Overview
Stage | Permitting |
Mine Type | Open Pit |
Commodities |
|
Mining Method |
|
Processing |
- Heap leach
- Carbon adsorption-desorption-recovery (ADR)
|
Mine Life | 7 years (as of Jan 1, 2014) |
Company | Interest | Ownership |
Waterton Nevada Splitter, LLC
|
100 %
|
Indirect
|
Mt. Hamilton LLC
|
100 %
|
Direct
|
Summary:
Mineralization at Mt. Hamilton consists of skarn hosted tungsten, molybdenum, and copper +/- zinc with later epithermal gold and silver. Gold mineralization is primarily hosted in a 200 to 300 ft thick skarn horizon, bounded by upper (200 ft thick) and lower (450 ft thick) hornfels units. The bounding hornfels had lower permeability and were therefore less receptive to late-stage mineralization. The interbedded skarn in the Centennial area was subject to late-stage, low-angle faulting. These faults were conduits to late mineralizing solutions and oxidation. The result is an oxide-hosted epithermal gold deposit overprinting a retrograde polymetallic skarn. The main Centennial precious metal mineralization is contained within a southeast dipping (15° to 20°) tabular zone that ranges from 20 to 250 ft in thickness. In the NE Seligman area, ore grade mineralization appears to be largely stratiform in shallow-dipping, bedding-parallel, structurally and chemically prepared zones with local high-angle, cross-cutting, possible "feeder" zones (Burgoyne, 1993). At Centennial, the mineralization is controlled by late low-angle structures that are discordant to bedding and oxidized to significant depth. Gold grades of samples within the retrograde alteration range from <0.001 oz/t Au (lower analytical method detection limit) to 0.995 oz/t. The occasional high grades appear to be associated with crosscutting structures and veins within the skarn as described below.
In the Centennial deposit, weathering and oxidation of original sulfide mineralization caused formation of oxide mineralization (with low sulfide mineral residuals) from which gold is recoverable by cyanide heap leaching. In general, the acid generating capacity of the surrounding carbonate rocks is low or nil, and their acid consuming capacity is high. Gold is present as free gold, residing in iron oxide minerals or quartz, and adsorbed on clay minerals. Sulfosalt-bearing veins may be associated locally with the higher grades of gold and particularly silver. These veins cut both skarn and intrusive rocks and are closely associated with zones of retrograde alteration. These veins range in thickness from about 2 to 60 cm. In the Seligman deposit the mineralization is similar to Centennial but is, on average, thinner. Widely spaced drilling between the two deposits indicates that they represent one contiguous mineralized system that could be connected by additional drilling. Locally, more sulfide minerals are preserved at Seligman in comparison to Centennial. As seen in the mine excavations of the NE Seligman deposit, veins seem to exhibit strong continuity along strike.
Summary:
Oxide mineralization at Mt. Hamilton is close to the surface and the resource lends itself to an open pit mining method. The mine design consists of two main pits with the approximate dimensions of 1,900 ft wide by 2,600 ft long by 800 ft deep; with a volume of 36 Myd3. The pit designs were segregated into at least three phases each for production scheduling with 90 ft wide ramps (including berm) at a maximum in-pit road grade of 10%. Mining operations at Mt. Hamilton have a stripping ratio 2.5:1, waste to ore, with mining taking place on the side of a hill at an approximate elevation of 9,000 ft amsl. Ore will be hauled from the pits to a primary crusher located on the southwest rim of the Centennial pit or stockpiled near the crusher for later use. Waste rock will be placed as valley fill in Cabin Gulch, a centrally located valley between Centennial and Seligman. The final waste rock storage facility will be regraded to 2.5 H/1V per State of Nevada regulations for reclamation.
The mine life is estimated to be seven years with an additional nine months of pit pre-stripping. The life-of-Mine (LoM) average mining rate is estimated at 3.5 Mt/y ore (10,000 t/d) and approximately 8.5 Mt/y waste.
Open pit mining will be by conventional diesel powered equipment, utilizing a combination of blasthole drills, hydraulic shovel, rubber-tired wheel loaders and off-highway 100 t trucks. Support equipment composed of graders, track dozers, and a water truck will aid in the mining of the Mineral Reserve and waste.
Processing
- Heap leach
- Carbon adsorption-desorption-recovery (ADR)
Source:
Summary:
Recovery of gold and silver from the Centennial Project will be performed by heap leaching and conventional ADR carbon-in-column processing. The dedic ted heap leach pad (leach pad), process ponds and ancillary facilities were designed to accommodate a leachable reserve of approximately 22.5 Mt of crushed ore from the mine at a rate of 10,000 t/d.
The proposed heap leach pad and process plant and facilities will have an approximate footprint area of 134 ac. Including the incline portal, secondary crusher pad, and heap leach pad, construction and operation will occupy virtually the entire area of the private parcel upon which it is located. The heap leach pad will be located on moderately sloping and generally uniform topography southwest of the pit in the valley. The leach pad will be roughly square in plan at an average pre-construction elevation of 7,400 ft amsl. The HDPE-lined base receiving ore will range from approximately 13% upslope from the stability berm and toe pa ........

Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Gold
|
Recovery Rate, %
| 76 |
Gold
|
Head Grade, oz/t
| 0.02 |
Silver
|
Recovery Rate, %
| 39 |
Silver
|
Head Grade, oz/t
| 0.2 |
Projected Production:
Commodity | Units | Avg. Annual | LOM |
Gold
|
koz
| 69 | 416 |
Silver
|
koz
| ......  | ......  |
Gold Equivalent
|
oz
| ......  | |
All production numbers are expressed as metal in doré.
Operational Metrics:
Metrics | |
Stripping / waste ratio
| 2.47 * |
Daily mining capacity
| 10,000 t * |
Daily milling capacity
| 10,000 t * |
Ore tonnes mined, LOM
| 25,463 kt * |
Total tonnes mined, LOM
| 88,468 kt * |
Tonnes milled, LOM
| 22,500 kt * |
* According to 2014 study.
Reserves at August 14, 2014:
Category | Tonnage | Commodity | Grade | Contained Metal |
Proven
|
1,240 k tons
|
Gold
|
0.029 oz/t
|
36.6 koz
|
Proven
|
1,240 k tons
|
Silver
|
0.198 oz/t
|
245.8 koz
|
Proven
|
1,240 k tons
|
Gold Equivalent
|
0.031 oz/t
|
|
Probable
|
21,260 k tons
|
Gold
|
0.024 oz/t
|
508.8 koz
|
Probable
|
21,260 k tons
|
Silver
|
0.198 oz/t
|
4,214 koz
|
Probable
|
21,260 k tons
|
Gold Equivalent
|
0.025 oz/t
|
|
Proven & Probable
|
22,500 k tons
|
Gold
|
0.024 oz/t
|
545.4 koz
|
Proven & Probable
|
22,500 k tons
|
Silver
|
0.198 oz/t
|
4,460 koz
|
Proven & Probable
|
22,500 k tons
|
Gold Equivalent
|
|
|
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