refinements for footwall red bed diagenesis in the sediment hosted stratiform copper deposits model the emplacement of copper in sediment hosted stratiform copper deposits requires the circulation of a low temperature chloride rich brine in rift filling footwall red beds probably driven by meteoric recharge in adjacent highlands the descending oxygen rich meteoric water may become saline probably by leaching of footwall evaporites or possibly by mixing with brines draining down from contemporaneous evaporite pans and evolve toward a moderately oxidized brine as oxygen is consumed during the diagenetic reddening of the initially nonred coarse grained clastic rift sediments under these conditions the pore solution attains its maximum ability to leach and transport trace amounts of copper from the red beds sediment hosted stratiform copper deposits may form where the brine crosses a redox boundary into reduced sulfide rich gray beds with further consumption of oxygen during reddening the brine may become highly reduced and able to take iron into solution possibly explaining synsediment hosted stratiform copper iron oxide alterations and deposits the timing of copper deposition is clearly linked to the diagenetic reddening of immature footwall sediments in rift basins a process considered to extend over millions of years

the sediment hosted stratiform copper ore system sediment hosted stratiform copper deposits comprise disseminated to veinlet cu and cu fe sulfides in siliciclastic or dolomitic sedimentary rocks sediment hosted stratiform copper deposits are extremely common though economically significant deposits are rare they account for approximately 23 percent of the world s cu production and known reserves in addition to being significant sources of co and ag three sedimentary basins the paleoproterozoic kodaro udokan in siberia the neoproterozoic katangan in central africa and the permian basin of central europe contain supergiant 24 million metric tons mt contained cu deposits sediment hosted stratiform copper deposits are the products of evolving basin scale fluid flow systems that include source s of metal and s source s of metal and s transporting fluids the transport paths of these fluids a thermal and or hydraulic pump to collect and drive the fluids and the chemical and physical processes which result in precipitation of the sulfides metal sources are undoubtedly red bed sedimentary rocks containing fe oxyhydroxides capable of weakly binding metals sulfur may be derived from marine or lacustrine evaporites reduced seawater or hydrogen sulfide bearing petroleum metals appear to have been transported at low to moderate temperatures in moderately to highly saline aqueous fluids with the temperature of the fluid largely dependent on the time of fluid migration in the basin s burial history these basinal fluids were focused to potential metal precipitation sites by thinning of the red bed sequence at basin margins by faults by differentially permeable sedimentary units by paleotopography within the basin or along the margins of salt diapirs fluid movement produced widespread basin scale alteration that has commonly been overlooked but can form an important exploration guide sulfide precipitation occurred due to reduction typically caused by reaction with carbonaceous rocks or petroleum the amount of sulfides present at any deposit may be either metals or sulfide limited or could have been controlled by the amount of available reductant e g petroleum while understanding of sediment hosted stratiform copper ore genesis at the deposit scale is relatively robust there are still significant questions in regards its position in terms of basin evolution a wide variety of basin architectures and processes can lead to the formation of sediment hosted stratiform copper deposits despite general agreement that sulfides postdate sedimentation the absolute age of mineralization in many deposits has been difficult to document and the available evidence suggests that deposits can form throughout a basin s evolution from early diagenesis of ore host sediments to basin inversion and metamorphism supergiant and giant deposits formed in basins which underwent prolonged periods of fluid flow and in which unique conditions allowed for the accumulation of large amounts of metal bearing fluid sufficient reduced s and large amounts of reductants

cadmium diagenesis in laurentian trough sediments the depth distributions of cd mn and fe in pore water and sediment were determined on three replicate box cores collected at a 325 m deep station in the laurentian trough the results reveal a surface layer in which the content of solid phase cd first decreases but then increases sharply with depth in contrast mn decreases regularly over the same depth interval in the oxygenated zone of this layer cd probably associated with organic matter is released to the pore water resulting in concentrations that are more than an order of magnitude higher than in the overlying water column some of the dissolved cd is returned to the water column and some migrates downward and is precipitated at depth this part of the cd cycle is virtually complete within the surface layer the base of which corresponds to the base of the zone of mn enrichment in the subsurface layer solid phase cd and mn show little or no concentration change however dissolved cd which reaches often non detectable concentrations 0 05 nm in this layer increases once again deep within the anaerobic zone and attains concentrations even higher than in the surface layer the presence of dissolved cd complexes revealed by 1 5 to 8 fold increases in electrochemically active cd in pore water following uv treatment as well as inconsistent distributions of dissolved and solid phase cd indicate complexities in diagenesis that merit further investigation

cenozoic stratigraphy and basin tectonics of the andes mountains 20 28 south latitude clastic sedimentary basins have evolved during the past 40 m y in the central andes lat 20 28 s in response to shifting patterns of magmatism and deformation the distribution of these basins and their genetic relations to uplifted areas are analogous to the basins and mountain belts of the north american rocky mountains during the late cretaceous and early cenozoic petroleum exploration has focused on zones underlying the upper cenozoic strata along the eastern margin of the andes mountain belt between about 40 and 25 ma a nonmarine basin extended across the region that is now the andes mountains between about 25 and 10 ma the western part of the former basin became the site of a volcanic arc sediment accumulation continued in the east where marine intercalations demonstrate the low elevation of the basin after 10 ma the volcanic arc remained active and locally widened and crustal shortening caused regionally important thrust and reverse faulted ranges during the past 10 m y up to 4 000 m of coarse clastic debris accumulated in a foreland basin on the eastern flank of the mountains meanwhile in the interior of the mountains over 4 000 m of fine grained strata and evaporites accumulated in local depocenters

