22 resources

7/29/2019 22 Resources

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Geologic Resources Many rocks and contained fluids have useful properties (e.g., quartz [abrasive], flint [tools], water) or canbe used as an input to chemical processes (e.g., hematite [iron ore], or crude oil [fuels, plastics]). All suchmaterials extracted from the earth (as opposed to grown) can be called ores or natural (earth) resources.

Most elements, even the 8+2 common elements, have to be concentrated above their overall abundancelevel to be usefully extracted, mainly because the purer form is cheaper and someone will sell it. Ores are

mined in response to human needs/desires, and are sought in response to anticipated demand and profit. A substance that is mined (or sought) is called a mineral (mining sense) Minerals (mining sense) are formed in a variety of geological settings, and usually involve unusually-high

available concentrations of a particular substance or unusual physical or chemical state.

v 0036 of 'Geologic Resources' by Greg Pouch at 2011-04-12 09:43:10LastSavedBeforeThis 2011-04-12 09:39:58C:\Users\GregAdmin\Documents\Geo101\22Resources.ppt on'GWPOUCHDELL1720'


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Geologic Resources3 Amounts of Earth Resources Used Annually in US4 Vocabulary

5 Vocabulary Diagrams

6 Mineral Economics in one over-simplified lesson7 Reserve Depletion

Graphs ( 8 Chart of crude oil prices since 1861; 9 Crude oil prices since 1861 ; 10 Price of Oil vs. Time ;11 US Proven Oil Reserves for 20th Century ;12 US Proven Oil Reserves for 20th Century ;13 Oilreserves-to-production (R/P) ratios ; 14 Oil reserves-to-production (R/P) ratios )

15 Classification by Use and Economics16 Classification by Geologic Origin

Sedimentary17 Sedimentary Processes > Organic Remains

18 Sedimentary Processes > > Fossil Fuels > Coal19 Sedimentary Processes>>Fossil Fuels > Petroleum20 Sedimentary Processes>>Fossil Fuels > Petroleum

21 Sedimentary Processes22 Sedimentary Processes>Weathering

23 Igneous Processes24 Metamorphic25 Hydrothermal/Metasomatic Fluids

26 Hydrothermal Diagrams27 Plate Tectonics

28 Plate Tectonics Map29 Divergent Boundaries30 Convergent Boundaries31 Greenstone Belts

32 Mineral exploration

33 Summary


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Amounts of Earth Resources Used Annually in US The overwhelming majority of solids is industrial minerals.

This does not include fuels (about 8 tons) or water (about 1,000 tons per capita, or 243 tons excluding

industrial users and agriculture).

Most of the consumption goes into building materials for roads and buildings.


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VocabularyOre a.k.a. Mineral (mining sense) A mineral (geological sense) oraggregate of minerals, more or less mixed withgangue, which can be won (extracted) at a profit ortreated at a profit. (Treasure)

Gangue Non-valuable minerals associated with ore. (Trash, junk)Country rocknon-valuable minerals not associated with ore but surrounding it.(Backdrop)

Deposit (subjective) A concentration or occurrence of a substance in sufficient degreeof concentration and of sufficient extent to warrant attention. Geologists look for

mineral and oil deposits.Reserve (Objective but conditional, has financial/legal implications) A deposit of amaterial that can be extracted legally and economically at the time of determination.This is primarily an economic/engineering term, meaning a deposit you can turn a profit

by extracting the deposit. Mineable.Reserves the sum total of all known reserve depositsResource (Conditional and subjective) A deposit that is currently or potentiallyfeasible.

Resources the sum total of all known reserve deposits, and known and unknownresource deposits. (It includes all deposits that can be mined, some resources that cannotnow be mined feasibly but could if prices or technology changed, and an estimate ofundiscovered deposits based on theories about the occurrence of the commodity and thedistribution of favorable environments.)


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Supply (Objective and not conditional) total amount on the planet. Estimates are based on ourunderstanding of the composition of the planet. [Open to better term.] This is NOT "supply" in"supply and demand".

