Sedimentary Ores
Metal |
Basin Type |
Relationship to mineralization |
Role of mudstones |
Process of mineral precipitation |
Source of metals |
Fluid temperature/ Receiving water type |
Metals carried in hydrothermal fluids rising from below |
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Pb, Zn, Ba |
Marine Rift |
High heat flow, vertical pathways, sufficient accommodation for marine flooding; seawater provides source of S |
Thick, organic-rich mudstones provide thermal blanket to allow high temperatures to develop |
Pb and Zn precipitate where rapidly-rising fluids intersect permeable strata or exit to seafloor; Ba precipitates distal to metals |
Organic-rich shales deeper in the sedimentary basin |
200-250oC Marine |
Cu |
Continental Rift |
Arid climate forms red beds and evaporites; vertical tectonics provide high relief, high heat flow, and pathways for fluids |
Hydraulic separation of oxidizing groundwater (high in Cu) from reducing groundwater (high in S) |
Cu precipitates where fluids mix around paleo-highs |
Mafic volcanic rock fragments in footwall aquifer |
100-150oC Lacustrine |
Ba |
Peripheral Foreland |
High water flux from accretionary prism caused by compression in subduction zone |
Organic matter reduces sulfate to sulfide, which dissolves BaSO4 and releases Ba++ to solution |
Ba precipitates where exiting fluids mix with SO4-rich seawater |
Organic-rich shales deeper in the sedimentary basin |
5oC Marine |
Metals carried in seawater at low temperature |
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Mn |
Passive Margin or Strike-slip |
Low sedimentation rates; basin geometry that restricts circulation |
Reducing muds in deep water export Mn to redox boundary where Mn oxides precipitate |
Mn accumulates where anoxic-oxic boundary intersects the seafloor; commercial grade if clastic/carbonate dilution is low |
Clastic sediments deposited below the chemocline in H2S-rich water or volcanic vents in deep water |
5-25oC Marine |
U, Mo |
Retroarc Foreland or Passive Margin |
Very slow sedimentation rates; restricted circulation |
Slowly-deposited muds provide host for abundant organic matter |
Metals from seawater absorb slowly onto organic matter |
River water flux of metal ions in solution |
5-25oC Marine |