Lecture 10 mineral resources and mining s

Mineral Resources and Mining
Click here for current mine news, pri
ce forecasts

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This is one of three employment centers
for geologists, and it is presently enjoying
a boom. The other boom employers are:

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The Petroleum Industry

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The Environmental Industry


Mineral Resources and Mining
Some definitions:

• Ore, Ore Mineral, Gangue, Resource < Reserve
• Reserves are profitable and also technically & legally extractable
• Commodities Au, Ag, Al, Coal, crude oil, Iron ore
• Is it profitable, i.e. “economic”? Consider futures price, costs of energy,

infrastructure, labor, processing and environmental protection & cleanup. To do
that we consider grade, type of deposit and type of processes feasible, special
environmental problems, etc.

Prospecting, Exploration & Development, Mining: often different
companies. Who should you work for when starting out?
Current conditions: Gold at 30 year high, crude oil futures near
record prices
As a geologist, you should keep an eye on Mineweb.com
Units 1 Metric Ton AKA tonne= 10^6 grams therefore a grade of 1 g/T = 1 ppm


Some Important Ores and a deposit
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Native Ores: Gold Au, Copper Cu, Platinum Pt
Base Metal Ores: Bauxite (mostly Gibbsite Al(OH)3),
Hematite Fe2O3, Magnetite Fe3O4
Sulfide Ores: Silver as Argentite Ag2S, Copper as
Bornite Cu5FeS4, Chalcopyrite CuFeS2, or Chalcocite
Cu2S, Mercury as Cinnabar HgS, Lead as Galena PbS,
and Zinc as Sphalerite ZnS
Oxide Ores: Uranium as Uraninite UO2, Titanium as
Ilmenite FeTiO3,
Deposit: Kimberlites for Diamond C

Steps in obtaining mineral commodities
1. Prospecting: finding places where ores occur.
2. Mine exploration and development: learn whether
ore
can be extracted economically.
3. Mining: extract ore from ground.
4. Beneficiation: separate ore minerals from other mined
rock. (Mill)
5. Refining: extract pure commodity from the
ore mineral. (Refinery)
6. Transporation: carry commodity to market.
7. Marketing and Sales: Find buyers and sell the
commodity.


Mining is an economic activity.
The decision to mine (or not to mine) a particular ore
deposit depends upon:
an analysis of costs, benefits and risks
These considerations are both:
• tangible (i.e. dollar profit)
and
• intangible (i.e. hopes of stimulating the economy,
fears of environmental damage)


3. Prospecting: finding where ores occur
Important Factors:
• Applying knowledge of association of ores with
specific geological settings.

• using remote sensing techniques such as satellite imagery, seismic reflection
profiles, magnetic field intensity, strength of gravity to detect geological
structures.
• photos useful in finding faults.
• small basaltic intrusions have prominent magnetic anomalies.
• dense ore bodies can have prominent gravity anomaly.
• developing detailed maps of rock types and geological structures (faults, folds,
intrusions).
• developing 3-d picture of geological structures containing ore.
• obtaining samples of ore for chemical analysis.

•W HERE DO W E LOOK ?


A review from your Geology 1200 Course
Recall that several processes can produce
magmas. All are initially basaltic in
composition. Basalts contain minor amounts
of precious metals.

Late Fractionation Pegmatites
Hydrothermal MOR


Au, Ag

MOTHER LODE

Magmas can form near
subduction zones when

water causes partial
melting of nearby
mantle. Granitic
magmas form by
fractionation of basaltic
magmas and by
assimilation. Once the
granite has frozen,
silica-rich late
fractionation waters
with dissolved metals
are left to intrude
nearby rock.
Most searches near continental volcanic arcs
e.g. Andes (Inca Gold) , Sierra Nevada (1849 gold rush)


Initially Basaltic, rising magma may become silica-rich through two processes.

Fractionation and Assimilation

Assimilation

Fractionation

Granitic melt genesis


Au, Ag

Metal-rich waters may originate from the magma or groundwater

Metal ores precipitate
near surface

Heated
groundwater
dissolves metals

Two mechanisms for metals emplacement near granitic intrusions (both occur)


Gold Ore

Ore mineral Gold Au

Gangue Mineral Quartz

Popular term “Mother Lode” initial placement
Ore Body


Placers: Gold is concentrated as a detrital sediment


Magma 2: formation at divergence zone

Black Smoker
on cracks near magma

MOR

Seawater gets into
cracks, heats up near
magma, dissolves metals Cu, Fe, etc
in mafic rocks, convection
currents return hydrothermal
waters to cold ocean waters
(also ion-rich). Sulfides precipitate
forming a Black Smoker
Decompression melting


Cu, Fe

Black Smokers
Example:
Sterling Hill

Island of Cyprus made of
Ophiolites with black smokers.
Source of copper that started
bronze age

/>Circulation of hot water in cracks at mid-ocean ridge dissolves metals in Basalt, (Copper, Iron, Zinc, Lead,
Barium) which are re-precipitated as various ores, often Sulfides. Accumulate in ocean sediments.


Magma formation 3: Plumes

Diamond exploration


C (diamond)

Subduction zones pull carbon down to depths necessary for Diamond
formation. Plumes rise from depths far below diamond formation depths. A
plume cutting across subduction zone will lift diamonds to the surface
Diamond exploration


Seamount Trails point to the Kimberlite

Plumes cause straight chains of seamounts on the ocean floor
The Atlantic rift has moved America west of several plumes.
These were once under the continent, sometimes under old subduction zones.
Use chains of seamounts to point to old positions of the plumes’ “hot spot”.
Extend those lines onto North American continent
Find where those projected lines cross sutures between PreCambrian Cratons
assembling North America. Now use Google Earth to search for Maars
Here is a set of links related to this topic:

Diamond exploration


Includes Bauxite enrichment from Laterites


Concentration of Aluminum as Bauxite Ore

From a Laterite similar to the one outside

Gibbsite Al(OH)3 is the main mineral in Bauxite ore


Petrology Field Trip to Bemco Mining District


2. Mine exploration and development: learn
whether ore can be extracted economically
• Define size, shape and grade of ore body.
Grade, G: mass of commodity per mass of ore.
Gold: 5 grams of Au per metric ton (106 grams of ore)
Grade = 5 x 10-6.
Aluminum: 400 kg of Al per metric ton of ore, G=0.4
• Drill cores, though expensive, can be used to determine
underground extent of ore
Estimate the mass of the commodity:
= volume of ore body x density of ore body x grade).
1 metric ton = “tonne” is 1000 kilograms


Design a profitable plan for mining.
/>
• Selecting appropriate mining techniques are just a
small part of it!
11 meters of core at 3.6 grams per
metric ton

• analysis of requirements to startup mine:

• capital, transportation, labor, cost of processing,
etc.
• complying with governmental regulations.
• mitigating environmental damage.


You MUST know
what you have, to
make a plan


3. Mining: extract ore from ground
• Types

of Mining:

• Surface Mining: Scoop ore off surface of earth.
• cheap.
• safe for miners.
• large environmental destruction.
• Underground Mining: Use of adits and shafts to reach deeply
buried ores.
• expensive.
• hazardous for miners.
• usually less environmental damage.


Gradual
shift toward
surface mining

Coal
mine
types
COAL