Proved: (=tested, measured) having reliable quantitative and qualitative estimates. (e.g. part of agas field whose extent has been delimited by drilling and whose composition has been measured.(Bird in the hand)

Exploration: initial finding of a deposit (looking for bird in the bush)A description of the formation and properties of a type of ore body is known as an

exploration model, and is vital to exploration and production. It is often named after aparticularly well-known or well-studied deposit, or after the process for generating thedeposit, like Kidd Creek massive sulfides from black smokers where hydrothermal fluidserupted underwater and precipitated the sulfides in strata, or hydrothermal gold veins whereboiling hydrothermal fluid precipitates gold at the zone of boiling, or buried bedrock valleyaquifers.

Development/Production/Management: detailed investigations carried out to help withexploitation (feeding and tending the bird in the hand)


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Vocabulary Diagrams

Banded Iron Formation

Extracted

Geologic-total="Supply" is the total amount on Earth.

Resources are subset of Supply.

Reserves are subset of Resources.

Some stuff already extracted would not be profitable now, so

would not be reserves, maybe not even resources.


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Mineral Economics in one over-simplified lessonIncreasing the value of a mineral usually increases its supply. Increasing the cost of a mineral usually leads

to less being found and developed.

There is almost always a significant lag-time between starting a mining operation and initial delivery, so

there are often dramatic short-term fluctuations in price super-imposed on an overall downward trend in

price for most minerals. Value of a mineral is related to:

Intrinsic copper is more valuable than sand. (a.k.a. unit value)

Time (the sooner, the better) Ore delivered next year is more valuable than ore delivered in 10 years.

Because exploration must be paid for up-front, interest rates are often the limit on reserves

Place (closer to consumer the better) Limestone in Chicago is more valuable than limestone in Fairbury.

For industrial minerals, the intrinsic value is usually very low compared to the place value

Costs are due to:

Exploration and Research

Production (salaries, equipment, fuel, supplies, processing costs)

Failures (dry holes, empty workings,)Transportation

Capital

Clean-up costs

Taxes

Much equipment and labor must be paid for before any production begins: this contributes to time value.

Shipping costs go into place value.

R D l i


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Reserve DepletionThere are several ways to deplete (reduce) reserves. (This assumes no recycling). Extract and don't replace (either no exploration or unsuccessful exploration) Make known reserves or resources illegal

banning mining in national forests or public lands or offshore Make known reserves uneconomic

declining prices/demand (alternatives, Depression)increasing extraction costs for labor or capital or shipping or regulatory compliance Make unknown resources unavailable

banning exploration or making it more expensiveGenerally, the opposites will increase reserves. Improved exploration models, exploration techniques, and

improved extraction techniques also increase reserves.


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Chart of crude oil prices since 1861


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Crude oil prices since 1861


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Price of Oil vs. Time

BP's Petroleum Price vs Time

$0

$20

$40

$60

$80

$100

$120

Year AD

Price

MoneyOfTheDay Price

Inflation-adjusted_2007 Price

Petroleum Prices from BP's Statistical Review of World Energy 2008 at http://www.bp.com/productlanding.do?categoryId=6929&contentId=7044622

h
http://www.bp.com/productlanding.do?categoryId=6929&contentId=7044622http://www.bp.com/productlanding.do?categoryId=6929&contentId=7044622


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Data from http://tonto.eia.doe.gov/dnav/pet/xls/PET_CRD_PRES_DCU_NUS_A.xls

US Crude Oil Reserves

0

5,000

10,000

15,000

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35,000

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45,000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

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MillionsofBa

rrels

0

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30

35

40

Years

U.S. Crude Oil Proved Reserves (Million Barrels)

U.S. Crude Oil Estimated Production from Reserves (Million Barrels)

US Reserves to Production, Years

US Proven Oil Reserves for 20th-21st Century

th
http://tonto.eia.doe.gov/dnav/pet/xls/PET_CRD_PRES_DCU_NUS_A.xlshttp://tonto.eia.doe.gov/dnav/pet/xls/PET_CRD_PRES_DCU_NUS_A.xlshttp://tonto.eia.doe.gov/dnav/pet/xls/PET_CRD_PRES_DCU_NUS_A.xls


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US Proven Oil Reserves for 20th Century

