The topaz-bearing rhyolites from the San Luis Potosi area (Mexico): characteristics of the lava and growth conditions of topaz

Abstract

Abstract. -In Mexico, the topaz-bearing rhyolites occur mainly in the San Luis Potosi area (San Luis Potosi and Guanajuato States). These rhyolites appear as domes related to the Tertiary extensional tectonism. Three domes of the San Luis Potosi volcanic field were selected for study, according to the color, the habits and the size of the topaz they contain, in order to determine the characteristics of the lava and the growth conditions of the topaz. These rhyolites are high-silica, metaluminous to slightly peraluminous and alkali-rich lavas. They are enriched in fluorine and in incompatible lithophile elements such as Rb, Cs, Ta, U and Th and depleted in Ba, Sr, Ca, Mg, Ti and Ni. Therefore, they are very similar to the topaz-bearing rhyolites from western United States. In Cerro El Gato dome, both amber-colored and colorless topazes crystallized in voids and fractures. Comparing these different crystals with respect to their growth environment, habits, chemical compositions and EPR characteristics provides an explanation for the crystallization conditions and color of topaz. Colorless topaz from Cerro El Gato crystallized at a temperature above 500 o C (lack of color centers) from fluids enriched in elements leached from the lava, whereas the amber-colored topaz crystallized below 500 o C (based on the presence of color centers) and from fluids richer in volatile elements (As). In Cerro El Lobo, the topaz have intermediate characteristics between the colorless and the amber-colored topazes of Cerro El Gato.

The fingerprint of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) based on cathodoluminescence properties and composition

“…However, the studies carried out by Zhang et al (2002) with topaz crystals of high- to ultrahigh-pressure metamorphic rocks (kyanite topaz-bearing quartzites) from Sulu terrane (Eastern China), have showed 0.35 ≤ X OH ≤ 0.55. With respect to the trace-element composition of topaz, other studies show significant variations in Ti, V, Cr, Mn, Fe, Cu, Zn, Ga and Ge (Leroy et al , 2002; Wasim et al , 2011; Wu et al , 2011; Breiter et al , 2013; Agangi et al , 2014, 2016).…”

Giant Fluorite Mineralization in Central Mexico by Means of Exceptionally Low Salinity Fluids: An Unusual Style among MVT Deposits

“…The Cenozoic magmatism in the area occurs as Oligocene hypabyssal and volcanic rhyolites and dacites, and minor granodiorite [4][5][6] ( Figure 2). Oligocene rhyolites in this region constitute a part of the San Luis Potosí Volcanic Field, and are typically highly evolved and fluorine-rich (topaz-bearing) rocks, hence the hydrothermal tin mineralization that is commonly associated with them [2,[20][21][22][23][24][25].…”

“…It is likely that fresh meteoric water carried fluorine in solution by means of its interaction with the local hypabyssal and volcanic rhyolites, which were F-rich [2,[20][21][22][23][24][25]. Although no relevant concentrations of fluorine have been detected in rhyolites of the study area (see the data for Río Verde in Reference [20], but these refer to a sole sample that is not representative of the broad extent of Oligocene volcanism in the region (see Figure 2)), such contents can be over 0.3% in Oligocene topaz rhyolites in central Mexico [20,21].…”

A cathodoluminescence-assisted LA-ICP-MS study of topaz from different geological settings

“…With respect to the trace element concentrations of topaz in other studies, Ti, V, Cr, Mn, Fe, Cu, Zn, Nb, LREE, HREE, Ta and W showed relevant variations (Leroy et al 2002, Wasim et al 2011, Wu et al 2011, Breiter et al 2013, Agangi et al 2014, 2016, Gauzzi et al 2018.…”