|Latitude & Longitude (WGS84):||41° 34' 6'' North , 73° 20' 24'' West|
|Latitude & Longitude (decimal):||41.56833,-73.34000|
|Köppen climate type:||Dfb : Warm-summer humid continental climate|
A series of at least 7 veins, primarily siderite and quartz, formed along minor faults trending about 120 degrees E and dipping SW at 75 to 90 degrees. The largest vein is 2 to 3 meters thick, at least 600 meters long and extends at least 60 meters down, probably much more. It is one of the largest deposits of siderite in North America. Drifts were cut on 3 of the veins, with 3 levels with separate adits and numerous shafts put in on the largest vein. Three of the 5 pure quartz veins in the area were also mined. Maps and plans of the veins and mines are shown by Bell and Mayerfeld (1982). Januzzi (1976) includes sketches and photographs from inside the mine. Besides siderite the locality is best known for its excellent pyrite crystals.
The first confirmed mining at this site was in 1750, about that time, Moses Hurlbut and Abel Hawley are said to have worked Mine Hill for silver and lead. About 1760 a company headed by two brothers named Brownson worked the mine energetically under the supervision of a German goldsmith named Feuchter; two shafts were sunk, one going down 175 feet from the top of the hill, into the vein of ore. This search for silver in the relatively sparse galena continued for several years until the available funds were exhausted.
A new company was organized; the vein traced down the surface of the hill toward the river and horizontal drifts were made. Several other companies followed, working the mine for silver and lead, but there was not enough galena and these late 18th century operations were short lived. The last operation recognized the iron potential of the ore, but did not pursue it.
By about 1816 Prof. Benjamin Silliman of Yale identified iron in the form of siderite as a valuable ore, this was followed by inspections in 1830 by Prof. Charles Shepard. At last the vein’s value as an iron-ore was appreciated, and by 1830 David Stiles began operating to extract it. His operations became tied up by lawsuits from previous operators or leaseholders.
Finally, in 1865, the Shepaug Spathic Iron and Steel Company was formed after exploring the prospect, running some of the ore through other furnaces, and seeking the best advice available from an economic geologist, mining engineers and metallurgists, plus four Yale professors: Brush, Porter, Dana and Silliman (senior, now 85 years old). Professor George Brush wrote on May 30, 1864: “The ore...is spathic, or sparry iron ore....something over 40% metallic iron, most highly prized of iron ores, comparatively rare...It produces a white pig iron…well adapted for conversion to steel.” Quality steel was being made in Prussia and Styria from siderite, so the thinking was that the presence of carbon in the iron ore would simplify the 3-step steel making process and allow a more direct, larger scale, and thus cheaper process.
In 1867, the company name changed to The American Silver Steel Company. It greatly expanded the mining and built the railbed, furnaces and facilities whose ruins are now preserved at the site. The steel works were not successful apparently because "Silliman had incorrectly assessed the ore's steelmaking potential, and that none of the experts it had hired could run the steelworks" (Gordon and Raber, 2000). They could not replicate the "feel" the Europeans had for their process (which lacked any method of directly measuring the carbon content) and the presence of carbon in the ore was of no consequence to the steel making process as it worked the same way with the roasted iron oxide ore (Bell and Mayerfeld, 1982).
After some problems with the blast furnace in 1868, the mining and smelting ran well, producing pig iron until 1872, when a change over to a hot blast ruined the furnace and all activity ended. Because the original plan was to produce quality, high-priced steel from the pig iron, this furnace was not competitive as solely a pig iron producer. The costly underground hard rock mining and the cost of roasting the ore to remove the sulfides and carbonate content were not incurred by the open pit, "soft ore" goethite mining operations elsewhere in the Connecticut/Massachusetts/New York iron mining district.
Sometime in the early 1900s the Columbia School of Mines arranged to use the mine for field study by students of mining engineering. They reinforced the middle drift adit with concrete. In the summer, the cool, moist air exiting this adit sends a breath of refreshing fog across the trail.
The mine is now part of the Roxbury Land Trust’s Mine Hill Preserve. The complex is listed on the National Register of Historic Places. The adits and shafts have been gated off to prevent human entrance but allow access by the bats that now make it their home.
Commodity ListThis is a list of exploitable or exploited mineral commodities recorded at this locality.
21 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Eifelian - Lochkovian|
387.7 - 419.2 Ma
|Ordovician? granitic gneiss|
Age: Devonian (387.7 - 419.2 Ma)
Description: (Including local terms Ansonia, Mine Hill, "Tyler Lake," "Siscowit") - White, light-gray, buff, or pink, generally foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and biotite, and locally garnet or sillimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss.
Comments: Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Ansonia Gneiss is here referred to as Ansonia leucogranite. On the basis of field and laboratory studies, Ansonia, Beardsley, Pumpkin Ground, and Shelton gneisses, previously considered stratigraphic units, are reinterpreted as plutonic. Ansonia is described as a strongly lineated and moderately foliated, fine-grained, garnet-bearing, biotite-muscovite leucogranite with a well-developed granoblastic texture. Intrudes Beardsley and Pumpkin Ground orthogneisses. Maximum age from zircons is 417+/-1.5 Ma. Conservative interpretation of isotopic data is crystallization between 393 and 419 Ma and therefore, authors assign an age of 406+/-13 Ma (Late Silurian to Early Devonian) to the Ansonia (Sevigny and Hanson, 1993) per CT007.
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
|Ordovician - Neoproterozoic|
443.8 - 1000 Ma
|Precambrian-Phanerozoic sedimentary rocks|
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529.