Since the first discovery of sulphides in 1793, the Vermont Copper Belt has yielded ore containing an aggregate of about 120 million pounds of copper. The orebodies occur in schists of Paleozoic (probably Ordovician) age in the middle-grade zone of metamorphism. In the Elizabeth Mine the main oreshoot, 6,000 feet in pitch length, follows the plunge of an overturned syncline and is localized by a bed of phlogopite-tremolite-carbonate rock along a strong zone of deformation on the straight limb of a fold. Sulphides were introduced later than both the folding and metamorphism of the rock and were emplaced by replacement together with some filling of potential open spaces. The ore consists of massive and disseminated sulphides, chiefly pyrrhotite, with enough chalcopyrite to yield a little under 2 percent copper in the ore as mined. Sparse accessory sulphides are pyrite, sphalerite, molybdenite, and traces of galena, tetrahedrite and tennantite. Where the wall rock is amphibolite, hornblende alters to biotite which, in extreme cases, is changed to sericite. In biotite schist, biotite and plagioclase are sericitized.No nearby magmatic source is evident but the Copper Belt occupies a peripheral position with respect to the area of great plutons of the New Hampshire Magma Series.

First Page Preview

First page PDF preview
You do not currently have access to this article.