Structure and rock alteration at the Elizabeth Mine, Vermont; Part 1

Abstract

The Elizabeth Cu mine in E-central Vermont is a concordant ore body lying within medium to high-grade metamorphic rocks of the Gile Mountain formation, believed to be Ordovician in age. The major structural features of the district are the E-dipping eastern limb of the Green Mountain anticlinorium, and the Strafford dome, which is marked by the development of an abnormal Christmas tree pattern of minor folds. Due to a flat northerly plunge, the easterly part of this structure crops out as a series of recumbent dextral folds in which the older rocks appear on the inside of the northerly-plunging V structures. Minor sinistral folds and flexures are common in the area, and both pre- and post-date the dextral folds associated with the Strafford dome. The Elizabeth ore bodies are bedded within the rock sequence at the contact of amphibolite and mica schists and are structurally related to the Christmas-tree pattern of folds. The ore is localized in fold positions and on straight limbs between fold positions. Schist breccia within the ore, ore infilling the space between parted bedding planes in drag fold positions, and veins filled with ore suggest that the ore was introduced into permeable zones formed during deformation and dated as middle and/or late Devonian (Acadian). It is believed that the major ore control in the district was the crushed and folded contact of thick competent amphibolite beds with incompetent schists interbedded with quartzites.