influence of a tundra freeze thaw cycle on sulfide oxidation and metal leaching in a low sulfur granitic waste rock abstract drill cuttings were collected at 1 m depths from an instrumented low sulfur experimental waste rock pile containing a 4c pyrrhotite that had been exposed to the extreme freeze thaw cycle of a tundra climate boreholes were drilled from the top to base in the center of the pile and near the core batter transition waste rock samples were analyzed for carbon sulfur and metal concentrations sulfur oxidation states and variation in iron and nickel forms due to oxidative dissolution of pyrrhotite results from x ray absorption spectroscopy and aqueous extraction experiments were used to relatively compare samples from various depths in the boreholes which indicate sulfide weathering fronts that decrease in intensity from the top to core to base at the center of the pile and from the core batter transition to the center of the pile the tundra climate and waste pile configuration produce a permafrost base a seasonally frozen core and an atmospheric like zone near the surface the fluctuation of the freeze thaw cycle caused the greatest sulfide weathering near the surface and lesser weathering in the core and base of the pile metal and sulfur rich leachate from the higher weathering zone likely is collecting on a variable and seasonal frozen surface beneath the surface layer that causes metals and s to precipitate and or sorb during a portion of the year the accumulation of sulfur and metals with the flux of this frozen surface produces a nickel and possibly an iron and sulfur enrichment zone beneath the surface layer in the center of the pile the weathering front from the top to core to base of the pile and from core batter transition to the core corresponds to a previously formulated leachate model but the enrichment zone below the surface zone is unique to this conceptual waste rock weathering model for this tundra climate

the behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite schwertmannite is a ubiquitous mineral formed from acid rock drainage ard and plays a major role in controlling the water chemistry of many acid streams the formation of schwertmannite was investigated in the acid discharge of the monte romero abandoned mine iberian pyrite belt sw spain schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of fe ii to fe iii and transformed with time into goethite and jarosite in a few hours schwertmannite precipitation removed more than half of the arsenic load from solution whereas the concentration of divalent trace metals zn cu pb cd ni and co remained almost unchanged in the laboratory natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid liquid mass ratio of 1 5 for 353 days during this time the ph of the solution dropped from 3 07 to 1 74 and the concentrations of sulfate and fe increased during the first 164 days schwertmannite transformed into goethite plus h3o jarosite but subsequently goethite was the only mineral to form some of the trace elements such as al cu pb and as were depleted in solution during the first stage as schwertmannite transformed into goethite plus h3o jarosite on the contrary the transformation of schwertmannite to goethite with no jarosite during the second stage released al cu and as to the solution despite the variation in their concentrations in solution approximately 80 of the total al and cu inventories and more than 99 as and pb remained in the solid phase throughout the entire aging process

the diavik waste rock project particle size distribution and sulfur characteristics of low sulfide waste rock three large scale instrumented waste rock piles were constructed at the diavik diamond mine in the northwest territories canada these experimental waste rock piles test piles are 15 m high and are part of an integrated field and laboratory research program to characterize and compare low sulfide waste rock and drainage at various scales during test pile construction samples of the 0 08 wt s for the higher s waste rock type the third test pile has a low permeability till layer and a low sulfide waste rock thermal layer covering a core of waste rock with average 0 082 wt s in the 0 08 wt s for the higher s waste rock particle size distributions for the lower and higher s waste rock are similar but the higher s waste rock has a higher proportion of fine grained particles sulfur determinations for discrete particle sizes of the 10 m scale from composite blast hole cuttings are lower than those calculated for the 0 05 wt s is of uncertain acid generating potential and effluent data indicate this waste rock generates acidic effluent whereas lower s waste rock does not produce acidic effluent consistent with the acid base accounting predictions

