L9 - Evaporites Flashcards
What are evaporites?
Chemically-precipitated rocks that form at or near the Earth’s surface from saturated brines via solar evaporation or diagenetic processes
What is brine?
Water with dissolved salts.
What are the primary sources of ions for evaporite formation?
- Marine influx and circulation
- Hydrothermal springs and mid-ocean ridge (MOR) circulation
- Groundwater and deep-seated springs
What are the economic uses of evaporites?
- Lithium: Used in ceramics, glass, aluminum production, batteries, and pharmaceuticals.
- Potash: Used as fertilizer and in the chemical industry.
What makes lithium significant for batteries?
It is the lightest metal, highly reactive, flammable, and used in battery technology.
Where are the largest reserves of lithium and potassium found?
- Lithium: 51% in Chile, 22% in Australia, 13% in Argentina.
- Potassium: 28% in Canada, 21% in Belarus, 18% in Russia.
Why is potassium irreplaceable as a fertilizer?
There are no substitutes for potassium in fertilizer.
What factors influence evaporite precipitation?
Climate, brine concentration, hydrology (restriction), brine composition, and biota.
Why are arid climates necessary for evaporite formation?
High temperatures and low humidity drive evaporation, leading to brine saturation and mineral precipitation.
How does brine concentration affect evaporite formation?
As water evaporates, brine becomes concentrated, leading to precipitation of minerals such as CaSO4 and CaCO3.
What is the role of hydrology in evaporite formation?
Restricted water bodies with limited inflow and outflow lead to increased salinity, promoting evaporite precipitation
Where do evaporites typically form?
- Continental playas and sabkhas: Pore water evaporation and shallow brine pools.
- Saline lakes and salinas: Evaporation of standing water bodies.
What is the Zechstein (Permian) case study?
It describes carbonate-evaporite cycles in the paleo North Sea, with thick halite deposits surrounded by carbonates and sulfates due to restricted conditions
What techniques are used in evaporite exploration?
- Regional depositional and climatic history studies
- Seismic surveys
- Wireline logging (e.g., gamma-ray, density)
- Borehole geochemistry
What are the advantages and disadvantages of industrial salars?
- Advantages: Simple process.
- Disadvantages: High operational costs, large environmental footprint, and extensive water usage.
What are the advantages of subsurface mining of evaporites?
Low operational costs and small environmental footprint.
What are some uses of evaporites for subsurface storage?
Industrial and nuclear waste, munitions, CO2 (CCS), and liquid hydrocarbons for emergency reserves.
What are the two main types of lithium deposits?
- Brine deposits: Found in salt flats, involve mining natural/artificial brine pools.
- Hard rock deposits: Lithium-bearing minerals in igneous rocks like pegmatites.
What is the environmental impact of lithium brine mining?
Immense water consumption in arid areas and potential leakage of brine into groundwater
What is Direct Lithium Extraction (DLE)?
A technique to extract lithium chloride, which is purified to produce lithium hydroxide.
What minerals are associated with hard rock lithium deposits?
Spodumene: LiAlSi2O6
Lithium micas: KLi2Al(Si4O10)(F,OH)2
What are the environmental concerns with evaporite mining?
High water usage, potential chemical leakage, strip mining, and sinkhole formation.
How do evaporites form?
Through brine oversaturation caused by solar evaporation or diagenetic processes.
What conditions are necessary for evaporite formation?
Arid climate, negative water balance, and restricted brine inflow and outflow
