What role did mules play in the patio process?

In the patio process, mules were essential for both the mechanical preparation and the chemical treatment of silver ore.12

• Crushing: Mules provided the power to operate arrastras, which were shallow, stone-paved pits. Large stone blocks attached to beams were dragged by mules around a central rotating post to grind the ore into a fine mud.1
• Mixing: Once the ore was spread across a courtyard or patio and combined with mercury, salt, and copper sulfate, mules were driven repeatedly through the mixture. By tethering the animals to a central post and compelling them to walk in circles, laborers ensured the reagents were thoroughly incorporated into the ore, facilitating the chemical reactions necessary to free the silver.12

This reliance on animal power was a defining feature of the method, which remained a primary technique for silver production for over 350 years until it was eventually replaced by the cyanide process.12