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MVT Deposits (Mississippi Valley Type Deposits). MVT Ores Sphalerite and Galena in brecciated, dolomitized limestone Sphalerite Galena Spalerite-galena-

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Presentation on theme: "MVT Deposits (Mississippi Valley Type Deposits). MVT Ores Sphalerite and Galena in brecciated, dolomitized limestone Sphalerite Galena Spalerite-galena-"— Presentation transcript:

1 MVT Deposits (Mississippi Valley Type Deposits)

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

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

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 o C Salinity : ~ 15wt% NaCl eq. Oil-bearing aqueous inclusions2-Phase Aqueous Inclusions Asphaltene Oil

13 Composition of MVT Fluids

14 Sulphur Isotopic Composition of MVT Deposits

15 1 m NaCl Zinc Speciation in Aqueous Liquid

16 Temperature ºC pH 10 ppm 100 ppm 1000 ppm ppm Solubility of Sphalerite as a Function of Temperature and pH 2m NaCl 0.01 mΣS SVP (Based on data of Ruaya and Seward 1986; Tagirov and Seward, 2010) Soluble Insoluble

17 Zinc Speciation in Aqueous Liquid

18 A constraint on MVT Ore Formation Can reduced sulphur be transported with zinc? Sphalerite will precipitate even in the presence of vanishingly small concentrations of H 2 S. Ore metals and reduced sulphur must be transported separately. Metalliferous brine containing 15 wt.% NaCl and 1000 ppm Zn 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 + + SO 4 2- = ZnS + Cl - + 2O 2 PbCl + + SO 4 2- = PbS + Cl - + 2O 2


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