1. MVT Deposits
(Mississippi Valley Type Deposits)

2. Spalerite-galena-bearing breccia
MVT Ores
Sphalerite and Galena in brecciated, dolomitized limestone
Spalerite-galena-bearing breccia
Sphalerite
Galena

3. Distribution of MVT Deposits

4. Zn-Pb Reserves and Production by Deposit Type

5. Grade and Tonnage Data for MVT Deposits

6. The MVT Districts of the SE United States

7. Geological Setting of Pine Point

8. Pine Point Ore and Host Textures
Dolomitized Limestone
Breccia infilled by sulphides
Oil seeps
Sphalerite-galena ore

9. Cross-section through the Pine Point Deposit

10. Cartoon of the Robb Lake MVT Deposit, Yukon

11. Karst Formation

12. Fluid Inclusion Data Th: 125 – 200 oC Salinity : ~ 15wt% NaCl eq.
2-Phase Aqueous Inclusions
Oil-bearing aqueous inclusions
Asphaltene
Oil

13. Composition of MVT Fluids

14. Sulphur Isotopic Composition of MVT Deposits

15. Zinc Speciation in Aqueous Liquid
1 m NaCl

16. 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 mΣS
SVP
300
Soluble
250
200
Temperature ºC
Insoluble
150
10 ppm
100 ppm
1000 ppm
10000 ppm
100 50 1 2 3 4 5 6 7 8 9 10 pH

17. Zinc Speciation in Aqueous Liquid

18. 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)

19. Towards a genetic model for MVT Pb-Zn deposits

20. 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