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Orvana has received approval to mine chalcocite, a mineral that is primarily copper, in a project here that the company says will create $2 billion in economic activity over 20 years.

Owing to the frequent presence of mechanically admixed chalcopyrite and chalcocite, the published analyses of erubescite show wide variations, the copper, for example, varying from 50 to 70%.

At Butte for instance, secondary chalcocite is clearly to be recognized.

In the easy recognition of the secondary copper sulphides, chalcocite, bornite, etc., the engineer finds a finger-post on the road to extension in depth; and the directions upon this post are not to be disregarded.

The present tendency at Butte is to consider as secondary chalcocite only certain sooty phases to be found in upper levels.