Gold at the underground Cisneros project is being produced from the Guaico and Guayabito deposits. Image courtesy of Antioquia Gold.
Construction on the project commenced in October 2015. Image courtesy of Antioquia Gold.
A water treatment plant has been installed at the Cisneros gold mine. Image courtesy of Antioquia Gold.

The Cisneros project is a high-grade gold mine located in Antioquia, Colombia, by Antioquia Gold. It comprises nine deposits with initial gold produced from the Guaico and Guayabito deposits.

Construction of the Cisneros mine started immediately after obtaining the environmental licence for the Guaico deposit in October 2015. The final permit for construction and mining was received in November 2016, following the grant of environmental licence for the Guayabito deposit.

First gold production at Cisneros was achieved in March 2019.

Antioquia Gold is expected to produce between 30,000oz and 40,000oz of gold a year during its initial mine life of six years.

Location and details of Cisneros project

The Cisneros gold mine is located approximately 55km north-east of Medellin and made up of ten concessions spread over 5,630ha. Gold is predominantly found at the deposit, along with smaller amounts of silver, copper and molybdenum.

The Guayabito deposit is an en-echelon style deposit, comprising zones with a strike length of 180m, depth of 300m and thickness of up to 5m.

The Guaico deposit is near identical to the Guayabito deposit, with zones having a strike length of up to 200m, sub-surface depth of 300m and thickness of up to 3m.

Cisneros mine geology

The majority of the Cisneros project area is located beneath an intrusive body of granodiorite to quartz diorite composition called the Antioquia Batholith, which is cut by north-west and east-northeast trending fault systems.

“Gold production at Cisneros is anticipated to begin in the fourth quarter of 2017.”

The batholith comprises granodioritic-tonalitic rocks with gold mineralisation contained within sulphide-rich (pyrite, chalcopyrite) quartz veins and breccias.

The main host rocks in the Cisneros district are granodiorites and local dykes of both aplitic and mafic composition belonging to late Cretaceous to early Tertiary period.

Described as a structurally controlled mesothermal lode gold system, the deposit is characterised by a high gold/silver ratio, great vertical continuity with little vertical zonation, and a broadly syntectonic time of emplacement. They are commonly associated with pyrite, arsenopyrite, tourmaline and molybdenite.

Reserves at Cisneros

The Cisneros gold mine is estimated to contain NI 43-101-compliant measured and indicated resources of 509,508t of ore containing 97,468oz of gold.

The inferred resources are estimated to be 495,771t containing 106,275oz of gold.

Mining and processing of ore at Cisneros gold mine

The Cisneros project uses trackless equipment to conduct a nominal 500tpd underground mining operation.

The first main production gallery of the Guaico Mine is located at an elevation of 1,160 above sea level (asl), approximately 115m below the mine portal, and is accessed through a 990m-long main ramp. Major mining equipment includes two Atlas Copco jumbo drills (one twin-boom, one single-boom), two Scoop trams (Cat R1500) and two haul trucks.

Ore from the Guayabito and Guaico deposits is being transported to the processing plant via a 2km mineral transport tunnel.

The central processing circuit is located at Guayabito, which comprises gravity, flotation, carbon-in-leach and dry tailings filtration equipment, in addition to an in-built cyanide destruction circuit.

The main components of the processing plant include the 500tpd jaw crusher, ball mill, vibrating feeder, cone crusher, and vibrating screen.

Cisneros gold mine construction

The underground mine development works include an ore extraction system using the 1160 Level as the base, and six production stopes along the main Guaico vein structures. All the electrical and surface infrastructure facilities at Guaico were commissioned by July 2016.

Other works at Guaico include the construction of a permanent bridge over the Nus River, the surface collar of the raise bored ventilation shaft, and a dewatering system.

Major construction works at Guayabito include the mine portal structure, retaining wall at the entrance, and earthworks and concrete platforms required for the installation of the processing plant.

Financing for Cisneros gold mine development

Antioquia Gold finalised the terms and conditions of a $16.38m term loan with Infinita Prosperidad Minera, in May 2017 by amending the existing $3.13m term loan. The company intends to use the proceeds from the new term loan for advancing the Cisneros project.

Antioquia Gold secured a $5m loan from Desafio Minero for the gold project in May 2014.

Key players involved

Antioquia Gold contracted independent consultant LINAMEC to review and validate the mineral resources at Cisneros.

The consortium comprising Mincivil, Estyma and Latinco was awarded a C$1.5m ($1.1m) contract for the construction of Cisneros gold mine in October 2015. The contractual scope includes civil works and mining activities, including a tunnel portal for ore extraction.

The environmental impact study (EIA) for the gold mine was prepared by a team of companies led by PI ÉPSILON Specialized Engineering Projects.

Logan Drilling was awarded a contract to conduct a 3,000m surface drilling scheme extending across the Nus, Guayabito and Guaico vein structures.