Hycroft

Overview

Hycroft gold-silver mine is located 50 miles west of Winnemucca, Nevada, USA. The open pit mining operation is 100% owned by Allied Nevada Gold Corporation which acquired its interest in 2007.

Initial exploratory drilling that targeted copper and sulphur mineralization was conducted in 1974. Homestake drilled it again in early 1980s and discovered shallow oxide gold mineralization. A small scale gold oxide heap leach mining operation started in 1983.

Hycroft is a conventional open pit mining operation that treats the oxide ore through heap leach methods and recovers the gold by using a Merrill Crowe method.

A $1.2 billion expansion would see the increasing of mining rate from 20 million tons per year in 2010 to 75 million tons per year in 2013. The expansion requires the use of larger mobile equipment, fixed crushing plants and increased solution treatment capacity. The approved heap leach expansion would increase annual gold production to approximately 300,000 ounces and silver production to over one million ounces by the end of 2013.

A further expansion would treat higher grade ore through a separate mill and flotation facility. Production is expected to average 582,260 ounces of gold and 29.1 million ounces of silver between 2015 and 2024 with the commencement of milling operations.

Location

Hycroft mine is located 87 km (56 miles) west of Winnemucca in Humboldt and Pershing Counties, Nevada, USA. The mine is accessible via Nevada Highway 49, an all-weather unpaved road.

Nevada is an American state located in the west of the country in the Great Basin area. Tourism, gambling and gold mining are the mainstays of its economy. Winnemucca is served by a transcontinental railroad and has a small airport.

The Hycroft property consists of 22 patented mining claims (1,794 acres) and 2,893 unpatented mining claims (59,595 acres). The mine is located on the western flank of the Kamma Mountains on the eastern edge of the Black Rock Desert.  There are no streams, rivers or major lakes in the area.

The climate is hot and arid. Dust storms could occasionally occur during the spring.

Geology & Mineralization

The Hycroft property consists of Tertiary to Recent age, fault-controlled, low-sulfidation gold zones that occur over an area measuring approximately three miles in a north-south direction by two miles in an east-west direction. The zones are hosted in volcanic rock eruptive breccias, flows and conglomerates associated with the Tertiary Kamma Volcanics and sand to conglomeratic debris flows associated with the Tertiary Sulphur Group.

The Hycroft deposit is a large, epithermal, low sulfidation, hot springs deposit. Gold and silver mineralization occurs as both disseminated and vein controlled, with gold values ranging from detection to 8.8 opt, and silver ranging from detection 647.5 opt. Radiometric dating indicate that the age of the main phase of mineralization is 4 million years.

The Brimstone Deposit is hosted within the hanging wall of the East fault. This portion of the deposit has been highly structurally prepared by four phases of alteration. Gold mineralization is thought to have occurred during a period of fracture controlled, chalcedony/pyrite/marcasite mineralization. Oxidation appears to be related to a deep acid leaching event.

Based on drilling results, mineralization extends to depths of at least 330 ft from the northwest corner of the Bay Area, to over 1,000 ft in the Brimstone deposit in the eastern portion of the Hycroft property, and over 2,000 ft in the southeastern Vortex Zone.

Mining & Operations

Hycroft operations are currently conducted via standard open pit mining methods for run-of-mine and crushed ore followed by heap leaching from the Brimstone and Cut-5 pits. A portion of the higher grade ore is crushed using a mobile crushing plant before being placed on the leach pad.

In 2010, the company began implementing an expansion of the existing heap leach operations to increase the mining rate from 35 Mtpa in 2011 to over 90 Mtpa in 2014. The expansion requires the use of larger mobile equipment, mobile crushing units and increased solution treatment capacity.

A further expansion to the Hycroft operation involves the addition of a 130,000 tpd mill and flotation plant, operating concurrently with the heap leach process, via large-scale, bulk tonnage, open pit mining methods. Mining will be conducted via typical truck and shovel mining methods. A total of 39 additional 320-ton haul trucks will be added to the 16 haul trucks already being used in the heap leach expansion.

The mining rate increases from an annualized rate of 80 million tons per year at the beginning of 2014 to a rate of 235 million tons per year at the start of 2016.

The ultimate mining fleet would comprise: Caterpillar 7495 Wire Rope Electric Shovels (4);  Hitachi EX5500 Hydraulic Shovels (3); Caterpillar 994 Front End Loader (1); Atlas Copco 271 Pit Viper Drills (14); Komatsu 930E Haul Trucks (55); Caterpillar D11 Class Dozers (5);  Caterpillar 16G Motor Graders (4);  20,000 gal. Komatsu 785E Water Trucks  (4);  Caterpillar 834H Rubber Tired Dozers (3); Komatsu D475 Track Dozers (2); Komatsu D375-A Track Dozers (2);  Backhoe (Three yd3) (1); Komatsu D65-W Track Dozer (1); 9,000 gal. Volvo A40D Articulated Water Truck (1); Komatsu PC200LC-8 Excavator (1).

Process 

Oxide ore is being processed through the heap leach method. Gold is being recovered through a Merrlill Crowe process and is subsequently further refined on site.

Lower grade oxide ore will be transported by truck to the heap leach processing facility and the sulfide and higher grade oxide and transitional ores will be transported to the milling and flotation facility. Lower grade oxide and transitional ores will be crushed and delivered to the heap leach pads.

Lower grade mill ore will be stockpiled throughout the life of the mine to allow for selectively processing higher grade ore through the mill. Once pit reserves are exhausted, the low-grade stockpiles will be processed through the mill as incremental feed. The reserve is expected to be exhausted in 2025 but processing of ore through the mill will continue through 2030.

The approved heap leach expansion would increase annual gold production to approximately 300,000 ounces and silver production to over one million ounces by the end of 2013. The processing flowsheet for the Hycroft milling expansion is expected to include: Crushing; Grinding; Rougher and cleaner flotation including rougher concentrate regrind; Concentrate leaching; Tails leaching; Pressure oxidation of the rougher concentrate (2021-2027); Merrill-Crowe metal recovery; and, Refining.

Production is expected to average 582,260 ounces of gold and 29.1 million ounces of silver between 2015 and 2024 with the commencement of milling and flotation operations.  The milling facility will be comprised of the following milling circuit: 2 x 36-foot (diameter) x 24-foot (long) SAG mill with dual drives; 2 x Vibrating SAG discharge screen to scalp oversize pebbles; 2 x Cone crushers to crush SAG screen oversize; 3 x 26-foot (diameter) x 42-foot (long) ball mills with dual drives; 3 x Cyclone feed pumps, one per ball mill; 3 x Cyclone clusters, one per ball mill; Oxide and transitional tails leach.

Environment & Community

The economies of Humboldt and Pershing counties depend to a large degree on mining, ranching, agriculture and tourism. There is a general acceptance of the mining industry in the area. Local communities benefit from mining activities taking place at Hycroft.

Mine closure and reclamation will be performed in accordance with BLM and State of Nevada regulations and guidelines.