US Silver Bow Mining Launches Underground Drilling at Rainbow Block in Montana

en.Wedoany.com Reported - On November 11, US mining company Silver Bow Mining announced the formal launch of underground diamond drilling at the Rainbow Block in the Butte Mining District, Montana. This marks the first resumption of underground exploration drilling in the district in more than 30 years. Operations are being conducted from a drill bay in the company's newly developed Rainbow Decline underground ramp, with the first phase testing the deep and peripheral extensions of 12 identified mineralized veins. Approximately 30,000 feet (about 9,144 meters) of underground drilling is planned for the remainder of 2026 and 2027.

The first underground drill station is located approximately 285 feet (87 meters) below the surface portal at an elevation of about 6,210 feet (1,893 meters). Drilling contractor NISS Drilling is using a KMN1.4 electric underground diamond core rig. Compared with surface drilling, underground drill stations allow holes to be collared from the side and below the orebody, adjust hole orientation, shorten the drilling distance to certain target intervals, and test the spatial geometry and continuity of veins from different directions. For steeply dipping, closely spaced vein systems, this approach can reduce the difficulty some surface holes face in accurately intersecting target structures.

The first batch of underground drilling will cover 12 veins. Southern targets include the State, Badger, Edith May and Auraria veins; northern targets include the Jessie, Rainbow Splay, Alice, Emily, Emily High-Grade, Rainbow, Boston and Jersey Blue veins. Among these, Badger and Emily are priority areas where previous surface drilling has already returned high-grade silver, gold, zinc and lead mineralization. The company plans to use underground drilling to verify the depth extensions of these mineralized zones while also testing other veins not yet included in the current inferred resource estimate.

Previous surface drilling has already provided specific targets for the underground program. On September 1, 2026, the company reported results from hole SBM26-03 on the Badger vein, returning 994.2 g/t silver equivalent over 4.0 meters, including 1,586.1 g/t silver equivalent over 2.3 meters. Results from hole SBM26-08 on the Emily vein announced on November 5 showed an average grade of 312.7 g/t silver equivalent over 11.2 meters, including 462.7 g/t silver equivalent over 3.6 meters. These results all lie outside the company's current inferred resource envelope and are important basis for the current underground infill and peripheral extension drilling.

The Rainbow Block is located in the Walkerville area of the historic Butte Mining District, covering approximately 878 acres of mining claims. Historical mining activity in the area was carried out mainly by Anaconda, which developed silver, zinc and copper veins over a long period. Silver Bow Mining is currently focused on evaluating silver, zinc, lead and associated gold mineralization, and includes indium, germanium, gallium, antimony, bismuth, manganese and copper within its comprehensive exploration scope. The company's geological model has identified 42 veins, and some historical underground workings and mining data have been re-surveyed and incorporated into a 3D geological model, providing a spatial basis for current drill hole design.

According to the mineral resource estimate as of December 31, 2024, the Rainbow Block contains approximately 10.4 million tonnes of inferred mineral resources at an average grade of 507.4 g/t silver equivalent, for a total of approximately 170 million ounces of silver equivalent. The resource estimate was prepared by Dahrouge Geological Consulting and is based on historical drill holes, 8 recent diamond drill holes, and more than 15,000 underground vein channel samples left by Anaconda. The resource model divides drill hole and underground sampling data into 42 veins. Note that these figures are inferred resources and are not mineral reserves.

The current underground drilling program builds on underground work approved in 2026. On May 18, the Montana Department of Environmental Quality (DEQ) formally approved the company's second amendment application for Exploration License No. 00857, allowing it to construct the Rainbow Decline and conduct underground drilling, surface drilling and bulk ore sampling. The underground plan includes a new ramp portal of approximately 16 feet by 15 feet, about 6,000 feet (about 1,829 meters) of underground development, and a planned connection to the 400-foot level of the existing Lexington Mine workings. The project will progressively establish new underground drill platforms, with additional drill stations later planned from the Chief Joseph Decline.

The license amendment also approves up to 7 surface drill pads and up to 53 surface core holes totaling approximately 102,000 feet of drilling; allows stockpiling of up to 10,000 tonnes of mineralized material for metallurgical test work; and permits excavation and stockpiling of up to 150,000 cubic yards of development waste rock. The company has posted a $2.188 million bond for related reclamation obligations. Approved exploration activities are scheduled to be completed by December 31, 2029, with site reclamation to be completed no later than December 31, 2031.

Subsequent drilling results will be integrated with surface exploration data, historical mining records and the existing geological model to reassess the spatial continuity and resource classification of the veins. The company plans to progressively add underground drill bays and working platforms as the Rainbow and Chief Joseph decline projects advance, providing data for mineral resource expansion, resource category upgrading and subsequent technical studies for underground mining.