North Bullfrog
Introduction
The North Bullfrog Project consists of patented and unpatented mining claims covering an area of approximately 68 km2 situated 10 km north of Beatty, Nevada, and 8 km north of the Bullfrog Mine*. The project represents a large, low-sulphidation, epithermal bulk-tonnage gold system hosted in volcanic and sedimentary rocks.
The North Bullfrog project includes eight prospective gold targets, one of which (the Mayflower) is envisioned as the initial phase of development and production containing an NI 43-101 estimated Indicated resource of 6.56Mt at 0.50 g/t gold for 106,298 contained ounces of gold (at 0.2 g/t gold cutoff grade as outlined in the "Technical Report and Preliminary Economic Assessment for Mayflower and North Areas at the North Bullfrog Project, Bullfrog Mining District, Nye County, Nevada, December 6, 2012" - available on SEDAR).
* This information is not indicative of the mineralization on the North Bullfrog property or the potential production from or any future mining of the North Bullfrog property.
Ownership
The project is 100% controlled by Corvus Gold.
Project Background
Gold was discovered in the Bullfrog district in 1904 resulting in an estimated production of approximately 112,000 ounces of gold and 869,000 ounces of silver through 1921 from high-grade vein systems that remained open along strike and down dip. There was only minor activity in the district after the initial production period until modern exploration at the North Bullfrog project area started up in 1974 and continued until 1996 during which time several companies mapped, sampled, and drilled several areas of gold mineralization. Declining precious metal prices in the late 1990s resulted in reduced interest in the area.
In 2005, the project was picked up and explored by Redstar Gold Corporation and International Tower Hill (ITH) entered into a joint venture with Redstar to explore the project in 2007.
Geology and Mineralization
The North Bullfrog project lies along a northerly trending district-scale fault system which extends from the Bullfrog mine into the project area and believed to be a regional control to gold mineralization. Numerous normal faults cut the volcanic sequence and localized vein-style gold mineralization in both areas. Basement Paleozoic limestone, shale and quartzite occur in the project area, locally as large rootless inclusions within volcanic debris-flow breccias. Unlike the Bullfrog mine area, the North Bullfrog contains abundant syn-volcanic intrusions, possibly indicating a more proximal magmatic/volcanic environment compared to the Bullfrog mine.
Two styles of precious metal epithermal mineralization are present at the project: 1) potentially high-grade, structurally controlled fissure veins and associated stockwork zones, and 2) low-grade disseminated or replacement deposits within altered volcanic rocks.
Exploration summary
ITH completed drilling programs in 2007 and 2008 which encountered significant mineralization at three target areas: Mayflower, Sierra Blanca and Pioneer. Results from drilling at the Mayflower target were used to for the calculation of an initial resource estimate (see below). ITH was targeting a multiple deposit concept for the property, which could support a central processing facility.
The project was spun out from ITH into Corvus Gold in August 2010. A 75-hole, 17,820-metre drill program was carried out from October 2010 to July 2011. The program was successful in defining a thick oxide mineralization in the northern portion of the property covering approximately 1.6 km2. A highlight of the 2010-2011 drill program included a hole that returned 13.7 metres (11.9 metre true width) of 5.9 g/t gold and 5.2 g/t silver, and a high-grade intercept of 6.1 metres grading 11.9 g/t gold and 8.8 g/t silver.
Work on an updated NI 43-101 resource estimate was completed in late September 2011. For 2012, a 2-phase drill program completed 4,000 metres of PQ core drilling and RC drilling to assess the resource expansion potential of the current deposit in step out holes and to follow-up on the Yellowjacket high-grade zone. A more extensive +300 hole, 30,000 metre second phase drill program is currently being permitted to follow up on the defined broad zones of bulk tonnage gold mineralization as well as the high-grade feeder zone and is expected to commence in Q1 2013.
