1. Precious Metals and Gems
Kirbie Brown
Mandy Daigle
Aimee Porter

2. Scarce Metals Present in Earth’s 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 Highlights Gold Silver
Platinum group elements (PGE)
Highlights
Geology
Mining
Production and the environment
Production and reserves

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

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 (CO2, SO2, 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
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
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 Utah
Porphyry copper deposits
Low grade gold
Grasberg mine in Indonesia
Utah
16 metric tons annually
Western Pacific

20. Gold Mining Placer mining Open-pit mining Bulk 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 SO2 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

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
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. www.pangea.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
../platinum.asp

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
Platinum 40%
Palladium 40%
Rhodium 9%
Iridium 6%
Ruthenium 4%
Osmium 1%

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 Highlights Diamonds
Beryl Group (emeralds and aquamarines)
Corundum Group (rubies and sapphires)
Highlights
Geology
Mining and Production
Classification, Trade, and Reserves

48. Background picture from www.mwdiamonds.com

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

64. The Corundum Group Rubies and Sapphires www.eastgems.com

65. Background picture from www.msgjewelers.com
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 world’s 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. 3rd 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. http://resourcescommittee. house
pangea.stanford.edu/.../ kurt-mining-methods.html
../platinum.asp