Information on the occurrence of As species and iron sulphide minerals in tailings is essential for predicting therelease of As over extended period of time. Tailings originating from a goldmine in northern Sweden with low content of trace elements except for As were used for this purpose. The dominating sulphides were pyrrhotite and arsenopyrite. The samples used in the study were post-cyanided, tailings slurries treated with Fe2(SO4)3 and H2O2 to form arsenates and Fe-hydrates for effective As-immobilization. Speciation of the As in ore and tailings samples revealed that mining processes have dissolved the majority of the arsenopyrite in the ore, causing secondary As phases to co-precipitate with newly formed Fe-hydrates. A minor part of the As retained in the tailings was assumed to be As (III)-species. Weathering cell tests (WCT) involving 32 weekly cycles of wetting and air exposure were conducted to assess the effect of weathering on the stability of As in the tailings. As-bearing Fe-hydrates remained intact during the early stages of the WCT; the low release of As during this period was probably due to the dissolution of solubleAs(III)-phases. During the later stages of the WCT, the release of As, Fe and S increased due to pyrrhotite oxidation and the destabilization of As-bearing Fe-hydrates. The majority of the originally present As was still associated with the tailings by the end of the test, but additional pyrrhotite oxidation with the pH falling to >3 could further destabilize these As-bearing Fe-hydrates. In the second part of the study,cyanided tailings were converted into a monolith by using a method called cemented paste backfill (CPB). Two mixtures of CPB were tested; CE with 1 wt. % of cement and CE-FA consisting 2 weight (wt.) % of cement together with 1 wt. % of biofuel fly ash. The stability of As in CPB-masses andun-amended tailings were evaluated using tank leaching tests (TLT) and WCT: s. TheTLT results showed that the CPB mixtures were not suitable for use inunderground backfilling because the As content of the CPB leachates increasedcontinuously over the course of the tests. The proportion of binders inCPB-materials is usually 3-7% because such loadings are required to create amonolithic mass that physically and chemically stabilizes arsenic species intailings. The addition of small quantities of binders in CE and CE-FA maytherefore have been insufficient to ensure that the monoliths were highly saturated, which is required to prevent the transport of oxygen and water through the CPB material. In the WCT, crushed CPB materials were used and the addition of binders caused only a minor increase in the leaching of As relative to that seen with unmodified tailings. The addition of binders has re-located a minor proportion of As in As-bearing Fe-hydrates into less acid-tolerant species. During the later stages of the WCTs, the CPB mixtures were treated with acid in order to consume the buffering minerals and simulate the formation of acid mine drainage (AMD). When acid was added to crushed CPB-materials, As-release increased due to the dissolution of Fe-hydrates. The addition of binders into tailings could pose more resistance to sulphide oxidation, which in turn means that the stability of As-bearing Fe-hydrates could be prolonged on long term. Results from the WCT suggested that the addition of low proportions of binders could have a positive effect on As-leaching in a long term perspective. A relatively new method called “Surfacepaste disposal” (SPD), where mixtures of low proportions of binders and tailings is placed as a cover on the un-amended tailings has shown promising results in terms of decreasing As-leaching and the generation of AMD. Future research will, therefore, focus on the stability of As in SPD-applications.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Mars is an ideal planet to study planetary evolution and development, as its crust has been preserved over its history, rather than continuously recycled through subduction, as has happened on Earth. In order to attain a more coherent understanding of martian evolution, we focused on the thermal and petrologic history of the martian lithosphere. We developed a model that calculates the thermal state and melt composition of Mars over time. This model provides insight into the planet's history and enables us to describe how the density and seismic properties have evolved over time. We calculated the temperature profile through the lithosphere and then fit an equation to pre-existing experimental data in order to produce a model to predict the composition of melt produced as a function of pressure and temperature. From the melt model, we see a trend from ultramafic to mafic composition over time. We calculated the density and seismic properties of the lithosphere and found that they increase over time, but decrease with depth, which is consistent with the recent observations of NASA's InSight mission. / Master of Science / Mars is an excellent location to study how planets change over time because its crust has remained intact, rather than being destroyed as segments of the crust move and push against each other, which happens on Earth. In order to understand how Mars has evolved over time, we built a model to show how the top part of the planet has changed over time. The model works by calculating the temperature of the rocks. We calculated these temperatures in the present day and at four, three, two, and one billion years ago. We took the temperatures and used them to calculate the elements that are present in the rocks. Knowing the chemistry of the crust made it possible for us to calculate the minerals present in the crust and upper mantle, which we used to calculate the density of the outer layers of Mars and the speed at which earthquake waves would travel through the layers. We found that the density and earthquake wave speeds decrease over the depth of the top part of the planet. Although usually an object that is denser at the top than bottom will flip over, we believe this will not happen on Mars because the rocks are thick enough to prevent them from flipping.

Coastal bluffs of Baldwin Peninsula, NW Alaska, provide excellent exposures of middle Pleistocene nonglacial marine sediment overlain by prodeltaic glaciomarine sediment, indicating that glaciers reached Kotzebue Sound while the shallow Beringian continental shelf was submerged. Because the thin valley glaciers could not have significantly depressed the crust, this glacial advance must have occurred during a global high sea level, most likely during marine oxygen isotope stages 11, 9, or 7. The glacier limit can be traced through the region based on contrasting surface morphology of drift-covered and driftless areas. Simple numerical modelling of valley glaciers in the Noatak and Kobuk River valleys suggests that glaciers flowed over easily deformable sediments, at least in the lower reaches of the valleys. The extent of epimerization of the amino acid isoleucine in fossils molluscs was utilized to estimate the age of the marine and glaciomarine sediments. The preferred molluscan genera were not abundant, but shells of the genus Astarte were. Laboratory pyrolysis experiments reveal that Astarte and Macoma epimerize at similar rates and both are faster than Mya. Epimerization measured in the free fraction of pyrolyzed shells is surprisingly low compared to fossil shells with similar extents of epimerization measured in the total hydrolysate. The pyrolyzed shells show evidence of lower rates of hydrolysis relative to epimerization compared to fossil shells, suggesting that the energy of activation for hydrolysis and epimerization may not be constant over the wide temperature range separating natural burial conditions and laboratory pyrolysis experiments. Overall, Astarte showed greater potential to lose amino acids by leaching, therefore this genus is less preferred for amino acid geochronology. The extent of glaciers in the Beringian Arctic appears to be controlled primarily by moisture availability. The strength of atmospheric circulation, and therefore moisture transport to high latitudes, is largely controlled by the difference in insolation between low and high latitudes. Periods with both high autumn latitudinal insolation gradients (the difference between 0$\sp\circ$ and 60$\sp\circ$N Sept insolation) and decreasing summer insolation that occur during submergence of the Bering/Chukchi continental shelf appear most conducive to glacier growth in northwestern Alaska.