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Mineral Resources
Summary of Indicated and Inferred Resources at North Bullfrog by Deposit
Metallurgical Results (click to expand)
Large diameter (12 inch) leach columns tested coarse crush material (80% of particles less than 50mm) from the Sierra Blanca and Jolly Jane areas. The tests achieved 60% - 69% gold recovery in the first 90 days of cyanide leaching. The gold recoveries after a leach and rinse time of 117 days was between 64% - 70% which support an overall Run of Mine recovery plan.
Initial Column Leach Test Results, North Bullfrog Project
Bulk Samples of Oxide Materials from the Sierra Blanca and Jolly Jane Resource Areas
|
Test No.*
|
Feed Size
|
Leach
/Rinse Time (days) |
Gold Extracted
(g/t) |
Gold Tail
Assay **(g/t) |
Calc.
Head Grade (g/t) |
Gold Rec.
(% Calc. Head Grade) |
|
SB P-1
|
80% -50mm
|
117
|
0.204
|
0.0860
|
0.290
|
70.3
|
|
SB P-2
|
80% -50mm
|
117
|
0.200
|
0.0860
|
0.286
|
69.9
|
|
JJ P-3
|
80% - 50mm
|
117
|
0.208
|
0.120
|
0.328
|
63.4
|
|
JJ P-4
|
80% -50mm
|
117
|
0.217
|
0.122
|
0.339
|
64.0
|
* SB - Sierra Blanca resource area; JJ - Jolly Jane resource area
Bottle roll tests were conducted on bulk samples from historical mine dumps found at Mayflower and reported on July 19, 2012. These results are plotted on a chart as seen below and compared with the average of the column tests at Sierra Blanca and Jolly Jane.
Mayflower Bulk Samples, North Bullfrog Project
Gold Recovery (%) in 96 hr Bottle Roll Tests at Varying Particle Sizes
|
Test No.
|
P80 -200 mesh
(-0.075mm) |
P80 -100 mesh
(-1.7 mm) |
P80 -1/4 inch
(-6.3 mm) |
P80 -3/4 inch
(-19 mm) |
P80 -1.7 inch
(-43 mm) |
| MF Bulk Sample 1 |
98.9%
|
65.1%
|
49.5%
|
51.9%
|
37.7%
|
| MF Bulk Sample 2 |
97.9%
|
78.6%
|
52.9%
|
53.6%
|
34.3%
|
Chart 1 – Comparison of Mayflower PQ Bottle Roll Test Data (composite MF PQ3) to Ongoing Column Leach Tests for Mayflower (composites PQ3 and PQ5) and Savage Valley (samples PQ1 and PQ4).
Mayflower PQ Core Composite Samples, Phase I Drilling, North Bullfrog Project Preliminary Gold Recovery in Column Leach Tests at 71 days (1704 hrs) of Leach Time Particle Size 80% -19 mm (-3/4 inch)
|
|
MF PQ 1
|
MF PQ 2
|
MF PQ 3
|
MF PQ 4
|
MF PQ 5
|
|
% Gold Recovery*
|
85%
|
74%
|
84%
|
82%
|
73%
|
*-based on Au head assay
Savage Valley PQ Core Composite Samples, Phase I Drilling, North Bullfrog Project Preliminary Gold Recovery in Column Leach Tests at 47 days (1128 hrs) of Leach Time Particle Size 80% -19 mm (-3/4 inch)
