osmium isotopes and crustal sources for platinum group mineralization in the bushveld complex south africa the bushveld complex in south africa is the largest layered mafic intrusion in the world and a major producer of platinum group elements pges economic mineralization is found in the merensky reef and the ug2 and ug1 chromitites and includes osmium bearing laurite ru ir os s 2 the laurite bearing samples have 187 os 186 os ratios of 1 28 1 60 which are more radiogenic than predicted for mantle derived 2 0 ga os 0 9 and indicate a system wide assimilation of crustal os the ug1 chromitite is stratigraphically the lowest and the least radiogenic 1 28 whereas the merensky reef is the highest and most radiogenic 1 41 1 60 hart and kinloch 1989 radiogenic os from crustal assimilation in mantle derived magmas or from hydrothermal fluids can account for these high isotopic ratios assimilation models require that os and by inference other pges are carried in al rich tholeiitic a magmas rather than high mg ultramafic u magmas pyritic black shales in contact with the intrusion may be high in radiogenic os and less than 1 shale assimilation in an a magma can explain the observed ratios late stage hydrothermal fluids driven by the heat of the intrusion could also have carried os and other pges from adjacent rocks into specific layers of the bushveld the os isotope data add to mounting evidence that pges in layered mafic intrusions may be derived from crustal sources and can no longer be considered as solely a product of mantle derived magmatic processes

sulfur based hazardous waste solidification existing uses for sulfur are relatively advanced and offer limited opportunities to consume significant new supplies currently sulfur is in net surplus on a global basis and with environmental regulations greater sulfur recovery from petroleum and gas processing is mandated the outlook is clear there will be substantial and growing surpluses in global sulfur supply in the foreseeable future sulfur prices are likely to be under pressure and producers could face substantial and growing disposal fees therefore new markets must be found for sulfur to avoid disposal crises one potential new market is the production of sulfur solidified concrete this is a thermoplastic composite of mineral aggregates bound together with chemically modified sulfur the product is more durable than portland cement there may be monetizeable benefits in reducing greenhouse gas emissions that would enhance the attraction of sulfur solidified cement applications the main objective of this study is to evaluate experimentally the potential use of sulfur as a solidifying agent for hazardous waste to achieve this objective the study reviewed the sulfur concrete literature analyzed locally produced sulfur evaluated a number of sulfur polymer modifiers and physical stabilizing agents designed a set of experiments and evaluated the produced product for its hydro mechanical chemical properties the results indicated that the manufactured sulfur polymer cement is an excellent candidate for waste management practices such as solidification stabilization of hazardous waste barrier systems for landfilling of hazardous waste and waste water treatment plants

filling the bushveld complex magma chamber lateral expansion roof and floor interaction magmatic unconformities and the formation of giant chromitite pge and ti v magnetitite deposits his mind was like a soup dish wide and shallow irving stone on william jennings bryan a compilation of the sr isotopic stratigraphy of the bushveld complex shows that the evolution of the magma chamber occurred in two major stages during the lower open system integration stage lower critical and lower main zone there were numerous influxes of magma of contrasting isotopic composition with concomitant mixing crystallisation and deposition of cumulates larger influxes correspond to the boundaries of the zones and sub zones and are marked by sustained isotopic shifts major changes in mineral assemblages and development of unconformities during the upper closed system differentiation stage upper main zone and upper zone there were no major magma additions other than that which initiated the upper zone and the thick magma layers evolved by fractional crystallisation the lower and lower critical zones are restricted to a belt that runs from steelpoort and burgersfort in the northeast to rustenburg and northam in the west and an outlier of the lower and lower critical zone up to the lg4 chromitite layer in the far western extension north of zeerust it is only in these areas that thick harzburgite and pyroxenite layers are developed and where chromitites of the lower critical zone occur these chromitites include the economically important c 1 m thick lg6 and mg1 layers exposed around both the eastern and western lobes of the bushveld complex the upper critical zone has a greater lateral extent than the lower critical zone and overlies but also onlaps the floor rocks to the south of the steelpoort area the source of the magmas also appears to have been towards the south as the mg chromitite layers degrade and thin northward whereas the lg layers are very well represented in the north and degrade southward sr and os isotope data indicate that the major chromitite layers including the lg6 mg1 and ug2 originated in a similar way extremely abrupt and stratigraphically restricted increases in the sr isotope ratio imply that there was massive contamination of intruding melt which hit the roof of the chamber and incorporated floating granophyric liquid which forced the precipitation of chromite kruger 1999 kinnaird et al 2002 therefore each chromitite layer represents the point at which the magma chamber expanded and eroded and deformed its floor nevertheless this was achieved by in situ contamination by roof rock melt of the intruding critical zone liquids that had an orthopyroxenitic to noritic lineage the main zone is present in the eastern and western lobes of the bushveld complex where it overlies the critical zone and onlaps the floor rocks to the south and the north where it is also the basal zone in the northern lobe the new magma first intruded the northern lobe north of the thabazimbi murchison lineament interacted with the floor rocks incorporated sulphur and precipitated the platreef along the floor rock contact before flowing south into the main chamber this exceptionally large influx of new magma then eroded an unconformity on the critical zone cumulate pile and initiated the main zone in the main chamber by precipitating the merensky reef on the unconformity the upper zone magma flowed into the chamber from the southern bethal lobe as well as the tml this gigantic influx eroded the main zone rocks and caused very large scale unconformable relationships clearly evident as the gap areas in the western bushveld complex the base of this influx which is also coincident with the pyroxenite marker and a troctolitic layer in the northern lobe is the petrological and stratigraphic base of the upper zone sr isotope data show that all the pge rich ores including chromitites are related to influxes of magma and are thus related to the expansion and filling of the magma chamber dominantly by lateral expansion with associated transgressive disconformities onto the floor rocks coincident with major zone changes these positions in the stratigraphy are marked by abrupt changes in lithology and erosional features over which succeeding lithologies are draped the outcrop patterns and the concordance of geochemical isotopic and mineralogical stratigraphy indicate that during crystallisation the bushveld complex was a wide and shallow lobate sill like sheet and the rock strata and mineral deposits are quasi continuous over the whole intrusion