sulfide mineral chemistry investigation of sediment hosted stratiform copper deposits nahand ivand area nw iran abstract copper mineralization in nahand ivand area nw iran appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones siltstones and shaly marl geochemical analyses of the nahand ivand deposits show as much 35 wt cu and 730 ppm ag in the gray sandstone electron probe micro analysis epma was used to determine the mineralogical composition and distribution patterns of copper and silver bearing phases mainly in pyrite and cu bearing sulfides the epma data were essential for evaluating the distribution and partitioning of potential economically valuable components between co existing minerals furthermore they contribute to a better understanding of the genesis of the nahand ivand copper deposits and will guide further exploration in the region the epma results from different types of pyrite reveal cu contents as high as 0 32 wt 1 10 wt and 2 88 wt for framboidal pyrite pyi overgrowths on framboidal pyrite pyii and diagenetic pyrite pyiii respectively this successive increase of copper from pyi to pyiii is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper rich digenetic pyrite because of hydrothermal overprinting pyrite has been replaced by djurleite roxbyite and other nonstoichiometric cu s minerals that include covellite the epma study indicates that covellite contains significant concentrations of ag locally 1 wt in contrast only trace amounts of silver have been detected in pyrite and other copper sulfides indicating that covellite is the major ag carrier in the ore according to textural relationships such open space filling impregnation and replacement textures and the epma results later stage copper bearing fluids were responsible for the silver enrichment in the nahand ivand deposits

early diagenesis of cadmium and cobalt in sediments of the laurentian trough abstract the depth distributions of hydroxylamine acetic acid extractable co and cd were determined in box cores from a series of stations along the 1200 km length of the laurentian trough these were compared with the concentrations of total co and cd and the distributions of extractable mn and fe in the cores as well as with the total cd concentrations in sedimenting particles collected with a sediment trap the results indicate a strongly contrasting behaviour of the two elements during early diagenesis consistent with their respective chemistries and particle associations cobalt occurs mainly in a non reactive form and is buried with the accumulating sediments a mobile component of co is associated with mn and fehydroxides and like these compounds follows a redox sensitive pattern of dissolution in the reducing zone of the sediment vertical migration enrichment by precipitation in the oxidized surface layer and redistribution along the bottom in paniculate form paniculate cd arrives at the sediment surface bound to biogenic material is rapidly solubilized during aerobic degradation of the organic matter and migrates vertically both into the reducing zone of the sediments where it precipitates and back into the water column where it may be recycled through biological processes in an estuary co will be concentrated in the oxidized layer of the sediments and tend to migrate landward while cd will be most abundant in sediments underlying regions where plankton production is high relative to dilution by terrigenous particles

glacial enrichments of authigenic cd and u in subantarctic sediments a climatic control on the elements oceanic budget we examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic cd inventory thereby decoupling cd from po4 we suggest that the precipitation of cd sulfide in suboxic sediments is the single largest sink in the oceanic cd budget and that the accumulation of authigenic cd and u is tightly coupled to the organic carbon flux into the seafloor sediments from the subantarctic ocean and the cape basin south atlantic where oxic conditions currently prevail show high accumulation rates of authigenic cd and u during glacial intervals associated with increased accumulation of organic carbon these elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon a third core overlain by circumpolar deep water cpdw as are the other two cores but located south of the antarctic polar front shows an approximately inverse pattern to the subantarctic record the contrasting patterns to the north and south of the antarctic polar front suggest that higher accumulation rates of cd and u in subantarctic sediments were driven primarily by increased productivity this proposal is consistent with the hypothesis of glacial stage northward migration of the antarctic polar front and its associated belt of high siliceous productivity however the increase in authigenic cd and u glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts suggesting greater partitioning of organic carbon into the sediments during glacial intervals lower oxygen content of cpdw and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes higher glacial productivity in the cape basin record very likely reflects enhanced coastal up welling in response to increased wind speeds we suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum however our calculations suggest low sensitivity of seawater cd concentrations to glacial doubling of the extent of reducing sediments the model suggests that during the last 250 kyr seawater cd concentrations fluctuated only slightly between high levels about 0 66 nmol kg 1 on glacial initiations and reaching lowest values about 0 57 nmol kg 1 during glacial maxima the estimated 5 lower cd content at the last glacial maximum relative to modern levels 0 60 nmol kg 1 cannot explain the discordance between cd and 13c such as observed in the southern ocean this low sensitivity is consistent with foraminiferal data suggesting minimal change in the glacial cd mean oceanic content

