Module 8

Question 1

What is an ore deposit

Answer 1

Rock where an unusually high concentration of an interesting compound/element has formed. It is economically viable to retrieve with available technology.
Does not include sand, gravel, limestone, clay, and gypsum deposits, despite their value as concrete/etc.

Question 2

What interesting compound/mineral is found and is referred to as the industrial minerals

Answer 2

Fluorite, borate and barite.

Question 3

Orthomagmatic Definition

Answer 3

Ortho means direct
Orthomagmatic means direct crystallization of magma. No partial melting, fractional crystallization, etc. The concentration of an orthomagmatic igneous rock reflects the original magma’s composition.

Question 4

Orthomagmatic ore deposit: Common compounds/elements found

Answer 4

-Orthomagmatic basalt intrusions can contain high concentrations of Platinum and Chromite.
-Orthomagmatic serpentinite diapirs (rises from subducting ultramafic oceanic crust) can contain high concentrations of chromite.
-An orthomagmatic igneous complex named Sudbury Igneous Complex is an impact structure where an asteroid’s impact caused melting in the mantle. Basalt dikes rose up through the overlying breccia, carrying up Nickel. Nickel is immiscible (does not mix well with magma) and thus recrystallizes into little blebs
-Diamonds in kimberlite pipes (xenolith in rising ultramafic intrusions)
-Gems and REE in pegmatites (magma forms large crystals over long period, but rare earth elements don’t fit into crystal structure)

Question 5

Komatiite: Time period capable of producing this rock, what is it

Answer 5

Archean Eon was only time mantle was hot enough.
Spinafex was the bladed texture specific to them. Texture looks like a a bundle of sticks with long radiating crystals coming from the center. High Mg, low SiO2

Question 6

Hydrothermal Ore deposit-Intrusion related

Answer 6

Porphyry copper
Magma rises, water is a volatile that extrudes and breaks up overhanging rock into a brecciated state. water carries up metals like Cu, Mo, and Au.
Ultimately, what’s left is a porphyritic intrusions with brecciated rock above where the fractures have had minerals precipitated in them in a crisscross pattern.
Skarn
If limestone is nearby, these waters will spread and precipitate minerals, creating a skarn. The minerals in the limestone are replaced by W, Fe, Cu, Zn
Polymetallic veins (Sn, Cu, Ag, Pb, Zn)
Epithermal Stockwork (Au, Ag, Hg)
Epithermal volcanigenic sulfide (Pb, Zn, Au)

Question 7

Hydrothermal alteration types

Answer 7

Potassic: Biotite, Orthoclase replaces feldspars; High pressure, high temperature
Phyllic/Sericitic: Fine grained white mica (sericite), quartz and pyrite; high temperature, high pressure
Argillic: Kaolinite (Clay)
Porpylitic: Calcite, Chlorite, Epidote, Albite; low pressure, low temperature

Question 8

Hydrothermal Ore Deposit-Associated to Tectonics

Answer 8

Lode Deposits in orogenic belts-orogenies cause regional metamorphism, which liberates heated water that precipitates gold veins in quartz
Carlin-type gold deposits in clay- Has argillaceous cap, limestone is altered with gold precipitation, pushes calcite out
Connate water can carry Pb and Zn out and create deposits outside sedimentary structures (Mississippi river)

Question 9

Sedimentary Deposits

Answer 9

Basin Wide
Chemical Precipitation-precipitation of minerals from solution due to chemical reactions
-Banded Iron Formations- Seawater precipitated iron in archean-proterozoic transition since atmosphere had 10% oxygen
-Phosphorites- from bones
-Borates/Lithium Brines- Playa lakes (dersert)
Placer Deposits (fluvial weathering takes large gems out of host rock)
-Diamonds, Gold
Supergene deposits
-Soil extreme leaching accumulates aluminum or nickel; Bauxite soil
Supergene enrichment-accumulates copper in water table

Question 10

What is Petroleum

Answer 10

AKA Crude Oil, low density, viscous, liquid mix of hydrocarbons.

Question 11

Classification of Petroleum:Types, how they differ

Answer 11

Differ by how many Carbon atoms per molecule
Natural Gas-1 to 4 atoms
Aromatics/Paraffins-5 to 35 atoms
Asphalts-35 to 60 atoms

Question 12

How petroleum forms

Answer 12

Not dinosaurs.
Unicellular algae, typically trapped in clay (black shale) beneath oceans or lakes.

Question 13

Age of Petroleum deposits (mostly)

Answer 13

Cenozoic, with some mesozoic and few paleozoic
cant go deeper than 6 km or it turns into gaseous state and dissapears.

Question 14

What geophysical methods are used to find basins

Answer 14

Gravimetry, Magnetometry

Question 15

Range of depth and temp for oil, and age

Answer 15

50 130 degrees celsius
1.5 to 4.5 kilometers depth
Cenozoic age

Question 16

“Recipe” for Petroleum

Answer 16

The Source:A sediment rich in organic material (black shale)
The Kitchen: Correct Depth, Temperature for it to cook.
The reservoir: Has been expelled into a porous and permeable medium FROM the shale, since shale is impermeable so you can’t retrieve the oil.
The Cap: An impermeable cap or aquitard for oil that stops the oil from leaking onto the surface. Often happens when you have a transgressive marine facies, covered by shale.
The trap: These reservoirs are mostly anticlines. They often have an impermeable cap. It is flanked by Saline water. Oil is less dense so it rises to the top of the anticline.

Question 17

Traps

Answer 17

Anticlines, faulted anticlines, salt domes (salt rises due to buoyancy in a diapir shape), “pinches”

Question 18

Petroleum Play, and Petroleum System

Answer 18

2 different philosophies on defining potential petroleum reservoirs.
Petroleum play defines all 5 components to show an example of where petroleum could be.
Petroleum system only defines the source rock, then lists possible environments that source rock could charge with oil.