Deposit Type
- Epithermal
- Breccia pipe / Stockwork
- Vein / narrow vein
Summary:
The Moss deposit is a steeply dipping (average 70°) quartz-calcite vein and stockwork system, which extends over a strike length of approximately 1,400 m in the project area, but can be traced for more than 5.6 km in total length.
The Moss vein system is considered a high level, low-sulfidation (adularia-sericite) epithermal gold-silver deposit in the classification of Heald et al (1987) and White and Hedenquist (1995). Low sulfidation epithermal deposits form from hydrothermal waters in the relatively near-surface environment, typically within 1.5 km of the earth’s surface (Taylor, 2007). They are commonly found associated with magmatism and volcanism, but are somewhat distal (vertically or laterally) from the actual center of magmatism, in environments where meteroric waters have mixed with and diluted magmatic waters.
Epithermal deposits comprise one of three sub- types: high sulphidation; intermediate sulphidation; and low sulphidation. Each sub-type is identified by characteristic alteration and ore-stage mineral assemblages, occurrences, textures and suites of associated geochemical elements. The designation of high sulfidation vs low sulfidation is based on the sulfidation state of the ore-stage sulfide suite, not the abundance of sulfides in the ore. However, precious metals mineralization at Moss is characterized by a low sulfidation suite of minerals and a very low sulfide content (<1%) as well.
The quartz-calcite vein textures at Moss (massive, breccia, vuggy, colloform), are typical of low sulphidation epithermal veins. Gold occurs as very fine native gold and electrum, and silver typically occurs as electrum and very fine grained acanthite, similar to other low-sulfidation precious metals deposits.
The very low (usually trace) levels of base metals in the Moss ores are also consistent with high- level low-sulfidation gold deposits. Alteration related to main-stage precious metals mineralization is confined to silicification and minor sericitization of wallrock adjacent to the veins.
The Moss mineralization differs from typical low- sulfidation precious metals deposits in its lack of adularia (possibly present, but not yet positively identified) and lack of deleterious elements such as arsenic, antimony, and mercury.
The mineralogy of the Moss vein system is simple and the mineralization is nearly void of all deleterious elements. Key elements are:
- Gangue consists of quartz and calcite with minor fluorite locally occurring as late stage veins and vug fillings.
- Gold mineralization is predominantly in the form of very fine grained native gold and silver-rich native gold grading to electrum (an alloy of gold and silver with Ag:Au >1:5).
- Silver occurs as electrum and within the silver- rich gold. Minor native silver has also been identified. In addition, minor amounts of very fine grained, grey to black sulphides (dominantly acanthite, Ag2S) are present as disseminations and occasionally in very thin grey bands in unoxidized or weakly oxidized parts of the veins. The silver minerals bring the overall Ag:Au ratio of the deposit to approximately 8:1.
- Base metals (Cu, Pb, Zn) are very low, especially in the upper parts of the system, but show a slight increase with depth, consistent with low-sulfidation epithermal veins.
- No arsenic or antimony minerals occur.
- Mercury is negligible.
Summary:
Exploitation of the mineral reserves in the Moss vein and adjacent stockworks on the patented lands will be by open pit mining methods with a conventional drill-blast-load-haul mining fleet.
The PEA mine design removes the patented claims boundary constraint by assuming the pit limits can be extended onto the adjacent Federal lands controlled by the BLM. This allows the PEA mine plan to access the mineral resources not available in the Phase II mine plan. Concurrent with expansion of the pit, the mine facilities would also need to be expanded onto the BLM lands. This would include an expanded heap leach pad to accommodate the additional mineralized material, and an expanded waste rock facility to accommodate the additional waste rock.
Processing
- Heap leach
- Merrill–Crowe
- Cyanide (reagent)
Flow Sheet:
Summary:
The most economically effective process has been identified as one that consists of heap leaching of crushed and agglomerated ore, followed by a Merrill Crowe metal recovery plant and refinery to produce gold and silver doré bars on site.
Ore grade material from the open pit will be crushed to 6.35 mm and then agglomerated with cement prior to loading on the heap leach pad in 10m lifts. The crushing circuit will employ three stages of crushing consisting of a primary jaw crusher, a secondary cone crusher, and two tertiary cone crushers. After agglomeration, the fine ore will be conveyed to the leach pad with a series of grasshopper conveyors feeding a radialstacker.
The expanded leach pad is based on the same operating parameters as the Phase II leach pad in terms of tonnes stacked daily, solution application rates, and lift heights. The expanded leach pad geotechnical design will be in accordance with Arizona BADCT protocols, and stacking will be accomplished v ........

Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Gold
|
Recovery Rate, %
| ......  |
Gold
|
Head Grade, g/t
| 0.7 |
Silver
|
Recovery Rate, %
| ......  |
Silver
|
Head Grade, g/t
| 8.33 |
Gold Equivalent
|
Head Grade, g/t
| 0.83 |
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Reserves at October 10, 2017:
Category | Tonnage | Commodity | Grade | Contained Metal |
Measured
|
5,138 kt
|
Gold
|
0.94 g/t
|
155 koz
|
Measured
|
5,138 kt
|
Silver
|
10.15 g/t
|
1,676 koz
|
Indicated
|
10,161 kt
|
Gold
|
0.62 g/t
|
201 koz
|
Indicated
|
10,161 kt
|
Silver
|
7.93 g/t
|
2,592 koz
|
Measured & Indicated
|
15,299 kt
|
Gold
|
0.72 g/t
|
357 koz
|
Measured & Indicated
|
15,299 kt
|
Silver
|
8.68 g/t
|
4,268 koz
|
Inferred
|
1,785 kt
|
Gold
|
0.44 g/t
|
5 koz
|
Inferred
|
1,785 kt
|
Silver
|
5.37 g/t
|
308 koz
|
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