Coal and Peat Fires: a Global Perspective Edited by Glenn B

CHAPTER 23 ◆ ◆ The “Volcanoes” of Midwestern Venezuela CHAPTER CONTENTS 23.1 The “Volcanoes” of Midwestern Venezuela Introduction Geologic Setting The “Volcanoes” Discussion and Conclusions Acknowledgments References The main gas vent of “Volcán de Las Monas”, where the ammonium sulfates tschermigite, godovikovite, and mascagnite were identified by the authors. In 1994, the vent was 1.6 m wide and 0.25 m high at its widest point, and a thermocouple temperature of 225 °C was measured 40 cm inside. This coal-fire is located in a hillside in a remote region of northwest- ern Venezuela, with no coal-mining activity. According to local inhabitants, the coal-fire started in the 1950s, with the maximum activity in the late 1980s and early 1990s, when intermittent columns of smoke were visible up to a few kilometers away. In 1990, the vents were completely lined with sulfates. In 2012, the maximum temperature measured had decreased to 52 °C and there were no sulfate mineral deposits. Photo by Franco Urbani, 1990. Coal and Peat Fires: A Global Perspective Edited by Glenn B. Stracher, Anupma Prakash and Ellina V. Sokol 610 Copyright © 2015 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/B978-0-444-59509-6.00023-5 23.1 The “Volcanoes” of Midwestern Venezuela Manuel David Soto Franco Urbani Coal-fire and ammonium sulfates at “Volcán de Las Monas”, Venezuela. Vent details are mentioned in the previous photo. Photo by Franco Urbani, 1990. Introduction Several sites with underground coal-fires, known locally as “volcán” (volcano), “volcancito” (little volcano) or “fumarola” (fumarole), have been reported in western Venezuela (Briceño-Méndez, 1876). During the last third of the sixteenth century, the Spanish Royal authorities distributed a questionnaire known as the “Geographical Rela- tions” to their colonies, with the goal of compiling a general description of all Spanish territories. On January 21, 1579, the principals of the city of El Tocuyo wrote “We declare that at eight leagues from this city (El Tocuyo), in the mountains located in the direction of the sunrise, there is a large volcano (Fumarola de Sanare) that has three mouths. It is always smoking and emits a sulfurous smell… When the weather changes its roars can be heard in this city, and sometimes after those roars, large earthquakes occur that alarm the Spaniards as well as the natives. Fur- thermore, at seven leagues in the same direction from this volcano, above the valley of Quíbor, and at seven leagues from this town, there was another smaller volcano (Volcancito de San Miguel) that used to smoke and blow ash, but it is now extinct because in the past four years it no longer smokes as it used to do for many years” (Ponce de León et al., 1579 and Urbani 1996). This was the first description of coal-fires in the Americas, although for this locality it took 410 years (Urbani et al., 1987) to be recognized as the result of coal-fire. Coal-fires are known in several regions of Venezuela such as the Perijá Cordillera near the border with Colombia, the southern part of the Mérida Andes, and also in eastern Venezuela; all are related to tertiary coal-bearing geological units that sporadically have been exploited commercially. In this chapter, we studied five coal-fires located in the northern half of Lara State (Figure 23.1.1), surrounding the towns of Quíbor and Quebrada Arriba. This study includes a description of the geology of the area of combustion, and identification and analysis of thermally altered rocks and minerals deposited in and around gas vents and ground fissures. Geologic Setting The study area is included in the Lara Nappes geological province (Stephan et al., 1985) that originated due to a southeast vergent nappe-piling event that occurred during the late Eocene—early Oligocene. The event was caused by the oblique convergence of the Caribbean plate on the northern portion of the South American plate, producing a complex tectonic imbrication of igneous and sedimentary units of Cretaceous age with Paleogene turbidites. Later, during mid-Tertiary times an extensional period with crustal thinning created a basin that was filled transgressively by several Miocene formations deposited unconformably over the previous units. The “Volcanoes” of Midwestern Venezuela 611 Figure 23.1.1. Location map of coal-fires in midwestern Venezuela. The black dots mark the locations of current or burnt-out coal-fires with their local names. Polygons identify further detailed maps. Map coordinates are in kilometers, UTM zone P19, datum PSA56. Modified fromSoto (1997). The five coal-fires in the state of LaraFigure ( 23.1.1) occur in three different geological formations: 1. The area south of Quíbor (Figure 23.1.2) is crossed by the Boconó Fault (the major seismogenic fault of western