The activities that take place at a mine site depend on whether a mine is in its exploration, production or closure phase.
Early exploration by prospectors seeks to identify the presence of a particular mineral in a given area to determine whether or not a mine is an eventual possibility. Once early exploration has established that there is a promising presence of mineralized rock, an advanced exploration project will be proposed to define the deposit and allow the mining activity to be planned. At this stage, only a limited amount of mineralized rock will be brought to the surface for analysis and it is not generally removed from the site.
However, advanced exploration can involve significant excavation, including the possibility of a mine entrance ramp or shaft and galleries to drive drilling equipment to the different underground exploration areas. Excavated rock brought to the surface will not be highly mineralized so it will only have low levels of radioactivity.
It will be categorized as clean waste rock if devoid of radioactive elements, or special waste rock, if it has some uranium content, but not enough to be considered ore. Site infrastructure will generally include pads to receive waste rock piles, holding ponds for mine and site run-off water, a water treatment plant, a fuel depot, ancillary buildings and a worker camp.
The next stage is the construction of the mine to be able to excavate the ore most effectively. Again, this consists of excavating shafts and galleries underground as well as setting up the mine ventilation system. The aboveground infrastructure (buildings, storage areas, water treatment facilities, etc) will also be constructed. Mining activity can then start.
The focus is on bringing ore to the surface and leaving non-mineralized rock in the mine where possible. In Quebec, the ore concentrations of uranium that have been found so far are below 1%, so it usually makes sense to crush the rock in a mill until it looks like sand and extract the uranium (the 1%) at the mine site, rather than transport the ore (the 100%) for processing at a distant site.
The mill consists of heavy-duty equipment and large vats for chemical reactions to take place. The extraction of uranium from the crushed ore is done through precipitation with various chemical reagents, resulting in a product called yellowcake. This is transported off-site for further refining.
The crushed rock from which the uranium has been extracted is known as tailings. Although the uranium has been extracted, the tailings contain about 85% of the radioactivity of the original ore because the tailings contain uranium decay products. A tailings management area, usually in the form of a tailings pond, will be constructed to collect these wastes.
Dust at the site will often be ore dust containing many radioactive elements and toxic metals. Equipment covered in dust must be decontaminated. Water recovered from the mine or run-off from the site must also be decontaminated before release to the environment.
When mining operations cease, the mine will be closed and the site will be rehabilitated. The milling facility, water treatment plant and other equipment will be dismantled.
Much of this will be radiation contaminated and will require special handling. Special waste rock and contaminated material may be placed in the mine excavations before sealing the mine, or buried under non-mineralized rock.
The mine site will then be graded and replanted.