| Title | First Results of the Vein Alteration in the Deep Well PGC1 of Irruputuncu Geothermal System, Andean Cordillera, Northern Chile |
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| Authors | Jeanne VIDAL, Patricia PATRIER, Christian BETANCOURT, Santiago MAZA, Diego MORATA |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | clay minerals, hydrothermal alteration, XRD, active geothermal system, Irruputuncu, Andean Cordillera, Chile |
| Abstract | The geothermal potential of the Irruputuncu active stratovolcano was explored with two magnetotelluric-transient electromagnetic campaigns as well as two deep exploration wells between 2009 and 2011. In this study, core samples from the first well PGC1 were investigated in order to estimate the hydrothermal alteration in the rock formations from 58 to 428m depth. The well intersects tuffs with fragments of andesitic and dacitic lavas and sedimentary rocks in the deepest part. X-Ray diffraction applied to the clay fraction allowed to identify the vertical distribution of the clay minerals along the well. In addition, microscopic observations of the alteration petrography give information about mineral parageneses associated to the hydrothermal events. The alteration petrography of core samples along the well PGC1 indicate a superimposition of several hydrothermal events. Quartz + Pyrite + Illite + R3 I/S ml + Chlorite + Corrensite + Anhydrite + Kaolinite + Opale observed are relicts of early hot stages ( greater than 150°C). Late stages lead to crystallization of Smectite + R1 I/S ml under temperatures close to the actual ones (~150°C). These minerals are observed as replacement of vitreous matrix and selective or total replacement of primary minerals but also in veins. The hydrothermal history seems complex and dominated by various factor such as temperature, physico-chemical properties of the fluid chemistry, time... Further petrographic investigations should be carried out in samples in order to better understand the mineralogical relationships and better constrain the hydrothermal history in the Irruputuncu geothermal field. |