a mineralogical and geochemical study of element mobility in sulfide mine tailings of fe oxide cu au deposits from the punta del cobre belt northern chile two flotation tailings sites ojancos and p cerda from the fe oxide cu au punta del cobre belt south of copiapo atacama desert northern chile are geochemically largely using sequential extractions and mineralogically compared main ore minerals are pyrite magnetite and or hematite and chalcopyrite gangue is dominantly calcite with minor quartz the host silicate assemblage is largely controlled by hydrothermal alteration and consists of variable amounts of the following minerals k feldspar ca amphibole biotite sericite chlorite tourmaline epidote quartz in this study both the ojancos and the p cerda tailings were deposited in valley dam impoundments and when they were filled new tailings were deposited upstream as a result high quantities of seepage migrated downstream into the older tailings impoundment at ojancos the recent upstream tailings have excess of acid potential 7 1 wt calcite and 3 5 wt pyrite whereas the older downstream tailings are characterized by alternations of several meter thick intervals with high neutralizing potential about 40 wt calcite and 2 wt pyrite and intervals with high acid potential about 3 wt calcite and 4 wt pyrite acid mine drainage amd with the precipitation of schwertmannite ph 3 15 and chalcoalumite ph 4 9 flows out at the interface between the uphill and downstream tailings strong downstream element transport is taking place and contributes to the formation of the cementation zone mainly gypsum ferrihydrite and goethite and locally jarosite in the older downstream impoundment the cementation zone ph 4 shows strong enrichment of heavy metals e g up to 6800 ppm cu 680 ppm zn 1100 ppm as mainly adsorbed and as secondary sulfides e g covellite in contrast at the p cerda tailings impoundment carbonates are homogeneously distributed and the overall neutralization potential exceeds the acid potential average of about 10 wt calcite and up to 2 5 wt pyrite the up to 5 m thick oxidation zones paste ph 6 9 8 3 at p cerda are characterized by interlayering of coarser dark gray unoxidized layers with fine grained fe iii hydroxide rich ochre to red brown colored horizons the hyperarid climate dries out first the coarse sulfide rich horizons of the tailings and limits so the oxidation which is restricted to the fine grained due to their higher moisture retention capacity however results indicate that during operation an important element transfer from the younger upstream tailings to the older downstream tailings impoundment took place possibly by sorptive transport at ferric polymers or colloids in the form of neutral mine drainage nmd this would explain the metal enrichments in the cementation zone which are mainly associated to the exchangeable fraction and not as secondary sulfides this results in both cases in ojancos mainly as amd and in p cerda mainly as nmd in fe iii input as ferric cation as ferric polymer or co3 complexes to the downstream impoundment this constitutes a very effective acid potential transfer to the older downstream material because oxidation via input of external fe iii produces 16 mol of protons per mol fes2 i e eight times more than via oxidation with oxygen in addition the created acidity favors dissolution of the abundant fe oxides magnetite and hematite of this ore deposit type providing so additional fe iii for sulfide oxidation

the diavik waste rock project measurement of the thermal regime of a waste rock test pile in a permafrost environment abstract the interior thermal regime of a field scale experimental waste rock pile in the northwest territories canada was studied test pile construction was completed in the summer 2006 and temperature data was collected continuously since that time to february 2009 the temperature data indicates the test pile cooled over the study period with an average heat energy release of 2 5 104 and 2 6 104 mj in 2007 and 2008 respectively the mean annual air temperature maat at the site was 8 9 c during the period between 2006 and 2009 with a permafrost table at a depth of 4 m in bedrock away from the pile because of this cold environment the upward movement rate of the 0 c isotherm into the test pile at its base was approximately 1 5 m a 1 during 2007 and 2008 thermistor strings installed immediately below the base of the test pile showed the test pile basal temperatures remained near and below 0 c during the study period furthermore due to low rates of sulfide mineral oxidation elevated temperatures in the interior of the test pile were not observed the average air velocity in the pore space in july 2007 and 2008 was about one third of that during january of each year based on temperature distributions therefore due to higher air velocity during the winter it is expected that heat transfer is greater during winter

arsenic and metal mobility from au mine tailings in rodalquilar almeria se spain in the old mining area of rodalquilar mine wastes soil and sediments were characterized and the results revealed high concentration of au ag as bi cu fe mn pb se sb and zn in tailings and sediments the contaminant of greatest environmental concern is as the mean concentration in the tailings was 679 9 and 345 mg kg in the sediments of playazo creek the groundwater samples from the alluvial aquifer showed high concentration of al as cd fe hg mn ni pb se sb and zn and very high concentration of chloride and sulfate which were above the concentration defined in the european standards for drinking water the presence of as in groundwater may be caused by the oxidation of arsenian pyrite the possible as desorption from goethite and ferrihydrite and the jarosite dissolution groundwater concentrations of cd fe mn and possibly cu were associated with low values of eh indicating the possible dissolution of oxy hydroxides of fe and mn the mobility of metals in the column experiments show the release of al fe mn cr cu ni v and zn in significant concentrations but below the detected values in groundwater however as cd sb se pb and au are generally mobilized in concentrations above the detected values in groundwater the possible mass transfer processes that could explain the presence of the contaminants in the aquifer and the leachates was simulated with the phreeqc numerical code and revealed the possible dissolution of the following mineral phases jarosite natrojarosite arsenian pyrite alunite chlorite kaolinite and calcite