multiple sulfur isotopes reveal a magmatic origin for the platreef platinum group element deposit bushveld complex south africa the platreef ore horizon of the bushveld complex south africa is the third largest platinum group element ore deposit in the world but the origin of its ore remains enigmatic a complex contact relationship between the igneous and footwall rocks of the bushveld complex coupled with evidence for widespread late stage hydrothermal processing obscures the original mineralization history of the platreef we constrain the parental magmatic origin of the platreef by exploiting multiple sulfur isotope contrasts across bushveld complex contact zones in order to see through the effects of postmineralization hydrothermal activity we report s isotope measurements made on samples collected along two profi les through the platreef into underlying metapelitic and metacarbonate footwall rocks in both profi les igneous rocks far from the contact have low 33 s values average 33 s 0 15 whereas metasedimentary rocks far from the contact have high 33 s values 33 s to 5 04 with a smoothly varying profi le between the two end members the midpoint in both isotope profi les is displaced into the footwall defi ning a classic advective dispersive tracer geometry this geometry is not present in the associated 34 s values the displacement of the 33 s front suggests fl uid transport and advection of s into the country rocks this was accompanied by back diffusion of the s isotope tracer into the platreef the platreef magma was apparently s saturated prior to emplacement and counterintuitively lost s during the formation of the present platreef ore horizon

re and os distribution and os isotope composition of the platreef at the sandsloot mogolakwena mine bushveld complex south africa abstract rhenium and os concentrations and os isotopic compositions were determined for a suite of previously characterized samples from a traverse across the platreef at the sandsloot mogolakwena mine of the northern limb of the bushveld complex the samples comprise five pyroxenites and five parapyroxenites contact rocks representing variable mixtures of calc silicate country rocks and magmatic rocks the isotopic data from the pyroxenites define a re os regression line with an age 2011 51 ma that agrees within uncertainty with the accepted age for the bushveld complex whereas the parapyroxenite data scatter about this trend the initial 187os 188os ratios of the pyroxenites 0 1820 0 1848 are similar to but slightly more radiogenic than previously published values for the merensky reef our preferred interpretation is that this section of the platreef formed from a well mixed crustally contaminated magma genetically related to that which gave rise to the merensky reef the platreef parental magma may also have experienced minor additional contamination by wall rock interaction during emplacement

petrology and mineralisation of the southern platreef northern limb of the bushveld complex south africa the platreef the putative local analogue of the merensky reef forms the floor to the mafic succession in the northern limb of the bushveld complex we define the platreef as the lithologically variable unit dominated by pyroxenite which is irregularly mineralised with pge cu and ni between the transvaal metasedimentary footwall or archaean basement and the overlying main zone gabbronorite we define the mineralisation around calcsilicate xenoliths within the main zone in the far north of the limb as a platreef style mineralisation the platreef ss has a strike extent of 30 km whereas platreef style mineralisation occurs over a strike length of 110 km the platreef varies from 400 m thick in the s to 30 modal in some intersections these are dominated by pyrrhotite with lesser pentlandite and chalcopyrite minor pyrite and traces of a wide compositional range of sulphides in the southern sector mineralised zones have cu grades of 0 1 0 25 and ni 0 15 0 36 massive sulphides are localised commonly but not exclusively towards the contact with footwall metasedimentary rocks magmatic sulphides are disseminated or net textured ranging from a few microns to 2 cm grains of pyrrhotite and pentlandite with chalcopyrite and minor pyrite much of the sulphide is associated with intergranular plagioclase or quartz feldspar symplectites along the margins of rounded cumulus orthopyroxenes the pges in the southern sector occur as tellurides bismuthides arsenides antimonides bismuthoantimonides and complex bismuthotellurides pgm are rarely included in the sulphides but occur as micron sized satellite grains around interstitial sulphides and within alteration assemblages in serpentinised zones the pt pd ratio 1 and pge grade may be decoupled from s and base metal abundance