genesis of kupferschiefer cu ag deposits by convective flow of rotliegendes brines during triassic rifting extensive and rich cu ag sulfide mineralization occurs in poland across the contact between the upper permian zechstein restricted marine sequence and the lower permian rotliegende continental volcanic and clastic sequence geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the rotliegende leaching metals from the volcanic detritus and up the flanks of basement highs possibly along fracture porosity to the pyritic kupferschiefer and zechstein limestone above thick evaporites in the lower zechstein preclude a vertical flow through model but metal zoning attitudes suggest that the brines overturned where the rotliegende pinched out against the highs and moved laterally along the base of the zechstein toward the basin centers presumably to sink back down into the rotliegende completing a convection cell a middle triassic paleomagnetic age for the metal zoning and kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the tethys ocean slow unicellular convection may be commonplace in sandstone basins where small lateral temperature gradients delta t exist but greater velocities are necessary to form large orebodies an anomalous tensional and thermal event such as rifting can increase velocities by increasing permeability slope angle or delta t the paleothermal structure of southwestern poland was determined by modeling the conductive heat flow in 14 one dimensional geologic sections which described the evolution of the basin architecture for 10 m y in the early triassic rifting was simulated by increasing the lower boundary condition from 500 degrees to 1 000 degrees c at 25 km this thermal pulse produced a surprisingly high delta t of 25 degrees c across the lubin ore district solely from differences in thermal conductivities between the basement high 4 2 w m degrees c the sandstone 2 5 w m degrees c and the shale basin center 1 25 w m degrees c unicellular convection patterns would be induced by the lateral boundary conditions of warm basement highs and cold shale centers and by the greater horizontal permeability these cells were 15 to 20 km long 400 m high and subhorizontal a slope angle of 2 degrees and a permeability of 1 d produces a convection velocity of 13 cm yr which with a copper solubility of 1 000 mg kg in 20 to 30 percent ca na cl brines in equilibrium with hematite can form the lubin deposit in less than 6 m y using a fracture permeability of 2 d and a solubility of 300 mg kg the time needed is less than 10 m y the konrad mine can be formed in similar time periods without the continuous recycling of the brine inherent in convective flow 20 times or more the metal solubilities needed to form the lubin deposits by a flow through model would be unreasonably high natural gases likely migrated along with the metalliferous brines and helped convection by creating secondary porosity and increasing the buoyancy of the fluids because the fluids are recirculated and not expelled convection provides a way in which secondary migration of methane and petroleum can occur effectively in solution as well as in separate phases

origin of the nchanga copper cobalt deposits of the zambian copperbelt the zambian copperbelt forms the southeastern part of the 900 km long neoproterozoic lufilian arc and contains one of the world s largest accumulations of sediment hosted stratiform copper mineralization the nchanga deposit is one of the most significant ore systems in the zambian copperbelt and contains two major economic concentrations of copper and cobalt hosted within the lower roan group of the katangan supergroup a lower orebody copper only and upper orebody copper and cobalt occur towards the top of arkosic units and within the base of overlying shales the sulfide mineralogy includes pyrite bornite chalcopyrite and chalcocite although in the lower orebody sulfide phases are partially or completely replaced by malachite and copper oxides carrollite is the major cobalt bearing phase and is restricted to fault propagation fold zones within a feldspathic arenite hydrothermal alteration minerals include dolomite phlogophite sericite rutile quartz tourmaline and chlorite quartz veins from the mine sequence show halite saturated fluid inclusions ranging from 31 to 38 wt equivalent nacl with homogenisation temperatures thtot ranging between 140 and 180 c diagenetic pyrites in the lower orebody show distinct relatively low 34s ranging from 1 to 17 whereas arenite and shale hosted copper and cobalt sulfides reveal distinctly different 34s from 1 to 12 for the lower orebody and 5 to 18 for the upper orebody there is also a clear distinction between the 34s mean of 12 1 3 3 n 65 for the upper orebody compared with 5 2 3 6 n 23 for the lower orebody the 13c of dolomites from units above the upper orebody give 13c values of 1 4 to 2 5 consistent with marine carbon however dolomite from the shear zones and the alteration assemblages within the upper orebody show more negative 13c values 2 9 to 4 0 and 5 6 to 8 3 respectively similarly shear zone and upper orebody dolomites give a 18o of 11 7 to 16 9 compared to lower roan dolomites which show 18o of 22 4 to 23 0 two distinct structural regimes are recognized in the nchanga area a weakly deformed zone consisting of basement and overlying footwall siliciclastics and a moderate to tightly folded zone of meta sediments of the katangan succession the fold geometry of the lower roan package is controlled by internal thrust fault propagation folds which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the ne faulting and folding are considered to be synchronous as folding predominantly occurred at the tips of propagating thrust faults with local thrust breakthrough the data from nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the lufilian orogeny sulfides tend to be concentrated within arenites or coarser grained layers within shale units suggesting that host rock porosity and possibly permeability played a role in ore formation however sulfides are also commonly orientated along but not deformed by a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization the ore mineralogy hydrothermal alteration and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate and metal enriched hydrothermal fluid at the site of mineralization there is no evidence at nchanga for a contribution of bacteriogenic sulfide produced during sedimentation or early diagenesis to the ores

