Shallow Temperature Measurements at Juncalito, a

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Shallow Temperature Measurements at Juncalito, a Geothermal Prospect, Central Andes, Chile Elías Lira*, Rodrigo Arcos, Jorge Clavero, Aldo Giavelli and…
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Shallow Temperature Measurements at Juncalito, a Geothermal Prospect, Central Andes, Chile Elías Lira*, Rodrigo Arcos, Jorge Clavero, Aldo Giavelli and Catalina Mayorga Energía Andina S.A., Darío Urzúa 2165, Providencia, Santiago, Chile *E-mail: a class= __cf_email__ href= /cdn-cgi/l/email-protection data-cfemail= 583d34312a39183d363d2a3f3139363c313639763b34 [email protected] /a script data-cfhash='f9e31' type= text/javascript /* ![CDATA[ */!function(t,e,r,n,c,a,p){try{t=document.currentScript||function(){for(t=document.getElementsByTagName('script'),e=t.length;e--;)if(t[e].getAttribute('data-cfhash'))return t[e]}();if(t&&(c=t.previousSibling)){p=t.parentNode;if(a=c.getAttribute('data-cfemail')){for(e='',r='0x'+a.substr(0,2)|0,n=2;a.length-n;n+=2)e+='%'+('0'+('0x'+a.substr(n,2)^r).toString(16)).slice(-2);p.replaceChild(document.createTextNode(decodeURIComponent(e)),c)}p.removeChild(t)}}catch(u){}}()/* ]] */ /script Abstract. The mapping of temperature variations at or below the earth surface constitutes a key geothermal exploration tool. In this work, the results of 25 days of shallow temperature measurements are presented. First, thirty-three temperature loggers were installed in an area of approximately 25 km² for a period of eight days. The purpose of this survey was to identify patterns of nearsurface lateral flow of thermal signatures associated with known hot springs. The results of these surveys showed relevant thermal anomalies not only associated with hot springs but also on other sites without hydrothermal discharge. A second survey of one-hundred temperature measurements was performed for seventeen field working days. The temperature measurements were obtained in an area of approximately 37 km². In this survey, thermal anomalies identified in the first survey were mapped at a higher level of detail. These results are complemented with Magnetotelluric and geochemical data, potentially delineating zones of upflow and outflow of a geothermal prospect. volcanoes, dome-complexes and lava and ignimbrite fields (Los Cuyanos-Sierra Nevada Volcanic Complex) (Clavero et al., 1997, 1998), which is interpreted to be the heat source of a geothermal system. The main structural feature corresponds to a high angle N-S thrust system that overrides volcaniclastic Permian-Triassic rocks (W) over Oligo-Miocene volcanic and syntectectonic sedimentary rocks (E), (Clavero et al., 1997, 1998). Five zones of thermal springs have been recognized in the northern, centre and southern parts of Juncalito area, the Río Negro springs being the ones with higher temperatures (up to 44°C) and larger flow (~20-30 l/s). A positive compositional indicator of a thermal resource is the silica concentration (130 to 160 mg/kg SiO2) of Río Negro springs indicating quartz equilibration temperatures of 140 to 160°C (Mayorga, 2011). 3 Shallow Temperature Surveys During March 10-17, 2011 thirty-three 1-meter deep temperature measurements were recorded in an area of aproximately 25 km² in the Pampa de Los Cuyanos, Río Negro and Ojos de los Cuyanos stream zones (Fig. 1, white triangles). One-hundred additional measurements were made between May 8-24, 2011 in an area of 37 km² in the same zones (Fig. 1, black triangles). Keywords: Geothermal, shallow temperature, exploration 1 Introduction For many decades, shallow temperature measurements have been used as key geothermal exploration tool. Subsurface temperature measurement at a depth of 1-meter is an efficient method for mapping thermal anomalies with a high level of detail. These thermal anomalies can be associated with interesting geothermal