the diavik waste rock project design construction and instrumentation of field scale experimental waste rock piles the physicochemical processes that affect acid mine drainage amd in unsaturated waste rock piles and the capabilities of small scale laboratory experiments to predict amd from waste rock are not well understood an integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated this paper describes the design construction and instrumentation of three field scale experimental waste rock piles test piles and six active zone lysimeters at the diavik diamond mine in the northwest territories canada the test piles are comprised of granitic and sulfide bearing metasedimentary waste rock excavated during open pit mining operations one test pile contains waste rock with a target s content of 0 08 wt s and the third test pile contains the higher sulfide waste rock 0 08 wt s and was re sloped and capped with a low permeability till layer and a low sulfide waste rock cover the first two test piles are approximately 15 m high with bases of 50 m by 60 m and the re sloped test pile has a larger base of 80 m by 125 m instrumentation was selected to measure matrix flow geochemistry of pore water and drainage gas phase o2 concentration temperature evolution microbiological populations waste rock permeability to air and thermal conductivity as well as to resolve mass and flow balances instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time instruments were installed at a density such that the number of instruments that survived construction 40 to 80 by instrument type was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles

the diavik waste rock project persistence of contaminants from blasting agents in waste rock effluent abstract during mining operations explosives are used to fragment rock into workable size fractions mine water chemistry can be affected by blasting agent residuals including nh3 no 2 no 3 cl and clo 4 at the diavik diamond mine northwest territories canada waste rock generated from open pit and underground mining is stockpiled on site three large scale test piles measuring 60 by 50 m at the base and 15 m in height along with four 2 2 m lysimeters each 2 m in height were constructed at diavik as part of a comprehensive research program to evaluate the quality of water emanating from waste rock stockpiles ongoing monitoring of the water chemistry since 2007 shows that blasting residuals comprise a large proportion of the dissolved constituents in the initial pore water and effluent leach tests conducted on freshly blasted rock from diavik indicate the mass of n released corresponds to a 5 4 n loss from the blasting explosives this mass is in the range for n loss reported for blasting operations at diavik during the period when the test piles were constructed the total mass of n released from the lysimeters was also within this range the three large scale test piles have only released a small fraction of the n estimated to be contained within them blasting of waste rock contributes so 4 2 to effluent through the oxidation of sulfide minerals in the rock during the blast during the initial flush of water the test pile that contained waste rock with the higher s content was observed to release higher concentrations of so 4 2 than the test pile with lower s content waste rock mass balance calculations based on the ratios of so 4 2 to total n can be used to estimate the relative contributions of sulfide oxidation within the test piles and so 4 2 released when s in the host rock is oxidized during blasting these calculations provide an estimate of s mass released during the first flush of the test piles

mobility of arsenic in groundwater in the obuasi gold mining area of ghana some implications for human health arsenic in drinking water from streams shallow wells and boreholes in the obuasi gold mining area of ghana range between 0 5 probably as a result of methylation and reduction reactions mediated by bacteria and algae concentrations of as in groundwaters reach up to 64 gl 1 being highest in deeper 40 70 m and more reducing 220 250 mv waters the as is thought to build up as a result of the longer residence times undergone by groundwaters in the deeper parts of the aquifer the proportion of as present as as iii is also higher in the deeper groundwaters deep mine exploration boreholes 70 100 m have relatively low as contents of 5 17 gl 1 possibly due to as sorption onto precipitating ferric oxyhydroxides or to localized low as concentrations of sulphide minerals median concentrations of inorganic urinary as from sample populations in two villages one a rural streamwater drinking community and the other a suburb of obuasi using groundwater for potable supply were 42 gl 1 and 18 gl 1 respectively the value for the community drinking groundwater is typical of background concentrations of urinary as the slightly higher value for the streamwater drinking community probably reflects different provenance of foodstuffs and higher as concentrations of water sources local to the village the low value obtained for the inhabitants of the obuasi suburb living close to and abstracting groundwater from the area of major mining activity suggests that groundwater can form a useful potable supply of good inorganic quality provided that deep long residence time sources are avoided

the diavik waste rock project implications of wind induced gas transport abstract wind induced gas transport in a test scale unsaturated waste rock pile was investigated at the diavik diamond mine northwest territories canada differential gas pressures were measured in 2008 at 49 locations within a field scale experimental waste rock pile test pile and at 14 locations on the surface of the test pile at 1 min intervals wind speed and direction were measured at 10 min intervals and decomposed into north south east and west vectors correlations between wind vectors and pressure measurements indicate that the wind influences pressure fluctuations in the test pile the strength of the correlation is roughly inversely proportional to the distance between the measurement ports and the atmospheric boundary the relationship between the magnitude of the wind vector and pressure fluctuations on the surface of the test pile is non linear however the relationship between internal and surface pressure measurements is linear suggesting that gas flow within the test pile follows darcy s law spectral analysis demonstrates that the dominant periods of the wind range from 1 to 14 d a 1 d analytical solution to the flow equation is used to demonstrate that long periods have the most pronounced effect on transient gas flow within the test pile and that the penetration depth of the wind induced gas pressure wave is a function of wind period and permeability of the test pile