|
|
SV PQ 1
|
SV PQ 2
|
SV PQ 3
|
SV PQ 4
|
SV PQ 5
|
SV PQ6
|
|
% Gold Recovery*
|
86%
|
84%
|
84%
|
68%
|
84%
|
63%
|
*-based on Au head assay
Mayflower PQ Core Composite Samples , Phase I Drilling, North Bullfrog Project Gold Recovery (%)
in 96 hr Bottle Roll Tests at Varying Particle Sizes
|
Sample
|
P80 -200 mesh
(- 0.075 mm) |
P80 -100 mesh
(-1.7mm) |
P80 -1/4 inch
(-6.3 mm) |
P80 -1.7 inch
(-43mm) |
|
MF PQ 1
|
97.2%
|
83.9%
|
67.3%
|
61.9%
|
|
MF PQ 2
|
95.0%
|
93.1%
|
76.9%
|
66.9%
|
|
MF PQ 3
|
92.8%
|
80.7%
|
73.8%
|
73.2%
|
|
MF PQ 4
|
81.3%
|
90.1%
|
67.3%
|
80.9%
|
|
MF PQ 5
|
91.8%
|
88.1%
|
63.8%
|
73.5%
|
|
MF PQ 6
|
98.7%
|
87.2%
|
73.3%
|
60.9%
|
Savage Valley PQ Core Composite Samples, Phase I Drilling, North Bullfrog ProjectGold Recovery (%)
in 96 hr Bottle Roll Tests at Varying Particle Sizes
|
Sample
|
P80 -200 mesh
(- 0.075 mm) |
P80 -100 mesh
(-1.7mm) |
P80 -1/4 inch
(-6.3 mm) |
P80 -1.7 inch
(-43mm) |
|
SV PQ 1
|
89.7%
|
87.4%
|
87.9%
|
81.0%
|
|
SV PQ 2
|
93.4%
|
88.3%
|
82.4%
|
75.8%
|
|
SV PQ 3
|
95.5%
|
92.4%
|
68.8%
|
87.9%
|
|
SV PQ 4
|
79.1%
|
76.5%
|
64.2%
|
55.2%
|
|
SV PQ 5
|
86.7%
|
83.8%
|
77.5%
|
79.5%
|
|
SV PQ 6
|
81.6%
|
76.3%
|
63.3%
|
51.0%
|
|
|
JJ PQ 1
|
JJ PQ 2
|
JJ PQ 3
|
JJ PQ 4
|
JJ PQ 5
|
|
% Gold Recovery*
|
77%
|
56%
|
76%
|
72%
|
73%
|
|
Sample
|
P80 -200 mesh
(- 0.075 mm) |
P80 -100 mesh
(-1.7mm) |
P80 -1/4 inch
(-6.3 mm) |
P80 -3/4 inch
(-19mm) |
|
JJ PQ 1
|
75.6%
|
85.6%
|
86.0%
|
85.2%
|
|
JJ PQ 2
|
81.1%
|
72.1%
|
61.4%
|
46.7%
|
|
JJ PQ 3
|
86.6%
|
80.9%
|
78.2%
|
70.1%
|
|
JJ PQ 4
|
87.8%
|
77.7%
|
70.3%
|
66.9%
|
|
JJ PQ 5
|
84.3%
|
81.3%
|
76.5%
|
72.8%
|
|
Sample
|
P80 -200 mesh
(- 0.075 mm) |
P80 -100 mesh
(-1.7mm) |
P80 -1/4 inch
(-6.3 mm) |
P80 -3/4 inch
(-19mm) |
|
SB PQ 1
|
88.0%
|
81.5%
|
69.0%
|
63.1%
|
|
SB PQ 2
|
93.7%
|
89.2%
|
84.8%
|
77.8%
|
|
SB PQ 3
|
71.6%
|
66.3%
|
58.4%
|
59.6%
|
|
SB PQ 4
|
92.8%
|
89.5%
|
86.5%
|
81.5%
|
|
SB PQ 5
|
85.9%
|
81.0%
|
74.6%
|
79.2%
|
|
SB PQ 6
|
94.2%
|
93.1%
|
90.7%
|
90.1%
|
|
SB PQ 7
|
90.0%
|
87.0%
|
84.2%
|
81.6%
|
Mayflower PQ Core Composite Samples, Phase I Drilling, North Bullfrog Project Final Gold Recovery in Column Leach Tests at 90-156 days of Leach Time Nominal Particle Size 80% -19 mm (-3/4 inch)
|
|
MF PQ 1
|
MF PQ 2
|
MF PQ 3
|
MF PQ 4
|
MF PQ 5
|
|
% Gold Recovery*
|
88.5%
|
89.7%
|
77.2%
|
89.0%
|
85.7%
|