The Wisconsin lead-zinc district, preliminary paper

This paper summarizes intermittent study through a six year period, using methods not hitherto applied to the district. The results have shown that the ores are richer in pyrite than formerly recognized, and probably also in wurtzite (now almost wholly converted to sphalerite). In zinc sulphide deposition rhythmic banding is common. It and the iron sulphide are both colloform. The ore minerals generally show crustification and the paragenetic order is simple. The presence of peripheral pyrite in many veins, as opposed to central marcasite, suggests acid solutions neutralized by contact with the wall rock.Structurally the ores are chiefly near the flanks of basins. Brittle dolomites are the most favored host rocks and the ores are clearly for the most part fracture fillings. Mineralized faults of small displacement are common and pass through the otherwise relatively impervious " oil rock," at least in some cases. The faults and folds are both believed to be the result of tectonic movements.When assembled as a whole, these field and laboratory data favor but do not conclusively prove that the ores are due to rising solutions, probably of ultimate magmatic origin; this concept supports other recent studies of a chemical and mineralogical sort.