Blending Ore

An example of relatively modern day mixing was the Cotter uranium mill in Canon City. Part of their feed came from the Swartzwalder mine near Golden, which had primary uranium ore - Pitchblende, which was primarily U02. Some of the head assays ran as high as 65% uranium, which caused most mills to have a bad case of heartburn. So this very high grade ore was mixed with lower grade ores at the Cotter mill to reduce the uranium content to the point that the mill process could handle it.
The Cotter mill used an acid leach process - a rarity - in contrast to the mills in NM - for example - which used a carbonate leach on the lower grade secondary ores, like Carnotite.
I know this because at the time I worked at the CO School of Mines Research Foundation in Golden, and we had a project to deal with this problem.
(IIRC, the old Cotter mill was recently used during the cleanup of Rocky Flats material.)
I remember being told that some areas of the Swartzwalder mine were so "hot" that no one could enter without full protective gear, and then for only a short time. A good example of having too much of a good thing.
We had a sample of the Pitchblende ore on display which must have been almost two feet across, and was solid ore.
BTW, the mine was named after a Golden junior high school janitor who originally discovered the deposit.
CJ