mobility and microbially mediated mobilization of gold and arsenic in soils from two gold mines in semi arid and tropical australia the mobility and microbially mediated solubilization of au and as in regolith materials from two au mines in australia i e the peak hill gold mine in semi arid new south wales and the hit or miss gold mine in tropical northern queensland was studied using a combination of geochemical and microbiological techniques gold is highly mobile in both environments the mobility of au increases with increasing degree of weathering of host materials and the resident microbiota are capable of mediating its solubilization the results of the microcosm experiments demonstrate that the activity of microorganisms needs to be taken into account when studying the mobility and solubilization of au in the australian regolith in primary unweathered mineralization material from the hit or miss mine 99 wt of au was extracted only in the strongest final step of the sequential extractions in concentrated aqua regia in alteration zone material from the peak hill gold mine 80 wt of au was associated with the operationally defined mn and fe oxides in contrast in auriferous soils overlying mineralization at both sites 90 95 wt of au was associated with the operationally defined exchangeable claybound and organic fractions microcosm experiments were incubated biologically active and inactive sterilized in 1 4 w v aqueous slurries at 25 c in the dark for up to 95 days in biologically active microcosms with soils from the peak hill and the hit or miss gold mines approximately 55 wt 907 ng g 1 d w soil and 20 wt 233 ng g 1 d w soil of the total au respectively was solubilized during the incubation in contrast no or significantly lower au concentrations were observed in biologically inactive microcosms the mobility and microbially mediated release of as was limited at both sites and appears to be mostly controlled by abiotic adsorption and desorption on mn and fe oxides arsenic has a low solubility in the more mobile fractions and is mostly associated with mn and fe oxides and the residual fraction the release of as was not elevated in biologically active compared to inactive microcosms from the peak hill gold mine in contrast in biologically active microcosms with samples from the hit or miss mine elevated concentrations of as were detected in solution compared to the biologically inactive experiments crown copyright 2006 published by elsevier inc all rights reserved

increasing arsenic mobility in the fine fraction of the dry stream sediments of the semi arid san antonio gold mining district baja california peninsula mexico the geochemical mobility of arsenic and some metals in the fine fraction of 20 alluvial sediment samples collected along the thalweg of the san antonio arroyo was assessed in the abandoned gold mining district of the semi arid southeastern baja california peninsula acid digested element concentrations were determined by treating the fine fraction of the sediments with concentrated hno3 via microwave heating a separate leaching of the diluted acid soluble as and some metals from the samples was carried out using 1 m hcl the most reactive as phase was extracted from the subsamples using an ascorbic solution of na citrate buffered at ph 8 the high abundance of sulphosalts tennantite cu12as4s13 and proustite ag3ass3 in the sediments from the head of the arroyo changes downstream to the predominance of arsenic trioxide arsenolite as2o3 and arsenate scorodite feaso4 2h2o acid digested as concentrations were always found to be high 230 270 mg kg 1 from the san antonio village until the end of the arroyo the concentration of reactive as and its relative contribution increased from low values of 2 3 mg kg 1 and 1 respectively at the upstream of the arroyo to 191 220 mg kg 1 and 75 89 in the middle and lower parts and is probably a result of as release from the mineral sulfide fraction of the tailings metallic contaminants exhibited different behavior with a peak of acid digested and diluted acid leached concentrations observed in the central part of the arroyo and an almost permanent geochemical mobility

the diavik waste rock project geochemical and microbiological characterization of drainage from low sulfide waste rock active zone field experiments abstract a field experiment was conducted at the diavik diamond mine to evaluate the potential for acid generation and metal release from the active layer of unsaturated waste rock piles in the arctic four active zone lysimeters azls were constructed in 2006 using high density polyethylene tanks filled with and surrounded by waste rock to evaluate the geochemical and biogeochemical characteristics in the upper 2 m of waste rock stockpiles two azls were filled with waste rock containing an average of 0 014 wt s predominantly as pyrrhotite type i azls and two azls were filled with waste rock containing an average of 0 035 wt s type iii azls the geochemistry and microbiology of the effluent from the azls was monitored for 4 years the effluent from the type iii azls was characterized by low ph

