When a full size stamp mill was not available, arrastras
were used to crush the ore. Arrastras were small circular
flat areas of land usually about 10-20 feet in diameter
with a pole in the center.
Attached to the pole was a rod or line running
out to a large heavy wheel.
A horse or mule was usually attached to the end of the wheel
area and would walk around in circles. As the animal walked,
the heavy wheel would crush
the ore underneath it. Arrastras were a crude way to crush
large pieces of rock into much smaller and more manageable
sized bits. In later years, iron arrastras (pictured on
the right) replaced the wheel method.
Stamp Mills were far more advanced than the early arrastras
although they both performed the same function. Stamp mills
ranged from one stamp on up to twenty or even fifty stamps
all operating together.
5 Stamp Mill
Each stamp was a large
piece of solid iron or other metals attached to a long shaft.
These shafts were usually attached to a cam with the other
stamps if there were more than one. This cam had usually
a wheel on its end that was driven by a belt system. A steam
engine was usually used to turn this wheel which lifted
the stamps and dropped them with all their weight on the
rocks that were to be crushed. Stamp mills would run 24
hours a day and as one can imagine, are extremely
Small 3 Stamp Mill
loud. They also tend to shake the ground as
they are dropped which can make it feel like there is a