The Paulsens deposit was mined in the 1930’s as the “Melrose Mine”, with 2,400 tonnes mined at an average grade of 12g/t gold for 900 ounces. Exploration activities in the latter part of the twentieth century led to the discovery and progressive growth of a significant mineral resource.
NuStar Mining Corp Ltd commenced modern underground mining in 2005. The mine was operated by Intrepid Mines Ltd between mid-2006 and mid-2010 following an initial merger between NuStar and Intrepid Minerals Corporation, and a subsequent merger with Emperor Mines Ltd in 2007. Gold production during this period averaged ~75k oz a year.
Northern Star Resources Limited purchased the mine and associated 365km2 tenement package in August 2010.
The Paulsen’s deposit lies within the Wyloo Dome; a northwest-southeast oriented doubly-plunging anticlinorium comprising an Archaean core (Metawandy Granite) and an unconformably overlying succession of Archaean to Early Proterozoic metasediments and metavolcanics (Fortescue, Hamersley and Wyloo Groups). The deposit is hosted by a large gabbro dyke and metasedimentary units of the Hardey Formation in the lower part of the 2775–2630 Ma Fortescue Group.
Paulsens is an orogenic-style gold deposit and consists of a series of deformed quartz veins localised within and along the margins of a folded, coarse-grained gabbro dyke that is locally termed the Paulsen’s Gabbro. Three styles of mineralisation are recognised; very fine-grained gold associated with massive pyrite (Upper Zone), coarse free-milling gold on “stylolites” (Lower Zone), and minor coarse gold on discrete structures in “bucky” internal quartz veins.
The predominant mining method at Paulsens consists of jumbo strike-drive development followed by up-hole long-hole open stoping. Airleg mining, once prevalent at Paulsens, has been a limited method in the recent past, but is now returning to become a more commonly employed method, particularly for extraction of narrow, very high grade structures.
The current Paulsen’s Treatment Plant uses a conventional CIP process with a capacity of 450,000 tonnes per annum, vastly increased from the original nameplate capacity of 240,000 tpa. The process consists of a 3 stage crushing plant followed by a single stage ball milling circuit incorporating gravity recovery and CIP process achieving 90-95% recoveries.