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

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gold diamond exploration in ghana

Gold & Diamond Exploration in Ghana

Patricia L. Frisch

New Mexico Bureau of Geology & Mineral Resources

geography of ghana
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
ghana and its neighbors
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
geography of ghana4
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!
geology formations stratigraphy
Geology: Formations & Stratigraphy
  • Tarkwaian (2.155 to 2.096 Ma)
    • Huni Quartzite
    • Tarkwa phyllite
    • Banket
    • Kawere
  • Upper Birimian (2.170 Ma)
  • Lower Birimian
ghana the heart of the gold coast
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!

nkroful
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
nkroful8
Nkroful
  • 1 ton/day * 23 ppb = 23 grams
  • The recovery is ~35%
  • So: are they lying?
  • Or, not working hard enough?
nkroful9
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
nkroful10
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
nkroful11
Nkroful
  • This was our first stop looking at gold in Ghana.
  • This is to be the richest and smallest deposit we visited.
gold mines we visited
Gold mines we visited
  • Bibiani
  • Awaso
  • Obuasi
  • Dunkwa
  • Prestea
  • Tarkwa

Tarkwa

gold fields tarkwa mine
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

gold fields wassa mine
Gold Fields: Wassa Mine
  • Inactive and flooded pit lake
  • 11 M tons reserve @ 1.55 g/ton
  • Good for jetskiing
  • Bad for jetskiiers
damang mine
Damang Mine
  • Paleoplacer! The only one on this trip.
  • Mine old streambeds, cutbanks.
  • Seams of gravels
  • Moral of the story: know your structural geology!
gold mines we visited17
Gold mines we visited
  • Bibiani
  • Awaso
  • Obuasi
  • Dunkwa
  • Prestea
  • Tarkwa

Prestea

bogoso gold ltd prestea
Bogoso Gold Ltd.: Prestea

Prestea Pit

Red: volcanics

Black: graphite schist

Au & Au-Arsenopyrite in the graphite schist

prestea
Prestea
  • Over 7 million oz reserve in this claim group
  • Background laterites have soil anomalies of 70-80 ppb Au
prestea20
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!
prestea21
Prestea
  • BiOx plant being built
  • Many “galamsey” still working the inactive areas
gold mines we visited22
Gold mines we visited
  • Bibiani
  • Awaso
  • Obuasi
  • Dunkwa
  • Prestea
  • Tarkwa

Obuasi

obuasi largest au mine in ghana
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!
obuasi25
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
obuasi biox plant
Obuasi: BiOx Plant
  • Sulfide eating bacteria eat the pyrite & arsenopyrite
  • 84% yield using BiOx
  • Currently world’s largest plant
  • 7% Au recovered panning tailings
obuasi work environment
Obuasi: Work environment
  • “heavy on the propaganda”
obuasi29
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
obuasi30
Obuasi
  • The reserves never go down
  • Production never slows
  • Everywhere you look, there’s gold
obuasi the unsaid
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
ashanti goldfields bibiani
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
bibiani
Bibiani
  • Recent pitwall failure
  • Pit grade 3.5 g/ton
  • Only underground mining currently
newmont exploration property ahafo project
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
ahafo project
Ahafo Project

3

1

Ore zone: shattered host with pyrite & Au

Hanging wall K-spar

2

4

Hanging wall mylonites

ahafo prospect
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
ahafo prospect39
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?

historically diamonds
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
more about diamonds
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…
u n debeers
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
akwatia
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
akwatia44
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
akwatia galamsey
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
akwatia galamsey46
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
akwatia galamsey47
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
akwatia galamsey48
Akwatia: Galamsey
  • Always being watched by many people
  • The man with the boots and the fanny-pack is in charge… everyone else is barefoot
akwatia town mine
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
diamond trade
Diamond trade
  • Diamonds are mined by the galamsey and the mine, but DeBeers will buy from anyone just to keep the illegal trading down
  • Diamond buyers go out to the prospecting pits and collect the diamonds as they are being sieved
  • Bort will get you about $40/ct.
  • High-quality cutable is more in the $300/ct. range
akwatia52
Akwatia
  • Mined since the 20’s
  • 100 million carats produced
  • 80% bort or industrial size
  • Ultramafic rocks crop out for 1 sq. km
  • Two diamond-bearing units identified
  • Cover of Mineralogical Record
conclusions
Conclusions
  • Ghana has temendous mineral wealth and outputs twice the GNP of neighboring countries
  • The government is amenable to mining operations and holds 10% of every mining company operating in Ghana
  • Ghana is tremendously underexpolored