Geoquímica de lantánidos de los yacimientos de fluorita de los distritos mineros de Taxco y Zacualpan, sur de México: implicaciones sobre el origen y la evolución de los fluidos

Abstract

We present and evaluate lanthanide contents measured by inductively coupled plasma mass spectrometry (ICP-MS) in fluorite samples from the fluorite deposits in Zacualpan and Taxco mining districts in the south of Mexico. The information is used to distinguish different generations of fluorite, to establish a correlation between mineralization episodes and the wall rock nature, and to identify postdepositional processes.The total lanthanide content of the fluorites are variable, and early- stage fluorite samples are usually enriched in LREE. The concentration of REE in fluorite is low in comparison with the volcanic and metamorphic rocks (∑REE > 100 ppm) and is generally high respect the carbonates (∑REE < 30 ppm). There is host rock influence. The higher REE concentra- tions are in fluorites hosted by volcanic rocks. The fluorite that replaced carbonate is characterized by low REE to very low concentrations. Fluorite samples associated with sulfurs are typically enriched in HREE. Nearly all fluorites show a negative Eu anomaly similar to the REE anomaly observed in the volcanic rock. Only some early stage dark, uranium rich fluorites, from la Azul deposit, have a strong positive Eu anomaly. Direct correlation between color and REE patterns is observed in some samples.In the Zacualpan mining district, only an episode of mineralization has been discriminated, where fluorite presents flat to HREE- enriched chondrite-normalized REE patterns.In the Taxco mining district and particularly in the “Mina la Azul”, multiple hydrothermal events of mineralization have been determined. The first generation of fluorite is formed by replacement of carbonates and is characterized by very low contents of lanthanides, chondrite- normalized REE patterns similar to the limestone, high strontium content and primary textures (e.g. massive fluorite and rhythmites). The second generation of fluorite is related to the entry of new fluid to the system and has higher REE concentrations, chondrite-normalized REE patterns similar to volcanic rocks, low strontium content and secondary textures (i.e. breccias, nodules). Most of the samples show a genetic relationship between fluorite and fluids of magmatic origin.

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

“…The precipitation of fluorite under low temperatures from low salinity fluids agrees with thermodynamic models in which the solubility of fluorite decreases steadily under 100 • C [50]. The possibility that fluorine was scavenged from F-rich local Oligocene acid volcanic and hypabyssal rocks is underpinned by the REE distribution pattern in the Las Cuevas fluorite [51], which is similar to that in fluorite deposits associated with felsic magmatism [52] and to that in the local Oligocene rocks [30,53].…”

Uranium in Fluorite, a Case Study: The La Azul Fluorspar Deposit, Taxco, Guerrero, Mexico

“…Relative uncertainty of uranium, thorium, samarium, and strontium measurements are below 5%. In previous studies conducted by the first two authors of this study, several episodes of mineralization have been recognized via combined geochemistry and (U-Th-Sm)/He dating [38,39]. The early uranium-rich fluorite mineralization has been dated at ~32 Ma, with later fluorite precipitation as young as ~10 Ma [38].…”

“…Fluorite crystals in La Azul display various colors, including white, gray, yellow, green, brown, and purple. The purple varieties are uranium-rich, as has been described previously in a number of deposits around the world [9,39,40], and were the study objectives of this work. The La Azul fluorite ore deposit paragenesis (schematized in Figure 2) is composed of fluorite with variable amounts of calcite, barite, calcedony, and quartz.…”

“…Fluorite crystals in La Azul display various colors, including white, gray, yellow, green, brown, and purple. The purple varieties are uranium-rich, as has been described previously in a number of deposits around the world [9,39,40], and were the study objectives of this work. In the La Azul mineralization, several of these uranium-rich fluorites also contains H 2 S, which can be easily identified by its characteristic rotten egg smell, and methane, which was identified via mass spectrometry [39].…”

“…Description of studied samples. Concentrations of Sr, U, Th, and Sm, along with their ages, were obtained from the authors of [38,39]. See images of these samples in Figure 4.…”