General

Question 1

Syngenetic Deposits

Answer 1

This term describes terms that were formed at the same time as the host rocks. They are most commonly sedimentary.

Question 2

Epigenetic deposits

Answer 2

These are ores that form after the host rocks. This is common within metasomatic and vein-related deposits.

Question 3

Hypogene and supergene deposits

Answer 3

Hypogene: ores that form because of an ascedning solution Ex: Mississippi-style Pb-Zn
supergene: ores that form because of a descending solution. Ex: meteoric waters in Bisbee

Question 4

Endogenetic and Exogenetic

Answer 4

Endogenetic refers to ores that form because of internal Earth processes. These are metamorphic or igneous processes.
Exogenetic refers to ores that form because of Earth surface processes, likely exogenetic. These are driven by external energy sources (primarily the sun).

Question 5

Associations of ultramafic, intrusive mafics, intrusive intermediates, and felsic intrusives with ores

Answer 5

UMF: Ni, Cr, Pr
Intrusive mafics (gabbro + niorite): Cu, Co, Ni, Fem Ti, V
Intrusive intermediates (andesites): Cu, Au
Granites: Be, Li, Sn, W

These differentiation of elements is driven by fractional crystalization within the Goldschmidt series.

Question 6

Economic Geology

Answer 6

The branch of applied geology concerned with the discovery, understanding and extraction of non-fuel resources from the Earth

Question 7

Mineral deposits

Answer 7

Earth materials that contain anomolous amounts of minerals or elements

Question 8

Ore deposits

Answer 8

Ore deposits or economic deposits are reflective of human need for the mineral and represent a sub-sector of mineral deposits that we mine. They are made of one or more ore bodies.

Question 9

World-class deposits

Answer 9

These are deposits in the uppermost 10% of the grade, tonnage plot (meaning the upper 10% of total reserves) they are important because as size increases economies of scale magnify and they also provide usually >70% of the supply of the mineral resource

Question 10

Periodic table trend: atomic radius

Answer 10

Atomic radius increases in the lower left of the table, francium is the largest

Question 11

Enrichment factor meaning

Answer 11

This is the ratio of the concentration of the element within ore deposits divided by the crustal abundance. Generally as crustal abundance decreases the enrichment factor increases.

Question 12

Trace metal abundance curve vs. major

Answer 12

The major elements follow a normal curve and ore deposits are on the uppermost tail. Trace elements are bimodal with the higher grade hump’s right tail being those that are ore deposits.

Question 13

$/ton of ore vs. tonnes production

Answer 13

As the $/tonne increases the tonnes produced decreases. Ex: Rhenium and diamonds have very few tonnes produced but have a major $/tonne value. Iron is produced in mass with a low $/tonne

Question 14

Ore minerals

Answer 14

These are minerals that are either opaque in thin section (according to normal geologists) or those that contain economically important minerals

Question 15

Mineral assemblages

Answer 15

These represent a form of chemical equilibria where the minerals co-evolve. They are usually intergrown, replace one another, and obey the phase rule.

Question 16

How can we plot most rocks in terms of their composition?

Answer 16

There can be a plot of the summation of (Ca, Mg, Fe2+) vs. summation of K and Na.

Question 17

Equilibrium

Answer 17

This describes a state without a spontaneous tendency to change. It can be stable, metastable, or unstable but always reflects some type of minima of PE.

Question 18

Chemical Equilibrium

Answer 18

This is where delta G is at a minimum

Question 19

Phase Rule

Answer 19

Prescribes the maximum number of phases (fluid, solid, or gas) at equilibrium through f=c+p-2 where c= # of components, p = #of phases, f= degrees of freedom

Question 20

Mineral Associations

Answer 20

These are minerals that often co-occur but are not always at equilibrium with one another upon formation.

Question 21

Goldschmidt Classification

Answer 21

Lithophile - elements that bond with oxygen - silicates and oxides
chalcophile - elements that bond with sulfur - MS
siderophile - Native elements, alloys, or with Fe
atmophile - gaseous elements

Question 22

Elemental partitioning

Answer 22

A term describing how minerals separate during phase changes. Generally, smaller radius low chare ions that substitute into Fe, Mg, Ca sites will be sequestered in the mantle and larger ions will make it to the crust.

Question 23

How do sizes of ions change with charge and with position in the periodic table and why is this important in crystals?

Answer 23

Cations are much smaller than anions so the anion-anion repulsion of atoms around a central cation is the major determinant of crystal structure. This means that the cation size (which dictates the distance between anions) is important.

Question 24

List the major mineral groups and what distinguishes each group

Answer 24

Oxides- MO_{x atmophile
Sulfides - MSx S <-> O at shallow depths or under oxidizing conditions
Sulphates - Mx (SO4)x
Carbonates
Phosphates
all three are potentially water soluble and form in acidic conditions
Salts
Silicates - Mx Sx Ox the most common mineral group in the crust
Native minerals - always CCC}

Question 25

What general principle governs substitutions in minerals?

Answer 25

Pauling’s rules;
1. the coordination number of the cation/anion is determined by the ration of their raii
2. bond lengths are determined by ionic charge and coordination number
3. shared polyhedra faces are less stable
4. higher valency cations are less likely to share faces
5. There are a few select types (size, charge) within a crystal.

Question 26

What are the three major geotherms?

Answer 26

Subduction zones - low T - ultrahigh P, goes through blueschist and eclogite facies ~10 C/km
Continental crust - Average ~ 22 C / km goes through the greenschist and amphibolite facies to eventually become granulite
Magmatic arc - high ~50 C/km These border greenschists and hornfels

Question 27

What is the brittle-ductile transition?

Answer 27

It is the point below the surface where rocks start behaving like viscous fluids mechanically, basically it is where they no longer follow Mohr-Coloumb failure criterion and instead deform indefinitely following fluid mechanics.

Question 28

Nernst Partition Coefficient

Answer 28

This is the ratio (K_{i^{a/b = ci a / ci b ) where c is the concentration of element i in phase a or b.
It is dependent on T, P, and composition but generally assumed constant for a given stage of magmatic evolution.}}

Question 29

Bulk solid to liquid partition coefficient

Answer 29

D = Σ f ⁱ K _i^x where fⁱ is the fraction of the element x in the system (not only in one phase.

Question 30

Element compatibility

Answer 30

This is the degree to which an element will substitute into the crystal lattice of a phase in a system. It is defined by K where if K>1 it is incompatible and there is more element in the melt than in the solids.

Question 31

Bowens Reaction Series

Answer 31

This is the tendency for mafic rocks and plagioclase (high Ca, Mg, and Fe ²⁺ ) crystalize at high temperatures deep underground and the silica rich rocks and K-spar crystalize at low temperatures near the surface