the behaviour of arsenic in muddy sediments of the bay of biscay france abstract we have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the bay of biscay france ranging in depths from 150 to 2 800 m at all stations major redox species oxygen nitrate ammonia total and reactive iron and manganese sulphate and sulphur reflect early diagenetic depth sequences of redox reactions comparable to other marine environments vertical distributions of dissolved and particulate as species and major redox species are related to changes in redox conditions and their major carrier phases such as fe and mn oxides arsenic diagenesis appears strongly dependent on fe cycling a subsurface maximum of dissolved as and surface enrichment of particulate as correspond to dissolution and precipitation of fe iii phases except for the shallowest and most bioturbated site flux calculations show three different vertical diffusive as fluxes two upwards and one downwards phase changes of recycled as result in local accumulations of reactive as at different redox fronts mass balance calculations indicate that the upward as flux toward the oxidized layer can explain the enrichment of hcl extractable particulate as in this layer a portion of the upward diffusing as can escape the sediment and may be fixed onto settling fe oxides by adsorption or co precipitation and contribute to reactive particulate as input i e as is recycled across the water sediment interface

release transport and attenuation of metals from an old tailings impoundment abstract the oxidation of sulfide minerals from mine wastes results in the release of oxidation products to groundwater and surface water the abandoned high sulfide camp tailings impoundment at sherridon manitoba wherein the tailings have undergone oxidation for more than 70 a was investigated by hydrogeological geochemical and mineralogical techniques mineralogical analysis indicates that the unoxidized tailings contain nearly equal proportions of pyrite and pyrrhotite which make up to 60 wt of the total tailings and which are accompanied by minor amounts of chalcopyrite and sphalerite and minute amounts of galena and arsenopyrite extensive oxidation in the upper 50 cm of the tailings has resulted in extremely high concentrations of dissolved so4 and metals and as in the tailings pore water ph 1 m thick geochemical modeling and mineralogical analysis indicate that the hardpan layer consists of secondary melanterite rozenite gypsum jarosite and goethite the minerals indicated mainly control the dissolved concentrations of so4 fe ca and k the highest concentrations of dissolved metals are observed directly above and within the massive hardpan layer near the water table at a depth of 4 m most metals and so4 sharply decline in concentration although dissolved concentrations of metals and so4 decrease below the water table these concentrations remain elevated throughout the tailings with up to 60 600 mg l 1 fe and 91 600 mg l 1 so4 observed in the deeper groundwater during precipitation events surface seeps develop along the flanks of the impoundment and discharge pore water with a geochemical composition that is similar to the composition of water directly above the hardpan these results suggest that shallow lateral flow of water from a transient perched water table is resulting in higher contaminant loadings than would be predicted if it were assumed that discharge is derived solely from the deeper primary water table the abundance of residual sulfide minerals the depletion of aluminosilicate minerals in the upper meter of the tailings and the presence of a significant mass of residual sulfide minerals in this zone after 70 a of oxidation suggest that sulfide oxidation will continue to release acid metals and so4 to the environment for decades to centuries

the mineral and aqueous phase evolution of sulfur and nickel with weathering of pyrrhotite in a low sulfide granitic waste rock abstract the release of s and metals from the weathering of waste rock pyrrhotite fe 1 x s is affected by oxidation pathways the presence and concentration of fe substitution metals e g ni and fe oxyhydr oxide products a 4c monoclinic pyrrhotite fe7s8 ni fe substitution of about 1 200 in a low sulfide waste rock was weathered in the laboratory and at a field site to identify the evolution of s oxidation distribution and coordination of ni and possible adsorption of ni on secondary fe minerals mineral phase s was present in the 2 1 0 4 and 6 oxidation states prior to its release as so42 into solution the thiosulfate s2o32 pathway of sulfide oxidation was indicated by the presence of polythionates and s2o32 sulfur as s2o32 was more persistent than sulfite so32 prior to oxidation to so42 the release of ni during the oxidative dissolution of pyrrhotite was influenced by its distribution in the grain diffuse throughout the grain solid solution mineral or concentrated in exsolved pentlandite fe ni 9s8 lamellae within the pyrrhotite with the oxidation of s ni coordination changed from bonding with reduced s species to bonding with oxygen prior to its release with so42 sulfur as so42 typically stayed in solution with release from the pyrrhotite but the solubility of released ni was dependent on leachate ph a near neutral ph induced the adsorption of ni onto fe oxyhydr oxides which formed during oxidation of the pyrrhotite in some grains ni was found concentrated in fe distal precipitates as opposed to the closer alteration layers zones of the sulfide grain subsequent dissolution of the fe oxyhydr oxides or desorption of ni with a change in ph provides a delayed release of ni into solution this improved understanding of the oxidation pathway of s coordination and release of ni and influence of fe oxyhydr oxides in the weathering of pyrrhotite will assist in determining appropriate reaction rate factors and element release rates for prediction of acid rock drainage

