The Geology of Metallic Mineral Deposits pt.2 (L21)

Question 1

What are Skarns?

Answer 1

deposits that are hosted by chemical sedimentary rocks affected by contact metamorphism

Question 2

how do skarns host some unusual silicate minerals?

Answer 2

due to reaction of hot fluids with the rock into which the intrusion was emplaced

Question 3

magmas generated at divergent boundaries tend to be ____

Answer 3

mafic in composition

Question 4

what is a more important contributor to the concentration of metals?

Answer 4

the interaction of seawater with oceanic crust beneath the seafloor

Question 5

What are “black smokers”

Answer 5

a volcanic vent where heated water, which is concentrated with metal ions, rises to the surface along fractures, and escapes through

Question 6

What happens to the crystals of the metallic sulphides that emanate from black smokers?

Answer 6

percipitate when the hot fluid mixes with the cold seawater, forming chimneys at the vent sites and free particles that settle and accumulate in pods (or mounds) on the seafloor

Question 7

what are the clouds of “black smoke”?

Answer 7

microscopic suphide crystals percipitated from the hot water as it rapidly cools

Question 8

what is a Volcanogenic Massive Sulphide (VMS)

Answer 8

A pod-like deposit formed from the black smoker

Question 9

why is it called Volcanogenic Massive Sulphide (VMS)?

Answer 9

its called this b/c its formation is associated with seafloor volcanism, and the orebody isn’t well defined in shape or structure (massive)

Question 10

how can some metal deposits be produced and what is an example?

Answer 10

by weathering and leaching

ex., bauxite (aluminum ore)

Question 11

Why is aluminum ore difficult to extract?

Answer 11

very abundant in continental crust but is generally so tightly bonded within silicate minerals

Question 12

Why was aluminum once an extremely valuable metal?

Answer 12

because it was so difficult to extract

Question 13

when did obtaining aluminum become much easier?

Answer 13

when it was discovered that aluminum also occured as an oxide mineral

Question 14

What is the Bayer Process?

Answer 14

process where the mineral Gibbsite is heated to drive off water, reacted with other chemicals under high heat, and an electric current is passed through a solution to seperate pure aluminum metal from bonded oxygen

Question 15

what is bauxite?

Answer 15

a highly weather tropical soil

Question 16

what is a simple sedimentary process that can form metallic mineral deposits?

Answer 16

minerals eroded from pre-existing rocks can be concentrated via physical transportation, sorting and deposition in clastic sediment deposits

Question 17

What happens to all rocks when exposed to weathering?

Answer 17

they break down to rock fragments and mineral grains. these mineral grains can include metallic minerals

Question 18

what are the rock fragments eroded from weathered rocks ultimately affected by?

Answer 18

downslope mass wasting and running water and transported downslope

Question 19

which areas are concentrated with gold and other heavy minerals?

Answer 19

areas affected by stream currents (light particles are washed away, thereby concentrating the larger and heavier particles in the bedload of the stream)

Question 20

when the stream flow suddenly slows ______

Answer 20

heavy particles settle out first

Question 21

how is panning done?

Answer 21

sediment and water are swirled and agitated in the pan and the suspended sediment is poured with the water

large particles are removed and panning is done again with smaller fractions

after washing a couple times, the residue containing the heaviest minerals is left behind and is called “pay dirt”

Question 22

what deposit does most of the iron mined today come from?

Answer 22

banded iron formation

Question 23

what are the characteristisc of banded iron formation?

Answer 23

actually composed of layers of iron oxide and chert
percipated as chemical sediment

banded iron formation doesn’t form today b/c the oxygen in the atmosphere rusts on land (so percipated before it can reach the sea)

most silica dissolved in sea is taken up by some organisms to make their skeletons so no longer deposited as true chemical sediment