Pyrite in Virginia

most pyrite mines in Virginia were in northern Louisa County
most pyrite mines in Virginia were in northern Louisa County
Source: Laura Caswell, Gold-Pyrite Belt of Virginia

Pyrite is a mineral composed of two elements, iron and sulfur. One atom of iron combines with two atoms of sulfur to create iron sulfide (FeS2). Because of its appearance and presence in metamorphic/volcanic rocks which can contain gold, pyrite is known as "fool's gold."

Pyrite has been mined in Virginia to obtain both iron and sulfur. The extract the sulfur, ore was heated to produce sulfur dioxide; the gas was bubbled through water to create sulfuric acid. In addition to its use in manufacturing and to produce gunpowder, sulfuric acid was used to refine oil to produce kerosene.

As the United States experienced the Industrial Revolution, sulfur was needed for manufacturing of glass, soap, bleach, textiles, paper, dye, medicine, sugar, rubber, and fertilizer. Between 1916-1917 as World War I raged in Europe and demand for gunpowder skyrocketed, the price per ton for sulfur tripled. In 1917, Virginia was the largest producer of pyrite in the United States and supplied over 1/3 of the total mined that year. After the demand sank following the end of World War I, the price dropped and pyrite mines closed.1

Major pyrite mines in Virginia included the Cabin Branch Mine on Quantico Creek in Prince William County and the Austin Mine in Stafford County. Louisa County was a major pyrite producer, with at least 19 sulfur-pyrite mines.2

There is a gold-pyrite belt in the Piedmont physiographic province. The gold and pyrite are part of the Chopawamsic Formation, formed from continental crust as volcanic and sedimentary rocks were metamorphosed around 470 million years ago. The pyrite ore was emplaced when the Chopawamsic Terrane was created or accereted to the edge of "Virginia" over 400 million years ago, or perhaps during the Alleghenian Orogeny 250 million years ago when Pangea was formed.

pyrite mines in the Piedmont are concentrated in a gold-pyrite belt on the western edge of the Chopawamsic Terrane
pyrite mines in the Piedmont are concentrated in a gold-pyrite belt on the western edge of the Chopawamsic Terrane
Source: US Geological Survey (USGS), Geology of the National Capital Region - Circular 1264, The Goochland-Chopawamsic Terrane Boundary, Central Virginia Piedmont (Figure 1)

The formation is part of the Chopawamsic Terrane, which in the Ordovician Period was an island arc or chunk of continental crust off the shoreline of what became Virginia. The Chopawamsic Terane was transported by tectonic movement and accreted to the coastline of Virginia. The collision of the island arc and the coastline triggered the Taconic Orogeny pushing up 20,000' high mountains and pressing continental crust down just as deep. Heat and pressure at depth produced hydrothermal fluids into which minerals dissolved. The fluids transported iron, sulfur, gold, and silica (quartz) through fractures in the bedrock, and when the fluids when cooled created zones and veins of mineral ores.3

pyrite was mined from the Chopawamsic Formation (purple) north of Mineral in Louisa County
pyrite was mined from the Chopawamsic Formation (purple) north of Mineral in Louisa County
Source: Virginia Department of Mines, Minerals and Energy, 1993 Geologic Map of Virginia

The Sulphur Mine in Louisa County was discovered in 1834. It was opened originally to obtain iron from the Chopawamsic Formation. The iron ore near the surface was a highly oxidized gossan, an ore rich in iron after other minerals were removed by weathering and leaching. The lens body was about 50' thick.

The gossan was excavated and smelted at the Rough and Ready and Victoria furnaces into pig iron. Mining stopped briefly in 1874 when the gossan deposit was exhausted and the miners reached harder bedrock enriched with pyrite. That bedrock was still rich in sulfur and required blasting to excavate.

The mine was re-opened in 1881, after dynamite was available rather than just black powder. When the mine reopened, industrial development had increased the demand for sulfur. As the name implies, the Sulphur Mine was reopened to obtain primarily sulfur rather than iron. One shaft was extended over 700' deep to harder bedrock before mining ceased around 1920, when the price for sulfur dropped after World War I ended and cheaper sources of sulfur were developed.

Reclamation of the Sulphur Mine occurred in the 1970's and 1980's, with a renewed effort in 2010-2011. Open shafts were closed and tailings piles were leveled. After adding limestone, soil was placed on top of the tailings and trees planted.