influence of freeze thaw dynamics on internal geochemical evolution of low sulfide waste rock abstract continuous monitoring of a 15 m high heavily instrumented experimental waste rock pile 0 053 wt s since 2006 at the diavik diamond mine in northern canada provided a unique opportunity to study the evolution of fresh run of mine waste rock as it evolved over annual freeze thaw cycles samples were collected from soil water solution samplers to measure pore water properties from twelve 4 to 16 m 2 basal collection lysimeters to measure basal leachate properties in the region underlying the crest of the pile the core and from basal drains to measure aggregate total pile leachate properties by 2012 monitoring of pore water geochemistry within the core structure of the test pile revealed an apparent steady state with respect to weathering geochemistry represented by i a flush of pre existing blasting residuals and applied tracers ii declining ph iii a stepwise progression and subsequent equilibrium with acid neutralizing phases depletion of available carbonates equilibrium with respect to aluminum hydroxide phases and subsequent iron iii hydroxide phases and iv concordant release of so 4 major cations ca mg k na si and trace metals al fe ni co cu zn distinct high concentration spring flushes characteristic of drainage in northern environments and primarily explained by a combination of fluid residence time and the build up of oxidation products over the winter were released from core drainage each season following the initial flush the concentration of all dissolved constituents steadily declined with distinct minimums prior to freeze up the opposite trend was observed in the cumulative pile drainage in which early season leachate dominated by snowmelt and batter flow had low concentrations and late season leachate dominated by contributions from the core of the pile indicated by season end merging of core and cumulative drainage geochemistry had higher concentrations northern waste rock pile drainage geochemistry is strongly influenced by freeze thaw cycling and varying core and batter subsystem contributions to total drainage a comprehensive understanding of thermal cycling in waste rock piles is an important component of temporal predictions of drainage water composition based on up scaling or reactive transport modeling

the diavik waste rock project initial geochemical response from a low sulfide waste rock pile abstract three large scale experimental waste rock piles test piles were constructed and instrumented at the diavik diamond mine in the northwest territories canada as part of an integrated field and laboratory study to measure and compare physical and geochemical characteristics of experimental low sulfide waste rock piles at various scales this paper describes the geochemical response during the first season from a test pile containing 0 053 wt s bulk drainage chemistry was measured at two sampling points for ph eh alkalinity dissolved cations and anions and nutrients the geochemical equilibrium model minteqa2 was used to interpret potential mineral solubility controls on water chemistry the geochemical response characterizes the initial flushing response of blasting residues and oxidation products derived from sulfides in waste rock exposed to the atmosphere for less than 1 year sulfate concentrations reached 2000 mg l 1 when ambient temperatures were 10 c and decreased as ambient temperatures declined to 1 as total caco 3 suggesting all available alkalinity is consumed by acid neutralizing reactions concentrations of al and fe were 1 respectively trends of ph and alkalinity and the calculated saturation indices for al and fe oxy hydroxides suggest that dissolution of al and fe oxy hydroxide phases buffers the ph the effluent water showed increased concentrations of dissolved mn 1 ni 1 co 1 zn 1 cd 1 and cu 1 as ambient temperatures increased manganese is released by aluminosilicate weathering ni and co by pyrrhotite fe 1 x s oxidation zn and cd by sphalerite oxidation and cu by chalcopyrite cufes 2 oxidation no dissolved metals appear to have discrete secondary mineral controls changes in so 4 ph and metal concentrations indicate sulfide oxidation is occurring and effluent concentrations are influenced by ambient temperatures and possibly increasing flow path lengths that transport reaction products from previously unflushed waste rock

microbial populations associated with the generation and treatment of acid mine drainage bacterial populations and water chemistry were profiled throughout the groundwater flow system associated with the nickel rim mine tailings impoundment ontario canada groundwater containing high concentrations of sulfate 2000 12 000 mg l and iron 500 4000 mg l flows from the tailings into an adjacent aquifer a portion of the plume then discharges to the surface where ferrous iron is oxidized creating low ph ph 3 conditions the remaining groundwater passes through a permeable reactive barrier which induces sulfate reduction and metal sulfide precipitation elevated populations of iron oxidizing bacteria iob and sulfur oxidizing bacteria sob are restricted to hydrologically defined zones of recharge and discharge sulfur oxidizers are highest in the tailings 1 27 103 most probable number mpn g where sulfide minerals are exposed to oxygen and oxygen rich recharge water iob were highest 9 56 105 mpn g where tailings derived effluent rich in fe ii discharges to the aerobic surface water environment populations of both iron and sob bacteria in the zone of active oxidation are low compared to those found at other less mature tailing sites active oxidation in the nickel rim tailings is occurring immediately above the water table where the water content is high the high water content limits oxygen ingress and sulfide oxidation and the associated populations of oxidizing bacteria are low populations of sulfate reducing bacteria srb are elevated in the tailings and in portions of the down gradient aquifer where organic carbon concentrations are high the highest population 3 73 107 mpn g of srb were found where sulfate bearing water migrates through the organic carbon rich permeable reactive barrier at locations with high populations of srb elevated populations of sob were also found suggesting sob in these zones are metabolizing the reduced sulfur species produced by the srb in adjacent but disparate redox microenvironments

