ESL 201 – Fundamental Techniques in Geology
Dr. C. Gil Wiswall
December 15, 1999

Centralia Coal Fire Analysis: Presence of Sulfur-bearing Mineral Deposits

Since 1962, a coalmine fire has spread underneath the surface of Centralia, located in the anthracite coal region in Columbia County, Pa. In Centralia, many measures have been taken to cope with the various problems resulting from the fire. Ultimately, almost the whole town has had to relocate to other areas due to fear of subsidence, water contamination, and air pollution from the noxious gases released through vents and fumeroles. Solid, multicolored deposits can be found on the surface surrounding these vents. The deposits are believed to be primarily sulfur-bearing minerals deposited hydrothermally on the surface by the escaping vapors. In this experiment, we collect five different deposits located around three different vents and one deposit located on an anthracite sample nearby a vent. We evaluate the six samples for mineral content, via X-ray diffraction analysis. The results indicate that all conclusive (3) vent deposits are sulfur-bearing minerals and one particular sample, on the anthracite, is native sulfur. The native sulfur, found on an anthracite sample rather then the surface surrounding a vent, is deposited from bacteria called Desulfovibrio desulfuricans. The bacteria use the carbon in the coal for energy and reduce anhydrite (CaSO₄) and gypsum (CaSO₄·H₂O) to hydrogen sulfide (H₂S) (Cooney and others, 1999). The hydrogen sulfide is then oxidized upon contact with the atmosphere, leaving native sulfur (S⁰) behind. Other minerals found include Tschermigite and Apjohnite. Apjohnite was recovered as a coating on a rock removed from the inside of a vent. Apjohnite usually is white to pale yellow, has a hardness of 1.5 to 2, and has encrustation (forms crust-like aggregate on matrices) habit (Barthelmy, 1999). Tschermigite, also known as ammonia alum, is soft (hardness = 1.5-2.0) and is usually white to colorless (Barthelmy, 1999). Tschermigite is very rare and only found natively in Czechoslovakia, but also has been reported to form as deposits around volcanic vents and fumaroles (Lowenstern, 1999). For the tschermigite and apjohnite, the sulfur compounds release from the coal and dissolve into the heated fluid, where they react with other dissolved ions present in solution. They are then carried to and deposited on the surface by these hydrothermal fluids. At the surface, the liquids cool and the sulfur minerals are precipitated from the solution. The presence of Tschermigite suggests that the coal mine fires of Centralia are quite similar to other high temperature regions on earth, particularly volcanically active areas.

Throughout much of Centralia there are cracks and holes in the ground with a harsh steam constantly pouring out. The trees are all dead and white in color and the ground is so hot your feet sweat. There is a sulfur smell to the steam and two hours of exposure was enough to give my colleagues and I headaches. Around these surface holes, or vents, different colored deposits are scattered in a wide range of sizes. These deposits are very interesting for they exhibit various colors and forms. It is the goal of our research to collect these deposits for observation and X-ray diffraction analysis. We infer that these samples are sulfuric in nature from the smell of the vapor rising from the vents. From the analysis, we hope to conclude that these deposits are primarily sulfur and/or sulfur-bearing minerals. Also, we hope to gather enough evidence to formulate a theory on how the deposits were extracted, transported, and deposited.

We chose to research the Centralia mine fire because of the great tragedy it presents. The residents of Centralia have had their lives shattered by the fires from stress of relocation and/or medical complications. Also, we chose Centralia because the area resembles a post-nuclear war wasteland and is very unique. The sulfury smell, rocky smoking hillsides, absence of people, and ghostly white smoldering trees present an eerie landscape sparking the interest of my colleagues and I. Specifically, we chose to concentrate our experiment on the vent deposits. The deposits are unlike any other surface rocks or features we observed in Centralia and we were very curious of there nature. From the experiment, we hoped to gain an understanding of the origin, methods of transportation and deposition, and classification of these deposits. We also wish to further our knowledge of the landscape characteristics and history of the Centralia mine fire.