0

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10000

15000

20000

25000

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35000

40000

45000

50000

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Date

MillionsofBarrels

0.00

10.00

20.00

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U.S. Crude Oil Proved Reserves (Million Barrels) from DOE>EIA

PricePerBarrel In 2003USD from BP

US Proved Oil Reserves are from US Dept. Energys Energy Information Agency, http://tonto.eia.doe.gov/dnav/pet/pet_crd_pres_dcu_NUS_a.htm

Price of oil is from last years Statistical Review from BP http://www.bp.com/downloads.do?categoryId=9003093&contentId=7005944
http://tonto.eia.doe.gov/dnav/pet/pet_crd_pres_dcu_NUS_a.htmhttp://tonto.eia.doe.gov/dnav/pet/pet_crd_pres_dcu_NUS_a.htmhttp://www.bp.com/downloads.do?categoryId=9003093&contentId=7005944http://www.bp.com/downloads.do?categoryId=9003093&contentId=7005944http://tonto.eia.doe.gov/dnav/pet/pet_crd_pres_dcu_NUS_a.htm


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Oil reserves-to-production

(R/P) ratios

Oi i ( / ) i


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Oil reserves-to-production (R/P) ratios

Classification b Use and Economics


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Classification by Use and Economics Water Soil Fuels are the only resources that are consumed, since it is their high-energy molecular state, and not the

actual atoms, that are sought, and they will converted to lower energy states in use (burning)The vast majority of energy consumed in the industrial world comes from fossil fuels. In the non-

industrialized nations, fuel mainly comes from wood or other organic fuels. We currently have hundreds

of years of coal reserves (Coal could be easily replaced for electricity with nuclear fission), decades ofoil reserves and, depending on what you call potentially feasible, decades to hundreds of years of oilresources.

We have been about to use the last oil for over a hundred years so far, and yet it is still rather cheap,especially when normalized to inflation or labor. Technology will continue to improve and we will keepfinding new reserves and extracting more from old ones, possibly at higher costs.

Because liquid fuels are rather convenient for vehicles, if we ever do replace crude oil, it will probably bewith coal-generated synthoil or with biogenic fuels like corn or soybean oil or ethanol.

Metallic ores are desirable for the contained elements and usually require refining.Mineral deposits often involve a high degree of concentration. This is often occurs due to sudden,

localized changes in chemistry, especially phase changes like ex-solution, vaporization, and weathering.Most metals occur in many different types of deposits. For example, gold can occur in veins, or as placer

deposits in stream sediments, where gold veins are weathered and the gold flecks are concentrated withcoarse sand in river bed.

Industrial minerals are rocks that are not refined before use. They have low intrinsic value, and most areused in huge quantities. (This is a very vague classification.)Mainly what separates them from metals are materials that are useful as is; the mineral/crystal/rock itself

is used, rather than something obtained from it. Emery (a mixture of corundum and garnet) is soldbecause garnet and corundum are hard, not because of the contained aluminum silicon, and iron.

Industrial minerals include gravel (a size range), sand (size or composition), clays for ceramics,limestone, fluorite, quartz for electronics, phosphate, salt, and abrasives. These are used in HUGEquantities for building materials and in other industrial processes, usually without much additional

processing.Typically, industrial minerals are unusually high concentrations of some industrially useful mineral orrock in a ood location with hi h urit .

Cl ifi ti b G l i O i i


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Classification by Geologic Origin Sedimentary

Organic Remains

Evaporites

Precipitates

Clastic Sediments

Weathering Products

Soil

Groundwater

Residuum

IgneousPrimary Minerals

Mineral Settling

Magmatic Segregation

Hydrothermal

Metamorphic

Hydrothermal

Minerals (like graphite and garnet)

S di t P > O i R i


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Sedimentary Processes > Organic Remains Organic Remains Many ores are accumulated organic debris, maybe altered by geologic processes.

Reduced compounds (hydrocarbons, lipids, and such) can be preserved if the organic matter (deadorganism or fecal matter or leaves) is deposited under reducing conditions. If slightly more oxidizingconditions, reduced organic matter like sugars and lipids might be rapidly eaten, but other constituents,such as phosphate or nitrate, may accumulate. Under fully-oxygenated conditions, only indigestibleconstituents (calcite or silica shells) are likely to accumulate. Organic-remains ores include phosphaterock and limestone, and fossil fuels.