role of late magmatic fluids in merensky type platinum deposits a discussion a number of features of platinum group element pge rich layers in layered intrusions provide evidence for the involvement of late magmatic fluids the presence of pegmatitic textures intergrowth of sulfides with intercumulus volatile rich phases high cl content in volatile bearing phases and association with graphite and fluid inclusions have been taken by some authors as evidence for postcumulus transport and deposition of pge by a fluid phase of late magmatic derivation we argue that these apparently hydrothermal features are the result of postcumulus processes superimposed on layers whose extensive uniform pge concentrations were formed by magmatic cumulus processes the association with pegmatites and volatiles arises from the relatively low solidus temperatures of orthocumulate layers which cause these layers to act as traps for fluids migrating through the crystal pile these fluids are mostly derived by vapor exsolution from fractionated intercumulus melt and are consequently enriched in ci redissolution of these fluids into vapor undersaturated trapped liquid in orthocumulate layers causes recrystallization and formation of gabbro pegmatites immiscible sulfide oxide liquid solidifies at near solidus temperatures in the interstitial pore space between early crystallizing silicate minerals and it is forced into areas occupied by late crystallizing ci bearing silicates this accounts for intergrowths of cu and pge rich sulfides with amphiboles and micas a ubiquitous feature of sulfide bearing gabbros further exsolution of a vapor phase during late stages of crystallization causes deuteric alteration formation of fluid inclusions and possible local redistribution of sulfides and pge cooling of this vapor phase may lead to precipitation of graphite at or below the orthocumulate solidus graphite deposition may be catalyzed by sulfides and pge

petrology geochemistry and the mechanisms determining the distribution of platinum group element and base metal sulphide mineralisation in the platreef at overysel northern bushveld complex south africa platinum group element pge mineralisation within the platreef at overysel is controlled by the presence of base metal sulphides bms the floor rocks at overysel are archean basement gneisses and unlike other localities along the strike of the platreef where the floor is comprised of transvaal supergroup sediments the intimate pge bms relationship holds strong into the footwall rocks decoupling of pge from bms is rare and the bms and platinum group mineral assemblages in the platreef and the footwall are almost identical there is minimal overprinting by hydrothermal fluids therefore the mineralisation style present at overysel may represent the most primary style of platreef mineralisation preserved anywhere along the strike chondrite normalised pge profiles reveal a progressive fractionation of the pge with depth into the footwall with ir ru and rh dramatically depleted with depth compared to pt pd and au this feature is not observed at sandsloot and zwartfontein to the south of overysel where the footwall rocks are carbonates there is evidence from rare earth element abundances and the amount of interstitial quartz towards the base of the platreef pyroxenites that contamination by a felsic melt derived from partial melting of the gneissic footwall has taken place textural evidence in the gneisses suggests that a sulphide liquid percolated down into the footwall through a permeable inter granular network that was produced by partial melting around grain boundaries in the gneisses that was induced by the intrusion of the platreef magma pge were originally concentrated within a sulphide liquid in the platreef magma and the crystallisation of monosulphide solid solution from the sulphide liquid removed the majority of the ipge and rh from it whilst still within the mafic platreef transport of pge into the gneisses via downward migration of the residual sulphide liquid fractionated out the remaining ipge and rh in the upper parts of the gneisses leaving a slick of disseminated sulphides in the gneiss with the residual liquid becoming progressively more depleted in these elements relative to pt pd and au highly sulphide rich zones with massive sulphides formed where ponding of the sulphide liquid occurred due to permeability contrasts in the footwall this study highlights the fact that there is a fundamental floor rock control on the mechanism of distribution of pge from the platreef into the footwall rocks where the floor rocks are sediments fluid activity related to metamorphism assimilation and later serpentinisation has decoupled pge from bms in places and transport of pge into the footwall is via hydrothermal fluids in contrast where the floor is comprised of anhydrous gneiss such as at overysel there is limited fluid activity and pge behaviour is controlled by the behaviour of sulphide liquids producing an intimate pge bms association xenoliths and irregular bands of chromitite within the platreef are described in detail for the first time these are rich in the ipge and rh and evidence from laurite inclusions indicates they must have crystallised from a pge saturated magma the disturbed and xenolithic nature of the chromitites would suggest they are rip up clasts either disturbed by later pulses of platreef magma in a multi phase emplacement or transported into the platreef from a pre existing source in a deeper staging chamber or conduit

