Ridgeway Mine

Two open pits were dug to extract the gold-bearing ore from the earth. Explosives were used to blast the ore out of the bottom of the mine pits. After the blast, the loose rocks were hauled in 85-ton trucks to temporary storage heaps near the edge of the pit at surface level.[4] There was roughly one truckload of waste rock hauled out of the pit for every truckload of gold ore and each truckload of gold ore contained only 1.5 to 3 ounces of gold.[5] Ridgeway's gold deposits were microscopic and a complex, multi-step process was needed to refine the heaps of ore into gold bars. A mill was used to crush the ore to an extremely fine powder of 200 mesh.[6] This powder was soaked in a mixture of sodium cyanide, lime and water in one of ten giant tanks. While the powder soaks the tiny flecks of gold within the ore dissolve into the cyanide solution.[5] After twenty-seven days the powder is removed and the remaining solution was filtered through activated charcoal which absorbs the gold out of the liquid in what is called a carbon in leach process. That gold-bearing carbon gets removed from the first solution and was put into a second solution that dissolves the gold for a second time. The second solution was put in a stripping column where high pressure vapor jets through the solution causing the dissolved gold to vaporize. The gold-bearing vapor escapes through the column and was captured and cooled to make a third solution. Once captured the third solution was used in an electrowinning process that uses electricity to deposit the gold out of the solution onto steel wool cathodes. This gold-plated steel wool undergoes a second round of electrowinning to deposit the gold onto stainless steel plates. At this point the gold deposits are thick enough to be mechanically scraped off of the stainless steel plates. The resulting scrapings were fed into a gold crucible and melted into doré bars.

The Carolina Slate Belt (CSB) originated in the Proterozoic or Cambrian age with a volcanic arc terrane, a chain of volcanoes that form on the edge of one continental plate when it has another continental plate subducted under it.[7] Another subduction of the eastern edge of the ancient North American continental plate (Laurentia) caused the Taconic orogeny and created a new mountain range on the eastern coast of North America. These new mountains eroded over time to form the Piedmont but while they stood their weight was just enough to metamorphose the old volcanic arc rocks into greenschist, a rock produced by some of the lowest metamorphic pressures. The eastern edge of the North American plate continued to be battered by the Avalonia continent, causing the Acadian orogeny, and the ancient African plate (Gondwana), causing the Alleghanian orogeny. These collisions squeezed the CSB, causing it to crack under pressure (shear) and creating intrusive granite from magma seeping up into the cracks.

The mine is located in a section of the CSB that trends from east to west. This is unusual for the CSB as it typically trends from northeast to southwest. To the north of the mine is a rock terrane called the Sawney's Creek volcanics and to its south is the Bear Creek turbidites. The Sawney's Creek terrane is older and was formed by volcanic activity. The newer Bear Creek turbidites were made from liquefied sediments that slid into place as part of a landslide. There are two mine pits and the gold ore in each one has its own unique geology. The North Pit's ore is a chert, a rock made from microscopic crystals of quartz that precipitated out of hot water from an underwater geothermal vent. These exhalative sediments need a deep geothermal vent whose water is hot enough to dissolve gold from inside the crust. The hot water precipitates the dissolved minerals onto the ocean floor as fine crystals when it mixes with cold ocean floor water and cools off. A later, epithermal (cooler geothermal vents closer to the surface) process concentrated the gold further by dissolving other minerals surrounding the gold and leaving the gold behind. The South Pit's ore is made from fine sediments of felsic (rich in feldspar and quartz) ash from a volcano that flowed underwater and settled into thin laminated layers.

Gold was first found in the Carolina Slate Belt in 1827[6] at the Haile mine in nearby Lancaster County. Placer mining, hydraulic mining and later use of the Newbery-Vautin chlorination process kept South Carolina mines in operation but by the year 1900 mining became unprofitable and had mostly stopped.[6] In the 1960s interest in mining the Ridgeway area increased after John Chapman found gold[6] while panning in nearby creeks. Amselco Minerals, a company later merged with Kennecott Minerals, began investigating Ridgeway after geologist Irving T. Kiff noticed similarities between Ridgeway's slate outcrops and outcrops at the Haile mine.[8] Kennecott Minerals began buying land for the Ridgeway mine in 1980 and began mining in 1988.[6] For most of its life the Ridgeway Mine was the only active gold mine in the eastern United States.[9]

Ridgeway began the mine reclamation process in 1999 after processing the last of the gold ore from the mine. The mine tailings (waste rock) needed to be contained and the North and South pits had to be flooded. The tailings at the Ridgeway mine are a pyrite-bearing rock which, when exposed to water and oxygen, causes acid rock drainage and environmental damage. Ridgeway designed an impoundment for the tailings that seals them off from both runoff (water) and the atmosphere (oxygen). If fresh water was allowed to run through the tailings it would constantly dissolve and oxidize the rock's sulfides. Ridgeway chose to keep the tailings in stagnant water that has already had a chance to fully saturate with sulfides.[1] The tailing impoundment was created by saturating the tailings with water, mining nearby saprolites and clay, sending the saprolites and clay through the ore mills and pouring them over the existing pile of tailings to create a layer over it.[31] The impoundment was then graded to give it steep sides and a flat top and grass was planted on it to prevent erosion. The Ridgeway mine recovery has been an ecological success with minimal seepage of acid water into the environment, a stark contrast to the nearby Barite Hill and Brewer gold mines that were both declared Superfund sites after being abandoned by their owners.[32]

Both mine pits are expected to fill with water by 2020[33] and the public may be able to access the South Pit Lake.[34] To make the lake safe for public use and to control environmental hazards management hopes to turn it into a meromictic lake, a self-regulated lake with distinct layers of water that do not mix.[35]^: ii To see if this was possible the South Pit Lake's physical, chemical and biological properties were measured in a limnology study from 2000 to 2004. The lake successfully achieved meromixis in the winter of 2001 and maintained it until the end of the study in 2004.[35]^: iii

The Strongbow Exploration company announced that it was investigating a possible new strike of gold within three miles of Rio Tinto's Ridgeway mine in 2011.[36] After releasing several press releases announcing positive test results from drilling samples[37] and the signing of property purchase option agreements with landowners[38] there has been no further communication on their Ridgeway exploration since December 2012.

Duckett, Roy. "The Kennecott Ridgeway Mine a Case Study in Sustainable Development" (pdf). Kennecott Minerals Company. Retrieved 14 August 2018.

Duckett, R.; O'Kane, M. (2006). "Hydraulic Placement Of A Dry Cover System - Design And Performance Monitoring Of The Kennecott Ridgeway Mine Tailings Dam Cover System" (PDF). Journal American Society of Mining and Reclamation. 2006 (2): 539–554. doi:10.21000/JASMR06020539.

"Confederate States Mint - Collectable Historical Coins".

Collins, Jan. Carolina Gold (PDF).