Gold Recovery During Cyanide Detox

In Heap Leach Pads

Pintail Systems Inc.

Presentation Authors

Caren Caldwell

Leslie Thompson

Cyanide is used in heap leach pads to complex gold and silver in the mining industry

Cyanide detoxification is required for mine closure.

PSI’s bio-detoxification process, which uses native bacteria, has proven to be more efficient than conventional chemical processes

Bacteria culture used in cyanide detox

Pintail Systems, Inc. was founded in 1987 by Leslie Thompson

Primary focus was on cyanide detoxification in gold and silver heap leach pads using native bacteria cultures.

In 1991,The Hecla Mining Company contracted with PSI to develop a treatment process for the Yellow Pine Mine using native bacteria cultures.

Located Near Yellow Pine, Idaho

Alpine Climate

1.2 Million Ton Spent Ore Heap

Environmentally sensitive area

Detox Goals

To degrade WAD cyanide to 0.2 mg/L or less in heap leachate solutions in one operating season

Prior to contracting with PSI, Hecla investigated chemical methods and was quoted 2 to 4 operating seasons.

Heap Bio-Detox

WAD Cyanide in Heap Effluent Solutions

0

10

20

30

40

50

1

29

25

50

59

71

85

94

10

7

11

4

12

1

12

8

13

6

14

6

15

5

Time, Days

WA

D C

ya

nid

e

Detox goal of 0.2 mg/l WAD cyanide was achieved in one operating season, (155) days

During the detox process, there was a significant increase in gold production

Increased gold production was unexpected and more than paid for the detox process

Increased gold recovery paid for mine operations through the end of detox

Mine closure was signed off by the Idaho Department of Environmental Quality

The Hecla Mining Company won the 1992 Pacific Northwest Pollution Control Association’s Idaho Award for the Innovative use of Bacteria in Improving Water Quality

1.3 million ton heap

Located near Parker, AZ

Detox goal was 0.2 mg/L total cyanide in heap leachate solution

Total cyanide closure goal of <0.2 mg/L TCN met in 111 days

Significant Gold Recovery Improvement.

>3000 oz.

Mine closure signed off by the State of Arizona DEQ

Located near Victor, Colorado

5 million ton cyanide-leached spent ore heap

Heap was water-rinsed for 4 years prior to bio-detox

Average detox solution temperature = 35 deg F

Altitude 10,000 ft above sea level.

Detox Goals

Detox WAD cyanide to 0.2 mg/L in heap leachate solution

Decrease the bond requirement for closure by the state of Colorado

l

Cripple Creek WAD Cyanide

0

0.5

1

1.5

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2.5

3

1 24 47 70 93 116 139 162 185 208 231 254 277 300 323 346

time, days

leach

ate

WA

D C

N,

mg

/L

Cripple Creek Gold Recovery

0.00

1000.00

2000.00

3000.00

4000.00

5000.00

6000.00

1 26 51 76 101 126 151 176 201 226 251 276 301 326 351

time, days

cu

mu

lati

ve o

un

ces g

old

Increased gold recovery duringcyanide detox

Met the goal of 0.2 mg/L WAD cyanide in heap leachate solution in 346 days

CC&V water rinse and peroxide treatment (30 pore volumes) did not detoxify cyanide to regulatory limits

Pintail bio-detox achieved cyanide limits with application of less than 3 pore volumes of treatment solution

Bond requirement for mine closure was reduced

Increased gold recovery paid for the detox process. The detox process actually became a profit center for the mine.

Yellow Pine1.2 million tons

CyprusCopperstone

1.3 million tons

Cripple CreekVictor

5 million tons

CyanideConcentration at start of detox

50 mg/L WAD CN in heap leachate solution

20 mg/L TCN in heap leachate solution

Just over 3 mg/L WAD CN in heap leachate solution

Cyanide concentration at end of detox

< 0.2 mg/L WAD CN heap leachate solution

< 0.2 mg/L TCN in heap leachate solution

< 0.2 mg/L WAD CN in heap leachate solution

Gold Recovery > 2700 >3000 oz >6700 oz

Treatment Days 155 days 111 days 350 days

Regulatory Goals Met

Yes Yes Yes

1Technical advances have produced more gold over the

last 160 years than the previous 6000.

2Majority of gold produced in the U.S. is from the Heap

Leaching Process

3Heap Leaching leaves 25 – 40% of the original gold in

the ore at mine closure

Pintail Bio-Processes are the solution to economically recover heap gold4

Cyanide typically recovers 55% to 75% of the gold in a heap leach pad. 25% to 45% residual gold is left in the heap.

Using PSI’s microbial treatment system has been shown to get significant recovery of residual gold during cyanide detoxification.

Ore Tonnage Ore Grade

(oz/ton)

Estimated

Total

remaining

gold (oz)

Estimated

PSI gold

recovery

Mine A 71,000,000 0.009 642,550 417,657

Mine B 81,000,000 0.008 648,000 421,200

Mine C 68,000,000 0.007 465,000 302,250

Mine D 23,000,000 0.008 174,000 113,100

Mine E 36,000,000 0.009 324,000 210,000

Mine F 150,000,000 0.010 1,500,000 975,000

Mine G 170,000,000 0.005 850,000 552,500

Totals 650,000,000 4,603,550 2,992,307

$1100/ oz gross $1300/ oz gross $1500/ oz gross

EstimatedPSI Gold Recovery

$900/ oz net $1100/ oz net $1300/ oz net

Mine A 417,657 $375,891,300 $459,422,700 $542,954,100

Mine D 113,100 $101,790,000 $124,410,000 $147,030,000

Mine F 975,000 $877,500,000 $!,072,500,000 $1,267,500,000

Potential profits based on $200/ oz production cost using PSI Bio Processes