modeling the merensky reef bushveld complex republic of south africa the merensky pegmatoid normal reef in the western bushveld complex is commonly characterized as a pyroxene rich pegmatoidal unit with a base that is enriched in chromite and platinum group element bearing sulfides overlying a leuconorite footwall models for its formation have ranged from those that view it as entirely a magmatic cumulate succession to those that have suggested that it is a zone of volatile induced remelting the consequences of the latter interpretation are investigated using the numerical modeling program iridium which links diffusive and advective mass and heat transport with a phase equilibration routine based on the melts program the initial system consists of a simple stratigraphic succession of a partially molten leuconorite overlain by a partially molten pyroxenite both initially at 1 190 c and 2 kbar 2 wt of a volatile fluid composed of 75 mol h2o 20 mol co2 and 5 mol h2s is then added to the lower 20 cm of the pyroxenite the system is then allowed to evolve under conditions of chemical diffusion in the liquid the addition of the volatile components results in a modest increase in the amount of melt in the pyroxenite however chemical diffusion across the leuconorite pyroxenite boundary leads to more extensive melting at and below the boundary with preferential loss of opx from the underlying leuconorite preferential re precipitation of sulfide and chromite and concentration of the pge at this boundary these results mimic actual mineral and compositional profiles across the merensky pegmatoid and illustrate that long term diffusion process can effectively produce mineralogical and compositional layering not present in the original assemblage

geochemistry and mineralogy of the platreef and critical zone of the northern lobe of the bushveld complex south africa implications for bushveld stratigraphy and the development of pge mineralisation the northern lobe of the bushveld complex is currently a highly active area for platinum group element pge exploration this lobe hosts the platreef a 10 300 m thick package of pge rich pyroxenites and gabbros that crops out along the base of the lobe to the north of mokopane formerly potgietersrus and is amenable to large scale open pit mining along some portions of its strike an early account of the geology of the deposit was produced by percy wagner where he suggested that the platreef was an equivalent pge rich layer to the merensky reef that had already been traced throughout the eastern and western lobes of the bushveld complex wagner s opinion remains widely held and is central to current orthodoxy on the stratigraphy of the northern lobe this correlates the platreef and an associated cumulate sequence that includes a chromitite layer known as the grasvally norite pyroxenite anorthosite gnpa member directly with the sequence between the ug2 chromitite and the merensky reef as it is developed in the upper critical zone of the eastern and western bushveld implicit in this view of the magmatic stratigraphy is that similar critical zone magma was present in all three lobes prior to the development of the merensky reef and the platreef however when this assumed correlation is examined in detail it is obvious that there are significant differences in lithologies mineral textures and chemistries mg of orthopyroxene and olivine and the geochemistry of both rare earth elements ree and pge between the two sequences this suggests that the prevailing interpretation of the stratigraphy of the northern lobe is not correct the critical zone of the northern lobe cannot be correlated with the critical zone in the rest of the complex and the simplest explanation is that the gnpa platreef sequence formed from a separate magma or mixture of magmas chilled margins of the gnpa member match the estimated initial composition of tholeiitic main zone type magma rather than a critical zone magma composition where the gnpa member is developed over the ultramafic lower zone hybrid rocks preserve evidence for mixing between new tholeiitic magma and existing ultramafic liquid this style of interaction and the resulting rock sequences are unique to the northern lobe the gnpa member contains at least seven sulphide rich horizons with elevated pge concentrations some of these are hosted by pyroxenites with similar mineralogy crystallisation sequences and pd rich pge signatures to the platreef chill zones are preserved in the lowest main zone rocks above the gnpa member and the platreef and this suggests that both units were terminated by a new influx of main zone magma this opens the possibility that the platreef and gnpa member merge laterally into one another and that both formed in a series of mixing quenching events involving tholeiitic and ultramafic magmas prior to the main influx of tholeiitic magma that formed the main zone

