Big Thunder Gold Mine (Gold Hill Lode), originally named the Gold Hill Lode, was discovered in 1882. The mining work was done by two German immigrants, Krupp and Engle. They did not know each other when they came to the Keystone area, but because they could both speak the same language, they became partners. They originally started higher up on the hill where there was an outcrop of indicator minerals. Not striking a rich vein, the miners moved down the hill to the current mine location. They were trying to intercept the Lucky Boy vein.

The Lucky Boy Mine is located on the next claim downstream from the Big Thunder, adjacent to the first half of the Big Thunder property. The miners learned what they could about the direction and angle of the Lucky Boy ore body. With this knowledge, they felt they could intercept the ore body by driving an adit into the hill at the current mine entry point.

Using hand equipment to drill holes in the solid rock, they
then placed the powder in the drill holes to blast the rock loose. The miners used the drilling process called double jacking. One miner would hold the steel drilling bit, and the other would hit it with a sledge hammer. Miners made a pattern of drill holes on the blast six to eight feet. The design formed by the series of drill holes was called a butterfly pattern. This pattern, similar to the shape of a butterfly with both wings outstretched, allowed the explosives to make a safe square excavation doing little to fracture the sides of the tunnel. A properly done blast would completely fracture the ore without damaging the integrity of the mine walls.

Air Rock Drill The effectiveness of the drill pattern was further increased by firing the four drill holes in the center of the blast face slightly earlier than the rest of the charges. This would fracture the rock and blow out a cone of ore from the center of the surface. As the next ring of explosives fired, the energy was directed toward the area that had been removed a fraction of a second earlier in the blast sequence. Directing the energy to the center of the tunnel would fracture the ore more efficiently and maintain the safety and integrity of the outer walls. If all of the drill holes were fired at the exact same instant, the integrity of the walls would be threatened, leading to possible cave-ins.

Because the adit is cut in solid rock, Big Thunder is one of the safest mines in the area. The rock stability allowed the miners to use very little timbering. Because of its safety, during times of war, the Big Thunder Mine was designated as Keystone's bomb shelter.

Old Keystone

Around 1900, steam and compressed air driven drilling equipment were introduced. This replaced hand drilling and greatly improved the progress miners made as they advanced into the mountain. The injection of water into the drill holes to remove the rock chips greatly increased the boring rate and reduced the amount of rock particles in the air. This reduction significantly decreased the incidence of silicosis, a disease of the lungs caused by inhaling rock dust.

Mining continued toward the Lucky Boy vein It is estimated that by 1907, the Big Thunder adit intersected the extension of the Lucky Boy vein about 330 feet into the mountain. The joy of discovery turned to disappointment when the miners found the Lucky Boy vein bad narrowed to a thickness measured in inches. The vein on the Lucky Boy property averaged 10 feet wide, containing one quarter ounce of gold per ton, but by the time it cut the Big Thunder adit it was not profitable to mine. After assessment of the vein was completed, the future of the mine looked dim and for a while development stopped.

In 1909, excitement again stirred for Big Thunder when the Columbia Mine was opened. The Columbia Mine was located on the property adjacent to the back half of the Big Thunder property. Ore from the Columbia was averaging over two ounces of gold per ton with some rich pockets running as high as 10 ounces per ton. It was found that the Columbia vein ran parallel to the Lucky Boy vein and continued toward Big Thunder. Knowing the Columbia vein might intersect the Big Thunder property, it was time to ~lengthen the Big Thunder adit.

In 1913, the miners started picking up trace minerals indicating gold bearing ore was nearby. The miners would have noticed the cuttings change to dark black, indicating they had intersected the Columbia vein, hopefully revealing a rich ore body that they had worked most of their lives to discover. One can imagine the excitement as the pyrite, arsenopyrite, graphite, and quartz started appearing in the drill hole cuttings. The Big Thunder miners had started in 1882 when they were about 35 years old. In 1914, 32 years later, the two miners were nearly 70 years old and had cut 680 feet into the mountain and 240 feet underground.

When they reached the Columbia formation, they removed the ore to form a large room called a stope. The stope eventually reached the dimensions of 20 feet wide, 35 feet high, and 60 feet long. Ore from the stope was taken to the Tykoon Mill, a custom mill that would process ore from small mines that could not afford to process ore themselves. The mill was located on the adjacent property just upstream from the Big Thunder Mine.

At this same time, World War I was gearing up, and the United States was increasing the war effort. The government L-208 order was issued, closing mines not producing war metals and minerals. 1914 marked the end of gold mining in the Big Thunder Mine.

When mines sit idle, they fill with water, equipment ages, and general deterioration result in extremely high start-up costs. Because of the deterioration, few of the mines in the Black Hills reopened after World War L The few mines that did open after the war were again closed by L-208 when World War II broke out. This second shutdown ended mining for most of the remaining mines in the Black Hills. Today, Homestake is the only underground gold mine operating in the Black Hills's. Although the underground workings were closed during World War II, Homestake's machine shop was pressed into action, making hand grenades for the war effort.

The owner of the Big Thunder Gold Mine, Julius Engle, held on to the mine until his death on November 4, 1921. Most owners hold on to the dream of "The Big Discovery." With modem mining techniques, gold may still be waiting to be discovered at Big Thunder.

Current exploration shows good potential for future gold mining in Keystone. Exploration companies have been working in the area and have leased mineral rights for many of the area mines. The company has also negotiated mining rights on the Big Thunder property at the 300 foot level and below.

Because Big Thunder Mine is the safest and best maintained mine in the Keystone milling district, it has been the center of exploration in the area. Big Thunder Mine contains most of the types of rocks, structures, and minerals of the district. An electric grid was placed over the area using the polarization method to determine the geological structure to a depth of 1,500 feet. The induced polarization method creates an electric current that passes into the ground along an electrode array. Electrical measurements are taken throughout the grid to determine the type and composition of the rock below the grid. Core samples were also taken to physically verify the electrical results.

In the future, there may be a modern gold mine producing gold below the 300 foot level of the current Big Thunder Gold Mine. Mining excitement is again alive in the historic Keystone mining district.