early diagenetic processes in the muddy sediments of the bay of biscay abstract in order to understand the early diagenesis processes occurring in continental margin environment modern sediments collected in six different sites from the bay of biscay have been studied these sites can be separated into two groups in the shallowest stations where sediments are highly bioturbated organic carbon levels are higher than 2 in the deepest stations sediments are much less bioturbated and organic carbon levels are lower in all sites the vertical distribution of redox sensitive species can be explained by the well established depth sequence of redox reactions based on the bacterially mediated oxidation of organic matter we have considered some alternative reaction pathways to explain the profiles of fe mn and n species these reactions deal with the ammonia oxidation by manganese oxide the aerobic denitrification and the oxidation of dissolved iron ii by nitrate or mn oxides vertical flux calculations with a simple diffusion model indicate that these reactions could account for the reduction of all the mn oxides and the oxidation of all the upward diffusing fe ii they may also be responsible for a significant part of the total dinitrogen production the relative importance of these pathways on early diagenetic processes and benthic fluxes has not been determined and must be examined with additional experimental works our study suggests however that the coupling between the benthic cycles of iron manganese and nitrogen could strongly influence the carbon cycling at the ocean floor

the diavik waste rock project water flow through mine waste rock in a permafrost terrain abstract a field experiment is being carried out at the diavik diamond mine in northern canada to investigate the influence of unsaturated flow behavior on the quality of drainage from mine waste rock piles in a region of continuous permafrost this paper is part of a series describing processes affecting the weathering of waste rock and transport of reaction products at this site here the focus is on unsaturated water flow and its role in mass loading two 15 m high instrumented test piles have been built on 60 m by 50 m collection systems each consisting of lysimeters and a large impermeable high density polyethylene hdpe liner collection lysimeters are installed nearby to investigate infiltration in the upper 2 m of the waste rock porosity water retention curves and hydraulic conductivity functions are estimated from field measurements and for samples ranging in size from 200 cm3 to 16 m3 net infiltration in 2007 is estimated to have been 37 of the rainfall for mean annual rainfall conditions early season infiltration freezes and is remobilized as the waste rock thaws wetting fronts migrate at rates of 0 2 0 4 m d 1 in response to common rainfall events and up to 5 m d 1 in response to intense rainfall pore water and non reactive solutes travel at rates of

metal fractionation in oxic sediments of an estuary affected by acid mine drainage south western spain abstract fractionation of fe cu zn as cd and pb was studied in 17 surface sediment samples of the ria of huelva in all the cases total concentration of these elements was high especially for fe 11 2 zn 1519 ppm followed by cu 1413 ppm pb 716 ppm as 442 ppm and cd 3 26 ppm the enrichment factors of these metals follow this order cd cu zn pb as fe with respect to the regional background the highest concentrations associated with exchangeable or labile fractions are shown by zn 85 of total concentration followed by cd 76 12 fe 58 41 cu 40 80 pb 37 44 and as 33 88 the main sources of metal input are the tinto and odiel rivers which discharge acidic water ph

measured and computed neutralization potentials from static tests of diverse rock types static tests typically are used in the initial stage of environmental assessments to predict the potential for acid mine drainage and also are used to monitor waste disposal at active mining operations the neutralization potential np of 19 sedimentary metamorphic and igneous extrusive rocks was measured by the sobek method to compare the results with those computed by using the quantitative mineralogy of the rocks and the np values that were deemed to be appropriate for the individual minerals most of the computed np values of the rocks are lower than the measured values but a close relationship is evident if the contents of carbonate minerals are low the np in non ultramafic igneous rocks typically is controlled by the amount of ca substitution in plagioclase whereas in ultramafic rocks the np contribution is dominated by the amount of olivine and serpentine compositional and np analyses of plagioclase concentrates indicate that the np systematically varies from 1 for the na end member to about 14 for compositions near that of the ca end member among several variables that can affect the sobek np values the volume and normality of the acid added to the sample are well known to influence the results however the temperature and duration of the acidification stage can also have a pronounced effect on the measured np of some rocks depending on their mineralogy fizz tests to estimate the carbonate content and the consequent acid addition are highly subjective and the no fizz rating is not to be taken literally the np results themselves provide a clear indication of whether a sample has been over acidified or under acidified in the test procedure

