Mineral Deposits (final exam) Flashcards
What is an ore deposit?
It is a mass of a useable material that is of sufficient size, concentration, and accessibility to be economically exploited
- covers everything from gold to coal to oil and gas
- this is a very vague definition which leaves itself to a lot of interpretation
- “deposit” varies from resource to resource
What are the 3 main ‘ingredients’ that determine a deposit for different resources
What is the other factor?
- source
- transport mechanism
- geological environment / depositional mechanism
also, time
What is the concentration factor equation?
Cf = Ce / Cc
Ce = economic concentration
Cc = average crustal concentration
Why do we care about mineral deposits? what are the uses?
Demand:
- economically valuable - make people money
- want to know how to use it in a judicial way
Scientific resource:
- knowledge about the atmosphere and the mantle and crust and the earth
Environmental remediation:
- figuring out how to reverse the negative environmental impacts and fix messes
- ex. acid mine drainage or soil and erosion management
What are the 4 big examples of environmental concerns that come with using mineral deposits
Acid mine drainage:
- acidic water runoff
- remediation: neutralization, ion exchange, bacteria
Air pollution:
- SO2, CO2, etc.
- Remediation: move away from fossil fuels?
Erosion:
- unwanted removal of material - disturbing the environment
- remediation: land management, re-vegetation
Tailings:
- waste material
- remediation: monitoring, engineering
What is the problem with the classic Igneous, Sedimentary, Metamorphic rock classification triangle
What did we change it to?
Mineral deposits are harder to classify with this triangle - especially because metamorphic classification is very complicated
Change to Magmatic, Sedimentary-surficial, and Hydrothermal
Explain Magmatic Processes and how it can impact deposits
- deposits formed by crystallization from a melt
- different kinds of magmas that melt mean different kinds of deposits
> mafic magmas (less silica): Fe, Cu, Ni, Au, etc.
> felsic magmas (more silica): Li, Cs, Sn, U, etc.
> intermediate magmas: not associated with deposits
What is the inheritance factor?
The source of magma determines its chemistry, which controls the kinds of deposits that can form
Explain Hydrothermal processes and how it can impact deposits
- deposits formed by circulating fluid
- different kinds of water make different kinds of deposits > water types: magmatic, metamorphic, basinal, meteoric, sea
- the deposit will depend on the water, temperature, rocks, etc.
What kind of environment is best for sedimentary-surficial deposits? Why are these kinds of deposits valuable?
A hot and humid environment is best
- they are valuable / economists like them because they’re on the surface which makes them easier and cheaper to mine
Explain sedimentary-surficial processes
Deposits formed by interaction with atmosphere and hydrosphere
- pedogenesis = formation of soils (dependent on local climate controls)
Enrichment of a pre-existing source
They are effectively and efficiently mined
They are the sole resource of certain metals
Where are some places in the world where we don’t typically mine and why?
Not really mining in desserts or up in north canada and greenland → hard to set up mines where people don’t live
Aren’t mining in the oceans - but there are more and more efforts to mine the seafloor
Where does gold mostly form?
Mostly along the ring of fire because of high volcanic areas
*shows that mineral deposits are not randomly distributed
What is the significance of ‘timing’ for mineral deposits and what are the two different types of changes?
Temporal patterns of mineral deposits are not random
Changes:
Recurrent
- changes that repeat themselves over time and are reversible
- ex. supercontinent cycle
Non-recurrent:
- changes that happen once and are permanent
- ex. Great Oxygenation Event, heat loss of the mantle
What is the preservation factor and how does it relate to ore deposits?
Preservation factor = things that are younger are more readily preserved
There are a lot more ore deposits that are younger compared to older (partly why most of our deposits come from the phanerozoic compared to the older eaons)
Briefly summarize the deposits/environmental capacity of the Hadean Eon
> minimal crustal preservation - meteorite bombardment - crustal overturning
proto-atmosphere, hydrosphere
**ore forming processes - no sedimentary/hydrothermal ores but possible igneous ores? (none preserved)
possible evidence of rocks on the moon?
*no real evidence of ore deposits
Briefly summarize the deposits from the Archean Eon
*oldest known ore deposits
- Isua Greenstone Belt
- all processes active
- tectonics just beginning to evolve to more modern processes
- life evolved!
- earth cooled down and became more rigid
- many ore deposits from the Neoarchean
Briefly summarize the deposits from the Proterozoic Eon
> maturation of processes
Great Oxygenation Event
Paleoproterozoic - beginning of supercontinent cycle - collision-related ore deposits
Mesoproterozoic - Anorogenic & rifting related ores
Neoproterozoic - ice ages and earliest phosphorus deposits
Briefly summarize the deposits from the Phanerozoic Eon
- most prolific period of ore formation
- very active period of time tectonically
- minimal destruction of crust
- disassembly of Gondwana, build up of Pangea, dispersal of Pangea
> dispersal = spreading-related ores
> assembly = collision-related ores - all fossil fuels formed here > because there were more complex organisms and because fossil fuels are pretty weak compared to rock - this is why we see these just from the younger eon
