MVT Deposits

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MVT Deposits
(Mississippi Valley Type Deposits)
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MVT Ores
Sphalerite and Galena in brecciated, dolomitized
limestone
Spalerite-galena-bearing breccia
Galena
Sphalerite
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Distribution of MVT Deposits
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Zn-Pb Reserves and Production by Deposit Type
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Grade and Tonnage Data for MVT Deposits
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The MVT Districts of the SE United States
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Geological Setting of Pine Point
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Pine Point Ore and Host Textures
Dolomitized Limestone
Breccia infilled by sulphides
Oil seeps
Sphalerite-galena ore
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Cross-section through the Pine Point Deposit
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Cartoon of the Robb Lake MVT Deposit, Yukon
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Karst Formation
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Fluid Inclusion Data
Th 125 200 oC
Salinity 15wt NaCl eq.
Oil-bearing aqueous inclusions
2-Phase Aqueous Inclusions
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Composition of MVT Fluids
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Sulphur Isotopic Composition of MVT Deposits
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Zinc Speciation in Aqueous Liquid
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Solubility of Sphalerite as a Function of
Temperature and pH
(Based on data of Ruaya and Seward 1986 Tagirov
and Seward, 2010)
350
2m NaCl 0.01 mSS SVP
300
Soluble
250
200
Temperature ºC
Insoluble
150
100
50
1
2
3
4
5
6
7
8
9
10
pH
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Zinc Speciation in Aqueous Liquid
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A constraint on MVT Ore Formation
Can reduced sulphur be transported with zinc?
Metalliferous brine containing 15 wt. NaCl and
1000 ppm Zn
Sphalerite will precipitate even in the presence
of vanishingly small concentrations of H2S. Ore
metals and reduced sulphur must be transported
separately.
Williams-Jones and Migdisov (2014)
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Towards a genetic model for MVT Pb-Zn deposits
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Genetic Model for MVT Deposits

• Oil and then brine released from clastic
  sedimentary basin
• Dissolution of reefal limestone creates porosity
  (Karst)
• Oil leaves residues in limestone
• Basinal brine leaches Pb, Zn from sandstones,
  shales
• Basinal brine transports metals to porous
  limestone reef
• dolomitizes limestone
• Backreef brine transport sulphate to reef
• Galena and sphalerite deposit as a result of
  mixing of
• metalliferous brine with sulphate-bearing brine,
  reduced
• by interaction with oil residues.

ZnCl SO42- ZnS Cl- 2O2
PbCl SO42- PbS Cl- 2O2