Northern Territory

Cosmo Mine, Northern Territory

Northern Territory, Australia

Cosmo Mine is located in the Northern Territory, Australia, historically an important gold mining center

The Northern Territory is comprised of a group of mineral tenements totaling over 2,000 km2 in the Northern Territory of Australia. The Northern Territory operation, which included the Cosmo mine and Union Reefs mill, was placed on care and maintenance effective June 30, 2017. Since that time, extensive exploration and advanced exploration programs have been carried out to assess the potential of a resumption of operations.

Quick Facts

Location Northern Territory, Australia
Mine Type Underground, decline access
2017 Production 20,595 ounces, Project placed on Care and Maintenance effective June 30, 2017
Deposit Type Disseminated Stratabound Turbidite hosted
Processing Union Reefs Mill - CIL
End Product Gold doré
Infrastructure 6,850 tpd
Mining method and processing

Underground mining activities at the Cosmo Mine were conducted using a decline from the southern wall of the Cosmo Open Pit. At the time that operations were suspended, mining activity was centered on the Eastern Lode, utilizing Avoca-style cut and fill stoping with regional sill and crown pillars.

Union Reefs Processing Facility

The Union Reefs processing facility, with a carbon-in-leach (CIL) circuit, has an overall capacity of 2.5 million tonnes per year or 6,850 tonnes per day. The processing plant is capable of recovering coarse gold by gravity concentration, and fine gold by cyanide leaching and adsorption on activated carbon. The plant is currently configured with a:

  • Three stage crushing circuit;
  • Two closed circuit ball mills, each with a hydrocyclone;
  • Gravity circuit including two Knelson concentrators;
  • Thickening circuit; and
  • Two stage CIL circuit
6,850
tonnes per day at
Union Reefs mill
2016
New discovery of Lantern
Deposit at Cosmo
2017
Placed on care and
maintenance June 30, 2017
Multiple exploration targets:
Cosmo/Lantern, Prospect, Crosscourse and Lady Alice pits at Union Reefs, Pine Creek and Maud Creek

Mark Edwards

Director, Northern Territory Mining Operations

Operating Data
2017(2) 2016(1) 2015 2014 2013
Gold produced (oz) 20,596 55,765 63,255 77,740 74,106
Ore processed
(tonnes)
259,730 646,848 725,002 868,399 719,337
Gold grade (g/t) 2.6 2.87 2.99 3.14 3.57
Recovery (%) 95.0 93.6 90.7 88.9 89.6

(1) - Kirkland Lake Gold acquired the Cosmo Mine through the business combination with Newmarket Gold, which was completed on November 30, 2016. Operating results for 2016 are provided for the entire 12-month period ended December 31, 2016.

Operating Data Image 1 Cosmo Water Sampling 2017
Operating Data Image 2 Titeline Rig at Union Reefs
Production Suspension

Kirkland Lake Gold suspended production at the Cosmo Mine, effective June 30, 2017. In the first six months of the year, a total of 20,595 ounces were produced at an average grade of 2.7 grams per tonne and an average operating cash cost of $1,661 per ounce sold.

Following the suspension of production at Cosmo, the Company expanded the ongoing exploration program at the mine, recognizing the significant potential that existed to identify new Mineral Resources, particularly at the recently-discovered Lantern Deposit. The Company also resumed active exploration programs on advanced regional targets.

Geology & mineralization

The Cosmo Mine property falls within the Archaean to Palaeo-Proterozoic Pine Creek Orogen, one of the major mineral provinces of Australia. The Pine Creek Orogen is a deformed and metamorphosed sedimentary basin up to 14km maximum thickness covering an area of approximately 66,000km2 and extending from Katherine in the south to Darwin in the north. It hosts significant mineral resources of gold, uranium and platinum group metals, as well as substantial base metals, silver, iron and tin-tantalum mineralization.

The Cosmo Mine mineralization occurs within the folded Koolpin Formation. This formation consists of interbedded siltstones, carbonaceous mudstones, banded ironstone, phyllites, dolerite sills and greywacke units. Mineralization at the Cosmo Gold Mine occurs within a marine siltstone package located between the Inner Zamu Dolerite sill and a +30m thick pyritic carbonaceous mudstone unit. Siltstones near the carbonaceous unit contact often contain nodular chert lenses, with the nodular units often interbedded with massive and banded siltstone units. The width of the gold hosting siltstones is 30 to 50m wide in the footwall of the F1 Fault and from several meters to 50+ meters wide in the hangingwall due to variably developed folding.

The newly discovered Lantern mineralization occurs within similar marine siltstone package situated stratigraphically lower than the Cosmo Mine sequence, between the Inner Zamu Dolerite sill and a second Dolerite sill known as the Phantom Dolerite sill. Gold mineralization occurs in selvages surrounding tensional quartz-carbonate veins formed in close proximity to major bedding parallel quartz-carbonate shear veins. Drilling indicates an apparent increase in coarser free gold occurring within both styles of veins at depth within the mineralized Lantern system.

The main sulfide minerals in the fresh rock are pyrite and arsenopyrite, with traces of sphalerite and chalcopyrite. Pyrrhotite occurs below depths of 300m and is mainly seen in the carbonaceous unit.

Exploration

An extensive program of surface and underground exploration has been completed since the beginning of 2018 in the Northern Territory, with approximately 240,000 metres of drilling expected to be completed by the end of 2019. To date, the drilling has involve using as many as four underground diamond drill rigs, two surface diamond drill rigs and one reverse circulation percussion drill rig. On April 30, 2018, the Company announced that high-grade, visible-gold bearing mineralization had been intersected 1,000 metres below surface down-plunge of former producing open pits at Union Reefs, the location of the Company’s processing facility. The results highlighted the potential that exists to establish additional sources of gold production in the Northern Territory. During the third quarter of 2018, drilling from the 920 and 610 exploration drifts commenced into the Lantern Deposit. On November 5, 2018, the Company reported additional high-grade, visible-gold bearing mineralization at the Lady Alice Deposit at Union Reefs and also announced the discovery of high-grade mineralization at depth to the south of the existing Mineral Resources at Union Reefs. On December 11, 2018, the Company announced that work in the Northern Territory was moving to the advanced exploration phase, with a focus on a potential resumption of mining and milling operations.

In 2019, drilling and development have been undertaken at the Cosmo mine to improve the understanding of the Lantern Deposit and support Mineral Resource definition and expansion. In addition, surface drill programs are being carried out at Union Reefs and at the Pine Creek target in support of Mineral Resource growth and definition. Total exploration expenditures for the first nine months of 2019, including capitalized exploration, totaled $82.0 million.

Subsequent to the end of Q3 2019, the Company commenced trial processing of Lantern material as part of the advanced exploration program. This trial processing using low-grade material is being undertaken to ensure that, upon a potential return to commercial operation, higher-grade ore will be processed efficiently with the mill having achieved a steady state of production.