## 2 Materials and Methods
### Methods  
#### 2.3.1 Physical and Chemical Characterizations  
The particle size distribution of the samples was analyzed using a Malvern Mastersizer S laser analyzer (0.05 to 880 \(\upmu\)m). The specific surface area was measured by micrometrics implementing the Brunauer-Emmett-Teller (B.E.T) method [28] and the relative density was measured by a helium pycnometer (AccuPyc 1330, Rouyn-Noranda, QC, Canada). Figure 1: Sampling localization, Lake Osisko, Rouyn-Noranda, Abitbi-Temiscamingue, Québec, Canada. A number was assigned to each sample, along with “S” for sediment and “V” for vase. The total sulfur and carbon were analyzed by an induction furnace (ELTRA CS-2000, Rouyn-Noranda, QC, Canada) with a detection limit of \(\pm\)0.09 wt. %. The samples were pulverized to 74 \(\upmu\)m and 130 mg was analyzed by the furnace. The blank samples within this analysis consisted of a sample containing tungsten and iron. The organic matter was analyzed by loss on ignition by heating the samples to 375 \({}^{\circ}\)C for 16 h [29]. The bulk chemical composition of the solid samples was determined by inductively coupled plasma atomic emission (ICP-AES, Perkin Elmer 3000 DV, Rouyn-Noranda, QC, Canada) after a total digestion of the solid samples using HNO\({}_{3}\)/Br\({}_{2}\)/Hf/HCl (HF and HCl added to dissolved silicate, and HNO\({}_{3}\) and Br2 to oxidize the sulfur) at the URSTM (Rouyn-Noranda, QC, Canada). The ICP-AES is calibrated using SY-4 which is an international rock standard. Moreover, a duplicate was analyzed for each of the six samples [22]. Major elements contents (Al\({}_{2}\)O\({}_{3}\), CaO, Cr\({}_{2}\)O\({}_{3}\), K\({}_{2}\)O, MgO, MnO, Na\({}_{2}\)O, P\({}_{2}\)O\({}_{5}\), Fe\({}_{2}\)O\({}_{3}\), SiO\({}_{2}\), TiO\({}_{2}\) and LOI) were analyzed using X-ray fluorescence in the whole rock at SGS (Canada). The detection limit of X-ray fluorescence (XRF) analysis is 0.1 wt. %. The pH, conductivity and redox potential, as well as the alkalinity and the acidity and dissolved metals, are measured on the pore waters after filtration. The acid generation potential (AP) is a measure of the total acidity that can be generated by a sample's oxidation. It is determined for a sample of vase and a sample of sediment by the following calculation: AP (kgCaCO\({}_{3}\)/t) = 31.25 \(\times\) %Sulfide [30]. Sulfides are considered to behave like pyrite. The main sources of acid are the oxidation of sulfurous minerals (especially pyrite and pyrrhotite), the dissolution of acidic salts and the hydrolysis of metal (Fe, Al). The neutralization potential (NP) is a measure of the amount of acid that can be consumed by a sample. It can be determined using chemical or mineralogical tests. The chemical tests consist of calculating the NP based on total carbonate (NP (kgCaCO\({}_{3}\)/t) = 83.3 \(\times\) %C\({}_{\text{inorg}}\)) and the mineralogical method [31] is based on the classification of minerals  
Figure 2: Pictures illustrating sample collection during winter, **(A)** Osisko Lake frozen, **(B)** driving the polyvinyl chloride (PVC) tube into the hole made in the ice, **(C)** PVC tube once retrieved containing the sample core, and **(D)** core sample, with black vase on the first few cm. according to their neutralization capacity. The NP is then the sum of each mineral's NP given by its proportion:  
\[\text{NP}=(1000\text{ kg}/\text{t}\div 100\%)\times\text{M}_{\text{CaCO3}} \times\sum\
olimits_{\text{i=1}}\text{n}(\text{R}_{\text{i}}\text{C}_{\text{i}} \div\text{M}_{\text{i}}) \tag{7}\]  
With R\({}_{\text{i}}\) being the relative reactivity of the mineral \"i\", C\({}_{\text{i}}\) its concentration (%), M\({}_{\text{i}}\) its molar mass and M\({}_{\text{CaCO3}}\) the molar mass of calcite. The interpretation of these static tests uses the acid balance and consists of comparing the AP and the NP in two ways, as follows.