Hydrothermal ventfauna, particularly vestimentiferan and polychaete worm tubes, are occasionally preserved in the geological record. The early stages of mineralisation are particularly important in defining whether or not preservation will occur, and they are poorly understood. This dissertation describes 3 separate studies of ventfauna undergoing early mineralisation associated with active seafloor vent systems. Tube samples of the polychaete worm Alvinella pompejana collected from 13°N on the East Pacific Rise were studied to identify the processes occurring during early sulphide mineralisation. Iron sulphide mineralisation is present within the walls of the organic dwelling tube, and is induced by microbialfauna preserved within the tube micro-layers. A laminated tube structure wasformed, comprising alternating layers of tube material and microbially templated iron sulphide-rich interlayers. The iron monosulphides mackinawite and greigite, have been identified as intermediate phases that occur as precursor minerals during theformation ofpyrite. Later marcasite mineralisation is observed toform over some of the pyritised organic layers. Later stagemineralisationprocesses in a selection offossil tube structures recoveredfrom an extinct sulphide mound on the Southern East Pacific Rise were studied. The similarity to existingfaunal assemblages suggests that these structures were also associated with Alvinella sp. polychaete worms. Two generations ofpyrite were identified along with a later stage chalcopyrite phase. Fine scale variability in tube wall geochemistry was demonstrated with electron micro-probe transects across the structures and this is inferred to reflect early mineralisation processes as identified in living polychaete worms. Sulphur isotope analyses of the different sulphide phases gave δ³⁴S values higher than any previously measured for chimney structures on a sediment-free ridge setting (δ³⁴S = 3.8-10.8‰). A two stage model is proposed whereby early pyrite / marcasite laminae originally laid down in association with biogenic tube structures, are replaced by euhedral pyrite, and later stage primary chalcopyrite precipitation. A study ofRidgea piscesae from the Juan de Fuca Ridge demonstrated that silicification processes proceed so rapidly that the vestimentiferan tubes can become mineralised during the worm's life cycle. The organic component of the worm tube is rapidly replaced by amorphous silica which undergoes dewatering toform opal-A. This mineralisation is then overgrown by barite laths, and microbially templated amorphous silica. With time, prograde mineralisation causes the further precipitation and consequent overprinting of the primary mineral suite with iron- and zinc-sulphides. Other observations from samples studied here include micro-tubes (-50 jjm length) associated with adult R. piscesae and a silicified mucus lining to inhabited worm tubes. Associated with the mucus lining is a ligament which runs along the inside of the tube, and is tentatively inferred to be a form of anchor, allowing the worm to rapidly retract into the tube when threatened. Once mineralisation has replaced the organic tube material there is scope for the tube structure to be preserved along with the host sulphide body. Understanding of the mechanisms of early sulphide and silica/barite mineralisation as inferred from detailed observations and measurements of tube worm samples is an important contribution to the growing field of hydrothermal palaeobiology.

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After open pit mining, the pit can either be backfilled or be filled with groundwater andbecome a pit lake. These lakes tend to be acidic and contains high concentrations ofmetals, which increases the environmental risks in the area. One of these pit lakes isRävlidmyran in the Skellefte ore district. This problem and this pit lake have created thepurpose of this thesis, which is to compare the different water types connected to an openpit, i.e. groundwater, surface water and the actual pit lake water, and to connect the waterwith geophysical readings. The purpose is also to compare ratios between elements to beable to gain more geochemical information.To gain information about the groundwater, several groundwater pipes have since a longtime back been installed in the area. The groundwater has thereafter regularly beensampled and analysed. The surface water has also been sampled regularly in differentspots. In the pit lake, a depth profile has been created by water sampling at differentdepths in the pit lake. The geophysical measurements used in this thesis are resistivityand induced potential measurements, and measurements were done with the slingrammethod.The water sampling indicated that all three types of water contained elevatedconcentrations of metals. The ratio between (Cu+Zn+Pb)/Na indicated that the pit lakehad the highest value. The measurement also indicated that the highest concentration ofdissolved metals is found under the chemocline in the pit lake, compared with other watertypes. Also, the ratio Fe/S were the highest under the chemocline in the pit lake, whichindicates e.g. dissolution of pyrite. When it comes to the ratio representing e.g. dissolutionof gypsum (Ca/S) it was below 1 all the time, except for in two groundwater pipes. The(Ca+Mg)/Na–ratio had the highest values in the pit lake and that indicates dissolution ofe.g. carbonates. This is not very surprising since the pit lake has been and are limedregularly.The geophysical investigations indicated increased electrical conductivity in a waste rockheap northwest of the pit lake, where the sampling indicated elevated copperconcentrations. The readings also show that the groundwater flow direction is againstLake Hornträsket north of the pit lake. They also indicated potential flow paths for thegroundwater. These can contain elevated concentrations of ore elements, which can beconfirmed by a sampling of the groundwater in that area. From the geophysical data, it isalso possible to see that one of the profiles are located along a possible groundwaterplume, based on a low resistivity area and the shape of the potential plume. / Efter brytning ur ett dagbrott, så kan dagbrotten ur efterbehandlingssyfte till exempel bliåterfyllt med antingen gråberg eller med vatten. Ifall dagbrottet blir återfyllt med vattenoch en dagbrottssjö skapas, så tenderar denna sjö att vara försurad och innehålla förhöjdahalter av metaller. Detta ökar de lokala belastningarna på miljön i området. En av dessadagbrottssjöar är Rävlidmyran som ligger i Skelleftefältet. Denna dagbrottssjö och dessbieffekter har skapat syftet med detta examensarbete, vilket är att jämföra olikavattentyper kopplade till Rävlidmyran (grundvatten, ytvatten och vatten i dagbrottssjön)samt att jämföra geokemin med geofysiska mätningar. Syftet är också att jämföramolkvoter mellan relevanta element för att i sin tur få mer geokemisk information.För att få fram mer information om grundvatten så har flertalet grundvattenrörinstallerats i området sen flera år tillbaka. Därefter har grundvattnet provtagits ochanalyserats regelbundet. Ytvattnet i området har också provtagits. I dagbrottssjön har enprofil tagits fram genom att ta vattenprover på olika djup i sjön. De geofysiskamätningarna som gjorts är resistivitet och inducerad potential mätningar, samtmätningar som utförts med slingram-metoden.Vattenprovtagningarna indikerade att alla tre vattentyper innehåller förhöjda halter avmetaller. Molkvoten (Cu+Zn+Pb)/Na visade att kvoten var högst under kemoklinen idagbrottssjön i jämförelse med de andra två vattentyperna. De kemiska analyserna avvattenproverna av de olika vattentyperna pekade också på att vattnet under kemoklineni dagbrottssjön innehöll en större mängd lösta joner. Kvoten Fe/S var också högst i dettavatten. När det kommer till molkvoten som bland annat representerar gipsutfällning ochgipsupplösning – Ca/S – så var det under 1 i hela området, med undantag för tvågrundvattenrör. Kvoten (Ca+Mg)/Na var högst i dagbrottssjön och det indikerarupplösning av exempelvis karbonater. Detta är inte helt oväntat, då dagbrottssjön kalkatsregelbundet sedan en lång tid tillbaka.De geofysiska utredningarna indikerade på förhöjd elektrisk konduktivitet i ettgråbergsupplag nordväst om dagbrottssjön, där vattenanalyserna påvisade en förhöjdkoncentration av koppar. Mätningarna visade även att grundvattnets riktning var motsjön Hornträsket, som är lokaliserad norr om dagbrottssjön. De indikerade ävenpotentiella flödesvägar för grundvatten. Dessa flödesvägar kan innehålla förhöjda halterav metaller, vilket kan bekräftas med hjälp av provtagningar av grundvatten i området.Från de geofysiska mätningarna är det också möjligt att se att en av profilerna är placeradlängs med en möjlig grundvattenplym, baserat på en låg resistivitet och den potentiellaplymens form.

