El Nino underground mine is located within the South Arturo gold project in Carlin Trend, Nevada, US. The project is located at the down plunge of the phase two pit of South Arturo.
Premier Gold Mines hold 40% stake in South Arturo, while the remaining 60% is held by Barrick Gold Exploration, a wholly-owned subsidiary of Barrick Gold Corporation. It is estimated to mine 40,000 tonnes (t) of ore from El Nino.
Mining activities at the El Nino underground mining project began in 2018, while first gold bar was produced in September 2019. Full production is anticipated to be achieved in 2020.
El Nino gold mine project location and geology
The El Nino underground mine within South Arturo is located in the prolific Carlin Trend, approximately 40km from Carlin, Elko County, Nevada.
The South Arturo Property includes the historic Dee pit and the El Niño underground mine.
The El Nino deposit is a Carlin-type deposit, with fine to very finely disseminated gold and arsenic-bearing pyrite.
The deposit hosts hydrothermal alteration along with collapse structures, which generated the breccias. The alteration and folding and faulting have led to poor rock quality in the deposits in generally and locally very poor ground conditions near the major faults.
El Nino gold reserves
As of December 207, the total proven and probable gold ore reserves at El Nino were estimated to be 85.9Mt, grading 9.7g/t of gold. The deposit is estimated to contain 26,800 ounces (oz) of gold.
Mining and processing at the El Niño underground gold project
The primary method of underground mining used is underhand cut-and-fill with cemented rock fill as the fill material. Major underground mobile equipment used consists of load-haul-dump units, haul trucks, jumbos, bolters, and other support equipment.
Access to the underground project is through a portal located at an elevation of 1,536m above sea level (asl) within the South Arturo phase pit. Ore from the decline is reclaimed using a twin portal decline.
The underground oxide ore is treated at an oxide mill at Barrick’s Cortez site, while the refractory ore is treated at Barrick’s Goldstrike operation. The heap leach mineralisation is proposed to be segregated at the South Arturo site for future processing.
The El Nino underground mine is anticipated to recover approximately 215,000t of ore at an average grade of 9.7g/t Au from 2018 to 2024.
The Cortez plant will comprise crushing, semi-autogenous grinding (SAG), ball milling, grind thickening, and carbon-in-column (CIC) circuit. Other infrastructure present is carbon-in-leach (CIL) circuit, tailings counter-current decantation (CCD), carbon stripping and reactivation circuits, and a refinery to produce gold doré.
Ore scheduled for roaster/CIL processing will be toll-processed in the existing roaster circuit at Goldstrike.
The project will make use of the existing South Arturo project infrastructure.
A new haul road was constructed to access the underground portals in phase two pit, as part of the underground development. Other new facilities developed include the backfill plant and cement storage facilities, power transmission lines, electrical substation, fuel and lube storage facility, and fresh water tank and piping.
Roscoe Postle Associates (RPA) prepared the technical report on the South Arturo mine, which hosts the El Nino underground project.