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

latent volcanic heat and further unique aspects of early diagenetic stratiform copper mineralization in the white pine presque isle district northern michigan the curious occurrence of copper rich early diagenetic sediment hosted stratiform copper mineralization in the finest grained facies of nonesuch greybeds in northern michigan has been previously attributed to the warming of cupriferous brines in the footwall copper harbor conglomerate by latent volcanic heat from the subjacent porcupine volcanics shield volcano that anomalous footwall warming is employed here to explain other unique aspects of the white pine presque isle mineralization the abrupt downward sulfide zoning from disseminated pyrite to chalcocite across the top of the cupriferous zone the absence of bornite and chalcopyrite in the cupriferous zone proper and the essential absence of pseudomorphs after pyrite euhedra and framboidal aggregates within the cupriferous zone proper as well as the relatively coarse grained character of disseminated chalcocite in the cupriferous zone

storms consolidated field illinois basin identifying new reserves in a mature area discovered in 1939 storms consolidated field in the central illinois basin has produced approximately 24 5 million bbl oil mainly from mississippian sandstone reservoirs yet may contain significant remaining reserves the field produces from a combination structural stratigraphic trap along the upthrown side of a major normal fault trend although the principal reservoir zone the waltersburg sandstone is mostly depleted another important interval the aux vases sandstone appears underexploited in many parts of the field description and analysis of the only continuous core through the aux vases has led to the identification of major lithofacies and their characterization in terms of reservoir quality the aux vases appears to represent a series of shallow marine bars separated by nonreservoir areas of siltstone shale and shaly sandstone log based mapping of reservoir distribution plus production and pressure data indicates significant lateral and vertical compartmentalization of the reservoir although insufficient data exist for full scale integrated reservoir characterization studies a trend surface analysis was performed on structural information across the field the results of this analysis were compared with reservoir distribution maps to identify areas for future drilling or recompletion

seismic reflection profiling studies of a buried precambrian rift beneath the wabash valley fault zone sixty eight kilometers of 12 fold seismic reflection data were collected in the wabash river valley of southwestern indiana and southeastern illinois to investigate the configuration of a basement structure inferred from regional gravity and magnetic anomaly data the seismic profiles were also positioned to cross faults of the wabash valley fault system in a number of locations interpretation of the seismic reflection profiles and detailed gravity and magnetic profile data provides evidence for a series of northeasterly trending grabens in the basement these grabens are filled with pre mt simon layered rocks and are overlain by paleozoic sedimentary rocks of the illinois basin beneath the wabash river near grayville illinois an interpreted graben the grayville graben is approximately 15 km wide and contains about 3 km of fill individual boundary faults for the graben cut prominent reflectors within pre mt simon rocks and display offsets of up to 500 m the interpreted configuration of basement

the diagenetic origin of stratiform copper mineralization coates lake redstone copper belt n w t canada extensive stratiform copper mineralization occurs in three upper proterozoic embayments along a 250 km long arcuate belt in the mackenzie mountains supergroup northwest territories canada mineralization is found in transgressive strata between the continental red beds of the redstone river formation and shallow restricted marine carbonates of the overlying coppercap formation a mafic volcanic succession lying stratigraphically beneath the red beds possibly provided copper bearing detritus to the red beds the coates lake deposit the object of this study contains cupriferous sulfides principally chalcocite bornite and chalcopyrite hosted by microbial laminated limestones and dolostones these carbonates are intercalated with red siltstones to form as many as seven red bed carbonate couplets within the 110 m thick transition zone regional and local studies indicate that the host sediments were deposited in a peritidal setting associated with a sabkha environment paragenetic studies reveal a consistent order of precipitation for gangue and ore forming minerals these minerals can be related to the diagenetic evolution of the host sediments their presence at the coates lake deposit may be divided chronologically into four syngenetic to early diagenetic stages syndiagenesis precipitation of gypsum anhydrite after gypsum dolomitization diagenesis 1 deposition of calcite with partial replacement of anhydrite preore pyrite authigenic silica with partial replacement of anhydrite and calcite and authigenic feldspar diagenesis 2 precipitation of copper bearing sulfides in the presence of reduced sulfur sulfate reducing bacteria and organic matter and partial replacement of preore pyrite anhydrite calcite and quartz and diagenesis 3 neomorphism of calcite mineralization identified with the second stage of diagenesis would have preceded the marked reduction in permeability associated with the formation of neomorphic calcite

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

recent sediment remolding on a deep shelf ross sea implications for radiocarbon dating of antarctic marine sediments abstract coarse bioclastic rich sands have been widely reported from the banks of the antarctic continental shelf but their origin is still poorly known we report on a suite of coarse sediments recovered from the top of the mawson bank in the northwestern ross sea radiocarbon ages of biogenic calcite for modern and apparently late pleistocene deposits range from 1085 45 to 20 895 250 yr b p discovery of soft tissue ascidian preserved as an incrustation on a pebble at 2 m depth indicates aggregation of the sediment within several months or a year of core recovery radiocarbon ages of acid insoluble organic matter aiom are less than those of the foraminifera calcite the aiom ages are also reversed in sequence indicating reworking of the sediment during deposition these observations and a review of recently published literature suggest that much of the bank top sediment in antarctica is presently undergoing remobilization under the influence of strong currents and or icebergs even under interglacical high stand sea levels these observations point out the need for careful integrated studies on high latitude marine sediment cores before resultant ages alone are used as the foundation for paleoglacial reconstructions

