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Gold & Diamond Exploration in Ghana

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  1. Gold & Diamond Exploration in Ghana Patricia L. Frisch New Mexico Bureau of Geology & Mineral Resources

  2. Geography of Ghana • Ghana is located on the Gold Coast in west Africa. • English • 239,460 square km • 10 Regions • Temp never below 25°C • Capital Accra

  3. Ghana and its neighbors • Ghana is extremely safe and politically stable • 20.5 M people • Christian/tribal religions • Ivory Coast: many refugees • Mortality rate 5.6% • AIDS very high (3%), but declining • 20% unemployment

  4. Geography of Ghana • Lake Volta: largest lake • World’s 3rd largest exporter of cocoa • World’s 6th largest producer of diamonds • Major gold & manganese producer • Rubber trees produce rubber • … slave trade still active!

  5. Geology: Formations & Stratigraphy • Tarkwaian (2.155 to 2.096 Ma) • Huni Quartzite • Tarkwa phyllite • Banket • Kawere • Upper Birimian (2.170 Ma) • Lower Birimian

  6. Ghana: the heart of the Gold Coast • Gold is found in eight belts in Ghana; we went to two: • Ashanti • Sefwi • Gold has been mined for centuries • Gold can be recovered on the surface, underground, in soil, in rock, … the amount of gold is unbelievable!

  7. Nkroful • Nkroful is a “galamsey” operation • Two shifts/day • 20 people total • ~1 ton/day rock • 23 ppb Au pyrite veins • 8 grams Au/day • Placer gold • Mostly fine gold

  8. Nkroful • 1 ton/day * 23 ppb = 23 grams • The recovery is ~35% • So: are they lying? • Or, not working hard enough?

  9. Nkroful • So why is the recovery low? • The plastic grass traps are short • No “bumps” in the traps • Water flow is too fast • Traps are too short

  10. Nkroful • But, … • It’s “free money” • 8 g/Au per day is ~$100/day • $100/day is an even $5/day/person • … or $150/month • Most professors make $150/month

  11. Nkroful • This was our first stop looking at gold in Ghana. • This is to be the richest and smallest deposit we visited.

  12. Gold mines we visited • Bibiani • Awaso • Obuasi • Dunkwa • Prestea • Tarkwa Tarkwa

  13. Gold Fields: Tarkwa Mine • 2nd largest Au in Ghana • Hydrothermal Au veins • Highgrade 3.5 g/ton • Average 1.5 g/ton • Cutoff 0.4 g/ton • ’97 to ‘03: 400,000 oz/year • 555,000 oz in ’03 • New processing plant: capacity to 800,000 oz. for 2004 • What changed? • Price of Au is up from <$200 to >$400/oz. Sampson Opaye, Wassa Mine Security

  14. Gold Fields: Wassa Mine • Inactive and flooded pit lake • 11 M tons reserve @ 1.55 g/ton • Good for jetskiing • Bad for jetskiiers

  15. Damang Mine • Paleoplacer! The only one on this trip. • Mine old streambeds, cutbanks. • Seams of gravels • Moral of the story: know your structural geology!

  16. Damang Mine

  17. Gold mines we visited • Bibiani • Awaso • Obuasi • Dunkwa • Prestea • Tarkwa Prestea

  18. Bogoso Gold Ltd.: Prestea Prestea Pit Red: volcanics Black: graphite schist Au & Au-Arsenopyrite in the graphite schist

  19. Prestea • Over 7 million oz reserve in this claim group • Background laterites have soil anomalies of 70-80 ppb Au

  20. Prestea • Pay attention to every class in school if you want to climb the ranks of exploration geologist! • Yan Bourassa has a master’s degree and is 30 years old. • Yan is the Senior Exploration Geologist for Bogoso Gold!

  21. Prestea • BiOx plant being built • Many “galamsey” still working the inactive areas

  22. Gold mines we visited • Bibiani • Awaso • Obuasi • Dunkwa • Prestea • Tarkwa Obuasi

  23. Obuasi: Largest Au mine in Ghana • Only mine that gives public tours • 20 million oz reserve • 30 million oz prospected potential • 29 million oz recovered since 1897 • 67 levels underground: 2 km deep • Visible gold in quartz veins • 632 square km of continuous patented highgrade claims!

