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MVT Deposits (Mississippi Valley Type Deposits).

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Presentation on theme: "MVT Deposits (Mississippi Valley Type Deposits)."— Presentation transcript:

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

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