Notes
Slide Show
Outline
1
Minerals and
Hydrothermal Systems
  • December 12, 2006
2
Ore Deposits
  • Most metallic ore deposits form from the precipitation of metal-bearing minerals from a hydrothermal fluid
  • Hyrdrothermal fluids are commonly acidic and reduced
3
Complex Ions
  • Most metals are quite insoluble on their own
  • Metals are usually transported as complex ions (metal ion joined to another molecule or ion)
  • Metals join with two ions most commonly
    • Cl- (chloride)
    • HS- (thiosulfide)
4
Chloride Complexes
  • Chloride complexes will form when:
    • Salinity is high
    • Temperature is high (>350C)


  • Chloride complexes will form with:
    • Sn4+, Mo, W, Ti
5
Thiosulfide Complexes
  • Thiosulfide complexes will form when:
    • Salinity is low
    • Temperature is low (<350C)


  • Chloride complexes will form with:
    • Au, Ag, Hg, Cu+
6
Either Complex
  • Some metals may be transported by either a chloride or thiosulfide complex. Such metals include:
    • Co, Ni, Cu2+, Pb, Sb, Sn2+, Zn
7
Mineral Stability
  • Minerals will either go into solution or precipitate depending upon the physical and chemical conditions of the fluid
  • If a mineral precipitates, the mineral that forms will be governed by the physical and chemical conditions of the fluid
  • eH and pH are dominant controls in mineral formation from hydrothermal fluids
8
Eh-pH Diagrams
9
Eh-pH Diagrams
10
Eh-pH Diagrams
11
Eh-pH Diagrams