midterm Flashcards
(47 cards)
what is the geochemical approach?
a problem-solving exercise using qualitative and quantitative geochemical data
How do we measure geologic time?
relative dating and geochronology
how does geochronology work?
radiometric dating
relies on the decay of radioactive parent isotopes into stable daughter isotopes at a predictable rate
ex: U-Pb dating
how does relative dating work?
A inclusion in a rock is younger than B due to cross-cutting relationships
what are the societal challenges relating to geochemistry?
Base metal (Pb, Cu, Zn) deposits
clean energy technologies
what is clifford’s rule? why is it important? examples?
“Economic concentrations of ore minerals, particularly magmatic sulfides, are found only in mafic or ultramafic rocks that have undergone sulfur saturation.”
ex: Sakatii (finland) sulfide deposit
how are diamonds made? where do we find them?
When the lithosphere dips below the diamond-graphite stability line, diamonds form. Diamonds are xenocrysts, meaning they are not formed within kimberlites but are instead transported to the surface by them. Kimberlites originate from the deep mantle and act as the primary host rocks for diamonds.
For diamonds to exist, the lithosphere must be thick enough to extend into the diamond stability field. Peridotite xenoliths are commonly found in kimberlites and provide insights into the mantle conditions.
how are kimberlite pipes helpful in prospecting? indicator minerals?
In Canada, due to glaciation, many kimberlite pipes are buried beneath thick layers of till. As a result, kimberlite indicator minerals (KIMs) are used for prospecting. An example of an indicator mineral is ilmenite. The composition of ilmenite from Kirkland Lake kimberlites and the overlying glacial sediments can help trace buried kimberlites.
how do peridotites relate to diamond exploration?
When searching for diamonds, peridotite is a key rock type to look for because it is the most common rock in the upper mantle. Peridotite is primarily composed of olivine, orthopyroxene, and clinopyroxene but lacks aluminum (Al) and potassium (K), meaning these elements must be hosted in other minerals within the peridotite.
Peridotites can be classified based on their mineral composition:
- Lherzolite –
- Harzburgite
in general, what are the properties used for metal deposit prospecting
Indicator minerals - minerals that are associated with the deposit that can be used for prospecting.
pathfinder elements- elements that are associated with the target element which can be used in prospecting
the secondary geochemical environment (above water table)
The primary geochemical environment - below water table, halo around mineral deposit
Mineral deposit - an anomalously high conc of an element of societal value
Lherzolite?
peridotite
Lherzolite – Contains olivine + orthopyroxene + clinopyroxene.
Harzburgite?
peridotite
Harzburgite – Contains olivine + orthopyroxene (lacks clinopyroxene).
Harzburgite is considered to have a higher diamond potential than lherzolite due to its association with deep, depleted mantle conditions.
Types of Peridotite?
Peridotites are classified based on their aluminum (Al)-bearing mineral phase, which varies with depth:
Plagioclase peridotite → Shallowest (low pressure, found in the upper lithosphere)
Spinel peridotite → Intermediate depth (found in the lithosphere)
Garnet peridotite → Deepest (high pressure, found in the lower lithosphere and asthenosphere)
At the Earth’s surface, plagioclase is the stable aluminum phase. However, as depth and pressure increase, spinel replaces plagioclase, and at even greater depths, garnet becomes stable
why do we look for garnet peridotite? why do we use it as an indicator mineral?
Diamonds form below ~5 GPa (about 150 km depth), which corresponds to the stability field of garnet peridotite.
Garnet peridotite is a key indicator rock when exploring for diamond-bearing kimberlites
Once garnet is found, its chemical composition must be analyzed.
Specific garnet compositions (e.g., high Cr-content G10 garnets) are associated with diamond stability conditions.
Garnet serves as an indicator mineral for tracing diamondiferous kimberlite pipe
Atomic mass
Atomic Mass Unit (AMU): Defined as mass relative to a carbon-12 atom.
In reality, the mass of a nucleus is always less than the sum of the individual masses of its protons and neutrons.
Example: The theoretical mass of a ²³Na nucleus is calculated as:
(11×massofprotons)+(12×massofneutrons)
(11×massofprotons)+(12×massofneutrons)
However, the observed atomic mass is slightly less, indicating a mass deficiency.
Where does the mass go in atomic mass deficiency?
This “missing mass” is converted into nuclear binding energy, the energy released when the nucleus forms from its nucleons (protons + neutrons).
Nuclear binding energy can be calculated using Einstein’s equation:
𝐸=𝑚𝑐^2
Nuclear Binding Energy Curve
The nuclear binding energy curve shows how tightly nuclei are bound together.
Iron (Fe) has the highest nuclear binding energy, making it the most stable element.
Implications:
- Fusion occurs up to iron (Fe), but elements heavier than Fe cannot be formed by fusion.
- Fission involves breaking apart heavy nuclei, releasing energy
The chart of nuclides
Represents different nuclear species based on proton and neutron numbers.
Does not account for electrons.
Shows isobars, isotopes, and isotones
classification of nuclides
Isobars: Same atomic mass but different elements.
Isotopes: Same number of protons but different number of neutrons (rows on the chart).
Isotones: Same number of neutrons but different elements (columns on the chart).
stable vs unstable nuclides
stable nuclides (stable isotopes): The nucleus remains unchanged over time.
Unstable (radioactive) nuclides: The nucleus spontaneously transforms into a different nucleus (i.e., a different element).
the band of stability
There are about 1400 known nuclides, but only ~270 are stable.
Even numbers of protons and neutrons increase stability: 168
Odd numbers of both protons and neutrons are rare, with only 4 stable nuclides.
The band of stability sits below the neutron = proton line on the nuclide chart.
bohr model of the atom
The energy of electron orbits is quantized, meaning electrons can only occupy specific energy levels.
Schrodinger’s model of the atom
Electrons are not in fixed orbits but exist in probability fields, forming an electron cloud around the nucleus.
This model is explained using quantum mechanics and describes the behavior of electrons in orbitals.
the four quantum numbers describing electron orbitals.
Principal Quantum Number (n = 1,2,3,4, etc.)
- Defines the size (volume) of the orbital.
Azimuthal Quantum Number (ℓ = 0 to n-1)
- Defines the shape of the orbital.
ℓ = 0 → s-orbital (spherical)
ℓ = 1 → p-orbital (dumbbell-shaped)
ℓ = 2 → d-orbital (complex shape)
ℓ = 3 → f-orbital (even more complex shape)
Magnetic Quantum Number (m = -ℓ to +ℓ, including 0)
- Defines the orientation of the orbital in space.
Spin Quantum Number (±½)
- Defines the spin of the electron (either +½ or -½).
