Red Mountain Mining (ASX:RMX) Increases Idaho Yellow Pine Antimony Project by 75%

21 November 2025

Price Sensitive Announcement $

• Red Mountain has increased the footprint of its “Yellow Pine Antimony Project” in the highly prospective Stibnite Mining District in Idaho, USA
• Following a positive field mapping program immediately after acquiring the project, the Red Mountain US based technical team was further encouraged by the highly attractive geology, and the Company has acquired additional claims increasing the project size by 75%
• Red Mountain’s Yellow Pine Antimony Project lies within 2km of Perpetua Resources’ (NASDAQ: PPTA, Market Cap approximately $4.3B) Stibnite Gold-Antimony Project, which has a Proven and Probable mineral reserve of 4.8Moz Au and 148 Mlbs Sb
• The RMX | RMXFF Yellow Pine Antimony Project also lies approximately 5km south of
  Resolution Minerals’ (ASX: RML) Horse Heaven Antimony-Gold Project, which has recently reported strong initial diamond drilling results for gold, including 253m @ 1.50g/t Au from surface, ending in mineralisation
• Antimony and Gold mineralisation at Stibnite and at Horse Heaven is controlled by regional faults and splays, and occurs within both the Idaho Batholith and surrounding older metasedimentary rocks
• Red Mountain’s Yellow Pine Antimony Project features share similar geology to Stibnite and Horse Heaven and includes all the necessary elements for the formation of economic goldantimony mineralisation, featuring prospective host rocks, a major northeast-striking fault with mapped tectonic breccias, and evidence of small historical workings, most likely seeking gold and/or antimony
• RMX’s Board views that the unprecedented critical shortage of Western supply of Strategic Metals and strong US & Australian Government interest in key metals will likely remain robust over the medium-to-long term, which provides high-conviction to fast-track its strategy
• The Yellow Pine Antimony Project is part of Red Mountain’s established portfolio of Strategic and Critical Metals projects in Tier 1 US mining jurisdictions

Overview:

Red Mountain Mining Limited , an Australia and United States based Critical Minerals exploration and development company with an established and growing portfolio in Tier-1 Mining Districts, is pleased to announce the expansion of its Yellow Pine Antimony Project within the Stibnite Mining District in Central Idaho, USA. Following a field mapping program in September immediately deployed after acquiring the project, the Company has now acquired additional claims, increasing its project size by 75%, immediately northeast of the initial project announced in September 2025. This increases RMX | RMXFF’s footprint in this highly sought-after district to 426 hectares.

Red Mountain’s Yellow Pine project is located less than 2km from Perpetua Resources’ (NASDAQ: PPTA; Market cap A$4.37 billion) Stibnite Gold-Antimony Project in central Idaho, USA and approximately 5km south of Resolution Minerals’ (ASX: RML; Market cap of approximately A$150 million) Horse Heaven Gold-Antimony project, which lies immediately west of Perpetua’s claims (Figure 1).

Strong results in the Yellow Pine Stibnite District highlight the exceptional prospectivity. The Stibnite Mining District was a major source of antimony in the first half of the 20th Century.

Recorded production from the Yellow Pine and Hangar Flats deposits between 1932 and 1952 totalled 39,930 tonnes of Antimony2. These two deposits and the West End Deposit, which produced gold and silver from 1978 to 1997, collectively comprise the Proven and Probable Reserve of 104 Mt @ 1.33g/t Au and 0.06% Sb for 4.8Moz Au and 148Mlbs Sb for Perpetua’s Stibnite Project2, which is the largest known stibnite deposit in the USA. Perpetua announced that they had broken ground on the early works construction for the Stibnite Project on October 21, 20253, following the placement of financial assurance and receipt of the signed Plan of Operations from the US Forestry Service; and also secured a total of US$333M (AU$513M) gross proceeds through a strategic equity investment of US$255M
from Agnico Eagle and JPMorgan on October 28, 20254 and a registered equity offering of US$71M and concurrent US$7M private placement on October 30 and 31, 20255.

Immediately west of Perpetua’s claims, Resolution Minerals has recently announced strong gold results from the first three holes drilled at their Golden Gate prospect. The three diamond holes returned exceptional broad intervals of gold mineralisation associated with the following results reported
:
HH-GG25-001C: 189.2m @ 1.30 g/t Au from 34m, ending in mineralisation.
HH-GG25-002C: 265.2m @ 0.60 g/t Au from surface, ending in mineralisation.
HH-GG25-003C: 253.0m @ 1.50 g/t Au from surface, ending in mineralisation.

The mineralisation is open at depth, as well as in all directions and RML is currently undertaking additional diamond drilling. RML interpret the mineralisation at Golden Gate to be related to a large intrusion-related system, similar to the gold-stibnite mineralisation at the Stibnite deposit.

Exploration potential of RMX’s Yellow Pine Antimony Project

2017 geological mapping by the Idaho Geological Survey shows that RMX’s claims feature similar prospective geology to that seen within the Perpetua Resources’ Stibnite Project area, with similar metasediments intruded by Idaho Batholith granite and cut by a major NNE-trending Tertiary fault and evidence of historical mining activity, most likely seeking gold and/or antimony (Figure 2).

The expanded claim block secures the northeast continuation of the main fault as it moves into a key structural corridor within the metasediments, significantly strengthening Red Mountain’s exploration position at the Yellow Pine Antimony Project and is expected to generate a series of new Antimony and Gold targets.

Field mapping by RMX’s field crew has confirmed the presence of tectonic breccias within quartzite associated with the main NNE-trending fault (Figure 2), indicating that hydrothermal fluid circulation occurred along the structure – a positive indicator for potential mineralisation. Red Mountain geologists have successfully located the two eastern historical workings mapped by the Idaho Geological Survey, which are small shallow pits targeting brecciated quartz veins prospective for gold and/or antimony (Figure 3)

Full ASX Announcement: https://hotcopper.com.au/threads/ann-red-mountain-delivers-major-increase-in-yellow-pine-antimony.8896042/