isotope and trace element patterns below the merensky reef bushveld complex south africa evidence for fluids abstract mineralisation in the merensky reef of the bushveld complex has recently been attributed to the ingress of fluids possibly via channels beneath depressions in the footwall of the reef referred to as potholes in this study samples from immediately below three potholes and from the same horizon a norite under normal reef have been analysed for oxygen and strontium isotopes chlorine and noble metals to investigate this possibility results from one pothole are interpreted as retaining the primary magmatic oxygen isotope signature with average 18o of plagioclase and orthopyroxene being 7 1 0 1 and 6 6 0 1 respectively and imply a 18 o melt of 6 8 interaction with an early magmatic fluid cannot be detected from the oxygen isotope patterns and therefore the importance of this process cannot be assessed results from this oxygen isotope study of the western lobe of the bushveld complex are practically identical to those obtained for the laterally equivalent horizons in the eastern lobe a second pothole shows more variability with the norite under the pothole reef showing secondary alteration of plagioclase to paragonite and epidote and orthopyroxene to serpentine and chlorite fresh plagioclase from these altered samples is only slightly depleted in 18o compared with normal reef however measured whole rock 18o values are up to 1 lighter than those predicted from mineral modes and suggest that the secondary assemblage contains a component depleted in 18o which could have been the result of exchange with a low 18o fluid this fluid interaction was probably a late stage relatively low temperature event secondary alteration of the footwall was accompanied by introduction of chlorine au contents also appear to be slightly enriched in the footwall under pothole reef

hydro mechanical evaluation of soil stabilized with cement kiln dust in arid lands this study evaluates the potential use of cement kiln dust ckd a waste product from the cement industry for enhancing the mechanical as well as the hydraulic properties of soils in arid lands stabilized products will play a major role in reducing slope failures pavement damage and the design of containment barriers for hazardous waste in arid lands various tests to determine the different physical properties of the stabilized matrix were conducted and the optimum mixture that produces maximum internal energy and minimum hydraulic conductivity was selected the effect of soaking and unsoaking of the treated specimens on the mechanical properties was also evaluated the effect of metal ion concentration and conjugate anions on the resultant hydraulic conductivity was evaluated the optimum percentage of ckd was calculated by using stress strain data newton s divided difference and simpson s integration technique the analyses have shown that 6 by weight of ckd is the optimum mix design which increases the shear strength and decreases the hydraulic conductivity to less than 10 9 m s therefore the treated soil could be used as a soil based barrier layer for containment of hazardous waste

the early cretaceous platform off northwest florida controls on morphologic development of carbonate margins abstract an analysis of approximately 3500 km of multifold and 1000 km of singlefold seismic reflection data correlated with two exploration wells and other available geologic information records the morphologic development of the early cretaceous carbonate platform margin off northwest florida early cretaceous depositional patterns apparently controlled the concurrent formation of gently dipping declivities 10 carbonate platform margin slopes in the vicinity of desoto canyon northeastern gulf of mexico we suggest that the pronounced along strike change in morphology reflects variations in platform width input of terrestrial clastics and overall sediment availability to the platform s seaward margin slope southeast of the canyon the early cretaceous slope bordered a relatively broad platform removed from terrigenous sediment input environmental conditions favored the uninterrupted development of skeletal and nonskeletal buildups along the paleo shelf edge which effectively prevented large quantities of shelf derived clastic sediments from moving seaward consequently as the carbonate platform grew and its height increased the declivity of its seaward slope also increased as predicted by models of long term carbonate platform development in contrast northwest of the canyon the slope bordered a narrower platform adjacent to a source of terrigenous clastics more vigorous cross platform transport of clastics and resultant adverse environmental conditions at the paleo shelf edge inhibited consistent development of carbonate buildups thereby creating only an intermittent sediment barrier to the adjacent slope resultant higher sedimentation rates on the slope caused it to aggrade and prograde along with the carbonate platform allowing the margin slope to maintain its gentle morphology throughout the early cretaceous

strontium isotope evidence for preserved density stratification in the main zone of the bushveld complex south africa the bushveld complex formed from two isotopically distinct magmas magma addition and mixing can be tracked by measuring initial strontium isotope ratios of cumulates rocks with ratios of 0 7065 lie below the lower 2 2 km of the main zone ratio 0 7085 whereas those with ratios of 0 7073 lie above it this unit represents a liquid layer intruded into the density stratified magma pile near the base of the chamber the merensky reef was produced by mixing of the pile with underlying trapped liquid enriched in precious metals

