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Precious Metals and Gems Kirbie Brown Mandy Daigle Aimee Porter.

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Presentation on theme: "Precious Metals and Gems Kirbie Brown Mandy Daigle Aimee Porter."— Presentation transcript:

1 Precious Metals and Gems Kirbie Brown Mandy Daigle Aimee Porter

2 Scarce Metals Present in Earths crust <0.1% Special properties led to technological marvels Four groups of geochemically scarce metals –Ferro-alloy metals –Base metals –Precious metals –Special metals

3 Precious Metals Focus –Gold –Silver –Platinum group elements (PGE) Highlights –Geology –Mining –Production and the environment –Production and reserves

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5 A Few Facts… Soft and malleable Extremely resistant to chemical attack Corrosion-free Better records for gold production than any other metal 43% held by banks 57% in bullion, coins, jewelry, and art Annual gold production of approximately 2,200 metric tons ($25 billion) 1991 –83% + of world consumption went into jewelry –6% in medals and official coins –6% in electronic equipment –2.2% in dental materials –2.8% in industrial applications gallery/images/Gold%203_jpg.jpg

6 Geology of Gold Deposits Found largely in native state or with silver in electrum Also forms telluride minerals Found as hydrothermal deposits (low grade gold) and paleoplacer deposits

7 Hydrothermal Deposits - Epithermal Consist of gold-containing veins, veinlets, and disseminations –Created by cool hydrothermal solutions (<250°C) that circulated through shallow crust Further divided into adularia-sericite deposits and acid-sulfate deposits

8 Hydrothermal Deposits – Epithermal: Adularia-Sericite Characterized by minerals adularia and sericite Near neutral hydrothermal solutions Linked to felsic and intermediate volcanism –Form massive veins with precious metal accumulations called shoots Western North America, western Pacific volcanic arcs, Saudi Arabia, and Ontario

9 Hydrothermal Deposits – Epithermal: Acid-Sulfate Characterized by minerals like alunite and pyrophyllite Created from acid hydrothermal solutions Confined to small fracture systems –Direct gases (CO 2, SO 2, and HCL) upward Forms acidic hydrothermal solution Nevada, Chile, and Dominican Republic

10 Hydrothermal Deposits – Epithermal: Sediment-Hosted Micron Gold Deposits Created by channeling of epithermal waters or brines through carbonaceous limestone –Gold dispersed through changed limestone Extremely fine-grained and found with optical and electron microscopes Concentrated in thin layers Nevada, Utah, and Sonora

11 Hydrothermal Deposits – Epithermal: Hot-Springs Adularia-sericite or acid-sulfate liquids from hot springs at surface –Encompassed by silica-rich deposits (sinter) or carbonate-rich deposits (travertine) –Easily removed by erosion Few deposits known California

12 Hydrothermal Deposits – Mesothermal Gold-containing quartz veins –Created deep within crust Deposition by fluids >250°C Enclosed by changed rocks that contain carbonates Divided into intrusion related, greenstone hosted, and turbidite hosted

13 Hydrothermal Deposits – Mesothermal: Intrusion-Related Veins Quartz veins with gold, silver, and base- metal sulfides Created around felsic intrusions –Liquid mixture of magmatic water and meteoric water –Depths of 5 + km Korea and Russia

14 Hydrothermal Deposits – Mesothermal: Greenstone-Hosted 10 + km Originate in metamorphosed mafic volcanic rocks –Contain chlorite Found as quartz veins adjacent to offshoots from huge crustal fractures California

15 Hydrothermal Deposits – Mesothermal: Turbidite-Hosted 10 + km Found in turbidites –Created by erosion of volcanic rocks Gold concentrated in iron-rich wallrocks

16 Kesler, Stephen E. Mineral Resources, Economics, and The Environment. Macmillan College Publishing Company, Inc., NY. 1994,

17 Placer and Paleoplacer Deposits Placer: alluvial deposit containing particles of a valuable mineral Primary gold source for thousands of years Most placers nearing exhaustion Witwatersrand paleoplacers of South Africa –Discovered in 1886 –Several gold-containing conglomerate layers –Mined approximately 32,000 metric tons of gold with an estimated reserve of 20,000 metric tons

18 Kesler, Stephen E. Mineral Resources, Economics, and The Environment. Macmillan College Publishing Company, Inc., NY. 1994,

