Environmental Geology lecture outline - metallic resources

Figure of the Hibbing Iron Mine in Minnesota. You are viewing about one third of the mine which is some 6 miles long. the red coloration is due to oxidation of the iron ore. As deep holes in the ground mines often fill up with water, and can lower the groundwater table in the area.

Introduction:

• Importance of metals and ores to society:
  • stone age, iron age, bronze age.
  • now in the aluminum, silicon or composite age.
• This is a figure showing some of the tailings associated with Hibbing iron mine in Minnesota. The blue arrows point to the long ridge that is composed totally of waste material from the Hibbing mine. The student stands on more tailings. Much of it is sand/gravel overburden, and relatively benign, but this gives you an idea of the volume of earth material involved.
• Useful framework = cradle to grave environmental perspective:
  • exploration: usually minimally invasive.
  • extraction: tailings, land reclaimation, mine saftey, lowering of groundwater table.
  • processing: energy used, waste byproducts, associated compounds used, acidic emissions (e.g. Ducktown Tennessee and Sudbury, Canada).
  • use and proper disposal: potential health effects (Pb, Hg), recycling.
• Utility of understanding geology from environmental perspective. Geologic association particularly useful - e.g. silver ore often has a lot of arsenic associated with it.
• Clark Concentration Factors:
  • Al 8.2% (background average) -> 35% (ore material), factor of 4.2
  • Copper .0055% -> .3% , factor of 54.
  • Tin .00021% - > 1% , factor of 4,761.
• Ore bodies as anomalies from concentration mechanisms, and the utility of geologic models:
  • residual weathering.
  • hydrothermal.
  • magmatic.
  • biogenic.
  • placer (sedimentary sorting).

Aluminum as an example:

• geologic formation factors: Al rich source rock, intense chemical weathering (tropical conditions), and preservation.
• major global deposits:
  • Australia.
  • Guinea.
  • Brazil.
  • Jamaica.
  • U.S. has fraction of percent of world's reserves.
• processing, environmental concerns and recycling:
  • 5-6 tons of bauxite ore --> 1 ton of metal
  • 1300 lbs of coke per ton required.
  • 244*10E6 Btu required, roughly equal to 17 tons of good coal.
  • recycling saves 90% of the energy.
  • Norway a major producer.

Uranium as an example

• NW Nebraska's deposits: Crow Butte Mine: Ferret exploration.
• initial lease site 3,000 acres, leases on additional 10-20,000 acres.
• geologic aspects:
  • White River Group strata (rich in volcanic ash).
  • basal conglomerate unit - Chadron aquifer, 400-800' deep.
  • underlying impereable Pierre Shale.
  • normal faults in the area.
  • U in pores, replacing organics: carnotite: complex U oxide
  • U precipitates under reducing conditions and is mobile under oxidizing conditions.
  • overlying Brule aquifer. Pump tests indicate minimal connection (where tested).
• mining technique used:
  • solution mining.
  • pump out more than inject so net flow towards and not away from the site.
  • sodium bicarbonate and hydrogen peroxide used as mobilizing agents.
• history of mining site:
  • in operation some 15 years.
  • about million pounds of U3O8 (yellowcake) per year.
• environmental concerns:
  • surface spills.
  • contamination of other aquifers.
  • induced seismicity (none produced)
  • several million dollar trust fund produced.
• three accidents to date:
  • pump malfunction caused 7,000-8000 gallon spill; DEQ $3,500 fine.
  • 23,000 gallon spill, some of which reached local creek. Below detectable limits of radium in water.
  • leak into Brule aquifer, 100,000 to 300,000 gallons (this part of aquifer unused).

Summary of related environmental concerns.

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