Man, Metals and Mayhem: Earth s Resources

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1 Man, Metals and Mayhem: Earth s Resources Renewable and nonrenewable resources Renewable resources Can be replenished over relatively short time spans Examples include Plants Animals for food Trees for lumber Renewable and nonrenewable resources Nonrenewable resources Significant deposits take millions of years to form Examples Fuels (coal, oil, natural gas) Metals (iron, copper, uranium, gold) Some resources, such as groundwater, can go in either category depending on how they are used The endowment of useful minerals ultimately available commercially include Reserves already identified deposits from which minerals can be extracted profitably As well as known deposits that are not economically or technologically recoverable 1

Ore refers to useful metallic minerals that can be mined at a profit and in common usage to some nonmetallic minerals such as fluorite and sulfur To be considered of value, an element must be

2 Ore refers to useful metallic minerals that can be mined at a profit and in common usage to some nonmetallic minerals such as fluorite and sulfur To be considered of value, an element must be concentrated above the level of its average crustal abundance and igneous processes Some of the most important accumulations of metals are produced by igneous processes that concentrate the desirable materials Metallic mineral resources and igneous processes Magmatic segregation & Pegmatites Separation of heavy minerals that crystallize early or enrichment of rare elements in the residual melt 2

Magmatic segregation Formation of Pegmatites: During last stages of magma cooling,

Heavy minerals crystallized early in cooling of pluton sink to bottom of magma

Important minerals: Magnetite, Chromite, Platinum Result: Pegmatites found as veins in

our gemstones come from pegmatites) Some pegmatite minerals Watery residual magma also

aquamarine) Tourmaline Corundum (var. ruby) Vanadanite Fluorite Quartz (var.

3 Magmatic segregation Formation of Pegmatites: During last stages of magma cooling, residual melt is volatile-rich and contains rare incompatible elements that do not fit into common minerals that form during initial cooling (e.g. rare earth elements such as lithium that have large atomic radii). Heavy minerals crystallized early in cooling of pluton sink to bottom of magma chamber, forming concentrated layers of metallic minerals (dark bands in photos) Important minerals: Magnetite, Chromite, Platinum Result: Pegmatites found as veins in country rock and at tops of plutons often containing rare minerals (in fact, most of our gemstones come from pegmatites) Some pegmatite minerals Watery residual magma also allows growth of very large crystals in pegmatites Beryl (var. aquamarine) Tourmaline Corundum (var. ruby) Vanadanite Fluorite Quartz (var. amethyst) Note: In one pegmatite dyke near Madawaska, north of Bancroft, which was mined for feldspar, a single crystal measuring 7 meters long and weighing 300 tons was extracted. 3

Hydrothermal Deposits Hydrothermal solutions Among the best known and important ore deposits Majority originate

$Move along fractures, cools, and precipitates the metallic ions to produce vein deposits Hydrothermal deposits are$ Ontario Divergent setting metals leached from country rock, due to convective flow, precipitated when fluid hit

Ontario Divergent setting metals leached from country rock, due to convective flow, precipitated when fluid hit

4 Hydrothermal Deposits Hydrothermal solutions Among the best known and important ore deposits Majority originate from hot, metal rich fluids that are remnants of late-stage magmatic processes or from leaching of country rock Move along fractures, cools, and precipitates the metallic ions to produce vein deposits Hydrothermal deposits are associated with igneous rocks Convergent setting metal-rich fluids derived from cooling pluton Beardmore District, Ontario Divergent setting metals leached from country rock, due to convective flow, precipitated when fluid hit cold seawater Below surface: hydrothermal fluids precipitate minerals in veins as they come in contact with cold seawater 4

Hydrothermal gold in quartz vein and metamorphic rocks Many of the most important metamorphic ore deposits are produced by contact metamorphism Sphalerite (zinc) Galena (lead) Chalcopyrite (copper)

carbonates dissolved and replaced by metallic minerals Weathering and metallic ore deposits Secondary enrichment concentrating metals into economically valuable concentrations Bauxite Principal ore

5 Hydrothermal gold in quartz vein and metamorphic rocks Many of the most important metamorphic ore deposits are produced by contact metamorphism Sphalerite (zinc) Galena (lead) Chalcopyrite (copper) Alteration of country rock by hot fluids generated during contact metamorphism Contact Metamorphism - fluids from cooling pluton interact with country rock in metamorphic aureole -minerals such as carbonates dissolved and replaced by metallic minerals Weathering and metallic ore deposits Secondary enrichment concentrating metals into economically valuable concentrations Bauxite Principal ore of aluminum (bauxite enriched in iron and aluminum oxides) too difficult to extract from strongly bonded silicates) Forms in rainy tropical climates from chemical weathering and the removal of undesirable elements by leaching 5

