Preparation and construction of geochemical model

Question 1

How does pit lakes form?

Answer 1

After open pit mining water fills the hole.
Can be groundwater, surface water or both - depends on climate and inflow.

Question 2

What is the relative depth?

Answer 2

The max depth compared to the mean diameter in %.
Low relative depth means more likely to mix over the course of a year.

Question 3

Describe three words connected to the overturning over water

Answer 3

Holomictic - all water turns over
Dimictic - turnover twice a year
Meromictic - turnover of all water does not occur

Question 4

What is the mixolimnion and monolimnion?

Answer 4

The mixolimnion is the upper part of a meromictic lake where mixing occurs. The monolimnion is deeper down and does not mix

Question 5

Describe the relative depth of normal lakes compared to pit lakes

Answer 5

Most natural lakes <2% relative depth. Mostly seasonal turnover of entire water column

Most meromictic lakes >5% relative depth

Pit lakes about relative depth 10-40%

Question 6

Name some pit lakes in Northern Sweden

Answer 6

Åkerberg
Udden (has low pH and some overturning)
Rävlidmyran (low pH)
Laver (pyrite nearby but has a pH of 7. Very deep lake)

Question 7

Why is there higher density in the bottom waters?

Answer 7

• Groundwater accumulates salinity and elements and flows in at larger depth.
• Precipitation in oxygen rich conditions -> sinks to reducing conditions -> free ions

Question 8

Why are pit lakes nutrient poor?

Answer 8

• They do not overturn
• Artificially made and less inflowing surface water with nutrients

Question 9

What does the pit lake water quality depend on?

Answer 9

Depends on surrounding geology
 Oxidation of some sulfides produce acid
 Alkalinity of groundwater can neutralize acid
 Wall rock composition
 Chemistry vadose zone
 Quality and quantity of run off
 Exposed rock can be major source of acid even if is located below GW table before and after the mine operation

Question 10

What are some remediation or prevention strategies?

Answer 10

 Flooding
 Backfilling
 Active methods e.g. liming
 Passive methods e.g. constructed wetlands
 Increasing primary production
 Induced stratification
 Consider waste piles/tailings in the nearby area
 Sulfur reducing bacteria

Question 11

Hur är stegen för att balansera en vittringsreaktion?

Answer 11

1. Allt Al och Fe till sekundära mineral (pH 6-8)
2. Si till Si(OH)4
3. Alkali- och alakaliska jordartsmetaller i lösning
4. Kolsyra som syra
5. Balansera laddning med H+
6. Balansera O2 och H+ med vatten
7. Kolla så att massa och laddning är balanserade