ghana

Information about ghana

Published on December 10, 2007

Author: funnyside

Source: authorstream.com

Content

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 Ghana:  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 Nkroful:  Nkroful 1 ton/day * 23 ppb = 23 grams The recovery is ~35% So: are they lying? Or, not working hard enough? Nkroful:  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 Nkroful:  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 Nkroful:  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! Damang Mine:  Damang Mine Gold mines we visited:  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 Prestea:  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! Prestea:  Prestea BiOx plant being built Many “galamsey” still working the inactive areas Gold mines we visited:  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! Obuasi:  Obuasi Obuasi:  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” Obuasi:  Obuasi Obuasi:  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 Obuasi:  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 Bibiani:  Bibiani Bibiani:  Bibiani 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 Hanging wall K-spar Hanging wall mylonites 1 2 4 3 Ore zone: shattered host with pyrite & Au 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 Prospect:  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 Akwatia:  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: Galamsey:  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: Galamsey:  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: Galamsey:  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:  Akwatia 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 Akwatia:  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

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