the kupferschiefer cu ag ore deposits in poland a re appraisal of the evidence of their origin and presentation of a new genetic model the kupferschiefer stratiform copper deposits in central europe have long been considered a classic example of syngenetic mineralization however metal zoning and host rock relationships determined during exploration around the recently discovered lubin district orebodies in southwest poland suggest that the ore may instead be late diagenetic the mineralization occurs as thin extensive blankets of sulphides in the pyritic organic rich basal units of the late permian zechstein restricted marine sequence and in the eolian weissliegendes sandstone at the top of the early permian rotliegendes continental rift sequence of bimodal volcanic rocks and redbeds it is directly underlain and controlled by irregular oval zones of rote faule rf a barren oxidized and reddened portion of the normally dark grey pyritic basal zechstein rocks in plan view the metals occur as successive belts enriched in copper silver lead and zinc which developed laterally from and encircle the rf zones the ore transgres

preservation efficiencies and accumulation rates for biogenic silica and organic c n and p in high latitude sediments the ross sea rates of biogenic sediment accumulation biogenic silica and organic c n and p and pore water flux have been established for a variety of depositional environments in the ross sea on the basis of 14c measurements in kasten cores sediment accumulation rates ranged from 250 cm kyr 1 in the coastal basin of granite harbor to 1 2 cm kyr 1 in the shelf and slope environments of the northern and eastern ross sea burial of biogenic material was most rapid in the southwestern ross sea where biogenic silica accumulation rates ranged from 2 to 31 g cm 2 kyr 1 and organic carbon accumulation rates ranged from 0 05 to 1 4 g cm 2 kyr 1 in the northern and eastern ross sea biogenic silica and organic carbon accumulation rates typically equaled 0 02 0 03 g sio2 cm 2 kyr 1 and 0 002 0 004 g c cm 2 kyr 1 flux core measurements were used to estimate seabed regeneration rates for biogenic silica organic carbon and phosphorus pore water fluxes in general showed much less variability across the ross sea than did the biogenic accumulation rates pore water silicate fluxes in the study area ranged from 0 6 to 5 3 g sio2 cm 2 kyr 1 whereas carbon fluxes ranged from 0 1 to 1 2 g c cm 2 kyr 1 and phosphate fluxes varied from 0 006 to 0 012 g p cm 2 kyr 1 seabed preservation efficiencies were calculated for biogenic silica organic carbon and phosphorus by combining the solid phase and pore water data the seabed preservation efficiencies for biogenic silica 1 86 were greater than for organic carbon 1 71 at all nine stations examined the preferential preservation of biogenic silica relative to organic carbon also was apparent in ross sea sediments because the biogenic silica organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment water interface sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data p preservation efficiencies remained relatively high 24 65 even when the accumulation rates were low 1 2 cm kyr 1 because of the near zero phosphate fluxes out of the seabed of the total p in the seabed 0 04 0 09 wt approximately 25 existed in the form of organic p the total amount of biogenic silica accumulating on the ross sea shelf is 2 3 1012 g sio2 yr 1 which is approximately an order of magnitude less than the ledford hoffman et al 1986 estimate that was based on 210pb chronologies biogenic silica accumulation rates in the southern central and western ross sea increased during the mid and late holocene reaching their maximum values during the past 500 to 1000 years

geological context mineralization and timing of the juramento sediment hosted stratiform copper silver deposit salta district northwestern argentina the juramento deposit in northwestern argentina exhibits several readily visible general characteristics of sediment hosted stratiform copper ssc mineralization it consists of fine grained disseminated base metal sulfides within marine to lacustrine graybeds the basal whitish late cretaceous lecho sandstone and shallow water carbonates of the overlying maastrichtian yacoraite formation that overlie a thick sequence of redbeds the pirgua subgroup the property has been examined and drilled in three successive exploration programs as a possible analog of world class mineralization in the copperbelts of central africa and the kupferschiefer the present report provides specific field and laboratory results that confirm the classification as ssc type mineralization the host graybeds are the basal sandstone and overlying oolitic and stromatolitic units of the yacoraite formation which are shown from textural studies to be carbonaceous and to have initially contained very fine grained disseminated syndiagenetic pyrite these sediments would have been sufficiently porous and permeable in early diagenetic time to allow an infiltration of metalliferous fluids from the underlying redbeds resulting in the observed progressive replacement of in situ pyrite by common base metal sulfides sphalerite galena argentiferous tetrahedrite and copper rich sulfides first chalcopyrite then bornite and finally chalcocite sulfur isotope analyses indicate that a portion of the sulfur of ore stage sulfides is isotopically heavier than that of pyrite possibly due to a contribution from associated gypsum ore stage sulfides are zoned vertically and obliquely through the mineralized zones from cupriferous sulfides at low stratigraphic levels to lead and zinc rich mineralization above with unreplaced pyrite remaining within upper yacoraite strata the zoned sulfides and their replacement textures the peneconformable configuration of the mineralized zones and the position of ore stage mineralization adjacent to a stratigraphically defined redox transition from redbeds upward into graybeds indicate an overprint of copper and accompanying ore stage metals on originally pyritic graybeds the influx of ore stage metals presumably in an oxidized low temperature brine terminated with a silicification event that effectively sealed the host carbonates these observations and the overall genetic interpretation are consistent with the general deposit scale genetic model for early diagenetic ssc mineralization the regional geologic context is also consistent with its classification as a ssc deposit it is hosted by post oxyatmoversion sediments and was formed in association with evaporites at a low paleolatitude in a major intracontinental rift system

