|The Black Angel Mine, Marmorilik|
The inner part of the mine extends below the inland ice. Its entrance is located some 600 m above the ground, halfway up a steep cliff side, and can be reached by cable car only.
Tailings from the mine was discharged as a slurry. The discharge rate was some 3,000 m³ per day carrying some 1,200 tons solids per day. The tailing solids were pyrite, and low grade zinc and lead ore, containing traces of heavy metals.
The discharge took place to the bottom of a small sill fjord, Agfardlikavsa. This fjord is around 5 km long and around 500 m wide, with a surface area of 1.9 mio. m², a maximum depth of 80 m and a mean depth of 40 m. The sill across its mouth has a threshold depth of 20 m. Outside of the sill, the depth increases abruptly to around 200 m, while the outer part of the fjord system has depths of more than 1,200 m.
The annual direct freshwater inflow (which occurs mainly in July and August) has a volume that equals the fjord volume. In January through June, the fjord is covered by ice with a maximum thickness of 1 m. Each winter, the growing ice can release up to 25 kg salt per m² to the underlying water body.
The extreme seasonal variation of external forcings causes a corresponding variation of the flushing, which in turn implies a highly varying mass budget and transport of dissolved metals. During the second half of the year, transports are strictly horizontal, but blocked by the sill at larger depths, so that horizontal transport can proceed only in the upper part of the water column. Metals released at the bottom of the fjord accumulate in the stagnant, saline water behind the sill.
During the first half of the year there is no freshwater inflow, and some 2 percent of the fjord's volume is frozen. The entire water body becomes homogeneous and well mixed. The metal concentration becomes evenly vertically distributed, and transport into the outer fjord system can take place above the sill. As an example, the total amount of dissolved lead varied between somewhere around 8 tons in the winter and roughly twice as much in the summer.