The Chinchillas silver-lead-zinc project is located within the Bolivian silver-zinc-tin belt, which stretches into northern Argentina. It is one of biggest silver discoveries in 2014 and estimated to contain indicated resources of 104 million silver-equivalent ounces. The project is owned by Puna Operations joint venture (JV), formed between Silver Standard Resources (SSR Mining) (75%) and Golden Arrow (25%) in May 2017.
The ore extracted from the open-pit mine is being processed at a rate of 2.9 million tonnes a year (8,000t a day). The Chinchillas mine is operated by Silver Standard and is estimated to have a life of 12 years.
Golden Arrow announced the positive pre-feasibility study of the project in March 2017.
Chinchillas project location, geology, and mineralisation
The Bajo de la Alumbrera (Alumbrera) copper-gold mine in Argentina is owned and operated by Minera Alumbrera (MAA).
The Chinchillas project is located within the Puna region, in Jujuy province, in the department of Rinconada, Argentina. The deposit is a part of the Puna geological belt.
Lead and zinc at the deposit occur as disseminated sulphides and matrix infilling within volcanic tuffs, and as matrix and fracture filling in breccias within the basement meta-sediments. The majority of the mineralisation occurs in thick layers within the volcanic tuffs and breccias. A second style of silver-lead-zinc mineralisation is also found.
The deposit is further categorised into two main zones, namely the Silver Mantos Zone in the western portion of the basin, and the Socavon Del Diablo Zone in the east. Most of the mineralisation in both the zones is contained within the basin and in the basement host rocks.
Mineralisation at the Silver Mantos basin is spread over multiple flat-lying layers or mantos, made up of strongly clay-altered volcanic tuffs and breccias. Mineralisation in the Socavon del Diablo zone is dominated by manto-style disseminated sulphides located within the shallow-dipping volcanic tuff horizons.
Chinchillas mine reserves
The Chinchillas mine was estimated to contain 11.7Mt of proven and probable ore reserves containing 58 million ounces (Moz) of silver grading 154 g/t, 310 million pounds (Mlb) of lead grading 1.20% and 127Mlb of zinc grading 0.49%.
Mining and processing of ore from Chinchillas silver deposit
Conventional open-pit mining method, using drilling and blasting followed by loading and hauling, is being practised at the Chinchillas mine.
The run-of-mine (ROM) ore is being delivered to the processing plant and stored in separate stockpiles before blending. The feed is reclaimed and fed to a large jaw crusher where it is crushed to 150mm and stockpiled.
Feed from the stockpile is reclaimed by a series of belt feeders and transferred through a conveyor to the primary semi-autogenous grinding (SAG) mill, which is operated in conjunction with a ball mill.
The grinding circuit is closed with cyclones, while the cyclone overflow undergoes flotation. Sodium meta-bisulphite is used as the primary zinc depressant, and xanthate and a secondary collector is used to recover lead and silver. Rougher and scavenger concentrates are cleaned after regrinding in a tower mill, and the resultant concentrate is fed to a thickener.
Flotation tailings from the lead circuit are fed to the zinc circuit. The sphalerite (zinc-sulphide) is activated with copper sulphate prior to flotation with xanthate. The rougher/scavenger concentrate is cleaned after regrinding and then sent to a thickener.
The thickened lead concentrates is filtered in pressure filters and bagged for delivery to customers.
Financing for Chinchillas project
The project received $1.5m in financing from Silver Standard, the operator of the neighbouring Pirquitas silver mine. It also obtained a $3m finance facility from an undisclosed investor based in Argentina.
Infrastructure facilities at the mine site
Access to the mine site is through the existing roads from Santo Domingo or the Pirquitas Mine. Most of the power required for the operations is procured from Santo Domingo. A new high-voltage (69kV) transmission line is constructed from Abra Pampa to the project site, over a distance of 66km.
Golden Arrow contracted Energold Argentina in November 2012 to conduct diamond drilling at the Chinchillas silver project.