Creating a searchable core

Homestake Mining Co. extracted nearly 7 million feet of solid-rock core samples during decades of exploration for gold. Crews used diamond-bit drills to extract the slender, cylindrical rock cores, most of which are long discarded. However, Homestake did donate 396,000 feet of surviving core ? 75 miles' worth ? to the Sanford Underground Laboratory.

This core archive is a unique scientific resource and a priceless window into 9 cubic miles of underground real estate. "This was a world renown mine," former Homestake Chief Geologist Kathy Hart says. "Every geology student studies it." The vast collection is easier to search now, thanks to a summer of work by Senior Geologist Kelli McCormick of the South Dakota Geological Survey and Chase Hamer, a graduate geology student at the South Dakota School of Mines and Technology (SDSMT)."The South Dakota Geological Survey has been tremendously helpful," SDSMT geologist Bill Roggenthen says. "A vast archive is great, but it's kind of like the Internet. It isn't useful unless you have a good search engine."Creating that search engine is a challenge. The cores are stored in flat boxes ? about 10 feet of core per box. More than 160 of the boxes are stacked on pallets, 84 boxes per pallet. The pallets are stored on the floor of the former Homestake machine shop ? a cavernous structure reminiscent of a 1930s warehouse scene from an Indiana Jones movie. More core boxes are stacked on tall, long shelves in a nearby building formerly used to house the hollow steel shafts for miners' jackleg drills.Homestake Mining Co. maintained meticulous records for the core, but since mining ended in 2001 the core collection has been moved several times. A single drill hole can be hundreds of feet long, and samples from the same hole often ended up on different pallets or even in different buildings.McCormick and Hamer opened boxes to make sure labels were correct. Then, often with help from Sanford Lab staff and interns, they reordered boxes on pallets to make samples easier to find. They also updated the computer database for the samples and created a "pallet map" to speed retrieval. Scientists and engineers will be able to search for core samples by geologic formation, by rock characteristics, by depth and by other parameters. "I think those who have seen the collection before will be impressed," McCormick says.Kathy Hart, now a consulting geologist with the Sanford Underground Laboratory, says the new archive will be useful in designing and excavating large caverns for underground campuses. "You have to know the geology before you design them."Scientists also will use the core archives. Sanford Lab Geologist Tom Trancynger said researchers already are requesting access to the archive ? and not just geologists. The core samples will provide valuable data for scientists studying hydrology, biology and the environment.To make the archive even more useful, Hart has scanned 40 boxes of documents called "drill logs," which describe the core samples. The logs are now available in a 90-gigabyte searchable file. Hart also is scanning and reorganizing Homestake's working maps of underground levels, which were hand-drawn by geologists then transferred, again by hand, to large linen maps called "bed sheets." Hart is working closely with the Homestake Adams Resource and Cultural Center in Deadwood, S.D., which is the repository for Homestake documents, maps, photographs and other materials.In addition, Hart is "cleaning up" a Vulcan database that can generate interactive, three-dimensional images of the underground at Homestake.The archiving project has not been completed. McCormick and Hamer reorganized about 40 percent of the collection ? or about 30 miles of core. Trancynger and others are working on plans to finish the job. Eventually, the core archive will become part of the Sanford Lab's geosciences laboratory. The South Dakota Science and Technology Authority has reopened Homestake as an underground laboratory the Sanford Underground Laboratory. The National Science Foundation is working on a proposal to convert the Sanford Lab into a national lab, commonly known as DUSEL.