The 250km2 Wallbrook tenement package is considered highly prospective for the discovery of significant gold mineralisation.View ASX Announcements
The Wallbrook tenement package covers 250km2 and is an amalgamation of tenements acquired from Newmont and Saracen Minerals in 2018.
In November 2018, Nexus completed a Tenement Sale and Purchase Agreement to acquire from Newmont the surrounding 190km2 tenement package adjacent to Nexus’ existing 60km2 Wallbrook Gold Project. Nexus acquired from Newmont the surrounding three tenements covering 190km2 for a total consideration of $13,100 and a 2% net smelter royalty on all mineral product extracted and recovered from the tenements. (ASX release 29 November 2018 – Nexus Completes Wallbrook Tenement Acquisition from Newmont).
Nexus had previously acquired the central Wallbrook exploration tenements from Saracen, in January 2018 for consideration of 1,490,000 Nexus shares. (ASX release 23 January 2018 - Nexus Wallbrook Gold Project Update).
Regional and Local Geology
The region is dominated by metamorphosed volcaniclastic sediments, andesite, basalt and other sedimentary and variously metamorphosed rock units. These rock units have been intruded by numerous small, variably mineralised, porphyritic intrusions. The majority of these intrusions identified to date are under cover or very weathered. Their composition varies from syenite to quartz monzonite to tonalite. These intrusions are discordant with respect to the lithological layering and major regional structures, suggesting emplacement late in the tectonic evolution of the greenstone belt, indicating mineralisation associated with the intruded porphyries may be relatively “local” to the position of the intruded porphyry.
Gold mineralisation has been identified and mined historically in a belt stretching from the Porphyry mining district to the Wallbrook area 8km to the southeast. Over 350,000 ounces of gold have been produced from multiple operations from 1921 to 2012. This same region today contains a current JORC 2012 mineral resource inventory of 31Mt @ 1.5g/t for 1.5M ounces gold (all Saracen Resources, see their 2017 Annual Report). None of these historically mined ounces nor the current mineral resource inventory are contained on Nexus tenements.
Nexus has commenced reviewing and integrating various historical data sets from the 250km2 tenement package which will be assembled and integrated into the current database.
Previous exploration has demonstrated that gold mineralisation in the district tends to occur on the margins of porphyritic intrusions. Mineralisation is known to occur within the margins of these porphyries themselves, and also within the intruded sheared and altered greenstone sequence lithologies and as mineralised quartz vein stockworks.
Geological mapping of the tenement package will focus on exploring for host rock alteration where surface outcrop is evident. Surface geochemistry data will be assessed and areas of limited or no coverage will be sampled in the search for high level gold anomalism.
The use of gravity surveys and high-resolution ground magnetic surveys have proven to be effective tools used to map the location of non-outcropping porphyritic intrusives and dyke stocks, above larger intrusive bodies. Induced Polarization (IP) / Resistivity surveys are also an effective exploration tool, with IP resistivity highs associated with possible intrusive bodies or siliceous alteration and chargeability highs with disseminated sulphides often associated with mineralisation. This work, in conjunction with factors determined as part of the Company’s R&D framework, will culminate in the drill testing of priority targets identified.
Nexus Exploration Activities
The Wallbrook Gold Project is considered underexplored and highly prospective for the discovery of significant gold mineralisation. Drilling recently completed by Nexus in the March 2019 quarter (see ASX releases 26/4/2019) and drilling completed by Nexus in 2018 (see ASX releases 16/10/2018 and 6/9/2018) has demonstrated this prospectivity. Within the Carosue Dam district 5 million ounces of gold resources are hosted in a similar geological setting to that underlying the Nexus tenement holding (see Saracen Annual Report 2018 – Mineral Resources and Ore Reserve Statement).
Crusader Prospect Drill Results
The mineralisation is closely associated with a quartz-goethite supergene stockwork in the oxide regolith profile. The stockwork intensity correlates closely with higher gold grades. In the fresh rock, high-grade mineralisation is present and to date appears constrained to a series of steeply dipping structures defined by quartz sulphide veining within a potassic altered volcaniclastic host rock. Future drill programs will test for depth extensions to the mineralisation intersected in this program, as well as testing for strike extent of the mineralised corridor that continues some 5km to the north of the drilling completed to date. The following highlights and drill results are from the March 2019 quarter.
- All 35 holes intersected gold mineralisation along a continuous 600m strike length – open at depth and for 5km to the north along a mineralised corridor
- High grade gold intersected (max 30.33g/t Au) within broad mineralised zones. Best results include:
- Hole#31 - 27m @ 3.18g/t Au (from 61m)
- incl. 4m @ 11.70g/t Au
- incl. 1m @ 30.33g/t Au
- and 9m @ 3.40g/t Au
- Hole#33 - 35m @ 2.85g/t Au (from 25m to EOH)
- incl. 15m @ 6.23 g/t Au
- incl. 1m @ 21.95g/t Au
- Hole#43 - 20m @ 1.71g/t Au (from 93m)
- incl. 7m @ 4.46g/t Au
- Hole#49 - 29m @ 2.85g/t Au (from 30m)
- incl. 8m @ 7.20g/t Au
- incl. 2m @ 16.93g/t Au
- incl. 1m @ 20.13g/t Au
- Hole#31 - 27m @ 3.18g/t Au (from 61m)
Paint Prospect Drill Results
Gold enrichment encountered in the first pass drill program in 2018 provided a broad low-grade mineralised halo, with mineralised intervals including 64m @ 0.32g/t Au, 48m @ 0.36g/t Au, 32m @ 0.43g/t Au and 40m @ 0.24g/t Au (see ASX release 6/9/2018).
Within these broad low-grade zones narrower higher-grade zones exhibiting brick-red coloured hematitic alteration were observed. Gold mineralisation in the Wallbrook area is known to be closely associated with quartz +/- pyrite and brick-red coloured hematitic alteration of high-level porphyry intrusives and their volcanic/ sedimentary host rocks.
Recent Nexus drilling intersected altered intrusive and volcanic rocks down to 300m depth across a width of approximately 800m and contain broad zones of prospective brick-red hematitic hydrothermal alteration and associated elevated gold mineralisation. Mineralised intervals received from the program include 20m @ 0.58g/t Au (incl 4m @ 2.17g/t Au), 20m @ 0.63g/t Au (incl. 4m @ 1.20g/t Au & 4m @ 1.17g/t Au), 20m @ 0.42g/t Au, 28m @ 0.25g/t Au, 16m @ 0.89g/t Au (incl. 8m @ 1.7g/t Au) and 16m @ 0.30g/t Au. Geological interpretation and modelling have commenced.