Thunder Mountain Gold Advances Ag-Au-Cu-Pb-Zn Massive Sulfide Resource Expansion Targets at South Mountain

Thunder Mountain Gold, Inc. (THM) released initial 2026 drill assay results from its South Mountain Project in Idaho on September 17, 2026. The data comes from an 8,500-foot diamond-core campaign targeting the DMEA massive-sulfide chimney, Kentucky Ridge, Bay State, and southeast step-outs.

Reported DMEA up-dip assays from three of the four completed holes are as follows:

• SM26-055: 7.40 m at 52 g/t Ag, 0.299 g/t Au, 308 ppm Cu, 506 ppm Pb, 0.22% Zn from 55.69 m, with an estimated true width of 49.56 m.
• SM26-055: 22.47 m at 86 g/t Ag, 0.105 g/t Au, 0.36% Cu, 310 ppm Pb, 0.52% Zn from 98.66 m, estimated true width 20.00 m, including 10.15 m at 141 g/t Ag, 0.179 g/t Au, 0.74% Cu, 382 ppm Pb, 1.00% Zn, including 7.43 m at 124 g/t Ag, 0.203 g/t Au, 1.01% Cu, 385 ppm Pb, 1.36% Zn, including 5.03 m at 133 g/t Ag, 0.179 g/t Au, 1.47% Cu, 318 ppm Pb, 1.95% Zn.
• SM26-056: 7.62 m at 67 g/t Ag, 0.046 g/t Au, 0.39% Cu, 122 ppm Pb, 1.95% Zn from 125.88 m, estimated true width 5.49 m.
• SM26-057: 2.11 m at 451 g/t Ag, 1.510 g/t Au, 201 ppm Cu, 4.44% Pb, 1.64% Zn from 40.23 m, estimated true width 1.98 m.
• SM26-057: 13.63 m at 117 g/t Ag, 0.086 g/t Au, 0.81% Cu, 352 ppm Pb, 0.94% Zn from 99.79 m, estimated true width 12.81 m, including 4.67 m at 234 g/t Ag, 0.196 g/t Au, 2.12% Cu, 454 ppm Pb, 2.44% Zn.

At Kentucky Ridge, the company reports approximately 80 m of down-plunge continuity and roughly 15 m of intense gossan, though assays remain pending. Holes at Bay State and the southeast step-outs intersected alteration, with assays also pending. The company noted no material damage from the Big Grass Fire.

Thunder Mountain Gold, Inc. (THM) is a junior developer with no revenue, a small but high-grade existing resource, and a market value near US$108 million. The equity has already re-rated from roughly US$0.38 in September 2025 to US$1.16 today, mostly on land expansion, financing, and a near-term production options review with Ocean Partners and MFD, not on a prior drill intercept.

The current release confirms that the DMEA chimney persists up-dip toward surface and that the system remains mineralized. That is a real positive, but the assayed widths are not a grade or scale transformation. The broad composites are materially lower grade than the existing resource, especially in zinc, and the high-grade portions are narrow.

Because most assays are pending, the release is an interim confirmation rather than a resource-changing event.

Thunder Mountain Gold, Inc. (THM), founded in 1935, is a U.S.-based junior explorer focused on precious and base metals. Its principal asset is the South Mountain Project in Owyhee County, Idaho, a historic Anaconda polymetallic Zn-Ag-Au-Cu-Pb carbonate replacement deposit. The company has invested approximately US$25 million since 2007, controls a land package of roughly 13,061 acres or more, and has rehabilitated underground development.

The existing NI 43-101 and S-K 1300 resource includes:

• Measured and Indicated: 223,000 short tons at 4.27 oz/t Ag, 9.02% Zn, 0.64% Cu, 0.94% Pb, and 0.059 oz/t Au.
• Inferred: 959,000 short tons at 5.67 oz/t Ag, 7.56% Zn, 0.80% Cu, 1.06% Pb, and 0.037 oz/t Au.

The company also owns the Trout Creek gold exploration project in Nevada, located near Nevada Gold Mines assets.