rock texture can explain the observed differences in debris torrent behaviour because debris torrents are the main sediment transport path from hilltop to valley bottom in the region these results confirm an important lithologic control on regional sediment transport while the exact numbers are uncertain we estimate that the sediment flux of volcaniclastic debris torrents in the watershed is five times higher than that of the intrusive debris torrents

fossil and recent debris flows in medium high mountains moravskoslezske beskydy mts czech republic abstract the significance of debris flows for the morphogenesis of the medium high mountains of central europe has long been neglected herein we provide evidence from the moravskoslezske beskydy mountains flysch western carpathians czech republic where fossil pleistocene debris flow events in spite of their low recent activity were important erosion and accumulation agents in shaping the mountainous terrain geomorphological and sedimentological analyses helped to differentiate between two classes of debris flow deposits deposits of the 1st class are relatively voluminous contemporary terraced landforms which originated in the pleistocene transport limited conditions recent activity of debris flows presented by the 2nd class accumulations is characterized by the presence of low magnitude events mostly originated during the reworking of older diamictons the inheritance of large volumes of old debris flow diamictons in steep mountainous terrain is the evidence of slow erosional transformation of the last glacial landforms pointing to the fact that recent topography of the mountains is not in full equilibrium with contemporary climatic and environmental conditions

turning dry holes from disasters to exploration wisdom decision tree to determine the key failure mode for segments in conventional petroleum prospects petroleum exploration is a risky business and dry holes wells that failed to find movable petroleum fluids are common especially in frontier and emerging basins and plays technically rigorous systematic and consistent postdrill analysis may convert dry holes from disasters to exploration wisdom and future success here we present a decision tree to determine the key failure mode for individual segments in conventional petroleum prospects and illustrate its utility with examples from the deep water taranaki basin offshore new zealand we hope that this decision tree or its customized versions will become the best practice in postdrill analysis across the exploration industry

the midcontinent rift system one of the most prominent features on gravity and aeromagnetic maps of the united states is a series of major generally linear anomalies that extend from central kansas to lake superior and then turn southward into central michigan figures 1 2 this system of anomalies clearly reflects major geological features and as such it must represent a very significant episode in the history of the north american continental lithosphere the geologic features associated with these anomalies particularly axial basins filled with basalt and immature clastic rocks along with evidence of crustal extension indicate that the episode was probably one of incipient rifting