An Expensive Hole In The Ground?
September 17, 2008
Aspen’s mining companies dug and drilled for 70 years. Some holes reached ore, others were expensive holes in the ground. The current push for core drilling to seek geothermal water could result in additional expensive and unproductive holes.
Geologists map earth’s surface, conjecturing what lies below. Areas penetrated by mines have been thoroughly studied ” there geologists see first-hand the complex nature of moving blocks of rock. Exhaustive studies were made of Aspen’s underground, beginning with J. E. Spurr in 1895. Spurr identified hydrothermal processes as the origin of Aspen’s ore bodies. In geologic time, not human time, extremely hot water carrying precious minerals forced its way from deep in the earth into numerous fractures surrounding Aspen. Much later, surface water worked its way down through the same fracture zones to rework the mineral deposits. Although this is a story of heat and water, it does not necessarily suggest developable geothermal energy.
When Spurr examined Aspen’s geology, mines extended to great depths. He did not report increasing temperatures as he descended the many shafts. Water, however, was often found. Water has always presented a problem for Aspen’s miners. The Smuggler mine pumped up to 3,500 gallons a minute from its 18th level, 1,400 feet below the surface. The company quit pumping in 1918, flooding 75,000 feet of mine workings.
Water rose nearly to the level of the Smuggler Number One tunnel, at 7,870 feet above sea level.
News accounts of Aspen’s approaching geothermal exploration reported “anecdotal evidence of high underground temperatures.” It is true that the Smuggler experienced high temperatures, high enough to stop operation in one of the tunnels that was situated well above the water level. The source of that heat was an underground fire that began around 1900. When exposed to oxygen, carbon can ignite on its own; such spontaneous combustion commonly occurs in coal mines. The fire spread and workers could neither work near it nor put it out. A concrete bulkhead was installed to plug the tunnel to prevent oxygen from reaching the fire. When they reopened the tunnel years later, the fire was still smoldering.
From 1946 to 1948, the U.S. Bureau of Mines and the Anaconda Mining Company implemented core drilling to find new ore deposits and to test geologic theories in the Smugger. Anaconda drilled a hole from the surface, producing the large scar you see between the Hunter Creek Valley and the Smuggler road. Today it looks like natural erosion, but it was caused by the large amounts of water used by Anaconda that simply ran down a barren hillside. Most holes were short, drilled horizontally from the inside of existing tunnels. Drillers encountered problems when working through brecciated ore zones. Breccia is rock associated with hydrothermal deposition and is common in Aspen’s mineral zones. Drill core recovery was reduced to about 12 percent whenever drilling through breccia.
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So what will Aspen’s geothermal explorers find? I believe if they drill as planned, outside of but close to old mining areas, they will have to drill through granite boulders left by glaciation, an expensive challenge to a drilling rig. They may encounter breccia near the fault zones. They may find water flowing at the contact between the glacial material and the sedimentary layers. In the fault zones they will find water that works its way down from the surface. That water could be as warm as 58 degrees fahrenheit, the year-round temperature of Aspen’s underground. Long before the explorers’ 3,000-foot goal they will reach the base rock, granite, an unlikely zone to discover geothermally heated water.
Aspen’s nearest geothermal source is far up Conundrum Creek, where an enterprising hotelier promoted a spa/lodge. Even without consulting a geologic map the historic record suggests a very low potential for geothermally heated water. Aspen’s mines pumped water for decades, water from the lowest levels, tunnels that crossed all the way from Smuggler Mountain to Aspen Mountain. Had any of the water been hot, or even warm enough for a bath, you would find evidence of bathhouses and swimming pools surrounding each mine where dirty and sore miners had awaited a turn at the Smuggler Spa.
Tim Willoughby’s family story parallels Aspen’s. He began sharing folklore while a teacher for Aspen Country Day School and Colorado Mountain College. Now a tourist in his native town, he views it with historical perspective. He can be contacted at email@example.com.