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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
Deposit type Disseminated Stratabound Turbidite hosted
Process CIL
End product Gold doré
Infrastructure 6,850 tpd at Union Reefs Mill
Resources & Reserves

Overview

The Cosmo Mine is an underground operation located 160 km south of the City of Darwin, in the Northern Territory, Australia. Ore 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.

The Cosmo-Howley corridor has several gold deposits including the Cosmo Mine, which commenced commercial production in early 2013. A targeted near mine gold exploration program has resulted in the discovery of new zones of gold mineralization at the Cosmo Mine in 2016.

Production Suspension

Kirkland Lake Gold will suspend production at the Cosmo Mine, effective June 30, 2017. This will allow the Company to focus its activities on an aggressive resource definition and exploration program at the mine, including the newly discovered Lantern deposit, and resume active exploration on advanced regional targets. The Cosmo Mine will be maintained in a state of readiness to allow operations to recommence when exploration, resource definition and the development planning phase is completed. The Lantern discovery has the potential to consider mining of higher tonnages at an increased grade, and a full appreciation of this development stage opportunity is required.

Operating Data

Empty 2016(1) 2015 2014 2013
Gold produced (oz) 55,765 63,255 77,740 74,106
Ore processed (t) 646,848 725,002 868,399 719,337
Gold grade (g/t) 2.87 2.99 3.14 3.57
Recovery (%) 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.

Exploration

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 resource expansion with the goal of increasing the life of mine reserves.

Recent exploration drilling was undertaken from the newly completed 640 Western Drill Drive, located near the lowest level of the underground mine and used as a strategic platform to access new targets. During 2016, significant drill intercepts were announced from the Sliver Lode and the newly discovered Redbelly and Taipan Lodes, all of which are adjacent to existing underground mine development. Drilling of these high priority targets is ongoing, and will lead to additional mining fronts at the Cosmo Mine in 2017.

Mining Method & Processing

Underground mining activities at the Cosmo Mine are focused on deepening the mine with development and exploration activities currently underway. The mine is accessed via a decline from the southern wall of the Cosmo Open Pit. Current mining activity is 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 treats ore from the Cosmo Mine, which is hauled via the Stuart Highway, the main transport link between the Southern States of Australia and Darwin. 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.

Gold mineralization is closely associated with arsenopyrite often seen within the nodular siltstone unit. The mineralization styles, both on the hangingwall and footwall of the major F1 Fault are very similar, with the main mineralization associated with, but not necessarily totally constrained within the nodular unit. 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 predominantly seen in the carbonaceous unit.