redox dependent changes in manganese speciation in baltic sea sediments from the holocene thermal maximum an exafs xanes and la icp ms study manganese mn enrichments in sediments of the deep basins of the baltic sea are believed to consist of ca mn carbonates that form from mn oxides following periodic inflows of oxygen rich north sea waters however a range of mn bearing mineral phases that besides mn carbonates e g ca rhodochrosite can include mn sulfides are known to be present in marine sediments with formation mechanisms that are sensitive to redox conditions in this study we use high resolution synchrotron exafs and xanes combined with la icp ms and micro xrf to investigate the nature of the mn enrichments in sediments from the holocene thermal maximum approx 8000 4000 cal yr bp at a site in the northern gotland basin analyses were performed on epoxy embedded sediment sequences we specifically address the role of changes in redox conditions in bottom waters as inferred from sediment molybdenum mo contents for mn sequestration we find that an up core increase in mo indicating a transition into more anoxic and sulfidic euxinic bottom water conditions is accompanied by a decline in total sediment mn contents while mn carbonates dominate the mn mineral fraction in the low mo interval in the more sulfidic high mo interval mn is associated with framboidal pyrite mn fe ratios in the sulfidic interval vary between the investigated sequences but reach values of up to 7 7 mol this exceeds ratios previously reported for sedimentary pyrite and exafs spectra indicate that sulfide bound mn is predominately tetrahedrally coordinated when mn fe ratios are high this suggests that mn is incorporated in other fe s phases such as mackinawite besides pyrite there is also evidence for the presence of a low concentration of mn associated with detrital aluminosilicates throughout the investigated intervals our results suggest that increased bottom water euxinia inhibited the formation of mn carbonate at this site during the holocene thermal maximum possibly due to a more rapid reduction of mn oxides in more sulfidic bottom waters c 2014 elsevier b v all rights reserved less

a process based approach to estimating the copper derived from red beds in the sediment hosted stratiform copper deposit model most estimates of the total tonnage of copper metal leached from footwall red beds to form sediment hosted stratiform copper deposits are based on the amounts of copper at ppm levels that might have been derived from the volume of red beds underlying given sediment hosted stratiform copper deposits that static calculation is replaced here with a process based approach in which the release of copper results from the progressive diagenetic alteration of the footwall aquifers by oxygen rich meteoric water driven by topographic recharge in highlands adjacent to the intracontinental rift basins hosting these deposits the total amount of liberated copper depends on the volume of meteoric water its oxygen content and the duration of the diagenetic leaching of copper estimates suggest that adequate amounts of copper may be derived from footwall red beds within reasonable periods of early and possibly more advanced diagenesis

climatic signals in lacustrine deposits of the upper yacoraite formation western argentina evidence from clay minerals analcime dolomite and fibrous calcite

geochemical characterization of a marine sediment core from the joides basin ross sea antarctica abstract the chemical fractionation of ten metals al ti cr fe cd cu mn pb zn and ni is reported for a marine sediment collected in the joides basin ross sea antarctica to evaluate their mobility and availability the bcr sequential extraction procedure was applied on 11 sections of the sediment the analyses performed both by icp oes and gf aas highlighted that most of the elements were in the residual phase showing a strong binding with the matrix and a low availability the bcr sequential procedure allowed us to have an insight into the chemical properties of the sediment and provided useful information about the redox state of the sediment itself and important indication on the availability and partitioning of different metals a chemometric treatment was applied on the dataset and it showed a separation between the superficial and the deep sections of the core the first being more influenced by the presence of mn and the second by an increase in al ti fe cr and pb concentrations

early diagenetic influences on iron transformations in a freshwater lake sediment abstract iron transformations in a calcium carbonate rich fresh water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter analysis of interstitial water shows that the observed redox sequence no 3 nh 4 mno 2 mn ii feooh fe ii so 2 4 s ii is roughly in agreement with that predicted by the gibbs free energy for the corresponding reactions in contrast to marine sediments these redox transitions occur in the uppermost sediments i e at depths of 0 4 cm deeper in the sedimentary sequence the depth profile for dissolved iron exhibits a steady non linear increase up to 400 mol dm 3 in this anoxic zone according to thermodynamic predictions iron ii minerals such as iron sulfide siderite and vivianite should precipitate while fe iii oxides should be completely dissolved however microscopic analysis showed that fe iii oxides were present throughout the studied sediment furthermore scanning electron microscope energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite these observations indicate kinetic control of iron transformations we have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron ii a rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions using the calculated rate constant we established that more than 1000 years would be required for the complete dissolution of fe iii oxides which is agreement with our observations and experimental data from the literature calculated precipitation rates of fe ii for a given mineral phase such as siderite yield a maximum value of 3 g feco3 g 1 dry sediment yr 1 such low rates would explain the absence of siderite and vivianite finally it can be inferred from the mn t fe t ratio in the sediments that this ratio depends on the redox conditions of the sediment water interface at the time of deposition thus this ratio can be used as paleo redox indicator in lacustrine sediments

