| Abstract: | Lithogeochemical sampling in the Guanajuato, Pachuca and Tayoltita silver mining districts of Mexico has revealed the presence of significant ammonium anomalies related to mineralized veins. The anomalies can be recognised in surface as well as in mine crosscut and drill core samples and persist over depths of several hundreds of metres. Ammonium haloes are best developed in the hanging walls of major veins but anomalous concentrations are also found in footwall regions. In all three areas ammonium is an effective pathfinder for epithermal precious-metal vein-style mineralization. Comparison with data for major and trace elements (Ca, K, Mg, Na, As, Ba, Cu, P, Rb, S, Sb, Sr, Zn) shows that ammonium often forms broader haloes with a more consistent relationship to the veins than other lithogeochemical indicators. Variations in ammonium geochemistry between deposits can be related to the availability of ammonium in the epithermal system, wall-rock lithology and the nature of the vein network.The results of this study suggest that ammonium geochemistry has considerable potential as an exploration tool for precious-metal vein deposits. |