19 By-Product Gold Important by-product of many base-metal mines –Porphyry copper deposits Low grade gold –Grasberg mine in Indonesia Utah –16 metric tons annually Western Pacific

20 Gold Mining Placer mining –Stream gravels containing gold moved over riffle system to catch gold Riffle made of Astroturf Open-pit mining Bulk mining –Allowed for recovery of low grade ores

21 Gold Mining cont. Underground mining –Over large areas –Extremely deep levels Hostile conditions –Newly broken rock up to 65°C –High humidity –Mud rushes if chilled water is used as a cooling element –Rock bursts »Some felt as earthquakes at the surface

22 Gold Production and the Environment Hydraulic mining problems –Sediment is disturbed, creating wastewater that was once dumped into river systems Amalgation –Mercury never recovered Remains a pollutant in old mining locations –Process still being used in Latin America and the Pacific Rim

23 Gold Production and the Environment cont. Cyanide process –Extremely toxic compound 50 to 250 mg can cause death –Yields gold-containing solution (pregnant solution) –Heap leaching was used once process was complete Cyanide solution leaks through bottom of abandoned heap- leach pads Roasting –Required to mine deep, sulfide-rich ores in the USA –Releases SO 2 and As gas

24 Gold Production and Reserves Measured in units of grams or troy ounces ( grams) Entire world production approximated at 130,000 metric tons –40% mined in last 30 years –85% since 1900 Produced in 67 countries –30% in South Africa –Nevada is leader in USA World reserves estimated at 44,000 metric tons –Adequate for only 20 years of production at present rates

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26 A Few Facts… Corrosive with high electrical conductivity Evolving from precious metal to industrial metal Main market is photographic film Also used in electrical and electronic applications, highly reflective mirrors, pharmaceuticals, batteries with zinc, dentistry, coins, solders, jewelry, silverware, and as an edible silver foil in India Annual production of about 15,000 metric tons –Approximately $2 billion

27 Geology of Silver Deposits Occurs in electrum, argentite, and many complex sulfide minerals Hydrothermal deposits Placer deposits By-product –Copper and lead mining

28 Epithermal Vein Deposits Most familiar deposit USA and Mexico Cerro Rico deposit (Bolivia) –Largest deposit in world –Quartz-silver-tin veins cutting silica-rich dome of volcanic rock –Deposit at 500°C from extremely saline liquids Precipitate ore down to <100°C Solution becomes less saline

29 Cobalt-Nickel-Arsenide Deposits Ontario –Veins consisting of native silver, cobalt, nickel, and iron arsenides within calcite and quartz Within sediments above and below massive gabbro intrusion Created from brines heated by the intrusion

30 Kesler, Stephen E. Mineral Resources, Economics, and The Environment. Macmillan College Publishing Company, Inc., NY. 1994,

31 By-Product Silver Mostly from gold and base-metal deposits Silver forms small inclusions and are difficult to separate –Australia, Utah, Ontario, and Alaska Chimney-manto deposits –Mexico and Peru Lead-zinc vein deposits –Idaho and Missouri Sediment-hosted copper deposits –White Pine in Michigan –Kupferschiefer in Germany and Poland

32 Silver Production and the Environment Underground mining Open pit mining Production dependent on presence with gold or base-metal sulfides –With gold Cyanide leaching –With base-metal sulfides Specific step in smelting process Relatively low recovery in each process

33 kurt-mining-methods.htmlpangea.stanford.edu/.../ kurt-mining-methods.html

34 Silver Production and Reserves 56 countries Industrial markets –Silver-free photographic film, video tape, and xerography Industrial, jewelry, and silverware encompass 95% of world silver consumption Production fallen short of consumption Reserves at 280,000 metric tons –Dependent on by-product silver

35 Platinum-Group Elements (PGE)

36 A Few Facts… Platinum, palladium, rhodium, ruthenium, iridium, and osmium –Occur together in geological settings –Can substitute for one another by atomic substitution –Similar chemical and physical properties First discovered in placers Form steel-gray nuggets Malleable High melting temperature Resistant to corrosion 300 metric tons annually

