Geochemistry of rare earth elements within waste rocks from the Montviel carbonatite deposit, Québec, Canada

Abstract

Several rare earth element (REE) mine projects around the world are currently at the feasibility stage. Unfortunately, few studies have evaluated the contamination potential of REE and their effects on the environment. In this project, the waste rocks from the carbonatites within the Montviel proterozoic alkaline intrusion (near Lebel-sur-Quévillon, Quebec, Canada) are assessed in this research. The mineralization is mainly constituted by light REE (LREE) fluorocarbonates (qaqarssukite-Ce, kukharenkoite-Ce), LREE carbonates (burbankite, Sr-Ba-Ca-REE, barytocalcite, strontianite, Ba-REE-carbonates), and phosphates (apatite, monazite). The gangue minerals are biotites, chlorite, albite, ankerite, siderite, and calcite. The SEM-EDS analyses show that (i) the majority of REE are associated with the fine fraction (< 106 μm), (ii) REE are mainly associated with carbonates, (iii) all analyzed minerals preferably contain LREE (La, Ce, Pr, Nd, Sm, Eu), (iv) the sum of LREE in each analyzed mineral varies between ~ 3 and 10 wt%, (v) the heavy REE (HREE) identified are Gd and Yb at < 0.4 wt%, and (vi) three groups of carbonate minerals were observed containing variable concentrations of Ca, Na, and F. Furthermore, the mineralogical composition of REE-bearing minerals, REE mobility, and REE speciation was investigated. The leachability and geochemical behavior of these REE-bearing mine wastes were tested using normalized kinetic testing (humidity cells). Leachate results displayed higher LREE concentrations, with decreasing shale-normalized patterns. Thermodynamical equilibrium calculations suggest that the precipitation of secondary REE minerals may control the REE mobility.

Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management

“…Indeed, they are found in many ARD cases [142,143] but most REE deposits are within geological settings that are not prone to ARD generation, such as pegmatites, carbonatites, and peralkaline igneous deposits, as well as within placers and clays ( [144] and references therein). Upon their release in near-neutral mine waters, REE concentrations are mostly controlled by secondary precipitation and sorption phenomena (Section 2.4) [145][146][147][148]. However, significant knowledge gaps remain as to the fate of REE released from mine wastes.…”

Nb and REE Distribution in the Monte Verde Carbonatite–Alkaline–Agpaitic Complex (Angola)

“…Although some authors propose a magmatic origin for these elements and barite in other carbonatites (e.g., [70]), the textural evidence and the mineral association with quartz suggest a hydrothermal origin for them, as it was also suggested in Tchivira [25]. Other carbonatites worldwide, for instance, Italian carbonatites [56,57]; the Amba Dongar complex, India [71][72][73]; the occurrences from Sichuan Province, China [74][75][76]; or the Montviel deposit, Canada [77][78][79][80]; may display similar late REE mineral associations. This interpretation poses a problem since it is difficult to deduce how hydrothermal processes distribute REE minerals within carbonatite.…”

Rare Earth Elements (La, Ce, Pr, Nd, and Sm) from a Carbonatite Deposit: Mineralogical Characterization and Geochemical Behavior

“…In addition, other authors showed that REE fractionation is promoted by an increase in pH [24,43,44]. Edahbi et al showed, using thermodynamic equilibrium calculations on the humidity cell leachate data, that REE concentrations decreased significantly (from 10 −8 to 10 −16 mg/L) when pH values increase from 2.6 to 10 [45].…”

“…The weathering of the different lithologies within the Montviel deposit was studied in a previous study [45], where it was demonstrated that the REE-bearing carbonates from the Montviel deposit generates various elements (e.g., Ba, Sr, F, Th, and REE) in mine drainage waters. It is known that the carbonates dissolution is incomplete in near neutral conditions [47][48][49], and that the carbonate dissolution rates are lowest in alkaline and neutral conditions and increase in acid conditions [50,51].…”

“…This methodology was successfully applied in another context [52]. Consequently, the interpretation of the weathering cell data will not be investigated further; the interested readers are invited to consult [45].…”