Apunte geológico y revisión histórica de la zona geotérmica de Pathé, Hidalgo.
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The Pathé geothermal zone, in the eastern portion of the Trans-Mexican Volcanic Belt, attracted a variety of scientists and explorers since late 18th century. Joseph Burkart (1798-1870), a German mining engineer disciple of Alexander von Humboldt (1769-1859), provided in 1836 elaborated geological descriptions of the zone; for these early reports, Pathé was the first geothermal system to be studied in Mexico under the modern science principles. At the beginning of the 20th century, this zone was investigated by the Mexican geologist José Guadalupe Aguilera Serrano (1857-1941), who described in 1907 the local volcanic rocks and their alteration. His main interest were the kaolin deposits of Yexthó, located one km to the west of the geothermal manifestations. By the middle of the century, the area was already explored for geothermal energy, which resulted in the first geothermal power plant in all America, operating between 1959 and 1972 with a nominal capacity of 3.5 MW.
Thermal manifestations of Pathé are placed in the junction of two regional fault systems, N-S and E-W, and are hosted by a volcanic unit (tuff and lava) of basic to intermediate composition and Upper Miocene age. Surface hydrothermal alteration is conspicuous and occurs largely controlled by faults of the two systems as well. Associated to N-S faults is a calcite-gypsum alteration assemblage, indicating oxidized, alkaline hydrothermal fluids. On the other hand, linked to the later E-W faults are the kaolin deposits; they are the product of an advanced argillic alteration that is characteristic of steam-heated environment and indicates acidic conditions (pH: 2 to 3) and temperature around 100 °C. Because of its unambiguous relation to faults together with the absence of recent (Quaternary) volcanism, Pathé is classified as a fault-controlled geothermal system (non-magmatic, extensional domain type). The successive alteration events suggest that hydrothermal activity is long-lived and dates back to before the Pliocene.