Salisbury Mine (Old Hill Mine; Ore Hill Mine), Salisbury District, Salisbury, Litchfield Co., Connecticut, USA

The "Ore Hill" mines are at present entirely below ground, and are operated by the "caving" method. The older works at the locality, which were formerly known as the “Brook” pit, are a little to the north of the main incline, and, like most of the other mines of the Salisbury district, were operated from the surface by “open“ methods. In the present workings the ore body is largely enclosed in Berkshire or Hudson [Walloomsac] schist, though a narrow layer of dolomite forms the greater part of the hanging wall. The dip of the rock is to the southeast at angles near 25°, and is subject to sudden changes. The incline descends along the foot wall at an angle of about 25°, but meets abrupt upward projections of this wall, which seem to recur at regular intervals approximating forty or fifty feet. About 170 feet vertically below the entrance to the incline, and about thirty feet above the lowest level, this foot wall comes up in a nearly vertical plane so as to cut off the ore. The foot wall wherever examined was found to be graphitic schist like that of the Berkshire formation in the vicinity, and the ore appears to be largely a replacement of this rock, in which are found irregular block-like masses of so-called "white horse." The “white horse” somewhat resembles the dolomite, but has soapy feel and contains 50 per cent or more of ferric oxide. It appears to be a mixture of iron carbonate and talc, and elsewhere in the Salisbury district it has been mined for the iron which it contains. At the surface it weathers to a brown color owing to the hydration of the iron oxide. The interruptions in the foot wall above described appear to be due to faults, along which the throw has been in most cases only a few feet. The hanging wall, which is exposed in the lowest level for a considerable distance, is a hard dolomitic marble, but in some places this is a garnetiferous and staurolitic schist. The peculiar relations at this mine are explained by interstratification of the dolomite and schist near their junction combined with normal faulting.