sequence stratigraphy of the upper jurassic mixed siliciclastic carbonate deposits in the north german basin lower saxony hildesheimer wald the wendhausen 6 core drilled in the hildesheimer wald 30 km se of hannover provides an insight into the oxfordian deposits of the north german basin consisting of the ornatenton heersum and korallenoolith formations eight facies are recognized based on the different fossil combinations sedimentary structures and the carbonate content a facies model of a mixture of a deltaic system and a carbonate ramp is presented based on the interpretation of these facies which helps the understanding of the facies and sequence stratigraphic evolution in the mixed system in the north german basin and could be applied to other shallow water mixed depositional systems sequences of three hierarchies are delimited small scale sequences are defined by the changes in components grain size and the vertical facies stacking patterns medium scale sequences are bounded by distinctive exposure surfaces these surfaces are characterized either by the enrichment of iron minerals or by irregular base of the lowstand channel fill sandstones overlying on them large scale sequences are derived from the facies proportion statistics of each medium scale sequence the similar trend between the regional sea level curve and the facies statistic curve implies that sea level fluctuations have a great control on the large scale sequence evolution during the oxfordian age sequence stratigraphic correlation was achieved at the medium scale sequence level and four surfaces of oxfordian age were correlated across the north german basin

accretion of the south florida platform late quaternary development stratigraphic information from high resolution seismic data obtained across the southwest florida platform indicates that the modern shelf is a constructional platform with pliocene pleistocene and holocene sediments resting on an eroded karstic miocene platform the miocene surface dips away from the coastline with significant breaks in slope occurring at the center of the shelf and at the shelf edge at the southwest corner of the platform this surface crops out to form a terrace this terrace lies along the west facing continental slope of the florida shelf and is progressively buried to the south by younger deposits reefs and sediment so that it has no surface expression in the florida straits a paired reef complex rests on the thickest post miocene sediments t at mark the edge of the modern shelf the deepest reef forms a well developed escarpment with its crest buried by approximately 15 m 50 ft of sediment the shallower reef is a low swale over most of its extent but develops into a large reef spit complex howell hook in the central part of the study area within the pliocene pleistocene and holocene sediments two stratigraphic units can be delineated 1 a lower progradational unit of pliocene pleistocene age that can be traced under the shelf edge reef and continuously onlaps the miocene surface and 2 an upper unit of late pleistocene holocene age which is composed of reef and pelagic sediment two sedimentary fans have been identified on the northern slope and floor of the florida straits the apices are set in at gaps in the carbonate ridge rimming the southern florida shelf at least nine complex sigmoidal oblique sequences are identified within the fans a reef buried by sediment of the last two sequences correlates with howell hook radiometric analyses of material dredged from this feature and from the outcrops of the second sequence yield ages of 7 7 11 ka indicating a holocene age for these sediments and suggesting a very high rate of shelf accretion

seismic expression of carbonate to terrigenous clastic sediment facies transitions of western florida shelf abstract transitions from carbonate to terrigenous clastic sedimentary deposits are commonplace in the mesozoic cenozoic section of the northwestern florida shelf on a regional scale these transitions are responsible for a large seismic velocity variation between the areas of the destin dome and the middle ground arch in the destin region clayey shales and sands are more prevalent interspersed with carbonates and evaporites with the result that seismic transmission velocities are relatively low toward the south on the middle ground arch the increased carbonate evaporite content of the section results in much higher velocities an example of this variation is that a reflection two way travel time of 2 sec corresponds to a depth from 2 5 to 2 8 km 1 5 to 1 7 mi in the dest n area while this same reflection time corresponds to a depth of 4 km 2 5 mi in the vicinity of the texaco 2516 well on the middle ground arch analyses of stacking velocities indicate that the transition is a gradual one to the north and west of middle ground arch on a local scale transitions or terminations related to facies changes erosion or sediment body geometries are a potentially important factor in prediction of reservoir rock on the as yet uncondemned 12 km 7 4 mi broad deep structural culmination west of the destin tests and on the untested 9 km 5 5 mi broad deep structure 20 km 12 4 mi south of the destin dome the deep exxon test on the destin dome encountered 20 m 66 ft of norphlet quartz sand with porosity ranging from 20 to 30 and permeability of 1 darcy this potentially excellent reservoir bed at a depth of 5 224 m 17 138 ft is more than 150 m 492 ft below the deep structural crest on the destin dome the sun test 25 km 15 5 mi east of the exxon well penetrated 6 m 19 6 ft of smackover oomoldic dolomit with porosities of 13 to 15 and failed to find any norphlet sand as it bottomed in louann salt immediately below the smackover a study of a combination of velocity analyses density and velocity logs and synthetic seismograms allows speculations that the deep destin dome and the structure on its south flank are still viable exploration prospects end of article last page 417