Phosphates are mined from rocks, usually shales or limestones, that contain unusually highconcentrations of the mineral apatite (Ca5(PO4)3(F, OH, Cl, CO3) ). Mostly used for fertilizer, somechemical feedstock. Sometimes, this is nearly pure apatite, in which case it is called phosphorite,sometimes it is mixed with enough calcite or clay to be limestone or shale.

Phosphate accumulation is associated with oceanic upwelling (cold, oxygen and nutrient rich bottomwaters coming to the surface, as happens off Peru). Under such conditions, there is a great profusionof life, and consequently death. Organic remains (soft-body parts, bones, fecal matter) sinks to thebottom. The great abundance of incoming organic matter may overwhelm the ability of bottomorganisms to consume this rain of food, and some goes undigested. Under anaerobic conditions, thereduced organic matter remains. Under slightly more oxidizing conditions, the reduced organic mattergets consumed, but the phosphate remains. Under normal oxidizing conditions, the phosphate getsconsumed or dissolved into seawater.

Limestones are accumulated shells of organisms. Limestone is quarried as cement-ore, for buildingmaterial, and as road-bed material (filler). Surprisingly much mining is of limestone, gravel, and sand.

Diatomites and Chert are also accumulated shells of organisms. Diatomite is mainly mined for use as afiltering agent and for Kitty Litter. Chert was used mainly in making stone tools with a cutting edge; notimportant in most places anymore, but chert and obsidian used to be big business.

S di t P > > F il F l > C l


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Sedimentary Processes > > Fossil Fuels > Coal Organic Remains

Coal is dead wood and leaves that accumulated in swamps (reducing conditions), underwent someorganic decay and geologic alteration. Peat is nearly unaltered wood and leaves. With heating andcompression, it alters (loses volatiles), becoming

brown coal->lignite->bituminous coal->anthracite->graphite (not coal)

Coal requires abundant plant growth, with remains accumulating in anoxic conditions (swamps). Illinois coals accumulated in low, coastal swamps in a shallow sea. Rises and falls in sea level

resulted in changing depths (and hence sediments) at a fixed location, so a series of cyclothems (cycliclayers of terrestrial and marine sandstones, clays, limestones, and coal, all deposited close to sea level)accumulated. Some of these cyclothems can be traced from the East Coast to Iowa.

The steep, bright-red hills on I-55 before Joliet are tailings piles (gangue) from coal mining. They arebarren due to high acid production from the weathering of pyrites associated with the other layers inthe cyclothems.

Sedimentar Processes> >Fossil F els > Petrole m


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Sedimentary Processes>>Fossil Fuels > Petroleum

Source (this is an oil shale)

Trap

Cook

Migrate

Petroleumincludes oil, natural gas, and tar sands. These are cooked, fluid remainsof reduced organic matter. Because they are liquid, they tend to move and are onlypreserved if they are trapped by the permeability distribution in a reservoir.

Formation(organic matter accumulates, oil cooks off it, oil migrates to oil trap or out)Organic matteraccumulates in fine-grained, low-permeability sediments, either

due to very high abundance of organic matter raining down overwhelming thesupply of oxygen, or low initial oxygen concentrations. [Most organic matterdoesn't get preserved] This organic mater progresses from dead organisms(fairly small molecules) to stuff very much like soil organic matter, and finally,with burial and heating, to kerogen (a type of organic matter found in rocks,HUGE molecules of various other biogenic molecules welded together, withmost of the oxygen, sulfur, phosphorous, and nitrogen missing [eaten by earlydigesters]) At this point, you have asource bed, which may be an oil shale.

With continued burial and heating, chunks of the kerogen molecules arecookedoff. These are the constituents of oil. With continued heating, more stuffbreaks off, and the oil molecules break down, and you get methane, oreventually, just carbon.

These oil droplets or gas bubbles somehow migrate into permeable sandstoneor limestone conduit beds. If nothing stops them, they migrate right to thesurface (due to their low density) and form oil seeps. Loss of volatiles andpartial digestion by bacteria can result in a tar sand.

