ABSTR ACTUnderstanding the biogeochemical behaviour of arsenic in the weathering and shallow subsurface environment depends critically upon determining the nature and distribution of the chemical species present in natural waters. To this end, coupled ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS) is widely used, though species fractionation during ultrasonic nebulization, and matrix-dependent ionization in the plasma are analytical issues that need to be addressed. Hexapole collision cell technology is shown to be effective in suppressing chloride-based polyatomic interferences. Irrespective of the analytical technique used, As(III)/As(V) ratios of natural waters may change substantially during storage due to (1) differential adsorption of arsenic species on hydrated ferric oxides (HFOs); and (2) microbial activity. A wide range of apparently contradictory speciation changes observed by various workers can be rationalized in terms of the differences of microbial consortia present in different water samples. Arsenic speciation in certain water types can be stabilized for days or even weeks by combined filtration, acidification and refrigeration whilst the addition of EDTA and the use of 0.1 mm filters is indicated for iron-rich waters and waters with high activities of redox-active bacteria, respectively. Although the use of hydrochloric acid has been reported elsewhere as resulting in the apparent oxidation of As(III), we show that for certain water types it acts as an extremely effective preservative of arsenic speciation.

The western Rhodope massif contains a significant number of 'battery grade' Mn-oxide deposits which are best developed in the area near Kato Nevrokopi, Drama district, N. Greece. Economic Mn-oxide ore concentrations are confined to fault zones and related karsts in marbles. The mineralisation has formed by weathering of hydrothermal veins that were genetically related to Oligocene magmatism.At Kato Nevrokopi, progressive and continuous weathering of primary, hydrothermal veins of rhodochrosite, mixed sulphide, quartz and 'black calcite' (calcite and todorokite) has resulted in the formation of the assemblage MnO-gel-(amorphous Mn-oxide)-todorokite-azurite-goethite-cerussite in the veins and the assemblage MnO-gel-nsutite--chalcophanite-birnessite-cryptomelane-pyrolusite and malachite and amorphous Fe-oxides in karstic cavities.The fs2 andfo2 of the hydrothermal fluids increased with time. The breakdown of the hypogene Mncarbonate was aided by the production of an acidic fluid due to the oxidation of sulphides. Precipitation of the supergene ores was caused by neutralisation of the fluids due to reaction with the host marble and to mixing of relatively reduced fluids with oxygenated surface water in a fluctuation water table regime. Zinc was also mobile during weathering and became concentrated in the intermediate Mn-oxides, effectively stabilising their structures. The mineral paragenesis records the progressive oxidation of the ore and the appearance of less hydrated Mn-oxides, low in alkalis and alkaline earths.

EPMA and SEM studies of tunnel-structured todorokite and nsutite and layerstructured chalcophanite and birnessite from the Kato Nevrokopi battery grade Mnmineralization were performed. The chemistry of todorokite, formed at hypogene and supergene environments in an increasing order of weathering, reflects different pH and oxidation conditions. The data also point to a clear dependence of the development of late stage hypogene and early supergene Mna+-oxide paragenesis on the host rock and protore composition and the mobilities of base metals (mainly Zn), alkalis and alkaline earths (mainly Ca).The chemistry and development of (large cation-bearing) nsutite as in situ oxidations and

At the 25th km main Mn-mine of Kato Nevrokopi, Macedonia, northern Greece, rancieite forms flaky to laminated aggregates encrusting vugs, and replacing pyrolusite and todorokite in massive deposits of the Falakron marbles. It has an unusually high ZnO (1.53-3.07 wt%) content and therefore it was named 'zincian rancieite'. The average (18 spots) chemical composition of rancieite by EPMA is (wt%): MnO2 62.01, CaO 6.83, ZnO 2.54, A1203 1.18, MgO 0.63 plus minor oxides (Fe203, K20 & SiO2), total of 73.98. Assuming H20-content as 26.02 (100 -73.98) wt%, these data reflect the following empirical formula: (Ca0.67Zn0.17A10.12Mg0.09 3+

The granular aquifer system of the western Chalkidiki peninsula covers