Modeling an Antique Grinding Mill of Guanajuato Silver Mines

Abstract

In 1557 Batolomé de Medina invented a new process for silver extraction. This process consisted on the amalgam of mercury (Quicksilver) and silver ore (known as backyard benefit or “benefico de patio” in antique Spanish). After forming the amalgam, the silver used to be extracted by melting the mercury. The process needed a granular sludge that was produced in two grinding mills; the first mill was similar to a modern hammer mill, and it broke the ore right outside the mine. The second mill (known as “arrastre” in Spanish), was a unique design that grinds the ore with millstones and water. In that time, this design was applied only in Mexico and South America, and it was one of the most productive processes worldwide. In this paper, detail analysis of the grinding mill (“arrastre” or “tahona”) is presented. The analysis is based on the original designs, and a procedure for reconstructing the dynamic parameters of the ancient mill is described. With this analysis, the restoration of antique artifacts incorporates actual loading conditions based on engineering data. Miners in the old days kept few documents, and the data restoration has required the analysis of information obtained from practical experience. Up to now, there are no archeological records of the dimensions and materials used in those days.