Venezuela) and one of its branches, the Río Turbio Fault. Three coal-fire sites occur south of the Boconó fault in the Villanueva Formation (Figure 23.1.2): Volcancito de San Miguel (VSM), the Fumarola de Sanare (FS), both known since 1579, and the Volcán de Gusama (VG), which started in 1990 after a large landslide. The Vil- lanueva Formation is a Late Cretaceous unit composed of black shale with minor amounts of sandstone, lime- stone, and chert that have been affected by a very low-grade (subgreen schist facies) metamorphism (Von der Osten and Zozaya, 1957). This is an allocthonous unit emplaced during the mid-Tertiary nappe-piling event of the Caribbean realm. No coal-bed outcrops are described in the literature and none were found during our fieldwork. 2. Outcrops south of Quíbor, but in the north side of the Boconó Fault, are composed of unconsolidated beds of sand and clay with minor lignite inliers of the Pliocene Pegón Formation (Jefferson, 1964). The coal-fire in the “Mina de Yay” (MY, Figure 23.1.2) started in 1985 when a lignite seam, 70 cm thick, ignited spontaneously after it was exposed by mining white clays used in the ceramic industry. 3. The Volcán de Las Monas (Figure 23.1.1), located north of the town of Quebrada Arriba, is a smoldering coal bed in the Miocene Cerro Pelado Formation. This formation unconformably overlies the pre-Neogene nappes. The unit is composed of thick packages of sandstone, intercalated with shale and scattered lignite beds (Liddle, 1928). 612 Soto and Urbani Figure 23.1.2. Location map of coal-fire sites south of Quíbor, Lara State, Venezuela. Abbreviations of coal-fire sites: VSM, Volcancito de San Miguel; VG, Volcán de Gusama; FS, Fumarola de Sanare; and MY, Mina de Yay. Rectangles around the sites locate more detailed maps. Geological units: K, Villanueva Formation, Late Creta- ceous. Tp, Morán Formation, Paleogene. Tn, Pegón Formation, Neogene. Map coordinates are in kilometers, UTM zone P19, datum PSA56. Modified from Soto (1997). The “Volcanoes” A summary of location, geological context, temperature, and probable origin of the five coal-fires sites is presented in Table 23.1.1. Samples richest in carbon were collected and analyzed in each locality (Table 23.1.2). All of the mineral samples collected were identified by X-ray diffraction (XRD) and with an electron microprobe-scanning electron microscope (EMP-SEM). The sample data are summarized in Table 23.1.3. At Volcancito de San Miguel, Fumarola de Sanare, and Volcán de Gusama (all within the Villanueva Formation) only dark (carbon-rich) slates were available for sampling. No coal beds have been found at either of these locali- ties, neither by previous regional–geological surveys nor in our own work. Therefore, the source of combustion is open to further research. On the contrary, at Mina de Yay and Volcán de Las Monas, lignite was sampled. Volcancito de San Miguel At this site (Figure 23.1.3) there are several vents that emanate hot humid gas with an acrid and pungent smell, at the top of a landslide with many ground fissures opened in the weathered slates of the Villanueva Formation ( Figures 23.1.4 and 23.1.5). The highest temperature measured in 1990 was 95 °C, about 60 cm inside the main vent at that time. However, the temperature recorded in 2012 was only 45 °C. The elders of nearby towns say that they have never seen emissions of smoke or vapor. The secondary minerals deposited in and around the gas vents are Ca, Fe, and Mg sulfates. Gypsum (CaSO4·2H2O) is dominant and can be found covering and agglutinating the ground surface up to a few square meters around the vents. In places exposed to rainfall gypsum shows groove dissolution while in niches protected from the rain 3+ appears with magnesiocopiapite (MgFe 4(SO4)6(OH)2·20(H2O)) which forms pale green and yellowish efflores- cence (Figure 23.1.6). In addition, anhydrite (CaSO4) is present along the foliation planes of thermally altered slates and found inside and around hot gas vents (Figure 23.1.7). The “Volcanoes” of Midwestern Venezuela 613 Table 23.1.1 General data for five coal-fires in Midwestern Venezuela. Site Location Geological Unit, Lithology Origin Observations Volcancito de 5.9 km S of San Villanueva Formation Coal bed or dark Known since 1579 San Miguel Miguel 1425 m of (Late Cretaceous). carbonaceous slates, 1986: 83 °C elevation above sea Dark carbonaceous exposed by landslides 1990: 95 °C at 60 cm level (easl) slates, probably with in steep mountain below the surface 69°30′25″W coal or carbon-rich side 1994: 85 °C 9°49′52″N inliers. Very low grade 2012: 45 °C metasediments Volcán de 4.3 km SE of Ditto. Ditto. Started in 1990 Gusama Cubiro 1991: 281 °C at 70 cm 1520 m easl inside the vent 69°32′56″W 1994: 27 °C inactive 9°45′54″N Volcán de 4.2 km NEE of Ditto.

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