oceanic topography and heatflow indications for a silent discharge of cold rock into the convecting earth the 2 5 km mean relative elevation of mid ocean ridges is arguably consistent with a steady state thickness of 100 km for the oceanic lithosphere here we explore some consequences of this particular value based on seismic models of the uppermost oceanic mantle we infer that no significant heat is added to normal asthenosphere following accretion at spreading centers therefore we adopt the view that kinematic thinning moderates the conductive thickening to yield the steady state thickness of 100 km we devise a method for estimating mean rates of thinning directly from topography age data with no assumptions on the detailed dynamics of delamination we find that delamination delivers a significant fraction 20 of the global downwelling discharge this large non subducting discharge of cold lithospheric material provides an explanation for the most robust features of upper mantle tomography and should be considered in studies of mantle cooling and mixing

arsenic content and groundwater geochemistry of the san antonio el triunfo carrizal and los planes aquifers in southernmost baja california mexico the san antonio el triunfo mining district located at a mountainous region 45 km south east of la paz baja california has been worked since the late 1700s mine waste material produced during 200 years of mineral extraction area poses a risk of local groundwater pollution and eventually regional pollution to the carrizal west basin and the los planes east basin aquifers there are different types of deposits in the mining area these are dominated by epithermal veins in which arsenopyrite is an important component carrillo and drever 1998a concluded that even though the amount of mine waste is relatively small in comparison to the large scale area significant as in groundwater derived from the mine waste piles is found locally in the groundwater this paper shows the results of geochemical analyses of groundwater samples from the san antonio el triunfo area and the carrizal and los planes aquifers during several years of monitoring 1993 1997 the highest values of total dissolved solids tds and as are in the mineralized area where the mining operations occurred 1500 ppm tds and 0 41 ppm as the lowest concentrations of tds and as are in general away from the mineralized area 500 ppm tds and 0 01 ppm as sulfate and bicarbonate alkalinity are in general high near the mineralized area and low away from it the arsenic concentrations vary seasonally especially after the heavy summer thunderstorms geochemical modeling minteqa2 and netpath and analysis of the regional geochemical evolution of the groundwater from the mining area towards the aquifer of los planes shows that the most likely hydrochemical processes include dilution precipitation of calcite and adsorption of as onto surfaces of iron oxyhydroxides ferrihydrite these processes act as natural controls to the extent and amount of as pollution in the carrizal and los planes aquifers

the diavik waste rock project geochemical and microbiological characterization of low sulfide content large scale waste rock test piles abstract two experimental waste rock piles test piles each 15 m in height 60 m 50 m were constructed at the diavik diamond mine in northern canada to study the behavior of low sulfide content waste rock with a similarly low acid neutralization potential in a continuous permafrost region one test pile with an average of 0 035 wt s 4 2 and dissolved metals with a decrease in ph to 1 ni 2 3 mg l 1 cu 3 7 mg l 1 zn 35 g l 1 cd and 3 8 mg l 1 co corresponded to decreases in flow rate which were observed at the end of each field season when the contribution of the total outflow from the central portion of the test pile was greatest bacteria were present each year in spite of annual freeze thaw cycles the microbial community within the type i test pile included a population of neutrophilic s oxidizing bacteria each year changes in the water quality of the type iii test pile effluent were accompanied by changes in the microbial populations populations of acidophilic s oxidizing bacteria and fe oxidizing bacteria became more abundant as the ph decreased and internal test pile temperatures increased irrespective of the cold climate conditions and low s content of the waste rock the geochemical and microbiological results of this study are consistent with other acid mine drainage studies indicating that a series of mineral dissolution precipitation reactions controls ph and metal mobility and transport is controlled by matrix dominated flow and internal temperatures

the pore water geochemistry and the mineralogy of the vadose zone of sulfide tailings waite amulet quebec canada low ph waters requiring treatment because of high concentrations of dissolved metals are being discharged from a decommissioned tailings impoundment at the former waite amulet zncu mine in northeastern quebec canada a detailed study of the vadose zone of the tailings comparing mineralogical and geochemical analyses of the tailings solids with geochemical analysis of the tailings pore water and pore gas indicates the presence of three zones within the tailings these zones include an upper sulfide depleted zone in which the sulfides have been extensively removed and oxidation is largely complete an intermediate zone where sulfide oxidation and acid neutralization reactions are occurring and an unoxidized zone below the depth of oxygen penetration where sulfides are unoxidized high aqueous concentrations of dissolved solids are being displaced downward from the sulfide depleted zone through the unoxidized zone toward the water table sulfide oxidation and acid neutralization reactions have generated concentrations of dissolved solids high enough to lead to the precipitation of a series of secondary solid phases precipitation dissolution reactions involving these solid phases control the concentrations of the major ions in the tailings pore water concentrations of dissolved metals are controlled by precipitation dissolution crystal structural replacement and adsorption coprecipitation reactions predictions based on the observed data and numerical simulations suggest that in the absence of an effective remedial program sulfide oxidation and h production will continue for several centuries