alternative sources of metals for stratiform copper deposits abstract the controversy between sedimentary and epigenetic emplacement of copper in stratiform copper deposits appears to be subsiding in favour of an essentially synsedimentary enrichment of sulphur e g disseminated pyrite and or sulphates which undergo biogenic reduction to sulphide followed by an early diagenetic addition of copper to the host sediment the source of the copper has yet to be conclusively identified since the copper is deposited upon migrating into reducing zones e g sulphide rich organic bearing black shales and sulphate bearing microbial laminated carbonates the closest source of copper could be the commonly adjacent red beds where oxidising conditions would favour solution of copper in the presence of interstitial brines the thickness of these red bed sections is typically measured in 100 s to 1000 s of metres and they commonly contain abundant immature detrital grains including mafic minerals which could provide sufficient trace element copper to form major ore deposits copper in red beds may also include metal initially absorbed on amorphous iron oxides and released during diagenetic reddening of these oxides to form haematite on the other hand the ubiquitous red beds might be discounted as a principal source of copper and could be considered for the most part to have behaved as permeable beds through which cupriferous solutions from other sources migrated toward the grey beds for example mafic volcanics are found in important quantities in stratigraphic sequences hosting several stratiform copper deposits and could contribute large volumes of metalliferous solutions during metamorphic dehydration alternatively these same volcanic rocks may suggest volcanic associated pene exhalative activity with hydrothermal fluids emptying into subsurface red bed aquifers rather than onto surface sediments as commonly proposed for exhalative models although fluids of 250 c are generally considered necessary to transport copper in significant quantities in sulphide bearing exhalations lower temperatures are sufficient for chloride complexing in the absence of sulphide the large volumes of red beds could also have a major cooling effect on initially hot solutions the pene exhalative model may be closely related to fault bounded hot spring models of the type envisaged for so called shale hosted submarine exhalative base metal deposits

late pleistocene holocene sedimentary fluxes of organic carbon and biogenic silica in the northwestern ross sea antarctica eight sediment gravity cores collected from thejoides and drygalski basins were analysed in order to understand late pleistocene holocene biogenic dux changes in the ross sea driven by paleoenvironmental changes core lithologies and magnetic susceptibility depth profiles were used for core logging and stratigraphic corre lation nineteen ams radiocarbon dates of bulk organic matter were used to set chrono logical constraints and calculate sediment accumulation rates these rates which vary from 1 4 38 cm ka i were used to obtain the burial f1uxes of biogenic components the highest f uxes occur in the deepest parts o the basins toc 0 05 0 2 g cm 2 ka i biogenic silica 1 5 5 g cm 2 ka i whereas topographic highs show the lowest values toc 0 010 1 g cm 2 ka i biogenic silica 0 1 1 4 g cm 2 ka i dramatic changes in both physical properties and fluxes record the establishment of open marine sedimentation conditions which occurred first in thejoides basin and then with a delay of ca 6000 years in the drygalski basin both toc and biogenic silica ouxes increase through the holocene though slightly difterently the high f1uxes of both lobe and biogenic ba suggest that sedi ment accumulation at basin sites is strongly influenced by lateral transport

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

distribution of living planktonic foraminifera in the ross sea and the pacific sector of the southern ocean antarctica abstract in order to determine the factors controlling the distribution of planktonic foraminifera as a proxy for reconstruction of paleoenvironments we present data on live assemblages collected in the southern ocean plankton tows and hydrographic measurements were taken in the upper 400 m of the water column at different sites in the ross sea site b and at the polar front of the pacific ocean site o during austral summers from 1998 to 2003 based on qualitative micropaleontological observations we discriminated between neogloboquadrina pachyderma dextral dex and n pachyderma sinistral sin in addition for n pachyderma sin we distinguished four morphs the first one 1 has a thickened test and depressed sutures the second morph 2 is represented by specimens characterized by a subspheric and heavily encrusted test the third morph 3 has a thin and lobate walled test the fourth one 4 represent the juvenile stage of n pachyderma sin and is characterized by a smaller average size the microfauna collected in the ross sea site b is characterized by the dominance of n pachyderma sin morphs 1 and 2 whereas low occurrences of turborotalia quinqueloba n pachyderma dex and neogloboquadrina dutertrei were noted in the first 50 m of the water column the water column at this station is characterized by a marked and shallow stratification and a marked thermocline during the sampling season at the ocean station site o the assemblage shows increasing diversification t quinqueloba g bulloides n pachyderma dex and few specimens of globigerinita uvula characterize the planktonic microfauna there is a predominance of non encrusted morphs and juvenile specimens 3 and 4 at this station the mixed surface layer is deeper than in the ross sea 60 70 m the pycnocline and the thermocline less marked the depth and the intensity of the deep chlorophyll maximum dcm influence foraminiferal distribution n pachyderma sin shows abundance peaks at or just below the dcm while g bulloides peaks above the dcm coiling direction of n pachyderma seems to be not controlled exclusively by sea surface temperature sst probably the two coiling types are genetically different results document that diversity of planktonic foraminifera number of specimens and variations in test morphology are related to regional differences in water properties temperature salinity and dcm depth