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Thesis (Ph.D.)--Indiana University, Dept. of Geological Sciences, 2005. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0146. Adviser: Edward M. Ripley. "Title from dissertation home page (viewed Feb. 9, 2007)."

Assessment of the potentially acidic, heavy metal-ladenleachates that leave deposits of sulfide ore mill tailings andevaluation of various possible options for mill tailingremediation are scientific problems of increasing practicalimportance. High costs may be associated with the mill tailingremediation, not least after recent changes in Swedish andEuropean environmental legislation. This thesis presents amethodology for studying and quantifying geochemical processesthat contribute to generation of so-called acid mine drainage(AMD). The methodology builds from first principles regardinggeochemical processes, and is based on geochemicalcharacterisation of the mill tailings combined with explicitmodel quantification of the effect of factors, such astemperature, pH, and mineral (BET) surface area, that influencemineral weathering rates. Application of the modellingmethodology to a case study site, Impoundment 1, Kristineberg,northern Sweden, including quantification of slow processesthrough literature rate laws, successfully reproduced the pHand relative concentrations of major ions in the impoundmentgroundwater. Absolute concentrations of most major ions, withthe exception of Zn, were 1-2 orders of magnitude higher in themodel than in the field, which is consistent with the commonlyobserved scale dependence of mineral weathering rates; however,application of a single calibration factor, Xr=10-2, to all weathering rate expressions, sufficed toaccount for this apparent scale dependence. Subsequent laboratory determination of mineral weatheringrates in Impoundment 1 tailings indicated that rates for themajor minerals pyrite (FeS2) and aluminosilicates were in fact 1-2 orders ofmagnitude lower in the ~50-year-old tailings than ratesreported in the literature. Weathering rates of chalcopyrite(CuFeS2) and sphalerite (ZnS) were by contrast 1-3 ordersof magnitude greater than predicted by the literature rate lawsthat were used in the modelling study. While the mechanism ofZn release requires further investigation for improved forwardmodel prediction, the underestimation of Zn concentration inImpoundment 1 by the model was resolved. The laboratory studyfurthermore indicated that the weathering rates of most majorminerals exhibited the same dependence on pH, temperature andsurface area as reported in the literature, and therebysupported the use of literature rate laws for model assessmentof dominant geochemical processes in tailings deposits, onceallowance is made for lower rates in older tailingsmaterial. Analysis of the dominant geochemical processes in the modelof Impoundment 1 indicated that slow weathering ofaluminosilicate minerals provided the bulk of protonattenuation and, as a result, considerably affected the rate ofdepletion of fast-reacting pH-buffering minerals. Inclusion ofthe kinetics of aluminosilicate dissolution and of thefeedbacks between slow and fast processes is thus potentiallycrucial for prediction of pH and its long-term evolution. Thesensitivity of modelled groundwater composition and pH to ironredox reactions, such as may be accelerated by acidophilicbacteria, indicated that, while iron redox cycling was low atthe present case study site, quantification of microbialmediation of these reactions may be necessary for predictingAMD quality under other conditions. The laboratory studies alsoindicated that application of common sterilisation techniques,such as is necessary for study of relative contributions ofabiotic and biotic weathering processes, had little effect onthe long-term (>30 days) abiotic element release rates inthe tailings. This study suggests that within certain limits, which appearnarrower than currently recognised in industrial predictionpractices, it is possible to predict the weathering behaviourof major minerals, and hence proton release and attenuation, inbase metal tailings under field conditions.