Evidence of a new geothermal prospect in the Northern-Central trans-Mexican volcanic belt: Rancho Nuevo, Guanajuato, Mexico

Abstract

Thermal manifestations are commonly found in central Mexico as result of the volcanic activity originating from the formation of the Trans-Mexican Volcanic Belt during the Quaternary. The Rancho Nuevo hot spring is one of them that has not been described before with a discharge temperature near 92 °C. The goal of the present study is to provide geothermal characteristics of thermal manifestations at Rancho Nuevo location based on geochemical and mineralogical results to explain deep-subsurface processes that occurred in the geothermal system. The presence of kaolinite, montmorillonite, opal, zeolite, barite, pyrite, and stibnite in altered soil sediments or around the hot springs identified by the techniques used in the present study, confirms the presence of hydrothermal activity. In addition, based on the X-ray diffraction, calcite precipitates at the surface of the thermal springs. This mineral association reflects deep geothermal processes and is eventually deposited in shallow zones. Fluid mixing processes and variations in redox conditions are suggested by mineral association and isotopic sulfur data. Finally, based on the physicochemical data provided by the water samples and the discharge conditions of the springs, stability diagrams were constructed for pyrite, barite, and zeolites using the Geochemist's Work Bench program to corroborate these data with the mineralogical results. The mineralogical results and distribution, as well as the N-S trend of mineral associations suggest interaction processes between geothermal fluid and rocks of the stratigraphic sequence, and active major faults, enabling the upward flow of deep geothermal fluids. The approach to the conceptual model of the Rancho Nuevo geothermal prospect reveals an attractive potential for the exploration of a viable geothermal resource in central Mexico. Keywords Geothermal potential • Rancho Nuevo geothermal prospect • Hot spring mineralization • Deep-subsurface processes ResumenEn el centro de México es común encontrar manifestaciones termales como resultado de la actividad volcánica que originó la formación del Cinturón Volcánico Trans-Mexicano durante el Cuaternario. El manantial caliente de Rancho Nuevo es una de ellas el cual no ha sido descrita antes cuya temperatura de descarga es de aproximadamente 92 °C. El objetivo del presente estudio es proporcionar las características geotérmicas de las manifestaciones termales localizadas en el poblado de Rancho Nuevo, considerando los resultados geoquímicos y mineralógicos, para explicar los procesos ocurridos a profundidad en el sistema geotérmico. La presencia de caolinita, montmorillonita, ópalo, zeolita, barita, pirita y estibinita identificadas

Influence of Mineral Deposition on the Retention of Potentially Hazardous Elements in Geothermal Spring Sediments

“…Calcite and aragonite are the most common minerals deposited from hot spring waters, which could be contributed by both abiotic and biotic processes [28,31,50,51,53]. Calcite crystalized out of the hot spring water with the significant reduction in water temperature [54], and its precipitation happened after that of clay minerals, which are abundant in hot spring sediments and form through a gelatinous substance precursor [55,56]. Aragonite precipitated out of spring water because of the rapid CO2 degassing [28].…”

“…The minerals in the hot spring sediments played important roles in the retention of the PHEs. For example, the enrichment of Sb in the hot spring sediments depended largely on Calcite crystalized out of the hot spring water with the significant reduction in water temperature [54], and its precipitation happened after that of clay minerals, which are abundant in hot spring sediments and form through a gelatinous substance precursor [55,56]. Aragonite precipitated out of spring water because of the rapid CO 2 degassing [28].…”

“…Aragonite precipitated out of spring water because of the rapid CO 2 degassing [28]. Ba in the sediments probably precipitated out of the hot spring water in the form of barite (BaSO 4 ), which has low solubility at the low temperatures in the surface environment [54].…”

“…In geothermal systems, As can be retained by the hot spring sinters [65], where As might be present as arsenate sorbed on hydrous ferric oxides and/or as nodular arsenide micro-mineralization [66]. Nonetheless, the positive correlations between As, Fe 2 O 3 , and SO 3 (Table 3 and Figure 7B) suggest that it was probably associated with the abundant pyrite in the hot spring sediments [54,67]. Cs in the hot spring sediments had positive correlations with CaO, MgO, SrO, and Na 2 O (Figure 7C), indicating that it was probably associated with carbonates and albite.…”