features. However, variations in near-surface temperatures could be caused by a number of non-geothermal factors, including changes in air temperature, soil moisture, near-surface groundwater flow and thermal inertia. The effects of these variables were qualitatively characterized during this survey. The temperature measurements were corrected for different non-geothermal factors. Changes in air temperature and daily solar radiation cycle were corrected by a simple moving average filter of the 12 and 24 hours respectively, but in general, at a depth of 1-meter, temperature variations induced by 24-hour solar radiation cycle are almost completely damped out (Elachi, 1987). The thermal inertia was considered in the duration of time series: beginning with a one-day delay after installation for the temperature to reach equilibrium. 2 Study Area Background Surface temperatures during the first survey varied from -8 to 27°C compared with the temperatures at a depth of 1meter that varied from 8 to 33°C. During the second survey, the surface temperatures varied from -5 to 9°C whereas that the temperatures at a depth of 1-meter varied between 4-42°C. Juncalito area is located in northern Chile, in the southern limit of the Chilean Altiplano, at an average altitude of 4100 m.a.s.l. The younger volcanism in the area is associated with a Pleistocene-Holocene NW-SE volcanic chain with a series of volcanic complexes, strato- 618 Figure 1. Location of the temperature loggers. Thirty-three temperature loggers were installed in an area of approximately 25 km² for a period of eight days (white triangles). In the second survey, one-hundred temperature loggers were installed in an area of approximately 37 km² (black triangles). Figure 2. One meter deep temperature measurements during the first survey. The temperatures varied between 8-33°C (blue to red color scale). Background image is shaded topography. 4 Results and Discussion Two main thermal anomalies were identified with temperatures >15°C which greatly exceeded the background temperature defined for the period and study area (<9°C). The western margin thermal anomaly is related to a hydrothermal discharge zone in the headwaters of Ojos de los Cuyanos stream. The second thermal anomaly of greater magnitude (~30°C) is related to Rio Negro springs and is NE-SW aligned. A third thermal anomaly of lower magnitude (~11°C) was identified near the Azufrera de los Cuyanos volcano. This anomaly is not related to known thermal springs and could be associated with a deep heat source. In the second survey, the thermal anomalies identified in the first survey were mapped at a higher level of detail. The thermal anomaly correlated to the headwaters of Ojos de los Cuyanos stream is aligned in N-S direction and suggests structural or lithological control. The thermal anomaly correlated to Río Negro springs shows different hydrothermal discharge zones. Thermal anomalies of lower magnitude were identified in the Pampa de Los Cuyanos and close to Azufrera de los Cuyanos and Juncalito volcanoes. First, the thermal anomaly located in Pampa de los Cuyanos could be associated with a thermal aquifer that discharges in the Río Negro and Ojos de los Cuyanos stream. Second, the thermal anomalies correlated to Azufrera de los Cuyanos and Juncalito volcanoes may be related to a deeper heat source. Figure 3. One meter deep temperature measurements during the second survey. The temperatures varied between 4-42°C (blue to red color scale). Red border represents a very distinctive conductivity anomaly defined by MT survey (<5 Ω.m). Background image is shaded topography. 