Lecture 15 resources 6 VMS

Question 1

What plate tectonics are we thinking about for VMS deposits

Answer 1

constructive plate margins (sea floor spreading) which forms new ocean floor (presence of

Question 2

what is the relationship between destructive plate margins and copper

Answer 2

there are more porphyry copper deposits at destructive plate margins.

Question 3

What the hydrothermal process

Answer 3

heat of the crystalising magma generates a system where cold seawater is drawn in - warms, interacts with the rocks and becomes boyaunt - back to the surface - discharges as a focussed discharge of hydrothermal, fluid and precipitating sulphate.

Question 4

where is the Cayman trough

Answer 4

between Cuba and mexico - part of the Caribbean

Question 5

Cayman trough

Answer 5

one of the deepest areas on the ocean floor.
- vent sites and chimney structures - hot hydrothermal fluid vented onto the sea floor which changes solubility of the fluid - rapid precipitation occurs.
cayman trough has increases of gold.

Question 6

what’s the content within the chimneys (VMS) how does this compare to porphyry

Answer 6

very enriched copper and zinc.
- 1-10% zinc
- 1-10% copper
much higher than porphyry which was at 0.7% copper.

Question 7

What are the location of major ODP/IODP drilling campaigns on massive sulfides

Answer 7

International ocean drilling programme
Ship that drills on the sea floor, actively investigates the ocean floor
Leg 158 TAG
Leg 169 middle valley
Leg 193 pacmanus
Leg 376 Brothers

Question 8

Trans-Atlantic geothermal (TAG) sulphide deposit

Answer 8

formation of TAG -
Precipitated sulphide, beneath that there is anhydrate pyrite stock work zone of alteration - as the fluids are drawn up they alter the host rock, discharged as a black smoke complex.

simple model to underpin all: Magma chamber source which is generating new crust (constructive plate margin) , hydrothermal system = influx of sea water. the reaction and heating up of rocks above sea water, returning to sea floor, black smoke and precipitation of massive sulphides.

Question 9

is TAG different from Cayman trough and bent hill

Answer 9

Both have sulphide mound, drawing in sea water, reacting and returning to surface, black smoke.

Question 10

what things precipitate at sulphite mounds for VMS?

Answer 10

Iron, copper, lead and zinc sulphide precipitate

Question 11

how is pacmanas different

Answer 11

another vent field
- they drilled through hydrothermal vents to understand systems better.

Question 12

what are complications with drilling?

Answer 12

• don’t want it to get stuck - prevelant at hydrothermal sites because of all the rubble.

Question 13

What deposits are found in VMS

Answer 13

Copper, zinc, lead in the ancient geological record

Question 14

are VMS geographically restricted

Answer 14

no, they occur everywhere but near plate margins - they need to come from the ocean into land via tectonic processes, they represent zones of previous seafloor activity - ancient mid-ocean ridges - now abducted onto land.

Question 15

Rio tinto mine copper mine, spain

Answer 15

Active 1873 -2001
reopened in 2020 for gold
viability of a mineral deposit - depends on multiple deposit types.
- because we can mine lower grade copper - can revisit less strongly mineralised sites.

Question 16

What are the three ways to make copper deposit

Answer 16

1) Arc environment - volcano and subduction zone, melting of the lower mantle generates magma - hydrothermal fluid takes copper into vein systems at higher concentrations

2) sedimentary basins - oxidised red beds, stripping copper from rock - separating at redox.

3) ocean ridges - volcanic massive sulphide, generated of constructive plate margins - heats up builds sulphide mound, takes copper from sig volume of rock and reprecipitates in smaller denser volume.