The role of hardpan formation on the reactivity of sulfidic mine tailings: A case study at Joutel mine (Québec).

The former Eagle and Telbel mine site (hereafter referred to as Joutel mine), located near the town of Joutel in the Nord-du-Québec (Canada) houses a tailings storage facility (TSF) that has been inactive since 1996. Fresh, unweathered tailings (beneath 10-30 cm of oxidized horizon) are characterized by an average sulfide content of 6-7 wt% and an average Fe-Mn-carbonate content of 20-40 wt%. The oxidation of Joutel's tailings under atmospheric conditions resulted in the precipitation of secondary phases such as ferric oxyhydroxides and gypsum. Accumulation of these secondary phases throughout the TSF caused cementation and agglomeration of grains, which decreased the porosity of the material in a horizon below the surface. This horizon, which is referred to as hardpan, is frequently encountered within fine, reactive tailings. Characterizations showed that hardpans have a highly compact texture. The formation of hardpans limits vertical water infiltration and oxygen diffusion and these layers greatly affect the global geochemical behavior of underlying tailings in the Joutel TSF by protecting the unweathered material from oxidation. As a result, the water quality of the TSF is largely controlled by the reactivity of the upper oxidized tailings horizon. Joutel's oxidized tailings showed an acidic behavior early during laboratory kinetic leaching tests despite the near absence of sulfides and neutralizing minerals. However, when unweathered tailings were added under oxidized tailings, the water became neutral and metal leaching rates were reduced. After over a year of laboratory leaching tests, hardpans formed within the columns and the natural phenomenon was reproduced under laboratory conditions.

Life cycle of the camel tick Hyalomma dromedarii (Acari: Ixodidae) under field conditions in Northern Sudan.

Engorged Hyalomma dromedarii females were placed for development in shade and sun (open non-shaded site) in April, August and December for two successive years. Engorged nymphs were also placed at the same sites in January, March, May, June, July and August. Preoviposition periods ranged between 9.8 and 11.7 days in the shade but longer in the sun in December (14.7 days). Egg production index was higher in August (0.72) than in April and December (0.46 and 0.39, respectively) in shade and in August compared to December in the sun (0.65 and 0.29, respectively). In shade and in sun, the prehatching periods were longer in December (50.7 and 48.2 days) than in April and August (25.6 and 29.0 days). Percentage hatchability ranged between 82 to 94.1% and 56.2 and 58.9% in the shade and sun, respectively. Number of eggs laid and eggs hatched were positively correlated with females' engorgement weights. There were high mortality rates of females in the sun and most of the eggs desiccated. Slight increased ambient and soil temperatures increased egg production, shortened preoviposition periods and decreased hatchability while increased humidity shortened preoviposition and prehatching periods and increased hatchability. Nymphal-adult moulting periods were long in January (20.7 days in the shade and 14.4 days in the sun) and short in August in the shade (7.8 days) while they were only 6 days in May and June in the sun. High numbers moulted in all months in the shade (ranges 23.3-29.5 nymphs). The mean mortality of engorged nymphs in the shade was very low. However, in the sun mortality was high (12.9-30 nymphs). Premoulting periods were negatively correlated with ambient temperature but positively correlated with humidity. In the shade, mean number of nymphs moulting increased with increased mean ambient temperature, humidity and rainfall.

Drop-off rhythms and survival periods of Hyalomma dromedarii (Acari: Ixodidae) fed on camels (Camelus dromedarius) in the Sudan.

Flat larvae and adult Hyalomma dromedarii (Acari: Ixodidae) were fed on camels' ears. Feeding periods and drop-off rhythms of engorged females and nymphs together with engorgement weights of females were recorded. Newly hatched larvae and newly moulted adults were released in nylon mesh bags at the base of a tree. Their survival periods were seasonally monitored. H. dromedarii behaved exclusively as two-host ticks under field conditions. Larval-nymphal feeding periods ranged between 16 and 27 days according to the season, whereas females fed for 6-9 days. The peak drop-off rhythms of nymphs and females occurred between 18:00 and 20:00 h. Engorgement weights of females at dropping ranged between 0.84 g on day 6 and 0.60 g on day 9 of attachment. Survival duration of the flat adults showed that 18.4%, 5.3% and 4.8% of ticks released in January, April and July, respectively, survived for 1 month. A very few number of ticks survived for extra periods of 3 months, 2 months and 1 month in January, April and July, respectively. Increased air temperature and lower humidity decreased survival duration. Larvae released in February, May, June and August died within 1 week, although they survived under laboratory conditions (35 degrees C and 49-90% Relative Humidity (RH) for 49-60 days.

Ticks (Acari: Ixodidae) infesting camels (Camelus dromedarius) in Northern Sudan.

Monthly total body tick collections from 13-20 camels were conducted for 2 consecutive years (2000-2001) in Northern Sudan. Tick populations were correlated with locality, season, predeliction site, sex and coat colour. Hyalomma dromedarii was found to be the predominant (89%) tick species infesting the camels. Other tick species found in very low numbers were Hyalomma impeltatum (7.7%), Hyalomma anatolicum anatolicum (3.3%), Hyalomma truncatum (0.29%), Hyalomma marginatum rufipes (0.25%), Rhipicephalus praetextatus (0.30%) and Rhipicephalus sanguineus group (0.09%). Nymphs of the genus Hyalomma were collected in significant numbers. Adult ticks significantly preferred to attach to the lower parts of the camel's body for feeding while the nymphs preferred the back of the animal. Female camels harboured more ticks than males while higher infestations were recorded on camels with a grey coat colour compared to those with a brown coat colour. Ticks were found on camels throughout the year and increased in numbers during March to October with a peak in September.