The Mt Nakru tenement covers 47km2 and encloses four known copper-gold systems known as Nakru-01 to Nakru-04.
After significant drilling by Coppermoly and former joint venture partners, an initial inferred resource was defined at the Mt Nakru project in 2012. As a result of further exploration work and drilling campaigns conducted over the past few years, including a 2018 campaign of 16 drill holes for 1997.5 metres, the resource has been updated and upgraded, with the first indicated resource category declared for the project in February 2019.
The updated mineral resource (inferred plus indicated categories) now totals 41.39 Mt grading 0.75% Cu, 0.23 g/t Au and 1.59 g/t Ag for 309 Kt Cu, 300 Koz Au and 2.1 Moz Ag at a cut-off grade of 0.3% Cu. This includes an Indicated Resource of 7.03 Mt grading 1.00% Cu, 0.28 g/t Au and 1.81 g/t Ag for 70Kt contained Cu, 64 Koz Au and 409 Koz Ag.
The Mt Nakru resource is comprised of deposits at two sites – Nakru 1 and Nakru 2 – which are approximately 1.5 km apart. Nakru 1 hosts an Inferred Mineral Resource of 35Mt @ 0.73% Cu, 0.25g/t Au & 1.45g/t Ag (JORC 2012). Nakru 2 hosts an Inferred Mineral Resource of 6.33Mt @ 0.85% Cu, 0.04g/t Au & 2.34g/t Ag (JORC 2012)1.
The resource estimate includes only the deposits within 200 meters from surface.
The Nakru 1 deposit was the focus of infill drilling in the 2018 campaign (see diagram below) and remains open to the north and south west down plunge.
The Nakru 2 deposit is open in all directions and a recent trenching program uncovered high-grade copper and zinc mineralisation just 500 metres north-west of the existing resource, confirming the potential of the prospect to host multiple high-grade polymetallic mineralised bodies. The program, conducted in 2019 at the Nakru 2 North West Prospect, traced high grade mineralisation at surface for 150m along strike, in excess of 50m down-dip and with variable width of 10-15m. Further exploration and drilling is planned at Nakru 2 North West in 2020.
At both Nakru 1 and Nakru 2, higher grades are concentrated in the upper levels and coupled with the overall shallow depth (<200m), an open-pit mine with conventional copper flotation processing is a foreseeable mining option.
Mineralisation has also been identified at Nakru 4 (one drill hole of 271.9 meters intersected 2 metres of 0.32% Cu from 29 metres) and Nakru 3 (multiple geochemical anomalies) where further exploration drilling is required to prove up resources.
Mt Nakru Geology
The Nakru deposits lie in the eastern portion of EL1043 and are hosted within the Nakru igneous complex consisting of mainly rhyolite and breccias.
Local geology at Mt Nakru is dominated by a rhyolitic ‘flow-dome’ complex that overlies Upper Eocene to Upper Oligocene age andesitic and basaltic volcanics. A thin blanket (2- 8 m) of Pleistocene to Recent tephra covers the local area.
Copper-gold at Nakru 1 and Nakru 2 is marked by surface geochemical anomalies and strong chargeability anomalies in Induced Polarisation data. Most mineralisation is veinlet and disseminated style hosted by strongly quartz-sericite altered volcanic breccias, with some thin veins of massive sulphide. More significant widths of massive sulphides occur at Nakru2 North-West. Sills of andesitic to dacitic composition cross-cut mineralisation and vary in thickness from less than 1m to 10m. Textural evidence indicates that mineralisation was emplaced at a high level in a submarine environment.
Drilling at both prospects has identified high grade copper and gold mineralisation extending over significant intersections only being interrupted by later stage mafic dykes and sills.
The geometry of the mineralisation, and relatively flat geological contacts intersected in the drilling indicates that the Nakru deposits may be categorised as volcanogenic hosted massive sulphide style (VHMS) (Tosdal , 2010), however due to lack of massive sulphide it is more likely to be non-generic type of low-sulphidation epithermal model hosted in a rhyolitic flow dome (eg. Tear, 2013).