florida a jurassic transform plate boundary magnetic gravity seismic and deep drill hole data integrated with plate tectonic reconstructions substantiate the existence of a transform plate boundary across southern florida during the jurassic on the basis of this integrated suite of data the pre cretaceous florida bahamas region can be divided into the pre jurassic north american plate jurassic marginal rift basins and a broad jurassic transform zone including stranded blocks of pre mesozoic continental crust major tectonic units include the suwannee basin in northern florida containing paleozoic sedimentary rocks a central florida basement complex of paleozoic age crystalline rock the west florida platform composed of stranded blocks of continental crust the south georgia rift containing triassic sedimentary rocks which overlie block faulted suwannee basin sedimentary rocks the late triassic jurassic age apalachicola rift basin and the jurassic age south florida bahamas and blake plateau marginal rift basins the major tectonic units are bounded by basement hinge zones and fracture zones fz the basement hinge zone represents the block faulted edge of the north american plate separating paleozoic and older crustal rocks from jurassic rifted crust beneath the marginal basins fracture zones separate mesozoic marginal sedimentary basins and include the blake spur fz jacksonville fz bahamas fz and cuba fz bounding the blake plateau bahamas south florida and southeastern gulf of mexico basins the bahamas fz is the most important of all these features because its northwest extension coincides with the gulf basin marginal fault zone forming the southern edge of the north american plate during the jurassic the limited space between the north american and the south american african plates requires that the jurassic transform zone connecting the central atlantic and the gulf of mexico spreading systems was located between the bahamas and cuba fz s in the region of southern florida our plate reconstructions combined with chronostratigraphic and lithostratigraphic information for the gulf of mexico southern florida and the bahamas indicate that the gulf was sealed off from the atlantic waters until callovian time by an elevated florida bahamas region restricted influx of waters started in callovian as a plate reorganization and increased plate separation between north america and south america africa produced waterways into the gulf of mexico from the pacific and possibly from the atlantic

the geological setting of the platinoid and base metal sulfide mineralization in the platreef of the bushveld complex in drenthe north of potgietersrus on the farm drenthe the platreef consists of a complex assemblage of norites melanorites pyroxenites serpentinites and xenoliths of dolomite it is a zone of up to 250 m thick between the basal contact of the complex and the overlying main zone norites the composition of the orthopyroxene shows a rapid increase from en 60 to en 70 in the lower 30 m of the sequence and a sharp drop from en 70 to en 60 at the top of the platreef this compositional break at the upper contact is due to a change from primary bronzite in the platreef to inverted pigeonitc in the main zone high temperature metamorphic assemblages are preserved in the larger xenoliths whereas their outer margins and the smaller xenoliths contain retrograde metamorphic mineral assemblages the igneous rocks display irregularly distributed zones of alteration to bronzite bastitites and serpentinites the alteration process was probably dominated by degassing of the xenoliths the distribution and composition of the major sulfide minerals indicate a change from a sulfur rich to a metal rich environment during the crystallization of the platreef pyrite monoclinic pyrrhotite pentlandite and chalcopyrite dominate the lower part of the platreef and hexagonal pyrrhotite pentlandite and chalcopyrite or cubanite prevail in the upper portion whole rock analyses show an upward decrease in the ni cu ratio from 1 95 to 1 70 large variations occur in the distribution and grade of ni cu and platinum group elements although highest values are associated with a zone of serpentinization the ni and cu values are unreliable indicators in predicting pt and pd concentrations in zones of major metal enrichment ni and cu correlate strongly while pt and pd have more significant correlations with ni than cu although the minerals of the platinum group elements are primarily associated with chalcopyrite the pt pd ratio decreases upward in the sequence the mineralization is considered to have been caused by the breakup of dolomite xenoliths that added co 2 h sub 2 o and s to the magma thus simultaneously lowering the solubility of sulfur in the magma and adding sulfur from an external source which resulted in the precipitation of an immiscible sulfide liquid

