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The Columbia property is located seven miles east of Lincoln and 45 miles northwest of Helena, in Lewis and Clark County, Montana.
In September 2009 Atna completed an NI 43-101 compliant mineral resource estimate for the Columbia Project. The estimate establishes a measured and indicated mineral resource of 16.6 million tons grading 0.045 oz/ton gold containing 741,680 ounces of gold. In addition, estimated inferred resources total 10.7 million tons grading 0.042 oz/ton gold containing 453,570 ounces of gold. Both estimates were calculated at 0.020 oz/ton gold cut-off grade. Significant silver values are also associated with the gold resource.
View, NI 43-101 Technical Report
The completion of the resource estimate demonstrates that Columbia has the size and economic potential required to fill Atna's growth pipeline.
The resource estimate is reported in the following tables at varying cut-off grades:
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Classification
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Tons
(x1,000)
|
Gold Grade
(oz/ton Au)
|
Contained
Ounces Gold
|
Silver Grade
(oz/ton Ag)
|
Contained
Ounces Silver
|
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0.010 oz/ton Au cut-off
|
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Measured
|
10,439
|
0.031
|
326,720
|
0.116
|
1,213,350
|
|
Indicated
|
22,401
|
0.029
|
644,560
|
0.093
|
2,074,110
|
|
Measured + Indicated (1)
|
32,839
|
0.030
|
971,280
|
0.100
|
3,287,460
|
|
|
|
|
|
|
|
|
Inferred
|
22,971
|
0.027
|
627,890
|
0.083
|
1,898,630
|
|
|
|
|
|
|
|
|
0.020 oz/ton Au cut-off
|
|
Measured
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5,370
|
0.047
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254,450
|
0.155
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831,100
|
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Indicated
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11,294
|
0.043
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487,230
|
0.116
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1,304,380
|
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Measured + Indicated (1)
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16,665
|
0.045
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741,680
|
0.128
|
2,135,480
|
|
|
|
|
|
|
|
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Inferred
|
10,705
|
0.042
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453,570
|
0.097
|
1,305,790
|
|
0.050 oz/ton Au cut-off
|
|
Measured
|
1,443
|
0.093
|
134,750
|
0.249
|
359,540
|
|
Indicated
|
2,489
|
0.089
|
220,980
|
0.175
|
435,880
|
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Measured + Indicated (1)
|
3,932
|
0.091
|
355,730
|
0.202
|
795,420
|
|
|
|
|
|
|
|
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Inferred
|
2,236
|
0.086
|
191,440
|
0.117
|
261,740
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(1) Rounding may cause totals to not precisely add up.
The resource estimate is based on 337 drill holes totaling 146,973 feet of drilling and 12,538 feet of surface trenching in 78 trenches carried out between 1989 and 1993. Bulk sampling, development studies, metallurgical testing, and environmental baseline studies were conducted during the same time period. The deposit remains open for possible extension both along strike and to depth.
A feasibility study was completed in 1991 by Phelps Dodge Mining Company, then our joint venture operator. The 1991 feasibility study showed positive internal rates of return for all gold prices above $375 per ounce. The study envisioned an open pit mine with a CIL mill using cyanide based gold recovery systems to produce 75,000 ounces of gold per annum over a 7.5 year life. This previous study does imply current economic viability. Atna retains the information and samples from this study including drill core and reverse circulation chips.
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Montana State law prohibits the use of cyanide based gold recovery for open pit mining. However, preliminary metallurgical test work indicates that 90 percent to 94 percent of the gold is recoverable by conventional gravity and flotation methods to produce a gold and silver concentrate. Final processing of this gold concentrate may be accomplished by conventional methods. Additional metallurgical test work and optimization studies will be carried out to determine the most economic treatment process. Baseline environmental water quality data collection has commenced at the site and the Company plans to commence feasibility study work.
The Columbia property is covered by middle Tertiary andesitic volcanic rocks. Gold and silver occurs with quartz-pyrite mineralization in several low-sulfidation, epithermal, quartz-adularia vein swarms. The vein systems are focused along north to northwest-trending faults and in stockwork and breccia flooding adjacent to the principal shears. The gold mineralized structures generally dip west and are up to 150 feet wide.
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