The state of Nevada is rated as the fourth best mining jurisdiction in the world in the latest Fraser institute ranking (2016) and is the fifth largest gold producing district in the world, with an estimated endowment of over 360 million ounces. Most of this is associated with Carlin-style mineralization, although many epithermal deposits also exist.
There are numerous large Carlin-style deposits including Carlin itself Goldstrike (Betze-Post-Miekle), Gold Quarry, Pipeline, Cortez Hills, Goldrush, Jerritt Canyon, Leeville, Getchell-Turquoise Ridge and Twin Creeks.
Many of these deposits are greater than 10 million ounces and some cluster in camps containing over 50 million ounces. Most ot these deposits are aligned on several trends, including the Carlin trend, the Battle Mountain-Eureka trend, and the Getchell trend. Some newer discoveries, such as Long Canyon, have been made in non-conventional areas and settings off these trends.
As a maor gold and silver producing state, Nevada is well appointed with mining-related goods, services and expertise, and has a well defined and relatively mining friendly legal framework.
Geographically, the region is known as the Basin and Range Province - a high desert region comprising north-south trending mountain ranges and valleys. The ranges reach heights of between 2,400 to 4,000 metres and are separated by broad valleys filled with colluvial gravels eroded from the adjacent ranges ("pediment"). Exploration is possible year round in all but the highest ranges.
About Carlin-style gold deposits
Carlin-style gold deposits are a distinctive style of gold deposit that is very different from the Archaean lode gold deposits of the Yilgarn Craton of Western Australia and the Abitibi Belt of Canada, the Proterozoic lode gold deposits of the Birimian of West Africa and the Central Lapland Greenstone Belt of Finland, and the Palaeozoic slate deposits of Victoria.
Carlin-style mineralization is relatively young in age (34-42 Ma (Eocene)) and formed by the alteration and replacement of carbonate rocks by gold-bearing hydrothermal fluids. The host carbonates are often hidden beneath less favourable and impermeable rocks that have been thrust over them. The footwall sequence containing the receptive carbonates is termed the "lowe plate", and the overlying sequence comprising less receptive host rocks is termed the "upper plate".
The overthrust upper plate rocks act like a seal above an oil reservoir, and gold-bearing hydrothermal fluids that have migrated up adjacent faults are trapped in the receptive carbonates. Carlin-style gold deposits occur in altered carbonates in and adjacent to these faults and also where these gold-bearing fluids have ponded beneath the upper plate seal or other impermeable barriers, particularly in structures such as anticlines, very much like oil. Mineralization can also occur in and around the fault zones themselves, and may even occur in the less favourable rocks of the upper plate where these structures pierce it.
This process is evidenced by the presence of silicification of the carbonates and the development of jasperoids (iron oxide-bearing silica alteration), often accompanied by strong gold, silver, mercury, antimony, bismuth, thallium and arsenic anomalism, and can lead to the creation of very large (>10 million ounce) and often high grade (>15g/t) gold deposits. The gold is usually very fine grained and metallurgically refractory but is commonly treated using pressure oxidation prior to conventional cyanide leaching with good recoveries.
In addition to the above, recent detailed sequence stratigraphy analysis of the carbonates has highlighted the importance of specific sedimentarry environments and facies within the carbonate host rocks that are more porous and therefore particularly favourable sites for gold mineralization. This has expanded areas of prospectivity both within the main trends and in other non-conventional environments in areas not previously considered prospective.