TITLE:
The Ancient Molinete, Plants, and Mercury Efficiency in Present-Day Artisanal Gold Mining, Northern Perú
AUTHORS:
William E. Brooks, Asunción Cano
KEYWORDS:
Amalgamation, Mercury, Molinete, Perú, Plants
JOURNAL NAME:
Archaeological Discovery,
Vol.14 No.1,
December
25,
2025
ABSTRACT: The molinete, a smaller version of the quimbalete or Inka mill, was also used to crush gold ore in the ancient Andes and its present-day use, though limited, continues. It consists of a large, movable upper stone, or chungo, and a lower, stationary stone, or muscha, that has a depression to seat the chungo. Each stone may weigh approximately one ton. The worker is seated and rocks the chungo, by foot on the lower, water-lubricated mushca. The weight of the chungo and back and forth motion crushes the ore thereby releasing the gold grains into the muddy slurry to which mercury is added to form a gold-mercury amalgam. After the amalgam is recovered, it is squeezed in a cloth to recover excess mercury, and then it is burned to volatilize the remaining mercury leaving an anthropogenic gold nugget. Spot geochemical sampling for Inductively Coupled Plasma (ICP) analysis of the molinete gold ore indicated average ~43 ppm Au and post-amalgamation mud contained average ~33 ppm Au which indicates an efficiency of ~23%. Local plants such as pegorondo or murmuncho were added to the muddy slurry in the muscha depression to aid amalgam recovery and help lubricate molinete movement; however, the use of these plants has been discontinued since the 1940s. Most importantly, since mercury is used with molinetes and quimbaletes to recover gold at artisanal gold processing sites today, then, the documented use of these artisanal ore-crushing mills in the past is consistent with mercury use for gold amalgamation in pre-contact Perú.