Geochemistry and geochronology of the Sierra de Gomez Limestone-hosted U deposit, Chihuahua: Implications for distribution of Rio Grande rift mineral deposits in northern Mexico

摘要

Uranium deposits form in a variety of settings. They are partially controlled by the secular evolution of Earth processes, including deposits in extension-related settings such as the intra-cratonic Rio Grande rift. Plio-Quatemary volcanism, mineral deposits, and hydrothermal spots occur along the Chihuahua Central Graben. The age of the Sierra de Gomez U-deposit is 1.8 Ma (based on LA-MC-ICP-MS dating on a uranophane monocrystal), which is contemporaneous with the late mineralization event of the Pena Blanca U-deposit, as well as Rio Grande Rift (RGR)-type deposits in Chihuahua and intraplate volcanism. Studies of fluid inclusions in fluorite and late calcite indicate the presence of hydrocarbons and CH4-rich brine. Homogenization temperatures range from 87 to 112 degrees C, and the mean composition (2.0 mol NaCl and 0.3 mol CaCl with CH4) is comparable to mineralizing brines in MVT deposits and carbonated hydrocarbon reservoirs. Evolution of C and O stable isotopic values for the calcite cement in the Sierra de Gomez Limestone-hosted U deposit illustrates that two separate calcite precipitation events occurred: (1) travertine filling karst structures in the presence of meteoric water and (2) U mineralization during deep hydrothermal fluid circulation that included interactions with a heat source and basement leaching. In a regional context, a metallogenic model suggests that the Chihuahua Trough area is deep enough to generate fluid migration by hydrothermal and/or compaction processes through RGR extensional faults until a favorable trapping horizon is reached. This causes uranium precipitation because water/rock interaction processes generate a local redox barrier. (C) 2016 Elsevier B.V. All rights reserved.