I'm no analyst, nor an expert, but for my peace and comfort I define exploration companies
according to the status of their resource and exploration stage.
I usually only count economical bodies and those that are potentially to be. So for me one
would be tier 1 and the other tier 2.

Next, at what stage of exploration are they.
Lowest confidence level of resource I value at 1% of in-ground. If it falls more in the indicated category then 2-3%. Measured and if with a N.I. 43-101 then 5%.
Add a Feasability study and it becomes 10%.
Arrange construction financing and start constructing a mine with necessary infrastructures and if becomes about 20%,
Producing mines at 40%.
These are just ball park percentages which are decreased if there are possible problems with structure (many narrow veins) or depth, politics or environmental concerns.
Desperate demand for the resource will add a premium.
Most buyouts are with a 30-50% premium.

Too many variables to give a more accurate description and I am still learning.