exogenic mineral deposits

Cards (9)

  • Placer deposits are concentrated by the action of moving water in rivers or the sea. 
  • Transport sorts sediment by:
    • Grain size 
    • Hardness 
    • Density 
    • Cleavage 
  • Less resistant minerals worn away or dissolved by water leaving resistant and insoluble minerals as placer deposits. 
  • Minerals found in placer deposits are:
    •  hard with no cleavage 
    • Chemically unreactive
    • Dense 
  • Placer deposits are found at places along rivers where the water slows down. 
  • Slow water:
    • Plunge pool 
    • Inside a meander bend
    • Rapids 
    • Floodplains 
    • Confluence 
    • Storm beach (marine) 
  • Cassiterite is insoluble and unreactive, it occurs in the hydrothermal veins in granite. 
  • Chemical weathering of granite produces clay minerals, unreactive quartz and cassiterite. These products are weathered and move downslope into streams. 
  • Cassiterite has a high density so is deposited sooner in areas of low energy.