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Cosmo Mine

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

Quick Facts

Union Reefs Milling Facility, Northern Territory Operations

Location Northern Territory, Australia
Mine type Underground, decline access
2017 Production Guidance 20,000 ounces, Project on Care and Maintenance
Deposit type Disseminated Stratabound Turbidite hosted
Process CIL
End product Gold doré
Infrastructure 6,850 tpd at Union Reefs Mill
Resources & Reserves


The Cosmo Mine is an underground mine located 160 km south of the City of Darwin, in the Northern Territory, Australia. Ore produced from the Cosmo Mine is processed at the underutilized Union Reefs Mill, located 60 km south of Cosmo Mine. Historically, the mill served as a central processing facility for surrounding gold deposits in the Pine Creek Orogen.

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.

Operating Data

Empty 2017(2) 2016(1) 2015 2014 2013
Gold produced (oz) 20,596 55,765 63,255 77,740 74,106
Ore processed (t) 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.


Advancement in the understanding of the mineralization at the Cosmo Mine has resulted in the definition of new exploration targets including the discovery of the Western, Lantern, Sliver, Taipan, and Redbelly Lodes. Growth programs focused on these areas are designed to target Mineral Resource expansion with the goal of increasing the life of mine Mineral Reserves.

On December 19, 2017, the Company announced results from 65 underground drill holes covering 23,553 m and nine surface drill holes for 4,184 m from surface drilling that were completed to test the expansion potential of the Lantern Deposit. The results substantially increased the deposit footprint, particularly to the north, and demonstrate the potential for significantly higher grades. The high-grade gold mineralization intersected from the new drilling exhibited a change from fine-grained free gold in Cosmo Deposit to increasing coarser-grained free gold in narrow quartz veins within Lantern.

Included in the new results was the highest-grade gold assay ever reported at Cosmo, totaling 4,750 g/t Au over 0.31 m (estimated true width “ETW” 0.2 m) in hole LU73020, which is located more than 250 m north of the current main Lantern Mineral Resource. Based on the latest drilling, the Lantern Deposit has now been identified over 500 m along strike, more than 1,200 m down-plunge and over 1,000 m vertically from surface, with a significant number of high-grade intersections and multiple occurrences of visible gold.

The positive results from the 2017 drill program at the Lantern Deposit, significantly increased the Company’s confidence that an economic deposit or deposits can be established in the Northern Territory, which would facilitate a resumption of mining and milling operations at the Cosmo Mine and Union Reefs Mill. In support of this goal, The Company’s 2018 work program will include an underground exploration development program on two levels, 320 m vertically apart, to access Lantern underground from the existing Cosmo underground infrastructure. This development will provide the first underground exposures of the Lantern mineralization, deliver improved drilling access and provide initial production platforms for the potential restart of operations in 2018.

Mining Method & 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

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.