Centralia is located in the anthracite coal region of Eastern Pennsylvania, in Columbia County. In the summer of 1962, a fire started in the Buck Mountain coal bed. At this time, there were about 1,100 residents with 545 families and businesses in Centralia (PDEP, 1996). The mine fire is believed to have started from an accidental fire at the landfill located at the southern end of the town. >From here, the fire spread igniting an open coalmine shaft and spreading throughout the abandoned mines. By 1983, the fire consumed approximately 195 acres of area (Logue and others, 1991), and the main road into town, Route 61, suffered severe subsidence damage (PDEP, 1996). In 1983, the Office of Surface Mining (OSM) was authorized by the Department of Health to reclaim public lands and private establishments deemed hazardous, and over 30 houses were moved away. The OSM released a report in 1983 estimating that the fire could spread to 3,700 acres and "burn for a century or more if left uncontrolled" (Logue and others, 1991). Hazards included subsidence, noxious gases, oxygen depletion, and particulate matter. "A study estimated it would cost $663 million to extinguish what some call "the granddaddy" of all mine fires", says Lynne Glover in the Tribune review. Because the estimated cost of relocation was only about 42 million, relocation was chosen as the answer to the fire. The coal bed will eventually burn out when the coal seem ends, so the neighboring towns are believed to be safe (Glover, 1998). In 1984, Congress set aside $42 million dollars and begins to relocate families and businesses. The Milton S. Hershey Medical Center released a report that concluded Centralians had higher incidences of respiratory disease, hypertension, gastrointestinal disease, arthritis, and depression in Feb. 1986 (Logue and others, 1991). In 1993, Route 61 is closed indefinitely after several attempts to repair it. The 53 remaining households are condemned but the remaining residents still refuse to leave. By 1996, there were <46 remaining residents (< 5% of the original) of Centralia (20 families) and the total costs of relocation exceed $35 million (PDEP, 1996).

The anthracite coal beds of eastern Pennsylvania cover an area of about 1250 sq. km and constitute over 97% of the total U.S. anthracite resources (Funk and Wagnall’s, 1999). There is approximately 15 billion tons of recoverable coal in this region, enough to supply anthracite for the next 400 years (Centralia Coal, 1999). The anthracite coal beds were deposited in the Pennsylvanian, ~300 ma. During this period of the Carboniferous, the region was predominantly lowlands and forested swamps periodically covered by shallow seas. Trees and ferns constitute the majority of the Pennsylvanian plant life. For coal to form, the plant matter must be deposited underwater to avoid oxidation to water and carbon dioxide. The plant matter was then transformed by biochemical and physical processes (metamorphic events from subsequent orogenies) into a dense consolidated carbon-rich rock (Levin, 1996). Different coals are produced in a succession depending on time and metamorphic stress starting with peat, to lignite, bituminous, and finally anthracite (Bell and Wright, 1985). Anthracite coal has the highest fixed carbon, 93-98%, and lowest volatile material of all coals. Anthracite is a hard, glossy black rock with concoidal fracture. Although harder to ignite, anthracite (ignition at about 225° C) releases large amounts of energy (7000 - 8000 cal./ kg) when burned with less smoke and soot as bituminous (ignition at about 150° C) and lignite coals (Funk and Wagnall’s, 1999; Glover, 1998; Mottana and others, 1978).

There are other places in Pennsylvania and around the world where underground coal fires burn. Pennsylvania has over 250,000 acres of abandoned mine lands and has >1/3 of the nations mine problems. There are over 45 mine fires burning across Pennsylvania. There are five underground fires in Allegheny County, five in Percy County, one in Westmoreland, and others in more isolated areas. There are also fires in Findlay Twp., West Elizabeth, Plum, and Clinton. "In all, the DEP estimates about 1,300 acres across the state are on fire underground" (Glover, 1998). One particular town, Youngstown, is under the wrath of the Percy fire that has been burning for over 30 years. There are about 60 homes resting on top of this fire now. Youngstown is reaching the critical decision point that Centralia reached in 1983, either extinguish the fire or relocate the whole town. Estimates conclude that extinguishing the Percy fire will cost $30 to $40 million, and over $650 million to put out all nationwide fires (Glover, 1998).

A very large underground fire burns through large coal beds in Northern China. The fires consume up to 200 million tons of coal each year. This fire is quite a bit larger then the largest Pennsylvania fire (Centralia), releasing almost "as much carbon dioxide into the atmosphere as do all the cars in the United States" (Kittl, 1999). The Chinese haven’t really paid much attention to the fire until recently. Now they monitor the fire with heat sensitive satellite photographs. Areas of subsidence have caused very large cracks in the surface and there are areas where one can observe the burning beds above them on the side of a cliff. The Chinese are now taking measures such as burying the coal with dirt and pouring a water-clay mix into surface cracks to cool the fire. They feel the only way to deal with these fires is to try to isolate them and let them burn out (Kittl, 1999).

