New Mexico Mineral Symposium — Abstracts

According to legend, Kopparberget, Sweden’s Great Copper Mountain, was discovered by a goat named Kåre. Today known as Falun, the mine has a long and colorful history. Its rich ore helped Sweden become a European power in the mid-1500s and the mine still has an impact on Swedish culture today.

Rocks at Falun are dominated by 1.8 to 1.9 Ga Palaeoproterozoic metavolcanics known as leptites that are interpreted to be felsic pyroclastics and rhyolitic ash deposited in a submarine environment. There are also some mafic and intermediate metavolcanics as well as metasediments interpreted as mudstone, turbidite, and greywacke in addition to some carbonate units. Plutonic rocks of various compositions intrude these rocks. The tectonic setting of these rocks was an extensional back-arc environment. Deformation metamorphism affected the region during the 1.8–1.9 Ga Svecokarelian Orogeny.

The ore deposit at Falun is hosted in the Leptite Formation. Most of these rocks are quartz and mica rich and traditionally called “ore quartzites” and “mica schists.” Both calcite and dolomite marble as well as skarn are also found at Falun Mine. All these rocks have been folded into a large, steeply plunging isoclinal syncline.

Seven types of ore are recognized at the mine:

1. Hard ore: veins and disseminated sulphides hosted in quartzite.
2. Compact pyrite ore (soft ore): massive sulphides with quartz and carbonate gangue minerals.
3. Sköl: altered rock related to fault zones that occasionally contain sulphides.
4. Native gold: found in quartz veins and lenses that post-date the sulphides.
5. Galena veins.
6. Compact ball ore: massive sulphide containing spherical inclusions of host rock.
7. Skarns.

The main ore deposit is a pyritic Zn-Pb-Cu-(Au-Ag) sulphide formed as a stratabound volcanic associated limestone-skarn (SVALS) deposit caused by exhalation in a submarine environment.

There is much debate over the early history of Falun. The legend of its discovery by Kåre the billygoat is deeply lodged in the folklore of the region, but archaeological evidence concerning the origins of mining is equivocal. Studies have yielded dates ranging from AD 589±97 to circa AD 1245. The earliest written record of mining operations at Falun is a document from 1288 that outlines the exchange of an estate for a share of the mine.
Prior to the mid-1700s, mine workers were employed by “Master Miners,” who were shareholders. The Master Miners arranged their own labor force and the processing of ore. The actual miners were peasants who were granted special rights. In the mid-1700s, employment shifted to the model of a more modern company, with miners employed by the mine, not a Master Miner.

Originally an open cast mine, miners soon worked underground in search of the richest ore. Firesetting was originally used to break rock. Black powder was first adopted for surface use in the late 1600s, but by 1710 it was used in both surface and underground applications. Dewatering was accomplished by hand or horsepower until the 1550s, when the first waterwheel was installed for this purpose. Waterwheels eventually provided the power for pumps, hoisting engines, and bellows.

Following extraction, ore was crushed and roasted in open fires. The roasted ore was then smelted, and lastly refined. Originally, copper was sent for refining to Germany and Holland. After 1619, refining was completed in Säter, Sweden. In the 1800s, processing of ore moved from open roasting to other techniques and by the early 1900s new plants were constructed for various wet separation methods.

Sweden was a major European power from the mid-1500s to the early 1700s. This was in part due to the rich ore of Falun Mine providing wealth to the kingdom. Peak production occurred in the mid-1600s, when it is estimated the mine produced half the world’s supply of copper.

Massive amounts of SO₂ were released into the atmosphere during ore roasting. The pungent scent of sulphur could be smelled up the 80 km away. Thick smoke caused twilight conditions at midday and the overpowering fumes made breathing difficult and caused problematic coughs and nosebleeds. The sulphurous air, however, did have some benefits. There were no mosquitoes, fewer reports of contagious diseases, and when plague spread throughout Sweden in 1710, the disease did not strike Falun.

By the late 1600s, an inspection by the Board of Mines concluded measures were necessary to secure the mine. Thus, it came as no surprise when the Great Collapse occurred in 1687. A massive amount of rock separating two galleries fell and produced a pit 100 m deep with rubble filling the collapse up to 350 m below the surface. This large area became known as Stora Stöten, the Great Pit. Fortunately, the collapse occurred on Midsummer Day when no one was working in the mine, thus there were no casualties. Soon after the collapse copper production began to decline, but the production of other metals, including zinc, gold, and silver, increased.

In 1888, the old shareholding system that had existed at the mine since the Middle Ages was modernized into a joint-stock company. This company expanded mining operations as well as diversifying into other industries. Falun Mine continued to operate until December 8, 1992. After over a millennium of mining, the economic ore had finally run out. The joint-stock company (STORA) is still in business, specializing in forestry and paper products.

Over the life of the mine, it is estimated that 30 million tons of ore were extracted, producing around 400,000 tons of copper. In addition to the metal riches that shaped Sweden’s history, the ore at Falun also impacted countryside and culture of the nation. Waste rock is used to create a unique paint known as Falun Red, which is very popular throughout Sweden. Artists, authors, and poets have used the Falun Red painted farmstead as a symbol of Swedish heritage.

Falun Mine was declared a World Heritage Site in 2001. Guided tours are offered to underground workings. Visitors can also walk around the surface mining complex and visit a museum on site.