Certain irregularities in the permeability in conduit beds can act as traps, whereoil accumulates in a reservoir. A trap is a place where the formation forms adownward facing concavity (otherwise, the oil would keep moving up) and anoverlying cap rock (relatively impermeable, and completely impermeable to oildue to complicated capillary considerations) prevents further upward migration.

Distribution: oil is rather widely distributed, considering its origins. A lot isassociated with rifting, due to good chances for anaerobic conditions and high heatflow. Compressive mountain ranges provide heating and structural trappingmechanisms, as do extensional zones.

Seeps+ Tar

Sedimentary Processes> >Fossil Fuels > Petroleum


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Sedimentary Processes>>Fossil Fuels > Petroleum Petroleum includes oil, natural gas, and tar sands.

Oil, Crude oil (Black gold, Texas tea) is any liquid hydrocarbon, usually about the consistency ofkerosene to olive oil. Carbon chains and rings with hydrogen, other elements in trace quantities. Somecan be used out-of-the-ground as a fuel or lubricant, but most requires treatment at refineries.

Natural Gas is usually, methane, although it can include ethane, butane or propane, light liquidhydrocarbons, and impurities such as CO2 or Nitrogen.

Tar (as in tar sands, a.k.a. "heavy oil") is crude oil that has lost volatiles by evaporation and digestion,and residually concentrated large molecules and non-volatiles, like vanadium and uranium. (i.e., tar isdegraded oil.) Usually the result of a trap being breached or never having existed, and aerobicdecomposition of crude.

Oil from a single field is usually pretty similar, but oil from different fields can be very different and requirevery different refining procedures, resulting in adjustments to price, sort of like the price penalties/bonuseson corn of differing water content (and delivery location), or on wheat based on water and protein content.

When you hear about the price of a "barrel of oil", that usually refers to either West Texas Intermediate orBrent Crude. These refer to hypothetical, desirable mixes of oil. Refiners pay for other oils as a percentageof these 'index' crudes, usually some lower amount. (The market price also specifies delivery location)

Occasionally, you see an oil well that is owned by one entity who is free to control the price, but that is rare.More often, oil wells are jointly owned by the landowner(s) (possibly a government), an oil company orconsortium thereof, and operators, and this leads to the same problems as any other joint operation, ofeveryone wanting to maximize their profits and minimize costs, so they generally agree to sell the oil atmarket-price*adjustment, pay certain production costs, and proceeds are split according to some contract.[This is why oil companies don't control oil prices.]

In addition to the people who actually sell oil by finding and producing it and those who buy oil to refine orburn, and brokers who deal with them, there are also financial speculators that buy and sell based on theirbeliefs about upcoming shortages or surpluses: speculators can drive bubbles and crashes that have little ifanything to do with actual production and consumption, and are responsible for "fear premium" or"instability premium"

Sedimentary Processes


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Sedimentary Processes Evaporites are sedimentary rocks that form in areas of high evaporation relative to influx of water.

Economically important evaporites include gypsum/anhydrite (which may get reduced to elemental sulfur bymicroorganisms), halite/rock salt, sylvite (KCl), nitrates, barite, and borates.

Precipitates are sedimentary rocks that form where a mineral precipitates directly out of solution. (Note thatevaporites are precipitates). In the early, reducing atmosphere, iron was soluble. When more free oxygen

accumulated in the atmosphere and oceans, banded iron formation (thin beds of chert and hematite) formed. Clastic sediments of economic importance include sand (sand for construction, source of amazingly puresilica, abrasive, ), gravel (for road material), and certain clays (ceramics, viscosity additive and sealant indrilling mud,) Placer deposits

Placers: a dense, weathering-resistant mineral can be concentrated in coarse sediments. Gold, tin, gems

Sedimentary Processes>Weathering


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Sedimentary Processes>WeatheringWeathering can produce ores, by what it removes or what it deposits nearby.

Residuum:by removing other constituents in solution, some elements are concentrated Bauxite (laterite)

Secondary enrichment: constituents are dissolved at the surface and deposited deeper (usually the water

table). Copper deposits often show this at the top.

