Characterization of the alteration minerals in domes and pyroclastic deposits of Paipa Geothermal Area, Colombia

Abstract

Hydrothermal alterations are indicators of the interaction of hot fluids with the mineral components of rocks that are: altered, reequilibrated, and transformed into new groups of minerals whose formation temperatures are known; the study of alteration minerals allows identification of active and fossil hydrothermal systems, being a crucial input for the characterization of areas with a potential for exploitation of the heat stored in rocks. In Colombia, the Paipa Geothermal Area (AGP), in the state of Boyacá, is conceived as one of the most promising zones, and this investigation provides details on the mineralogy of alterations. The results of the determination of alteration minerals are presented for three sites within the AGP: ALFAGRES quarry, CEMEX quarry and southeast dome of Alto de los Godos, where the volcanic rocks are associated with the periphery of the seal cap of the geothermal system, constituted also by the clayey levels of Churuvita and Une sedimentary formations. The analysis of 54 samples was conducted by X-Ray Diffraction (XRD) on randomly oriented clay-sized fractions by the smear method, and oriented powder by the glass slide, ethylene glycol solvation, and sample heated to 500°C. Although the following clay mineral phases are common to the three sites: smectite (montmorillonite), halloysite-7Å, kaolinite, and illite, there are also some secondary mineralizations: zeolites (mordenite) and dickite (ALFRAGRES), and chlorite (Alto de Los Godos). Other minerals such as quartz, feldspars, and halloysite-10Å are present in at least two of the sites. The clay minerals from the group of zeolites and kaolin found indicate different stages of advance of the argillic and intermediate argillic alterations; the presence of interstratified illite-smectite (I/S) is related to a state of phyllic alteration. The alterations were caused by hydrothermalism that reached temperatures in the 100-200°C range, being later accentuated and masked by weathering processes