619 Lira, E. 2011. Estudio de Temperatura de suelo a 1 m de profundidad. Proyecto Juncalito. Energía Andina S.A. (Unpublished), 31p. Chile. The thermal evidence detected shows a strong and direct geographical relationship with a very distinctive conductivity anomaly (<5 Ω.m, red border) suggesting the presence of thermal fluids that discharge into Rio Negro and Ojos de los Cuyanos stream (possible “outflow” zone). This very distinctive conductivity anomaly defined by MT survey, with an abrupt limit (structurally controlled) to the west and a convex geometry, suggesting an “upflow” zone of the potential geothermal system under the southwest flank of Los Cuyanos volcanic Complex. Mayorga, C. 2011. Geoquímica de Fluidos del área de Juncalito. Proyecto Juncalito. Energía Andina S.A. (Unpublished), 26p. Chile. References Olmsted, F., Welch, A. & Ingebritsen, S., 1986. shallow surface temperature surveys in Basin and Range province, USA- I. Review and evaluation. Geothermics, 15, 251-265. Olmsted, F.H., 1977. Use of temperature surveys at a depth of 1 meter in geothermal exploration in Nevada. United States Geological Survey Professional Paper 1044-B, 25 p. Clavero, J., Mpodozis, C. & Gardeweg, M., 1997. Mapa geológico del área del Salar de Wheelwright, versión preliminar, escala 1:100.000. SERNAGEOMIN. Chile. Sladek, C., Coolbaugh, M. & Zehner, R., 2007. Development of 2Meter Soil Temperature Probes and Results of Temperature Survey Conducted at Desert Peak, Nevada, USA. Geothermal Resources Council Transactions, 31. Clavero, J., Mpodozis, C. & Gardeweg, M., 1998. Mapa geológico del área del Salar de Piedra Parada, versión preliminar, escala 1:100.000. SERNAGEOMIN. Chile. Sladek, C., Coolbaugh, M. F., & Kratt, C., 2009. Improvements in shallow (2-meter) temperature measurements and results of long term studies conducted at Desert Queen, Nevada. Geothermal Resources Council Transactions, 33. Coolbaugh, M., Faulds, J., Kratt, C., Oppliger, G., Shevenell, L., Calvin, W., Ehni, W., & Zehner, R., 2006a. Geothermal potential of the Pyramid Lake Paiute Reservation, Nevada, USA: Evidence of previously unrecognized moderate-temperature (150-170 C) geothermal systems. Geothermal Resources Council Transactions, 30. Trexler, D.T., Koenig, B.A., Ghusn, G. Jr., Flynn, T., \& Bell, E.J., 1982. Low-to-moderate-temperature geothermal resource assessment for Nevada: area specific studies, Pumpernickel Valley, Carlin and Moana: United States Department of Energy Geothermal Energy Report DOE/NV/10220-1 (DE82018598) Coolbaugh, M.F., Sladek, C., Kratt, C., Shevenell, L., & Faulds, J.E., 2006b. Surface indicators of geothermal activity at Salt Wells, Nevada, USA, including warm ground, borate deposits, and siliceous alteration. Geothermal Resources Council Transactions, 30. Coolbaugh, M., Sladek, C., Faulds, J., Zehner, R. & Oppliger, G., 2007. Use of Rapid Temperature Measurements at a 2-meter Depth to Augment Deeper Temperature Gradient Drilling. ThirtySecond Workshop on Geothermal Reservoir Engineering. Departamento General de Aguas (DGA) del Ministerio de Obras Públicas, 2008, Levantamiento hidrogeológico para el desarrollo de nuevas fuentes de agua en áreas prioritarias de la zona norte de Chile, Regiones XV, I, II Y III. Departamento de Ingeniería Hidráulica y Ambiental. Pontificia Universidad Católica de Chile (Unpublished). Chile. Elachi, C., 1987. Introduction to the Physics and Techniques of Remote Sensing, John Wiley and Sons, New York, 413 p. Einarsson, G.M & Kristinsson, S.G., 2010. Thermal Imaging of Geothermal Features. Proceedings World Geothermal Congress 2010. Bali, Indonesia, April 25-29 2010. Giavelli, A. 2011. Levantamiento MT/TDEM, Análisis de datos y propuesta de interpretación. Proyecto Juncalito. Energía Andina S.A. (Unpublished). Chile. Kratt, C., Coolbaugh, M., Peppin, B., & Sladek, C., 2009. Identification of a new blind geothermal area with hyperspectral remote sensing and shallow temperature measurements at Columbus Salt Marsh, Esmeralda County, Nevada. Geothermal Resources Council Transactions, 33. LeSchack, L.A. & Lewis, J.E., 1983, Geothermal prospecting with Shallo-Temp surveys, Geophysics, 48, 975-996. 620
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