The Loudville vein was worked intermittently as late as 1861. It follows a fault fracture between walls of gneiss, but at the southwest end of the vein some of the minerals are disseminated through the Triassic sandstone and conglomerate. This feature indicates that the sediments were unconsolidated at the time of mineralization. The fault zone resembles many analogous fissures which give forth hot mineral-bearing waters in the Basin and Range region of Nevada, for the charged waters have impregnated the sands which cover the fissures.
The Loudville vein contains numerous well-formed crystals. Barite was the first mineral deposited, and it is readily recognized as a heavy, easily scratched substance with one set of cleavage planes at right angles to two others. Gray metallic galena and resinous cleavable sphalerite or zinc blende occupy much of the space between the barite plates. Hard hexagonal crystals or white masses of quartz coat and even replace the barite plates. Spike-shaped crystals of calcite and siderite line many of the cavities and coat the quartz. A patient search will be rewarded by the finding of other minerals, including pyrite, chalcopyrite, pyromorphite, wulfenite, malachite and azurite.
The old shaft has been closed and the tunnel at the river level has collapsed, hence the only exposures are in the open cuts. The most interesting is the one at the south end, where the barite plates are disseminated through the sandstone.
Another series of pits can be found easily about 100 yards west of the road to West Farms and about one mile north of the Loudville deposit. The vein attains a maximum width of three feet between walls of gneiss, and it occupies a fault fracture which seems to be continuous with the Loudville zone. Included in the vein are many fragments of a black phyllite resembling the Leyden argillite, as well as pieces of gneiss. The minerals are identical with those found in the Loudville deposit, but the specimens of quartz, galena and sphalerite are more spectacular.
The Hatfield vein occurs in a rock of igneous origin, known as the Williamsburg granodiorite. It is exposed at the west edge of the valley, about 200 feet from Federal Highway 5, at the northern limit of the settlement called West Hatfield. The workings are full of water, and the very thorough mining activities carried on by mineral collectors and by Smith College and Amherst classes have reduced the waste pile to negligible proportions. Early collections and records reveal that the vein is essentially like those farther south. At Hatfield, West Farms and Loudville the fractures do not parallel the systems in the Triassic sediments and lavas.
A galena-bearing vein outcrops near the Whately-Williamsburg town line at the north end of the Northampton reservoir. Leyden argillite forms the walls of a fault fissure. Barite is absent from this vein, but fine quartz, pyrite and chalcopyrite coat the walls. Coarse comb quartz encrusts the older minerals, together with breccia fragments and cubes of galena. The vein is remote from the valley and differs in mineralogy and texture from those within the valley. Other deposits like it have been found in the nearby hills.
Fig. 23. Geologic map of the region in the vicinity of the lead veins near Leverett.
1. Only barite in these veins 2. Best mineral locality 3. Best place to see fault 4. Slickensides and tension cracks show direction of movement on fracture making opening for vein 5. Best place to see quartz replacing barite along crush zones in vein
The Leverett lead vein is the most interesting of the group because it is so well exposed that the nature of the vein system is admirably displayed. The deposit lies in a series of overlapping, nearly vertical fault fissures in gneiss. Slickensides and tension cracks on the walls of the veins indicate that the movement was nearly horizontal from northeast to southwest. Wherever a fracture begins to narrow and close up, another begins to widen and become conspicuous a few feet to the northwest of it. Several different fissures appear along the length of the mineral zone.