  24. Obuasi

  25. Obuasi • Obuasi has Au in quartz, pyrite & arsenopyrite • Historically used a smelter to roast sulfide ores • Arsenic in soil & air caused severe health problems: • arsenocosis was prevalent • Soot fallout was killing plants • Wells dug in the local area were ~150 ppb to 10 ppm As (WHO limits were 50 ppb, now going to 10 ppb) • Now, use BIOX (Biological Oxidation) plant to eat sulfide ores instead of roasting

  26. Obuasi: BiOx Plant • Sulfide eating bacteria eat the pyrite & arsenopyrite • 84% yield using BiOx • Currently world’s largest plant • 7% Au recovered panning tailings

  27. Obuasi: Work environment • “heavy on the propaganda”

  28. Obuasi

  29. Obuasi • Visible gold in quartz • ~90% ore is not sulfides • Single shaft, no declines • 7000 tons/day milled • Majority to CIL plant • Tailings have <1% As

  30. Obuasi • The reserves never go down • Production never slows • Everywhere you look, there’s gold

  31. Obuasi: the unsaid • Since our visit three weeks ago, they have had a tailings dam breach. • This is the second breach in three years. • Image • Production • Environmental safety • Cost

  32. Ashanti Goldfields: Bibiani • Sefwi belt • 600 m deep underground, 2 km long • 9.5 g/ton Au average grade underground • 85% recovery • 2.5 M oz to 1968 • ’97 to today: 2.5 M oz • Reserves: 2.5 M tons + 3.1 M tons at 6 g/t

  33. Bibiani • Recent pitwall failure • Pit grade 3.5 g/ton • Only underground mining currently

  34. Bibiani

  35. Bibiani

  36. Newmont Exploration Property: Ahafo Project • This prospect potential was discovered in a 88-91 German/Ghanean map project • This is a camp: no mine yet, but lots of drillcore • Core is split and crushed on site • Only large well-respected companies can do this • Most geochem done in Ghana

  37. Ahafo Project 3 1 Ore zone: shattered host with pyrite & Au Hanging wall K-spar 2 4 Hanging wall mylonites

  38. Ahafo Prospect • Some interesting points: • ’93: soil geochem confirmed anomalies of 7 g/ton • 720 sq. km elevated soil Au • Over 40 km on-strike ore yielding over 7 M oz. • No arsenopyrite • Barren graphite schists (=ore at Prestea!) • Au associated with late-state alteration

  39. Ahafo Prospect • This deposit will go into production beginning ’06 • First open pit • Then underground under the pit Room for work! Want a job? Want a thesis project? Want to live in Ghana?

  40. Historically, diamonds… • Diamonds are smuggled out of Ghana to fund rebel fighting in Sierra Leone • Estimated 70% diamonds being produced are smuggled out of Ghana • U.N. Security Council resolution to end smuggling of diamonds • End smuggling, end arms funding, end fighting

  41. More about diamonds • The diamond trade is strongly controlled worldwide by DeBeers • Diamonds are laser etched with a serial number • Strict laws on who is allowed to sell rough diamonds, • who is allowed to buy rough diamonds…

  42. U.N. & DeBeers • DeBeers now controlls Ghana Consolidated Diamonds as of the 1990’s • Prior: 70% diamonds smuggled to black market • $8 million additional collected in first joint year • … still complaints over illegal diamond trade

  43. Akwatia • Akwatia is the only mine producing primarily diamonds • Many small “galamsey” operations exist • About 15 other companies that recover Au hold licenses to mine for diamonds on their properties

  44. Akwatia • This area is being stripped for diamonds • Soil goes through a 1 cm sieve • Sieved material is slurried • Diamonds are heavier than quartz • Quartz is skimmed off the surface • Remaining material is hand-sieved for diamonds

  45. Akwatia: galamsey • These miners are mining on Akwatia property in an area “not commercial enough” • They pay a sliding fee to be allowed to mine; the greater the grade, the higher the fee

  46. Akwatia: Galamsey • Waste from the mine is trucked to the river and dumped • Galamsey pay a fee • Clay muck is broken up in ½ 55 gallon drums and clay washed off

  47. Akwatia: Galamsey • Slurry is given to panners • Use a wooden box with window screen • Wash away the clay • Concentrate the diamonds • Scoop off the quartz into the river

  48. Akwatia: Galamsey • Always being watched by many people • The man with the boots and the fanny-pack is in charge… everyone else is barefoot

  49. Akwatia

  50. Akwatia: town & mine • Daily Graphic newspaper reports that Akwatia is in poverty and has some of the highest levels of cholera and malaria seen in Ghana. Why? • Human activity at the riverside soils the river • Pits are not backfilled immediately since galamsey are still mining there