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Lecture 2

EPSC445 Lecture 2: min dep 1119.docx


Department
Earth & Planetary Sciences
Course Code
EPSC 445
Professor
Anthony E Willia- Jones
Lecture
2

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11/19 Min dep
Crude oil transporting mineral/
Composition of aqueous fluid
Composition of MVT
Data from oil field brine and fluid inclusions
Cl and Na similar number for these two composition of fluid inclusion and oil field brine
Metal make up of lead and zinc
oIn order to make economic mvt type deposit, we need this much concentration
Sulphur isotopic composition of MVT deposits
+50~-50~60
We know that sulphate likes heavy isotope
Reduced sulphur likes light isotope
Sedimentary sulphide is negative in numbers
Getting sulphur from sed. Sulphide we get negative numbers
Sea water of Phanerozoic sea water
Where did we get the sulphur? Shale basin and coral reef and back reef facies (left to
right in order) where do metals come from? From shale basins; shale enriched in metals
like lead and zinc. Fluids are brines, they got 15~20weight % NaCl
oEnvironment perpetuous for metal, leaching metals and move up to the coral reef
oOil comes from shale basins, where we have source bed and our petro migrate
upward til it finds reservoir.
oOil into oil field brine- dewatering sed basins where oil goes first and water
coming up behind of it. (following)
oWhat about sulphur
MVT deposit positive in sulphur mostly
Digeneti sedimentary sulphide that are negative in source
Black shale with disseminated pyrite
Sulphur coming from shale basins we see negative value but generally
positive value
Where does positive sulphur come from? Standard model: Sedimentary
basins deeply buried below the sea water surface. Back reet facies has
sulphur in oxidized form, in sulphate in evaporate. Our positive value in
different deposits come from there. Metal comes from shale to reet and
sulphur from back reet to reef. Oil moving thru and sulphate hits oil then-
>oxidizing to make reduced sulphur S+6 to S -2
Oil move to reservoir and sulphate So4 comes in from reet and
gets reduced b.c of reacting with oil and the net result is sulphur
reduced to H2S. Zn2+ meet with H2S and deposit
Alternative hypothesis: skip out aqueous fluid, transport metal in
hydrocarbon when meeting with sulphur and deposit/ 3rd one,
transport of sulphur in the oil (petroleum)
Carbon seams->association btw uranorite and carbon in that
Africa region;nanoparticleof uranorite in hydrocarbon; hydrocarbon
capable of moving uranium. Nanoparticle grow into a huge nugget
and bits of uranorite detritus are aggregates of nanoparticles.
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