Dry out cleared land soil essentially converted to brick Weathering and ore deposits Other deposits, such as many copper and silver deposits, result when

6 O horizon (humus veneer) Formation of Bauxite Deposits in Soil Profile: need rainy tropical to subtropical climate Bauxite the principal ore of aluminum A horizon (zone of leaching) B horizon (zone of accumulation) Leaching of highly soluble components (Ca, Na, K, and Si), accumulation of less soluble aluminum and iron oxides in upper soil profile (especially B horizon). C horizon (decomposed regolith) Regolith (unaltered rock) In other words, mining bauxite involves mining soil (best developed in tropical rainforest areas) Dry out cleared land soil essentially converted to brick Weathering and ore deposits Other deposits, such as many copper and silver deposits, result when weathering concentrates metals that are deposited through a low-grade primary ore Placer deposits Placers deposits formed when heavy metals are mechanically concentrated by currents Involve heavy and durable minerals Examples include Gold Platinum 6

Each time a flood occurs, heavy minerals which were once randomly scattered within the sediments end up resting on the new stream bed created by the scouring action of the flood Thin section photo

7 Placer Deposits: Heavy mineral concentrations formed by the sorting action of water Paleoplacers also important (e.g. Witwatersrand, South Africa) Most of the concentration of heavy minerals occurs during flooding, when current velocity and winnowing are at a maximum. Each time a flood occurs, heavy minerals which were once randomly scattered within the sediments end up resting on the new stream bed created by the scouring action of the flood Thin section photo Placer gold deposit in ancient river deposit But what happens when resources are mined? Sulphide deposits are dominated by the mineral pyrite (FeS 2 which is not profitable to extract iron from). Pyrite-rich tailings are left to weather in piles at the mine site Chemical weathering of pyrite produces sulphuric acid! 2FeS O 2 + 2H 2 O = 2Fe SO H + Where does the acid go? Into rivers, lakes, and groundwater supply (if one is not careful enough to contain this stuff) Acidified water can mobilize metal ions from minerals in bedrock due to intensified weathering (so free up ions of lead, zinc, copper, chromium, arsenic and aluminum) Note that high concentrations of lead, zinc, copper and chromium are toxic to many plants and animals (including humans) Note also that high concentrations of aluminum possibly increase incidence of Alzheimer s disease in humans Actually, many other, more complex, reactions also occur, but you get the idea! 7

8 Acidification of already acidic water! Most sulphide deposits in Ontario occur in Archeanage igneous and metamorphic rocks (of the Canadian Shield) Surface and groundwater in these areas are naturally acidic- acid mine drainage exacerbates the release of toxic metals from bedrock It is likely that metal poisoning in northern areas is directly linked to the effects of acid mine drainage (more studies are required to investigate the scale of these effects). Cyanide leaching Chemically stable minerals such as gold are difficult to separate from unwanted minerals But can be mobilized in a cyanide solution Cyanide leaching involves spraying a sodium cyanide (NaCN) solution (at 250 to 500 parts per million) on finely ground ore or tailings (waste rock) Cyanide leaching, cont d The gold forms a water-soluble chemical compound with the cyanide called a pregnant solution which is then run over activated carbon to extract the gold. Some companies process the ore in vats allowing the cyanide to be recycled. Most operations store the waste cyanide in ponds with plastic liners that break easily, allowing the solution to contaminate the ground water. But what if it escapes? Don t want to be around if it does! Symptoms of cyanide poisoning The effects of cyanide ingestion are very similar to the effects of suffocation. This is because cyanide stops the cells of the body from being able to use oxygen, which all cells need to survive. General weakness, confusion, bizarre behavior, excessive sleepiness, coma, shortness of breath, headache, dizziness, and seizures The skin of a cyanide-poisoned person can sometimes be unusually pink or cherry-red because oxygen will stay in the blood and not get into the cells. The person may also be breathing very fast and have either a very fast or very slow heartbeat. Sometimes the person s breath can smell like bitter almonds Chronic cyanide poisoning can lead to death 8

9 The amalgam process Outdated in developed countries, but still used in developing countries (cheap and easy method) In this process, up to 150 kg of mercury is combined with a ton of metallic ore, an amalgamation of the mercury and other metallic minerals is formed. In crudest methods, mercury is then boiled off, leaving the gold The amalgam process, cont d This guy is boiling mercury off gold-mercury amalgam in an open pan, using a propane torch! Effects of mercury use to be discussed later End of Lecture (whew) 9

Real-Life Applications: Economic Mineral Deposits

Real-Life Applications: Economic Mineral Deposits Economic Minerals Economic minerals are minerals that can be extracted, processed and marketed for a profit. Various factors determine if a mineral is