material balance assessment of the new albany chesterian petroleum system of the illinois basin the new albany chesterian petroleum system of the illinois basin is a well constrained system from which petroleum charges and losses were quantified through a material balance assessment this petroleum system has nearly 90 000 wells penetrating the chesterian section a single new albany shale source rock accounting for more than 99 of the produced oil well established stratigraphic and structural frameworks and accessible source rock samples at various maturity levels a hydrogen index hi map based on rock eval analyses of source rock samples of new albany shale defines the pod of active source rock and extent of oil generation based on a buoyancy drive model the system was divided into seven secondary migration catchments each catchment contains a part of the active pod of source rock from which it derives a petroleum charge and this charge is confined to carrier beds and reservoirs within these catchments as accountable petroleum petroleum losses or undiscovered petroleum a well constrained catchment with no apparent erosional or leakage losses is used to determine an actual petroleum charge from accountable petroleum and residual migration losses this actual petroleum charge is used to calibrate the other catchments in which erosional petroleum losses have occurred petroleum charges determined by laboratory pyrolysis are exaggerated relative to the actual petroleum charge rock eval charges are exaggerated by a factor of 4 14 and hydrous pyrolysis charges are exaggerated by a factor of 1 7 the actual petroleum charge provides a more meaningful material balance and more realistic estimates of petroleum losses and remaining undiscovered petroleum the total petroleum charge determined for the new albany chesterian system is 78 billion bbl of which 11 4 billion bbl occur as accountable in place petroleum 9 billion bbl occur as residual migration losses and 57 6 billion bbl occur as erosional losses of the erosional losses 40 billion bbl were lost from two catchments that have highly faulted and extensively eroded sections anomalies in the relationship between erosional losses and degree of erosion suggest there is potential for undiscovered petroleum in one of the catchments these results demonstrate that a material balance assessment of migration catchments provides a useful means to evaluate and rank areas within a petroleum system the article provides methodologies for obtaining more realistic petroleum charges and losses that can be applied to less data rich petroleum systems

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

lopatin analysis of maturation and petroleum generation in the illinois basin a modified lopatin approach was used to evaluate the present day maturity of paleozoic source rock units across the illinois basin timing of generation regional porosity trends and basin paleostructure during major generative events ten cases were modeled at 100 locations to test assumed paleogeothermal gradients post pennsylvanian overburden thicknesses and rates of erosional stripping lopatin predicted maturities for the herrin number sign 6 coal and the new albany shale are in good agreement plus minus 0 02 r sub o with measured maturities if 500 3 000 ft of post middle pennsylvanian strata and were deposited and subsequently eroded between the permian and mid cretaceous and if paleogeothermal gradients were within a few degree c km of present day gradients predicted mean reflectance levels range from 1 0 to 4 0 r sub o at the base of the potsdam megagroup 0 7 to 3 5 at the base of the know megagroup and 0 6 to 1 3 at the base of the maquoketa shale excluding only a small high maturity area in southeastern illinois the knox and potsdam section attained oil generation 475 300 ma while the maquoketa and the younger new albany shale reached the oil window much later 300 250 ma because most significant structures in the basin formed after 300 ma any pre maquoketa source rocks were alreadymore within the gas zone and may have been largely spent by the time known structures formed any know or deeper traps in the basin will probably contain gas be restricted to old structures earlier than 300 ma or stratigraphic traps and will hold pre 300 ma generated hydrocarbons which subsequently cracked to gas less

palaeoproductivity in the ross sea antarctica during the last 15 kyr bp and its link with ice core temperature proxies a detailed study of organic carbon content obtained from two sediment cores collected in the joides basin western ross sea antarctica was carried out the variations observed during the last deglaciation and the holocene were compared to the high resolution climatic records epica dc and taylor dome preserved in the ice the importance of the carbon content as a proxy for palaeoclimatic and palaeoenvironmental changes was investigated a dramatic decrease in the ross sea palaeoproductivity was observed during the antarctic cold reversal 12 5 14 kyr bp another decrease in total organic carbon in the second half of the holocene after 5 6 kyr bp confirms the climate worsening observed in previous studies

southern ocean dust climate coupling over the past four million years dust plays a central part in ocean biogeochemical cycles by supplying iron and other essential micronutrients to regions where marine productivity is limited by the availability of iron martinez garcia et al present a marine record of dust and iron supply to the southern ocean during the past four million years the data derived from leaf waxes establish that previous records of dust flux from antarctic ice cores are broadly representative of a larger area importantly the dust and iron supply rose sharply 1 25 million years ago suggesting that increased dust supply may be a major influence on the more severe swings between the glacial and interglacial climate of the late pleistocene dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean1 2 indeed dust supply to the southern ocean increases during ice ages and iron fertilization of the subantarctic zone may have contributed up to 40 parts per million by volume p p m v of the decrease 80 100 p p m v in atmospheric carbon dioxide observed during late pleistocene glacial cycles3 4 5 6 7 so far however the magnitude of southern ocean dust deposition in earlier times and its role in the development and evolution of pleistocene glacial cycles have remained unclear here we report a high resolution record of dust and iron supply to the southern ocean over the past four million years derived from the analysis of marine sediments from odp site 1090 located in the atlantic sector of the subantarctic zone the close correspondence of our dust and iron deposition records with antarctic ice core reconstructions of dust flux covering the past 800 000 years refs 8 9 indicates that both of these archives record large scale deposition changes that should apply to most of the southern ocean validating previous interpretations of the ice core data the extension of the record beyond the interval covered by the antarctic ice cores reveals that in contrast to the relatively gradual intensification of glacial cycles over the past three million years southern ocean dust and iron flux rose sharply at the mid pleistocene climatic transition around 1 25 million years ago this finding complements previous observations over late pleistocene glacial cycles5 8 9 providing new evidence of a tight connection between high dust input to the southern ocean and the emergence of the deep glaciations that characterize the past one million years of earth history