interaction of floor rocks with the platreef on overysel potgietersrus northern transvaal the platreef on the basal contact of the rustenburg layered suite has been studied on the farm overysel 30 km north of potgietersrus the major element trace element and sr isotope geochemistry of the platreef feldspathic pyroxenite and the adjacent floor rocks is presented the immediate floor rocks consist of a suite of highly metamorphosed banded tonalitic gneisses with leucotonalitic veins to the south the floor rocks are metamorphosed sediments of the transvaal sequence these were intruded by granites which show signs of metamorphism close to the layered suite one facies of the granite yielded an age of 2 504 or 0 109 b y with an initial 87 sr 86 sr ratio of 0 7035 or 6 the cumulate textured pyroxenites of the platreef are geochemically different from other units of the rustenburg layered suite in having a high and variable initial 87 sr 86 sr ratio ranging from 0 7104 to 0 7227 with an average of 0 7160 calculated at 2 05 b y whereas overlying gabbro has a ratio of 0 7079 other ratios such as rb sr and ba zr are anomalously high in the platreef ranging from 0 05 to 0 26 and 16 to 44 respectively these data and the presence of relatively sodic plagioclase biotite and quartz suggest substantial assimilation of siliceous material the sedimentary transvaal sequence forming the footwall to the platreef to the south of overysel and consisting of dolomites and banded iron formation because of their low 87 sr 86 sr ratios and low k 2 o rb and sio 2 cannot produce the observed anomalies the banded tonalitic gneisses and associated veins are an unusual suite of rocks pyroxene geothermometry indicates that they have been metamorphosed to or 900 degrees c rb sr ratios range from 0 02 to 0 21 and 0 to 1 8 percent k 2 o 87 sr 86 sr ratios at 2 05 b y range from 0 7024 to 0 7258 total assimilation of these rocks cannot have produced the anomalous features of the platreef however their low k 2 o contents and high 87 sr 86 sr ratio in relation to their present low rb sr suggest that they have undergone a partial melting or loss of fluid component as a result of contact metamorphism however there are isotopic grounds for rejecting this as the sole source of contamination the granite close to the platreef has a high rb sr ratio initial 87 sr 86 sr ratios of 0 73 to 0 79 at 2 05 b y ago and 3 9 percent k 2 o total assimilation of these rocks could produce the trace element characteristics of the platreef but only if over 60 percent assimilation has occurred major element considerations preclude this a partial melt or fluid phase generated from these granites could have been the contaminant a composition calculated to produce the observed trace element and isotopic features of the platreef with less than 25 percent contamination has 150 ppm sr 87 sr 86 sr of 0 8 9 000 ppm ba 600 ppm rb and 10 ppm zr

hydro mechanical evaluation of stabilized mine tailings in this study mine tailings waste was stabilized using a combination of lime fly ash type c and aluminum treated samples were subjected to mineral identification for evaluating the formation of ettringite and gypsum also unconfined compression hydraulic conductivity and cyclic freeze and thaw tests were performed to evaluate the hydro mechanical properties of the stabilized samples experimental results have shown that the application of lime and fly ash type c to high sulfate content tailings has improved its plasticity workability and volume stability moreover upon addition of aluminum to lime and fly ash in a sulfate rich environment ettringite and calcium sulfo aluminate hydrate are formed in these samples application of 5 lime 10 fly ash type c in combination with 110 ppm aluminum resulted in the formation of a solid monolith capable of producing more than 1 000 kpa of unconfined compressive strength and reduced tailings permeability to 1 96 10 6 cm s 1 which is less than the recommended permeability of 10 5 cm s 1 by most environmental protection agencies for reusability of solidified stabilized samples the permeability of the treated tailings samples remained below the recommended permeability even after exposing the treated samples to 12 freeze and thaw cycles therefore based on the experimental results it is concluded that treatment of high sulfate content tailings with lime and fly ash combined with the availability of aluminum for reactions is a successful method of solidifying highly reactive mine tailings

a chronostratigraphic framework for the north central kaapvaal craton the bushveld complex and the vredefort structure abstract sufficient geochronological data are available pertaining to the north central part of the kaapvaal craton to construct a chronostratigraphic framework for the rock units involved in the vredefort event from the basement rocks at 3170 ma to the waterberg soutpansberg groups deposited between 2025 and 1425 ma the resulting framework forms a convenient chronological guide to the geological evolution of this area and the timing of events such as that at vredefort the basement on which the supracrustal rocks were deposited stabilised from 3170 to 3060 ma but metamorphism and metasomatism of these rocks occurred up to 2800 m y ago in different parts of the craton the first unit of the wits triad the volcaniclastic dominion group was deposited at 3060 ma on the stabilising basement this was followed by the dominantly clastic witwatersrand supergroup and the overlying ventersdorp supergroup the dominantly volcanic ventersdorp rocks are 2700 m y old and form the last unit of the wits triad a considerable time gap of 200 300 ma separates the triad from the lowermost units of the overlying transvaal sequence the age of these volcanic and clastic protobasinal rocks is poorly constrained between 2500 and 2300 ma they may in fact represent eroded remnants of a more extensive depositional cycle the mainly clastic sedimentary part of the transvaal sequence pretoria group has been dated at 2224 ma the upper part of the transvaal sequence rooiberg group is only constrained by the age of the intrusive bushveld complex the bushveld basic layered rocks are well dated at 2060 ma as are the subsequent granites at 2050 ma the vredefort event which post dates the bushveld complex is reasonably well constrained by the age of the bronzite granophyre at 2000 ma deposition of the waterberg and soutpansberg groups which post date the bushveld complex is poorly constrained between the age of the bushveld granites and younger alkaline intrusives at 1425 ma but these sediments and volcanics were probably formed between 2025 and 1752 ma the waterberg group may therefore contain debris from the vredefort structure

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale