Magnetics Interpretation Assists Drill Targeting in 2021
Last Chance Gold Anomaly.
Inversion modelling of the magnetics data has identified a distinct remnant signature associated with mapped Cretaceous granites. The modelled remnant signature indicates the likely presence of a roofed intrusive system extending east-west to the south of the main Last Chance surface gold anomaly, which could be a probable heat and metal source for Cretaceous age hydrothermal activity.
Mapped Cretaceous granites occur to the southeast of Last Chance near the Wood River and are well identified in the airborne magnetics as a magnetic low feature and with associated hornfels magnetic highs found along their periphery (Figure 4*). These same magnetic characteristics are seen to the west where no granites are mapped at surface, suggesting a series of buried (or roofed) granite plutons exist below the surface.
Inversion modeling in the area of the Last Chance gold anomaly indicates that the depths to the top of the interpreted intrusions range between 500 to 2,000 metres, with a number of possible intrusive apophyses and/or controlling structures with related alteration extending close to surface (Figure 5*). While no direct relationship between the Cretaceous granite and gold mineralisation has been recognised at Last Chance, their close association with IRGS deposits seen elsewhere in the Tintina Gold Province (e.g. Fort Knox and Pogo) is a favourable association that assists interpretation and targeting at Last Chance.
Regional fault systems are strongly evident in east-west oriented alternating magnetic low and high bands across the project area, especially just north of the Last Chance target area. These are likely active regional subsidiary shears or back-thrusts associated with neotectonic motions occurring along the major Denali fault system nearby and a north propagating fold-thrust belt that is actively uplifting the Alaska Range. Smaller accommodating faults are seen in the magnetics as two distinct groups; a northwest striking set occurring mostly on the west side of the project area and a northeast striking set occurring on the east side of the project area (Figures 2 & 3*). These northwest and northeast orientations emanate from a position centred on the Last Chance Gold Target where there is a gentle bend in the regional east-west fault system.
Additional work is required to distinguish between structures active during gold mineralisation and the more recent active neotectonic faults unrelated to mineralisation. Drilling to date has uncovered brittle re-activated fault systems which were once pathways for hydrothermal fluids as well as more recent barren fault-gouge structures. The magnetic interpretation provides the beginnings of a structural framework that can continue to be refined with additional data and will form the foundation for targeting structural hosted gold mineralisation.
Selection of the most favourable structural conduits above the interpreted granites will be aided by the alteration and geochemical data acquired from mapping, surface sampling, drilling and satellite spectral analysis completed during 2020.
White Rock expects to be able to drill test structural positions with the potential for high grade gold mineralisation during the 2021 field season that is expected to commence mid-June.
New VMS Targets.
In addition to the targeting of gold mineralisation at Last Chance, the magnetics interpretation has provided significant improved understanding of the VMS potential that extends across the tenement package to the north of Last Chance.
Reconnaissance mapping and sampling identified six target areas with outcropping VMS mineralisation at Horseshoe, Bib, Bib West, Ringer, Peaches and Grapple (refer ASX Announcement from 1st February 2021). Magnetics identifies a clear stratigraphic domain that hosts these western VMS mineral occurrences.
The prospective Magnetic VMS Domain provides an area of focus for more intense prospecting in conjunction with more detailed surface sampling and geophysical surveys across the new target areas early during the 2021 field season. Given the association of pyrrhotite, a magnetic iron sulphide mineral, with the VMS occurrences, it is expected that more detailed surface magnetics will be modelled to provide more definitive drill targets of the VMS horizon beneath the extensive talus cover that covers up to 95% of the prospect target areas.
It is expected that surface prospecting will define targets for drill testing during the second half of the 2021 field season.
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About White Rock Minerals Ltd
White Rock Minerals Ltd (ASX:WRM) is a diversified explorer and near-stage producer, headquartered in Ballarat, Victoria. The Company's flagship exploration project is Red Mountain in central Alaska. At Red Mountain, there are already two high grade zinc - silver - gold - lead VMS deposits, with an Inferred Mineral Resource of 9.1 million tonnes @ 12.9% ZnEq for 1.1 million tonnes of contained zinc equivalent. The Company is also exploring its recently discovered large intrusion related gold anomaly at Last Chance, also located in the Tintina gold belt of Alaska, home to multi-million gold ounce deposits like Pogo, Fort Knox and the Donlin Project. The Company also has the Mt Carrington project, located near Drake, in Northern NSW, which is a near-production precious metals asset with a resource of 341,000 ounces of gold and 23.2 million ounces of silver on an approved mining lease, and with a Gold First PFS and JORC Reserve. White Rock Minerals is listed on the Australian Stock Exchange.
White Rock Minerals Ltd