Soils

Groundwater

I P


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Igneous Processes Primary mineral throughout rock: if the mineral is rare enough, like diamonds or really large crystals of

quartz, the mere occurrence of a mineral may be significant enough to warrant mining.Breaking rock apart is expensive.Diamonds and gems and large crystals in pegmatites fall into this rare category.

Mineral Settling: In a fluid magma, early-formed crystals can settle out; dense, to bottom; light, to top.

This can often occur in gabbroic intrusions. Chromite, magnetite, platinum. Magmatic Segregation

As a magma cools, it may separate into two immiscible components.In some mafic/ultramafic magmatic segregation deposits, one is siliceous and the other is sulfide or oxide

rich. The denser sulfide or oxide fluid settles to the bottom of the intrusion and solidifies. Nickel, copper.More often, an aqueous phase separates out, causing the freezing point of the silicic magma to drop

suddenly (origin of most porphyries). The resulting metasomatic fluids may be highly enriched in ore-forming elements and can form hydrothermal deposits (below).

Metamorphic


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Metamorphic Certain (geologic) minerals occur in metamorphic rocks, like corundum (rubies, sapphires, abrasive), garnet

(gem, abrasive), and graphite (used in pencil "leads") that are worth mining.

Contact metamorphism, especially with limestones and dolomites, often results in precipitation of minerals,

which may be ore.

Finally, metamorphism often produces hydrothermal fluids that can cause hydrothermal ore deposits.

Hydrothermal/Metasomatic Fluids


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Hydrothermal/Metasomatic Fluids Hydrothermal deposits (from hot fluids) are associated with igneous or metamorphic activity. Typical

minerals are sulfides, some oxides, and silicates. Hydrothermal fluids are hot, ion-rich fluids. Hydrothermal fluids can come from

the de-hydration of clays and other hydrous minerals during metamorphism,

the residual fluids left after a magma has crystallized,ex-solution of an aqueous phase from a magma,deep circulation of groundwater into hot regions,water expelled from sediments at great depth (and temperature).

Hydrothermal fluids contain ions that did not go into minerals or that got leached from minerals: H+,metals, sulfide, sulfate, carbonate, Hydrothermal fluids are generally hot, acidic, and very ion-rich. Theacidity makes it very easy for feldspars and mafics to be hydrolyzed, resulting in big clay-altered zones(useful for exploration). The acids can leach any metal ions out of minerals, especially ones that dont quite

fit into their crystal structure (substitutions), extracting trace constituents from surrounding rocks. Where the circulating fluids undergo a sudden change of pressure, temperature, or chemistry, precipitates

often form as the mineral-stability changes with PT.For example, where hydrothermal fluids are expelled into cold sea water, sulfides, that had been stable in

solution, are suddenly over-saturated and precipitate, giving black smokers.Gold deposits often occur in the upper part of hydrothermal circulation cells, where the metasomatic

fluid reaches low pressure and boils: water and chlorine go into a vapor phase, and gold, which had beencomplexed with the chlorine in aqueous solution, precipitates out, along with quartz and other minerals.

Where hydrothermal fluids encounter limestone or dolomite, the acids react with the carbonates and thischanges the chemistry of the water, and lots of weird minerals precipitate.

In disseminated deposits (typical with copper), the ore is distributed through a large volume of rock (insmall, pervasive joints). In veins (typical of gold), the minerals are deposited in thin, tabular fractures(usually scattered joints with filling). Pegmatites are a special case of veins, where the crystals areunusually large, and often have high concentrations of very rare elements, such as beryllium.

In many hydrothermal systems, hydrothermal fluids discharge occurs below water, and a smoker depositoccurs, which is sulfide precipitating from metasomatic fluid where it hits cold seawater and forms a

layered sulfide deposit on a seafloor.

Hydrothermal Diagrams


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Hydrothermal Diagrams

Plate Tectonics


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Plate Tectonics In "recent" times (last billion years), plate tectonics has closely controlled the occurrence and distribution of

geological environments favorable to deposition of many ores. Other ores have little if any relationship toplate tectonics, and are instead controlled by weather (e.g. laterites) or currents (e.g. phosphorites) or

The connection between plate tectonics and ores is indirect. Certain rock types or structural settings favorcertain types of ore deposits, and these are often found associated with certain plate tectonic settings, but therelationships are non-unique. For example, copper is often associated with basalt, regardless of how itoccurs. Granites have their associated ores (tin-tungsten, lead-zinc, silver, gold, molybdenum).