37 A Few More Facts… Used for: –Increasing speed in chemical reactions through catalysis –Highly corrosive environments –Extremely high temperature situations –Catalytic converters –Diesel-powered vehicles –Catalyst in oil refining –Production of nitric acid –Fuel cells - Electrical and electronics - High-resistance wires - Memory devices - Special solders - Automotive oxygen sensors - Dental and medical applications - Nozzles for glass and ceramic fiber extrusion

38 Geology of PGE Deposits Minor production from placer deposits Major production from magmatic deposits correlated with mafic igneous rocks –Layered igneous complexes –UG-2 chromitite –Nickel-copper sulfide ore

39 Layered Igneous Complexes Dominant deposit Merensky Reef of the Bushveld complex (South Africa) –Between chromitite and vanadium-containing magnetite layers –Consists of coarse-grained, mafic silicate minerals –Result of magmatic immiscibility –Hypothesized that PGEs scavenged by hydrothermal solutions from deeper parts of Bushveld complex

40 UG-2 Chromitite Deposit Consists largely of chromite Three times as much rhodium per metric ton as Merensky Reef Platreef (Bushveld) –Veinlets of PGE-bearing sulfide minerals in ultramafic rocks

41 Nickel-Copper Sulfide Ore Least important source Created by separation of immiscible sulfide magmas PGE production sufficient only where a large nickel production exists –Australia

42 PGE Production and the Environment Almost exclusively underground mining –500 to 1000 meters –Problems Removing enough ore to meet production requirements Need to mine large areas Potholes Geothermal gradient causes hazardous conditions Separation of sulfide mineral-PGE concentrate –Matt rich in PGE is created Dissolved and different metals are separated by ion exchange

43 PGE Production and the Environment cont. Similar environmental problems as base- metal smelters Some forms of PGEs are toxic Main problem –Platinosis Respiratory and dermatological symptoms

44 PGE Production and Reserves Production in South Africa, Russia, USA, Zimbabwe, Australia, Canada, Finland, Colombia, Ethiopia, and Japan Future lies in jewelry and investment markets 56,000 metric tons in reserves –Platinum40% –Palladium40% –Rhodium9% –Iridium6% –Ruthenium4% –Osmium1%

45 Craig, James R. et al. Resources of the Earth: Origin, Use, and Environmental Impact. 3rd ed. Prentice Hall, NJ. 2001,

46 Gems 150 natural compounds used as gems –Diamonds, emeralds, rubies, alexandrite, and sapphires sell at highest prices –Followed by amber, aquamarine, jade, opal, pink topaz, spinel, and tourmaline with intermediate values –Agate, amethyst, and zircon with lower values No distinctive chemical composition Crystal structure defines clarity, color, and brilliance Retailed in cut and polished forms Formed by many different processes

47 Gems cont. Focus –Diamonds –Beryl Group (emeralds and aquamarines) –Corundum Group (rubies and sapphires) Highlights –Geology –Mining and Production –Classification, Trade, and Reserves

48 Diamonds Background picture from

49 A Few Facts… Measured in carats (0.2 grams) Annual world production –50 million carats worth $5 billion Would fit in a cube 2.86 meters on one side Metastable at Earths surface

50 Geology of Diamonds Found as xenocrysts in kimberlite –Found in thick continental crust Forms kimberlite pipes that shoot upward from deep, dike- like bodies –Pipes include rock and mineral fragments and diamonds held together by magma »Magma originated in mantle and brought up diamonds »Rose rapidly May be hosted by lamproite –Similar to kimberlites Also found in metamorphic rocks

51 Geology of Diamonds cont. Diamond placer deposits –Wider geographical distribution –Deep erosion of diamond pipes –Some placers traced to mines that cannot be mined Arkansas and Atlantic Coast of USA –May be derived from deeply eroded kimberlites Angola, Chana, Guinea, Sierra Leone, Tanzania, and Zaire

52 Kesler, Stephen E. Mineral Resources, Economics, and The Environment. Macmillan College Publishing Company, Inc., NY. 1994,

53 Diamond Mining and Production Early days –Recovered ore by rotary pans and hand- sorting Security problems, limited extent of operation, and resulted in poor recoveries 1896 –Discovered that diamonds stick to grease Allowed for large-scale mining and processing

54 Diamond Mining and Production cont. Open pit and underground mining –Placer mining very thorough Beach placers –Mined using large dikes to inhibit surf Offshore mining –By divers using suction tools placed on shore or small boats Deeply submerged beach zones –Mined from offshore ships