Sulfur (S) is distributed in the crust in mineral forms such as iron pyrites, sphalerite, galena, gypsum, barite, and others. It also "occurs native in the vicinity of volcanoes and hot springs" (Hammond, 1975). Sulfur is yellow, has a low specific gravity (2.0), and is brittle (Cepeda, 1994). The sulfur in the deposits comes from mineral and organic sulfur in the anthracite. The sulfur in Anthracite can be divided into three categories: pyritic sulfur, sulfate sulfur, and organic sulfur (Alvarez and others, 1997). Pyritic sulfurs, also called sulfide sulfurs, constitute anywhere between 25-75% of the total sulfur and are contained in minerals such as pyrite and marcasite (FeS₂) and sphalerite (ZnS) (Chinchon and others, 1991). During combustion, sulfide sulfurs release in the form of their oxides at about 500° C.

2 FeS₂ + 5 O_{2 ®} 4SO₂ + 2FeO

The organic sulfurs, 20-70% total sulfur, are sulfurs incorporated into the organic molecules of the plant material and also release around 500° C. Sulfate sulfurs usually are in the form of gypsum (CaSO₄) and decompose to CaO and CO₂ at 500° C. The sulfates don’t release as sulfur dioxide until 1060° C, a temperature where 13.70% of the initial sulfur still remains. Thus a large percent of the sulfur still remains in the form of anhydrites (Alvarez and others, 1997; Chinchon and others, 1991).

Sulfur oxides, primarily sulfur dioxide (SO₂), are released in gaseous form into the atmosphere. For underground fires, the sulfur byproducts are, in part, dissolved into the heated surface groundwater and transported to the surface. Other byproducts are released in gaseous form. Sulfur has a low melting point (175° F) and is easily dissolved. The sulfur oxides react with other ions in the fluids and/or the atmosphere and precipitate out sulfur-bearing minerals during condensation at the cooler surface.

Native Sulfur can form if the proper conditions are met, low temperatures and the presence of an energy source. At these conditions, bacteria called Desulfovibrio desulfuricans use the carbon in the coal as the energy source (Cooney and others, 1999) in a reaction that reduces the sulfur from anhydrites (CaSO₄) and gypsum (CaSO₄·H₂O) minerals in the coal. The sulfur is then released in the form of hydrogen sulfide (H₂S), which is then oxidized in the atmosphere to form native sulfur (Cepeda, 1994).

Deposit samples were collected from 3 different sites. Site 1 and site 2 are separated by approximately 100 feet and are located in a ravine on the west side of Route 61 at the subsidence damage site. Site 3 is located to the Northwest of sites 1 & 2 at the landfill where the coal beds initially caught fire.

Site 1: Site 1 was a small area at the bottom of the ravine. From Site 1, we collected one sample labeled "white crystal". White crystal deposits were scattered lightly over about a 25 sq. ft area. The "white crystal" was concentrated in roughly a 6 x 3 inch area that was located next to a fissure to the downhill. The fissure was an 8 to 10 inch crack in the surface with water seeping out and moist soil surrounding it.

Site 2: Site 2 was the surroundings of a larger fissure on the eastern side of the ravine. It was located about halfway up the hillside and steam/smoke was escaping from the hole and surrounding cracks. From this site, we collected four samples labeled: "yellow chunk", "white chunk", red chunk", and "green crystal". The red, yellow, and white chunk deposits were massive in nature, brittle, and homogenously deposited around the vent. The three different colors exhibited no visual zoning and apperared to be similar. Large masses, up to ~4 inches in diameter, displayed color changes within crystal itself. Some samples displayed all three colors within themselves.

The "green crystal" deposits were found on a relatively rectangular sample of anthracite roughly 24in. x 10in. x 3in. in size located downhill from the vent. The anthracite was charring on the underside and the crystal deposits were located on the side of the rock at the junction of the side and top faces. The anthracite sample was located about 5 feet downhill from any visual vent activity and did not appear to be associated with the vent itself at this particular time.

Site 3: Site 3 was located a couple hundred feet northwest of the first two sites, at the landfill. This area was the landfill where the fire initially ignited the coal seam. There are many fissures scattered around the area and the ground is exceptionally warm here. Site 3 is a large hole in the bedrock with steam pumping out and a white film covering all the associated rocks. The deposit is scraped from a rock taken from inside the vent. The sample appears to be a white, porous film baked onto the rock.

The samples were collected in plastic zip-lock bags and labeled accordingly. The samples were then crushed into a fine powder using a mortar and pestle. The powder was analyzed by X-ray diffraction and peaks were correlated on a sulfate database to search for sulfur-bearing minerals. Results are printed and placed in a data table.

The data table is provided in figure 1: