Mineral Deposits of Southwest Wisconsin. — Blake. 247 
white mamillary masses, contrasting sharply with the dark- 
brown or black of the jack. Any galenite present is usually 
associated with, or planted, in the midst of this barite. 
We may easily account for the formation of sheets of 
barite in the veins upon the hypothesis that carbonate of 
baryta, a soluble salt flows downwards from the surrounding 
rocks into the fissures and beds, and there meeting with sul- 
phate of lime in solution, formed by the decomposition of 
the walls during the deposition of zinc blende, is changed 
into the insoluble sulphate, calcite being formed at the same 
time. In fact, we find numerous crystals of calcite planted 
upon the surfaces of barite. 
Barite is objectionable, commercially, in connection with 
either the blende or galena. It is so heavy that it is sepa- 
rated with difficulty from galenite in the jigs, and it cannot be 
separated from the jack; consequently, in the treatment of 
mill-stuff containing heavyspar a mixture of jack, heavyspar, 
and pyrites is obtained ; and although by the new process now 
employed the pyrite can be removed, the barite remains. 
Although innocuous metallurgically, its weight and bulk in- 
crease the cost of handling, freighting, and smelting, and 
make the blende-concentrate nearly valueless. In some of the 
deposits the barite may be nearty all separated by careful 
hand-culling, and, when clean, can be sold at a price which 
pays a little more than the cost of breaking and saving it. 
Pyrites — Marcasite. 
The pyrites, generally known to the miners as " sulphur," 
is chiefly marcasite. It occurs next to the walls of the crev- 
ices, or coating the masses of dolomite, and is tightly at- 
tached to them, while the blende is superimposed. As mined, 
the two minerals are broken and thrown down together, and 
the coarser parts are then separated by hand. The layers of 
marcasite vary from one-sixteenth of an inch to several inches 
in thickness, and when thick enough to detach from the 
sheets of blende, the marcasite is saved for sale. At the Hel- 
ena mine large quantities have been saved and sold at $3 per 
ton. It carries a little iron oxide on the surface, a little ad- 
hering rock, some calcite, and a trace of jack. Analysis of 
the piles in bulk shows 46 per cent, of sulphur. It is a very 
free-burning pyrite, and does not contain arsenic or antimony. 
