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The structural state (i.e., order-disorder) of minerals and other solids analyzed in an electron microprobe or scanning electron microscope may notably affect the back-scattering of incident beam electrons. Structural heterogeneity, as it is commonly observed in radiation-damaged minerals, may thus contribute to signal intensity variations in back-scattered electron (BSE) images. Such structural BSE effects are easily overlooked because they may be insignificant in cases of minerals with high internal Z contrast. Correspondingly, it has generally been assumed that BSE images of single-crystals of minerals are mainly controlled by the sample’s chemical heterogeneity. However, structural heterogeneity cannot be neglected in the discussion of BSE images; this is especially the case if crystals only show minor Z variations. We show with two examples that radiation damage (i.e., gradual to complete destruction of the crystal lattice) results in a significant increase of the back-scatter coefficient. The phenomenon is assigned to lowered penetration depths of electrons and thus related to electron channelling contrast. The BSE of natural zircon crystals is in most cases predominantly controlled by radiation damage. Annealing studies revealed that after structural reconstitution, the BSE intensity is notably decreased and much more uniform, in spite of the same chemical heterogeneity (especially concentrations of Hf and U) as before the treatment. As an even more unambiguous example we present observations on irradiation-damaged silicon. Damage up to complete amorphization was produced upon implantation of Si ions. Consequently there are no chemical variations and no Z contrast in this case. Examples show that the degree of structural damage needs to be considered in the discussion and interpretation of BSE images of radiation-damaged minerals.

At the TAG hydrothermal mound, large amounts of anhydrite in the high-T upflow zone may be responsible for sulphide Delta (super 34) S ratios that are 30/00 heavier than those for all other sulphides at sediment-free mid-ocean ridges. In contrast, the Delta (super 34) S ratios for sulphides and baryte from the propagating tip of the Valu Fa Ridge (Lau back-arc) are the lowest recorded for volcanic-hosted massive sulfides at such centres; this is attributed to magmatic contributions to the seafloor hydrothermal system

A study was carried out of the isotopic and chemical compositions and dissolved SO4(2-) contents in mine water from a mined and backfilled ore vein at a polymetallic sulphide deposit in Freiberg, Germany, to investigate the SO4(2-) sources and mixing processes. The main SO4(2-) sources are soil seepage water, groundwater and sulphide oxidation. About 50% of SO4(2-) in the mine water at the deepest accessible level of the ore vein originates from sulphide oxidation. Anthropogenic sources may be responsible for mine water with anomalous stable isotope compositions and anion and metal concentrations. Hydrochemical and stable isotope compositions of waters in the central Freiberg and Morgenstern mines were determined to evaluate whether the same trends occurred as for the backfilled ore vein and what additional processes may operate on a larger geological scale. Most of the flowing mine waters follow the same mixing trend as for the backfilled ore vein. Anthropogenic sources such as sewage water and industrial wastewater were observed to be of importance. No obvious decrease in the intensity of sulphide oxidation in the unflooded part of the Freiberg mine has occurred over the last 10 years. The dual isotope approach is useful to constrain better the sources of SO4(2-) and for pollution assessment in long-term observation studies., A study was carried out of the isotopic and chemical compositions and dissolved SO4(2-) contents in mine water from a mined and backfilled ore vein at a polymetallic sulphide deposit in Freiberg, Germany, to investigate the SO4(2-) sources and mixing processes. The main SO4(2-) sources are soil seepage water, groundwater and sulphide oxidation. About 50% of SO4(2-) in the mine water at the deepest accessible level of the ore vein originates from sulphide oxidation. Anthropogenic sources may be responsible for mine water with anomalous stable isotope compositions and anion and metal concentrations. Hydrochemical and stable isotope compositions of waters in the central Freiberg and Morgenstern mines were determined to evaluate whether the same trends occurred as for the backfilled ore vein and what additional processes may operate on a larger geological scale. Most of the flowing mine waters follow the same mixing trend as for the backfilled ore vein. Anthropogenic sources such as sewage water and industrial wastewater were observed to be of importance. No obvious decrease in the intensity of sulphide oxidation in the unflooded part of the Freiberg mine has occurred over the last 10 years. The dual isotope approach is useful to constrain better the sources of SO4(2-) and for pollution assessment in long-term observation studies.

Sphalerite oxidation commonly occurs under acid mine drainage (AMD) conditions, resulting in the release of SO4(2-), Zn and potentially toxic trace elements which can lead to the pollution of rivers and oceans. O and S isotope studies of the SO4(2-) produced may contribute the understanding of the sphalerite oxidation mechanisms and aid in the interpretation of field data from AMD sites. Batch oxidation experiments were carried out using Fe-rich sphalerite under aerobic abiotic conditions at initial pH values of 2 or 6 for 2-100 days. The O and S isotope composition of the SO4(2-) produced showed that during the first 20 days molecular O2 was the exclusive O source for SO4(2-) at both initial pH values. The lack of isotope enrichment processes between SO4(2-) and sphalerite indicated that O2 was the electron acceptor from sphalerite S. As oxidation proceeded a sufficient amount of released Fe(II) was oxidised to Fe(III) by O2 so that electrons could be transferred from sphalerite S sites to adsorbed hydrous Fe(III), and O from the hydration sphere of Fe was incorporated into the SO4(2-). Enrichment of 32S in SO4(2-) relative to sphalerite may also result from sphalerite oxidation by Fe(III). The incorporation of O2 into SO4(2-) during oxidation was associated with an O isotope enrichment factor. Comparison with O and S studies of other sulphides indicates that there is no general oxidation mechanism for acid-soluble sulphides., Sphalerite oxidation commonly occurs under acid mine drainage (AMD) conditions, resulting in the release of SO4(2-), Zn and potentially toxic trace elements which can lead to the pollution of rivers and oceans. O and S isotope studies of the SO4(2-) produced may contribute the understanding of the sphalerite oxidation mechanisms and aid in the interpretation of field data from AMD sites. Batch oxidation experiments were carried out using Fe-rich sphalerite under aerobic abiotic conditions at initial pH values of 2 or 6 for 2-100 days. The O and S isotope composition of the SO4(2-) produced showed that during the first 20 days molecular O2 was the exclusive O source for SO4(2-) at both initial pH values. The lack of isotope enrichment processes between SO4(2-) and sphalerite indicated that O2 was the electron acceptor from sphalerite S. As oxidation proceeded a sufficient amount of released Fe(II) was oxidised to Fe(III) by O2 so that electrons could be transferred from sphalerite S sites to adsorbed hydrous Fe(III), and O from the hydration sphere of Fe was incorporated into the SO4(2-). Enrichment of 32S in SO4(2-) relative to sphalerite may also result from sphalerite oxidation by Fe(III). The incorporation of O2 into SO4(2-) during oxidation was associated with an O isotope enrichment factor. Comparison with O and S studies of other sulphides indicates that there is no general oxidation mechanism for acid-soluble sulphides.