55 Diamond Mining and Production cont. Kimberlite mining –Begins with open pit but changes to underground as depth increases Block caving or sublevel caving –Crush ore to tiny fragments to free diamonds Ore passed through pans and cyclones –Concentrates heavy minerals »Grease tables and X-ray sorters –1906 Largest diamond in history –11cm x 6cm, 3,206-carat Cullinan diamond

56 Diamond Classification, Trade, and Reserves Graded according to size, quality, color, and shape Divided into 11 groups based on size –Further sorted by shape, quality, and color –Main divisions are gems and industrial diamonds Cut into wide range of shapes –Enhance appearance

57 Diamond Classification, Trade, and Reserves cont. Produced in 21 countries –Including Australia, Botswana, Zaire, South Africa, Namibia, Brazil, China, India, Russia, Canada, Sierra Leone, Lesotho, and Kazakhstan Sold by Central Selling Organization (CSO) –De Beers –Primary function is to alleviate and capitalize on wholesale prices Reserves at about 300 million carats –Only six times higher than annual world production

58 The Beryl Group – Emeralds and Aquamarines

59 A Few Facts… Beryl: common beryllium-aluminum silicate –Forms many important gem stones –Develops crystals with few imperfections and good color Emeralds – green Aquamarines – pale blue or bluish-green Heliodor – yellow Morganite - pink

60 A Few More Facts… Chromophores: trace elements that affect the colors in beryl group gem stones –Emerald Chromium and vanadium –Aquamarine Iron –Heliodor Manganese, iron, and titanium –Morganite Manganese and iron

61 Geology of the Beryl Group Found in beryllium deposits –Narrow calcite veins cutting carbonaceous shale –Where veins near granitic intrusions cut ultramafic rocks Best gems arise from pegmatites and hydrothermal veins –Slow cooling allowed for growth Some aquamarines found in placers

62 Production of the Beryl Group Emeralds –Brazil, Colombia, Russia, and Zambia Aquamarines –Brazil Nearly all production from bedrock deposits and regolith Gems irregularly distributed –Most work done by hand

63 Reserve estimates not known Without detection of a large deposit that can be mechanically mined, production will remain a small business Beryl Group Reserves

64 Rubies and Sapphires The Corundum Group

65 A Few Facts… Corundum: oxide of aluminum –Creates gems when in well-developed transparent crystals with good color Red corundum – ruby –Chromophores - chromium Blue corundum – sapphire –Chromophores - iron and titanium –Wide industrial use Background picture from

66 Geology of the Corundum Group Corundum not stable in presence of quartz –Will react to form other minerals –Reactions limit geologic environments available to corundum Need quartz-free rocks with copious aluminum –Bauxite »Metamorphosed Low-silica mafic rocks –Peridotite and hydrothermally altered limestones

67 Production and Reserves of the Corundum Group Production primarily in Australia, Cambodia, Myanmar, Nigeria, Sri Lanka, and Thailand –Mostly from placer deposits Dominated by poorly funded, small businesses –Extremely dependent on local politics Least secure supply of all precious gems Reserves are not known

68 The Future of Precious Metals and Gems Industrial applications continue to increase Predictions –the world has outgrown the need for mineral commodities as investment vehicles, and possibly even as ornaments and art objects (Kesler) –synthetic gems are supposed to satisfy the worlds gem buyers (Kesler) Mandatory need for exploration –Precious metals and gems has dimmest reserve outlook of all mineral commodities –Future may be dependent on improved recoveries as by-products

69 Works Cited Craig, James R. et al. Resources of the Earth: Origin, Use, and Environmental Impact. 3 rd ed. Prentice Hall, NJ. 2001, Kesler, Stephen E. Mineral Resources, Economics, and The Environment. Macmillan College Publishing Company, Inc., NY. 1994, Nevada Commission on Mineral Resources Division of Minerals. Digging Deep Into Mining. 21 Mar Sources for Pictures

70 photogallery/images/Gold%203_jpg.jpghttp://resourcescommittee.house.gov/subcommittees/emr/usgsweb/ photogallery/images/Gold%203_jpg.jpg pangea.stanford.edu/.../ kurt-mining-methods.html


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