Great Northern Mining (ASX:GNM) Major Discovery of a 1km-Long Antimony Vein – Surface Rock Chip Samples Assaying up to 7.1% Sb

19 December 2025

Price Sensitive Announcement $

Highlights:

• The Company has submitted the required applications for a mineral prospecting permit to expand the footprint of the Catalyst Ridge Project.
• The expanded area is considered highly prospective for Antimony with the onground exploration team identifying a quartz-stibnite (antimony sulphide) vein that extends for up to 1km strike and observed widths of up to 6m.
• Initial rock chip samples have returned highlight assays up to 7.1%, 6.2% and 3.5% antimony with other associated metals up to 23.3 g/t silver and 0.4% tungsten.
• Additional samples will be taken in the field before the end of the year with results expected in early 2026.
• The quartz-antimony vein structure appears to be in a similar geological and structural setting to the Colosseum Gold deposit and therefore also considered highly favourable for gold mineralisation at depth.
• The Company also plans to conduct DDIP to detect the depth of sulphide mineralisation to firm up drill targets for zoned antimony near-surface as well as gold down dip.

Overview:

Great Northern Minerals Ltd has announced it has received rock assay results from the initial sampling program at its Catalyst Ridge Project. In addition, the Company has submitted the required applications to strategically expand the overall footprint of the Catalyst Ridge Project to 20.48km2

Overview:

Geochemical Sampling Program – Antimony Gulch Quartz-Stibnite Vein

A major field program was mobilised in the field in October 2025 which focused on stream sediment sampling across all the Catalyst Ridge tenure where a total of 125 samples were collected. The aim of this program was to identify any highly elevated areas for REE that require further investigation. At the time of writing the stream sediment data is still under review and QAQC. The program also involved assessing the potential of areas of open ground adjacent to the Catalyst Ridge claims where a total of 8 rock samples were conducted which were taken at the prospect now known at Antimony Gulch.

During the program an old adit mine shaft was observed in open ground which appeared to be mining stibnite antimony sulphide minerals that occur within a quartz veins. Samples from the mine dumps in some cases displayed spectacular coarse bladed stibnite minerals up to 6cm in length (Figure 1). The vein at the adit appears to be over 1m in width and strikes north-northwest and dipping steeply to the east. Interestingly the vein occurs within a felsic quartz-K-feldspar-plagioclase granitic or rhyolite intrusive. Assays from the dump material out of the mine returned assays of:

• 258579: 7.06% antimony, 23.3 g/t silver and 0.41% tungsten;
• 258578: 6.16% antimony, 5.2 g/t silver;
• 258576: 3.53% antimony, 12.6 g/t silver; and
• 258577: 1.9% antimony, 5.2 g/t silver.

Walking north-northwest and steadily up hill, the Antimony Gulch quartz-stibnite vein can be traced for approximately 1 kilometre and offset by various east or northeast-trending cross faults (Figure 2).

Due to time constraints, only 6 other samples were taken along the vein to the north where the vein pinches and swells with widths up to 6m in places. Visible stibnite minerals have not yet been observed exposed at surface during this limited timeframe however assays indicate the vein remains highly elevated in antimony as well as silver and tungsten with samples up to 431 ppm antimony, 4.1 g/t silver and 94.3 ppm tungsten within the central portions of the vein (Figure 2). More detailed mapping and sampling work is required to assess this potential. It should also be noted that the adit occurs at a lower elevation than many other parts of the exposed vein to the north suggesting a classic vertical zonation pattern displayed by many mineral deposits.

Company Notes:

Non-Executive Chairman, Eddie King, commented: “The expansion of the Catalyst Ridge Project to include the additional land holding, combined with the discovery of a significant stibnite-quartz vein and high-grade antimony in initial samples, reinforces the strategic potential of this region. We are excited about the geological similarities to known deposits in the area and look forward to advancing exploration to unlock further value for our shareholders.”

Full ASX Anouncement: https://hotcopper.com.au/threads/ann-significant-1km-antimony-vein-discovered.8947837/