Divergent boundaries (Rifting, passive margin, mid-ocean ridge)In early stages, salt layers and other evaporites. Petroleum is common due to the thick accumulation of

sediments, often anoxic (source bed); later heating from volcanic activity (cooking) and complicatedstratigraphy and faulting (traps) [some early, some late]. In late stages, the passive margin accumulatesthe dead-stuff deposits. Igneous activity brings the standard suite of basalt-associated ores (mainlycopper and zinc sulfides), and some molybdenum associated with granites if there's felsic magmas.

In oceanic setting, the volcanic activity causes hot springs, smokers, and mineral brines, often rich incopper. Chromite is found in lenses in gabbroic intrusives.

Oceanic Subduction (trench, island arc, volcano chain)Wet partial melting of oceanic lithosphere (and possibly mantle) extracts gold, copper, silver, which

occur in hydrothermal deposits, often associated with porphyries. [Circum-Pacific]When these magmas pass through continental crust, the continental crust may also be leached resulting in

tin-tungsten, molybdenum, and lead-zinc-silver deposits, all found landward of the arc.Back-arc basins can also get all the divergent boundary deposits.

Continental collisions involve former divergent and ocean-continent convergent boundaries, and so caninclude those deposits, probably re-worked by metamorphism. Magmatism associated with the melting ofcontinental crust gives rise to pegmatites, tin-tungsten, uranium, molybdenum, Cu-Pb-Zn, Ag, Au andothers. The structural deformation and heating of sediments can produce extensive oil deposits.

Greenstone belts are some of the richest mining provinces in the world and have deposits associated withfelsic magmatism, including copper, Cu-Pb-Zn, gold, silver,ultra-mafic magmatism (nickel sulfides), andsome strange sedimentary gold associated with iron formation.

Plate Tectonics Map


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Plate Tectonics Map

Divergent Boundaries


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Divergent Boundaries

Convergent Boundaries


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Convergent Boundaries

Greenstone Belts


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Greenstone Belts

Mineral exploration


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Mineral exploration Depending on the type of organization, an exploration program may take two forms

What mineral deposits and other resource would we find in PLACE? This is one of the things geological

surveys do. Here, you start with an area, determine its geological settings through time, and figure out

what types of mineral deposits might be found there. (like looking in the freezer)

Where would we find SUBSTANCE? This is typically the mode of an oil or mining company. Some

engineer or economist/accountant figures out what minerals will be in demand and raises/assigns money

to conduct the exploration. Geologists find exploration models of the desired substance, then regions to

explore. (like deciding what store to go to)

In both cases, much of the work consists of examining airphotos, well logs, and geophysical maps, first to

map the tectonic setting/regional geology, selecting favorable regions and mapping them in more detail, to

narrow in on fields, then prospects, which, if confirmed become deposits. Then accountants re-appear. If

they decide to go ahead, then engineers appear along with more geologists and detailed, site levelexploration/development work begins, resulting in mines. Accountants keep re-appearing, often annoying

and re-organizing the geologists and engineers (seewww.dilbert.com ).

Economic Minerals
http://www.dilbert.com/http://www.dilbert.com/


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Economic Minerals Industrial civilization requires huge amounts of materials.

Economic minerals include water, petroleum and other fossil fuels, industrial minerals, ores, and soils.

Economic minerals can thought of in terms of supply, resources, and reserves.

Reserves are legally allowed and economically viable at the time the reserve estimate. Reserves are

objective but conditional.

Resources include reserves and various categories like undiscovered+profitable,

discovered+unprofitable Resources are subjective.

Supply (total) is objective and unconditional.

Most materials can form in several ways. Exploration models guide exploration and development.

Economic minerals form in a wide variety of geologic settings, from infiltration of rainwater into theground and beach sand accumulating to explosive exsolution events forming copper and gold deposits.

Plate tectonics, through its control on tectonic environments and especially igneous activity, is one of the

major constraints on the distribution of (economic) minerals.