Pyrite and gold mining in Louisa County has left Contrary Creek as a severely damaged stream. Excavations at the Arminius, Boyd Smith, Sulphur, and Allah Cooper mines exposed sulfur-rich bedrock. Pyrite is a mineral from which the sulfur easily combines with oxygen to create sulfates. There are no pyrite crystals on Virginia Beach; they all oxidized and dissolved during transport towards the Atlantic Ocean.

Rainwater reaching sulfur-rich rocks on Contrary Creek has continued to dissolve acid minerals long after mining has ceased. The sulfates dissolve in groundwater, lowering the pH to levels that no longer support life. The resulting acid drainage from sulfur-rich rock still damages Contrary Creek significantly, though it is diluted by Lake Anna.4

In Carroll County, the "Gossan Lead" was mined for copper and iron prior to the Civil War. After World War II, the Gossan Lead produced pyrite for manufacturing sulfuric acid. The ore was shipped to Pulaski for roasting to extract the sulfur. Iron was a valued byproduct, shipped by rail to the steel mills in Birmingham, Alabama.

The Gossan Lead deposit consisted of a series of elongated lenses; mineralization may have occurred in multiple phases. The sulfides were emplaced in a brecciated zone, likely when thrust faults moved and hot water flowed more readily.

Sulfides near the surface were altered into sulfates, carbonates, or other soluble compounds Rain and groundwater transported the soluble compounds deeper into the weathering bedrock, where they were precipitated to create an enriched mineralized zone. Above that zone, the "gossan" layer was enriched with iron oxides.

The US Geological Survey examined the Gossan Lead after World War II, in a search for possible remaining copper deposits. The Bureau of Mines drilled 25 holes, with over 9,000' of exploration borings. The Federal agencies found a gossan layer as much as 30' thick. Below it:5

The body of secondary sulfides lies in a nearly horizontal position between the unaltered primary sulfides below and the leached oxidized gossan cap above. Copper is one of the most easily transported and precipitated metals, and considerable enrichment may be attained in the secondary zone.

Cabin Branch Mine

Minerals of Virginia

Pyrite Mining on Contrary Creek

Virginia Iron in the Colonial Era

Links

References

1. "Cabin Branch Pyrite Mine (1889-1920)," National Park Service, https://www.nps.gov/prwi/learn/historyculture/cabin-branch-mine.htm; "Cabin Branch Pyrite Mine Historic District," nomination form to National Register of Historic Places, https://www.dhr.virginia.gov/VLR_to_transfer/PDFNoms/076-0289_Cabin_Branch_Pyrite_Mine_Historic_District_2002_Final_Nomination.pdf (last checked August 7, 2020)
2. "Louisa County, Virginia Sulfur-Pyrite Mines," The Diggings, https://thediggings.com/usa/virginia/louisa-va109/mines?commodity=sulfur-pyrite (last checked August 6, 2020)
3. Scott Southworth, William Chapin Burton, "Geology of the National Capital Region: Field Trip Guidebook," Circular 1264, US Geological Survey, 2004, p.225, , (last checked August 7, 2020)
4. Eddie L. Wood, "Mine Spoil Reclamation In The Contrary Creek Watershed In Louisa County, Virginia," Masters Thesis, University of Montana, 1973, p.1, https://scholarworks.umt.edu/cgi/viewcontent.cgi?article=6983&context=etd; Richard S. Mitchell, Arthur S. Katz, "Minerals from the Sulphur Mine, Louisa County, Virginia," Rocks & Minerals, Volume 52 Number 5 (1977), pp.275-278, https://doi.org/10.1080/00357529.1977.11761973; "Sulphur Iron Mine," The Diggings, https://thediggings.com/mines/usgs10067658; "Sulphur Mine," Mindat.org, https://www.mindat.org/loc-23578.html; "Mining Heydey," Free Lance-Star, April 30, 2015, https://fredericksburg.com/mining-heyday/article_316b0b11-35dc-541e-8953-a519f5e1ae82.html; Andrew H. Knoll, A Brief History of Earth, Custom House, 2021, p.95, https://www.google.com/books/edition/A_Brief_History_of_Earth/_T7yDwAAQBAJ (last checked September 13, 2021)
5. R. J. Wright, N. D. Raman, "The Gossan Lead, Carroll County, Virginia," US Geological Survey, 1948, pp.1-3, p.6, p.15, https://pubs.usgs.gov/of/1948/0003/report.pdf; M.H. Kline, T.J. Ballard, "Investigation of the Great Gossan Lead, Carroll County, VA," Bureau of Mines, September 1949, https://hdl.handle.net/2027/mdp.39015078495978 (last checked August 8, 2020)


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