Type of deposit debatable. Old references suggest it is a stratabound deposit, enriched by regional metamorphism. But in recent years it has become recognized that the deposits are located along a major thrust fault - the primary evidence being ultramafic tectonic slivers which occur all along the stratigraphic horizon of the deposits. The deposits themselves may be thrust fault slivers of aluminous rock, or they may be hydrothermal deposits - or a combination of both. The old Chester emery mines are divided into two groups: North of Rte 20 - Marcia Mine, Sackett Mine, and Snow Mine. South of Rte 20 - Old Mine, Melvin Mine, and Wright Mine. The most frequented site is the Old Mine, located closest to Rte. 20. This mine, the Melvin, and the Sackett are actually mining complexes involving combinations of open cut and underground workings. The Marcia and Snow mines are mostly underground workings, and the Wright mine is largely an open cut. The Old Mine is the most extensive, having been opened first and operated the longest, involving perhaps half a mile of horizontal levels interconnected by stopes and internal shafts. The open pit at this mine is actually a collapsed section of the second level. (Note: Persistent reports of "schorl" from these sites are attiributed to mis-identifications of ferrohornblende crystals. Schorl has not been proven to exist here. Reports of azurite are mis-identifications of carbonate-cyanotrichite. Azurite has not been found here. "Corundophyllite," which was listed for these mines, was discredited as a species and has therefore been dropped from this list and the individual mine lists.)
The following mineral list includes all species reported for the group of mines.
Ref: G. Fred Lincks (1978) The Chester Emery Mines. Mineralogical Record 9:235-242
Ref: A. Plante (1992) Western Massachusetts Mineral Localities, Valley Geology, Greenfield, Mass.
